First lactation milk production of cows of the Simmental breed reared in Bulgaria.

The present study involves 1946 cows of the Simmental breed population, which is relatively new in Bulgaria, formed at the beginning of the century. The cows included are reared in 44 farms under selection control and have lactated in the period 1999-2017. Simmental cows are characterised with high milk production under the conditions in our country. The average (LSМ) milk yield of primiparous cows per 305-day lactation period is 5016±70.81 kg, with fat content of the milk of 4.217±0.024% and protein content of 3.398±0.013%, and per full lactation period (354.5±8.68 milking days), the figures are respectively 5564±128.0 kg, 4.253±0.024% and 3.413±0.014%, respectively. The farm and the year of calving are proved to have an effect on all milk production indexes examined (P < 0.001). The average milk yield in the different farms varies from 4106±176.9 to 7035±130.4 kg, with more than 45% of the farms indicating average milk yield above 5000 kg. The calving season affects the variation (P < 0.05) in the normal and full lactation milk yield and does not affect the milk quality. Those cows which calved in the winter and spring have the highest milk, dairy butter and milk protein yield, and those which calved in the autumn – have the lowest.