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Title: Efficacy of mineral supplementation to growing cattle grazing winter-wheat pasture in northwestern Oklahoma

Author
item Gunter, Stacey
item Combs, Gerald

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2019
Publication Date: 7/17/2019
Citation: Gunter, S.A., Combs, G.F. 2019. Efficacy of mineral supplementation to growing cattle grazing winter-wheat pasture in northwestern Oklahoma. Translational Animal Science. https://doi.org/10.1093/tas/txz031.
DOI: https://doi.org/10.1093/tas/txz031

Interpretive Summary: Supplemental feeding of grazing cattle is a powerful tool for producers and can provide positive net returns to the livestock enterprise. Wheat pasture is a unique resource to the Southern Plains because income is derived from both the grain crop and the cattle body weight gain by the grazing cattle. The potential profit is exceptionally good, hence why producers decline to engage in supplementation to augment cattle performance. Mineral analysis has shown that wheat herbage is deficient in calcium relative to the nutrient requirements for growing cattle. So, cattle performance may be increased by supplementing with free-choice mineral mixtures high in calcium. At the USDA, Agricultural Research Service in Woodward, Oklahoma we examined the practice of providing free-choice mineral mixtures to cattle grazing winter-wheat pasture over a two-year period to provide additional calcium. Cattle offered minerals had up to a 43% faster average daily body weight gain than cattle not offered minerals and at the end of the grazing period, supplemented cattle weighed as much as 6% more than non-supplemented cattle. Mineral intakes averaged 4.4 ounces/day, resulting in a cost of supplement to pound of added body weight gain of $0.09 (assuming a mineral cost of $0.025/ounce). Overall, supplementing minerals to cattle grazing winter-wheat pasture increased average daily body weight gain in a cost-effective manner.

Technical Abstract: Two experiments were conducted to evaluate the efficacy of mineral supplementation of cattle grazing winter-wheat pasture. In Experiment 1 (fall), 120 steers and heifers (body weight = 232 kilograms) were assigned randomly to 4 blocks of replicated pastures during the second week of November in 2008 and 2009 and all herds (6 animals/pasture; 4.9 hectare/pasture) were allowed to graze for 84 days. In Experiment 2 (spring), 216 steers (body weight = 248 kilogram) were assigned randomly to 5 blocks of replicated pastures during the second week of February in 2009 and 2010 and all herds (12 or 6 animals/pasture; 4.9 hectare/pasture) were allowed to graze for 84 days. Half the pastures in both experiments received a free-choice mineral mixture (Wheat Pasture Pro; Land O’Lakes Purina Feed, LLC; St. Paul, MN; calcium, 16% and phosphorus, 4%); mineral feeders were weighed weekly to determine mineral intake. All pastures were planted in early September of each year (67 kilograms of seed/hectare) and fertilized with 50 kilograms of urea-nitrogen/hectare. Standing herbage dry matter was determined in each pasture midway between weigh dates by clipping wheat to the ground in 10 transects/pasture. Data were analyzed by analysis of variance, with treatment as the fixed effect and pasture, animal sex (Experiment 1), and block as random effects. In Experiment 1, cattle offered minerals had a 43% faster average daily gain (P = 0.02; 0.73 kilograms) than cattle not offered minerals (0.51 kilograms); hence, supplemented cattle weighed 6% more (P = 0.04; 286 kilograms) after 84 days than non-supplemented cattle (271 kilograms). In Experiment 2, cattle offered the mineral supplement had a faster average daily gain (20% increase; P = 0.04; 1.00 kilograms) than cattle not offered minerals (0.83 kilograms). Further, supplemented cattle weighed 4% more (P = 0.03; 326 kg) after 84 days than non-supplemented cattle (312 kilograms). In both experiments, daily standing herbage dry matter averaged 1,381 kilograms/animal and never differed (P = 0.47) between treatments. Mineral intakes averaged 135 (Experiment 1) and 124 (Experiment 2) grams/day, resulting in a cost of supplement to kilogram of added BW gain of $0.05 and $0.34, respectively (assuming a mineral cost of $0.88/kilogram). Overall, supplementing minerals to cattle grazing winter-wheat pasture increased average daily gain in a cost-effective manner.