Response of Dairy Heifers to Diethylstilbestrol

Abstract

The effect of feeding diethylstilbestrol (DES) on the feed consumption, growth, and reproduction of dairy heifers was studied during the period from 6 months of age to first calving. Seven of 13 Holstein heifers received, in addition to a standard grain ration, 10 mg. of DES per animal daily. Individual roughage intakes were recorded daily. During the 280-day period from 6 to 15 months of age, the DES treatment stimulated a highly significant increase in the average daily roughage dry matter consumption (0.97 lb. per heifer). The increase in average daily liveweight gain (0.09 lb. per heifer) for the DES-fed animals was not statistically significant. Consequently, there was a slight but non-significant reduction (−5.8%) in feed efficiency for the DES-fed heifers. During the period from 15 to 24 months of age, the average roughage dry matter intake of the DES-fed heifers was consistently higher; however, the average difference (1.23 lb. per heifer) was not statistically significant. The increased feed intake for the DES-fed heifers did not result in significant increases in liveweight gains either before or after conception. Average body measurements at 6, 12, 18, and 24 months indicated that DES had no significant effect on skeletal growth. The DES treatment did produce a highly significant increase in mammary gland length during the period from 6 to 12 months of age. However, there was no significant difference in subsequent milk production. Average ages at first estrus, average length of the estrous cycles, and breeding efficiency during the first service period did not differ significantly. No differences in the structure or function of the reproductive organs due to DES treatment were detected. However, the average birth weight for the calves of the DES-fed heifers was significantly lower (13.1 lb.) than the average birth weight for the control calves. Reproductive performance following first calving did not suggest any significant physiological differences due to the withdrawal of the DES treatment.