Sheep Experiment Station Research Articles

Genetic parameters for Mycoplasma ovipneumoniae nasal DNA copy number provide progress to promote domestic and bighorn sheep coexistence on public lands

Discord between domestic sheep producers and bighorn sheep conservationists primarily involves concerns over the transmission of Mycoplasma ovipneumoniae between domestic and wild sheep. To discern if selective breeding within the Rambouillet could serve to reduce transmission, a genetic approach utilizing an existing phenotype was evaluated for additive genetic variance. The phenotype employs the measure of nasally shed bacterial DNA, or M. ovipneumoniae nasal DNA copy number (MONCN). Following estimation of the additive genetic variation associated with MONCN, the heritability and repeatability for this trait was calculated. The level of MONCN was measured at least three times per year at the U.S. Sheep Experiment Station (USSES) from ewes ranging from 1 to 7 years of age. Repeated measures animal models were evaluated from 320 ewes with a total of 1223 samples (mean = 3.8 per ewe). The MONCN values ranged from 0 (non-detected) to 71,654 copies per 2 μl of extracted nasal swab DNA. Four genetic models were evaluated with the categorical model having the highest heritability (0.12 ± 0.09) and repeatability (0.60 ± 0.05). Fixed effects included season/year (n = 9) and ewe age (n = 7). Outcomes from this research resulted in heritability estimates from which breeding values can be estimated to select USSES ewes and rams for reduced MONCN. This research provides a practical approach that can be immediately implemented to manage domestic sheep to be more compatible with bighorn sheep on public lands, providing positive welfare benefits for both species.

Assessment of genetic diversity and population structure of U.S. Polypay sheep from breed origins to future genomic selection.

Knowledge of past and present genetic diversity within a breed is critical for the design and optimization of breeding programs as well as the development of strategies for the conservation of genetic resources. The Polypay sheep breed was developed at the U.S. Sheep Experiment Station (USSES) in 1968 with the goal of improving productivity in Western U.S. range flocks. It has since flourished in the more intensively managed production systems throughout the U.S. The genetic diversity of the breed has yet to be documented. Therefore, the primary objective of this study was to perform a comprehensive evaluation of the genetic diversity and population structure of U.S. Polypay sheep using both pedigree- and genomic-based methods. Pedigree data from 193 Polypay flocks participating in the National Sheep Improvement Program (NSIP) were combined with pedigree records from USSES (n = 162,997), tracing back to the breed's origin. A subset of these pedigreed sheep from 32 flocks born from 2011 to 2023 were genotyped with the GGP Ovine 50K BeadChip containing 51,867 single nucleotide polymorphisms (SNPs). Four subgroups were used for the pedigree-based analyses: 1) the current generation of animals born in 2020-2022 (n = 20,701), 2) the current generation with a minimum of four generations of known ancestors (n = 12,685), 3) only genotyped animals (n = 1,856), and 4) the sires of the current generation (n = 509). Pedigree-based inbreeding for the full population was 2.2%, with a rate of inbreeding of 0.22% per generation. Pedigree-based inbreeding, Wright's inbreeding, and genomic inbreeding based on runs of homozygosity were 2.9%, 1.3%, and 5.1%, respectively, for the genotyped population. The effective population size ranged from 41 to 249 for the pedigree-based methods and 118 for the genomic-based estimate. Expected and observed heterozygosity levels were 0.409 and 0.403, respectively. Population substructure was evident based on the fixation index (FST), principal component analysis, and model-based population structure. These analyses provided evidence of differentiation from the foundation flock (USSES). Overall, the Polypay breed exhibited substantial genetic diversity and the presence of a population substructure that provides a basis for the implementation of genomic selection in the breed.

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.

