Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/12/1999
Publication Date: N/A
Citation: Interpretive Summary: A variety of production strategies have been introduced for ruminant animals with the main focus on their ability to increase lean tissue accretion and decrease fat deposition. Energy source of the diet (alfalfa- pasture vs restricted-fed all-concentrate in combination with ionophore supplementation (ingredients to alter ruminal fermentation) were investigated for their potential effects on enhancing lamb growth and performance. When energy and protein intake is equalized for both feed sources (i.e., forage vs concentrate) diet alone had a major influence on visceral organ mass and carcass tissues components. Resulting increases in energy and protein requirements by visceral and carcass tissues in lambs grazed alfalfa (forage) may explain the differences observed between forage vs concentrate diets. Ionophore supplementation had very little influence on growth and performance.
Technical Abstract: In Exp. 1, 72 Targhee lambs (initial BW 22.1 kg) were used to determine the effects of energy source (alfalfa pasture vs limit-fed, all concentrate) and ionophore addition on performance, visceral organ mass, and carcass characteristics. There were no differences in ADG or gain/feed due to ionophore supplementation. Lambs that grazed alfalfa had greater liver, omasum, abomasum, small intestine, cecum, and large intestine weights than did lambs fed the concentrate diet. Lambs fed the concentrate diet had greater hot carcass weights, larger loin eye areas, and greater dressing percentages than lambs that grazed alfalfa. In Exp. 2, lambs offered the concentrate diet had greater DM and OM digestibilities than lambs offered alfalfa (89.5 and 91.1 vs 72.4 and 74.2 percent, respectively). Apparent and true N digestiblities were greater for the concentrate diet than for alfalfa (90.9 and 101.7 vs 77.7 and 91.9 percent, respectively). Likewise, grams of N retained per day were twice as great with the concentrate diet than with alfalfa (14.9 vs 6.0 g/d). The greater visceral organ mass and resulting increases in energy and protein requirements in lambs that grazed alfalfa were probably responsible for the lesser hot carcass weight and dressing percentage compared with lambs fed 100 percent concentrate.