Influence of breed, number of suckling lambs, and stage of lactation on ewe milk production and lamb growth under range conditions

Milk production and lamb growth were characterized in 118 multiparous, 3- to 7-yr-old Rambouillet, Columbia, Polypay, and Suffolk ewes under spring sage range and high mountain meadow grazing from 28 to 98 d postpartum. Daily milk yield as measured by the lamb suckling weight differential technique did not differ (P greater than .05) among breeds, although milk production of Suffolk ewes tended to be higher than that of the other three breeds. Within the Rambouillet, Columbia, and Polypay breeds, total estimated yield of ewes with twins was 13 to 17% higher than that of ewes with singles, whereas in the Suffolk breed, suckling twins increased total milk yield 61% over that of ewes with singles. Twin lambs induced a larger differential in dam milk production in late lactation (70 to 98 d) than in earlier lactation (28 to 70 d). Number of lambs did not influence milk protein, Ca, or P content (P greater than .05). Fat levels in colostrum and 4-d milk were elevated 14 and 20%, respectively, in ewes suckling twins compared with ewes suckling singles. Under range conditions, Suffolk ewes suckling single or twin lambs lost more BW (12 and 21% of 4-d postpartum body weight, respectively) than Rambouillet (4 and 7%), Columbia (5 and 8%), or Polypay (8 and 8%) ewes. Correlation coefficients of milk production and lamb growth rate were positive and significant (P less than .05) up to 56 d of age. Growth rate was less closely associated with milk production for twin than for single lambs.     

Body weight changes and subsequent lambing rates of western whiteface ewes grazing winter range

The objective was to describe body weight change (BWC) and subsequent lambing performance of Columbia, Polypay, Rambouillet, and Targhee ewes that grazed shrub-dominated range in winter of 1989, 1990, and 1991. In December (winter), after breeding each year (yr; October to December), ewes were moved to range. Depending upon severity of climatic conditions and vegetation accessibility, ewes grazed winter range for 30 to 60 days (d). Body weights were measured 2 d before grazing commenced (initial) and 2 to 7 d after ewes were transported off range (exit). Total BWC was calculated by subtracting finial BW from initial BW. All data were analyzed within each breed, as repeated measures using mixed models with age and year included in the model. For all breeds, 2-yr-old ewes were lightest going on to winter range and had the lowest lambing rate. Ewes lost weight while grazing winter range, but mature BW, once achieved, was restored annually with the exception of the 7-yr-old Columbia and Targhee ewes. Regardless of breed or age, ewes were able to achieve lambing rates > 1.5 lambs following early- and mid-pregnancy weight loss. Lambing rates were greater in older ewes, which generally experienced substantial negative BWC during winter grazing.     

Reproductive response of ewes to immunization with Fecundin (ovandrotone)

Ewes of five crossbred genotypes (total of 221 ewes) were immunized with a commercial preparation of androstenedione-7HSA in DEAE dextran adjuvant in a 2-yr trial. In yr 1 ewes were allocated within genotype to a 2 x 2 application of immunization and premating flushing. In yr 2 they were allocated within previous Fecundin treatment into either Fecundin-treated or control groups. First-time immunization with Fecundin increased ovulation rate by .70 ova/ewe in yr 1 and by .85 ova/ewe in yr 2 (P less than .05). Ewes treated in both years produced fewer ova than those treated in the 2nd yr only (P less than .05), but they did not differ in litter size. Although Fecundin reduced conception to first mating, the overall conception rate was not affected. Litter size of treated ewes was increased by .19 and .38 lambs/ewe lambing (P less than .05) in yr 1 and yr 2, respectively. Fecundin treatment in yr 1 produced a carry-over effect in yr 2 by increasing litter size by .26 lamb/ewe (P less than .05) while reducing conception to first mating. The litter size of ewes with two ovulations was reduced by Fecundin treatment in yr 1 (P less than .05) but showed no consistent pattern in yr 2. Overall, ewes with two ovulations produced .7 to .8 more lambs than ewes with one ovulation, and ewes with three ovulations produced .4 more lambs than those with two ovulations. Ewes of different genotypes did not differ in their response to Fecundin.     

