Effect of Feeding Urea on Reproductive Efficiency in Michigan Dairy Herd Improvement Association Herds

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Abstract
Information on feeding practices in Michigan Dairy Herd Improvement Asso- ciation (DI-IIA) herds to determine if feeding urea affected reproductive effi- ciency in dairy cattle was obtained through a survey form distributed by county extension personnel. Calving in- terval (days) was from DHIA records. Adjusted calving interval (ACI) was cal- culated by subtracting from the calving interval the number of days the dairy- man waited from calving to first breeding as a herd policy. Percent of cows sold for sterility was also from DI-IIA records. A total of 3,157 herd-year observations representing 85,281 calving intervals was from the 5 years 1965 to 1969. Of the 3,157 herd-year observations, 1,709 were in herds fed urea. In herds which used urea, daily urea intake averaged 80.6 g (range 9 to 370 g). Approximately 5070 of this came from urea-treated corn silage and the remainder from concentrate. The mean ACI for herds fed no urea was 314.4 days compared to 315.7 days for herds fed urea. The ACI for herds fed 1 to 60 g urea was 313.4; 61 to 120 g, 317.8; 121 to 180 g, 316.5; and over 181 g, 313.7 days. These differences were not significant. Cows sold for sterility in nonurea herds was 2.15% ver- sus 2.40% for all urea. This small differ- ence is of no practical significance.