Influence of body weight, age, and weight gain on fertility and prolificacy in four breeds of ewe lambs

Breeding ewes to lamb at 1 yr of age can improve profitability for some production systems. The first objective of this study was to evaluate the effect of age and weight at breeding and total postweaning weight gain on reproductive performance of ewe lambs. The second objective was to compare the effects of weight and age variables in four major sheep breeds (Columbia, Polypay, Rambouillet, and Targhee). Weights, ages, and the binary traits of fertility (pregnant or nonpregnant) and prolificacy (one lamb born vs. two or more) were collected on 2,055 ewe lambs at the U.S. Sheep Experiment Station, Dubois, ID, from 1984 through 1988. The effects of age and weight at breeding and total weight gain from weaning to breeding on fertility and prolificacy were analyzed with a logit model in a maximum likelihood analyses. Differences (P < 0.001) among breeds for fertility were identified, with a 93% fertility rate for Polypay ewe lambs compared with lower fertility rates in Columbia, Targhee, and Rambouillet ewe lambs (50, 60, and 75%, respectively). The percentage of multiple births (prolificacy rate) also was higher (P < 0.001) in the Polypay (47%) than in Columbia, Targhee, and Rambouillet breeds (1, 13, and 14%, respectively). Averaged across breeds, weight at breeding had a positive effect on fertility and prolificacy (P < 0.001), whereas total weight gain from weaning to breeding had a positive effect only on fertility (P < 0.027). In separate analyses for each breed, increasing age (P < 0.001) and weight at breeding (P < 0.001) increased the probability of pregnancy in Rambouillet ewe lambs. The probability of pregnancy for Targhee ewe lambs increased (P < 0.005) with weight at breeding. Increasing weight at breeding increased (P < 0.004) the probability of multiple births in all breeds. Increasing total postweaning weight gain increased (P < 0.007) the probabilities of multiple births in Rambouillet and Targhee ewe lambs. In conclusion, Polypay ewe lambs were superior in fertility and prolificacy to Columbia, Rambouillet, and Targhee under Western range conditions. Improved reproductive performance of Columbia, Rambouillet, and Targhee ewe lambs may be achieved by increasing age and weight at breeding and postweaning gain.     

Implications of carbohydrate sources and rate of body weight gain on puberty in ewe lambs in tropical climate conditions

Tropical Animal Health and Production - The objectives were to evaluate the effects of two non-fibrous carbohydrate sources and the rate of body weight gain on puberty status in ewe lambs. Sixty...     

Influence of PMSG and time of artificial insemination on fertility of progestogen-treated sheep in confinement

The need for pregnant mates' serum gonadotropin (PMSG) in breeding confined sheep by artificial insemination (AI) at progestogen-synchronized estrus was assessed in 152 adult crossbred ewes brought into season by a controlled light regimen. One-half of the ewes received 500 IU PMSG after intravaginal progestogen treatment; all ewes were inseminated either 54, 57 or 60 h after sponge removal or at 54 and again at 60 h. Based on progesterone determinations 18 d after AI, conception rates with single insemination 54, 57, or 60 h and double insemination at 54 and 60 h were 76, 72, 47 and 72%, respectively, among ewes receiving PMSG, compared to 17, 22, 47 and 43%, respectively, among ewes not give PMSG (P less than .01) Lambing rates were higher (P less than .01) with PMSG (67, 67, 37 and 61%) than without PMSG (11, 11, 26 and 33%). While there was only a small increase (.06 less than P less than .05) in litter size with PMSG, fecundity decreased (P less than .01) from 1.4 to .3 when PMSG was not used. These data indicate that, even with controlled lighting to induce estrous activity, additional stimulation of ovulation by PMSG at progestogen-synchronized estrus is necessary for normal fertility when confined sheep are bred by AI.     

