Causes of variation in milk yield and lactation length of Jersey cattle in Western Nigeria

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Abstract
Summary: Studies on 59 first four completed lactations of 37 imported Jersey cattle in Western Nigeria showed that their mean lactation length (248·4 days) and average milk yield (1257·4 kg) were inferior to those of their counterparts in other tropical countries. Lactation length following the birth of female calves was longer and milk production greater than those subsequent to male births but the differences were small (P > 0·05). Peak milk production was reached at the third lactation. Influence of season of calving on lactation length was slight; mean milk yield was significantly highest (P < 0·05) among October-December calvers, while the July-December period appeared to be more propitious for milk production. The regression coefficients of lactation length and milk yield on age of dam at calving were negative and unimpressive (P > 0·05), being −2·108 ± 2·661 and −19·106 ± 17·130 respectively. Analysis of variance for weight of milk with lactation length as a covariate revealed that although lactation length was a major (P < 0·001) determinant of milk production, both the period of calving and lactation number had recognizable bearing on milk yield. All interaction effects were trivial (P > 0·05). The period of study was 1968–74.