Dairy performance of Holstein-Friesian cattle and their crosses under semi-arid environment of Eastern Kenya
A total of 1,338 records made by Kenya Holstein-Friesian (K-llF) and crossbred (CB) cattle during 1972 to 2000 were used to evaluate 305-day adjusted lactation milk yield, milk yield per day of calving interval, calving interval, age at first calving and the lactation curves. Effects of genetic group, parity, season, years and their interactions, on the dairy traits were evaluated by the least-squares ami maximum likelihood method. The gamma function, Y, = a nbe (·c 11), was used to study the lactation curve parameters: starting yield, rate of increase to peak yield, time taken to attain peak yield, rate or decline Irom peak yield ami persistency. KHF cows performed better than CI3 cows in 305-day adjusted milk yield (P < 0.001), milk yield per day or calving interval (I' < U.UUI) and ill persistency (P < 0.01), but were not significantly different (P > 0.05) from the CB cows in starting yield, time taken to attain peak yield, age at first calving and in calving interval. The rates of increase and of decline were highest CorCB cattle (P < 0.05 and P < 0.001, respectively). The least square means for 3U5-day milk yield, milk yield per day of calving interval, rate or increase to peak yield, rate or decline from peak yield and persistency [or K-UF cattle were 1714.80 ± 40.13 liters, 3.Y3 ± 0.24 liters per day, 1.08 ± 0.07 liters per month, 0.35 ±,0.02 liters per month and 12.28 ± 0.62 liters per month, respectively, compared to 1107.15 ± 57.68 liters, 2.4() :I~ 0.28 liters per day, IAO -I- (J.Ot) liters pn month, (),.')() -I- o.(n liters per month aud 8.76 ± 0,89 liters per month, respectively for the CD cattle. Milk yields increased from first parity to peak at third and fourth parities and declined thereafter. Interaction between genetic group ami parity were not significant for 305-day yield and milk yield per day of calving interval. Milk yields were lowest during the dry seasons [allowed by the long rains season. The milk yields 01" CB cattle were not significantly different from those of the K-HF cattle during the long rains. There was no significant effect of pari9' on any of the parameters of the lactation curves. The rates or increase and decline Irom peak milk yields were highest during the dry season. For buth genetic groups of cattle, persistency was found to be luwest during dry seasun and highest in the short rain season. The age at first calving (AfC) was higher for animals that were bum in the earlier year classes but was nut significantly affected by other factors. Calving intervals (Cl ) tu subsequent calving were shorter fur cows at third and fourth parities but higher intervals in earlier and later parities. CI was neither affected by seasun nor by the interaction between season a IIII genctic gruup. It was concluded that under the J\SJ\L ecosystem studied, K-IIF cows call produce more milk than crosses 1II10er good pastures and supplementation CD cows were Elster in attainillg peak yield and also decline Irom peak, while K-IIF had better persistency.