B-1050 MAY 1966 ;:’..’:'_~ -~ ‘t2? {l}, ’;:é._: w. “ TEXAS A&M UNIVERSITY TEXAS AGRICULTURAL EXPERIMENT STATION R. E. Patterson, Director, College Station, Texas REPRODUCTIVE EFFICIENCY CONTENTS Summary ............................................................................................... .- 2 The Potential ........................................................................................ .. 3 The Male ............................................................................................. -- 4 Some Causes of Infertility in Rams .................................................... .. 5 Nutrition ....................................................................................... .. 5 High Temperatures ....................................................................... .. 5 Disease ........................................................................................... .. 6 Fertility Testing of Rams.-. .............................. ................................ -. 7 The Ewe ................................................................................................ .. 7 Effect of Age ............................................................................... .. 7 Breeding or Management Factors Affecting Longevity ................................................................. .- 8 Effect of Size and Condition ....................................................... .. 8 Culling or Selection Practices Relating to Fertility ............................................................... __11 Influence of Season ...................................................................... .13 Influence of Temperature ............................................................ .13 Flushing ....................................................................................... ..15 Multiple Lambing ........................................................................ __15 Use of Hormones ....................................... ................................ ..15 Diseases ........................................................................................ __16 Literature Cited ...... ........................................................................... .-17 S U M M A R Y Improved lamb production will strengthen the competitive position of the Texas sheep industry. A real opportunity exists for improvement in reproductive efficiency since the average lamb crop weaned in Texas over the past 5-year period was approxi- mately 75 percent. In comparison, individual flocks have weaned up to 120 percent lamb crop. Small experimental flocks have a lambing rate of 150 percent. The best reproductive rate is obtained when mature fine-wool ewes, 3 to 5 years of age, are bred to fertile rarns of another breed. The ewes should be smooth, open- faced and in medium to strong flesh, weighing 120 or more pounds. They should have lambed regularly in previous years and preferably raised twins. Both ewes and rarns should be ‘free of infectious disease. Also, the animals should be protected from heat stress at mating and during gestation. Maximum reproductive efficiency is obtained when ewes are bred in the fall to lamb in the spring, but it may be desirable to deviate from this due to other factors to be considered in the management program. Adequate nutrition is necessary during gestation to insure well-developed lambs and to prevent losses from pregnancy disease. Data are included to indicate degree of loss in reproductive efficiency associated with various degrees of deviation from the optimum. Observations over the state indicate the following as some of the main causes of poor lambing results. Lack of size or development of yearling ewes, High percentage of yearling ewes in the flock, Poor condition of mature ewes, Heat stress during mating or gestation, The increasing tendency to breed at the seasons of low fertility, Heavy death losses of lambs due to poor nutrition of ewes or adverse weather conditions at lambing, Lack of culling for reproductive efficiency. productive iciency t Fine-Wool Sheep ice Shelton, John T. Morrow and O. D. Butler* . pectively, geneticist, Livestock and Forage Research Center, regor; former assistant professor and head, Department of imal Science, Texas A&M University. IN TEXAS AND MUCH of the Southwest, income from the sale of wool usually exceeds that obtained from the sale of lamb and mutton. While many consider this a favor- able status of the wool industry, it also denotes an unfav- orable situation of the market lamb industry. Improved lamb production with continued high levels of wool income will help improve the competitive position of the sheep industry. Lamb production depends on fertility of the ewe flock and growth rate of lambs from birth to market. This bulletin summarizes investigations from this and other locations concerning variables known to affect repro- ductive efficiency of sheep. Reproductive efficiency is influenced by variations in the occurrence of estrus, ovulation rate, conception, main- tenance of pregnancy and lamb mortality. All of these variables, except lamb mortality, are considered in this publication. The Potential Assuming once per year lambing, the production of an individual ewe may vary from none to two lambs. With multiple lambing, two lambs per ewe per year is no longer the theoretical upper limit. However, it is the overall performance of the flock expressed as number of lambs raised per 100 ewes bred which is of greater economic importance. There are instances where individual flocks ap- proached or even exceeded the theoretical 200 percent in national lambing competition. Lamb drops as high as 150 percent have been realized from Rambouillet ewes under commercial conditions. This can be compared with data in Table 1 which indicate the realized lamb crop for Texas and the United States as a whole. The low lamb crop realized usually is dictated, in part, by environmental conditions of the ewe flock and the feasibility of improving the environment depends on many variables. However, producers should know the factors contributing to fertility so that they may alter their management practices wherever possible to obtain maximum reproductive efficiency. A realistic upper limit under production conditions for once per year lambing in Texas might be 120 percent for range flocks and somewhat higher for more intensively managed farm flocks. TABLE 1. AVERAGE LAMB CROP (LAMBS WEANED PER 100 EWES IN FLOCK) FOR TEXAS AND U. S.* 1O year average 195o_59 1960 1961 1962 1963 1964 inclusive Texas 73 80 79 75 73 69 U. S. 93 95 95 94 95 92 *From U. S. Department of Agriculture, Statistical Reporting Service. The Male In the reproductive process, the male is less frequently the limiting factor (Figure 1). Infertile rams, 0r those of low Fertility, primarily affect the number of ewes which conceive, but they may also be a factor in the number of multiple births. The reproductive organs of the male are diagrammeid in Figure 2 and sperm cells are pictured in Figure 5. The males may reach puberty as early as 4 to 5 months or any time thereafter when they approach or exceed approximately 9O pounds in weight, depending on breed. They should be removed from the ewes before this time. Ram lambs may be used during their first season with a few ewes for progeny test purposes. Well-developed rams are capable of a full-breeding load as a yearling or at any time thereafter as long as the ram remains healthy and vigorous. With advancing age, after 2 or 5 years, libido (sexual drive) is likely to decrease, but a ram may give good service up to 8 years of age. w Figure l. Well developed, vigorous rams usually are highly fertile, but producers should be aware of potential detriment- al factors such as epididymitis and high environmental temperatures. 