Effect of herd, genotype, month and year of calving on the performance in dairy cattle. 1st Paper: Milk production

In a representative survey milking and reproductive performance of cows were analysed in a database in the first (n=16.959), second (n=8.060), third (3.113), fourth (1.014) and fifth parity (359) from 53, 51, 42, 28 and 13 herds, respectively. The data cover six genotypes from an upgrading crossbreeding program using Holstein-Friesian genes lasting for a 3-5 years period (1989-1993) depending on number of parity. Overall mean and standard deviation for the full data set in the first parity was 5.495 plus/minus 1.201 kg with higher ones in the subsequent (2-5) lactations. The ranges of yields were between 6.213 plus/minus 1.464 and 6.324 plus/minus 1.603 kg with relatively limited fluctuations among parities. In the first parity butterfat content attained 3.67 plus/minus 0.46 percent which tended to decrease until 3.56 plus/minus 0.45 percent in the subsequent lactations. Similar tendencies were recorded for milk protein content the highest and the lowest values of which were 3.31 plus/minus 0.21 and 3.28 plus/minus 0.20 percent, respectively. For all three milk production traits significant differences were obtained among herd averages in all parities. As for the first parity the majority (56.6 percent) of herd averages for ECM305 was in the class ranging from 4.501 to 5.500 kg. In case of subsequent parities higher share of cows were found in upper production classes. For the second and third parity the herd average was within the range of 7.501-8.000 kg and it exceeded the level over 8.000 kg in another one. With advancing Holstein-Friesian gene ratio the mean values for ECM305 among genotypes seemed to increase in all parities. At least in the first, second and third parities just the opposite tendency was observed with butterfat percentage. Simultaneous decrease of milk protein percentage was also shown with increasing Holstein-Friesian gene ratio. Effect of month of calving on ECM305 was present in all parities as well. Cows having been calved in winter months such as January, February and early spring in March produced more milk than their counterparts with summer calving dates. Least milk production was shown by cows with late summer parturition