Genetic parameter estimates for bull prolificacy and its relationship with scrotal circumference in a commercial beef cattle population

The commercial beef cattle industry relies heavily on the use of natural service sires. When artificial insemination is deemed difficult to implement, multi-sire breeding pastures are used to increase reproductive rates in large breeding herds or to safe-guard against bull injury during the breeding season. Although each bull might be given an equal opportunity to produce offspring, evidence suggest that there is substantial variation in the number of calves sired by each bull in a breeding pasture. With the use of DNA-based paternity testing, correctly assigning calves to their respective sires in multi-sire pastures is possible and presents an opportunity to investigate the degree to which this trait complex is under genetic control. Field data from a large commercial ranch was used to estimate genetic parameters for calf count (CC; 574 records from 443 sires) and yearling scrotal circumference (SC; n=1961) using univariate and bivariate animal models. Calf counts averaged 12.2±10.7 and SC averaged 35.4±2.30 cm. Bulls had an average of 1.30 records and there were 23.9±11.1 bulls per contemporary group. The model for CC included fixed effects of age during the breeding season (in years) and contemporary group (concatenation of breeding pasture and year). Random effects included additive genetic and permanent environmental effects, and a residual. The model for SC included fixed effects of age (in days) and contemporary group (concatenation of month and year of measurement). Random effects included an additive genetic effect and a residual. Univariate model heritability estimates for CC and SC were 0.178±0.142 and 0.455±0.072, respectively. Similarly, the bivariate model resulted in heritability estimates for CC and SC of 0.184±0.142 and 0.457±0.072, respectively. Repeatability estimates for CC from univariate and bivariate models were 0.315±0.080 and 0.317±0.080, respectively. The estimate of genetic correlation between CC and SC was 0.268±0.274. Heritability estimates suggest that both CC and SC would respond favorably to selection. Moreover, CC is lowly repeatable and although favorably correlated, SC appears to be weakly associated with CC.

PSIII-8 Genetic Parameter Estimates for Bull Prolificacy and Its Relationship with Scrotal Circumference in a Commercial Beef Cattle Population

The commercial beef cattle industry relies heavily on the use of natural service sires. Either due to the size of breeding herds or to safe-guard against injury during the breeding season, multiple-sire breeding pastures are utilized. Although each bull might be given an equal opportunity to produce offspring, evidence suggest that there is substantial variation in the number of calves sired by each bull in a breeding pasture. DNA-based paternity assignment enables correct assignment of calves to their respective sires in multi-sire pastures and presents an opportunity to investigate the degree to which this trait complex is under genetic control. Field data from a large commercial ranch were used to estimate genetic parameters for calf count (CC; n=623) and yearling scrotal circumference (SC; n=1962) using univariate and bivariate animal models. Average CC and SC were 12.1±11.1 calves and 35.4±2.30 cm, respectively. Average number breeding seasons per bull and bulls per contemporary group were 1.40 and 24.9, respectively. The model for CC included fixed effects of age during the breeding season (in years) and contemporary group (concatenation of breeding pasture and year). Random effects included additive genetic and permanent environmental effects, and a residual. The model for SC included fixed effects of age (in days) and contemporary group (concatenation of month and year of measurement). Random effects included an additive genetic effect and a residual. Univariate model heritability estimates for CC and SC were 0.237±0.156 and 0.456±0.072, respectively. Similarly, the bivariate model resulted in heritability estimates for CC and SC of 0.240±0.155 and 0.461±0.072, respectively. Repeatability estimates for CC from univariate and bivariate models were 0.517±0.054 and 0.518±0.053, respectively. The estimate of genetic correlation between CC and SC was 0.270±0.220. Parameter estimates suggest that both CC and SC would respond favorably to selection and that CC is moderately repeatable.

Estimates of Genetic Variation for Angus Gestation Length

The objective of this study was to estimate variance components for gestation length within the American Angus breed. Data (n = 148,649) from the American Angus Association, containing cattle born between 2000 to 2020, were used for the analysis. Based on a cow’s reproductive biology, gestation length records were determined acceptable if between 266 and 290 days (n = 114,857). Gestation length mean and standard deviation were 278.6 and 4.6 days, respectively. Average Information Restricted Maximum Likelihood (AIREML) was used to estimate variance components for the gestation length. A single trait animal model included random effects of direct and maternal additive genetic variance and fixed effects of dam age rounded to the nearest year, calf gender and contemporary group. Contemporary group was determined as herd, year of birth and season of birth combinations. Contemporary groups containing less than five animals were excluded from analysis. Phenotypic variance for gestation length was estimated at 18.9. Direct and maternal heritability estimates for gestation length were 0.59±0.01 and 0.10±0.01, respectively. Further analysis evaluated the fixed effects of year and dam age on gestation length. From 2000 to 2020, an increase in one year decreased (P < 0.01) gestation length by 0.09 days. Gestation length differed (P < 0.01) by age of dam. Gestation length LSMEANS for 2, 3, 4, 5, 6, 7 and 8 year old cows were 277.7, 278.6, 279.0, 279.2, 279.3, 279.5 and 279.6, respectively. Heritability estimates within Angus breed suggest gestation length has a high capacity for genetic change. Results suggest gestation length has decreased over the past two decades and is shorter in younger cows.