4 Figure 2. Male reproductive system: A. testis, B.’ epididymis, C. body of epididymis, D. tail of deferent duct, F. spermatic vessel and nerves, G. .u vesicular gland, I. Cowpers gland, J. prostate di Hf J penis, S. retractor penis muscle, T. Bladder, U. s pelvis, V. rectum, X. urethral process. A healthy, vigorous ram has a tremendous A for sperm production and thus an almost unlimited ‘a, ical breeding potential. The normal ejaculate I usually will contain about 4 billion sperm. In o of observations (1), so-me rams mated as many as daily and averaged 26 times daily for a short while less vigorous ones mated 12 to 15 times d extended periods. However, since a short intense; ing season is desired under conditions which are-j somewhat less than ideal, a standard and appar, isfactory practice is to use three rams per 100 ewes. good conditions and when rams are strong and v_ a smaller number may be used during the cool 5 More rams should be used with yearling ewes, ~1 weather, in very large pastures and when very y; old rams are being used. Multi-sire matings usually are preferred, as to single-sire matings, although the efficiency y, ram is much less with multi-sire matings. Caution be taken in mixing several rams with a group of i a small enclosure. Under these conditions, one ri tend to dominate the others (2) and in effect, j sire mating with even a larger number of ewes i practiced. If the dominant ram is infertile or r 3. Types of sperm cells from rams — (A) normal and (B and C) abnormal types due to heat degeneration. 'ile, possibly from fighting, serious consequences 1 result in that fewer ewes might become pregnant. FSome Causes of Infertility I m Rams The major causes of infertility in rams are under- ition, disease and high environmental temperatures. ‘TRITION Under Texas conditions, no single nutrient deficiency . own to be a specific cause of infertility of rams. ever, general undernutrition often has been observed contributing factor. In these cases, development or gition of the animal is a good indication of the nutri- . state. The nutritional elements most likely to con- t; to undernutrition in the ram are energy, protein, i phorus and vitamin A, but a long continued deficiency y of these will manifest itself in the appearance of animal. i H TEMPERA TURES High environmental temperatures contribute to low- breeding efficiency of the ram in two respects. The ‘i is reduced mating desire from climatic stress. The 0nd, and much more serious, is the direct effect of ‘perature on sperm production. For many years it has been known that high temperatures can cause a failure of germ cell production in males of many species, including sheep (3). This first grew out of the observation that cryptorchid animals, those with testicles retained in the body, were sterile (4). From this it was established that the scrotum serves a thermoregulatory function in which the temperature olf the testes is maintained at approxi- mately 96° F., 7 degrees below the internal body tem- perature. Spermatogenesis will be interfered with, when environmental conditio-ns make it impossible for the animal to maintain normal scrotal temperature. Under Texas conditions, practically all rams are affected to some degree during the summer, but the problem is likely to be severe only when temperatures remain above 90° F., with an extended period of high humidity. In drier atmospheres, severe temperature stress or seminal degeneration does not usually occur below 100° F. The length of exposure, such as hours in the day or number of days of high tem- peratures, are also important factors. Under extreme con- ditions, a complete cessation of sperm production may occur, with up to 8 weeks required for complete recovery, Figure 5. Over a period of years. data have been collected at College Station, McGrego-r and Sonora. Most data on improved breeds of sheep show some drop in semen quality during the summer, but the degree of this effect 5 IOU T 80- 60- PERCENT 40- ----- SONORA COLLEGE S"l‘A'I'lON 0 | 1 | a l | | | | APR. MAY JUNE JULY AUG, SEPT. OCT. NOV. SEASON OF YEAR Figure 4. Influence of season of year on estimated total live sperm production per ejaculate of fine-woolrams expressed as a percent of values obtained for April. has been quite variable. Some results of evaluating semen quality of rams at College Station and Sonora are shown in Figure 4. Only rams of fine-wool breeding (Ram- bouillet and Delaine Merino) are represented, but a different group of rams and different seasons are repre- sented at each location. Except for total sperm produc- tion at Sonora, all seminal characteristics measured showed some drop in summer or early fall months. The degree of effect was much greater at College Station and recovery came much later. Examination of the data suggests that at Sonora nea.rly all rams would have remained fertile throughout the summer but would have had lowered total breeding efficiency. However, at College Station it ap- pears that 4O to 5O percent of the fine-wool and all the medium-wool rams would probably have been "sterile dur- ing late summer or fall. Complete recovery of all rams did not occur until after September. Rams which had a sterile period early in the summer recovered earlier than those showing a sterile period later in the season. Other con- clusions from this series of studies indicate that. (a) rams of m.edium-wool breeding are affected more severely than fine-wool rams, (b) heavy use of rams adversely affects semen quality, (c) late spring or summer shearing has a beneficial effect, (d) young rams, particularly lambs or yearlings, are more severely affected than mature rams, particularly if they are fat going into the summer season. No complete solution is known, but consideration of the foregoing facts offers some suggestions for minimizing the effect of high environmental temperatures on fertility. 6 Use of a larger number of rams on a rotation) usually is advantageous. Also, removing rams fr flock to shade and rest during the day has some L: tage (5). Under range conditions in the Edwards or West Texas where late fall breeding is practice'- enviro-nm-ental temperatures are not a serious prob msna s1; Any disease which brings about an extended of fever or elevated body temperature can cause inf] of rams. In recent years, a disease known as epidi (Figure 5), specifically associated with the repr organs of rams has been identified. This condition, p) by infectious agents known as Actinabacillu; semi Brz/cel/a 012i: has been identified in Texas Texas survey (7) the overall incidence of affect was 7 percent, but the incidence in individual flocks- from O to 5O percent. This disease appears to be (_ ing. Rams with this defect are not completely i. manently sterile, but the presence of the disea flock has been definitely associated with a lowere, crop. Affected anim"ls shoul-d be sold for slaughi Affected rams usually show one or more e g or swollen testicle or epididymis or some part Most producers can train themselves to identify i animals by palpating the testis. Producers should, the structure and texture of the normal testis, av deviation from the normal in terms of an enlarg A hardening