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Effect of Intravaginal Devices¹ and Synovex-H Implants on Feedlot Performance, Cyclic Activity and Reproductive Tract Characteristics of Beef Heifers^,2

South Dakota State University, Brookings 57007

Abstract

Ninety-six yearling Hereford heifers ( = 232 ± 3 kg) were stratified on the basis of weight and then allotted randomly within weight groups into 16 pens of six each. Treatments were Hei-Gro® (deviced or nondeviced; HG), Synovex-H® (implanted or nonimplanted) and location in the feedlot relative to steers (isolated or nonisolated) imposed in a 2 x 2 x 2 factorial design with two replicates. During the growing phase, estrous activity was monitored by weekly rectal palpation of the reproductive tract of three heifers from each pen. Incidence of standing estrus, as determined by daily visual observation, was recorded for the first 21 d of the finishing phase. Heifers implanted with Synovex showed higher (P<.05) average daily gains and final shrunk weights than nonimplanted heifers during the growing phase. Synovex also resulted in increased (P<.05) weight gain during the finishing phase and produced heavier (P<.05) hot carcass weights. HG did not significantly (P>.05) affect any performance traits reported. Synovex or HG treatments had no effect on estrous activity of the heifers. Location significantly (P = .05) affected estrous activity during the finishing phase. HG caused reproductive tract scarring and infection (P<.01). Heifers treated with the HG + Synovex combination had more severe (P<.05) infection than those treated with HG alone. Heifers not isolated from steers had larger (P<.05) ovaries than isolated heifers, although no difference (P>.05) was found in ovarian weight.

¹ Hei-Gro®, devices supplied through the courtesy of Agrophysics, Inc., San Francisco, CA.

² Published with the approval of the Director of the South Dakota Agr. Exp. Sta. as Pub. No. 1699 of the Journal Ser.

³ Present address: Mauston, WI.

⁴ Dept. of Anim. Sci.