Genetic impact of external Targhee sires at the U.S. Sheep Experiment Station: a case study of introgression

Sheep breeders requested that the U.S. Sheep Experiment Station (USSES) to participate in national genetic evaluation through the National Sheep Improvement Program (NSIP). The reasons included the need for (1) a comparison of the productivity of industry and United States Department of Agriculture (USDA) lines, (2) transparency of USDA flocks, (3) genetic ties for NSIP by sampling of industry flocks, and (4) development of premium genetic lines for public release. In response, USSES began to incorporate external sires from NSIP participating flocks into the USSES Targhee flock. Our objective, based on a pedigree analysis, was to test if introgression of external genetics into the flock was achieved. The pedigree included 13,189 animals with mean maximum generations, mean complete generations, and mean equivalent complete generations of 4.2, 1.8, and 2.6, respectively. The mean generation interval was 3.1 yr. The reference population was defined as lambs born from 2021 to 2023 (n = 792). Two additional populations were defined as the current mature ewe flock (n = 123) and the current mature rams (n = 14). The Genetic Conservation Index averaged 7.7 for the full population and 25.7 for the reference population. Overall inbreeding was 0.003 for the full population and 0.006 for the reference population. The rate of inbreeding was 0.0003 per generation. Average relatedness was 0.015 for the full population and 0.018 for the reference population. The effective number of founders, effective number of ancestors, and founder genome equivalents contributing to the reference population were 60, 39, and 19.1, respectively. The ratio of the effective number of founders to the effective number of ancestors was 1.5, indicating the presence of genetic bottlenecks. Measures of effective population size ranged from 102 to 547. Of the 704 offspring produced by external sires, 17 ram lambs and 132 ewe lambs were retained for breeding. The USSES sires produced 299 offspring with 2 ram lambs and 51 ewe lambs retained. Incorporating external sires resulted in a cumulative percentage of genetic variance of 48.8, 49.1, and 44.2 of external genetics for the reference population, current mature ewe flock, and current mature rams, respectively. Stakeholder needs were addressed by introgression of external sires and participation in NSIP, but future selection practices need to be modified to maintain a minimum of 50% USSES core genetics in the flock.

Combined purebred and crossbred genetic evaluation of Columbia, Suffolk, and crossbred lamb birth and weaning weights: systematic effects and heterogeneous variances

Despite the benefits of crossbreeding on animal performance, genetic evaluation of sheep in the U.S. does not directly incorporate records from crossbred lambs. Crossbred animals may be raised in different environments as compared to purebreds. Systemic factors such as age of dam and birth and rearing type may, therefore, affect purebred and crossbred performance differently. Furthermore, crossbred performance may benefit from heterozygosity, and genetic and environmental variances may be heterogeneous in different breeds and their crosses. Such issues must be accounted for in a combined (purebred and crossbred) genetic evaluation. The objectives of this study were to i) determine the effect of dam age and birth type on birth weight, and dam age and birth-rearing type on weaning weight, in purebred and crossbred lambs, ii) test for heterogeneous genetic and environmental variances in those weights, and iii) assess the impact of including weights on crossbred progeny on sire estimated breeding values (EBV). Performance records were available on purebred Columbia and Suffolk lambs. Crossbred information was available on lambs sired by Suffolk, Columbia or Texel rams mated to Columbia, Suffolk, or crossbred ewes. A multiple-trait animal model was fitted in which weights from Columbia, Suffolk, or crossbred lambs were considered different traits. At birth, there were 4,160, 2,356, and 5,273 Columbia, Suffolk, and crossbred records, respectively, with means (SD) of 5.14 (1.04), 5.32 (1.14), and 5.43 (1.23) kg, respectively. At weaning, on average at 122 (12) d, there were 2,557, 980, and 3,876 Columbia, Suffolk, and crossbred records, respectively, with corresponding means of 39.8 (7.2), 40.3 (7.9), and 39.6 (8.0) kg. Dam age had a large positive effect on birth and weaning weight in pure and crossbred lambs. At birth, however, the predicted effect was larger in crossbred and Suffolk lambs. While an increase in a number of lambs born and reared had a strong and negative influence on birth and weaning weight, the size of the effect did not differ across-breed types. Environmental variances were similar at birth and weaning, but additive variances differed among breed types for both weights. Combining purebred and crossbred information in the evaluation not only improved predictions of genetic merit in purebred sires but also allowed for direct comparisons of sires of different breeds. Breeders thus can benefit from an additional tool for making selection decisions.

Using whole genome sequence to compare variant callers and breed differences of US sheep

As whole genome sequence (WGS) data sets have become abundant and widely available, so has the need for variant detection and scoring. The aim of this study was to compare the accuracy of commonly used variant calling programs, Freebayes and GATK HaplotypeCaller (GATK-HC), and to use U.S. sheep WGS data sets to identify novel breed-associated SNPs. Sequence data from 145 sheep consisting of 14 U.S. breeds were filtered and biallelic single nucleotide polymorphisms (SNPs) were retained for genotyping analyses. Genotypes from both programs were compared to each other and to genotypes from bead arrays. The SNPs from WGS were compared to the bead array data with breed heterozygosity, principal component analysis and identifying breed associated SNPs to analyze genetic diversity. The average sequence read depth was 2.78 reads greater with 6.11% more SNPs being identified in Freebayes compared to GATK-HC. The genotype concordance of the variant callers to bead array data was 96.0% and 95.5% for Freebayes and GATK-HC, respectively. Genotyping with WGS identified 10.5 million SNPs from all 145 sheep. This resulted in an 8% increase in measured heterozygosity and greater breed separation in the principal component analysis compared to the bead array analysis. There were 1,849 SNPs identified in only the Romanov sheep where all 10 rams were homozygous for one allele and the remaining 135 sheep from 13 breeds were homozygous for the opposite allele. Both variant calling programs had greater than 95% concordance of SNPs with bead array data, and either was suitably accurate for ovine WGS data sets. The use of WGS SNPs improved the resolution of PCA analysis and was critical for identifying Romanov breed-associated SNPs. Subsets of such SNPs could be used to estimate germplasm composition in animals without pedigree information.

Model definition for genetic evaluation of purebred and crossbred lambs including heterosis

Crossbreeding is a common practice among commercial sheep producers to improve animal performance. However, genetic evaluation of U.S. sheep is performed within breed type (terminal sire, semi-prolific, and western range). While incorporating crossbred records may improve assessment of purebreds, it requires accounting for heterotic and breed effects in the evaluation. The objectives of this study were to: 1) describe the development of a paternal composite (PC) line, 2) determine the effect of direct and maternal heterosis on growth traits of crossbred lambs, 3) estimate (co)variance components for direct and maternal additive, and uncorrelated maternal environmental, effects, and 4) provide an interpretation of the estimates of random effects of genetic groups, and to use those solutions to compare the genetic merit of founding breed subpopulations. Data included purebred and crossbred records on birth weight (BN; n = 14,536), pre-weaning weight measured at 39 or 84 d (WN; n = 9,362) depending on year, weaning weight measured at 123 d (WW; n = 9,297), and post-weaning weight measured at 252 d (PW; n = 1,614). Mean (SD) body weights were 5.3 (1.1), 16.8 (3.9) and 28.0 (7.6), 39.1 (7.2), and 54.2 (8.7) kg for BN, WN (at the two ages), WW, and PW, respectively. In designed experiments, the Siremax, Suffolk, Texel, Polypay, Columbia, Rambouillet, and Targhee breeds were compared within the same environment. Estimates of heterotic effects and covariance components were obtained using a multiple trait animal model. Genetic effects based on founders' breeds were significant and included in the model. Percent estimates of direct heterosis were 2.89 ± 0.61, 2.60 ± 0.65, 4.24 ± 0.56, and 6.09 ± 0.86, and estimates of maternal heterosis were 1.92 ± 0.87, 4.64 ± 0.80, 3.95 ± 0.66, and 4.04 ± 0.91, for BN, WN, WW, and PW, respectively. Correspondingly, direct heritability estimates were 0.17 ± 0.02, 0.13 ± 0.02, 0.17 ± 0.02, and 0.46 ± 0.04 for BN, WN, WW, and PW. Additive maternal effects accounted for trivial variation in PW. For BN, WN, and WW, respectively, maternal heritability estimates were 0.16 ± 0.02, 0.10 ± 0.02, and 0.07 ± 0.01. Uncorrelated maternal environmental effects accounted for little variation in any trait. Direct and maternal heterosis had considerable impact on growth traits, emphasizing the value of crossbreeding and the need to account for heterosis, in addition to breed effects, if crossbred lamb information is included in genetic evaluation.

Single Nucleotide Polymorphism Effects on Lamb Fecal Egg Count Estimated Breeding Values in Progeny-Tested Katahdin Sires

Estimated breeding values (EBV) for fecal egg counts (FEC) at 42–90 days of age (WFEC) and 91–150 days of age (PFEC) for 84 progeny-tested Katahdin sires were used to identify associations of deregressed EBV with single-nucleotide polymorphisms (SNP) using 388,000 SNP with minor-allele frequencies ≥0.10 on an Illumina high-density ovine array. Associations between markers and FEC EBV were initially quantified by single-SNP linear regression. Effects of linkage disequilibrium (LD) were minimized by assigning SNP to 2,535 consecutive 1-Mb bins and focusing on the effect of the most significant SNP in each bin. Bonferroni correction was used to define bin-based (BB) genome- and chromosome-wide significance. Six bins on chromosome 5 achieved BB genome-wide significance for PFEC EBV, and three of those SNP achieved chromosome-wide significance after Bonferroni correction based on the 14,530 total SNP on chromosome 5. These bins were nested within 12 consecutive bins between 59 and 71 Mb on chromosome 5 that reached BB chromosome-wide significance. The largest SNP effects were at 63, 67, and 70 Mb, with LD among these SNP of r² ≤ 0.2. Regional heritability mapping (RHM) was then used to evaluate the ability of different genomic regions to account for additive variance in FEC EBV. Chromosome-level RHM indicated that one 500-SNP window between 65.9 and 69.9 Mb accounted for significant variation in PFEC EBV. Five additional 500-SNP windows between 59.3 and 71.6 Mb reached suggestive (p < 0.10) significance for PFEC EBV. Although previous studies rarely identified markers for parasite resistance on chromosome 5, the IL12B gene at 68.5 Mb codes for the p40 subunit of both interleukins 12 and 23. Other immunoregulatory genes are also located in this region of chromosome 5, providing opportunity for additive or associative effects.