is cause to suspect the ram. A recently p vaccine for this disease has received only limited in Texas. This disease is thought to be passed fr, ram to another by mounting. Incidence of the A can be reduced by starting with a group of lambs and keeping them separate at all times y; rams. There also is circumstantial evidence that i ease can be passed by rams to the ewes resulting i tion or birth of weak or dead lambs. it ;» _, W, Figure 5. Enlarged testicles due to e pididymitis. both testicles may be affected. i “rtility Testing of Rams testing of rams has been used to a limited t there are serious limitations. None of the hods of collecting semen for examination are tisfactory. Semen obtained by means of the yagina provides a good basis for estimating the rams. Most rams in Texas are too wild to artificial vagina without spending much time in The second method of semen collection is by the , electro-ejaculator. Using this procedure, sam- 1 be collected from a large number of rams in a Vie. However, the correlation between fertility quality rating of samples obtained by this is not high (8). A good rating of semen ob- this method is almost a positive assurance of if the ram is vigorous and has a normal mating jith no physical limitations. However, if all rams poor semen quality by this procedure were dis- :21 large number of goo-d rams would be sacrified. id test at a later date will help clear up some of i.“ tionable rams. ithirid collection procedure that has been used to a 7 extent consists of allowing the ram to serve the d aspirating semen from the vagina. This ewe i a restrained ewe or one which is in a normal heat ifpreviously treated with stilbestrol. A good estima- if the fertility of a ram can be obtained by this i ercial rams. This procedure usually can be _~ satisfactorily for testing a small number of gentle isuch as stud rams. iecause of the equipment and training required, fer- gitesting of rams must be done by a qualified vet- ian or specialist with experience in this field. The Ewe gEwes may reach sexual maturity as early as 7 months y have been grown out properly. Commercial pro-- 3 in some areas call for placing these ewe lambs with in order to lamb at 1 year of age. In general, this inot proved satisfactory in Texas. Spring-born, range- ure, but it is not very practical for a large number“ raised ewe lambs seldom have the size necessary for breeding at this early age. Fall-born ewe lambs out of a milk-lamb program may have a-dequate size to breed their first year, but this requires that they be bred in spring or summer when often they are losing weight. Ewe lambs were exposed to rams in the spring and summer for 2 years at the Livestock and Forage Research Center, McGregor, with only a 15 percent lamlb crop realized. This could no doubt be improved if environmental limita- tions such as temperature, nutrition and parasitism in the summer could be improved. Subject to seasonal or other restrictions, the ewe be- gins to exhibit heat periods when she reaches an adequate stage of development (approximately 85 po-unds and up). In young ewes (lambs or yearlings) this heat period usually is of low intensity and lasts from 12 to 2O hours, while older ewes show a much more active heat period which may last 5O to 36 hours. Ovulation occurs near the end of the heat period. This suggests that if a ewe is mated only once, she should be mated in the latter part of the heat period. However, under natural conditions, each ewe usually is mated several times if enough vigorous males are present; thus, timing is relatively unimportant. The estrous cycle (perio-d of time from one heat period to the next) lasts approximately 17 days, but may vary 1 or 2 days. The gestation period (time from mating to parturition) lasts approximately 149 days fo-r all breeds except the So-uthdown, which usually is shorter. Ewes dropping twin lambs usually have a shorter gestation period. (EFFECT? OF AGE Age of the ewe influences fertility. Management decisions relating to age include age to breed, desirable age to cull and any management decisions which might pos- sibly alleviate the effects of age on reproductive perform- ance. Lambing at 18 months may yield satisfactory results if this can be worked into the management program; otherwise, lambing at 2 years of age is the standard prac- tice. The effect of age on ewe performance under range conditions at the Ranch Experiment Station, Sonora, is shown in Table 2. These data (9)c indicate an annual TABLE 2. RELATION OF AGE TO PERFORMANCE OF RAMBOUILLET EWES UNDER RANGE CONDITIONS (SONORA) Number Average Pounds of Percent Percent lambs |amb' Percent Fleece of bqdy dry weaned ewes weight Obie“ welghl ewes Born Raised per lost pounds vahonf pounds ewe bred 871 94.3 30.0 77.4 65.7 42.7 3.5 9.5 679 103.3 11.8 106.9 97.0 66.8 3.1 9.9 525 112.8 11.4 116.4 103.2 72.7 3.7 9.7 427 115.0 11.5 113.8 99.8 74.7 4.4 9.4 339 117.2 9.8 118.9 105.3 71.8 5.8 9.2 241 117.3 12.9 114.1 101.2 67.2 6.3 8.6 216 115.2 19.9 105.5 90.3 57.4 10.3 7.9 150-- 14o-- ,’ \ 13o-- I 120" / 110-r 1oo~- 90-- 80 ~- 70 ." 60 ‘ .._....._% LAMBS BORN OF EWES LAMBING y ____% LAMBS RAISED OF EWES BRED 5° EWES LAMBING REPRODUCTIVE EFFICIENCY IN PERCENT O 4 1 l | | I I | I | | | I I 2 3 4 5 6 7 8+ AGE OF EWE IN YEARS AT LAMBING Figure 6. The relation 0f age of ewes t0 various measures of reproductive performance (McGregor flock data). increase for up t0 5 years in pounds of lamb weaned per ewe bred and then a fairly constant decline. A somewhat similar analysis involving data collected at McGregor is shown in Figure 6. Data from both stations indicate that a major deterrent to good breeding performance stems from poor results with yearling ewes. The average flock may contain 25 percent or more yearlings. Thus, a major effort should be made to maximize the performance of this age group. Ewe performance tends to drop after 6 years of age. However, assuming that perennially barren ewes and those with broken mouths and bad udders are removed, aged ewes are likely to perform better than yearlings, even to the advanced age of 8 years. This, plus the comparative value of aged ewes and cost of replacement ewe lambs or yearling ewes, strongly suggests that aged ewes should re- main in service as long as they are capable of producing lambs. The exact age at which culling is necessary de- pends on environmental conditions. A decline in breeding performance seems to begin earlier in the McGregor flock than in the Sonora flock. This may be related to the rate of early development since the ewes in the McGregor flock are grown out much faster as lambs. Although not shown by these data, the more extreme length of productive life often is obtained on ewes raised under range conditions and later trans- ported to the improved conditions often found in farm flock-type operations. BREEDING OR MANAGEMENT FACTORS AFFECTING LONGEVITY Length of productive life is a valued characteristic of breeding sheep. Many producers have expressed a desire 8 to select for this characteristic. The heritability of v7 gevity is not known; however, by comparison with si ' productive traits, one would predict it to be low. _ addition, there are the added complications of extens' record keeping, and an inability to measure this I acteristic until the animal is approaching or has passed w stage of maximum usefulness. {These complications p the ‘fact that some selection ‘fdlr longevity is auto .3 in nature unless ewes routinely are culled at a constj age, tend