Analysis of the variation of cow's milk energy with lactating curve model in relation to heredity, calving number and calving season.
1993
Itano S. | Okubo T.
This study was performed for the purpose of finding the parameters of lactating curve, and to determine the effects of mother family line, calving number and birth season on them. First lactating data on 66 Holstein cows' raised in the Animal Husbandry Experiment Station, the University of Tokyo, were applied to Wood's mathematical model. In addition, for other parameters, the days after calving at peak milk energy yield, per metabolic body size, milk energy yield at starting lactation, peak milk energy yield, and average milk energy yield among lactating 10th month, were calculated by transforming the above formula. These lactating parameters were compared among three mother family lines, each calving number and birth season, respectively. The results were as follows: 1) There was a small difference of lactating parameter values among mother family lines, provided that parameter "a" of Royalwalker line and parameter "Ptp", "P" of Empress line were higher than those of other lines. 2) The effect of calving number on the parameter was strong, particularly in relation to the level of milk energy yield. 3) The decrease of milk energy after peak yield was influenced by past heat stress. 4) Quantitative levels of milk energy were affected mutually by calving number and birth season.
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