140 Targhee Sire Benchmarking at the U.S. Sheep Experiment Station

Abstract The Targhee breed was developed at the U.S. Sheep Experiment Station (USSES) starting in 1926, and has become an established range breed used commercially in the Western U.S. Our objective was to benchmark the performance of industry-based (external) Targhee sires with those currently in use at USSES. Nineteen Targhee sires from 12 flocks were incorporated into the USSES breeding flock starting with the 2015 breeding season. Data were measured through 2022 for 3 production and 12 wool traits with a range of 180 to 1,967 records per trait. Externally sourced sires averaged 38.3 progeny (7 to 78), with 0 to 4 ram lambs (15 total) and 0 to 15 (106 total) ewe lambs retained per sire in the flock. They were ancestors of 984 grand-progeny. USSES sires averaged 25.0 progeny (5 to 52), with 0 to 1 ram lambs (2 total) and 0 to 8 (53 total) ewe lambs retained per sire. They had 275 grand-progeny. Pedigree data was used to compute the marginal genetic contributions for each sire to the current flock using ENDOG. External sires had a cumulative contribution of 31.9 percent (0.4 to 3.9) while the USSES sires contributed 1.4 percent (0.0 to 0.9). Using R, fixed effects examined were age of dam, lamb sex, lamb birth year, grazing group, and type of birth/rearing. Significant variation explained in a trait by main effects (P < 0.005), and their two-way interactions (P < 0.001), were included in the final linear mixed models fitted. Externally sourced and USSES sires were assigned to separate genetic groups to account for the anticipated differences in genetic base. Using WOMBAT, a univariate animal model was fitted to estimate variance components and predict estimated breeding values for each lamb trait. Selection of random effects was based on log-likelihood ratio tests. Final models fitted and estimated heritabilities are summarized in Table 1. Total litter weight at 120 days per ewe lambing (TW120) was evaluated using a repeated measures model with direct additive and permanent environmental random effects of the ewe. Genetic group solutions were not significantly different (P > 0.05) for any traits evaluated. Since both sire groups originated from the same population, this suggests significant selection divergence had not occurred between industry and USSES flocks. Incorporation of external Targhee sires increased the genetic diversity of the USSES flock. It also strengthened industry ties to the USSES flock, which will benefit the commercial genetic evaluation conducted by the National Sheep Improvement Program. USDA is an equal opportunity provider and employer.

ASAS-SSR Triennial Reproduction Symposium: Looking Back And Moving Forward-How Reproductive Physiology Has Evolved: Male reproductive behavior: sensory signaling in the brain of low-performing domestic rams.

Rams are selected for genetic traits a producer desires to propagate in his flock. Even though practically all sheep are naturally bred, rams are rarely evaluated for expression of sexual interest or behavior. Research at the U.S. Sheep Experiment Station reported that the proportion of rams with limited interest in ewes was nearly 30% of the total number of breeding rams. Breeding soundness tested rams with low sexual interest sire less than 16% of the lamb crop. Although producers recognize the problem, their usual solution is to increase the number of rams in breeding flocks decreasing the risk of open ewes. Increased costs and a lack of genetic progress are clearly important considerations, but the biological question as to what controls sexual interest remains intriguing. Circulating concentrations of testosterone do not differ by sexual interest among rams. However, following exposure to estrous ewes, sexually active, but not inactive, rams exhibit an increase in LH pulsatile activity, a biological response to sexual stimuli. This begs the question as to whether sexually inactive rams recognize sexual cues. Using c fos activity as an indicator of neural activity, differences in the olfactory pathway were compared among sexually active and inactive rams. Differences in fos activity were not detected in the olfactory bulb or medial amygdala. However, sexually inactive rams had lower fos activity in the central amygdala, bed nucleus of the stria terminalis, and medial preoptic area of the hypothalamus following exposure to sexual evocative olfactory stimuli. This suggests sexually inactive rams detect olfactory cues but have decreased vigilance to sensory stimuli and a muted response to sexual signals in areas of the brain required for the execution of sexual performance. With the amygdala receiving and integrating sensory signals from many areas of the brain, sexually inactive rams may lack normal reward mechanisms contributing to their lack of sexual interest. Rams with limited sexual interest have decreased dopamine synthesis and a lower expression of dopamine D2 receptors following exposure to sexual stimuli. Thus, a tempered reward pathway in combination with decreased vigilance and sensory processing in the amygdala may reduce stimulation and/or responsiveness in areas of the brain required for expression of sexual behavior.

Validation of an improved Anaplasma antibody competitive ELISA for detection of Anaplasma ovis antibody in domestic sheep.

