Epsilon Open Archive

Abstract

Genotype by environment interaction (G×E) is one of the issues the dairy farming industry faces due to the globalization of using artificial insemination with genetically superior bulls to improve the performance of their herds. This includes distribution of genetic material to multiple environments within countries and between countries. The major concern is that animal rank may change across the environments which mean that the best animals in one environment are not the best in another environment. In this thesis, the genetic variation and G×E effect on fertility traits was investigated in Nordic cattle. Two types of fertility traits were studied, 1) automatically recorded fertility traits based on the physical activity measuring devices and, 2) traditional fertility traits based on the AI recording.

In Paper I, genetic parameters were estimated for interval for calving to first high activity (CFHA); duration of high activity as an indicator of estrus duration (DHA); and strength of high activity as an indicator of estrus strength (SHA), all based on activity measurements from cows in commercial herds. These parameters were compared with parameter estimates for interval from calving to first insemination (CFI). It was found that CFHA shows higher heritability than CFI. Moreover, the two traits were strongly genetically correlated. Consequently, the selection criteria for fertility may be improved by including “time from calving to first high activity”, because it reflects the ability of the cow to return to reproductive cycling and heat after calving.

In Paper II, Seasonality of estrus activity traits with respect to the month of calving was investigated. It was found that the summer calving season was associated with shorter CFHA than winter, spring, and fall seasons. Moreover, there was evidence for genotype by environment interaction for CFHA with calving season. However, DHA and SHA were less affected by seasonal variation. The results might be useful for the interpretation of seasonal variation in estrus expression traits and fertility traits in Holstein cows kept in the temperate climate zone.

In Paper III, the objectives were to estimate genetic parameters of fertility traits derived from activity tags (CFHA, DHA, and SHA), and estimate the genetic correlation between the CFHA and yield of energy corrected milk at 70 days in milk (ECM70). Parameters were estimated as a function of production level, expressed as herd average yield using reaction norm model in Danish Holstein cows. Heterogeneous genetic variation was found for all traits as a function of production environment, but the genetic correlation estimate of the trait between low and high production environment showed no evidence for G×E effect. The genetic correlation between CFHA and ECM70 decreased with increasing the production level implying that the unfavorable genetic correlation between fertility and milk yield could is reduced in improved production environments.

In Paper IV, the G×E interaction effects were studied on CFI in first parity Holstein cows in Denmark and Sweden, with environments defined as calving month and geographic location (in 8 North-South location classes). It was found that that cows calving in September had the shortest CFI. Cows in the northernmost location class had the longest CFI. Furthermore, there was a G×E effect between cold and warm calving months. However, CFI genotypes showed little interaction with geographic location. The obtained results are useful for improving genetic evaluations of Holstein cow fertility using data from a wide range of geographic locations and seasons.