Published online by Cambridge University Press: 27 March 2009
The birth weight of Friesian and Holstein calves in Western Nigeria was generally lower than that recorded in other tropical countries. This was attributed to a low plane of nutrition during pregnancy and a consequent reduction in length of gestation of the dams. On average, pure-bred Friesian, pure-bred Holstein and Holstein x Friesian calves weighed 29·1, 30·8 and 30·7 kg respectively at birth. Male and female Friesian, Holstein and cross-bred calves averagely weighed 29·9 and 28·2 kg, 29·9 and 31·7 kg, and 32·6 and 28·8 kg respectively. Both the sex differences and breed x sex interaction were not significant.
Positive correlation coefficients of 0·45, 0·38 and 0·26 found between calf birth weight and gestation length for the Friesians (P < 0·05), Holsteins (P < 0·01) and their crosses (P > 0·05) respectively suggest that gestation length had a significant effect on Friesian and Holstein calf birth weight. In many cases, parturition occurred 8–16 days earlier than expected.
Calves born during the rainy season (April–September) were approximately 10% heavier at birth than those born during the dry season (October–March). The heaviest calves were born during the second half (July–September) of the rainy season. The breed x sex x season of calving interaction was significant for the Holstein breed (P < 0·05). Holstein male calves born during the rainy season were significantly (P <; 0·05) heavier than those born during the dry season. Friesian dams with three or more parities and Holstein dams that were 3 years old and above produced calves that were significantly (P < 0·01) heavier at birth than calves of younger dams.