Variants Within Genes EDIL3 and ADGRB3 are Associated With Divergent Fecal Egg Counts in Katahdin Sheep at Weaning

Gastrointestinal nematodes (GIN) pose a severe threat to sheep production worldwide. Anthelmintic drug resistance coupled with growing concern regarding potential environmental effects of drug use have demonstrated the necessity of implementing other methods of GIN control. The aim of this study was to test for genetic variants associated with resistance or susceptibility to GIN in Katahdin sheep to improve the current understanding of the genetic mechanisms responsible for host response to GIN. Linear regression and case-control genome-wide association studies were conducted with high-density genotype data and cube-root transformed weaning fecal egg counts (tFEC) of 583 Katahdin sheep. The case-control GWAS identified two significant SNPs (P-values 1.49e-08 to 1.01e-08) within introns of the gene adhesion G protein-coupled receptor B3 (ADGRB3) associated with lower fecal egg counts. With linear regression, four significant SNPs (P-values 7.82e-08 to 3.34e-08) were identified within the first intron of the gene EGF-like repeats and discoidin domains 3 (EDIL3). These identified SNPs were in very high linkage disequilibrium (r² of 0.996–1), and animals with alternate homozygous genotypes had significantly higher median weaning tFEC phenotypes compared to all other genotypes. Significant SNPs were queried through public databases to identify putative transcription factor binding site (TFBS) and potential lncRNA differences between reference and alternate alleles. Changes in TFBS were predicted at two SNPs, and one significant SNP was found to be within a predicted lncRNA sequence with greater than 90% similarity to a known lncRNA in the bovine genome. The gene EDIL3 has been described in other species for its roles in the inhibition and resolution of inflammation. Potential changes of EDIL3 expression mediated through lncRNA expression and/or transcription factor binding may impact the overall immune response and reduce the ability of Katahdin sheep to control GIN infection. This study lays the foundation for further research of EDIL3 and ADGRB3 towards understanding genetic mechanisms of susceptibility to GIN, and suggests these SNPs may contribute to genetic strategies for improving parasite resistance traits in sheep.

Genetic analysis of sexual dimorphism in growth of Jamunapari goats of India

A genetic study of sexual size dimorphism (SSD) in Jamunapari goats was carried out to identify differences between sexes in genetic control of body weight at birth and at 3 (weaning), 6, 9 and 12 months of age. A total of 6,687 kids out of 264 sires and 1,704 dams were used in the study. Estimates of SSD were derived from male:female body weight ratios. Males were 9.9, 6.8, 9.3, 13.7 and 16.8% heavier than females at birth and at 3, 6, 9 and 12 months of age, respectively, demonstrating modest SSD. Phenotypic standard deviations were larger for male kids and tended to be proportional to body weight means. However, males also had somewhat greater phenotypic coefficients of variation and total resemblance among relatives. Additive direct genetic correlations between body weights of males and females exceeded 0.96 at birth and weaning. Corresponding additive maternal correlations exceeded 0.99. Additive direct correlations between sexes were somewhat less than unity for postweaning weights but exceeded 0.80 in multi-trait models. Our results indicated that body weights could be treated as the same trait in males and females, but the use of different phenotypic variances for the two sexes would improve accuracies of breeding value predictions. High genetic correlations between body weights in males and females suggest limited opportunity to use sex-specific selection to create or modify SSD or create divergent body weight phenotypes between sexes.

PSXI-9 Heterotic and breed effects in crossbred lambs

Given its benefits on animal performance, crossbreeding is common commercially. Genetic evaluation of sheep in the U.S. is performed within breed type (terminal, maternal wool, range, hair). While incorporating crossbred records may improve assessment of purebreds, it requires accounting for heterotic and breed effects in the evaluation. The objectives were to i) determine the generalized effects of direct and maternal heterosis on growth traits of crossbred lambs, and ii) estimate covariance components for direct and maternal additive, and uncorrelated maternal environmental, effects among those traits. Data included body weights (BW) at birth (BN; n = 14395), pre-weaning (WN; n = 9298), weaning (WW; n = 9230), and post-weaning (PW; n = 1593). Mean (SD) BW were 5.3 (1.1), 22.2 (8.7), 39.1 (7.2), and 54.2 (8.7) kg for BN, WN, WW, and PW, respectively. Estimates of heterotic effects and covariance components were obtained using a multiple trait animal model. Genetic effects based on founders’ breeds were included, being significant. Estimates of direct heterosis were 3.04 ± 0.61, 2.62 ± 0.64, 3.99 ± 0.54, and 5.97 ± 0.86%, and estimates of maternal heterosis were 1.86 ± 0.87, 4.42 ± 0.79, 3.69 ± 0.66, and 3.77 ± 0.90%, for BN, WN, WW, and PW, respectively. Direct heritability estimates were 0.17 ± 0.02, 0.13 ± 0.02, 0.18 ± 0.02, and 0.47 ± 0.04 for BN, WN, WW, and PW, respectively. Additive maternal effects defined trivial variation in PW. For BN, WN, and WW, respectively, maternal heritability estimates were 0.17 ± 0.02, 0.10 ± 0.02, and 0.07 ± 0.02. Uncorrelated maternal effects defined little variation in any trait. Direct and maternal heterosis had considerable impact on growth traits, emphasizing the value of crossbreeding and the need to account for heterosis, in addition to breed effects, if crossbred lamb information is included in genetic evaluation.

Evaluation of resistance to gastrointestinal helminth nematodes in two naturally infected indigenous Nigerian goat breeds

Tropical goat breeds often have at least modest resistance to gastrointestinal nematode parasites (GIN), but enhancement of GIN resistance is important for breed improvement. This study compared changes in fecal egg count (FEC), packed cell volume, and body weight in Red Sokoto (RS) and Sahelian (SH) male and female weaner kids and adult goats. The RS is found throughout Nigeria, but the SH is found only in the arid Sahel. Goats were evaluated fortnightly for 20 times (MT) under normal grazing conditions and natural GIN infection over 9.5 months, beginning in the dry season (November) and ending at the end of the subsequent wet season (August). Animals were dewormed at the start of the study and during the rainy season (MT 18). Breed differences in FEC and PCV were not observed in weaners. Weaner females had lower FEC than males but were rapidly re-infected after deworming, perhaps in association with attainment of puberty. Adult SH goats of both sexes had lower FEC than RS goats in MT 8 through 17, suggesting a stronger acquired immune response. The FEC in lactating females of both breeds increased rapidly after deworming, to ≥ 3000 eggs per gram of feces at MT 19 and 20. The optimal time to evaluate GIN resistance in weaners was during the early rainy season, but the decision to focus on the initial high FEC near MT 15 or wait until mobilization of the acquired immune response near MT 17 requires further consideration.

Genetic diversity and population structure of Jamunapari goat in India using pedigree analysis

Pedigree records of 6821 Jamunapari goats of India were collected from 1980 to 2011 and used to evaluate the population structure and genetic diversity in this flock. Animals born between 2009 and 2011 represented the current reference population. The average pedigree completeness index (PCI) and numbers of equivalent complete generations (EqG) were estimated for the entire (PCI = 0.18, EqG = 2.24) and reference (PCI = 0.31, EqG = 3.45) populations. The average generation interval was 3.33 years. The average inbreeding coefficient and the average relatedness were 0.46 and 1.06%, respectively, for the entire population and 0.77 and 3.87% for the reference population. The rate of inbreeding was 0.06% per generation. The effective population size (N_e), estimated from increases in inbreeding coefficients between the first and third equivalent complete generations, was 52.65, but periodic introductions of unrelated breeding males resulted in average inbreeding levels in the reference population that were lower than those predicted from the estimate of N_e. Effective numbers of founders (f_e), ancestors (f_a), founder genomes equivalents (f_g), and non-founder genomes (f_ng) were 51, 39, 25.8, and 48.2, respectively. The f_e/f_a ratio in the reference population was 1.31 and indicated that occasional bottlenecks had occurred in the population. The 14 most influential ancestors contributed 50% of the genetic variability in the reference population, with a maximum individual contribution of 9.25%. Approximately 1.9% of the initial heterozygosity had been lost from the population, indicating that substantial genetic diversity still exists in this flock.

Direct and correlated responses to selection for autumn lambing in sheep

Background

Seasonal reproduction limits productivity, flexibility, and profitability in commercial sheep production. Hormonal and (or) photoperiodic manipulation can be used to control estrous cycles in sheep and reduce limitations that are imposed by the seasonal anestrous but are often impractical or incompatible with the extensive management systems preferred for ruminant livestock. Thus, the current study investigated the use of selection to improve realized fertility (i.e., the proportion of ewes that lambed) following an out-of-season spring joining period (May and June) in a crossbred sheep population.