Effects of number of lambs suckled and supplemental protein source on lactating ewe performance

Effects of number of lambs suckled and supplemental protein source on ewe performance were determined. Lactation performance of ewes nursing twin or triplet lambs was compared in Exp. 1 and 2. In Exp. 1, ewes giving birth to and nursing triplets produced 21% (P less than .05) more milk/unit metabolic body weight, were 10% more efficient in the conversion of feed to milk and produced 26% (P less than .05) more kg of lamb/ewe on d 42 of lactation than did ewes giving birth to and nursing twins. In Exp. 2, lactation performance of ewes giving birth to triplets and rearing only two lambs was compared with performance of ewes giving birth to triplets and rearing three lambs. Ewes rearing three lambs produced 28% (P less than .08) more milk and were 26% (P less than .05) more efficient in converting feed to milk than were those rearing two lambs. This suggests that direct nursing stimulation of the mammary gland is responsible for the improvement in milk production observed when ewes nurse additional lambs. The efficacy of slowly degradable protein sources for improved lactation was studied in Exp. 3 and 4. When blood meal was fed to twin-rearing ewes at 3.30% of the diet (25% of total dietary protein), milk production was greater (3,176 vs. 2,506 g/d, P less than .05) and efficiency of milk production was greater (1.05 vs .79 g milk/g feed, P less than .05) than when ewes were fed supplemental soybean meal. Ewes in this experiment fed supplemental meat and bone meal also tended to produce more milk than those fed soybean meal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between aging and nutritionally controlled growth rate on heat production of ewe lambs

The hypothesis of this study is that ewes that have equal body weights, but differ in chronological age due to nutrient restriction, do not differ in metabolic rate. The objective of this study was to determine how reducing growth rate nutritionally alters the relationship between heat production per unit body weight and aging. Fasting heat production of 12 Dorset ewe lambs at 114 +/- 2 d of age was determined, and ewes were assigned to treatments. Treatments consisted of two different feeding levels of the same diet (ME = 2.5 Mcal/kg DM and 16.6% CP). The High treatment was offered 4.5% of their weekly BW per day, and the Low treatment was offered 2.5% of their weekly BW per day. Each treatment consisted of six animals that remained within treatment for the remainder of the study. Indirect-calorimetry measurements were repeated every 6 wk. Treatments differed in both the linear and quadratic term for fasted BW on age (P < 0.001). The rate of BW gain decreased as ewes aged in the High treatment, and the rate of BW gain increased as ewes aged in the Low treatment. The heat production:BW (HP:BW) ratio decreased in the High treatment as ewes aged and was described well by a previously reported prediction equation, but the ratio in the Low treatment was not described by this same equation. Describing the HP:BW ratio on age response with treatment-specific decay functions fit the data better than the pooled treatment function (P < 0.001). The HP:BW ratio decreased rapidly in the Low treatment following feed restriction, but remained elevated compared to the High treatment as animals aged. After excluding the initial measurements in the Low treatment that were taken before nutritional treatments were imposed, the HP:BW ratio was best described by a linear decrease. In conclusion, this study suggests that a previous model taking into account proportion of mature body size is a reasonable predictor for heat production across breeds of sheep growing in nutritionally adequate environments; however, it cannot be extended to sheep that are proportionally smaller in their mature BW due to nutritional restriction.     

The effect of breeding ewe lambs on subsequent two-year-old ewe performance

This study was undertaken to determine if breeding ewe lambs (hoggets) would influence subsequent two-year-old (two-tooth) ewe liveweight and reproductive performance and their lamb's performance to weaning. Two-tooth Romney ewes that had been bred and lambed as a hogget (n = 505) were compared with those of 196 ewes that were bred as a hogget but did not lamb and 235 ewes that were not presented for breeding as a hogget. Hogget lambing resulted in reduced (P < 0.05) two-tooth liveweight and body condition score at breeding although still present this liveweight difference was reduced by two-tooth lamb weaning. Two-tooth ewes that had previously lambed as a hogget had greater (P < 0.05) returns to service rates and lower (P < 0.05) fecundity (multiple-bearing/two-tooth bred) than those that were bred for the first time. Two-tooth lamb liveweights were unaffected by hogget lambing. These results show that hogget lambing had a small negative effect on subsequent two-tooth reproductive performance. This was most likely caused by reduced liveweight at two-tooth breeding and indicates that farmers need to ensure management practices are in place to reduce the impact of hogget lambing on two-tooth liveweight.     

