Genetic and phenotypic relationships between milk protein percentage, reproductive performance and body condition score in New Zealand dairy cattle

摘要

Recent research from the Australian In-Calf and New Zealand Monitoring Fertility projects have demonstrated that low milk protein percentage in early lactation is phenotypically linked to poor reproductive performance. The purpose of this study was toquantify the phenotypic and genetic relationship between body condition score (BCS), protein percentage (and other milk production traits) and the reproductive measures used to predict the female fertility breeding value in New Zealand's Animal Evaluation System: probability of mating in the first 21 days of a herd's mating period (PM21) and the probability of having a calf born to AI (CAI). Data on 99,870 first lactation cows, recorded as part of Livestock Improvement's and Ambreed's progeny test schemes were used for both a phenotypic analysis and to estimate genetic parameters. Effects of breed, heterosis, BCS, protein percentage and dairy conformation were statistically significant in logistic regression analyses on both CAI and PM21. Genetic correlations between protein percentage and PM21 and CAI were 0.18 and 0.20 respectively and genetic correlations of BCS and PM21 and CAI were 0.48 and 0.38 respectively. These results show that selection for protein percentage is unlikely to have a large effect on reproductive performance, while BCS is a promising tool to aid in selection for improved fertility.