Abstract
Production of beef-cross-dairy calves from dairy cows increases the value of non-replacement calves born to the dairy herd. The use of beef-breed sires may impact on calf birth weight, gestation length and pre-weaning growth rate of calves, which in turn influences the profitability of the dairy farm. The aim of this case study was to compare the birth weight, gestation length, and pre-weaning growth of progeny born to mixed-aged dairy cows on a single farm which were artificially bred to a selection of Angus and Hereford bulls, typical of those used over dairy herds in New Zealand. The birth weight, gestation length and pre-weaning growth of 980 calves sired by 65 sires were compared. Mean progeny birth weight (range 33.3–41.4 kg), gestation length (range 276.1–288.6 days), age at weaning (range 70.3–88.3 days) and pre-weaning ADG (range 0.63–0.76 kg/d) differed among sires (p < 0.001). There was a negative genetic correlation (−0.31) and positive phenotypic correlation (0.36) between gestation length and birth weight. Age at weaning was negatively correlated with birth weight (genetic: −0.56, phenotypic: −0.57). Bulls used in this study, and other bulls with similar genetic merit for birth weight and gestation length would be suitable for mating mixed-aged dairy cows in New Zealand.
Highlights
New Zealand dairy herds are usually spring-calving and have a mean replacement rate of 22% [1,2], which is usually achieved by breeding around 60% of the herd to high-geneticmerit, dairy-breed, bulls
The aim of this study was to quantify the effect of sire on birth weight, gestation length, and age at weaning achieved by progeny born to mixed-aged dairy cows bred to a selection of Angus and Hereford bulls on a single dairy farm
The lighter calves from Angus bulls than from the Hereford bulls used in this case study was consistent with previous literature that reported a 1.4–3.5 kg greater birth weight for Hereford than Angus calves [12,19,20,21,22]
Summary
New Zealand dairy herds are usually spring-calving and have a mean replacement rate of 22% [1,2], which is usually achieved by breeding around 60% of the herd to high-geneticmerit, dairy-breed, bulls. The primary interest of the dairy farmer when choosing a service sire to generate non-replacement calves, is the health and production of the dairy cow [2]. Key traits of importance for these service bulls include birth weight of the calf, as a determinant of calving difficulty, and gestation length, as a determinant of subsequent calving date. Artificial rearing systems in New Zealand usually involve weaning calves at a fixed live weight, and the period of milk feeding is the most expensive phase in the lifecycle of dairy-beef calves. Age at weaning is an important contributor to the cost of rearing dairy-origin calves for beef production, with fast-growing calves consuming less feed
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