Effects of growth potential and protein supplementation on steers grazing fall pasture in the Northern Great Plains

Cattle of varied genetic growth potential may respond differently to management strategies because of altered nutrient demands for growth. An option for postweaning calf management is use of improved pastures for grazing. A 3-yr study (1990 to 1992) was conducted to evaluate the effects of supplemental soybean [Glycine max (L.) Merr.] meal (SBM) on performance of Bos taurus steers (average weight 471 lb) of high-(Charolais-sired) or moderate- (Hereford-sired) genetic growth potential. Each year, 23 wear 1 and 3) or 24 year 2) steers grazed pastures of a Russian wildrye [Psathyrostachys juncea (Fischer) Nevski]-wheatgrass hybrid [Elytrigia repens (L.) Neuski] x [Pseudoroegneria spicata (pursh.) Love] complex. One-half of the steers were individually fed SBM (1 lb/d, as fed) 5 d/wk in 1990 and 7 d/wk in 1991 and 1992. Crude protein of consumed forage, as determined from esophageal masticate, averaged 15.1, 14.8, and 12.6 in mid-October and 10.5, 14.5, and 7.0% of organic matter (OM) in mid-December of 1990, 1991, and 1992, respectively. Steers of high genetic growth potential gained 1.4 lb/d compared witb 1.2 lb/d for moderate growth potential steers (P < 0.05) and SBM supplemented steers had greater gains (P < 0.01) than nonsupplemented steers (1.5 vs 1.1 lb/d). Forage OM intake was affected by year (P < 0.01) and genetic potential for growth (P < 0.05). Forage OM intake averaged 8.8, 9.4, and 7.5 lb/d for 1990, 1991, and 1992, respectively, and 9.0 and 8.1 lb/d for high- and moderate-growth potential steers. Supplementation with SBM was cost effective for steers grazing regrowth in irrigated Russian wildrye-wheatgrass hybrid pastures in the fall.