Usefulness of subjective ovine milk scores: I. Associations with range ewe characteristics and lamb production

Range ewes are commonly evaluated for milking ability by producers to determine the ewe's ability to rear lamb(s). The U.S. Sheep Experiment Station has subjectively scored (low, average, high) a ewe's milking ability within 24 h of lambing for many years. The relationship of subjective milk scores with lamb production was investigated using lambing records of Columbia (n = 1,731), Polypay (n = 1,129), Rambouillet (n = 1,704), and Targhee (n = 1,638) ewes. The incidence of high milk scores increased from less than 10% at first parity to 29 to 40% at second and greater parities. At maturity, Columbia ewes (38%) had the highest percentage of high milk scores. A positive association existed between ewe BW and her milk score at third and later parities. Ewes with high milk scores gave birth to heavier lambs (P < 0.05), whereas ewes with low milk scores were associated with lighter (P < 0.05) lambs at birth. Ewes with low milk scores weaned less (P < 0.05) total weight than ewes with better milk scores across all age groups for all breeds. Lighter weaned litter weights from ewes with low milk scores were linked to lighter birth weights and fewer weaned lambs. Differences for litter weight weaned between ewes with average and high milk scores were generally observed at 2 and 3 yr of age, when litter weights were heavier among ewes with high milk scores (P < 0.05) for all breeds. Between the ages of 1 and 3 yr, Columbia, Polypay, Rambouillet, and Targhee ewes with an average milk score weaned heavier (P < 0.05) litters (average differences of 10, 9, 13, and 12%, respectively) than ewes with low milk scores. For all breeds at all ages, individual lamb weaning weights were heavier (P < 0.05) when they were reared by ewes with high milk scores compared to lambs reared by ewes with low milk scores. Results suggest that milk score is an economically important trait in these four breeds and should be considered in management and breeding objectives; at a minimum, the incidence of low milk scores should be kept as small as possible.     

Inheritance of fecal egg count and packed cell volume and their relationship with production traits in sheep infected with Haemonchus contortus

This study describes responses to artificial infection with Haemonchus contortus in ewes and lambs of 50% Dorset, 25% Rambouillet, and 25% Finn-sheep ancestry and provides estimates of genetic parameters for measures of parasite resistance. One hundred ninety-eight ewes out of 64 sires, and 386 lambs out of 25 sires were evaluated in autumn and spring of 2 yr. Ewes were dewormed shortly after weaning their lambs and lambs were dewormed at about 120 d of age. One week after deworming, ewes and lambs were dosed with approximately 10,000 infective larvae of H. contortus. After infection, BW, fecal egg counts (FEC), and packed cell volume (PCV) were measured weekly for 7 wk in lambs kept in drylot and fortnightly for 11 wk in ewes on pasture. Summary traits were defined as initial PCV, mean BW across all times, and means for PCV (MPCV) and log-transformed FEC (MLFEC) at wk 3 to 7 after infection for lambs and wk 3 to 11 after infection for ewes. Ewes and lambs did not lose weight overall in any year or season, but there was no consistent effect of year or lambing season on mean LFEC or mean PCV during infection in either ewes or lambs. Yearling ewes were less resistant to infection than older ewes, with lower PCV (P < 0.05) and higher LFEC (P < 0.05). During infection, PCV was positively correlated with BW and negatively correlated with LFEC in both ewes and lambs. In lambs, heritabilities were 0.39 (P < 0.01) for PCV, 0.10 (P < 0.05) for LFEC across all measurement times, and 0.19 (P < 0.01) for three measures of LFEC taken at the peak of infection. Heritability estimates for ewes were 0.15 (P < 0.05) for PCV and 0.31 (P < 0.01) for LFEC. Repeatabilities for LFEC and PCV across measurement times were moderate in ewes and lambs. Correlations between dam and lamb records for MLFEC were generally low, suggesting different mechanisms of resistance in lambs and nonlactating ewes. Ewes with higher genetic merit for growth as lambs were less resistant to infection as adults, but genetic merit for fertility and prolificacy were not related to parasite resistance. Lambs with higher genetic merit for body weight were more resistant to infection. Selection for resistance to H. contortus is therefore possible and should not adversely affect growth of lambs and fertility of ewes in this production environment.     

Performance of Polypay, Coopworth, and crossbred ewes: I. Reproduction and lamb production.

