Supplement level and stocking rate effects on stockers grazing rye-ryegrass pastures.

Level of supplement (SUP) has various associative effects on forage intake, total diet, and performance per animal and unit land area. The objective of this study was to quantify ADG and gain/ha of stockers grazing a mixture of 'Maton' rye and 'TAM-90' of annual ryegrass at 3 stocking rates (STK) and receiving 3 levels of SUP. Stocking rates in a fixed stocking design with two pasture replicates per treatment were 3.7, 5.2, and 7.2 hd/ha based on initial stocker weights of 270 kg/animal (half-Simmental steers and heifers). A ration containing 98% cracked corn plus Rumensin 80, salt, dicalcium phosphate, and dried molasses was group fed daily at 0 (PAS), 0.4% BW (.4BW), and 0.8% BW (.8BW). Stocking was continuous from Dec. 20 to May 17 (148 d). Average daily gain was greatest (P<.01) at 1.5 kg/d from .8 BW, and similar for 0.4 BW and PAS at 1.28 and 1.15 kg/d, respectively. The ADG were similar for calves stocked at 3.7 and 5.2 hd/d, 1.37 and 1.47 kg/d respectively, and both were higher (P<.01) than ADG of 1.05 kg/d at the highest STK of 7.2 hd/ha. The ADG among the nine treatments ranged from 0.51 kg/d from PAS when stocked at 7.2 hd/ha to 1.5 kg/d from .8 BW when stocked at 3.7 hd/ha. The .4 BW SUP level was more efficient (P<.01) at each STK compared to cattle receiving .8 BW. The SUP:extra gain ratios for .4 BW were 4.7:1, 5.4:1, and 10.6:1 when stocked at 7.2, 5.2, and 3.7 hd/ha, respectively; whereas, ratios for .8 BW were 7.2:1, 7.8:1, and 15.9:1, respectively, when stocked at 7.2, 5.2, and 3.7 hd/ha. Gain per animal efficiencies of SUP were maximized at .4 BW at both high and medium stocking rates, and were minimized at .8 BW and low stocking rate. Gain per ha of 543 kg was least on PAS and 7.2 hd/ha, and greatest from .8 BW and medium stocking rate (5.2 hd/ha) at 1083 kg/ha (P<.01). Management strategies for stocking rate and supplementation are uniquely linked to animal weight, animal prices, pasture and supplement costs, ADG, and selling margin. [ABSTRACT FROM AUTHOR]