Development of optimal genetic evaluations for teat and udder structure in Canadian Angus cattle

Abstract

Despite their heritability and influence on female productivity, there are currently no genetic evaluations for teat and udder structure in Canadian Angus cattle. The objective of this study was to develop optimal genetic evaluations for these traits in the Canadian Angus population. Guidelines recommended by Beef Improvement Federation (BIF) were used to score teat and udder structure in 1,735 Canadian Angus cows from 10 representative herds. Cows scored ranged in parity from 1 to 13; however, >70% of cows were parity ≤4. Scores ranged from 1 (large, bottle shaped) to 9 (very small) for teats and from 1 (very pendulous) to 9 (very tight) for udders. Consistent with parity distribution, >70% of teat and udder scores were ≥6. Teat and udder scores (TS9 and US9, respectively) were modeled using a multiple trait animal model with random effects of contemporary group (herd-year-season) and additive genetic effect, and fixed effects of breed, parity group, and days between calving and scoring. To test good versus poor structure, a binary classification of 1 or 2 (TS2, US2) [comprised of scores 1 to 5 = 1 (poor structure) and scores 6 to 9 = 2 (good structure)] was created. Further, to assess the impact of grouping less frequently observed poor scores, a 1 to 7 scale (TS7, US7) was created by combining teat and udder scores 1 to 3. Analyses for teat and udder scores on scales TS9, US9, TS7, US7, and TS2, US2 were compared. In addition, both threshold and linear animal models were used to estimate variance components for the traits. Data treatment and models were evaluated based on correlation of resulting estimated breeding value (EBV) with corrected phenotypes, Spearman’s rank correlation coefficient, average EBV accuracies (r), and deviance information criteria (DIC). TS9, US9 scales for teat and udder scores and linear models performed best. Estimates of heritability (SE) for teat and udder score were 0.32 (0.06) and 0.15 (0.04), respectively, indicating these traits were moderately heritable and that genetic improvement for teat and udder scores was possible. Estimates of phenotypic and genotypic correlations for teat and udder score were 0.46 (0.02) and 0.71 (0.09), respectively. Estimates of genotypic correlations with birth weight (BW), weaning weight (WW), and yearling weight (YW), ranged from −0.04 (0.10) to −0.20 (0.12), verifying the importance of selecting for improved teat and udder score as individual traits, alongside performance traits.

Genome-wide association study for mammary structure in Canadian Angus cows

“…The collection of DNA samples for animal genotyping was done in accordance with the Canadian Code of Practice for the care and handling of farm animal [16]. Detailed methods and materials are described by Devani et al [7].…”

“…Detailed descriptions of teat and udder scoring in Canadian Angus cows, population structure, and animal management were provided previously by Devani et al [7]. In short, teat and udder scores were recorded by 3 trained individuals for 1,735 Canadian Angus cows from 10 herds across Alberta.…”

“…Detailed description for phenotype collection are described previously [7]. Observed teat and udder scores, on 1,735 Canadian Angus cows that ranged in parity from 1 to 13, varied from score 1 (large bottle shaped teats and pendulous udders) to score 9 (small symmetrical teats and well suspended udders).…”

“…Previous studies have demonstrated that individual differences in bovine mammary structure is genetically influenced with heritability value estimates ranging from low to moderate [7,8]. In addition, there is significant potential for identifying the genetic contributions and biological mechanisms that lead to individual variation observed in this complex system.…”

“…Since genetic evaluations and selection in beef cattle are evolving to include traits that impact efficiencies as well as animal health and welfare [15], the Canadian Angus Association (CAA) has recently developed a genetic evaluation for teat and udder score for Canadian Angus cattle. Covariance components and genetic parameters were estimated for teat size and udder suspension in Canadian Angus cows [7], however, the genes and molecular pathways associated with these traits remain unidentified. Therefore, the objective of this study was to perform a genome-wide association study aiming to identify genomic regions, potential candidate genes, and the biological mechanisms underlying teat and udder structure in Canadian Angus cattle.…”