Abstract
Pre-wean performance of lambs from Barbados Black belly (BB) and West African (WA) type ewes managed at pasture at the Blenheim Sheep Multiplication and Research Project was studied. Lamb pre-weaning performance was analysed for the period 1999 to 2004. Birth weight, weaning weight and pre-weaning growth rate of lambs were analysed according to the GLM procedure. The fixed effects in the model were year of birth, season of birth, season of conception, birth type, sex and breed. Significant differences (P<0.05) were observed between year, sex and birth type for the parameters birth weight, pre-weaning average daily gain and weaning weight. There were no significant differences (P>0.05) between WA and BB for birth weight (2.78 vs. 2.71 kg), weaning weight (12.26 vs. 11.69 kg) or pre-weaning growth rate (124 vs. 115 gd-1), respectively. Season of birth effect was significant (P<0.05) for birth weight and pre-wean average daily weight gain but not weaning weight (P>0.05). Temperature humidity index (THI) was significantly (P<0.05) higher in the wet compared to the dry season 79.60 (±0.13) vs 77.98 (±0.24), respectively. Litter size distribution by season indicated that there was only a 4.1% reduction in litter size in the dry season. Rectal temperature (RT), respiration rate (RR), and infrared thermography were used to assess the thermoregulation of ewes in the wet season. Rectal temperatures and respiration rate (br min-1) were taken at 8:00AM before they went out to pasture and at 3:00PM when they returned. Rectal temperature and RR data were subjected to repeated measure analysis. Both types showed no significant difference (P>0.05) with regards to their thermoregulatory processes, with the exception of RT which was higher (P<0.001) for WA in the afternoon. Rectal temperature for BB and WA was 38.34 and 38.41oC in the morning whereas it was 39.14 and 39.45oC in the afternoon, respectively. Barbados Black belly showed a 2.8 fold increase in RR when they returned from pasture compared to 3.0 fold increase for WA ewes. Heat was lost in the facial area and underbelly and between the legs in the morning and when they returned from pasture in the afternoon heat lost was observed throughout the entire body surface including facial areas. It was concluded that although these breed types are well adapted to this tropical climatic region, better pasture management needed to be implemented to improve thermoregulation of these ewes at pasture as the environmental impact of climate on pre-wean performance of lambs produced from these ewes remains a limiting factor.
