Measures of before and after breeding daily gains of dairy replacement heifers and their relationship with first lactation milk production traits

Abstract

A field study was conducted to study the relationships between average daily gain (ADG) of heifers and their first lactation milk yield. To predict the body weight (BW) the heart girth of 4058 heifers was measured by AI-technicians. Based on these measurements and national milk recording data, the ADGs before and after breeding were calculated. Other variables collected were after calving BW, calving age, and milk production yields on first lactation. After edits the final data included 2194 Ayrshire (Ay) and 738 Friesian (Fr) heifers and their 7215 relatives. Data used for calving BW and ADGs after breeding was 43% smaller because of missing information. The average BW and age at breeding were 356 kg and 483 days for Ay and 376 kg and 484 days for Fr, respectively. The after calving BW for Ay was 502 kg and for Fr 520 kg. The weights correspond to ADGs of 660 g (S.D. 99 g) and 695 g (S.D. 114 g) before breeding, and 497 g (S.D. 190 g) and 492 g (S.D. 196 g) after breeding for Ay and Fr breeds, respectively. The average 305-day milk yield for Ay was 6198 kg and for Fr 6440 kg. Positive genetic correlations between growth rate before (0.13±0.11) and after (0.34±0.17) breeding and milk yield as well as calving BW and milk yield (0.26±0.13) were found. The environmental correlation between ADG before breeding and milk yield was positive (0.13±0.04), while the ADG after breeding and milk yield was uncorrelated (−0.01±0.04). Based on the feeding trials a negative environmental correlation between ADG before breeding and milk yield could have been expected. It was concluded that the negative effect could not be estimated, because of the disturbance caused by herd effect. Also, the fact that most of the heifers had been reared within recommended limits of ADG could have affected the results.