Six ewe genotypes, generated by mating Coopworth (C), Polypay (P), and Suffolk (S) rams to Polypay and Coopworth-type (Ct) ewes, were exposed to Hampshire rams for spring lambing from 1986 through 1990. Data from 1,092 exposures and 1,044 resultant lambings were used to analyze reproductive traits and lamb growth rates. Overall conception rate averaged 95% and ranged from 93% for S x Ct ewes to 97% for P x Ct ewes. Mean litter size at birth averaged 1.63 and ranged from 1.45 for C x C ewes to 1.75 for S x P ewes. Ewes from P dams had higher mean litter size (P less than .01) than those from Ct dams (1.73 vs 1.54), but differences between sire breeds were not significant. Incidence of lambing assistance was similar for ewes producing single or multiple lambs. Lamb birth weight influenced the level of assistance rendered to single-bearing but not to multiple-bearing ewes. Lambing assistance was not related to lamb survival, probably because the high surveillance level minimized trauma before assistance was rendered. Incidence of required assistance declined over subsequent parities. Lamb birth weights were affected by ewe genotype and increased with increasing ewe age. Survival of single-born lambs averaged 94% and was not affected by dam genotype. Survival of twins averaged 85%, ranging from 79% for lambs from S x Ct ewes to 89% for lambs from P x P ewes. Suffolk-sired ewes produced the heaviest mean birth and weaning weights for both singles and twins. Coopworth-sired ewes weaned heavier single lambs but lighter twins than P-sired ewes.     

Genetic analysis of litter size in Targhee, Suffolk, and Polypay sheep

Data on litter size, weaning weights at 60, 90, and 120 d, postweaning gains from weaning to 120 or 365 d of age, fleece weight, and fiber diameter from Targhee, Suffolk, and Polypay flocks participating in the U.S. National Sheep Improvement Program were used to estimate genetic parameters for litter size and genetic relationships between early-life traits and future litter size. Records on 7,591 lambings by 3,131 Targhee ewes, 10,295 lambings by 5,038 Suffolk ewes, and 6,061 lambings by 2,709 Polypay ewes were used. Heritability estimates for litter size ranged from .09 to .11 across breeds; repeatability ranged from .09 to .13. Additive genetic effects on litter size were generally positively, and occasionally significantly, correlated with animal additive genetic effects on weaning weights and postweaning gains. Genetic correlations (r(a)) ranged from .08 to .48 in Targhee and from .17 to .43 in Suffolk but were close to 0 in Polypay (-.14 to .09). Additive maternal effects on weaning weight were positively associated with litter size in Suffolk and Polypay; this correlation was negative (-.23 to -.35), but not significant, in Targhee. Fleece weight was not strongly associated with litter size; (r(a) = -.09 to .21). However, fiber diameter had a significant undesirable correlation with litter size (.30) in Targhee. Estimates of phenotypic correlations of litter size with early-life traits were uniformly small (-.02 to .08). Thus, although occasional genetic antagonisms between litter size and early-life traits were observed in these data, none appeared large enough to prevent simultaneous genetic improvement in both traits.     

Performance of Polypay, Coopworth, and crossbred ewes: II. Survival and cumulative lamb and wool production over 4 years.

Six ewe genotypes, generated by mating Coopworth (C), Polypay (P), and Suffolk (S) rams to P and Coopworth-type (Ct) ewes, were exposed to Hampshire rams for spring lambing from 1987 through 1990. Data from 1,013 exposures and 973 resultant lambings were used to analyze reproductive traits and cumulative ewe productivity over 4 yr. Ewe body and fleece weights were also analyzed. Ewes from S sires weaned the heaviest lambs and ewes from P sires weaned the largest number of lambs, resulting in similar total weight of lamb weaned per ewe mated. Coopworth-sired ewes weaned the least total weight of lamb per ewe mated. Ewes weaning twins produced 54% more total litter weight per ewe than those weaning singles. Annual ewe survival averaged 95%, ranging from 93% for S x P and C x P ewes to 97% for P x Ct and C x Ct ewes. When cumulative number and weight of lamb produced was assessed on the basis of all ewes starting the trial, P-sired ewes were highest, followed in order by daughters of S and C sires. Suffolk-sired ewes (67 kg) were 13% heavier than daughters of P rams and 19% heavier than daughters of C rams. Adjustment of lamb production for ewe metabolic body size resulted in C-sired ewes being more efficient than the heavier S-sired ewes. Coopworth-sired ewes produced 32% more wool than ewes sired by the other two breeds. Differences in wool production between ewes weaning one or two lambs were small.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of Vitamin E and Selenium Supplementation in Late Gestation on Lamb Survival and Pre-Weaning Growth

