Effects of energy or protein supplements and stage of production on intake and digestibility of hay by beef cows.

In two consecutive years, primi- and multiparous, spring-calving Hereford and Hereford x Angus cows (n = 32, yr 1; n = 42, yr 2) were used to determine the effects of supplements and lactational status on forage intake, digestibility, and energy intake. Cows were randomly alloted to treatments after being blocked by age, breed, and weight. Supplements fed during gestation provided .55 kg/d of CP from a 40% CP, soybean meal-based supplement (PROTEIN) or a 20% CP, soybean hull-based supplement (ENERGY). After calving, cows remained on the same supplement or were switched. In yr 2, a 40% CP supplement was also fed postpartum at nearly the same rate as ENERGY to provide twice the supplemental CP and energy as PROTEIN. Prairie hay (< 5% CP) DMI was measured directly and DM digestibility estimated for two 7-d periods during late gestation and early lactation. Gestating cows fed PROTEIN consumed 1 kg/d more hay DM and hay DM digestibility was greater (P < .001) than for cows fed ENERGY. Lactating cows also consumed more hay when fed PROTEIN than when fed ENERGY or HI PROT, but hay DMI was not affected. Total ME intake was similar for cows fed PROTEIN and ENERGY in late gestation or early lactation. Results indicated that ENERGY will decrease low-quality forage digestibility for prepartum cows and can decrease forage intake for both pre- and post-partum cows. Increasing the total energy intake of grazing cattle by feeding supplements is difficult after protein requirements are met.