Abstract
Some advantages in pasture-based dairy production are realized worldwide. However, effects of grazing management on reproduction of dairy cows are still obscure. Thus, the objective of this study was to investigate the influence of different managing period on reproduction of dairy cows raised in grazing and non-grazing periods. The records utilized for this analysis were collected by 3 dairy farms in Ashoro town of Hokkaido from April 2004 to September 2010. The farms raised cows in pasture all day from the middle of May to the middle of November every year. Surveyed farms tended to have seasonal breeding for utilizing pasture efficiently during the grazing period. The farms also inclined to show relatively high parity and many services per conception of cows. By comparison with averages of reproduction traits of dairy cows in Hokkaido, the mean of first service conception rate in the surveyed farms was lower. The average of conception rate per insemination in the farms was lower than the Hokkaido average. The means of postpartum first service days, days open and calving interval days in the farms were shorter than the average. In addition, the means of estrus detection rate and pregnancy rate were higher than the average. The cows inseminated in the grazing period showed shorter postpartum first service days than the ones serviced in the non-grazing period. In addition, the cows impregnated in the grazing period showed shorter day’s open and calving interval days than the ones fertilized in the non-grazing period. On the other hand, the cows calved in the grazing period had no significant difference in reproduction traits with the ones delivered in the non-grazing period. The effects of dairy management for utilizing pasture for cows and increasing milk yield in the grazing period on reproduction of cows raised in different periods were identified.