Results

Over 17 years, estimated breeding values (EBV) for fertility in selected (S) ewes increased by 0.175 (0.01 per year). The mean EBV for fertility of S ewes was greater than that of control ewes by year 10 (P = 0.02), and the fertility of adult (≥ 3 years old) ewes reached 0.88 ± 0.05 by year 17. Lambing began approximately 140 days after the introduction of rams, and 64% of the S ewes that lambed did so in the first 17 days of the potential lambing season, which indicated that most of the S ewes were cycling at the time of ram introduction and were not induced to cycle by the introduction of breeding males (i.e., the so-called “ram effect”). Animals in the S line had modest increases in body weight and scrotal circumference. A modest negative trend in the additive maternal effect on birth weight was observed but was reversed by additional selection on EBV for maternal birth weight. The heritability of litter size in autumn lambing was low (0.04) and could potentially limit the response to selection for this trait.

Conclusions

Selection improved realized ewe fertility in out-of-season mating, with absolute increases of approximately 1% per year in the percentage of joined ewes that lambed in the autumn. Genetic antagonisms with other performance traits were generally small. A modest antagonism with maternal breeding values for birth weight was observed but it could be accommodated by selection on EBV for maternal birth weight. Our results support results of previous studies that indicate that these selected ewes had one of the shortest seasonal anestrous periods reported for temperate sheep breeds and that spring-lambing lactating ewes from the selection line were capable of relatively rapid rebreeding in the spring.

Genome-wide association study to identify genetic loci associated with gastrointestinal nematode resistance in Katahdin sheep

Resistance to gastrointestinal nematodes has previously been shown to be a moderately heritable trait in some breeds of sheep, but the mechanisms of resistance are not well understood. Selection for resistance currently relies upon faecal egg counts (FEC), blood packed cell volumes and FAMACHA visual indicator scores of anaemia. Identifying genomic markers associated with disease resistance would potentially improve the selection process and provide a more reliable means of classifying and understanding the biology behind resistant and susceptible sheep. A GWAS was conducted to identify possible genetic loci associated with resistance to Haemonchus contortus in Katahdin sheep. Forty animals were selected from the top and bottom 10% of estimated breeding values for FEC from a total pool of 641 sires and ram lambs. Samples were genotyped using Applied Biosystems™ Axiom™ Ovine Genotyping Array (50K) consisting of 51 572 SNPs. Following quality control, 46 268 SNPs were included in subsequent analyses. Analyses were conducted using a linear regression model in plink v1.90 and a single‐locus mixed model in snp and variation suite. Genome‐wide significance was determined by a Bonferroni correction for multiple testing. Using linear regression, loci on chromosomes 2, 3, 16, 23 and 24 were significantly associated at the genome level with FEC estimated breeding values, and we identified a region on chromosome 2 that was significant using both statistical analyses. We suggest a potential role for the gene DIS3L2 for gastrointestinal nematode resistance in Katahdin sheep, although further research is needed to validate these findings.

163 Annual differences in fecal egg counts in a forage-based ram test

The objective was to determine the magnitude of yearly differences in parasite load in growing ram lambs. Data were obtained from the Southwest Virginia Agriculture Research and Extension Center in Glade Spring, VA. The center conducts a forage-based ram growth test during the summer where rams also undergo a parasite challenge. Data consisted of 488 Katahdin rams tested from 2012 to 2018. Rams were dewormed at delivery, and at the start of the test, each ram received an oral dose of 5,000 H. contortus larvae adjusted for body weight. Fecal egg count was measured 70 d later when rams were on average (SD) 200 (18) d old. Fecal egg counts were not normally distributed. The Box-Cox procedure indicated that a log transformation was appropriate, but the residuals were not normally distributed for several linear models. A zero-inflated negative binomial generalized linear mixed model was used for data analysis with the glmmTMB package in R. The model included fixed effects of centered and scaled weight, centered and scaled age, year, birth type, and rearing type, and the random effect of consignor. Birth type, rear type, and age were not significant (P &gt; 0.10). The least square mean (SE) fecal egg counts by year were 344 (118) for 2012, 623 (214) for 2013, 574 (195) for 2014, 1,125 (409) for 2015, 745 (253) for 2016, 408 (142) for 2017, and 239 (86) for 2018. Differences in summer precipitation could affect average parasite load. Despite similar total summer precipitation, 2012 had 1 extremely wet month whereas, 2015 had consistent precipitation throughout the summer. We conclude that producers should not compare fecal egg counts across years because the overall average may be multiple-fold different from year to year. Ranking rams within year will be more effective to select for improved parasite resistance.

Phenotypic resistance of indigenous goat breeds to infection with Haemonchus contortus in northwestern Nigeria

Two studies at the National Animal Production Research Institute (NAPRI), Zaria, Nigeria, compared Red Sokoto (RS), Sahelian (SG), and West African Dwarf (WAD) goats after experimental or natural infection with Haemonchus contortus. In the first study, 20 RS, 17 SG, and 14 WAD kids were challenged at 6 months of age with 5000 L₃ larvae of H. contortus. Fecal egg counts (FEC), packed cell volumes (PCV), and body weights (BW) were recorded 0, 28, 35, and 42 days after infection. The FEC and PCV were affected only by time of measurement. In the second study, 322 RS and 97 SG kids were produced at NAPRI over 3 years, weaned at 4 to 6 months of age, dewormed, returned to contaminated pastures, and evaluated 28 and 35 days later. Effects of breed, year, breed × time interaction, and breed × year interaction were observed for PCV and BW; FEC was only affected by time of measurement, year and breed × year interaction. The FEC were larger and PCV were smaller on day 35 compared to day 28 and in year 2 compared to years 1 and 3. The SG kids were notably smaller than RS kids in year 2, with higher FEC and lower PCV, but FEC were larger for RS kids in years 1 and 3. Differences in parasite resistance among these Nigerian goat breeds were therefore small and likely reflected underlying differences in growth, development, and disease history.

Evaluation of Rambouillet, Polypay, and Romanov-White Dorper × Rambouillet ewes mated to terminal sires in an extensive rangeland production system: body weight and wool characteristics1,2

Though lamb sales account for the majority of annual receipts on U.S. sheep operations, wool is an important income source for many Western flocks. Crossing fine-wool sheep with prolific or composite hair sheep breeds can increase lamb production, but fleece quality and marketability may be reduced by a greater content of nonwool fibers (e.g., med and kemp). The objectives of this study were to compare BW and wool characteristics of Rambouillet, Polypay, and Romanov-White Dorper × Rambouillet (RW-RA) ewes under extensive rangeland management conditions. Ewe BW was collected before mating (fall) and 30 d postlambing (spring) each year from 1 yr up to 4 yr of age. In spring and fall, Rambouillet and Polypay ewes were similar in BW (P ≥ 0.94). Spring BW did not differ (P = 0.13) between RW-RA and Polypay, but Rambouillet ewes were heavier than RW-RA in the spring (P = 0.02). Both Rambouillet and Polypay ewes were heavier (P < 0.07) than RW-RA in the fall. Greasy fleece weight and mid-side wool samples were collected from ewes at 1 and 4 yr of age. Clean fleece weights (CFW) were estimated from average laboratory scoured yield of mid-side wool samples composited within-breed. Average fiber diameter (AFD), SD of fiber diameter (SD-FD), and percentage med (%M), kemp (%K), and total medullated fibers (%T) were quantified on individual mid-side wool samples. There was no difference in 1-yr-old CFW among breed types (P ≥ 0.96). Four-yr-old Rambouillet ewes had heavier CFW (2.29 kg; P < 0.001) than 4-yr-old Polypay (1.83 kg) and RW-RA ewes (1.86 kg), which were not different (P > 0.99). Within 1- and 4-yr-olds, AFD differed among breed type (P < 0.001) and was the finest for Rambouillet (20.1 and 21.9 µm, respectively), intermediate for RW-RA (22.8 and 24.8 µm), and coarsest for Polypay (24.2 and 26.7 µm). Also within 1- and 4-yr olds, SD-FD was lowest in Rambouillet, intermediate in Polypay, and greatest in RW-RA (P < 0.01). Wool from RW-RA ewes had greater %M, %K, and %T (P < 0.001) than wool from Rambouillet and Polypay ewes, which were not different (P > 0.99). Results indicated superior wool production for Rambouillet compared with the coarser, more variable wool produced by Polypay and RW-RA. Still, past research reported greater lamb production in Polypay and RW-RA ewes which, under recent market conditions, would be associated with greater annual gross revenue for these breed types than for Rambouillet.

Genetic and phenotypic aspects of early reproductive performance in Raeini Cashmere goats

This study used pedigree information and data collected from 1979 to 2012 at the Raeini Cashmere goat breeding station, located in Baft City in Kerman Province in southeastern Iran. Genetic and phenotypic parameters for early reproductive traits of breeding does, including total numbers of kids born at first kidding (LSB1), total numbers of kids weaned at first kidding (LSW1), total birth weight of all kids born at first kidding (LWB1), total weaning weight of all kids weaned at first kidding (LWW1), and age at first kidding (AFK), were estimated using a Bayesian approach via Gibbs sampling. Posterior means for heritability estimates of LSB1, LSW1, LWB1, LWW1, and AFK were statistically significant, with values of 0.12, 0.23, 0.17, 0.15, and 0.46, respectively. Low-to-moderate additive genetic variation was present for the studied reproductive traits. Estimated genetic correlations among LSB1, LSW1, LWB1, and LWW1 were statistically significant and ranged from 0.12 between LWB1 and LWW1 to 0.72 between LSB1 and LSW1. Corresponding phenotypic correlation estimates were also statistically significant and ranged from 0.04 between LWB1 and LWW1 to 0.55 between LSB1 and LSW1. Posterior means of genetic and phenotypic correlations between AFK and other studied traits were statistically significant only for LSB1 and LWB1. For LSB1, LSW1, LWB1, and LWW1, we conclude that genetic and phenotypic improvement in any of these traits in Raeini Cashmere does would favorably influence all of the other traits. However, does that first kidded at younger ages have smaller litters at birth and lower litter birth weights at their first parity.

