Comparison of Random Regression Test-Day Models for Production Traits of South African Jersey Cattle
Abstract
This study aims to identify the most appropriate random regression test-day model (RRTDM) for the South African Jersey dairy breed, using Legendre Polynomials (LP) to model the lactation curve. The data comprised of production test-day records for milk yield (MY), fat yield (FY) and protein yield (PY) from 33,852 multiparous cows. Genetic parameters were estimated using single trait RRTDM using AIREML90. The fixed effects fitted were Herd x Test-day x Birth Year of the Cow x Calving year x Parity x Number of Milkings (HTDBCPNM), production system (PROD) (TMR, pasture or both), age at first calving (AFC) and inter-calving period (ICP), and fixed regressions on age class-season-district. Random effects were direct additive, permanent environmental and residual effects. The estimated heritabilities for MY, FY and PY were 0.254, 0.182 and 0.170, respectively. The genetic correlations between total milk production and persistency were low (0.06 to 0.24). Overall, the heritability estimates of all the traits analysed were low to moderate.
Domains
Animal geneticsOrigin | Files produced by the author(s) |
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