Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/1999
Publication Date: N/A
Citation: Interpretive Summary: Today's consumers are demanding leaner meat products because of perceptions that fat consumption leads to health problems. The type of feeding system, especially the finishing system used for ruminant animals, has been shown to affect the time required for finishing ruminants as well as the efficiency of feed utilization by the animal. This study evaluated either (1)finishing lambs on grain with an anabolic implant as an adjunct to promote any additional lean tissue accretion without increasing fat accretion or (2) forage grazing as the finishing phase after concentrate feeding. Finishing lambs on alfalfa forage after concentrate feeding reduced fat accretion by 25 percent without decreasing lean accretion. The use of trenbolone acetate implants while finishing lambs on a concentrate diet increased body weight gain and lean tissue accretion (100 percent) without affecting fat accretion. Data support the idea that animal feeding systems that use inherent biological functions relative to growth can enhance lean meat production.
Technical Abstract: Targhee x Hampshire lambs (average BW 23 kg) were used in two experiments to determine the effects of finishing on concentrate with an anabolic implant or forage grazing after concentrate feeding on growth, organ and viscera weights, and carcass tissue accretion. In Exp. 1 and 2 lambs were penned by sex and assigned for slaughter at initial (23 kg), intermediate (37 kg), or end BW (ewes, 47.7; wethers 50.4 kg). From 23 to 37 kg BW, lambs were fed all-concentrate diets in drylot (DL) or grazed on alfalfa (ALF). Experiment 1 was a 2x2 factorial with 28 lambs; factors were wether vs ewe lambs and unimplanted vs DL implanted with trenbolone acetate-estradiol benzoate. 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 implanted than for unimplanted wethers. Ewes did not respond to the implant. Fat accretion was not affected by implantation. Experiment 2 was a 2x3 factorial with 42 lambs; factors were wether vs ewe lambs and drylot during growing and finishing phases (DL-DL) vs drylot during growing and alfalfa grazing during finishing (DL-ALF) vs alfalfa grazing during growing and finishing phases (ALF-ALF). In Exp. 2, ADG of DL-DL lambs was greater (P<.01) than ADG of DL-ALF or ALF-ALF lambs. In Exp. 2, DL-ALF and ALF-ALF lambs had overall hindsaddle lean gain equal to those on DL-DL with less mesenteric fat and 100 g less separable fat. Finishing lambs on alfalfa reduced fat accretion without decreasing lean accretion, whereas trenbolone acetate implants for lambs fed concentrate increased BW gain and lean accretion without affecting fat accretion.