Genome-wide association study for stayability measures in Nellore–Angus crossbred cows1

Abstract

Beef cow stayability is a complex, economically important trait often used as an indicator of a cow's potential lifetime productivity. Stayability is defined as capability of a cow to maintain a perfect record up to 6 yr of age. This age is commonly cited as a financial break-even point, where initial costs of cow development and maintenance are recovered by her cumulative net income from yearly calf receipts. Later-maturing Bos indicus-Bos taurus crossbred cows may experience reproductive difficulty early in life but have a high potential for a long reproductive life span. It was the objective of this study to identify genetic variants associated with measures of beef cow stayability. A population of B. indicus-B. taurus crossbred cows (n = 305) from central Texas was used. Phenotypes for various measures of stayability to 6 yr of age were produced by artificially imposing five different culling criteria on data from the population. Cows were scored either as a 1 (indicating a perfect record through 6 yr) or a 0 (indicating failure at or before 6 yr), under each criterion. Genome-wide association studies (GWAS) were conducted for each criterion using univariate procedures and prefitting the fixed effect of cow contemporary group. SNP associations for two criteria surpassed the false discovery threshold of 0.15, when a cow was scored as 0 upon her first failure to wean a calf, regardless of reason, through 6 yr (criterion 2), and when a cow was scored as 0 upon her first failure to give birth to a calf, through 6 yr (criterion 3). Associated SNP were found on bovine chromosomes (BTA) 1, 2, 5, 9, 18, and 21 for criterion 2 and on BTA 1, 5, 11, 15, and 24 for criterion 3. A critical region on BTA 5: 43-50 Mb was identified for each criterion. Due to the similarities to prior work, the tendency for B. indicus cattle to experience reproductive difficulties early in life, and due to the large proportion of cows that left the herd at an early age under these criteria, these results suggest that the associations are likely driven by an early life trait such as age at puberty or rate of heifer development.

Cattle adapted to tropical and subtropical environments: genetic and reproductive considerations

“…In general, maternal performance as indicated by calf quality was not considered when cows were annually evaluated for removal in those investigations. Engle et al (2018) reported a genomic region on BTA 5 associated with the probability of avoiding Nelore-Angus crossbred cows remaining in the herd until 6 yr of age, also known as stayability. Components of longevity include reproduction success, udder health and structure (Tolleson et al, 2017), and incisor conditions as aged cows (Riley et al, 2001).…”

Reproductive efficiency Nellore and crossbred cows submitted to administration of melengestrol acetate (MGA) after FTAI protocols

“…Thus, when using Bos indicus x Bos taurus crossbred cows, we observed higher conception and pregnancy rates compared to Nellore cows. This is probably due to the combined advantages of heterosis and adaptation to the tropical climate of crossbred animals, as reported by studies by (Engle, et al, 2018).…”

“…When comparing the Nellore and crossbred animals, we found that the Nellore females had a lower conception rate compared to the other groups (P < 0.05), and the crossbred animals, both without and submitted to the administration of MGA Premix®, showed higher rates of pregnancy (P < 0.05; Table 1). (Engle, et al, 2018). Therefore, understanding the differences between zebu and crossbred females is important for the establishment of correct procedures, regarding the management and evaluation of reproductive parameters, for later adoption of adequate reproductive biotechnologies (Pereira, et al, 2015).…”

Genome-wide association study for stayability at different calvings in Nellore beef cattle

“…Selection for STAY is difficult because it usually presents low heritability, ranging between 0.08 and 0.14 [ 6 , 7 ], in addition to be a sex-limited trait measured late in female’s life, normally at 76 months of age. All these factors decrease the expected genetic gain when this trait is included as selection criterion.…”