Designing supplements for stocker cattle grazing wheat pasture,

Abstract

Abstract Supplementation of cattle grazing wheat pasture is of interest to 1) provide a more balanced nutrient supply and feed additives such as ionophores or bloat preventive compounds, 2) substitute supplement for forage where it is desirable to increase stocking rate in relation to grazing management and/or marketing decisions, and 3) substitute supplement for forage under conditions of low forage standing crops. Two different strategies for providing energy supplements to growing cattle on wheat pasture are presented. One was to develop a “small package” (i.e., target intake of 0.91 to 1.36 kg/d on an as-fed basis), self-limited monensin-containing energy supplement to provide additional degradable OM relative to rumen degradable N and increase nonammonia N supply per unit of ME. The supplement very consistently increased ADG by approximately 0.22 kg and increased profit by $15 to 31/steer depending on supplement cost and profit potential of the cattle. The sorghum grain-based supplement contained (as-fed basis) 4% fine mixing salt, 165 mg/kg of monensin, and 0.75% magnesium oxide. Monensin limited intake, but MgO at concentrations up to 1.75% did not limit intake. Modification of the formula for every-other-day hand-feeding resulted in similar improvements in ADG as achieved with the self-limited supplement. An additional study using small numbers of ruminally cannulated steers in a completely randomized design compared the effects of monensin or lasalocid vs. no ionophore on wheat pasture bloat. Monensin decreased (P < 0.05) both the incidence and severity of bloat and was more efficacious than lasalocid for prevention of bloat. A second strategy was to feed two types of energy supplements (i.e., high-starch, corn-based supplement vs. high-fiber by-product feed-based supplement) at a level of 0.75% of BW. Over the 3-yr study, mean daily supplement consumption was 0.65% of BW. This energy supplementation program increased ADG by 0.15 kg and allowed stocking rate to be increased by one-third. Type of supplement did not influence ADG, supplement conversion, or the substitution ratio of supplement for forage. Supplement conversion was approximately 5 kg of as-fed supplement•kg of increased gain−1•ha−1 and was substantially less than conversions of 9 to 10 that have traditionally been used in evaluating the economics of energy supplementation programs for wheat pasture stocker cattle.