乳牛의 泌乳曲線에 影響하는 環境效果 및 曲線類型 推定에 관한 硏究

Studies on the Estimation of Environmental Effect and Types of Lactation Curve in Dairy Cattle

Studies were made of the environmental effects on average lactation curves. Environmental influences have been assumed to dominate the shape of lactation curves, so some attentions were carried out about the effects, year and season of calving and lactation number. The traits influencing lactation curve were averaage initial daily milk production, index of the cow’s capacity to utilize energy for milk production, decay rate, persistency, day of peak yield and coefficient of determination. Parameters of lactation curve were defined by a gamma-type function for 666 lactations from cows representing 33 sires. The results obtained were summarized as follows. 1. In the average effects of every traits, the least-square means of Ln average initial daily milk production(Ln a), index of cow’s capacity to utilize energy for milk production(b), decay rate(c), persistency, day of peak yield, peak yield and coefficient of determination(R²) were 2.33, 25.81 × 10⁻², 5.49 × 10⁻³, 907.52, 46.24day, 22.69㎏ and 82.27, respectively. 2. Generally, peak production increased and day of peak yield and persistency decreased as the cow matures. The curve for the first lactation remained fairly flat and low, compared with later ones, which became progressively steeper during this declining phase. Peak yields and Ln average initial daily milk productions of the first(I), second(II), third(III) and fourth or later(IV≤) lactation were 18.66, 23.28, 24.13 and 24.69㎏, respectively and 9.39, 9.68, 11.47 and 10.70㎏, respectively. In the effects of season of calving, Ln a was low in the spring while b and c peaked. Cows calving for winter appeared more persistent(1013.42) and longer to reach peak yield(50.25 days) than summer. 3. In this study, it was found that 82.6% of total records were typical lactation curves and 17.4% were atypical lactation curves. Concave and downhill-shaped curves were found 3.3% and 12.6% of total lactation curves, respectively.