to inidicate that extensive programs selecti specifically for longevity under commercial conditi are not justified at present. ~‘~ A However, management factors affecting longe I should receive immediate consideration. The rate of ea development is related to length of productive life. I was first noted between species or between breeds. Meri: sheep grow at a slower rate than Rambouillets but usu remain in the productive flock for a longer time. M The rate of early development also is related to lend of productive life. Data collected at Sonora show phenomenon applies as well to range-raised fine-w’, sheep. Figure 7 shows the relationship of weaning -‘ yearling weights to length of productive life. Tho data show that extremely heavy ewe lambs (above pounds) or yearling ewes (above 115 pounds) do v remain in the breeding flock as long as those grown o ‘ at a slower rate. Likewise, underdeveloped yearling e " remain in the productive flock for a shorter period. Ho, ever, lightweight ewe lambs apparently are satisfactory l given an opportunity to develop properly before enteri the breeding flock. An explanation for the effect ! developmental rate on longevity is not known, but t p phenomenon has some important implications for livest producers. Under commercial conditions, consideratip should be given to selling or extensive culling of heat commercial ewe lambs and keeping lambs with mo intermediate weights for replacement purposes. This pr tice would partially eliminate the automatic select,‘ against twins in range flocks. EFFECT ‘OF SIZE AND CONDITION Size, development and fatness appear to be the Q to much of the observed variation in reproductive rd formance. opment from the influence of condition or amount of Analysis of data collected on the Sonora station of’ indicates a direct linear increase in all aspects of reprod tive performance as yearling body weight increases up l‘ approximately 115 pounds. This is realized throu fewer dry ewes, a higher percentage of lambs born .|f I raised, larger lambs and greater longevity in the produc' I flock. The combined effects result in approximately 4. It is difficult, if not impossible, to visuaW distinguish size as a measure of skeletal growth and dev m1] WEANING WEIGHTS OF EWE LAMBS 5.5 L SHORN BREEDING WEIGHT OF YEARLING EWES 5.0 - 00o n‘;- OlIIII Illjjll 4.5 - 4.0 - T 3.0 4b 50 6o 7o so 905 10o 11o 120 13o 14o I BODY WEIGHTS ‘ e 7. Relation of body weights of lambs and yearlings to length of time in the breeding flocks. TOTAL LIFETIME LAMB PRODUCTION IN POUNDS g POUNDS LAMB PRODUCED PER EWE BRED, 1st. SEASON ONLY U1] POUNDS OF LAMB WEANED PER EWE BRED 350 —- I l 4 l KN KN 30o - -:-:-:¢:o' - . . . _____ _ _ - .45 250 — '40 - 35 -# '30 - 25 v a YW.~“._ l. 200- — m“ llllllllllllllIlllllllllll Ill I 150 '- _ 20 100 - 333;; ‘f.’ q (IEIHH HMEI HHEI CIHNVEIM SNVI .E[O SCINIIOE 50 - 2525252 'il'|'il'|'ii'|'iiiiiifii1'|'iii1'|‘ii1'iiiiii111ilfiini I Below 75-85 85-95 95-105 2 2 75 " ligure 8. Yearling ewe weight at start of the first breeding season. P‘ O U1 | r—* r-I U! 11> HO" P-‘O Lfl<2 (‘D 80a- 70 " MCGREGOR DATA (>0 <- SONO RA DA TA 40 -- / - I F so -» POUNDS LAMB WEANED PER EWE BRED 20-- b 0-l-r::::::::::::¢t::: so 9p 100 110 120 130 140 150 160 AVERAGE WEIGHT OF EWE Figure 9. The relation of breeding weight of mature ewes to overall lamb~ production. pounds increase in lifetime lamb production for each 1 pound increase in yearling body weight. This is sufficient to justify making necessary changes in management pro- grams to insure that ewes are properly developed, Figure 8. Overdevelopment has an adverse effect on both first season and lifetime performance, but this is an infre- quent occurrence under range conditions. The influence of size on reproductive performance of mature ewes as expressed by shorn body weight at breeding has been analyzed utilizing data collected at Sonora and McGregor. The Sonora station flock has been managed similarly to range flocks of the area. The flock at McGregor has been managed on a higher plane of nutrition, as are many flocks used in slaughter lamb production. However, ewes in the latter flock have been on a fall and winter lambing program which is somewhat detrimental to reproductive efficiency. The pounds of lamb weaned per ewecas related to body size is shown in figure 9. Pounds of lamb weaned per ewe is the most accurate measure of overall per- formance because it combines several components of lamb production into a single measure. Weaning weights of Sonora lambs represent actual weaning weights at approx- imately 6 months. The weaning weights of McGregor TABLE 3. THE RELATION OF CONDITION SCORE TO REPRODUCTIVE PERFORMANCE OF FALL-LAMBING EWES ON THE McGREGOR $1’ lambs represent 120-day weights. These data clearly s to indicate that physiological maturity is reached for t breed at approximately 125 pounds. As body wei increases up to this value, all aspects of reproducti (percent ewes lambing, percent lambs dropped and rai and lamb weights) increase in an almost direct lin manner. Above 125 pounds, theT-‘percent of ewes lambii dropped slightly in both flocks: but the number of l t, born per ewe lambing continued to increase, even A extreme weights. i These two opposing trends cancelled each othengiiw results showing that continued increase in body wei was neither beneficial nor detrimental in mature However, if cash outlay or resource expenditures w involved in bringing about the larger weights, the 120, 130-pound ewe would be most efficient. Larger -- generally weaned larger lambs. This was more true w single lambs although it was partially cancelled by A tendency for more twins to be born from larger ewes. i, In an attempt to distinguish between the effect size and condition, the ewes in the McGregor flock » scored for condition at mating. These ewes were grou into the three classes: fat, medium and thin. The r tionship of condition score to reproductive performanc shown in Table 3. i These data again indicate that thin or underdevelo animals perform poorly. There is a tendency for f: fat ewes to lamb, but those which do have higher lam, rates similar to the medium-fleshed ewe. Thus, fat anii may represent inefficient use of resources. If dry have not been identified in the flock, fat ewes may be those which are perennially dry or infertile and w" be expected to give poor breeding performance. In. case, the fat woul-d be the result, not the cause, of _ reproductive performance. i High environmental temperatures adversely a many aspects of animal reproduction. The presen excess fat tends to aggravate heat stress. Exceedingl animals on the McGregor station, particularly young I’ or ewes not of fine-wool breeding, are often dry, this problem can be reduced by a period of feed Q Poun - l. tihi-“I. ""'"'=" '32’??? P3551" “mbmg P°ZZil'.§.i°.Tb‘ “m” . dfcaeivce ewes in poinds lambing* rah“: ewes bred 53d A Fat 358 147.8 79.3 150.0 93.3 6, Medium 668 129.5 84.4 135.3 92.8 Thin 129 111.8 77.5 117.0 74.4 *The percent of ewes lambing is low, but is generally in line with that expected of fall-lambing ewes. **Number of lambs born per 100 ewes lambing. ***Based on 120-day weights. 