An accurate and simple-to-perform new version of a competitive ELISA (cELISA) kit that became commercially available in 2015 for testing of cattle for antibody to Anaplasma marginale was validated for detection of Anaplasma ovis antibody in domestic sheep. True positives and negatives were identified using nested PCR (nPCR) as the gold standard. Negative bovine control sera supplied with the kit were used to calculate % inhibition (%I), designated bovine control ELISA (BcELISA), and this was compared to %I calculated from negative ovine sera derived from hand-raised, pathogen-free sheep, designated ovine control ELISA (OcELISA). The receiver operating characteristics area under the curve was 1.0 with a p value <0.001 regardless of the source of the control sera. The cutoff values for negative BcELISA and OcELISA were <30%I and <27%I, respectively. Our work confirmed that this Anaplasma antibody cELISA kit version 2 can be used with the serum controls supplied in the kit to test for A. ovis antibody in domestic sheep. Furthermore, this work confirmed the historically high infection prevalence (>93%) at the U.S. Sheep Experiment Station (Dubois, Idaho), in spite of efforts to reduce the possibility for iatrogenic transmission there, suggesting high levels of tick-borne transmission.

Delaying sheep grazing after wildfire in sagebrush steppe may not affect vegetation recovery

Although many land managers prohibit grazing for 2 years after a fire, little research has been conducted to determine the interaction of grazing with vegetation recovery after fire. In a study conducted in sagebrush steppe rangelands after a 2000 wildfire at the United States Sheep Experiment Station in Idaho, the influence of delay and season of sheep grazing on vegetation recovery was measured. A moderate level of sheep grazing was started 1, 2, or 3 years after fire in the autumn or 2 or 3 years after fire in the spring. Pseudoroegneria spicata, the dominant perennial grass, and Crepis acuminata increased in the autumn and non-grazed treatments, whereas perennial forb and Crepis acuminata cover declined in the spring grazing treatments beginning the second year after fire. There was no impact of sheep grazing on cover of Bromus tectorum, an important exotic winter annual grass, probably owing to the lack of autumn germination. In this study, moderate sheep grazing had subtle impacts on vegetation recovery after fire, with spring grazing having more negative consequences. Management decisions on when to start grazing livestock after fire should consider pre-fire ecological conditions, post-fire climatic conditions, and current knowledge of impacts of grazing on plant recovery.

Postfire Recovery of Sagebrush Communities: Assessment Using Spot-5 and Very Large-Scale Aerial Imagery

Abstract Much interest lies in long-term recovery rates of sagebrush communities after fire in the western United States, as sagebrush communities comprise millions of hectares of rangelands and are an important wildlife habitat. Little is known about postfire changes in sagebrush canopy cover over time, especially at a landscape scale. We studied postfire recovery of shrub canopy cover in sagebrush-steppe communities with the use of spectral mixture analysis. Our study included 16 different fires that burned between 1937 and 2005 and one unburned site at the US Sheep Experiment Station in eastern Idaho. Spectral mixture analysis was used with September 2006 Systeme Pour l’Observation de la Terre-5 (SPOT-5) satellite imagery to estimate percent shrub canopy cover within pixels. Very large-scale aerial (VLSA) imagery with 24-mm resolution was used for training and validation. SPOT-5 image classification was successful and the spectral mixture analysis estimates of percent shrub canopy cover were highly correlated with the shrub canopy cover estimates in the VLSA imagery ( R 2 = 0.82; P Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) communities recovered approximately 27 yr after fire, with an average shrub cover of 38%. These results are consistent with other field-based studies in mountain big sagebrush communities.

