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Feedlot Performance of Hysterectomized and Ovariectomized Heifers¹

Washington State University, Pullman 99164

Abstract

Seventy-five crossbred heifers (mean weight 304 kg) were stratified by weight and source and placed in eight pens. Four duplicate treatments were randomly assigned to pens as follows: (1) intact-control (n = 19), (2) intact + melengestrol acetate (MGA, n = 20), (3) hysterectomy (n = 17) and (4) ovariectomy (OVX, n = 19). All heifers were preconditioned for 2 mo before beginning the finishing study. Surgery was performed through a high lumbar incision approximately 3 wk before the finishing study began. Group 2 heifers were fed .4 mg·head^–1 · d^–1 MGA. Blood samples were collected at 28-d intervals throughout the 112-d finishing phase. Ovaries were collected at slaughter and carcass data were obtained 24 h after slaughter. On d 112, progesterone was higher (P<.05) in hysterectomized heifers than in other treatment groups. Serum progesterone concentration was nondetectable (<.35 ng/ml) in OVX and MGA heifers. There were no differences (P>.05) in feed efficiency or carcass characteristics among the four treatments. Hysterectomized and MGA heifers had similar (P>.05) average daily gains, which were higher (P<.15) than control and OVX heifers. These data suggest that the elevated levels of progesterone from the maintained corpora lutea and the subsequent absence of estrous activity in the hysterectomized heifers are advantageous for promoting growth in feedlot heifers.

¹ Scientific Paper No. 6640 College of Agriculture Research Center, Washington State Univ., Pullman. Project 0137.

² The authors acknowledge the Washington Beef Commission for funding this project; Dr. Colin Campbell and the Upjohn Co., for supplying MGA; Dr. A. Belanger for progesterone anti-serum; and Dr. E. L. Martin, Orvil Sears, and Milt Russell for their assistance in data collection.

³ Reprint requests; Dept. of Anim. Sci.