Production and reproductive performance of the Kenyan Ayrshire cattle

Abstract

Data consisting of 4475 lactation records of Kenya Ayrshire cattle made from 1980 to 2005 were used to study the genetic and environmental effects on production and reproductive traits. The data were analysed by the least square techniques of Proc GLM of SAS@program. The overall means were 3009.8 ± 1098 kg for 305-d milk yield (MY), 487.5 ± 151.6 days for calving interval (CI), 39.4 ± 7.2 mo for age at first calving (AFC) and 357.8 ± 171.4 days for lactation length (LL). Respective heritability estimates obtained were 0.12 ± 0.05 and 0.044 ± 0.032, 0.091 ± 0.05 and 0.12 ± 0.04, while repeatability estimates for 305-d MY, LL and CI were 0.35 ± 0.01, 0.38 ± 0.01 and 0.10 ± 0.001 respectively. The genetic trend in CI and AFC were -0.6 d/year and -0.01 mo/year respectively and significant (P<O.OOl). The respective phenotypic trends were -0.35 d/yr and -0.31 mo/yr and non-significant (P>0.05). Positive, and non-significant (P>0.05) phenotypic (11.7 kg/yr) and environmental (13.8 kg/yr) trends for 305-d MY were obtained. A negative and significant (P<0.05) genetic trend of -2.1 kg/yr over the study period for 305m-d MY was estimated, indicating a decline in milk yield. The phenotypic correlations between AFC and CI, MY and CI and MY and AFC were 0.088, -0.008 and 0.024 respectively. The genetic correlation between CI and AFC was 0.57 suggesting that these traits could be controlled by similar genes. A positive genetic correlation between AFC and MY in the first lactation obtained implied that cows with high potential for MY in first lactation were older at first calving. However, low and negative genetic correlation (-0.48) between AFC and MY in lifetime lactations obtained indicate that cows calving at early ages had on the overall high lifetime MY. The moderate negative genetic correlation between MY and CI (-0.48) indicate that high producing cows had shorter calving intervals.