Prescribed fires in Artemisia tridentata ssp. vaseyana steppe have minor and transient effects on vegetation cover and composition

AbstractQuestion: What is the impact of prescribed fires on the cover and composition of vegetation in Artemisia tridentata ssp. vaseyana steppe?Location: United States Department of Agriculture, Agricultural Research Service, United States Sheep Experiment Station, eastern Idaho (44°14′44′’ N, 112°12′47′’ W).Methods: Multiple prescribed fires were lit in 2002 and 2003 in an Artemisia tridentata ssp. vaseyana (mountain big sagebrush) steppe ecosystem that was relatively free of exotic plants. Measurements of cover components and plant species frequencies were taken pre‐ and for 2 to 3 years post‐fire.Results: Cover of forbs and grasses returned to pre‐fire levels after two years. Shrub cover declined from 36 to 6% in the first year post‐fire. Fire reduced the frequencies of three species, A. tridentata ssp. vaseyana, Festuca idahoensis, and Cordylanthus ramosus, of rangeland plants. Frequencies of four plant species, Hesperostipa comata, Polygonum douglasii, Chenopodium fremontii and Chenopodium leptophyllum increased, but only P. douglasii increased for more than a year.Conclusion: This study demonstrates that in an Artemisia tridentata ssp. vaseyana steppe ecosystem without significant non‐native species or anthropogenic disturbances vegetative cover and species composition of the herbaceous community are only minimally altered by fire. The herbaceous component returned to pre‐fire conditions within three years of a fire.

Prescribed fires in Artemisia tridentata ssp. vaseyana steppe have minor and transient effects on vegetation cover and composition

Question What is the impact of prescribed fires on the cover and composition of vegetation in Artemisia tridentata ssp. vaseyana steppe?Location: United States Department of Agriculture, Agricultural Research Service, United States Sheep Experiment Station, eastern Idaho (44°14′44″ N, 112°12′47″ W).Methods: Multiple prescribed fires were lit in 2002 and 2003 in an Artemisia tridentata ssp. vaseyana (mountain big sagebrush) steppe ecosystem that was relatively free of exotic plants. Measurements of cover components and plant species frequencies were taken pre- and for 2 to 3 years post-fire.Results: Cover of forbs and grasses returned to pre-fire levels after two years. Shrub cover declined from 36 to 6% in the first year post-fire. Fire reduced the frequencies of three species, A. tridentata ssp. vaseyana, Festuca idahoensis, and Cordylanthus ramosus, of rangeland plants. Frequencies of four plant species, Hesperostipa comata, Polygonum douglasii, Chenopodium fremontii and Chenopodium leptophyllum increased, but only P. douglasii increased for more than a year.Conclusion: This study demonstrates that in an Artemisia tridentata ssp. vaseyana steppe ecosystem without significant non-native species or anthropogenic disturbances vegetative cover and species composition of the herbaceous community are only minimally altered by fire. The herbaceous component returned to pre-fire conditions within three years of a fire.Nomenclature: USDA Natural Resources Conservation Service, Plants database http//plants.usda.gov/

Measuring Plant Cover in Sagebrush Steppe Rangelands: A Comparison of Methods

Methods that are more cost-effective and objective are needed to detect important vegetation change within acceptable error rates. The objective of this research was to compare visual estimation to three new methods for determining vegetation cover in the sagebrush steppe. Fourteen management units at the US Sheep Experiment Station were identified for study. In each unit, 20 data collection points were selected for measuring plant cover using visual estimation, laser-point frame (LPF), 2 m above-ground-level (AGL) digital imagery, and 100-m AGL digital imagery. In 11 of 14 management units, determinations of vegetation cover differed (P < 0.05). However, when combined, overall determinations of vegetation cover did not differ. Standard deviation, corrected sums of squares, coefficient of variation, and standard error for the 100 m AGL method were half as large as for the LPF and less than the 2-m AGL and visual estimate. For the purpose of measuring plant cover, all three new methods are as good as or better than visual estimation for speed, standard deviation, and cost. The acquisition of a permanent image of a location is an important advantage of the 2 and 100 m AGL methods because vegetation can be reanalyzed using improved software or to answer different questions, and changes in vegetation over time can be more accurately determined. The reduction in cost per sample, the increased speed of sampling, and the smaller standard deviation associated with the 100-m AGL digital imagery are compelling arguments for adopting this vegetation sampling method.

Influence of body weight, age, and weight gain on fertility and prolificacy in four breeds of ewe lambs1

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.