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.     

Parameter estimates for number of lambs born at different ages and for 18-month body weight of Rambouillet sheep

Genetic parameters were estimated using REML with animal models for number of lambs born and 18-mo body weight in Rambouillet sheep. Number of lambs born was modeled either as repeated measurements on the same trait or as different traits at different ages. The original data for number of lambs born were separated according to age of the ewe into two classes: 2 and 3 yr, and older than 3 yr. Numbers of ewes with lambing records for the age classes were 653 and 466 with 1,106 and 1,118 records, respectively. For the data set that included all ages, the number of ewes was 684 with 2,224 records, and for 18-mo body weight the number of ewes measured was 557. For number of lambs born, the animal model included random genetic, permanent environmental, and residual environmental effects and fixed effects for age of ewe, year of lambing, and month of year of lambing. Lambing day within season was used as a covariate. For 18-mo body weight, year of birth of ewe was used as a fixed effect. Actual age in days when the ewe was weighed was used as a covariate. Estimates of heritability for number of lambs born by age group were .04, for 2- and 3-yr old ewes, and .06, for ewes greater than 3 yr old, from the two-trait (two age of ewe classes) analyses and .06 when all ages were included. Estimates of heritability for number of lambs born from the single-trait analyses were somewhat less than estimates from two-trait analyses. Estimate of genetic correlation between number of lambs born for the 2 and 3 yr and the >3 yr classes was near unity (1.00), which suggests that a repeated measures model for number of lambs born is adequate for making selection decisions. Estimate of genetic correlation between number of lambs born and 18-mo body weight was .35 with a heritability estimate of .48 for 18-mo body weight. The estimate of genetic correlation suggests that selection for increased number of lambs born would result in increased 18-mo body weight.     

Weaning weight inheritance in environments classified by maternal body weight change

In good environments, cow intake is sufficient for their own growth and for milk production to support their calf. In poor environments, cows lose BW or may reduce milk supply to maintain themselves. Heritability for direct genetic and maternal components of weaning weight as well as the correlations between these components might be expected to vary according to these circumstances. The purpose of this study was to estimate heritability and genetic correlations for the direct genetic and maternal components of weaning weight classified in 2 environments according to maternal BW gain and to identify whether a single heritability estimate is appropriate for the differing environments experienced by cows from year to year. Data used in this analysis was obtained from the Red Angus Association of America and consisted of 96,064 cow BW observations and 27,534 calf weaning weight observations. A dam's change in BW from one year to the next was used to classify each calf's weaning weight into 1 of 2 environmental groups, those being good or poor. Best linear unbiased estimates of the change in cow BW with age were obtained from analysis of cow BW using a repeatability model. If the phenotypic change in cow BW exceeded this average BW change, the calf's weaning weight associated with the end of this time frame was classified as having been observed in a good environment. If not, the calf's corresponding weaning weight was classified as having occurred in a poorer than average environment. Heritability estimates of 0.24 +/- 0.03, 0.24 +/- 0.03, 0.13 +/- 0.02, and 0.14 +/- 0.02 were obtained for weaning weight good direct, poor direct, good maternal, and poor maternal, respectively. Correlations between direct genetic and maternal weaning weight components in the good and poor environments were -0.47 +/- 0.08 and -0.20 +/- 0.09, respectively. These variance components are not sufficiently distinct to warrant accounting for dam nutritional environment in national cattle evaluation.     