Effects of rearing triplet lambs on ewe productivity, lamb survival and performance, and future ewe performance

Increasing prolificacy has been proposed to be the most effective way to increase the biological efficiency and profitability of sheep production. However, use of prolific breeds and genes with major effects on ovulation rate can increase prolificacy to levels that may not be desirable or sustainable in extensive rangeland production systems. This study thus evaluated effects of triplet births on ewe productivity and ewe and lamb performance. An initial study used 666 purebred Polypay litters to compare ewes with triplet litters that were required to raise all the lambs (Treatment A) with those whose triplet litters were reduced to 2 lambs (Treatment R). Adult Polypay ewes had an average litter size of 2.35 lambs per litter. The frequency of litters of 3 or more lambs was 43.2%; 56.0% of lambs were born in litters of 3 or more lambs. Ewes that had singles weaned fewer lambs and less body weight (BW) of lambs (P < 0.001; 0.94 lambs and 40.4 kg, respectively) than ewes that had twins or triplets. Ewes with triplet litters in Treatment A weaned more lambs (P < 0.01) and more BW of lambs (P < 0.05) than ewes that had triplets in Treatment R (2.13 lambs and 62.9 kg, respectively, vs. 1.79 lambs and 55.0 kg, respectively), and weaned more lambs than ewes that had twins (1.77 lambs; P < 0.01). However, neither group of triplet-bearing ewes weaned more BW of lambs than ewes that had twins (58.9 kg; P ≥ 0.34). In 2 sets of data involving 442 purebred Polypay litters and 987 litters from Polypay or Romanov‒White Dorper × Rambouillet ewes mated to terminal sires, ewes were required to raise all triplet-born lambs. Death losses for triplets in these studies (39.6 and 31.6%, respectively) were higher than those in Treatment A of the initial study (26.2%), resulting in greater numbers of lambs weaned for triplet, compared to twin, litters (1.79 vs. 1.68, respectively; P = 0.02) but no greater weight of lambs weaned (54.3 vs. 55.4 kg, respectively; P = 0.17). Based on these 3 sets of data, ewes that were required to rear triplet lambs weaned 0.20 more lambs per litter than ewes that had twins but also had 0.75 additional dead lambs per litter, and thus a lamb mortality overhead of 3.75 additional dead lambs for each additional weaned lamb. We conclude that there is an intermediate optimum prolificacy level for extensive rangeland production systems. If optimum prolificacy is exceeded, removal and artificial rearing of surplus lambs are necessary to avoid increased lamb death losses.

Genetic parameters for ewe reproductive performance and peri-parturient fecal egg counts and their genetic relationships with lamb body weights and fecal egg counts in Katahdin sheep

This study estimated genetic parameters for ewe reproductive traits [number of lambs born (NLB) and weaned (NLW) per ewe lambing] and fecal egg counts (FEC) during the peri-parturient rise (PPR) for use in genetic evaluation of Katahdin sheep. Data included NLB and NLW for 23,060 lambings by 9,295 Katahdin ewes, 1,230 PPR at lambing (PPR0) for 750 ewes, 1,070 PPR at approximately 30 d postpartum (PPR30) for 611 ewes, BW at birth, weaning, and (or) post-weaning for 12,869 lambs, and FEC at weaning and (or) post-weaning for 4,676 lambs. Direct additive, permanent environmental, and residual (co)variances were estimated in univariate and bivariate animal models. Fixed effects included effects of ewe management group and ewe age for all traits, and, for PPR, a continuous effect of days between lambing and measurement. Effects of litter size on PPR0 and number of lambs suckled on PPR30 were included in univariate models but excluded from bivariate models for PPR and NLB or NLW. Heritability estimates in univariate models for NLB, NLW, PPR0, and PPR30 were 0.09 ± 0.01, 0.06 ± 0.01, 0.35 ± 0.06, and 0.24 ± 0.07, respectively. Estimates of permanent environmental variance as a proportion of total phenotypic variance were 0.02 ± 0.01 for NLB, 0.03 ± 0.01 for NLW, 0.05 ± 0.06 for PPR0, and 0.13 ± 0.07 for PPR30. Direct additive, phenotypic, permanent environmental, and residual correlations between NLB and NLW were 0.88 ± 0.03, 0.74 ± 0.004, 0.54 ± 0.15, 0.74 ± 0.003, respectively; corresponding correlations between PPR0 and PPR30 were 0.96 ± 0.07, 0.46 ± 0.03, 0.98 ± 0.50, 0.18 ± 0.05, respectively. The additive genetic correlation (rd) between ewe reproductive traits and PPR ranged from 0.12 to 0.18. Estimates of rd between lamb BW and subsequent ewe NLB and NLW ranged from 0.07 to 0.20, and those between PPR and lamb BW ranged from -0.03 to 0.29. The rd between ewe reproductive traits and lamb FEC ranged from 0.27 to 0.40, and those between PPR and lamb FEC ranged from 0.56 to 0.77. Correlations between maternal additive effects on BW and direct additive effects on PPR were low (-0.08 to 0.10), and those between maternal additive effects on BW and direct additive effects on ewe reproductive traits were variable (-0.36 to 0.11). We conclude that FEC in growing lambs and peri-parturient ewes are controlled by similar genes and that modest, but manageable, genetic antagonisms may exist between FEC and ewe productivity.

Genetic parameters for fecal egg counts and their relationship with body weights in Katahdin lambs

Reliance on anthelmintic drugs to control internal parasites in sheep is no longer sustainable because of the development of resistance to these drugs in parasite populations. Genetic selection may offer an alternative long-term solution, as differences in parasite resistance exist both within and among sheep breeds. However, selection for parasite resistance may have correlated effects on other production traits. The objectives of this study were to estimate genetic parameters for weaning (WFEC) and postweaning (PWFEC) fecal egg counts (FEC) and assess their relationship with birth (BWT), weaning (WWT), and postweaning (PWWT) BW in Katahdin lambs. The study used WFEC (n = 2,537), PWFEC (n = 3.421), BWT (n = 12,869), WWT (n = 10,961), and PWWT (n = 7,812) from 12,869 lambs measured between 2003 and 2015 in 13 flocks enrolled in the U.S. National Sheep Improvement Program. Animal and sire models were fitted to the data using the ASReml statistical package. Records were corrected for fixed effects of dam age, joint effect of type of birth and rearing, and management group (defined by joint effects of flock, sex, and birth year and season); lamb age in days at each measurement time was fitted as a covariate. Maternal additive and maternal permanent environmental effects were not significant (P > 0.05), but litter effects influenced (P < 0.01) both WFEC and PWFEC. Heritability estimates ranged from 0.18 to 0.26 for WFEC and 0.23 to 0.46 for PWFEC, depending on the model used. Heritability estimates from sire models were higher than estimates from animal models. Direct additive, litter, residual, and phenotypic correlations between WFEC and PWFEC were 0.82, 0.25, 0.15, and 0.29, respectively. Bivariate analyses revealed low to moderate correlations between BW and FEC. Moderate heritabilities for FEC in this study indicated that genetic progress for this trait can be achieved in Katahdin lambs and that selection for low FEC should have little or no effect on BW.

Evaluation of Rambouillet, Polypay, and Romanov-White Dorper × Rambouillet ewes mated to terminal sires in an extensive rangeland production system: Lamb production

Ewe productivity (i.e., total number or weight of lambs weaned per breeding ewe) is a key indicator of lamb production efficiency. This study compared various measures of ewe productivity and ewe and lamb performance among ewes of 3 breed types mated to rams of 4 terminal-sire breed types in an extensive rangeland production system. Purebred Rambouillet ( = 212), purebred Polypay ( = 236), and crossbred Romanov-White Dorper × Rambouillet (RW-RA; = 231) ewes were produced from locally adapted Polypay and Rambouillet ewes and then annually mated to Columbia, Suffolk, Columbia × Suffolk, or Suffolk × Columbia sires for up to 4 yr, beginning at 1 yr of age. The cumulative number and weight of lambs weaned through 4 yr were greater for RW-RA (5.9 lambs and 153 kg, respectively) and Polypay ewes (4.9 lambs and 123 kg, respectively) than for Rambouillet ewes (2.9 lambs and 99 kg, respectively) and also were greater for RW-RA ewes than for Polypay ewes (all < 0.001). Greater productivity of RW-RA and Polypay ewes, compared with Rambouillet ewes, was driven by greater lambing rates (ewes lambing per ewe exposed) as ewe lambs (87 and 77 vs. 31%, respectively; < 0.001) and greater ( < 0.001) litter sizes as ewe lambs (1.3, 1.3, and 1.0, respectively) and adult ewes (2.1, 2.0, and 1.6, respectively). The RW-RA ewes also had greater longevity ( < 0.01) and cumulative lambing rates ( < 0.001) than Polypay and Rambouillet ewes. Lamb BW at birth and weaning in adult ewes favored less-prolific Rambouillet ewes ( < 0.001), but after adjustment for type of birth and rearing and weaning age, differences in weaning BW among ewe breed types were small and not significant ( = 0.08). Effects of sire breed type on measures of cumulative ewe productivity were not significant ( > 0.74), but Suffolk-sired lambs had the heaviest adjusted birth weights ( = 0.01) and Columbia-sired lambs tended to have the lightest adjusted weaning weights ( = 0.12). Combined effects of heterosis and additive breed effects were associated with greater lambing rates in ewe lambs, larger litters at all ages, and substantially greater number and weight of lambs weaned for Polypay and RW-RA ewes than for Rambouillet ewes.

