Rate, Composition and Efficiency of Growth in Feedlot Steers Reimplanted with Growth Stimulants

Abstract

Eighty Charolais-cross steer calves (283 kg) were fed a moderately high-energy (2.89 Mcal ME/kg) diet for 189 d to examine the effects of reimplantation of 36 mg of zeranol (Ralgro) or 200 mg progesterone plus 20 mg estradiol benzoate (Synovex-S) on the rate, composition and efficiency of gain, skeletal size and carcass parameters in a comparative slaughter trial. The implant treatments included unimplanted controls (C), Ralgro initially (R1), Synovex-S initially (S1), Ralgro initially and a reimplant at 84 d (R2) and Synovex-S initially and a reimplant at 84 d (S2). Both implants increased (P less than .06) gains by 8.1% from 0 to 84 d. Ralgro and Synovex-S increased (P less than .01) daily gains by 11.5% and 25.2%, respectively, from 84 to 189 d. The duration of the response to a single implant appeared to be in excess of 140 d; thus, reimplantation did not further increase daily gains. Reimplantation did improve (P less than .05) feed utilization in Ralgro implanted steers, however. Ralgro and Synovex-S increased (P less than .01) the rate of empty body (EB) protein accretion by 14.1% and 24%, respectively, without affecting EB fat growth. The efficiency of protein gain per unit protein (P less than .05) or energy intake (P less than .04) was improved, but the efficiency of energy gain per unit energy intake was not affected by implantation. Carcass weights of implanted steers were 5% greater (P less than .04) when adjusted to an equal carcass fatness. Both growth stimulants increased hip height (P less than .02), wither height (P less than .08) and body length (P less than .08) over C steers at slaughter.

The effects of implant strategy on finished body weight of beef cattle

“…This study confirms that anabolic implants increase mature body size of steers as reported by Preston (1978), Loy et al (1988), and Owens et al (1995) and increase BW at a common grade or body composition (Preston et al, 1990). In agreement with our results, Preston et al (1990) concluded that implanted steers should be harvested at 39.5 kg heavier BW and im-…”

Alterations in metacarpal characteristics in steers and heifers sequentially implanted with Synovex from 45 days of birth.

“…In our experiment carcass weight of steers was increased similarly to that reported by Apple et al (199 l ) , but our results indicate that the increase in carcass weight of steers was not associated with an increase in longissimus muscle area. In support of our data, Loy et al (1988) reported two implants of Synovex-S increased steer carcass weight 17.9 kg compared with controls but did not alter longissimus muscle area. It is of interest that the response in heifer carcass weight and longissimus muscle area observed in the current trial is more similar to that observed in steers receiving estradiol + progesterone + trenbolone acetate than to that in steers receiving estradiol + progesterone.…”

“…While in the feedlot (Period 41, implanted calves gained weight at a greater rate ( P c .01) in the first two 28-d periods and tended to gain weight at a greater rate in the third 28-d period ( P = .09) and in the final 40-d period ( P = .12) ( Table 5). Reimplantation with anabolic growth promoters in the feedlot has been effective in increasing calf performance in some studies (Owens et al, 1980;Laudert and Davis, 1983) but has resulted in no additional response in others (Rumsey et al, 1984;Loy et al, 1988). The present data suggest that the response in ADG from implant administered on d 0 of Period 4 had expired by d 56.…”

“…(199 1 1, who reported four implants of trenbolone acetate increased both shoulder and wither height in Hereford x Freisien heifers at slaughter, or with Loy et al (19881, who reported steers treated with one or two implants of zeranol or Synovex-S had slightly greater wither height and body length than nonimplanted controls. However, increases in hip height due to steroid implants are generally small compared to increases in body weight (Loy et al, 1988). Table 4 presents least squares means of live weight for implanted and nonimplanted steers and heifers.…”

Effect of repeated implants of oestradiol-17β on beef palatability in Brahman and Braham cross steers finished to different market end points

“…What was of note in the present study was that repeated implants of oestradiol did not cause further decreases in marbling score. This was in contrast to Mader et al (1985) and Loy et al (1988) who reported that repeated implantation with low-potency oestrogenic implants resulted in further decreases in marbling, compared with a single implant. A point of difference may be that in the present study the old implants were removed as new ones were inserted into the ear, which would have resulted in a more constant delivery of oestradiol to the animal compared with programs that simply reimplanted.…”