Abstract
Beef-breed bulls are used in dairy herds to produce a calf of greater value for finishing than calves sired by dairy bulls. There is limited research about which beef-breed bulls are most appropriate, and whether any negative impact on cow performance in terms of milk production and rebreeding should be considered. The aim of this case study was to compare the body condition score, milk production, and rebreeding performance of mixed-aged dairy cows bred to a selection of Angus and Hereford beef-breed bulls. Body condition score, post-calving live weight, milk production, rebreeding performance, and survival of 952 mixed-aged dairy cows artificially bred to 65 Angus and Hereford bulls were compared. There was no effect of service sire on post-calving live weight, days in milk, milk production, or inter-calving intervals of mixed-aged cows. Service sire had an effect on the calving day due to differences in gestation length (p < 0.001), although this did not translate into an effect on days in milk. A longer gestation length negatively influenced pregnancy rates, and greater birth weight of the calf negatively influenced survival to rebreeding (p < 0.05), indicating the potential for an effect of service sire. Selection of beef-breed service sires for dairy cows should include emphasis on lighter calves and shorter gestation lengths. The general absence of the service sire effect on the parameters measured in this study indicated that any of the service sires used in this experiment would be appropriate for use over dairy cows.
Highlights
New Zealand dairy herds are usually spring-calving and have a mean replacement rate of 22% [1,2], with replacements usually generated by breeding about 60% of the herd to high-genetic-merit, dairy-breed bulls
The service sire did not affect the Body condition score (BCS) of cows at calving, pregnancy detection or late lactation, or post-calving live weight (Table 1)
There were no differences in the post-calving, late-summer, or at end-of-lactation body condition scores, post-calving live weight, milk production, inter-calving interval, or
Summary
New Zealand dairy herds are usually spring-calving and have a mean replacement rate of 22% [1,2], with replacements usually generated by breeding about 60% of the herd to high-genetic-merit, dairy-breed bulls. The remaining cows in the herd are often bred to beef-breed bulls, to produce a calf of greater value for beef production than that of a calf sired by a dairy bull [3,4,5]. These cows would typically be the later-mated cows as it is desirable to generate replacements from cows calving in the first 6 weeks [6]. It is of interest to establish if there is any difference in the milk production or rebreeding success among cows mated to different
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