Variance components for direct and maternal effects on body weights of Katahdin lambs

The aim of this study was to estimate genetic parameters for BW in Katahdin lambs. Six animal models were used to study direct and maternal effects on birth weight (BWT), weaning weight (WWT), and postweaning weight (PWWT) using 41,066 BWT, 33,980 WWT, and 22,793 PWWT records collected over 17 yr in 100 flocks. Models included fixed effects of management group, dam age, type of birth (for BWT) or birth and rearing (for WWT and PWWT), and lamb age at weighing (fitted as a covariate for WWT and PWWT; all < 0.05). Variance components for random effects were estimated in sequentially more complex models and tested for significance with likelihood-ratio tests. A model that fitted only an additive animal effect overestimated additive variance for all BW, resulting in larger estimates of direct heritability than models that included maternal effects. Maternal effects explained variation ( < 0.05) in all BW. Heritability estimates for optimal models were 0.15 ± 0.01 for BWT, 0.18 ± 0.02 for WWT, and 0.20 ± 0.02 for PWWT. Estimates of maternal heritabilities were 0.14 for BWT, 0.10 for WWT, and 0.06 for PWWT, with SE = 0.01. Permanent environmental maternal effects explained 4 to 6% (±1%) of total phenotypic variances for these BW. Litter effects included temporary environmental effects common to littermates and a proportion of the dominance genetic variance and accounted for 16 to 19% (±1%) of phenotypic variance. Correlations between additive direct and maternal genetic effects were -0.14 for BWT, -0.23 for WWT, and -0.04 for PWWT but differed from 0 ( < 0.05) only for WWT. The total heritability predicted the total response in direct and maternal genetic effects from mass selection and was 0.23 for BWT, 0.20 for WWT, and 0.23 for PWWT. Direct and maternal additive, maternal permanent environmental, residual, and phenotypic correlations between BWT and WWT were 0.53 ± 0.05, 0.58 ± 0.06, 0.51 ± 0.06, 0.39 ± 0.01, and 0.44 ± 0.01, respectively; those between BWT and PWWT were 0.45 ± 0.06, 0.58 ± 0.08, 0.36 ± 0.08, 0.33 ± 0.01, and 0.37 ± 0.01 respectively; and those between WWT and PWWT were 0.85, 0.99, 0.92, 0.77, and 0.81, respectively, with SE ≤ 0.02. Therefore, both direct and maternal effects had an important impact on BW in Katahdin lambs. Models that included both additive and permanent environmental maternal effects as well as a temporary environmental litter effect should result in more accurate estimates of breeding values and better selection decisions.

Responses of Sri Lankan indigenous goats and their Jamnapari crosses to artificial challenge with Haemonchus contortus

Goat farming plays an important role in the Sri Lankan rural economy. Sri Lankan indigenous (SLI) goats and their crossbreds are reared mainly under extensive management and indiscriminately exposed to pathogens and parasites. This study was designed to evaluate resistance to haemonchosis in SLI goats and their Jamnapari crossbreds (JCB) in the dry zone of Sri Lanka. Twenty SLI and 20 JCB 4-month-old male goats were artificially challenged with 5000 H. contortus L₃ larvae_. Faecal egg counts (FEC), body weights, FAffa MAlan CHArt (FAMACHA®) scores, packed cell volumes (PCV), red blood cell counts, total and differential white blood cell counts, blood haemoglobin contents, serum total protein and albumin contents, and serum pepsinogen and antibody levels were determined at 0, 21, 28, 35 and 42days after challenge. Effects of measurement time were significant for all variables (P<0.05). Breed effects approached significance (P=0.06) and measurement time×breed interaction was significant (P<0.05) for FEC. Peak FEC occurred at day 35 in both goat types, and JCB goats had higher FEC than SLI goats at days 28 (P<0.001), 35 (P<0.10), and 42 (P<0.10). Means for FEC at day 35 were 1783±446 eggs per gram of feces (epg) for SLI kids and 3329±850 epg for JCB kids. Haematological parameters, serum chemistry, and FAMACHA scores suggested that SLI goats were recovering from parasitic infection by day 42, whereas JCB goats had increasing severity of anaemia. Means for PCV in SLI goats decreased from 26.8±0.7% at day 0 to 19.7±0.9% at day 35 and thereafter increased to 20.2±0.9% at day 42. Means for PCV in JCB goats declined from 25.9±0.6% at day 0 to 17.2±0.9% at day 42. Eosinophilia was observed in both genotypes. The JCB goats were heavier than SLI goats and had higher antibody titres, reflecting higher levels of parasitism. Both goat types significantly increased in body weight during the experiment and therefore tolerated parasite infection without severe production losses. We concluded that SLI goats were more resistant to haemonchosis than JCB goats, but that JCB goats were somewhat resilient to parasitic infection. Substantial variability in measurements associated with parasite infection in both breeds indicated potential to improve parasite resistance. Phenotypic information should be coupled with genomic information to identify appropriate breeding goals for future selection programs.

Association between FAMACHA scores and fecal egg counts in Katahdin lambs

The FAMACHA system was introduced to the U.S. just over 10 yr ago to allow selective deworming of lambs with anemia associated with and retard the development of anthelmintic resistance. The FAMACHA system was initially developed as a predictor of packed cell volume (PCV), but correlations between FAMACHA and fecal egg counts (FEC) have also been reported. It is important to understand factors that influence FAMACHA scores among farms to improve management of gastrointestinal nematodes. The objectives of this study were therefore to quantify associations between FAMACHA scores, FEC, BW, and age in Katahdin lambs at 2 different measurement times in 8 flocks in the eastern U.S., and to assess consistency of relationships between FAMACHA and FEC among flocks. Data came from 1,644 Katahdin lambs from 7 flocks sampled at approximately 90 d of age, and 1,295 lambs from 6 flocks sampled at approximately 120 d of age over a 5 yr period. Residual correlations among log-transformed FEC (LFEC), FAMACHA scores, BW, and lamb ages at each measurement time were determined. Repeatability of each variable was also determined as residual correlations among repeated measures. At both 90 and 120 d of age, correlations of FAMACHA scores with LFEC and BW were significant ( < 0.001), but numerically modest (0.25 and -0.16, respectively at 90 d; 0.31 and -0.16, respectively at 120 d), demonstrating that higher FAMACHA scores were associated with higher FEC and more likely to be observed in lighter lambs. A small negative correlation was observed between FAMACHA score and lamb age ( = -0.05, = 0.05, 90 d; = -0.11, < 0.001, 120 d) indicating that younger lambs were more likely to have elevated FAMACHA scores. Thus, younger and lighter lambs will likely be more susceptible to parasitism and may need to be managed more diligently than older or heavier lambs. In addition, FAMACHA scores have potential to improve breeding value estimates in programs designed to genetically improve parasite resistance.

Whole genome structural analysis of Caribbean hair sheep reveals quantitative link to West African ancestry

Hair sheep of Caribbean origin have become an important part of the U.S. sheep industry. Their lack of wool eliminates a number of health concerns and drastically reduces the cost of production. More importantly, Caribbean hair sheep demonstrate robust production performance even in the presence of drug-resistant gastrointestinal nematodes, a rising concern to the industry. Despite the growing importance of hair sheep in the Americas their genetic origins have remained speculative. Prior to this report no genetic studies were able to identify a unique geographical origin of hair sheep in the New World. Our study clarifies the African and European ancestry of Caribbean hair sheep. Whole-genome structural analysis was conducted on four established breeds of hair sheep from the Caribbean region. Using breeds representing Africa and Europe we establish an objective measure indicating Caribbean hair sheep are derived from Iberian and West African origins. Caribbean hair sheep result from West African introgression into established ecotypes of Iberian descent. Genotypes from 47,750 autosomal single nucleotide polymorphism markers scored in 290 animals were used to characterize the population structure of the St. Croix, Barbados Blackbelly, Morada Nova, and Santa Ines. Principal components, admixture, and phylogenetic analyses results correlate with historical patterns of colonization and trade. These patterns support co-migration of these sheep with humans.

Factors affecting fecal egg counts in periparturient Katahdin ewes and their lambs

Selection for low fecal egg counts (FEC) can be used to genetically enhance resistance to gastrointestinal nematode parasites in growing lambs, thereby reducing the frequency of use of anthelmintics, facilitating marketing of organic lamb, and reducing the risk of development of anthelmintic resistance by the parasite. Recording of FEC in lambs has, therefore, been incorporated into several national sheep genetic evaluation programs. Ewes in late gestation and early lactation are also vulnerable to parasite infection and commonly experience a periparturient rise in FEC. This study was designed to assess factors associated with the periparturient rise in FEC in Katahdin ewes and associated changes in FEC in their lambs. Data came from 1,487 lambings by 931 Katahdin ewes from 11 farms in the Eastern United States. Fecal egg counts were measured in ewes at approximately 0, 30, and 60 d postpartum and in their lambs at approximately 60, 90, and 120 d of age. Approximately 1,400 lambs were evaluated at each measurement age. Data were analyzed separately for ewes and lambs and also initially analyzed separately for each measurement time. Repeated-measures analyses were then used to evaluate responses across measurement times. In ewes, FEC peaked at approximately 28 d postpartum, and we concluded that informative periparturient FEC could be obtained from 1 wk before until approximately 5 wk after lambing. Yearling ewes had higher FEC than adult ewes ( < 0.01), and ewes that nursed twin or triplet lambs had higher FEC than ewes that nursed single lambs ( < 0.01). In lambs, FEC increased through approximately 120 d of age. Lambs from yearling ewes and lambs nursed in larger litters were, like their dams, at greater risk of parasitism ( < 0.05). Ewes and lambs in these groups would benefit from enhanced monitoring of parasite loads at lambing and in early lactation. Correlations () between FEC in lambs at 90 d of age and FEC in ewes at 0, 30, and 60 d postpartum of 0.05 to 0.09 ( ≤ 0.05) support the presence of a genetic relationship between these 2 indicators of parasite resistance.

