Intake, digestibility, and nitrogen retention by sheep supplemented with warm-season legume hays or soybean meal

The increasing cost of feed supplements necessitates evaluation of alternatives for ruminant livestock grazing poor quality warm-season grasses. This study determined how supplementing bahiagrass hay (Paspalum notatum Flügge cv. Pensacola) with soybean [Glycine max (L.) Merr.] meal or warm-season legume hays affected intake, digestibility, and N utilization by lambs. Dorper x Katadhin crossbred lambs (30.6 +/- 5.5 kg; n = 42) were fed bahiagrass hay (73.8% NDF, 8.1% CP) for ad libitum intake and supplemented with nothing (control), soybean meal, or hays of annual peanut [Arachis hypogaea (L.) cv. Florida MDR98; 46.2% NDF, 14.7% CP], cowpea [Vigna unguiculata (L.) Walp. cv. Iron clay; 62.2% NDF, 11.7% CP], perennial peanut (Arachis glabrata Benth. cv. Florigraze; 43.3% NDF, 15.2% CP), pigeonpea [Cajanus cajan (L.) Millsp. cv. GA-2; 78.6% NDF, 12.2% CP], or soybean (cv. Pioneer 97B52; 59.0% NDF, 13.5% CP). Legume hays were supplemented at 50% of total diet DM, and soybean meal was supplemented at a level (4.25% of diet DM) that matched the average dietary CP content (10.8%) of the legume hay-supplemented diets. The cowpea, pigeonpea, and soybean were harvested at respective maturities that maximized DM yield and nutritive value, and the peanuts were first cuttings. Diets were fed to 6 lambs per treatment for 2 consecutive 21-d periods. Supplementation with hays of annual and perennial peanut, cowpea, and soybean increased (P < 0.01) DMI vs. control, but apparent DM digestibility was only increased (P = 0.03) by supplementation with annual or perennial peanut hay. Compared with the control, N intake, digestibility, and retention were increased (P < 0.01) by supplementation with legume hay or soybean meal. Responses were greatest when annual or perennial peanut hays were fed. Ruminal ammonia concentration was increased (P < 0.01) by all legume hay supplements vs. the control. Microbial N synthesis and ruminally degraded OM were increased (P = 0.03) by perennial and annual peanut hay supplementation, but efficiency of microbial synthesis was not different (P = 0.52) among diets. Unlike other supplements, annual and perennial peanut hays increased DM and N intake and digestibility and improved microbial N synthesis; therefore, they were the best supplements for the bahiagrass hay under the conditions of this study.