The incidence of genotypes at codon 171 of the prion protein gene (PRNP) in five breeds of sheep and production traits of ewes associated with those genotypes1,2

Scrapie is one of several transmissible spongiform encephalopathies of livestock. Disease susceptibility is linked to polymorphisms in the normal prion protein gene that encodes the mammalian prion precursor. Codon 171 of this gene is a major determinant of scrapie susceptibility. Selection for arginine (R) at codon 171 is encouraged by the USDA to decrease the incidence of scrapie. Objectives of this study were to determine the frequency of R allele variants at codon 171 in a sample of sheep from five breeds (Columbia, Hampshire, Rambouillet, Suffolk, and Targhee) and western white-faced commercial ewes and to determine whether the R allele is associated with ewe and lamb production traits. Genotyping was performed on 532 ewes and 901 lambs from the University of Wyoming flock, in addition to 820 rams from 52 sheep producers from Wyoming and surrounding areas, using a DNA mismatch assay that discriminated the R allele from others at codon 171. Genotyping was performed by DNA sequencing on 127 rams representing all breeds, except Hampshire from the USDA Sheep Experiment Station at Dubois, ID. The 171R allele was found in all five breeds and in the commercial western white-faced ewes. Genotype frequencies varied (P < 0.001) by breed in ewe and ram populations. Influence of R-allele frequency on ewe lambing records and individual lamb records was analyzed for Columbia (62, 161, 121), Hampshire (89, 193, 162), Rambouillet (87, 179, 133), Suffolk (67, 178, 161), and commercial sheep (227, 463, 324) for numbers of ewes, total number of ewe production records, and individual lamb records, respectively. Suffolk ewes without the R allele (non-R/non-R) gave birth to more (P <or= 0.005) multiple lambs than heterozygous non-R/R ewes. Homozygous non-R/non-R Suffolk ewes weaned lighter (P = 0.02) individual lambs but more (P = 0.03) total weight of lamb than heterozygous non-R/R ewes. Although ewes genotyped homozygous non-R/non-R or heterozygous non-R/R at codon 171 from the commercial flock gave birth to more (P <or= 0.002) multiple lambs than ewes genotyped R/R, differences were not detected (P = 0.14) in total weight of lamb weaned. Production traits of Columbia, Hampshire, and Rambouillet ewes did not differ (P >or= 0.08) by ewe genotype. Lamb birth and weaning weights were not influenced (P >or= 0.12) by lamb genotype in any of the breeds or in the commercial flock. In this population, ultimate lamb production was only influenced by genotype at codon 171 in the Suffolk flock.

Estimates of genetic parameters and genetic change for reproduction, weight, and wool characteristics of Rambouillet sheep

Records were for Rambouillet sheep from data collected from 1950 to 1998 at the U.S. Sheep Experiment Station, Dubois, Idaho, USA. Number of observations were 44,211 for litter size at birth and litter size at weaning, 35,604 for birth weight, 34,114 for weaning weight, 39,820 for fleece weight, 39,821 for fleece grade, and 3574 for staple length. Genetic parameters from both single- and two-trait analyses for prolificacy, weight, and wool traits were estimated using REML with animal models. Direct heritability estimates from single-trait analyses were 0.09 for litter size at birth, 0.06 for litter size at weaning, 0.27 for birth weight, 0.20 for weaning weight, 0.51 for fleece weight, 0.16 for fleece grade, and 0.58 for staple length. Estimates of direct genetic correlation between litter sizes at birth and weaning was 0.76 and between birth and weaning weights was 0.60. Estimates of genetic correlation between fleece weight and staple length was positive (0.45), but negative between fleece weight and fleece grade (−0.47) and between staple length and fleece grade (−0.52). Estimates of genetic correlations were near zero between birth weight and litter size at weaning, small and positive between birth weight and litter size at birth, and moderate and positive between weaning weight and litter size traits. Fleece weight, fleece grade, and staple length were slightly but negatively correlated with both litter size traits. Estimates of correlations between weight traits and fleece weight were positive and low to moderate. Estimates of correlations between weight traits and fleece grade were negative and small, while estimates between weight traits and staple length were positive and small. Breeding values from both single- and seven-trait analyses calculated using the parameters estimated from the single- and two-trait analyses were compared across years of birth with respect to genetic trends. Estimated breeding values averaged by year of birth from both the single- and seven-trait analyses for the prolificacy and weight traits increased over time, while those for fleece weight decreased and those for the other wool traits were unchanged. Estimated changes in breeding values over time did not differ substantially for the single- and seven-trait analyses, except for traits highly correlated with another trait that was responding to selection (i.e., litter size at birth, which was highly correlated to both litter size at weaning and weaning weight).