Gene expression profiles of hair and wool sheep reveal importance of Th2 immune mechanisms for increased resistance to

Management of gastrointestinal parasites is a critical issue for sheep producers worldwide. Increases in the prevalence of drug-resistant worms have complicated parasite control and increased economic losses. Therefore, other methods of parasite control need to be assessed, including the use of genetically resistant animals in breeding programs. Hair sheep breeds such as the St. Croix have greater parasite resistance than conventional wool breeds. However, the immune mechanisms that control parasite resistance in hair or wool breeds have not yet been fully determined, and information on cytokine expression profiles for both wool sheep selected for increased resistance and hair sheep is limited. Our objective was to investigate gene expression differences in 24 parasite-resistant hair and 24 susceptible wool sheep to identify immune effectors associated with resistance to . One-half of the lambs were infected and sacrificed at 3 or 27 d after infection. Remaining lambs were not infected. Breed differences in expression of genes associated with Th1 and Th2 immune responses in lymph nodes and abomasal tissue were determined. Th2-associated genes included IL-4, IL-13, IL-5, IgE, the α chain of the IL-4 receptor, and the α chain of the high-affinity IgE receptor (FcεRI). Th1-associated genes included interferon gamma (IFN-γ), the p35 subunit of IL-12 (IL-12 p35), and the β1 and β2 chains of the IL-12 receptor (IL-12 Rβ1 and IL-12 Rβ2, respectively). In both hair and wool sheep, infection with resulted in greater expression of IgE, IL-13, IL-5, and IL-12 p35 and somewhat reduced expression of IFNγ in lymph nodes. In abomasal tissue, parasite infection resulted in greater IgE, IL-13, FcεRI, and IL-12 p35 expression in infected lambs compared with control lambs. Between breeds, hair sheep had a stronger Th2 response after infection than wool sheep, with increased expression of IgE and IL-13 and decreased expression of IFNγ in lymph nodes and increased expression of IL-13 and decreased expression of IL-12 p35 in abomasal tissue. Expression of IL-4 in lymph nodes did not differ between hair and wool lambs, and IL-4, IL-5, IL-12 Rβ1, and IL-12 Rβ2 expression was too low to measure at the times sampled in abomasal tissue.

Effects of birth-rearing type on weaning weights in meat sheep are systematically associated with differences in mean performance among flocks

Background

Adjustment of body weights for systematic environmental effects such as dam age and litter size is essential for accurate prediction of breeding values in meat sheep and often accomplished by pre-adjusting records using simple multiplicative adjustment factors, which are derived as ratios of least-squares means of weights of lambs in target and reference classes. However, increasing use of multibreed genetic evaluations that incorporate data from both purebred and commercial flocks has generated concerns regarding the ability of simple additive or multiplicative adjustment factors to properly correct for environmental effects in flocks that differ widely in mean performance. Thus, consistency of adjustment factors across flocks and systematic effects of the level of flock performance on these factors were evaluated using data from the US National Sheep Improvement Program.

Methods

We used birth and weaning weights of lambs from 29 flocks that had at least 500 records per flock and represented several terminal-sire sheep breeds. Effects of lamb sex, dam age class and litter size on birth weights, and of dam age class and combined effects of type of birth and rearing on weaning weights were evaluated. Interactions between these effects and flock were assessed. Bias associated with different adjustment protocols was evaluated for high- and low-performance flocks.

Results

Effects of litter size and differences between yearling and adult dams varied (P < 0.001) among flocks. For weaning weights, additive adjustment factors were not associated with the level of flock performance, but multiplicative adjustment factors were strongly and inversely related to flock means for weaning weights (W). Flock-specific adjustment factors (F = αW^β) reduced bias in adjusted weaning weights associated with differences in flock performance. By contrast, simple multiplicative adjustment factors were appropriate to adjust birth weights.

Conclusions

Differences in weaning weights among single, twin, and triplet lambs were inversely related to the level of flock performance. Use of simple multiplicative adjustment factors led to adjustment bias when applied across flocks with large differences in mean performance. This bias was reduced by using additive adjustment factors or multiplicative factors that were derived as simple exponential functions of flock means for weaning weight.

Fecal egg counts for gastrointestinal nematodes are associated with a polymorphism in the MHC-DRB1 gene in the Iranian Ghezel sheep breed

Genetic variation among sheep breeds in resistance to gastrointestinal nematodes (GIN) has been demonstrated in several production environments. Relationships between the ovine major histocompatibility complex and resistance to GIN have been studied, but few studies have systematically examined this issue in less-developed and semi-arid regions. The aim of the current study was to explore associations between fecal worm egg counts (FEC) for several GIN and polymorphisms in the DRB1 gene. One hundred male lambs were selected at 4–6 months of age from weaned animals in five flocks (n = 20 per flock). Body weights were determined, FAMACHA scores based on color of the ocular mucous membranes were assigned as an indicator of anemia, and blood and fecal samples were collected twice to evaluate FEC and blood packed cell volume (PCV) and for DNA isolation. A repeated-measures analysis of variance was used to test effects of genotype on FEC. The model included fixed effects of flock, genotype, time of measurement (1 or 2), and flock × time and genoype × time interactions, and a random (repeated) effect of lamb. Two genotypes (A1A1 and A1A2) were observed following digestion of Region 1 of Ovar-DRB1 with PstI. Genotypic frequencies were 0.73 for A1A1 and 0.27 for A1A2. FEC differed between Ovar_DRB1 genotypes A1A1 and A1A2 for Marshallagia marshalli, Strongyle, and total nematode FEC. Observed FEC were 30–41% lower for genotype A1A1. Differences among genotypes were consistent across measurement times, with no effect of genotype × measurement time interaction for any parasite class (P ≥ 0.34). A significant association was observed between FAMACHA scores and lamb PCV, and the residual correlation between these two variables was -0.51 (P < 0.001). FAMACHA scores can thus be used to detect differences among lambs in PCV, and polymorphic markers of Ovar-DRB1 have potential value as an indicator of parasite resistance in applied animal breeding programs on sheep farms in this region.

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: VIII. Quality measures of lamb longissimus dorsi

Quality measures of lamb longissimus dorsi were evaluated in 514 crossbred wether lambs to assess sire breed differences. Wethers were produced over 3 yr from single-sire matings of 22 Columbia, 22 U.S. Meat Animal Research Center (USMARC)-Composite (Composite), 21 Suffolk, and 17 Texel rams to adult Rambouillet ewes. Lambs were reared to weaning in an extensive western rangeland production system and finished in a feedlot on a high-energy finishing diet. One of three harvest groups were randomly assigned to each lamb, and lambs were transported to The Ohio State University abattoir when the mean BW of wethers remaining in the feedlot reached 54.4, 61.2, or 68.0 kg. After harvest, subjective lean quality scores were assigned and LM pH (immediately after and 24 h after harvest), color (quantified as Minolta L*, a*, and b*), intramuscular fat (IMF), cooking loss percentage, and Warner-Bratzler shear force (WBSF) were determined. Statistical models included fixed effects of sire breed, year of birth, and harvest group and random effects of sire (nested within sire breed and year) and maternal grandsire. Year and harvest group were significant (P < 0.04) for all traits, except harvest group was not for WBSF and lean quality (P > 0.28). At comparable numbers of days on feed, Texel-sired wethers had the greatest (more desirable; P < 0.01) subjective lean quality scores while Composite- and Suffolk-sired lambs were intermediate and Columbia-sired lambs had the lowest (less desirable). Minolta L* values were greater (P < 0.02) for Texel- than Columbia-sired lambs, although this difference is not visually discernible by humans. No significant (P > 0.05) sire breed effects were detected for LM pH at or 24 h after harvest, Minolta a* and b*, IMF, percentage of cooking loss, and WBSF at comparable numbers of days on feed. At comparable chilled carcass weight, significant (P < 0.01) sire breed effects were detected for subjective lean quality score. Texel-sired lambs had greater scores than Columbia- and Suffolk-sired lambs, but Composite-sired lambs did not differ from lambs sired by the other sire breeds. Sire breed effects were not detected (P > 0.15) for LM pH at or 24 h after harvest, Minolta L*, a*, and b*, cooking loss percentage, IMF, and WBSF at comparable chilled carcass weight. Therefore, results of the present study indicated that the 4 sire breeds produced crossbred lamb carcasses that had similar and desirable LM quality measurements, meeting consumer expectations.

