The effect of herd size on the yield and proximate composition of milk in active cattle populations in the region of Warmia and Mazury (NE Poland).

The milk yield of 24 934 cows from herds monitored by the National Animal Breeding Center, Branch in Olsztyn, was analyzed. The data were collected in the years 1997–2006. The cows were divided into three groups, based on herd size: group I of up to 20 cows, group II of 21–50 cows and group III of more than 50 cows. Additional criteria for the above division were the number of successive 305-day lactations and full lactations as well as the length of inter-calving intervals. The objective of this study was to determine the effect of herd size on the yield and proximate composition of milk in active cattle populations in farms in north-eastern Poland over a ten-year period, taking into account lactations of normal length and full lactations, inter-calving interval (ICI) duration and lifetime cow productivity. The average yield over 305-day lactations was 6579 kg milk (6723 kg FCM), 273 kg fat (4.15%), 213 kg protein (3.24%), 309 kg lactose (4.70%) and 841 kg dry matter (12.78%). Cows in the largest herds (> 50 head) were characterized by the highest productivity, and cows in the smallest herds (≤ 20 head) – by the lowest. The latter produced milk with the highest fat content (4.16%) and the lowest protein content (3.21%). In herds comprising more than 50 animals, cows with the longest ICI (> 525 days) were marked by the highest milk production in full lactations (11 010 kg). As regards lifetime productivity, the highest values were noted in cows used for 3.44 years in the smallest herds (19 809 kg milk). In the largest herds cows were used for the shortest period of time (3.31 years), and their lifetime productivity reached 17 185 kg milk.