1U _ EFFECT OF RESTRICTED FEED INTAKE ON FAT EWES IN r OF BREEDING SEASON Percent ewes Lambing Iambing rate Number Breeding ewes weight Yearling ewes—-Rambouillet breeding _ 49 123.5 71.4 f~ feed 113 112.1 89.4 Mature ewes—-Rambouillet breeding I 63 141.2 92.1 153.4 ,- feed 55 130.9 90.9 146.4 (ll in advance of the breeding season. This does ly to aged fine-wool ewes which previously have anibing regularly, because they apparently are less ly affected by heat stress. Some data on this p’ enon is shown in Table 4. Note the different a of the two groups to a period of feed restriction i breeding. Treatments consisted of drylot confine- ion a submaintenance ration for a time sufficient to i about the weight losses indicated. Feed restriction virminated at a minimum of 2 weeks before placing with rams. g INC OR SELECTION PRACTICES TING TO FERTILITY ince fertility or overall reproductive efficiency is of the most important components of a successful I enterprise, this factor also should receive considera- gin selection practices. Selection or culling for fertility have goals of improving fertility in the current breed- lock or in future generations. The first goal deals a function known as repeatability, the value of one it ’s record as an indication of performance in sub- ’: t seasons. The second objective would deal with phenomenon of heritability or the degree to which 5 '0rity or inferiority would be passed from one gen- 'on to the next. In general, repeatability of reproduc- tive performance is moderate to high, whereas heritability generally is low. However, these are not fixed quantities and depend greatly on the conditions involved. Culling practices related to improvement of fertility in the flock have been investigated using data from the Sonora and McGregor flocks (11). The data relating to such factors as age, size, condition and so forth should be considered in selection or culling practices. Data relative to using one season’s record as an indicator of subsequent performance are shown in Tables 5 and 6. With range-raised yearling ewes, lack of size and development is likely‘ to be the major limiting factor. In this case, failure to breed the first year seriously affects total lifetime performance. sons, ewes which were dry as yearlings closely approached However, in following sea- the performance of ewes which lambed their first year. Thus, culling of similar ewes generally would not be recommended because of failure to breed their first season. Where lack of size an-d development is not a limiting factor, ewes dry in a given year generally will perform less satisfactorily in following season, Table 6. This is true because a dry group will contain many permanently infertile animals which generally cannot be identified visually. The desirability of culling these ewes is largely an economic question and a management decision to be made from year to year depending on sale value and cost or availability of replacement ewes. In most cases, a dry mature ewe will produce more satisfactorily than range- raised yearling ewe replacements. A ewe raising twin lambs is a better prospect than a ewe raising a single, and a ewe which has lost one or more lambs is the least desirable prospect of the three but would be preferred over a dry ewe. Culling a ewe which raised only a single or a ewe which lost one or both ‘TABLE 5. LIFETIME PRODUCTION—SONORA DATA—-CONTRASTING EWES WHICH WERE WET AND DRY THEIR FIRST YEAR IN FLOCK Lifetime record Excluding first year‘ 2T9 Number Ewe Percent lambs Total production Percent lambs Total production ' n ewes years Born Raised Pounds per Pounds per Bom Raised Pounds per Pounds per ewe ewe bred ewe ewe bred 217 1125 74.8 65.3 215.7 41.6 92.6 80.9 215.7 51.5 302 1536 96.3 83.3 277.0 54.4 95.4 83.3 225.7 55.3 6. RELATION OF ONE INFERTILE SEASON TO REPRODUCTIVE PERFORMANCE THE FOLLOWING SEASON'OF MATURE RAMBOUILLET EWES iISONORA AND McGREGOR STATION Sonora ifdcita (Mature ‘ewesl McGregor data (Yearling ewes) McGregor data (Mature ewes) Percent lambs Number Number Percent lambs Percent lambs Number ewes Born Raised ewes Born Raised ewes Born Raised 178 88.2 75.8 56 108.9 91.1 43 104.7 83.7 978 97.0 87.1 238 125.7 115.1 497 131.6 113.5 ll lambs generally is not recommended unless some additional fault is present. Numerous analyses have shown that a ewe, dry 2 years in succession, is a very poor breeding prospect and always should be culled (12). Producers should estab- lish a practice of identifying such dry ewes by ear notching at shearing or drafting into a separate pasture. If dry ewes are not culled after one dry season, they always should be culled at the second. Selection for fertility with a goal of long-term im- provement in reproductive efficiency has not been prac- ticed widely in commercial flocks and may not be justified because of the low to moderate heritability and the co-m- plicated record keeping required. If management prac- tices and nutritional level are such that twin-born lambs or the highly fertile ewes are not discriminated against, some selection for fertility is automatic in nature. If fertility information is available in ram selection, it should be looked on with favor. Selection directly for fertility in both experimental or stud flocks should receive considerably more attention than at present. Recent reports (13, 14, 15) indicate that some aspects of fertility such as the occurrence of multiple births may be more responsive to selection than previously thought. There is little o-r no evidence that inheritance is a major factor in the number of dry ewes. One of the simpliest schemes in selecting for fertility would be to use only twin-born rams and to favor twin- born ewes where possible. Other procedures would favor animals born as twins under less favorable conditions such as age of ewe, season, etc. or to have collateral relatives with a high level of twinning. In addition to fertility selection, particularly ovulation or lambing rate, there are certain easily identified, highly heritable characteristics which also are related to reproductive efficiency. In many cases, these should receive emphasis in selection pro- 12 grams. One characteristic is size or rate of growth. Sel I . tion for increased size may reflect genetic differences well as the effect of a favorable environment. Increas in size usually will result in improved fertility and shoul’ be lo-oked a.t favorably at least up to the weight ran representing physiological maturity -for the breed involv (115 to 125 pounds for Ramboulillet). Increases in si above this range may not contribute to improved efficien if of the flock. A large number of body wrinkles are adversely relate; to fertility (16, 17) but generally this is not a probl with sheep in this country. Reports (18, 19, 20) sho that open-faced animals are more fertile than those wit wool covering the face. The adverse effects of wool the face seem to result from partial blinding; however other unexplained physiological factors also appear to i involved. _ v A study of this question seems to indicate the fol lowing conclusions: A wool-blind animal, or one pot-Q » tially capable of becoming blind, should be culled . identified, Figure 10. An animal completely open-fac below the level of the eyes is desired, but it should i. approached most cautiously using records or estimates i; wool production and visual face-covering scores. It emphasis on face covering without careful consideration a ‘wool production usually will result in some loss of i weight. The adverse effects of face covering are less seri in flocks shorn twice per year or in those grazed in bru L: rangelands where the wool around the eyes is pulled it, while animals graze. The presence of wool covering j the face is more serious in flocks grazing ranges wh needlegrass or speargrass is prevalent. Too much emp sis on the absence of face cover in purchase of ewes f’ fall lamb production or for a multiple-lambing progr; may result in a ewe that is less satisfactory for out-of-s I Figure l0. Selecting for more open-faced sheep is one means of selecting for increased fertility. tluction. This is not a direct effect of face cover- is probably the result of genes from nonfine-wool zving been introduced to obtain the open-faced l 'stic. NCE 0F SEASON Iltheir natural state, sheep are almost completely breeders which mate in the fall and drop lambs ispring. Domestication has caused the breeding to be extended. Breeds or types of sheep vary {in this respect, and fine-wool sheep, such as Ram- ‘; are recognized as being the least restricted in reeding habits. Numerous reports have shown -~ e Rambouillet ewes will exhibit estrus at any ijof the year, but many will show a short anestrous §,.