Evaluation of Columbia, U.S. Meat Animal Research Center Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: VI. Measurements of live-lamb and carcass shape and their relationship to carcass yield and value

Linear measurements on live lambs and carcasses can be used to characterize sheep breeds and may have value for prediction of carcass yield and value. This study used 512 crossbred lambs produced over 3 yr by mating Columbia, U.S. Meat Animal Research Center (USMARC) Composite, Suffolk, and Texel rams to adult Rambouillet ewes to assess sire-breed differences in live-animal and carcass shape and to evaluate the value of shape measurements as predictors of chilled carcass weight (CCW), weight of high-value cuts (rack, loin, leg, and sirloin; HVW), weight of trimmed high-value cuts (trimmed rack and loin and trimmed, boneless leg and sirloin; TrHVW), and estimated carcass value before (CVal) and after trimming of high-value cuts (TrCVal). Lambs were produced under extensive rangeland conditions, weaned at an average age of 132 d, fed a concentrate diet in a drylot, and harvested in each year in 3 groups at target mean BW of 54, 61, and 68 kg. Canonical discriminant analysis indicated that over 93% of variation among sire breeds was accounted for by the contrast between tall, long, less-thickly muscled breeds with greater BW and CCW (i.e., the Columbia and Suffolk) compared with shorter, more thickly muscled breeds with smaller BW and CCW. After correcting for effects of year, harvest group, sire breed, and shipping BW, linear measurements on live lambs contributed little to prediction of CCW. Similarly, after accounting for effects of CCW, linear measurements on live animals further reduced residual SD (RSD) of dependent variables by 0.2 to 5.7%, with generally positive effects of increasing live leg width and generally negative effects of increasing heart girth. Carcass measurements were somewhat more valuable as predictors of carcass merit. After fitting effects of CCW, additional consideration of carcass shape reduced RSD by 2.1, 3.6, 9.5, and 2.2% for HVW, TrHVW, CVal, and TrCVal, respectively. Effects of increasing carcass leg width were positive for HVW, TrHVW, and TrCVal. We also observed positive effects of increasing carcass length on TrCVal and negative effects of increasing cannon bone length on HVW and CVal. Increasing shoulder width had positive effects on CVal but negative effects on TrHVW. Differences in lamb and carcass shape were significantly associated with carcass yield and value, but the additional accuracy associated with use of these measurements was modest relative to that achieved from use of only shipping BW or CCW.

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: V. Postweaning growth, feed intake, and feed efficiency

This study was conducted to quantify differences in feed efficiency among 4 sire breeds using records from 1,109 crossbred lambs over 3 yr. Lambs were produced from mating Columbia, USMARC-Composite (Composite), Suffolk, and Texel rams to adult Rambouillet ewes. After weaning, lambs were finished on a high-energy diet in group-fed pens. Efficiency was assessed at 45 and 90 d on study, 50 and 60 kg of BW, and 6.6 and 9.1 mm of fat depth between the 12th and 13th ribs. Sire breed affected most of the traits that were measured. At 90 d, Suffolk-sired lambs had gained 13 to 19% more BW (P < 0.001), were 7 to 13% heavier (P < 0.001), and had consumed 4 to 11% more (P < 0.001) ME than the other breed crosses. However, at 90 d, G:F (59.9 vs. mean of 56.2 g BW gain/Mcal of ME; P < 0.01) and residual BW gain (RG; 0.94 vs. -0.33 kg BW; P < 0.05) were greater for Suffolk-sired lambs than for the other 3 sire breeds. Also, RG for Suffolk-sired lambs was greater (P < 0.01) at 6.6 and 9.1 mm of fat depth (0.62 vs. -0.24 kg and 0.87 vs. -0.33 kg of BW, respectively) and at 60 kg of BW (0.73 vs. 0.31 kg of BW) than for the other sire breeds. At 90 d, Columbia-sired lambs had the greatest (P < 0.01) residual feed intake (RFI; 7.01 vs. mean of -2.33 Mcal ME for the 3 other sire breeds). At 60 kg of BW, Texel- and Composite- (-2.34 Mcal ME, combined) had more favorable (P < 0.01) RFI than Columbia-sired lambs (6.42 Mcal ME), and Suffolk-sired lambs (0.49 Mcal ME) were intermediate and not different from the other 3 sire breeds. At 6.6 mm of fat depth, Columbia- and Suffolk- (3.30 Mcal ME, combined) had greater (P < 0.001) RFI than Texel-sired lambs (-4.23 Mcal ME); at 9.1 mm of fat depth, Columbia-sired lambs had the greatest (P < 0.05) RFI (7.35 vs. -2.11 Mcal ME for the other breeds combined). In summary, except for ME intake at 90 d, Suffolk-sired lambs were equal or superior to Columbia-, Composite-, and Texel-sired lambs for BW, BW gain, ME intake, G:F, RFI, and RG to 90 d, 60 kg of BW, and 9.1 mm of fat depth. Breed rankings were consistent across the study period for G:F and RG, but rankings changed over time for RFI.

Circannual changes in progesterone secretion in intact ewes, luteinizing hormone secretion in ovariectomized estradiol-implanted ewes, and prolactin secretion in three sheep breeds anticipated to differ in seasonality of reproduction

Changes in progesterone secretion in intact ewes (7 or 9 per breed) and luteinizing hormone secretion in ovariectomized, estradiol-implanted ewes (9 or 10 per breed) were monitored for 12 mo in Suffolk, tropically adapted St. Croix, and OOS ewes. The OOS line is a composite population of 50% Dorset, 25% Rambouillet, and 25% Finnish Landrace breeding that was selected for 10 yr for ability to lamb in October and early November. Ewes were isolated from rams, and blood samples were collected twice weekly. Circulating prolactin concentrations were also determined from blood samples collected near the summer and winter solstice and vernal and autumnal equinox. Intact OOS ewes entered anestrus later, began the subsequent breeding season sooner, and had a shorter seasonal anestrus than Suffolk and St. Croix ewes (P ≤ 0.005). St. Croix ewes did not differ from Suffolk ewes in date of onset or cessation of breeding or duration of anestrus (P ≥ 0.06). Breed differences in duration of luteinizing hormone inhibition in ovariectomized ewes were essentially identical to those observed for duration of anestrous. Prolactin concentrations varied during the year: annual changes were larger in relatively seasonal Suffolk ewes than in tropically-derived St. Croix ewes (P<0.01), and OOS ewes were intermediate to, and tended to differ from (P<0.10), the other two breeds. We conclude that OOS ewes developed by selection for fertility in spring matings had an abbreviated seasonal anestrus that is one of the shortest ever reported for temperate breeds, and that tropical St. Croix sheep did not have a shorter seasonal anestrus than Suffolk sheep under temperate conditions and ram isolation.

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: IV. Postfabrication carcass component weights

Postfabrication carcass component weights of 517 crossbred wether lambs were analyzed to evaluate 4 terminal-sire breeds. Wethers were produced over 3 yr from single-sire matings of 22 Columbia, 22 USMARC-Composite (Composite), 21 Suffolk, and 17 Texel rams to adult Rambouillet ewes. Lambs were reared to weaning in an extensive western rangeland production system and finished in a feedlot on a high-energy finishing diet. When wethers reached a mean BW of 54.4, 61.2, or 68.0 kg, they were transported to The Ohio State University abattoir for harvest. After refrigeration for approximately 24 h, chilled carcass weight (CCW) was measured, carcasses were fabricated according to Style A of Institutional Meat Purchase Specifications, and postfabrication weights were recorded. At comparable numbers of days on feed, Suffolk-sired lambs had heavier (P < 0.04) neck, breast, shoulder, foreshank, rack, loin, leg, sirloin, roast-ready rack, trimmed loin, and boneless leg cuts than progeny of the other sire breeds. Boneless sirloins were heavier (P < 0.01) for Suffolk-sired than Composite-sired lambs but did not differ from those for Columbia- or Texel-sired lambs. Columbia- and Suffolk-sired lambs had heavier (P < 0.01) hindshanks than Texel-sired lambs. Suffolk-sired lambs had heavier (P < 0.01) high-value cuts (rack, loin, leg, and sirloin) and trimmed high-value cuts than progeny of the other sire breeds. Cutting loss (CCW - wholesale cut weights) and high-value trimming loss were greatest (P < 0.02) for Suffolk-sired lambs and least for Texel- and Composite-sired lambs. Sire breed did not affect (P > 0.06) flank weight. Data adjusted to comparable CCW reduced the number of significant sire-breed effects and changed sire-breed rankings of carcass component weights, for which sire breeds differed. After adjusting, Suffolk-sired lambs had lighter (P < 0.05) loins than Columbia- and Composite-sired lambs, Composite-sired lambs had heavier (P < 0.05) high-value cuts than Suffolk-sired lambs, and Suffolk- and Columbia-sired lambs had heavier (P < 0.05) necks than Texel-sired lambs. At predicted backfat thickness of 6.6 mm, Composite-sired lambs had a greater (P < 0.05) percentage of high-value cuts than Suffolk-sired lambs before but not after trimming. Producers can use these results to select terminal-sire breeds that will complement their production system and improve lamb value.

