Effect of Genetic and Environmental Factors on Linear Udder Conformation Traits and Milk Yield in Bunaji and Friesian X Bunaji Cows
The effects of evaluators, sex of calf, breed, sire, parity, month of calving and season of lactation on linear udder conformation traits and milk yield was investigated in the dairy herd of the National Animal Production Research Institute, Shika, Zaria, Nigeria. Seven linear udder conformation traits coupled with milk yield of 25 Bunaji and 25 crossbred (Friesian x Bunaji) cows were measured between 2007 and 2008. The measurements were taken monthly by three evaluators for the complete lactation length of the cows, resulting in 1275 cumulative records, (750 from Friesian x Bunaji and 525 from Bunaji). The seven udder conformation traits; rear udder height (RUH), rear udder width(RUW), Udder-hock distance (UD), udder cleft(UC), fore teat position(FTP), rear teat placements(RTP) and teat length(TL), were measured in centimeter using flexible tape. The result showed that all the genetic and environmental factors considered had significant effect (p<0.05) on the linear udder conformation traits and milk yield. RUH, RUW, TL and milk yield increased with parity, from the 1st to the 5th parity. UD decreased with parity. The males bearing cows had larger udder size with wider teats placement (FTP and RTP) and stronger ligament (UC) than their female counterparts did. In addition, the male bearing cows had significantly (p<0.05) higher milk yield than the female bearing cows. The crosses had larger udder with strong ligament (UC) and longer teats that were further apart in front (FTP) and closer in the rear (RTP) view than the pure Bunaji. The crosses produced higher milk yield than the pure Bunaji. Milk yield was higher in early wet season (April – June), while the late dry season (January – March) had the lowest milk yield. It is therefore suggested that in selecting for udder conformation and milk yield, these genetic and environmental factors should be considered.