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Title: Effect of mineral supplementation on the performance by stocker cattle grazing winter wheat pasture

Author
item Gunter, Stacey
item Combs, Gerald

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/2/2010
Publication Date: 7/12/2010
Citation: Gunter, S.A., Combs, G.F. 2010. Effect of mineral supplementation on the performance by stocker cattle grazing winter wheat pasture. Western Section of Animal Science Proceedings. 61:134-137.

Interpretive Summary: All animal procedures in the following experiments were conducted in accordance with the recommendations of the Consortium (1988) and were approved by the USDA ARS Southern Plains Range Research Station Institutional Animal Care and Use Committee. In Exp 1, eight 4.9-ha pastures located on the Southern Plains Experimental Range of the USDA, Agricultural Research Service near Ft. Supply, Oklahoma were plants to wheat (67 kg/ha of seed) the first 2 wk of September 2008. Before planting, seedbeds were prepared by offset disking in June then harrowing as needed to control weeds. Pastures were fertilized before the last harrowing during the last week of August according to soil test recommendations for N, P, and K requirements from the Oklahoma State University Soil and Water Testing Laboratory (Stillwater, OK) with 50 kg/ha of N from urea. On November 12, 4 of the 8 pastures were stocked (1.2 calves/ha) with 6 calves (n = 24; 8 heifers and 16 steers; initial BW = 193 ±'1.2 kg) and grazed until February 5 (84 d). Grazing was initiated on November 12 after plant leaves were at least 20 cm in length. The initial set of calves was removed from pasture on February 5. On February 5, 12 new steer calves (initial BW = 217 ±'1.18 kg) were stocked on each of all 8 pastures (2.5 steers/ha) and were removed on April 30 (84 d). During the fall 84-d grazing period, the 4 unused pastures were grazed in a different experiment using stocking rates similar to pastures that were used in the present experiment. Half of the pastures were randomly selected in the fall and spring grazing periods and calves were offered a free-choice mineral supplement (Wheat Pasture Pro; Land O Lakes Purina Feed, LLC; Saint Paul, MN) in ground-type mineral feeders (Sioux Steel Company; Sioux City, SD). The mineral mixture used contained 15 to 17% Ca and 4% P from CaCO3 and Ca2PO4, 5.5% Mg from MgO, 18.5 to 22.0% NaCl, 220,500 IU of vitamin A/kg, and trace minerals (1,250 ppm of Mn from MnSO4, 650 ppm of Cu from basic CuCl, 2,185 ppm of Zn from ZnSO4, 22 ppm Se from NaSeO3-, and 65 ppm of I from ethylenediamine dihydroiodide). The other pastures received no salt or supplement of any kind. Mineral feeders were weighed initially then on a weekly basis to determine mineral intake.

Technical Abstract: To evaluate the efficacy of mineral supplementing stocker cattle grazing wheat pasture, 2 experiments were conducted. In Exp 1, 72 steer and heifer calves (avg BW = 228 kg) were randomly assigned to 12, 4.9-ha pastures on November 12 at 1.2 calves/ha (4 pastures), and February 5 at 2.5 calves/ha (8 pastures) for 84-d. In Exp 2, 38 steers (avg BW = 248 kg) were randomly assigned to 12, 2.5-ha wheat pastures on February 24 for 84 d at 2.4 steers/ha. In Exp 2, pastures were planted with either conventional tillage or a no-till drill. In Exp 1 and 2, half the pastures received a free-choice mineral mixture (Wheat Pasture Pro; Land O Lakes Purina Feed, LLC; St. Paul, MN; Ca, 16% and P, 4%) provided in ground-type mineral feeders (Exp 1: completely random design; Exp 2: 2 x 2 factorial); feeders were weighed weekly to determine intake. All pastures were drilled the first of September 2008 (67 kg of seed/ha) and were fertilized with 50 kg of urea-N/ha. Standing herbage DM was determined in each pasture every weigh date by clipping wheat to the ground along 122 cm of drill row at 10 transects. Data were analyzed by AOV with treatment as the fixed effect and pasture as the random effect. In Exp 1, cattle offered the minerals had a 45% faster ADG (P < 0.01; 0.75 kg) than cattle not offered minerals (0.52 kg); hence, the supplemented cattle weighed 8% more (P < 0.01; 308 kg) after grazing than non-supplemented cattle (289 kg). In Exp 2, supplementation did not interact (P > 0.43) with tillage. Also, steers offered the mineral had a 30% faster ADG (P = 0.03; 1.12 kg) than steers not offered minerals (0.86 kg) and the supplemented cattle weighed 6% more (P = 0.03; 341 kg) after grazing than non-supplemented cattle (320 kg). In both experiments, daily standing herbage DM averaged 1,536 kg/animal and never differed (P > 0.12) between treatments. Mineral intakes averaged 73 (Exp 1) and 168 (Exp 2) g/d, resulting in a cost of supplement to kilogram of added BW gain conversions of $0.26 and $0.64 assuming a mineral cost of $0.88/kg. Overall, there was an improvement in ADG and the supplement to added BW gain conversion seemed profitable.