(a failure to exhibit estrus) in the spring. The 'e of or sudden joining with rarns plays a part in tion of this anestrus. ent studies show other factors relating to repro- efficiency vary with season as well as the occur- iof estrus. Heat periods are likely to be less intense iately before or after the anestrus. Ovulation with- p, frequently occurs at this time. As a result, the l conception rate as a percent of the cycling ewes still lower in the early spring. In addition, the incy of twin or multiple ovulations are higher in ‘t, s- , ., ed at McGregor and are shown in Table 7 and e 11. These data were based on 6-week mating i- starting on March 21, ]une 21, September 21 and _ , ber 21. Overall results indicate it is possible to l ce lambs any season, but considerable variation in “uctive efficiency should be expected. The low t, apparently is obtained from matings in April, and I ighest ovulation rate occurs in September. In this , temperature apparently acted to lower the lambing > below that of the December mating. Lambs born I spring matings will be dropped over a longer period ' e. Within the Rambouillet breed, different groups i es will vary widely in the degree of seasonal restric- dfou A CONSTANT PLANE or NUTRITION e data on which these conclusions are based were PERCENT WITH MULTIPLE OVULATIONS PERCENT WITH MULTIPLE BIRTHS SOT- 70" 60-- 40-- min‘ MULTIPLE OVULATIONS OR MULTIPLE BIRTHS AS A PERCENT OF TOTAL EWES OVULATING OR LAMBING MARCH JUNE SEPT. MATING PERIODS Figure ll. Influence of season on frequency of multiple ovula- tion or multiple births. tion due to breeding, age (young ewes are more restricted) and, apparently, geographic location. INFLUENCE OF TEMPERATURE High temperature is a major obstacle to efficient livestock production in Texas and much of the South, and its effect is particularly marked on the reproductive process in the sheep. Table 7 presents data showing the ovula- tion and lambing rate of aged Rambo-uillet ewes by season. These data indicate fewer lambs were obtained from the June and September mating periods than the potential indicated by total ovulations. This apparently can be attributed to some of the various effects of temperature on reproduction. However, the loss would be expected to vary considerably in different years and differing sets of environmental conditions. As many as five different functions have been iden- tified whereby fertility of the sheep is adversely affected by high environmental temperatures. Since the climatic aspect of the animals’ environment is difficult to alter 7. INFLUENCE OF SEASON OF YEAR ON THE OCCURRENCE OF ESTRUS, OVULATION AND LAMB PRODUCTION OF AGED RAMBOUILLET Total lambs dropped** Total ovu- Total number Percent showing Percent lations as Percent ewes percem o; percem of of ewes estrus ovulating percent of ewes lambing ewes in ewes l‘ ‘ l" 9'°"P* group lambing A h 116 84.5 92.6 105.6 66.1 83.9 127.0 ‘ 167 96.4 94.7 140.8 g 76.5 96.5 126.2 _’ mber 142 97.2 100.0 175.4 84.5 126.8 150.0 mber 114 99.1 98.1 151.9 87.0 135.2 - 155.3 vsed on an observational laparotomy of a sample of half of the ewes in each group. sed on the lambing results from the sample half not laparotomizad. l3 Figure l2. Fall-born lambs often are small and weak as a result 0f heat stress 0n the ewe during gestation. Extreme cases usually can be prevented by good management practices. and improved adaptation of the species is a slow process, no simple or complete solution to the heat stress problem has been developed. The first step in overcoming this problem is knowing the ways heat stress lowers fertility and some of the factors which contribute to or lessen heat stress. Perhaps the most serious effects of environmental temperature on fertility is lowered semen quality o-f the male. In the ewe, extreme heat stress causes a period of anestrus in midsummer. Other workers (21, 22) have shown conclusively that heat stress at any time from mat- ing to approximately 8 days after mating can cause embry- onic losses in sheep. The physiological mechanism in- volved here is not understood completely, but it a the ovum is damaged to the extent that it does not d, beyond the early stage-s of cell division.“ Workers tioned previously were dealing with a constant _. while the sheep were confined in a temperature i chamber. Although temperatures equal to or abo F. for a part of the day are a common occurrence the mating season in the South,i"i"this does not sufficient stress under natural conditions to cause loss. However, this may not be true of more e, conditions when temperatures are above 100° F. mi the day. In one experiment at McGregor, the ef cooling yearling ewe-s for a short time after a July =1 was investigated. In this case a small, nonsignific crease in the lamb crop was obtained by cooling at {j The importance of this factor needs further investi Extensive work at McGregor (25, 24) has show environmental temperatures can cause fetal dwarfingj ure 12) and increased death loss of lambs. Extrem ditions also can cause complete embryo loss (25), does not appear to be a major loss under natural y tions. Reduced birth weight of lambs is almost univi observed at fall lambing, but this can be of major or: importance, depending on the presence or abse ._ other complicating factors. Some factors are tion of the ewe, age of the ewe, breeding of the amount of shade (Figure 14). movement is the most practical procedure for r; Figure l3. Good shade with air movement is the most practical procedure for reducing heat stress. 