Phenotypic, genetic and environmental trends in Kenya Sahiwal cattle

Abstract

Records covering a 20 year period (1964-1983) on Sahiwal cows at the National Sahiwal Stud, Naivasha were used to estimate phenotypic, genetic and environmental trends of 305- day milk yield, calving interval, birth weight and age at 55 kg liveweight (AGE55) by best linear unbiased prediction (BLUP) procedures while genetic parameters were estimated by the maximum likelihood procedure. All the traits studied were regarded as the traits of the dam. The number of records analysed were 4837, 4272, 4837 and 3544 for milk yield, calving interval, birth weight and age at 55 kg liveweight, respectively. The means of 30S-day milk yield, calving interval, birth weight and AGE55 were 1662~8.3 kg, 426.2+1.5 d, 22.7+0.04 kg and 97.8±..0.7 d , respectively. Year of calving or birth affected al I the four traits studied. Season of birth affected AGE55 only. Parity affected all the traits except calving interval while sex of calf affected birth weight, calving interval and AGE55. The respective repeatability and heritability estimates were 0.46±..0.02 and 0.27+0.06 for milk yield; 0.39+0.20 and 0.15~0.lO for calving interval; 0.48+0.05 and 0.40~0.07 for birth weight; and O.46±..0.03 and 0.35+0.05 for AGE55. The respective environmental changes -15.42+5.0 kg for annual phenotypic, genetic and we re: -11 .56~5. 3, 3. 57±..0.64 CI. nd 305-day m i Ik yiel d; 2. 43±..0.63, -0.23+0.03 Clnd 2.65+0.64 d for calving interval; xii i -0.02.::0.02, 0.004~0.003 and -0.03~0.02 kg for birth weight; and 5.26.::0.25, -0.05~0.04 and 5.31~0.26 d for AGE55. All the environmental trends were highly significant (p<O.Ol).AI I phenotypic trends were highly significant (p<O.Ol) except for birth weight. Genetic trends were highly significant Cp<O.Ol) except for birth weight and AGE55. In al I the four traits the correlations between environmental and phenotypic trends were highly significant (p<O.Ol). Although the annual genetic changes were in the direction of the breeding objectives, the annual genetic change in milk yield was lower than expected.