Effects of Growth Potential and Protein Supplementation on Steers Grazing Fall Pasture in the Northern Great Plains

Abstract

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 (Year 1 and 3) or 24 (Year 2) steers grazed pastures of a Russian wildrye [Psathyrostachys juncea (Fischer) Nevski]-wheatgrass hybrid [Elytrigia repens (L.) Neuski] × [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 with 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. Research Question Regrowth of harvested, irrigated hay fields in the Northern Great Plains can provide a higher quality forage for fall grazing than nonirrigated native range-land. This high quality regrowth may be suitable for young animals with high nutritional requirements for growth. However, protein needs of 6- to 9-mo-old calves may be greater than what is available from pasture alone, depending upon desired growth rates. Protein requirements of calves are affected by growth rate, and genetic potential for growth may alter responses to different management systems. The objective of this study was to evaluate soybean meal (SBM) supplementation for calves of two growth potentials grazing irrigated pastures in the fall after weaning. Literature Summary Efficiency of beef production is affected by rate and efficiency of gain during the postweaning period. Use of cattle with varied growth potentials or the use of different management schemes can alter this efficiency. Research has shown increased weight gains by cattle fed protein supplements along with moderate quality forages compared with cattle fed these forages without supplements. Protein supplementation may affect forage intake and digestion depending upon the forage quality. Study Description A 3-yr study (1990 to 1992) was conducted in the fall after weaning to evaluate supplemental SBM for steers (average weight 471 lb) of high- or moderate genetic potential for growth. Each year 23 or 24 steers grazed regrowth from pastures of a Russian wildrye-wheatgrass complex for about 80 d. Half of the steers were individually fed SBM (1 lb/d) 5 d/wk in 1990 and 7 d/wk in 1991 and 1992. The CP content of the forage consumed averaged 13.2, 12.6, and 10.6% in mid-October and 8.8, 12.3, and 6.0% in mid-December of 1990, 1991, and 1992, respectively. Applied Questions What rates of gain can be expected from weaned steer calves grazing fall pasture regrowth in the Northern Great Plains and is supplementary protein valuable? Using regrowth in Russian wildrye-wheatgrass pastures in the fall for growing cattle can result in weight gains of 0.9 to 1.5 lb/d. Gains may be increased 0.4 lb/d by supplementing with SBM at 1 lb/d. Do steers of differing genetic growth potential benefit equally from SBM supplementation? Cattle of both high- and moderate-growth potential benefit equally from added SBM. Forage needs can be determined based upon body weight (BW), with forage intake being an equal percentage of BW for steers of high- or moderate-growth potential.