Performance of light vs heavy steers grazing Plains Old World bluestem at three stocking rates

Live weight gains of light and heavy calves grazing Plains Old World bluest em at three stocking rates were Evaluated during the summers of 1997 and 19 98. Initial weights of mixed-breed lightweight steers (LHT) were 141 SD = 1 7 kg (n = 214) in 1997 and 160 SD = 23 kg (n = 193) in 1998. Initial weight s of mixed-breed heavy steers (HWT) were 265 SD = 17 kg (n = 115) in 1997 a nd 248 SD = 13 kg (n = 126) in 1998. Initial stocking rates for both sizes of steers were as follows: light, 392 kg of live weight/ha; moderate, 504 k g of live weight/ha (increased to 616 kg live weight/ha in 1998); and heavy , 840 kg of live weight/ ha. Averaged gain and gain/hectare are reported as stocking rate by steer type within year. Heavy steers had greater ADG than LHT steers during both years. Forage intake, expressed as a percentage of BW, was greater (P = 0.05) for LHT (3.1%) than for HWT (2.8%) calves. Grazi ng time (min/d; 1998 only) was greater (P = 0.05) for LHT (665) than for HW T (624) steers. Forage CP and in vivo digestible organic matter (DOM) were slightly greater (P < 0.05) in pastures grazed by HWT vs LHT cattle. Gain/h ectare was greater (P < 0.05) for LHT than for HWT calves at all three stoc king rates during both years. A linear decline in ADG was observed (P < 0.0 7) as stocking rates increased for HWT steers in 1997 and LHT steers in 199 8. However, ADC; did not decline with increasing stocking rate for LHT calv es during 1997 or HWT calves during 1998. Forage intake was not different a mong stocking rates in either 1997 or 1998. Grazing time was greatest (P < 0.05) for steers in the moderate and heavy stocking rates. Forage in vivo D OM decreased (P < 0.05) as stocking rate increased. Both LHT and HWT steers had lower (P < 0.05) ADG at all three stocking rates during 1998 compared with 1997. Despite lower ADG, LHT steers had greater gain/hectare than HWT steers during tooth 1997 and 1998.