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Effect of Introduction of Urea on Feeding Behavior of Holstein Heifers¹

Monell Chemical Senses Center and School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348

ABSTRACT

Effects of introduction of urea upon feeding behavior were studied in dairy heifers that never had been exposed to urea. Twelve dairy heifers (158 ± 40 kg) exhibited no significant aversion or preference in 20 two-choice preference tests with tap water versus tap water adulterated with urea (1 to 64 x 10^-2M). Ammonia intoxication was avoided by limiting liquid volumes offered so that urea intake would not exceed .35 g/kg body weight during the 30-min test period. In single stimulus preference tests with five pairs of heifers (156 ± 24 kg), animals fed urea versus soy protein diet during the daily 6-h test period did not decrease consumption until day 3 of exposure. Heifers provided with urea diet spent as much time feeding, but eating rate was decreased. They remained averse to urea diet after we fed soy protein diet for 4 days. We postulate the decreased consumption of urea diets fed below toxic amounts is not due to taste and/or odor per se but probably results from association of the flavor of urea diets with a malaise produced by ammonia.

¹ Supported in part by Biomedical Research Support Program Grant 5 S07 RR5464, and the Fund for the Study of Feeding Behavior, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania.