Reaction norm model to describe environmental sensitivity across first lactation in dairy cattle under tropical conditions

Abstract

Reaction norm models have been widely used to study genotype by environment interaction (G × E) in animal breeding. The objective of this study was to describe environmental sensitivity across first lactation in Brazilian Holstein cows using a reaction norm approach. A total of 50,168 individual monthly test day (TD) milk yields (10 test days) from 7476 complete first lactations of Holstein cattle were analyzed. The statistical models for all traits (10 TDs and for 305-day milk yield) included the fixed effects of contemporary group, age of cow (linear and quadratic effects), and days in milk (linear effect), except for 305-day milk yield. A hierarchical reaction norm model (HRNM) based on the unknown covariate was used. The present study showed the presence of G × E in milk yield across first lactation of Holstein cows. The variation in the heritability estimates implies differences in the response to selection depending on the environment where the animals of this population are evaluated. In the average environment, the heritabilities for all traits were rather similar, in range from 0.02 to 0.63. The scaling effect of G × E predominated throughout most of lactation. Particularly during the first 2 months of lactation, G × E caused reranking of breeding values. It is therefore important to include the environmental sensitivity of animals according to the phase of lactation in the genetic evaluations of Holstein cattle in tropical environments.

Productive and reproductive performance of Holstein cows in Agreste, Pernambuco, from 2007 to 2017

“…In the southern region, for instance, Silva et al (2011), Ludovico et al (2015) and Bondan et al (2018) found an average production of 28.62, 31.78 and 25.50 kg/cow/day, respectively. In the southeast region, Bignardi et al (2015) and Villadiego et al (2016) recorded an average value of 24.25 and 22.9 kg/cow/day, respectively. In countries such as the United States and Canada, these values were considerably higher, as demonstrated by Stoop, Thompson-Crispi, Cartwright and Mallard (2016) and García-Muñoz, Singh, Leonardi and Silva-Del-Río (2017), where average daily productivity was 36.68 and 39.78 kg/day, respectively, demonstrating the difference in milk production in more specialized countries, where technologies and selection programs have been in use for some time.…”

Genome-wide association study for reproduction traits in a Brazilian Holstein population

“…However, Yokoo et al (2012) consider that the reduction of age at first calving (AFC) and the calving interval (CI) can significantly affect herd productivity due to its influence on calf production during the life of the dam and on the female's ability to re-conceive as soon as possible after the first delivery. In tropical regions, Holstein animals suffer from the adversities of the climate, so it is important to carefully monitor the reproductive indices regardless of the production system, as Bignardi et al (2015) concluded heritability increases as the environment becomes more favorable.…”