This study was conducted to evaluate vitamin E injection and Se in a mineral supplement in late gestation on lamb survival and pre-weaning growth performance. Ewes were grouped in pens based on their fetal count and BW. The feed provided to ewes in late gestation included alfalfa hay, corn, and protein supplement according to NRC (1985) recommendations. Ewes in late gestation were assigned to a 2 × 2 factorial arrangement of treatments within fetal count (single, twin, and triplet + quad). Treatments were no vitamin E or 900 IU of vitamin E injected i.m. per week and 10 or 90 ppm of Se in a mineral supplement fed ad libitum. Within each pen of ewes (8 to 10 head), approximately one-half of the ewes received injectable E beginning 4 wk before the first expected lambing; the other one-half received no vitamin E. Vitamin E treatments ended at lambing time; however, ewes remained on their respective mineral sources during lactation. Lambs were provided access to creep (16% CP, 83% TDN, and fortified with 35,000 IU of vitamin E, 0.27 g of Se, and 50 g of chlortetracycline/909 kg of creep feed) initiated at an average 10 d of age to weaning. Weekly injection of 900 IU of vitamin E did not affect birth BW (BBW) of lambs. However, 90 ppm of Se fed ad libitum improved BBW of lambs (5.06 vs 4.88 kg, P<0.10) with all of the improvement occurring in lambs born to 6- to 7-yr-old ewes (P<0.01). Vitamin E increased (P<0.05) the pre-weaning performance of lambs from 1- to 2- and 6- to 7-yr-old ewes but did not improve the performance in lambs from 3- to 5-yr-old ewes. Multiple-birth lambs from ewes treated with vitamin E had increased survival in 1 of 2 experimental yr (P<0.05). Survival of single-birth lambs was not effected by vitamin E or Se treatment. These results demonstrate that supplementation of 90 ppm of Se fed ad libitum to ewes during late gestation and throughout lactation improved BBW of lambs from 6- to 7-yr-old ewes, and weekly injection of 900 IU of vitamin E to ewes during late gestation increased the pre-weaning growth of lambs from 1- to 2- and 6- to 7-yr-old ewes and may increase the survival of multiple-birth lambs.     

Influences of gender, time of castration, genotype, birthtype and feeding regimen on lamb longissimus fiber type proportions

Two trials examined genetic and environmental influences on muscle fiber type proportions. Trial 1 compared Polypay and Coopworth x Polypay male lambs either left intact or castrated early, mid or late in growth. Trial 2 compared Hampshire-sired lambs (females, early castrate wethers and late castrate wethers) from Suffolk x Coopworth dams and whiteface x Coopworth dams. Half the lambs in each trial were raised from weaning to 52 kg slaughter weight in drylot; the other half were reared to 41 kg on pasture before being finished in drylot. Analysis of longissimus tissue samples revealed no significant differences among rams, wethers and ewes in proportions of muscle fiber types. Early castration increased the proportion of alpha red fibers in Trial 1 (P less than .01) but not in Trial 2. Polypay lambs had a higher proportion of beta red fibers (P less than .05) than the Coopworth x Polypay lambs, but no differences were seen between the genotypes of Trial 2. Single-born lambs in Trial 1 had a 6% higher proportion of alpha white fibers (P less than .05) than twin-born lambs; however, this difference was not detected in Trial 2. Drylot lambs had a higher proportion of beta red fibers than pasture-reared lambs, the difference being 5% (P less than .01) in Trial 2. Muscle fiber type proportions were not found to be related to growth rate and carcass fatness, and no evidence of differential fiber transformation was found in this trial.     

Lambing date and lamb production of spring-mated Rambouillet, Dorset and Finnsheep ewes and their F1 crosses

