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Implanting Young Bulls with Zeranol from Birth to Four Slaughter Ages: I. Live Measurements, Behavior, Masculinity and Carcass Characteristics^{1, 2,}

Kansas State University, Manhattan 66506

Abstract

Seventy-two Simmental bull calves were allotted randomly at birth to either a zeranol (Ralgro®) implanted (I) treatment or a nonimplanted control (C) group. At birth, bulls assigned to the I treatment were implanted with 36 mg of zeranol and reimplanted at average intervals of 84 d until slaughter. Calves were weaned at 7.2 mo, preconditioned for 2 wk, and randomly assigned by treatment to slaughter ages of 12.0, 13.8, 15.7 and 17.4 mo and fed an 83% concentrate diet until slaughter. At 7.7 mo and all slaughter ages, live weights and hip heights were similar (P>.10), but I bulls had lower (P<.05) masculinity scores than C bulls. Scrotal circumferences for I bulls were smaller (P<.05) at 7.7, 12.0, 13.8 and 15.7 mo, but similar (P>.10) at 17.4 mo to C bulls. Behavioral observations of passive bunting, mounting attempts, facility rubbing and overall activity were less (P<.05) for I bulls than C bulls from 12.0 to 13.8 mo but similar (P>.10) from 13.8 to 17.4 mo. Aggressive bunting was less (P<.05) for I bulls during five of the seven observation times for the 12.0-to-13.8-mo period only. Slaughter and carcass weights and dressing percentages were similar (P>.10) for I and C bulls. Skeletal maturity and marbling scores, fat thicknesses, yield grades and 9-10-1 lth rib fat percentages were higher (P<.05) and lean maturities, forehead hide weights, high dermis thicknesses, femur measurements and 9-10-1 lth rib bone weights and percentages were lower (P<.05) for I than C bulls. Rib eye areas and carcass masculinity traits of jump muscle and crest of I bulls were less (P<.05) at 13.8 mo but reached similar (P>.10) development to C bulls at 15.7 mo. Testicle weights of I bulls were lighter (P<.05) at 12.0, 13.8 and 15.7 mo, but similar (P>.10) to C bulls at 17.4 mo. Growth traits (all weights plus hide and femur measurements) and maturation traits (skeletal and lean maturities, marbling scores, fat thicknesses and pizzle eye sizes) increased the most from 12.0 to 13.8 mo and 13.8 to 15.7 mo, respectively. We concluded that implanting young bulls with zeranol from birth to slaughter had minimal effects on live measurements, improved carcass desirability and delayed masculinity and behavioral development.

¹ Contribution No. 85-442-J, Dept. of Anim. Sci. and Ind., Kansas Agr. Exp. Sta., Manhattan 66506.

² The authors are grateful to Ecco Ranch, Buffalo, KS for their cooperation in this research.

³ Present address: Coop. Ext. Serv., Washington State Univ., Pullman 99164-6230.

⁴ Present address: Dept. of Anim. and Range Sci., Montana State Univ., Bozeman 59715.