The influence of empty body weight and mature weight of the genotype on energy density of empty body gain in growing lambs

From data reported by authors who had serially determined the chemical composition of the empty body of growing lambs of a wide range of genotypes, the energy density of empty body gains (E/G) at intervals from 20 to 50 kg empty body weight (EBW) were estimated. Energy density of empty body gain was related to the EBW of these lambs and to an approximation of the mature weight for the genotype (MW) obtained from a separate data set. The addition of MW to the function relating E/G to EBW increased the r2 from .793 to .940 and reduced the residual standard deviation from .550 to .300 Mcal/kg. Combining EBW and MW as predictors of E/G provided the following function: E/G = 5.718 + .093 (EBW) - .036 (MW). Energy density of empty body gain was approximately constant across all genotypes when comparisons were made at a constant EBW/MW. Thus, both EBW and mature weight of the genotype are closely related to E/G and should be considered important for accurately predicting net energy of gain requirements for growing lambs.     

Effects of selenium supply and dietary restriction on maternal and fetal body weight, visceral organ mass and cellularity estimates, and jejunal vascularity in pregnant ewe lambs

To examine effects of nutrient restriction and dietary Se on maternal and fetal visceral tissues, 36 pregnant Targhee-cross ewe lambs were allotted randomly to 1 of 4 treatments in a 2 x 2 factorial arrangement. Treatments were plane of nutrition [control, 100% of requirements vs. restricted, 60% of controls] and dietary Se [adequate Se, ASe (6 microg/kg of BW) vs. high Se, HSe (80 microg/kg of BW)] from Se-enriched yeast. Selenium treatments were initiated 21 d before breeding and dietary restriction began on d 64 of gestation. Diets contained 16% CP and 2.12 Mcal/kg of ME (DM basis) and differing amounts were fed to control and restricted groups. On d 135 +/- 5 (mean +/- range) of gestation, ewes were slaughtered and visceral tissues were harvested. There was a nutrition x Se interaction (P = 0.02) for maternal jejunal RNA:DNA; no other interactions were detected for maternal measurements. Maternal BW, stomach complex, small intestine, large intestine, liver, and kidney mass were less (P < or = 0.01) in restricted than control ewes. Lung mass (g/kg of empty BW) was greater (P = 0.09) in restricted than control ewes and for HSe compared with ASe ewes. Maternal jejunal protein content and protein:DNA were less (P < or = 0.002) in restricted than control ewes. Maternal jejunal DNA and RNA concentrations and total proliferating jejunal cells were not affected (P > or = 0.11) by treatment. Total jejunal and mucosal vascularity (mL) were less (P < or = 0.01) in restricted than control ewes. Fetuses from restricted ewes had less BW (P = 0.06), empty carcass weight (P = 0.06), crown-rump length (P = 0.03), liver (P = 0.01), pancreas (P = 0.07), perirenal fat (P = 0.02), small intestine (P = 0.007), and spleen weights (P = 0.03) compared with controls. Fetuses from HSe ewes had heavier (P < or = 0.09) BW, and empty carcass, heart, lung, spleen, total viscera, and large intestine weights compared with ASe ewes. Nutrient restriction resulted in less protein content (mg, P = 0.01) and protein:DNA (P = 0.06) in fetal jejunum. Fetal muscle DNA (nutrition by Se interaction, P = 0.04) concentration was greater (P < 0.05) in restricted ewes fed HSe compared with other treatments. Fetal muscle RNA concentration (P = 0.01) and heart RNA content (P = 0.04) were greater in HSe vs. ASe ewes. These data indicate that maternal dietary Se may alter fetal responses, as noted by greater fetal heart, lung, spleen, and BW.     

饲喂苜蓿干草对越冬母羊体质量增加及日粮消化率的影响

本研究分析饲喂苜蓿（Medicago sativa）干草对越冬母羊体质量增加和日粮消化率的影响。从5组（SA1、SA2、SA3、SA4、SA5）暖季放牧母羊中各选取18只健康母羊,随机分为对照组和试验组,每组9只,对照组和试验组平均体质量差异不显著（P＞0.05）。对照组不使用苜蓿干草,试验组中苜蓿干草占日粮干物质的比例为11.4%～17.1%。结果表明,SA2、SA3、SA5试验组使用苜蓿干草提高日粮粗蛋白含量并保持适宜的能量蛋白比[消化能（MJ）∶粗蛋白（g）为（1.06~1.08）∶10],可使越冬母羊不掉膘并降低日粮成本。试验组日粮的粗蛋白和中性洗涤纤维消化率均高于对照组,而干物质消化率均低于对照组。     