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: I. Ewe productivity and crossbred lamb survival and preweaning growth

A 3-yr study was conducted to comprehensively evaluate Columbia, Suffolk, USMARC-Composite (Composite), and Texel breeds as terminal sires in an extensive rangeland production system. The objective was to estimate breed-of-ram effects on ewe fertility, prolificacy, and dystocia, and sire breed effects on lamb survival and growth until weaning at approximately 132 d of age. Data were from 22 Columbia, 22 Composite, 21 Suffolk, and 17 Texel rams with 957 exposures to 574 adult Rambouillet ewes (3- to 7-yr-old at lambing), 908 lambings, and 1,834 lambs. Ram breed did not affect ewe fertility (mean = 94.9%; p = 0.73), total number born per ewe lambing (mean = 2.02 lambs; p = 0.20), number born alive per ewe lambing (mean = 1.90 lambs; p = 0.24), or number weaned per ewe lambing (mean = 1.45 lambs, p = 0.94). Dystocia rates were different (p = 0.01) for ewes mated to Columbia (12.2%), Composite (13.5%), Suffolk (25.7%), and Texel rams (31.9%) during 1 yr of the study, but differences among ram breeds were not repeatable (p ≥ 0.38) during the other 2 yr. Suffolk-sired lambs were heavier (p ≥ 0.02) at birth (5.5 kg) and weaning (40.3 kg) than lambs sired by the other breeds, which did not differ (p ≥ 0.34) for birth weight (mean = 5.3 kg). Texel-sired lambs (37.4 kg) were lighter (p ≥ 0.02) at weaning than Columbia- (38.8 kg) and Composite-sired (38.4 kg) lambs, which did not differ (p = 0.40) for weaning weight. Sire breed effect approached significance (p = 0.06) for lamb survival to weaning; estimated survival probabilities were 0.87 (Columbia), 0.89 (Composite), 0.93 (Suffolk), and 0.86 (Texel) for lambs reared by their birth dam. Interaction between sire breeds and birth weight affected (p < 0.001) lamb survival and revealed that lightweight Columbia- and Suffolk-sired lambs had a greater risk of death than lightweight lambs sired by Composite and Texel rams, but risk of death did not increase substantially for heavyweight lambs from any of the breeds. When mated to adult Rambouillet ewes in an extensive rangeland production system, the use of Suffolk rams is warranted to improve preweaning growth of market lambs and is not predicted to affect ewe fertility, ewe prolificacy, dystocia, or lamb survival compared with the other sire breeds we tested.

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: II. Postweaning growth and ultrasonic measures of composition for lambs fed a high-energy feedlot diet

Over 3 yr, postweaning growth patterns and changes in ultrasonic measurements of fat depth (FD) and LM area were assessed for 1,049 crossbred ewe and wether lambs (Ovis aries) produced by mating adult Rambouillet ewes to 1 of 22 Columbia, 22 USMARC-Composite (Composite), 21 Suffolk, or 17 Texel rams and raised to weaning under extensive Western rangeland conditions. After weaning, lambs were transitioned to a high-energy finishing diet in a feedlot, weighed weekly for 13 to 16 wk, and scanned using ultrasound at 2-wk intervals to estimate FD and LM area between the 12th and 13th ribs. Lambs sired by Suffolk rams were 5 to 12% heavier (P < 0.05) at start of test, grew 14 to 22% faster (P < 0.001), and were correspondingly 7 to 14% heavier (P < 0.001) after 90 d on test than lambs sired by rams of the other 3 breeds. At this time, lambs sired by Texel rams were 5% lighter (P < 0.01) than Columbia- or Composite-sired lambs, which did not differ (P > 0.20). Columbia-sired lambs had less FD (8.9 mm) but smaller LM areas (15.6 cm(2)) at 90 d on test (both P < 0.01) than lambs sired by rams of the other breeds (average of 9.8 mm for FD and 16.6 cm(2) for LM area), which did not differ for either measurement at this time. At 60 kg, predicted FD differed among sire breeds (P < 0.001) and were similar for Suffolk- (7.6 mm) and Columbia-sired (7.9 mm) lambs, intermediate for Composite-sired lambs (9.1 mm), and largest for Texel-sired (10.1 mm) lambs. At a BW of 60 kg, LM area differed between all pairs of sire breeds (P < 0.05), and was largest for Texel-sired lambs (16.7 cm(2)), followed by Composite-, Suffolk-, and Columbia-sired lambs (15.7, 14.8, and 14.5 cm(2), respectively). At a predicted FD of 9.1 mm (the boundary between U.S. Yield Grades 3 and 4), the predicted LM area for Suffolk-sired lambs (16.2 cm(2)) was similar (P > 0.10) to that of Texel-sired lambs (16.0 cm(2)) and superior (P < 0.01) to that of Composite- (15.7 cm(2)) and Columbia-sired lambs (15.4 cm(2)). Lambs sired by Suffolk rams were thus equal or superior to lambs sired by the other 3 breeds in growth, FD, and LM area at comparable ages, fatness at 60 kg, and LM area at a FD of 9.1 mm, but inferior in LM area to Texel- and Composite-sired lambs at comparable BW.

Patterns of estrous cycles, estrous behavior, and circulating prolactin in spring and summer in ewes selected for autumn lambing and exposed to ambient or long-day photoperiods

Estrous behavior in response to ambient and long-day photoperiods was evaluated in ewes developed by 10 years of selection for ability to lamb in autumn. Following October lambing, 67 ewes were moved indoors and exposed to long-day (16L:8D) or ambient photoperiods from February 2 until July 6. Two vasectomized rams with marking harnesses were housed with each group. Estrous behavior was monitored twice weekly. Ewes from the selection line were unresponsive to long days, with no effects on estrous behavior, frequency of ovulation, or circulating prolactin. Adult ewes were anestrus for only 34±3 d, but 2- and 3-years-old ewes were anestrus for 72±7 and 57±10 d, respectively. Frequencies of ovulation based on circulating progesterone concentrations in March, May, and June were 97%, 95% and 52%, respectively, indicating that many ewes that did not exhibit estrus still ovulated. Prolactin concentrations increased from 10 ng/ml in February to 27 ng/ml in March and 173 ng/ml in June but were not affected by light treatment. Ten ewes that failed to exhibit estrus behavior for at most 24 d during the main study were then monitored for 74 additional long days. Nine of 10 ewes did not exhibit estrus for periods similar to 1 or 2 estrus cycles during this period, but eight ewes re-initiated cycles by the end of the study on September 18. Selection for ability to lamb in autumn thus resulted in ewes with an abbreviated seasonal anestrus and reduced sensitivity to long days.

Longitudinal changes in ultrasonic measurements of body composition during growth in Suffolk ram lambs and evaluation of alternative adjustment strategies for ultrasonic scan data

Four equations were used to compare alternative procedures to adjust ultrasonic estimates (y) of backfat thickness (BF) and LM area (LMA) for BW using data from a series of 7 scans on 24 Suffolk ram lambs born in 2007. Equations were linear, linear + quadratic, allometric (y = alphaBW(beta)), and allometric + BW (ABW; y = alphaBW(beta)e(gammaW)). Goodness of fit was very similar between equations over the range of the data. Resulting adjustment equations were tested using 3 serial scans on winter-born Suffolk (n = 150), Hampshire (n = 36), and Dorset (n = 43) rams and 52 fall-born Dorset rams tested at the Virginia Ram Test in 1999 through 2002. Partial correlations (accounting for the effect of year) between predicted and actual measures ranged from 0.78 to 0.87 for BF and 0.66 to 0.93 for LMA in winter-born rams and from 0.70 to 0.71 for BF and 0.72 to 0.78 for LMA in fall-born rams. No significant differences in predictive ability existed between equations for BF or LMA (P > 0.05), and there was no indication that the allometric equation was a better predictor than linear within the range of the data. Adjustment equations were also tested using serial scan data from 37 Suffolk ewe lambs born in the same contemporary group as the rams used to derive the prediction equations but fed for a substantially slower rate of BW gain. Correlations between predicted and actual values of BF and LMA indicated lambs were too young and small at the first scan (77 d, 32.4 kg) to reliably predict carcass measures at typical slaughter weights. For prediction using data from the 2 subsequent scans, at mean ages >96 d and mean BW >39 kg, correlations between predicted and actual values were 0.72 to 0.74 for BF and 0.54 to 0.76 for LMA. Little difference existed between equations for predicting BF. For LMA, the ABW form was a weaker predictor than the others, and the linear equation was slightly superior to allometric. Therefore, it appears the linear and allometric forms are both suitable for use in central ram test and performance-tested farm flocks.

Phenotypic and genetic associations between lamb growth traits and adult ewe body weights in western range sheep

Data from the Montana State University Targhee flock were used to estimate genetic and environmental relationships between lamb BW and adult ewe BW, condition score, and prolificacy. The flock was managed under commercial western range conditions typical of the area. Data included records from 12,154 lambs born to 2,930 dams and 200 rams between 1960 and 2005. Lamb traits included BW at birth and approximately 45 d, 120 d (weaning), 12 mo, and 18 mo of age and fleece characteristics at 12 mo of age. Adult traits included ewe litter size; BW and BCS at weaning, in late gestation, and in early lactation; and adult fleece measurements. Multiplicative factors were used to adjust (pre)weaning lamb BW for effects of age of dam, type of birth and rearing, and lamb sex and to adjust adult litter sizes for effects of ewe age. An animal model was used to estimate genetic relationships. Models for lamb traits included fixed effects of year of birth and, for postweaning data, lamb sex and random additive genetic effects and, for (pre)weaning BW, additive genetic maternal and permanent environmental maternal effects. Models for adult traits included fixed effects of year of birth, year of record, and, when appropriate, numbers of lambs born or born and reared and random additive genetic and animal permanent environmental effects. Heritability estimates for lamb birth weight, 45-d BW, weaning weight, yearling weight, 18-mo BW, fleece weight, staple length, and spinning count were 0.19, 0.07, 0.12, 0.32, 0.38, 0.32, 0.31, and 0.25, respectively. Maternal heritabilities for lamb birth, 45-d, and weaning weights were 0.15, 0.09, and 0.08, respectively. Heritability estimates for adult traits were 0.12 for litter size, averaged 0.43 for BW and 0.13 for body condition, and were 0.44, 0.37, and 0.25 for adult fleece weight, staple length, and spinning count, respectively. Correlations between genetic effects on adult BW and direct and maternal genetic effects on lamb BW ranged from 0.21 to 0.96 (P < 0.05) and 0.29 to 0.53 (P < 0.05), respectively, with residual correlations ranging from 0.05 to 0.95. Correlations of lamb traits with adult body condition and number of lambs born were generally not different from zero; genetic and residual correlations ranged from -0.52 to 0.69 and -0.39 to 0.31, respectively.