Genome-wide association study of age at puberty and its (co)variances with fertility and stature in growing and lactating Holstein-Friesian dairy cattle.

The authors measured AGEPprog, height, length, and BW in approximately 5 000 Holstein-Friesian or Holstein-Friesian × Jersey crossbred yearling heifers across 54 pasture-based herds managed in seasonal calving production systems. They also obtained calving rate (success or failure to calve within the first 42 days of the seasonal calving period), breeding rate (success or failure to be presented for breeding within the first 21 days of the seasonal breeding period) and pregnancy rate (success or failure to become pregnant within the first 42 days of the seasonal breeding period) of phenotypes from their first and second lactations. The cows were genotyped using the Weatherby’s Versa 50K SNP array (Illumina, San Diego, CA).

The estimated heritabilities of AGEPprog, height, length, and BW were 0.34, 0.28, 0.21 and 0.33 respectively. In contrast, the heritabilities of calving rate, breeding rate and pregnancy rate were all <0.05 in both first and second lactations. The genetic correlations between AGEPprog and these fertility traits were generally moderate, ranging from 0.11 to 0.60, whereas genetic correlations between AGEPprog and yearling body-conformation traits ranged from 0.02 to 0.28. The genome-wide association study (GWAS) highlighted a genomic window on chromosome 5 that was strongly associated with variation in AGEPprog. Four regions were also identified, located on chromosomes 14, 6, 1, and 11 (in order of decreasing importance), that exhibited suggestive associations with AGEPprog.

Conclusions: Moderate genetic correlations between AGEPprog and breeding, calving, and pregnancy rate traits indicate that selection for earlier AGEPprog will improve genetic merit for fertility during lactation. It is suggested that AGEPprog could add value as an early predictor of fertility estimated breeding values (EBVs). Genomic EBVs for AGEPprog exhibited a correlation of 0.41 with independent validation phenotypes adjusted for fixed effects. There was one genomic region in the GWAS analysis, located on chromosome 5, that is likely to harbour a quantitative trait locus (QTL) for the AGEPprog trait. Window genome-based EBVs produced for this region on chromosome 5 explained about 11% of the variance in the validation phenotypes.

These results contribute to a growing understanding of the genetic make-up of AGEPprog, and may also offer insight into correlated traits, such as fertility during lactation. Further investigation into the association between the identified genomic regions and variance in key fertility traits such as calving, breeding, and pregnancy performance is warranted.