The reproductive performance of 255 Rambouillet (R), Dorset (D), Finnsheep (F) and F1 ewes born in 1978-1979 (group I) and 1979-1980 (group II) and managed in a semiconfinement fall/winter lambing system was evaluated through 4 yr of age of all ewes and through 5 yr for a portion of group I ewes. Ewes were with rams from approximately May 1 to late September each year, with a 2-wk break late in July/early August. Traits considered were fertility (ewes lambed/ewes exposed), lambing date, litter size, lamb survivial and 70-d lamb weights. Breeds and crossbred groups differed significantly in lambing date, with DR crossbred ewes earliest and F ewes latest. Repeatabilities for groups I and II were .31 and .22, .24 and .24 and .11 and .07 for lambing date, fertility and litter size, respectively. There was no significant heterosis in lambing date, although DR ewes in both groups I and II were superior to (D + R)/2, by about 1 wk on average. There was significant positive heterosis for fertility and traits of which fertility is a component in FR ewes in group I, but none in group II. The FD ewes showed negative heterosis for litter size, -.23 (P less than .05) for group I and -.09 for group II. The results indicate: F and FD ewes are not well adapted to the Mediterranean climate where this experiment was conducted; there is little, if any, useful heterosis in crosses among these three breeds for lambing date or other reproduction traits and RD and R ewes are most suitable of the groups tested, while late onset of the breeding season limits the usefulness of even 50% Finnsheep ewes for an autumn lambing system in this environment.     

Ovulation rate, lambing rate, litter size and embryo survival of Rambouillet sheep selected for high and low reproductive rate

Ewes from lines selected for high and low reproductive rate and a control line bred and selected randomly were endoscopically examined 3 to 5 d after breeding to determine ovulation rates in the fall of 1985, 1986 and 1987. Fertility (ewes lambing per ewe exposed), lambing rate (lambs born per ewe exposed) and litter size (lambs born per ewe lambing) were evaluated at lambing in the spring of each year. Embryonic survival was estimated as the number of lambs born per corpora lutea. Ovulation rates were 1.28, 1.73 and 1.46 for low, high and control lines, respectively. More (P less than .01) single ovulations occurred in low-line ewes than in the other two lines; high-line ewes had more (P less than .01) twin ovulations than did low- or control-line ewes. Fertility did not differ among lines. Selection line affected (P less than .01) lambing rate at first and all services. Control-line ewes had mean lambing rates at first and all services that were intermediate between those of the low and high lines, which were different from each other. Line x age of ewe interactions existed (P less than .01) for lambing rate at all services and litter size at first and all services. High-line ewes had lower lambing rates and litter sizes as 2-yr-olds than other lines, but their performance increased steadily to 6-yr-olds, whereas the low and control lines remained relatively constant. Embryo survival differed (P less than .10) between lines, being 74%, 63% and 67% for low, high and control lines, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: II. Reproduction of F1 ewes in fall mating seasons

Objectives were to estimate effects of sire breed (Dorset, Finnsheep, Romanov, Texel, and Montadale), dam breed (Composite III and northwestern whiteface), mating season (August, October, and December), ewe age (1, 2, and 3 yr), and their interactions on reproductive traits of F1 ewes. A total of 1,799 F1 ewes produced 3,849 litters from 4,804 exposures to Suffolk rams during 35-d mating seasons over 3 yr. Ewes were weighed at breeding. Conception rate and ewe longevity (present or absent at 42 mo of age) were determined. Number born and litter birth weight were recorded, and number and weight at weaning and 20 wk of age were analyzed separately for dam- and nursery-reared litter mates. Total productivity through 3 yr of age for each ewe entering the breeding flock was calculated as the sum of 20-wk weights for dam- or nursery-reared lambs. Interactions of sire breed x mating season, sire breed x ewe age, and mating season x ewe age were generally significant, whereas interactions of sire breed, mating season, and ewe age x dam breed were seldom detected. Interactions of sire breed x mating season were often due to changes in rank as well as magnitude, indicating the importance of matching sire breed to a specific mating season. The number born to Dorset-, Texel-, and Montadale-sired ewes was not affected by dam breed; however, Finnsheep-sired ewes out of northwestern whiteface dams were more prolific than Finnsheep-sired ewes out of Composite III dams, and the opposite situation existed for Romanov-sired ewes. Least squares means of sire breeds (P < 0.001) for total productivity of dam-reared lambs were 98.5, 103.5, 106.9, 124.6, and 154.9 kg/ewe entering the breeding flock for Texel, Dorset, Montadale, Finnsheep, and Romanov, respectively. Superior reproduction of Romanov-sired ewes was due to greater conception rate and prolificacy for each mating season and ewe age, as well as greater ewe longevity. Total productivity of F1 ewes by Composite III dams (125.6 kg) was greater (P < 0.001) than for ewes born to northwestern whiteface dams (109.7 kg), and the effect of mating season increased (P < 0.001) from August to October to December. Litter weight at 20 wk of age of 2- and 3-yr-old ewes was similar but greater (P < 0.001) than for 1-yr-old ewes. Experimental results provide comprehensive information about the appropriate use of these breeds in crossbreeding systems to meet specific production-marketing objectives.     

