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Effects of Dietary Urea on Reproduction in Ruminants¹

North Carolina State University, Raleigh 27607

Abstract

The influence of dietary urea on reproductive performance in ruminants was studied in four experiments involving 153 Angus and 87 Hereford cows, 70 Dorset and 106 crossbred ewes, four Holstein bulls, and four Suffolk and four Dorset rams. The animals were fed conventional diets consisting of corn silage or poor quality hay supplemented with either urea or soybean meal. The experimental diets supplied similar amounts of nitrogen and energy.

The incidence and regularity of estrus and percent females calving or lambing from service during one estrous period were not affected by dietary urea. The calving and lambing rates of cows and ewes fed diets containing urea were approximately equal to that of females fed soybean meal. Feeding urea during early and late pregnancy did not appear to affect either embryonic development or parturition in beef cows. The ovulation rate of ewes was not influenced by dietary urea, and length of time ewes were fed the experimental diets prior to mating did not influence subsequent fertility and reproductive rate. The effects of diets on cow and calf weight gains were not significant.

The characteristics of fresh semen as well as storage capacity of diluted semen from Holstein bulls were not affected by dietary urea. Ram fertility, as measured by percent ewes lambing to service during one estrous period and lambing rate of ewes bred, was not affected by diet. The results of these experiments demonstrate that high roughage diets can be supplemented with urea without reducing reproductive performance.

¹ Paper No. 3925 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh.

² Present address: Animal Science Department, Texas Tech. University, 79409.