Effect of different factors on lactation curve in buffalo cows

Abstract

Four hundred and nine first-lactation Bulgarian Murrah buffalo cows, having calved on the farm of Agricultural Institute - Shumen within the period 1964-2005, were assigned with the aim to study the effects of different factors on lactation curve. Using the software products LSMLMW and MIXMDL, eleven LS-analyses were carried out, the sources of variance included in the models being: the fixed effects of age at first calving, pregnancy-related status, lactation month, days in milk, calendar month of calving, and period of calving. The results indicate that lactation month exerts substantial specific effect on the variance of average test-day milk (F= 310.35; Р<0,001), defining the lactation curve as statistically significant. The effect of the factor days in milk determines steadiest lactation curve in the buffaloes with longest lactation period and, at the same time, relatively little differences in average test-day records. The effect of age at first calving is only expressed in significantly higher peak yield in the case of latest calving, test-day records being not affected. The environmental factors, calendar month of calving and period, have unsubstantial effect on lactation curve.