| Abstract: | Two experiments were conducted to ascertain the effect of active immunization against somatostatin (SRIF) upon beef cattle growth and performance. Upon completion of a 154 d growing-phase immunization study, 26 Charolais crossbred steers remained paired by treatment for an 84 d experiment to determine the effect of active immunization against SRIF in finishing beef cattle. Immunized steers (T; 361 kg) were injected with protein conjugated SRIF at 2 wk intervals over the 84 d period. The 13 control steers (C; 329 kg) were similarly injected with conjugate protein alone. Immunized steers exhibited a 90% greater plasma GH concentration immediately following an arginine challenge than did C steers. Passive immunization failed to produce an increase in plasma GH concentrations of the four C steers selected for immunization. Daily empty body gain was improved 6.1% (P<.10) by immunization and feed efficiency was improved 5.5% (P>.10). Hot carcass weight (HCWT) was greater (P<.10) for T (298 kg) than C (280 kg) steers. Overall means for carcass protein (%) and carcass fat (%) were 14.9 and 31.7, respectively. Immunization had no effect (P>.15) on quality grade, yield grade, ribeye area, kidney pelvic and heart fat or 12th rib fat thickness. In a second study, 70 young, crossbred nursing calves (34 heifers, 36 steers) were used to evaluate the effect of age, sex and booster injection frequency upon response to SRIF immunization. Calves (10 wk old) were assigned to one of three immunization treatments: a placebo injected control (C), triweekly booster injection (3W) and booster injections given on a geometric progression schedule (GP). Immunization failed to produce a detectable antibody titer to SRIF in either sex. Rate of gain was similar (P>.10) among the steer groups and averaged.86 kg/d. Control heifers grew faster (.90 kg/d) than steers and also grew faster (P<.10) than the immunized heifers (.80 kg/d). Actively immunized steers maintained a rate of gain advantage during the finishing phase to produce carcasses similar in composition to those of the control steers. Immunized steers tended to demonstrate a greater GH secretory potential in response to a challenge, yet GH concentrations were not elevated. In an immunization study with young calves, no antibody titer to SRIF was developed and a growth response was not observed. |
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