2019 Volume 10 Issue 1 Pages 17-21
Relationships among maternal nutritional status before calving, gestation period and calf size were investigated in Japanese Black cattle. The study included a total of 55 cows that calved between 2010 and 2011. Based on the average pregnancy period of Japanese Black cows（285 days）, the study animals were divided into two groups: 14 cows that calved within this period（Group 1）and 41 cows that calved after due date（Group 2）. The mean change in heart girth from 2 weeks before calving to the day of calving or calving due date was significantly greater in Group 1（0.36 ± 3.79 cm）than in Group 2（-0.71 ± 4.00 cm on due date and -2.27 ± 4.00 cm on calving date）indicating poorer nutritional status in cows that had delayed parturition. The sex ratio of calves, calving season and age of the cows, which have been shown to affect gestation period, were similar between the two groups. When two farms with two different feeding programs were compared, the mean change in heart girth was significantly lower in the farm having poorer nutritional adequacy than in the other farm with better nutritional adequacy. The former farm also had a significantly longer gestation period compared to the other farm. These results suggest that suboptimal nutritional status during pregnancy was one of the causes of delayed calving. In the study groups, the head circumference of calves at birth increased and was significantly correlated with the gestation length, whereas the birth weight of calves was not associated with the gestation length. Together, the results of our study suggest that the poor nutritional status of cows in the prenatal period can lead to delayed calving and a larger calf head. Good nutritional management of pregnant cows plays a key role in preventing delayed calving associated with large calf head.