Genetic correlation of ram sexual performance with ewe reproductive traits of four sheep breeds

Rams express differences in sexual performance during the breeding season. Breeding rams with high sexual performance scores as measured during a sexual performance test can improve flock fertility. Whether selecting rams for high sexual performance score will indirectly improve ewe reproductive performance is not known. The objective of this study was to estimate the genetic correlation between sexual performance scores of rams and reproduction of ewes. Sexual performance scores of rams and reproductive performance (number of lambs born per ewe exposed and number of lambs weaned per ewe exposed) from four breeds were analyzed with univariate and bivariate animal models using REML. A total of 4685 records for sexual performance scores of rams were obtained from the US Sheep Experiment Station (Columbia, n = 807; Polypay, n = 1668; Rambouillet, n = 1208; and Targhee, n = 1002). Reproductive performance of ewes was based on 35,154 records (Columbia, n = 7693; Polypay, n = 9229; Rambouillet, n = 10,954; and Targhee, n = 7278). Estimates of heritability for sexual performance score of rams were larger for the Columbia (0.31±0.09) and Polypay (0.30±0.08) than that for Rambouillet (0.14±0.07) and Targhee breeds (0.17±0.08). Overall breed heritability estimate was 0.22±0.04. Heritability estimates for number of lambs born were larger (0.05–0.11) than for number of lambs weaned (0.02–0.05). Estimates of genetic correlation between sexual performance score and number of lambs born were near zero (−0.09 to 0.02) except for the Columbia breed (0.24±0.20). Estimates of genetic correlation between sexual performance score of the ram and number of lambs weaned varied by breed (Columbia, 0.28±0.26; Polypay, 0.00±0.25; Rambouillet, −0.17±0.25; and Targhee, 0.32±0.28). Overall breed genetic correlations of sexual performance of rams with number of lambs born and weaned were 0.00±0.10 and 0.00±0.12, respectively. Because of the low heritability of ewe reproductive traits and their apparently nil to low genetic correlation with sexual performance scores of rams, selection and use of rams with high sexual performance scores would not be expected to result in much indirect response for improved reproduction of ewes.

Seven new ovine progressive pneumonia virus (OPPV) field isolates from Dubois Idaho sheep comprise part of OPPV clade II based on surface envelope glycoprotein (SU) sequences

Seven new ovine progressive pneumonia virus (OPPV) field isolates were derived from colostrum and milk of 10 naturally OPPV-infected sheep from the US Sheep Experiment Station in Dubois, Idaho, USA. Sixteen sequences of the surface envelope glycoprotein (SU) from these seven Dubois OPPV field isolates and SU sequence from OPPV WLC1 were obtained, aligned with published SRLV SU sequences, and analyzed using phylogenetic analysis using parsimony (PAUP). Percent nucleotide identity in SU was greater than 95.8% among clones from individual Dubois OPPVs and ranged from 85.5 to 93.8% between different Dubois OPPV clones. SU sequences from Dubois OPPVs and WLC1 OPPV had significantly higher percent nucleotide identity to SU sequences from the North American OPPVs (85/34 and S93) than caprine-arthritis encephalitis virus (CAEVs) or MVVs. PAUP analysis also showed that SU sequences from the Dubois OPPVs and OPPV WLC1 grouped with other North American OPPVs (85/34 and S93) with a bootstrap value of 100 and formed one OPPV clade II group. In addition, Dubois and WLC1 SU amino acid sequences had significantly higher identity to SU sequences from North American OPPVs than CAEV or MVV. These data indicate that the seven new Dubois OPPV field isolates along with WLC1 OPPV are part of the OPPV clade II and are distinct from CAEVs and MVVs.