Synchronization of estrus and reproductive performance of ewes treated with synthetic progestogens administered by subcutaneous ear implant or by intravaginal sponge pessary

Experiments were conducted to compare the efficacy of synthetic progestogens administered by subcutaneous ear implant or intravaginal sponge to induce a synchronized estrus in adult ewes and ewe lambs and to evaluate reproductive performance (fertility and litter size) to breeding at the synchronized estrus. Experimental animals were representative of three strains maintained in total confinement and exposed to a synthetic light regimen which alternated at intervals of 4 mo from 18 h day length to 10 h day length/24 h. Treatments were applied at different times of the year at the end of a low light cycle. Implants contained Norgestomet (3 mg) impregnated in a polymethacrylate polymer (Implant H) or impregnated in a silastic polymer containing 1.05 (Implant S1), 1.78 (Implant S2) or 2.60 mg (Implant S3) Norgestomet, respectively. Intravaginal sponges contained 40 mg Fluorogestone Acetate. Implants or sponges were left in situ for 12 d and 500 IU pregnant mares' serum gonadotropin was injected im at the time of removal. Following treatment with Implant H, 96% of ewes were judged to be in estrus at 48 h after implant removal. Fertility of adult ewes and ewe lambs (6 to 7 mo of age at time of breeding) at the synchronized estrus were similar after implant H or sponge treatment, but litter size was higher (P less than .05) for adult ewes treated with sponges. The percentages of adult ewes marked by rams within 60 h after removal of silastic implants or intravaginal sponges were similar. There was a tendency for ewe lambs to be marked later than adult ewes and for adult ewes treated with Implant S1 and Implant S2 to be marked earlier than ewes treated with Implant S3 or sponges. Higher percentages (P less than .05) of adult ewes and ewe lambs lambed to breeding at the synchronized estrus after treatment with Implant S2 or Implant S3, respectively, than after treatment with Implants S2 or sponges.     

Effect of season and lactation on postpartum fertility of Polypay, Dorset, St. Croix and Targhee ewes

The objective of this study was to compare rebreeding activities of spring- vs fall-lambing Polypay, Dorset, St. Croix and Targhee ewes that either suckled their lambs for 40 d or had lambs weaned at birth. Seasonal effects of male fertility were reduced by utilizing an excess number of fertile rams in the spring. Plasma concentrations of progesterone were monitored to assess days to the first normal ovulation, days to conception and estrous vs anestrous activity. Breed, season and lactation affected the rebreeding performance. Dorset ewes had similar conception rates between spring and fall but a shorter interval from lambing to first ovulation in the fall. Polypay and Targhee ewes were the opposite; they had higher conception rates in fall than in spring matings with no seasonal influence on postpartum interval. Postpartum ewes in the fall had higher conception rates, and fewer of these ewes became anestrous or had estrous cycles of abnormal duration than of those ewes lambing in the spring. Ewes that suckled for 40 d in the spring had delayed estrous activity, but when these ewes became estrual they had higher conception rates than ewes whose lambs were weaned at birth. Lactation had no inhibitory affect on the postpartum interval of fall lambing ewes. These data suggest that the response of different breeds to various components of postpartum fertility varies with season and management of the flock.     

Fertility, embryo survival and litter size in lines of Targhee sheep selected for weaning weight or litter size

Conception rate, prenatal survival and litter size were recorded for 444 ewes of two age groups from five lines of grade Targhee sheep: two unselected control lines, HC1 and DC(C); two lines selected for 20 yr for increased 120-d weight, HW and DH(W); and a line selected for 18 yr for increased multiple births, T. Line T was equal or superior to the control lines in conception rate, prenatal survival and litter size in both age groups, although most of the differences were not significant. The W selected lines were inferior to the C and T lines in fertility and tended to be lower in prenatal survival, among mature ewes, resulting in a significantly lower number of lambs born per corpus luteum in the W lines than in the other two groups. Among yearlings, C ewes were non-significantly lower in fertility than T and W ewes, while W ewes were significantly lower than C and T ewes in prenatal survival. The T line ewes had higher overall reproductive performance than either of the other two groups. Ewes with two ovulations had a significantly higher conception rate than ewes with single ovulations. Gestation period was exceptionally uniform with a coefficient of variation of 1.3% and little difference due either to line or litter size. It was concluded that selection for multiple births improved overall reproductive performance, whereas selection for increased growth rate had an adverse effect on several components of reproduction, leading to a net decline in fitness.     

