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The objective of this study was to analyse the effect of stage of lactation on daily milk yield, and milk fat and protein content in Tsigai and Improved Valachian ewes. Breed lactation curves for daily milk yield, and milk fat and protein content were modelled as a sub-model of the three-trait animal model based on repeated test-day records that were collected by the Breeding Services of the Slovak Republic between 1995 and 2010. Data included 188403 (Tsigai) and 352094 (Improved Valachian) ewe’s performance records. Pedigree file included 35484 (Tsigai) and 66994 (Improved Valachian) animals with genetic ties to ewes with milk performance data. The fixed part of the model included parity, litter size and stage of lactation. The effect of days in milk (i.e. stage of lactation) was fitted using Ali and Schaeffer lactation curve. The random part of the model included flock-test day effect, direct additive genetic effect, and permanent environmental effect of ewe nested within lactation. Due to limited number of test-day records in the first and the eighth month of lactation and related difficulties in modelling milk traits in these phases of lactation, the lactation curves were plotted between days 30 and 210. During lactation period the daily milk yield curves were decreasing, while milk fat and protein content were increasing. Because of higher changes at the beginning of lactation balanced with higher changes at the end of lactation in Tsigai and smaller changes at the beginning of lactation balanced with smaller changes at the end of lactation in Improved Valachian, 150d milk yield and average milk fat and protein content were almost the same in both breeds.

The effect of stage of lactation on daily milk yield, and milk fat and protein content in Tsigai and Improved Valachian ewes