Abstract
In a 100-head dairy farm, a sudden increase in calve mortality was observed after 100 first-calf heifers were additionally introduced over a period of six months in order to increase the herd size. The mortality rate was 7.5% （8/107） before the introduction of new heifers but increased to 18.6% （19/102）. This difference was statistically significant （p<0.05）, and the causes of mortality were mainly diarrhea and pneumonia. To reduce the mortality, the following husbandry improvements were suggested: 1） the amount of milk fed increased from 0.6 to 0.85 kg on a dry-matter basis at three weeks old; 2） maintenance of calves with diarrhea on milk feedings; 3） per calf space increased from 0.66 to 1.69 m2; 4） more dry bedding supplied; 5） thorough disinfection of calf pens and 6） placement of additional water buckets for ad libitum access. These changes resulted in a significant reduction in the mean number of treatments （5.7 ± 3.0 vs. 8.8 ± 4.6; p<0.01）. The blood total cholesterol level, a marker of nutritional status, increased significantly from 66.1 ± 15.6 to 127.3 ± 37.4 mg/dℓ （p<0.01）. These results indicate that the increased mortality was largely attributable to poor nutritional and environmental management.
