The effect of calving season and age at calving on production traits of South African dairy cattle

Abstract

Lactation records of South African Holstein and Jersey cows were classified into six calving seasons and 18 age x lactation classes using several trials involving analysis of variance and estimation of fixed effects of calving age on test-day as well as 305-day yields. Best Linear Unbiased Estimates for the effect of season and age x lactation were derived using an animal model following the prediction of daily milk, butterfat and protein yields on fixed days-in-milk and of cumulative 305-day yields by linear interpolation. For both breeds, test-day and cumulative 305-day yields were higher for cows calving in mid-winter (June/July) compared to cows calving in mid-summer (December/January). Daily yields early in the lactation were more influenced by calving age than daily yields towards the end of the lactation. Cows that calved at younger ages in lactations 1 and 2 produced less milk compared to cows calving at older ages over the entire lactation. Second and later parity cows had higher test-day yields than heifers for most stages of the lactation. These estimates can be used to adjust test-day and cumulative yields for the effect of season and age class, thereby enabling the determination of herd levels and the derivation of standard lactation curves and projection factors for South African Holstein and Jersey cows.

South African Journal of Animal Science, Vol 31, Issue 3, Oct – Dec (2001) pp.205-214

Key Words

Age at calving, Best Linear Unbiased Estimates, Holstein, Jersey, Season of calving