Body weight and tissue gain in lambs fed an all-concentrate diet and implanted with trenbolone acetate or grazed on alfalfa

Targhee x Hampshire lambs (average BW 23 +/- 1 kg) were used in two experim ents to determine the effects of finishing on concentrate with an anabolic implant or forage grazing after concentrate feeding on growth,organ and vis cera weights, and carcass tissue accretion. In Exp. 1 and 2 lambs were penn ed by sex and assigned for slaughter at initial (23 kg), intermediate (37 k g), or end BW (ewes, 47.7; wethers 50.4 kg). From 23 to 37 kg BW, lambs wer e fed all-concentrate diets in drylot (DL) or grazed on alfalfa (ALF). Expe riment 1 was a 2 x 2 factorial with 28 lambs; factors were wether vs ewe la mbs and unimplanted vs DL implanted with trenbolone acetate-estradiol benzo ate. There were no differences in organ and viscera weights due to implant status. However, ADG (P < .03) and lean gain (P < .02) were greater for imp lanted than for unimplanted wethers (507 vs 357 g and 1,314 vs 656 g, respe ctively). Ewes did not respond to the implant. Fat accretion was not affect ed by implantation. Experiment 2 was a 2 x 3 factorial with 42 lambs; facto rs were wether vs ewe lambs and drylot during growing and finishing phases (DL-DL) vs drylot during growing and alfalfa grazing during finishing (DL-A LF) vs alfalfa grazing during growing and finishing phases (ALF-ALF). In Ex p. 2, ADG of DL-DL lambs was greater (P < .01) than ADG of DL-ALF or ALF-AL F lambs. Lambs on ALF-ALF had smaller (P < .05) livers and rumen/reticulum weights but heavier (P < .04) kidney, omasum, small and large intestine, an d cecum weights than those on DL. In Exp. 2, DL-ALF and ALF-ALF lambs had o verall hindsaddle lean gain equal to those on DL-DL with less mesenteric fa t and 100 g less separable fat. Finishing lambs on alfalfa reduced fat accr etion without decreasing lean accretion, whereas trenbolone acetate implant s for lambs fed concentrate increased BW gain and lean accretion without af fecting fat accretion.