Abstract: Thirty-two crossbreed heifers (246�10 kg) were used in 98 day feedlot growth performance trial to evaluate the effect of ovariectomization (intact vs. spayed) and feeding system (energy intake) on growth performance and carcass characteristics. Treatments were: Ovariectomized heifers fed a 2.16 Mcal NEm kg 1 of diet throughout the 98 day trial (OVX- HHS); ovariectomized heifers fed a 1.72 Mcal NEm kg 1 of diet during first 70 day and then switched to a 2.16 Mcal Nem kg 1 of diet for the remaining 28 day (OVX-LHS); intact heifers fed a 2.16 Mcal NEm kg 1 of diet throughout the 98 day trial (INTC-HHS) and intact heifers fed a 1.72 Mcal Nem kg 1 of diet during first 70 day and then switched to 2.16 Mcal Nem kg 1 of diet for the remaining 28 day (INTC-LHS). There were no interactions (p>0.20) between spaying and feeding system on feedlot performance. Spaying did not affect DMI (p>0.20). However, it increased (p<0.10) ADG (12.3%), feed efficiency (6.3%), dietary NEm (5%) and NEg (6%). The increase in dietary NE due to spaying reflects a reduced maintenance energy requirement and/or leaner gain. Dry matter intake was lower (12.5%, p<0.01), but ADG (p<0.10) and feed efficiency (22.6%, p<0.01) were greater for HHS than for LHS feeding system. There were no treatment effects on carcass characteristics were detected. Spaying implanted beef heifers enhances feedlot growth-performance. This effect is not influenced by dietary energy density.
A. Plascencia , R.M. Valenzuela , A. Barreras , M. Cervantes , V.M. Gonzalez and R.A. Zinn , 2008. Influence of Ovariectomization (Spaying) and Feeding System on Performance and Carcass Characteristics of Implanted Beef Heifers. Journal of Animal and Veterinary Advances, 7: 354-358.