Growth and reproductive performance of beef females fed high urea-containing diets.

Abstract

Two thirds of the total nitrogen in a poor quality 50% forage diet was supplied in 1) soybean meal, 2) equal parts of soybean meal and urea, and 3) urea. These diets were fed to 12 sets of monozygotic twin heifers averaging 148 kg and 235 days of age. The twins were used in an imcomplete-block experiment with each pair of twins being considered a block. The diets were assigned to the twin pairs at random and then these diets were randomly assigned within a pair. The heifers were bred when the lighter twin of a pair reached 272 kilograms. Diets had no effect (P > .05) on length of estrous cycle, services per conception, birth weight of calves, milk yield, average daily gain of calves, and interval from calving to first estrus and conception. Gestation length (P < .05) and cow weight at first conception (P < .01) and calving (P < .05) were longer and heavier, respectively, in the females given the soybean meal diet. There were no differences (P > .05) in the ruminal characteristics of steers fed either the urea or soybean diets with either soybean oil or molasses substituted on an equal weight basis. Replacing molasses with soybean oil increased (P < .05) the dry matter and gross energy digestibility of the diets. Fecal nitrogen losses were greater (P < .05) in the soybean meal diet with molasses. Data from this trial indicate that urea can furnish to-thirds of the total nitrogen in diets of beef females without adversely affecting reproduction