Genetics of reproductive performance in seasonal calving dairy cattle production systems

Abstract

Profitable seasonal calving dairy production systems require a cow that will establish pregnancy early in the breeding season implying a quick return to service post-calving and good pregnancy rates. Genetic selection provides an opportunity to achieve this goal so therefore the objective of this study was to estimate the necessary genetic parameters for fertility traits, pertinent to seasonal calving herds, in order to facilitate genetic selection for fertility. The data, following editing, consisted of parity 1 to 3 records on up to 397,373 Holstein-Friesian dairy cows in Ireland. Variance components for the defined interval fertility traits (age at first calving, calving to first service interval, calving interval), binary fertility traits (submission rate in the first 21 days of the breeding season, pregnant to first service, pregnant in the first 42 days of the breeding season, calved in the first 42 days of the calving season) and the count fertility trait (number of services) were estimated using univariate animal models and covariances among traits were estimated using bivariate sire models. Heritability estimates of the nine fertility traits (including age at first calving and survival) varied from 0.01 to 0.07 within parity one to three. The coefficient of genetic variation for the fertility traits varied from 3.3% to 15.3%. Calving to first service interval, within parity, was moderately positively genetically correlated (0.54 to 0.75) with calving interval and was, in general, moderately negatively correlated with both submission rate (-0.68 to -0.29) and pregnant in the first 42 days of the breeding season (-0.36 to -0.14). Calving interval was moderately positively correlated (0.24 to 0.68) with number of services. Irrespective of parity, the genetic correlations between calving interval with calving in the first 42 days of the calving season, and submission rate with pregnant in the first 42 days of the breeding season were all negative. The genetic correlations among calving in the first 42 days of the calving season, submission rate and pregnant in the first 42 days of the breeding season were all positive. All fertility traits were generally antagonistically genetically correlated with lactation milk yield, but most were moderate to strongly favourably correlated with survival to the next lactation. This study provides the necessary genetic parameters to undertake national genetic evaluations for fertility to help achieve the fertility targets in seasonal calving herds.