Effect of excess degradable intake protein on early embryonic development, ovarian steroids, and blood urea nitrogen on days 2, 3, 4, and 5 of the estrous cycle in mature ewes

Two trials were conducted to determine whether feeding excess degradable intake protein (DIP) during a synchronized estrous cycle and the first 5 d after breeding alters early embryonic development, ovarian steroids, or BUN concentrations in ewes. Ewes were group-fed in Trial 1 (T1) and individually fed in Trial 2 (T2) either 100 (control; T1, n = 15; T2, n = 12) or 200% (high-protein; T1, n = 16; T2, n = 12) of the NRC protein recommendation for maintenance during a synchronized estrous cycle until surgery in the next cycle. Ampullae (AMP), isthmi (IST), and uterine horns (UT) of high-protein and control ewes were removed on d 2 (T1), 3 (T2), 4 (T1), or 5 (T2) after breeding. In T1, jugular blood samples were taken once daily starting on d 2 of the synchronized cycle, and in T2 on d 2, 9, 15, 16, and 17, and in both trials from estrus (d 0) to the day of surgery. Ampullae, IST, and UT flushings were examined microscopically for the presence of embryos, embryo condition, and embryo cell number. There was no trial x treatment interaction (P > or = 0.10), so data for both trials were pooled. Concentrations of BUN were higher (P < 0.05) in high-protein-fed ewes than in control ewes during the synchronized cycle and the first 5 d of the next cycle. Progesterone concentrations of the synchronized cycle did not differ (P > 0.10) between treatments. During the first 5 d of the next cycle, estradiol-17beta concentrations were lower (P = 0.06) in high-protein-fed than in control ewes. Progesterone increased (P < 0.05) to higher concentrations by d 5 in high-protein-fed ewes than in control ewes. More (P < 0.05) embryos were found in AMP of high-protein-fed ewes than in AMP of control ewes on d 4. Fewer (P = 0.05) embryos were found in UT of high-protein-fed ewes than in UT of control ewes on d 4. More embryos were found in UT of high-protein-fed ewes than in UT of control ewes on d 5. Fewer (P = 0.05) embryos were found in IST of high-protein ewes than in the IST of control ewes on d 5. Embryos of high-protein-fed ewes had more (P < 0.05) cells than embryos from control fed ewes on d 5. Feeding ewes excess DIP protein during an estrous cycle and the first 5 d after breeding initially impeded embryo transport; thereafter, embryo transport and development through the oviduct was accelerated.     

High linoleic acid safflower seed supplementation for gestating ewes: effects on ewe performance, lamb survival, and brown fat stores

Objectives of this study were to determine whether feeding high-linoleic safflower seed to gestating ewes increases cold tolerance and survival in lambs, and whether brown adipose tissue (BAT) stores in lambs are affected by prepartum safflower seed supplementation. In Trial 1, 234 gestating ewes (122 in yr 1 and 112 in yr 2; 75.5 and 81.2 +/- 0.6 kg initial BW for yr 1 and 2, respectively) were allotted randomly to one of two dietary treatments (four pens*treatment(-1)*yr(-1)). Ewes were fed alfalfa-based diets containing (DM basis) either 2.8 (LF) or 5.7% (HF) dietary fat beginning 55 (yr 1) and 42 (yr 2) +/- 1 d prepartum. In Trial 2, 40 Rambouillet cross ewes gestating twins (82.9 +/- 1.7 kg BW) were used in 2 yr (20/yr) and were fed diets containing (DM basis) either 1.9 (LF) or 4.9% (HF) dietary fat beginning 53.4 +/- 1.4 d prepartum. The basal diet was 37.5% each of grass and alfalfa hays and 25% corn silage (DM basis). Cracked safflower seeds (18% CP, 32% fat, 25.6% linoleic acid; DM basis) were used as the supplement in HF, whereas safflower meal and corn were used as the supplement in LF for both trials. At parturition, one lamb from each ewe was selected randomly for slaughter. Perirenal (PR) and pericardial (PC) BAT was excised and weighed, and the carcass was frozen for compositional analysis. In Trial 1, more lambs from HF 0.03; 15.4 vs. 5.8 +/- 2.8%), and dams survived (P = 0.03; 88.4 vs. 78.3 +/- 2.9%), fewer died due to starvation (P = there was a tendency for fewer to die due to pneumonia (P = 0.07; 0.0 vs. 1.7 +/- 0.6%). Ewes fed HF tended to wean more lambs per ewe (P = 0.09; 1.4 vs. 1.2 +/- 0.06) but had similar lamb weight weaned per ewe (P = 0.51; 23.1 +/- 1.22 kg). In Trial 2, prepartum ewe plasma NEFA and glucose concentrations increased with advancing gestation (P < 0.001). Lamb rectal temperature tended (P = 0.08) to be higher in LF lambs and tended (P = 0.06) to increase following parturition. Perirenal BAT weight did not differ among treatments (33.01 +/- 1.66 g; P = 0.28; 0.62 +/- 0.30% BW; P = 0.60). Lambs from LF dams tended (P = 0.08) to have greater PC BAT weight; however, the effect was not significant when expressed as a percentage of BW (0.13 +/- 0.007; P = 0.98). High-linoleic safflower seeds fed during the last 45 d of gestation may be beneficial in improving lamb survivability. Our data do not indicate this response was a result of increased BAT stores. More research is necessary to determine mechanisms that enhance lamb survival when high-linoleic saf-flower seed is fed during gestation.     

