Test day data on 6,310 primiparous Finnish Ayrshire cows were used in the estimation of genetic parameters for daily milk production. Two different random regression (RR) submodels were fitted to describe individual lactation curves, a five parameter logarithmic (ASM) and a normalized fourth order orthogonal (OPM) polynomial. Estimates of heritabilities for test day yields and genetic correlations between individual days obtained by RR models were compared to those from a multitrait (MT) model. (Co)variance components for RR models were estimated using EM-REML and animal model. Significantly higher heritabilities were found with both ASM (0.41-0.58) and OPM (0.29-0.52) compared to those from MT analysis (0.23-0.34). Heritabilities estimated with both ASM and OPM seemed to follow a similar pattern being highest at the beginning and end of lactation. As expected, genetic correlations between consecutive test days were high (0.81-0.98), decreasing when test day intervals increased and turned negative when tests were 200 or more days apart. With the MT model genetic correlation reached its lowest (0.35) between test days 1 and 305
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 23: Opening: plenary; technology; transfer; beef cattle; dairy cattle; pigs., , 307–310, 1998
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