Genetic evaluation of in-line recorded milkability from milking parlor and automatic milking systems

C. Carlström¹, G. Pettersson², K. Johansson³, E. Strandberg¹ H. Stålhammar⁴and J. Philipsson¹.

¹SLU, Dep. of Animal Breeding and Genetics, P.O. Box 7023, 750 07 Uppsala, Sweden, ²SLU, Dep. of Animal Nutrition and Management, Kungsängen Research Center, 753 23 Uppsala, Sweden, ³Växa Sverige, P.O. Box 7023, 750 07 Uppsala, Sweden, ⁴Viking Genetics, P.O. Box 64, 532 21 Skara, Sweden; caroline.carlstrom@slu.se

Selection against slow milking cows is of great interest in order to save time and to make efficient use of expensive equipment in dairy herds with modern milking systems. In Sweden 28% of the cows are milked in automatic milking systems (AMS) and another 27% in conventional parlors (CMP). The aims of this study were 1) to estimate heritabilities and genetic correlations for milkability traits based on observations from commercial herds with AMS or CMP, 2) to estimate genetic correlations for milkability across milking systems, and 3) to study the opportunities for an efficient genetic evaluation model using data from both milking systems.

Data came from 19 herds with AMS and 74 herds with CMP. In total, information from 13,176 Swedish Holstein cows with 1,335,589 observations and 9,303 Swedish Red cows with 1,358,849 observations were included. Average flow rate was used as a common milkability trait for both systems, whereas milking time and box time was used from CMP and AMS, respectively. Univariate and bivariate repeatability models were used to estimate heritabilities within system, and genetic correlations across traits, lactations and systems.

Estimated heritabilities were in the range of 0.25-0.51 and similar for both systems. Even though the traits were differently defined in the two systems, the corresponding traits were genetically closely related (0.93-1.00). The results clearly indicated that it is possible to achieve accurate genetic evaluations of milkability traits, not only for sires of cows but also for individual cows across milking systems.