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Growth and Reproductive Performance of Bulls and Heifers Fed Purified and Natural Diets. VI. Growth, Estrus, Conception Rate, Gestation and Milk Production of Females

U.S. Department of Agriculture,¹ Beltsville, Maryland 20705

Abstract

IN a preliminary study one beef heifer from each of two twin sets was fed either a purified diet containing urea as the sole source of dietary nitrogen or a natural diet after 7 months of age to study the influence of diet on reproduction. Although data are limited, there seemed to be only small differences in conception rate, estrous cycle and gestation length, birth weight of calves, time and weight at puberty and percent protein and fat in milk.

In the second study 14 Angus females were fed purified diets containing either urea or isolated soy protein as the sole sources of dietary nitrogen or a natural diet after 84 days of age to determine the influence of diet on growth and reproduction. Heifers fed the urea purified diet reached puberty at 634 days of age while heifers fed either isolated soy protein or the natural diet attained puberty at 364 and 308 days, respectively. Females fed the urea purified diet weighed less and gave less milk at first lactation than the soy protein diet and natural diet fed females. First calves from the urea fed females gained slower and weighed less at weaning than the other calves. Females fed urea averaged 53 days longer between calving and first estrus, but the difference was not significant. There was no significant effect on estrous cycle, conception rate, death rate of calves or gestation length due to diet. Results from both studies indicate that beef females will reach puberty and reproduce even when reared from a very early age on a protein-free (urea containing) purified diet.

¹ Ruminant Nutrition Laboratory, Nutrition Institute, A.R.S.