Effect of heifer frame size on their subsequent reproductive performance and preweaning performance of their calves

The effects of heifer frame size on subsequent performance and the preweaning growth of calves were evaluated using records collected from the Waterburg Estates at Otjiwarongo, Namibia. Based on hip height at 18 months of age, heifers were assigned to three different frame size groups: small (< 124 cm), medium ( 124 to 135 cm), or large (> 135 cm). Calving rate ( CR), calving date ( CD), postnatal calf survival rate ( CSR), reproductive efficiency ( Sandex), weaning rate ( WR), birthweight ( BW), weaning weight ( WT) and preweaning average daily gain ( ADG) were collected from first ( n = 830), second ( n = 623) and third and greater parity ( n = 571) cows. Frame size of heifers significantly influenced ( P < 0.001) CR in second and third and greater parity. The postnatal CSR was similar for all frame size and parity groups. WR of large frame size, second-parity cows was less ( P < 0.001) than that of small and medium frame size animals. Birthweights of calves born to large frame size animals were significantly higher ( P < 0.05) than the small and medium frame size animals. Small frame size animals, as first parity cows, had calves with lower ( P < 0.05) WTthan those weaned by medium and larger frame size animals. In first parity cows, calves of large frame size had greater ADG ( P < 0.05), but in second parity cows the calves from medium frame size ( P < 0.05) out performed those of small and large frame size, while calves from third and greater parity cows of medium and larger frame size had greater ( P < 0.05) ADG than cows with a small frame size. Male calves were heavier ( P < 0.05) at birth, at weaning and grew faster ( ADG) than their female counterparts. Due to the later calving dates ( P < 0.05), the reproductive efficiency ( Sandex) of large frame size at second and third and greater parity groups was lower ( P < 0.001). Therefore, selecting cattle for the extensive hot and dry climatic regions of Southern Africa, the recommended cow frame size should be a medium frame.