The aim of this study was to determine the effect of age at first calving on the milking
performance of primiparous Jersey cows (261 cows). Analyses were conducted on 2461 test day
milking samples from 17.09.2007 to 26.07.2016. The primiparous cows were divided into four
groups according to their age at first calving (≤ 24, > 24–26, > 26–28, > 28 months), and their
daily milk yields were compared. Fourfold contingency tables were prepared to investigate the
distribution of the population of cows calving at different ages and the peak daily milk yield.
The significance of the association between factors was estimated using Fisher's exact test. To
illustrate the course of 305-day lactation in primiparous cows varying in age at first calving,
linear graphs were plotted with linear trends for daily milk yields. Primiparous Jersey cows
calving at the age of > 26–28 months of life had the highest daily milk yield. In terms of the
contents of basic milk constituents in the first lactation, the most advantageous age at first
calving was > 24–26 months of life. However, a younger age at first calving (≤ 24 months) was
associated with a lower somatic cell count in milk as well as a more favourable lactation curve
for daily milk yield. The results of the study may suggest that Jersey cows calving at an earlier
age (up to 24 months) may have a longer productive life and thus better performance
parameters.
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