Effects of level and source of dietary selenium on maternal and fetal body weight, visceral organ mass, cellularity estimates, and jejunal vascularity in pregnant ewe lambs

Pregnant Targhee ewe lambs (n = 32; BW = 45.6 +/- 2.2 kg) were allotted randomly to 1 of 4 treatments in a completely randomized design to examine the effects of level and source of dietary Se on maternal and fetal visceral organ mass, cellularity estimates, and maternal jejunal crypt cell proliferation and vascularity. Diets contained (DM basis) either no added Se (control) or supranutritional Se from high-Se wheat at 3.0 ppm Se (SW) or from sodium selenate at 3 (S3) or 15 (S15) ppm Se. Diets were similar in CP (15.5%) and ME (2.68 Mcal/kg of DM) and were fed to meet or exceed requirements. Treatments were initiated at 50 +/- 5 d of gestation. The control, SW, S3, and S15 treatment diets provided 2.5, 75, 75, and 375 microg of Se/kg of BW, respectively. On d 134 +/- 10 of gestation, ewes were necropsied, and tissues were harvested. Contrasts, including control vs. Se treatments (SW, S3, and S15), SW vs. S3, and S3 vs. S15, were used to evaluate differences among Se levels and sources. There were no differences in ewe initial and final BW. Full viscera and liver mass (g/kg of empty BW and g/kg of maternal BW) and maternal liver protein concentration (mg/g) and content (g) were greater (P < 0.04) in Se-treated compared with control ewes. Maternal liver protein concentration was greater (P = 0.01) in SW vs. S3 ewes, and content was greater (P = 0.01) in S15 compared with S3 ewes. Maternal jejunal mucosal DNA concentration (mg/g) was greater (P = 0.08) in SW compared with S3 ewes. Total number of proliferating cells in maternal jejunal mucosa was greater (P = 0.02) in Se-fed compared with control ewes. Capillary number density within maternal jejunal tissue was greater (P = 0.08) in S3 compared with SW ewes. Selenium treatment resulted in reduced fetal heart girth (P = 0.08). Fetal kidney RNA (P = 0.04) and protein concentrations (mg/g; P = 0.03) were greater in Se-treated compared with control ewes. These results indicate that supranutritional dietary Se increases cell numbers in maternal jejunal mucosa through increased crypt cell proliferation. No indications of toxicity were observed in any of the Se treatments.     

营养限制与补偿对蒙古羔羊体重和血液中生长相关激素的影响

试验研究不同能氮水平的营养限制与补偿对蒙古羔羊体重和血液生长相关的激素影响。选用内蒙古草原上健康的、平均体重15 kg左右的蒙古羔羊64只,随机分为对照组(CG)、限制1组(RG1)和限制2组(RG2)三个组,营养限制期(60 d)分别饲喂ME 10.88 MJ/kg、CP 13.0%(CG),ME10.88 MJ/kg、CP 8.9%(RG1),ME 8.62 MJ/kg、CP 5.7%(RG2)三个营养水平的日粮;营养补偿期(90 d)各组饲喂同一能氮水平饲粮(ME 9.75 MJ/kg,CP 12%)。结果表明:①随着营养水平的逐步降低,在限制末期,RG1组和RG2组羔羊的平均体重显著低于CG组(P<0.05),在补偿期,RG2组平均日增重显著高于CG组(P<0.05)。②在限制末期RG2组血液中GHRH及RG1、RG2组血液中GH浓度显著高于CG组(P<0.05),而RG2组血液中SS、IGF-I浓度显著低于CG组(P<0.05)。在补偿期,RG1、RG2组血液中IGF-I浓度有升高的趋势(P>0.05)。结果提示,营养限制所导致的羔羊血液中GHRH浓度升高和SS浓度降低可能是其在限制期血液中GH浓度升高及其在补偿期快速生长的原因之一。