ESTIMATION BREEDING VALUE FOR HEAT TOLERANCE (HT EBV) IN BUNAJI DAIRY CATTLE

Abstract

The study was conducted at the Abubakar Tafawa Balewa University Dairy Research and Development Center Gubi campus to estimate the breeding value for heat tolerance (HT EBV) in Bunaji dairy cattle. A total of twenty four (24) Bunaji dairy cattle were used for the study out of which fifteen (15) were lactating during the period of the study. The heat stress parameters used in the experiment were; rectal temperatures [Morning Rectal Temperature (MRT), Evening Rectal Temperature (ERT) and Increased Rectal Temperature (IRT)] and Subsequent Day Milk Yield (SDMY). The result from the study revealed a significant (P < 0.05) variation within the Bunaji breed in all the parameters studied, except the IRT. The cows with tag numbers B162 and B429 recorded the lowest value of mean MRT of 37.4 ℃ each while B430 recorded the highest of 38.6 ℃. The B158 recorded the lowest value of mean ERT of 38.3℃ while B177 recorded the highest of 39.3℃. The B162 recorded the highest value of mean SDMY of 4.0 l/day with mean IRT of 0.1 ℃, mean regression coefficient of -0.11 l/℃, a significant negative correlation (P < 0.05) of -0.71, an intercept of 4.1 l/day, mean % decline in SDMY per unit increase in IRT of 2.7 %/℃ and an estimated breeding value for heat tolerance (HT EBV) of +61.6% /℃. The B193 recorded the lowest value of mean SDMY of 0.7 l/day with mean IRT of 1.2 ℃, mean regression coefficient of -0.54 l/℃, a significant negative correlation (P < 0.05) of -0.93, an intercept of 1.2 l/day, mean % decline in SDMY per unit increase in IRT of 45 %/℃ and HT EBV of -25.0%/℃. The findings from this study showed that, there were significant variations (P < 0.05) in HT EBV within the Bunaji dairy cows used, thus selective breeding is recommended in order to improve the population mean of HT EBV of the Bunaji breed in the farm.