多浪羊一年两产繁育技术的初步研究

采用孕酮阴道栓和孕马血清促性腺激素相结合的方法对秋季空怀和春季早期断奶的多浪羊母羊进行同期发情处理,探讨综合性频密繁育技术。结果表明:在一年两产的频密繁育过程中,秋季空怀母羊与春季早期断奶母羊同期发情率无显著性差异(97.2%vs 96.0%)(P>0.05);分别对上述同期发情的母羊实施人工授精,受胎率有显著性差异(82.9%vs 54.0%)(P<0.05);平均产羔数(1.4 vs1.3)及产双羔母羊比率(37.9%vs 26.7%)均无显著性差异(P>0.05)。试验证明,对多浪羊母羊实施频密繁育技术处理,可以实现一年两次产羔,提高母羊的生产性能。     

Effect of liveweight and condition score of ewes at mating, and shearing mid-pregnancy, on birthweights and growth rates of twin lambs to weaning

AIMS: To determine the effects of liveweight and condition score of ewes at mating, and shearing mid-pregnancy, on birthweights and growth rates of twin lambs from birth to the time of weaning, and; to determine whether any effect of condition score is independent of liveweight. METHODS: Romney ewes (n=435) which conceived within a 17-day mating period and successfully gave birth to and reared twin lambs to weaning were used. Ewes were managed during pregnancy so that their total liveweight increased at a level equivalent to the expected growth of the conceptuses. Approximately half of the ewes were shorn 70 days after the mid-point of mating, and the remainder were left unshorn, at which time they had 6-months' wool growth. All lambs were weighed within 12 h of birth and again at weaning. RESULTS: There was a significant linear relationship (R2=0.99) between mean group liveweight and condition score of ewes at mating (difference of 7.3 kg per 1.0 unit condition score). Liveweight of ewes at mating had small but significant (p<0.05) positive effects on both birthweights and growth rates of twin lambs to weaning. Ewes that had condition scores of 3.5-4.0 (scale 0-5) at mating gave birth to significantly (p<0.05) lighter lambs than ewes that had condition scores <3.5. The condition score of ewes at mating was positively associated with growth rates of lambs, although this effect was largely explained by variation in the liveweight of ewes at mating. Twin lambs born to ewes shorn mid-pregnancy were significantly (p<0.05) heavier at birth (by 0.4 kg) and at weaning (p<0.05) than those born to unshorn ewes. The heavier weaning weights of lambs born to ewes shorn mid-pregnancy were due to a heavier birthweights rather than increased growth rate. CONCLUSIONS: Liveweight and condition score of ewes at mating had small positive effects on growth rates to weaning of twin lambs. Shearing mid-pregnancy increased birthweights and weaning weights of twin lambs. To achieve high weaning weights of twin lambs, farmers should ensure ewes attain high liveweights and condition scores at mating and shear mid-pregnancy. It is speculated that the effects of liveweight and condition score of ewes at mating on weaning weights of twin lambs would be greater than those observed in the present study under conditions in which nutrition of the dam is below optimum.