Measuring plant diversity in the tall threetip sagebrush steppe: influence of previous grazing management practices.

In July 2000, a 490-ha wildfire burned a portion of a long-term grazing study that had been established in 1924 at the US Sheep Experiment Station north of Dubois, Idaho, USA. Earlier vegetation measurements in this tall threetip sagebrush (Artemisia tripartita spp. tripartita) bunchgrass plant community documented significant changes in vegetation due to grazing and the timing of grazing by sheep. A study was initiated in May 2001 using 12 multiscale modified Whittaker plots to determine the consequences of previous grazing practices on postfire vegetation composition. Because there was only one wildfire and it did not burn all of the original plots, the treatments are not replicated in time or space. We reduce the potential effects of psuedoreplication by confining our discussion to the sample area only. There were a total of 84 species in the sampled areas with 69 in the spring-grazed area and 70 each in the fall- and ungrazed areas. Vegetation within plots was equally rich and even with similar numbers of abundant species. The spring-grazed plots, however, had half as much plant cover as the fall- and ungrazed plots and the spring-grazed plots had the largest proportion of plant cover composed of introduced (27%) and annual (34%) plants. The fall-grazed plots had the highest proportion of native perennial grasses (43%) and the lowest proportion of native annual forbs (1%). The ungrazed plots had the lowest proportion of introduced plants (4%) and the highest proportion of native perennial forbs (66%). The vegetation of spring-grazed plots is in a degraded condition for the environment and further degradation may continue, with or without continued grazing or some other disturbance. If ecosystem condition was based solely on plant diversity and only a count of species numbers was used to determine plant diversity, this research would have falsely concluded that grazing and timing of grazing did not impact the condition of the ecosystem.

Models with nuclear, cytoplasmic, and environmental effects for production traits of Columbia sheep.

Statistical models (16) were compared for birth weight of 24,741 Columbia lambs recorded at the U.S. Sheep Experiment Station (USSES; 1950 to 1998). The goal was to estimate fractions of variance due to cytoplasmic line (c2; n = 590) and sire x cytoplasmic line interaction (sc2; n = 12,831) with other nuclear and environmental effects included in the model. The basic model included direct genetic (fractional variance, a2; n = 26,623), maternal genetic (m2, with direct-maternal correlation ram), and maternal permanent environmental (p2m; n = 6,385) effects. The model with sc2 was significantly (P < 0.05) better than the basic model with c2, but with other random effects added, sc2 became zero. Significant (P < 0.05) variance components were associated with random dam x year (dy2) and dam x number born (dn2) interaction effects. Estimates with all effects in the model were: a2, 0.26; m2, 0.24; ram, -0.05; p2m, 0.02; c2, 0.00; dn2, 0.04; dy2, 0.08; sd2, 0.04; sc2, 0.00. Estimates for a2, m2, and ram were the same for all models. Estimate of p2 changed when other effects were added to the model. The largest estimates for nongenetic effects were: p2m, 0.06; c2, 0.00; dy2, 0.14; sd2, 0.13; and sc2, 0.04. Parameter estimates were similar regardless of whether fixed genetic groups (n = 84) were in the model. For weaning weight (120 d, n = 23,903), estimates of variances of effects added to the basic model were all near zero (a2, 0.14; m2, 0.09; ram, 0.23; p2m, 0.04). For fleece weight (FW, n = 29,024) and number born (NB, n = 29,688), animal permanent environmental effects were added to the model (p2a; n = 7,741 and 7,840) and ram was dropped. For these traits, effects not in the basic model had small variances. For FW, estimates with the full model were: a2, 0.52; m2, 0.01; p2m, 0.00; p2a, 0.06; c2, 0.00; dy2, 0.00; sd2, 0.02; and sc2, 0.06, and for NB they were: a2, 0.08; m2, 0.00; p2m, 0.00; p2a, 0.02; c2, 0.00; dy2, 0.00; sd2, 0.00; and sc2, 0.01. Cytoplasmic effects were not important. Unusual random effects in the model did not change estimates for basic parameters. Although some effects were significant, especially for BW, effects on genetic evaluations are likely to be small.

Estimates of genetic parameters and genetic change for reproduction, weight, and wool characteristics of Targhee sheep.