14 Good shade wi i s. Shade in the pasture is not 1n itself assurance shading. The habit of sheep grazing into the pull them away from available shade, or the i instinct may cause a large flock to gather around which is adequate for only a few head. High ure has a direct effect 0n nutrition of the ewe i‘. reduced grazing time and through voluntary reduc- feed intake to reduce endogenous heat production. ewes or ewes with nonfine-wool breeding are more seriously. Confining to barns or enforced (26) of the ewes (Figure 13) plus adequate i ental feeding in late gestation will usually alleviate fetal dwarfing (27). Where this phenomenon has Lobserve-d or remains a problem, matings should eduled so lambing will not occur before early ber. HING 1 lushing has been one of the most extensively investi- i and discussed practices relating to sheep fertility. '» still is not possible to provide producers with clear- jvice about the value of this practice. A majority i. ' literature relating to this subject reports a favorable se; however, many experiments with negative or ing the amount of feed available to them just be- i, some weight response must occur from flushing. T23 the general exception of fat yearling ewes or medium- ewes bred in hot environment, any gain in body ht would be expected to result in increased lamb crop ped. Knowledge of the flock’s condition should p; one to estimate the approximate response to flush- Data collected in the Edwards Plateau (28, 29) lving over 4,000 ewes shows a modest increase of 8.4 lent in lambs marked (approximately 2 weeks of age) if obtained by flushing. This was 1.5 percent more than ated requirements to equal the feed costs. Other i (50) indicates that no advantage should be expected flushing yearling ewes since one ovf the primary ilntages expected from flushing would be an increase umber of twin births. These are neither expected nor from yearling ewes. This work further clarified period likely to give the greatest response as one equal 1 greater than one estrous cycle prior to mating. It appears that flushing should be strongly considered aged ewes in thincto moderate flesh. The flushing iod should be initiated at least 3 weeks and preferably if a longer period prior to mating. A good flushing ion should provide an increase in energy with adequate itein and vitamin supplementation. These commonly ld be approximately equal parts of sorghum grain and ‘sistent results are not recorded. Flushing generally having the ewes on a rising plane of nutrition or' mating in hopes Olf increasing the lamb crop obtained. ' cottonseed meal fed at the rate of 1/2 to yl-pound daily. Oats or corn may be substituted for the sorghum grain. Alfalfa hay at a higher level may be used to substitute for both ingredients. MULTIPLE LAMBING The nutrients expended by the ewe in lamb produc- tion are comparatively minor, except during the 6 weeks prior to lambing and 8 weeks after lambing. On a high level of nutrition or intense management, ewes may become very fat; whereas, under adverse conditions the remainder of the year may be required to regain the weight loss associated with lamb production. When ‘ewes are on a high level of nutrition, or when this is practical, the possibility of lambing more than once per year sho-uld be considered. Since sheep have a gestation period of approx- imately 5 months (149 days), theoretically it should be possible to obtain two lamb crops per year. In practice this is not possible because ewes will not consistently breed back early enough after lambing. The only ewes at McGregor that lambed twice in a 12-month period were those that lost their lamb or lambs at or shortly after lambing. Since ewes will not uniformly breed while nursing lambs, multiple lambing should be practical only in connection with early weaning. Age at which the lambs are weaned has a major influence on the frequency lamb- ing can occur. ewes have produced two lamb crops in as little as 14 months. Over a 4-year period, a group of mature ewes has dropped as high as 242 percent lamb crop, but heavy death losses reduced the number weaned to approximately 160 percent. With more intense supervision to cut down death loss of lambs (O35 percent) and with earlier wean- ing, it should be possible to improve this. Other workers (51) using crossbred ewes and weaning lambs at 4 weeks, along with confinement rearing, obtained a lamb crop of 252 percent dropped and 225 percent raised. USE OF HORMONES The possibility of using exogenous hormones to stim- ulate fertility in sheep has long held the interest of pro- ducers and research personnel. Many have successfully accomplished this on a research basis, but as o-f this writing this practice has no-t been successfully adapted to commercial practice. Several gonadotropic hormone prep- arations have been used successfully to stimulate ovulation. but numerous problems have been encountered in adapting these preparations to commercial practice. These products have not been successfully produced synthetically and are available only from animal origin. They are both expen- sive and of questionable standardization and purity. This, plus the natural animal variation has made it impossible to develop a dosage relationship which will give two lambs. Less than two would be of no advantage and m.ore than 15 In experiments at the McGregor station - two is undesirable.‘ A second problem has been that ovulation occurring as a direct result of gonadotropic stimulation usually occurs without coincident estrus, and mating does not occur. It is possible to circumvent this problem by establishing the estrous cycle with vasectomized rams and injecting gonadotrophins (500-1000 I.U.) in the pro-estrous phase (13-15 days) of the cycle (32). A second procedure is to treat the ewe with progesterone prior to gonadotrophin therapy (33). This adds sub- stantially to the expense and has not given consistent re- sults. These problems combine to make the procedure relatively unworkable in commercial practice, but daily progress is being made in this area and it is likely that a workable procedure will be available in the near future. Two other hormone preparations have been used in connection with efforts to improve sheep fertility. One has been the synthetic steriod, diethystilbestrol. Use of this product causes only psychic heat or estrus and is more likely to reduce or delay the lamb crop than improve it (34). A second group of compounds investigated are the synthetic products with progestational activity. Several, when used in oral form or as intravaginal suppositories have proved highly effective in synchronizing estrus in sheep; however, conception rate at the first or sychronized estrus has been variable and often low. Most ewes remain largely synchronized at the second estrus at which fertility is normal, but the variation in length of estrous cycle com- pounded with normal variation in the length of the gestation period provides for only a modest degree of synchronization of lambing (35). These limitations, plus the cost involved impose serious limitations on the use of ~- this practice (36). DISEASES Any diseased condition which seriously affects the well-being of the animal could be expected to adversely affect reproductive performance. On a worldwide basis, several pathogenic organisms have been identified (Bruce/- la ovir, Vibrio fetus. Toxoplasma and Streptococci) which are associated with reproduction of sheep (37). Most have not been identified as being present or as being a major causeqof loss in Texas. There is circumstantial evidence which indicates the organism“ that causes epididy- mitis in rams can cause abortion or the birth of weak or dead lambs. Vibrionic abortion caused by a bacteria-like organism, Vibrio fetus, is specifically associated with abortion in the ewe. This disease is fairly widespread in the northwestern part of the United States, but has not been identified as l6 a cause of serious loss in Texas. Producers losin from abortion should get the advice of veterinaf experts in this field. One condition producers should be familiar . known variously as pregnancy disease, ketosis, _ paralysis and twin lamb disease. This is not ca an infectious agent but is of ‘nietabolic origin. i losses from this condition occur in Texas and i other states. Extensive research has been done A: disease (38, 39), and the physiological basis occurrence seems to be fairly well understood. r ease occurs primarily among ewes bearing twin f and in the late stage of pregnancy. The great de p energy (glucose or blood sugar) by two fetus exceeds that available from daily