Partitioning variation in measurements of beef carcass traits using ultrasound1

Ultrasound technology provides cattle breeders with a quick, noninvasive, and inexpensive way to measure carcass data on live animals. Ultrasound data are used as indicator traits in cattle genetic evaluations for economically relevant carcass traits. Ultrasound cattle genetic evaluations assume homogeneous additive genetic and residual variance. Thus, the objective was to partition phenotypic variance in ultrasound carcass measurements into components for additive genetic effects, technicians, contemporary groups within technicians, and residual and to examine the homogeneity of these variances among image interpretation laboratories. Records of longissimus muscle area (LMA), percentage of intramuscular fat (IMF), and subcutaneous fat depth (SFD), measured using ultrasound, were provided by the American Angus Association (n = 65,967), American Hereford Association (n = 43,182), and American Simmental Association (n = 48,298). The data also included contemporary group, technician, imaging lab, and a three-generation pedigree for each animal. Variance components for ultrasound carcass measurements were first estimated with univariate animal models for each breed and imaging laboratory using derivative-free restricted maximum likelihood. Then, treating data from each imaging laboratory as separate traits, genetic correlations between laboratories for LMA, percentage of IMF, and subcutaneous fat were estimated with trivariate animal models. The technician explained 12–27%, 5–23%, and 4–26% of the variance for IMF, SFD, and LMA, respectively, across all three breeds. Variance due to technician was often greater than variance due to additive genetic effects but almost always less than that explained by the contemporary group. Within breeds, estimates of additive genetic variance for LMA, SFD, and IMF differed (range divided by mean) among laboratories by 4.5%, 21.5%, and 39.4 % (Angus); 31.6%, 15.0%, and 49.1% (Hereford); and 19.9%, 46.6%, and 55.3% (Simmental), respectively. Likewise, estimates of residual variance for LMA, SFD, and IMF differed among laboratories by 43.4%, 22.9%, and 43.3% (Angus); 24.9%, 15.2%, and 79.2% (Hereford); and 26.4%, 32.5%, and 46.2% (Simmental), respectively. Genetic correlations between labs across breeds ranged from 0.79 to 0.95 for IMF, 0.26 to 0.94 for SFD, and 0.78 to 0.98 for LMA. The impact of the observed heterogeneity of variance between labs on genetic evaluation requires further study.

Best linear model to explain variability in the growth in Blanco Orejinegro cattle and effect of the serological status for bovine viral diarrhea and bovine leukosis

The cattle breed Blanco Orejinegro (BON) is an important animal genetic resource in Colombia that needs to be studied to identify its productive benefits for Colombian livestock. The aim of this work was to establish the best linear model that explains the variability for birth weight, weaning weight and yearling weight, and estimate the effect of the serological status for Bovine Viral Diarrhea (BVD) and Bovine Leukosis (BL) in BON cattle in Colombia. The information on animal weighings belonging to 14 BON cattle herds, was collected and cleansed. Using the least squares method, 12 linear models were evaluated including as fixed effects, factors such as herd, sex, weighing month, birth order, season (rainy or dry), birth year, and contemporary group (formed by the concatenation of the factors herd, sex, and birth year). The weighing age was included as a covariate for weaning and yearling weights. For the selection of a model that best describes each parameter, the criteria for choosing models, such as Akaike information criterion (AIC), Bayesian Information criterion (BIC), coefficient of determination (R2), and the sum of squares of the error (SSE), were considered. The model that included the contemporary group showed the best fit, being also the best to describe the three parameters evaluated, since, of the four criteria considered for its evaluation, AIC and SSE showed the lowest values and the highest R2. With this model, weight predictions with higher precision were able to be performed. Employing indirect ELISA screening tests of blood plasma, the serological status of each animal was estimated for BVD and BL viral infections. The serological status of these two viral infections was included in the best-fit model. There was no significant effect of the serological status on the parameters evaluated, so there are indications that animals that came in contact with the virus were not affected during growth.

206 Quantifying the effect of phenotypic factors on pedigree lamb performance using the Irish national database; Sheep Ireland

This study aimed to quantify the effect of phenotypic factors including birth type, rearing type, age at first lambing, lactation number and their interactions on pedigree lamb performance at 40days and 100days of age (weaning), where nutritional requirements were met at luxury levels. A dataset containing 644,330 lamb weight records from 2010–2017 were retrieved. Two datasets were created; 47,694 forty day weights (20–65 days of age and weighing 12-32kg) and 46,088 weaning weights (66–120 days of age and weighing 20-55kg). The PROC HPMIXED model (SAS 9.4) included gender, age, breed-class, contemporary group and interactions, i.e. birth type*rearing type, and lactation*age at first lambing, with dam as the random effect. At forty days and weaning respectively, lambs born and reared as singles weighed heaviest (20.95kg and 36.83kg) and lambs born and reared as triplets weighed lightest (16.83kg and 31.29kg). There was no difference between lambs born as twins and reared as twins and those born as triplets and reared as singles (18.11kg, 18.38kg and 33.00kg and 33.12kg). Lambs born as singles and reared as twins and those born as twins and reared as singles did not differ (19.01kg, 19.20kg and 34.30kg and 34.64kg), (Table 1, P < 0.01). In first and second lactation respectively, ewes that lambed for the first time as hoggets produced heavier lambs at forty days (18.12kg and 19.30kg) and at weaning (33.06kg and 34.58kg) than ewes who lambed as ewe lambs (16.88kg, 18.54kg and 31.40kg and 33.59kg). By third lactation, weights did not differ between progeny of ewes who first lambed as ewe lambs or hoggets (20.00kg, 19.41kg and 33.77kg and 34.64kg), (Figure 1 and 2, P < 0.05). In conclusion, rearing type significantly alters pedigree lamb performance at forty days and weaning regardless of birth type. By third lactation, production is similar regardless of age of first lambing.