Genetic parameters from both single-trait and bivariate analyses for prolificacy, weight, and wool traits were estimated using REML with animal models for Targhee sheep from data collected from 1950 to 1998 at the U.S. Sheep Experiment Station, Dubois, ID. Breeding values from both single-trait and seven-trait analyses calculated with the parameters estimated from the single-trait and bivariate analyses were compared across years of birth with respect to genetic trends. The numbers of observations were 38,625 for litter size at birth and litter size at weaning, 33,994 for birth weight, 32,715 for weaning weight, 36,807 for fleece weight and fleece grade, and 3,341 for staple length. Direct heritability estimates from single-trait analyses were 0.10 for litter size at birth, 0.07 for litter size at weaning, 0.25 for birth weight, 0.22 for weaning weight, 0.54 for fleece weight, 0.41 for fleece grade, and 0.65 for staple length. Estimate of direct genetic correlation between litter size at birth and weaning was 0.77 and between birth and weaning weights was 0.52. The estimate of genetic correlation between fleece weight and staple length was positive (0.54), but was negative between fleece weight and fleece grade (-0.47) and between staple length and fleece grade (-0.69). Estimates of genetic correlations were near zero between birth weight and litter size traits and small and positive between weaning weight and litter size traits. Fleece weight was slightly and negatively correlated with both litter size traits. Fleece grade was slightly and positively correlated with both litter size traits. Estimates of correlations between staple length and litter size at birth (-0.14) and litter size at weaning (0.05) were small. Estimates of correlations between weight traits and fleece weight were positive and low to moderate. Estimates of correlations between weight traits and fleece grade were negative and small, whereas estimates between weight traits and staple length were positive and small. Estimated breeding values averaged by year of birth from both the single- and seven-trait analyses for the prolificacy and weight traits increased over time, whereas those for fleece weight decreased slightly and those for the other wool traits were unchanged. Estimated changes in breeding values over time did not differ substantially for the single-trait and seven-trait analyses, except for traits highly correlated with another trait that was responding to selection.

Estimates of genetic parameters and genetic change for reproduction, weight, and wool characteristics of Columbia sheep.

Genetic parameters from both single-trait and bivariate analyses for prolificacy, weight and wool traits were estimated using REML with animal models for Columbia sheep from data collected from 1950 to 1998 at the U.S. Sheep Experiment Station (USSES), Dubois, ID. Breeding values from both single-trait and seven-trait analyses calculated using the parameters estimated from the single-trait and bivariate analyses were compared with respect to genetic trends. Number of observations were 31,401 for litter size at birth and litter size at weaning, 24,741 for birth weight, 23,903 for weaning weight, 29,572 for fleece weight and fleece grade, and 2,449 for staple length. Direct heritability estimates from single-trait analyses were 0.09 for litter size at birth, 0.06 for litter size at weaning, 0.27 for birth weight, 0.16 for weaning weight, 0.53 for fleece weight, 0.41 for fleece grade, and 0.55 for staple length. Estimate of direct genetic correlation between littersize at birth and weaning was 0.84 and between birth and weaning weights was 0.56. Estimate of genetic correlation between fleece weight and staple length was positive (0.55) but negative between fleece weight and fleece grade (-0.47) and between staple length and fleece grade (-0.70). Estimates of genetic correlations were positive but small between birth weight and litter size traits and moderate and positive between weaning weight and litter size traits. Fleece weight was lowly and negatively correlated with both litter size traits. Fleece grade was lowly and positively correlated with both litter size traits, while staple length was lowly and negatively correlated with the litter size traits. Estimates of correlations between weight traits and fleece weight were positive and low to moderate. Estimates of correlations between weight traits and fleece grade were negative and small. Estimates of correlations between staple length and birth weight (0.05) and weaning weight were small (-0.04). Estimated breeding values averaged by year of birth from both the single-trait and multiple-trait analyses for the prolificacy and weight traits increased over time, but were unchanged for the wool traits. Estimated changes in breeding values over time did not differ substantially for single-trait and multiple-trait analyses, except for traits highly correlated with another trait that was responding to selection.