Effects of limit feeding a high-grain diet on puberty and reproductive performance of ewes.

In Exp. 1, 39 ewe lambs (initial BW 29 +/- .1 kg) were used in a 2 x 2 factorial arrangement with two breeds (Polypay and Targhee) and two diets (high-forage and high-grain) to examine the effects of restricting intake of a high-grain diet on onset of puberty and lamb performance. The experimental diets were fed from 13 to 40 wk of age. The high-forage diet was composed of 80% alfalfa cubes and 20% supplement. The high-grain diet was 90% concentrate and 10% alfalfa cubes. Feed intake of the diets was controlled so that lambs fed the high-grain diet had the same growth rate as those fed the high-forage diet. Plasma insulin concentration was higher (P < .001) for lambs fed the high-grain diet than for those fed the high-forage diet. However, no diet effect on age at puberty was observed. In Exp. 2, 88 mature Targhee ewes were used to determine the effects of limiting intake of a high-grain diet on pregnancy and number of lambs born per ewe. Intake of the high-grain diet was restricted to achieve similar ME intake between diets. There were no diet effects on number of lambs born per ewe or subsequent lamb performance. Ewes fed the high-forage diet had a lower (P < .001) weight gain than those fed the high-grain diet. It was concluded that restricting intake of high-grain diets is an effective alternative to feeding high-forage diets for meeting the nutrient requirements of ewe lambs and gestating ewes; however, no improvements on reproductive performance were observed.