Brady Campbell, Program Coordinator, OSU Sheep Team
Marketing lambs at a high lean to fat carcass ratio is important in producing consistent and quality retail lamb products.
Lambs fed high concentrate diets finish at a younger age when compared to forage fed lambs. However, lambs fed high concentrate diets accumulate more carcass fat than lambs on grazed forage diets. The use of either growth promotants or forage finishing diets may provide producers with alternative options to produce lean lambs at similar growth rates and ages when compared to high concentrate-fed feedlot lambs. In order to make these comparisons, two experiments were conducted.
The first experiment compared the effects of implantation (non-implanted vs. implanted) on lamb sex (ewe vs. wether) in a feedlot to determine its effects on lamb performance and carcass characteristics. Results from this experiment showed that when compared to non-implanted wethers, implanted wethers had an increase in BW (114.4 vs. 110.2 lbs.), ADG (1.9 vs 0.8 lbs.), and lean muscle gain (2.9 vs 1.4 lbs.). Interestingly, ewes did not respond to the implant as no differences were reported.
In the second experiment, non-implanted feedlot and pasture housed lambs were used to determine the effect of grazing alfalfa on lamb performance, carcass characteristics, and organ growth of finishing lambs. Lambs were placed into three groups based upon growing and finishing phase diets: lambs grown and finished in a feedlot on a high concentrate diet (FL-FL), lambs grown and finished on an alfalfa pasture (ALF-ALF), or lambs grown in a feedlot on a high concentrate diet and finished on an alfalfa pasture (FL-ALF). Results from this experiment showed that when compared to FL-ALF and ALF-ALF treatment groups, lambs in the FL-FL treatment group had a greater ADG during the finishing phase (0.8 vs. 0.6 – 0.5 lbs.) and cumulative ADG (0.8 vs. 0.6 lbs.). Lambs in the ALF-ALF treatment group had a larger omasum, small intestine, large intestine, and cecum weights when compared to high concentrate grown and finished diets. This information illustrates that forage fed lambs maintenance requirements are greater than those of high concentrate fed lambs due to the need for more energy to maintain a larger digestive system. This explains why those lambs in the FL-FL treatment group exhibited a greater ADG when compared to lambs in the FL-ALF and ALF-ALF treatment groups. During the finishing phase, lambs in the FL-FL treatment group spent fewer days on feed when compared to FL-ALF and ALF-ALF treatment groups. When comparing feeding phase strategies at harvest, lambs in the FL-ALF and ALF-ALF treatment groups yielded less fat when compared to FL-FL treatment groups (1.5 vs. 1.8 lbs.).
Overall, implanted wethers fed a high concentrate diet increased BW, ADG, and lean muscle mass without affecting fat deposition. However, implantation had no effect on ewes fed a high concentrate diet. Lambs grazing alfalfa pastures yielded less carcass fat while maintaining lean mass growth when compared to concentrate fed lambs. Therefore, producers may benefit from implanting wethers in a feedlot setting or finishing lambs on a high protein pasture to finish heavier lambs without increasing carcass fat.
McClure, K. E., M. B. Solomon, and S. C. Loerch. 2000. Body weight and tissue gain in lambs fed an all-concentrate diet and implanted with trenbolone acetate or grazed on alfalfa. J. Anim. Sci. 78: 1117-1124.