Inheritance of Lactation Curve in Swiss Brown Cattle

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Abstract
Lactation curves for milk and fat yield were estimated for 159,541 Swiss Brown cows by 2 models: yi = atibe-cti [1]: yi = A(ti-to)Be-C(ti-to) [2]. In these yi and ti are yield and day in lactation at the ith milk recording. The b and B are associated with the increase, c and C with the decrease of production, a and A are constants associated with production and to indicates the time of the initial production. Model [2] gave smaller mean squared errors than Model [1] and less curves with negative estimates for B or C than for b or c in Model [1]. Heritabilities for measures of persistency ranged from 0.19-0.29. The C was not correlated genetically with 305 day yield and was positively correlated with 100-day yield. Genetic correlations between persistency and 305 day yield were 0.05-0.16 and between persistency and 100 day yield -0.23 to -0.35. This indicates that breeding for 100 day yield would decrease persistency, while breeding for 305 day yield would not affect it adversely.