feed intake. especially true if the ewes are not on a good program or if some management procedure, such ment, shearing or other stress factors, causes th i; off feed for a period in late pregnancy. Unde conditions, a heavy and often incomplete breakdi body fat occurs resulting in an accumulation of k v al-dehydes in the blood. If the concentration 0i compounds becomes high enough, the disease i’ Early symptoms are loss of appetite, lethargy and ; i; of the teeth, which progresses to loss of vision :' inability to stand or move about. In the final sta ewe will be down with the head pulled back to o i The animal may not die for several days after ~ the final stage of the disease. If caught in the-v stages, the disease often can be reversed and the saved, but the condition rapidly becomes irreversi cause of permanent damage to vital organs or Giving of glycerol or propylene glucol by me drench or stomach tube is the best treatment. Ail fi-ounce dose should be administered at 6- to 12-ho vals until the ewe is back on feed or until it is that no benefit is being obtained. When the ewe on feed, she should be fed a good ration contai adequate supply of readily available energy. Ew ing symptoms of this condition should receive at r pound of concentrates daily and “ad lib” roughage- Prevention is much more important than pregnancy disease. Two primary precautions are l mended. One is to provide heavy ewes in late p i with supplemental energy (approximately 3A- concentrate). It is equally important to prev '5' situation that might cause the ewes to be under interrupt feeding for a day or more. Techniques; permit identification of twin bearing ewes w rangers in preventing this disease in their flocks. Literature Cited ,5‘: ‘is? 10. IL 13. 14. 15 16. 17. 18. 19. 20. 2L Lambourne, L. j. 1956. Mating behavior. Proc, of Ruakura Farmers Conf., Dept. of Agr. New Zealand. Hulet, C. V., S. K. Ercanbrack, R. L. Blackwell, D. A. Price and L. O. Wilson. 1964. Mating behavior of the ram in the multi-sire pen. jour. of Anim. Sci. 21:865. McKenzie, Fred F. and V. Berliner. 1937. The reproduc- tive capacity of rams. Mo. Agr. Expt. Sta. Res. Bu. 265. Moore, Carl R. 1924. Properties of the gonads as con- trollers of somatic and physical characteristics. VIII. Heat application and testicular degeneration: the function of the scrotum. Am. jour. of Anat. 54:557. Whiteman, j. V., W. L; Basler and M. B. Gould. 1964. Continuous vs. night breeding in producing fall born lambs. Okl. Agr. Expt. Sta. Misc. Pub. 74 page 5-10. Livingston, C. W. jr. and W. T. Hardy. 1964. Isolation of Actionobacillus seminis from ovine epididymitis. Am. jour. Vet. Res. 25:660. Livingston, C. A. and H. A, Osborne. 1965. Personal communication. Hulet, C. V., W. C. Foote and R. L. Blackwell. 1964. Effects of natural and electrical ejaculation on predicting fertility in the ram. jour. of Anim. Sci. 25:418. Campbell, F. R.. 1962. Influence of age and fertility of Rambouillet ewes on lamb and wool production. Texas Agr. Expt. Sta. MP-596. Shelton, Maurice. 1959. Importance of size and proper development in respect to breeding performance of Ram- bouillet ewes. Tex. Agr. Expt. Sta. - PR-2081. Shelton, Maurice. 1962. Relation of one dry season to sub- sequent reproductive performance of fine wool ewes. Texas Agr. Expt. Sta. PR-2258. Wiggins, E. L. 1956. Cull those dry ewes. Nat. Wool Grower 46:52. Turner, Helen N. 1962. Breeding Merino sheep for mul- tiple births. Wool Tech. and Sheep Breeding IX:19. Turner, Helen N., R. H. Hayman, L. K. Triffit and R. W. Prunster. 1962. Response to selection for multiple births in the Australian Merino. A 'Prog. Rpt. An. Prod. 4:165. Young, S. S. Y., Helen N. Turner and C. H. S. Dolling. 1965. Selection for fertility in Australian Merino sheep. Aust. jour. of Agri. Res. 14:460. Moule, G. R. 1960. The major causes of low lamb mark- ing percentages in Australia. The Aust. Vet. jour. 56:154. Fels, H. E. 1964. The association between neck wrinkle and fertility in Merino ewes in Southwestern Australia, Aust. jour. Exp. Agric. Anim. Husb. 4:121. Shelton, Maurice and O. L. Carpenter. 1957. face covering to productivity in Rambouillet Sheep. Relation of Texas Agr. Expt. Sta. PR-1929 Terrill, C. E. 1941. Face covering in range sheep. U. S. Dept. Agr. A. H. D. N0. 49. Cockrem, F. 1960. A progress report on research on face cover. Proc. New Zealand Soc. Anim. Prod. 20:61. Alliston, C. W. and L. C. Ulberg. 1961. Early pregnancy loss in sheep at ambient temperatures of 70° and 90° F. as determined by embryo transfer. jour. of Anim. Sci. 20:608. 22. 23. 2i 30. 3L 32.. 35. 34. 35. 36. 37. 38. 39. Dutt, R. H., E. F. Ellington and w. w. Carlton. I Fertilization rate and early embryo survival in she ‘ unsheared ewes following exposure to elevated air t, tures. jour. of Anitn. Sci. 18:1508. ‘ Shelton, Maurice. 1964. Relation of birth weight t_ losses and to certain productive characters of -= lambs. jour. of Anim. Sci. 25:555. Shelton, Maurice. 1964. Relation of environmen i; perature during gestation tobifth weight and mor lambs. jour. of Anim. Sci. 25:560. a Shelton, Maurice. 1965. Effect of heat stress and _ implants during gestation on lambing performance a i production. jour. of Anim. Sci. 24:288. Shelton, Maurice. 1965. An interaction of tern shade and shearing treatment on heat stress of sheep. Agr. Expt. Sta. PR-2337. "T Goode, Lemuel. 1964. Effects of summer conf' upon ewe productivity. jour. of Anim. Sci. 25:906. Campbell, F. R., j. H. jones and W. T. Hardy. i Response of range ewes to flushing. Tex. Ag. Ex PR-2111. " Campbell, F. R., j. H. jones and W. T. Hardy. ‘ Flushing range ewes with cottonseed meal and pellets.' Agr. Expt. Sta. PR-2162. i Hulet, C. V., R. L. Blackwell, S. K. Ercanbrack, g Price and R. D. Humphrey. 1962. Effects of "- length of flushing period on lamb production. j; Anim. Sci. 21:505. . Copenhaver, j. S. and R. C. Carter. 1964. Early w‘ and multiple lambing. Mimeo. Dept. Anim. Husb., Agri. Expt. Sta. Neville, w. E., 1i, o. M. Baird and o. EfiSell. f Influence of pregnant mare serum and cooling on the ing percentage of ewes. jour. Anim. Sci. 20395 Robinson, T. j. 1956. The artificial inseminati Merino sheep following the synchronization of oes I ovulation by progesterone alone and with pregnant] serum. Aust. jour. of Agric. Res. 7:194. Price, D. A. and W. T. Hardy. 1955. Treatment of. ewes with estradiol cyclopentylpropionate to control br — a field trial. jour. of the Amer. Vet. Med. Asso. 1’ Evans, j. S., R. H. Dutt and E. C. Simpson. 1962. ing performance in ewes after sychronizing estrus by 6-methyl-17-acetoxy-progesterone. jour. of Anim.? 21:804. * Hinds, F. c., P. j. Dziuk and j. M. Lewis. 1964. of estrus and lambing performance in cycling ewes ‘ methyl-17-acetoxyprogesterone. jour. of Anim. Sci. 2 Hartley, W. j. and B. W. Boyes. 1964. Incidence of? perinatal mortality in New Zealand with particular -j_ to intra-uterine infections. New Zealand Vet. jour. i Reid, R. L. 1960. Studies on the carbohydrate _ of sheep. IX. Metabolic effects of glucose and gly ’ undernourished pregnant ewes and in ewes with pr toxaemia. Aust. jour. of Agri. Res. 11:42-57. Reid, R. L. 1965. Nutritional physiology of the p,‘ ewe. jour. of the Aust. Inst. of Agric. Sci. 29:215. [Blank Page in Original Bulletin] Texas AG-M University Texas Agricultural Experiment Station College Station. Texas 77843 414%»; Director Publication-Annual Report or Bulletin or Report o! Progress Permit 1105 OFFICIAL BUSINESS p, =. 1);‘ Penalty tor pri payment of -