Influence of Dietary Protein Source and Level on Histological Properties of Muscle and Adipose Tissue of Lambs

The muscle and adipose tissue histological properties in wether and ewe lambs of Gentile di Puglia breed, fed diets including two protein sources [soybean meal (SB) and SB plus distillers dried grain with solubles (DD)] and three protein levels (12.5, 15.7, and 18.9%) were evaluated. Muscle samples were collected from the longissimus/rump, cut, and stained (reciprocal aerobic and anaerobic stains) for muscle fiber typing and fat cell characterization. Fibers were classified as alpha-red, beta-red, and alpha-white. Lambs fed SB had larger alpha-white (p < 0.10) and smaller-diameter beta-red and alpha-red fibers (p < 0.05). Among dietary protein levels, lambs fed 12.5% protein exhibited the highest percentage of alpha-red and the greatest diameter of alpha-white fibers, whereas wethers had a higher percentage of alpha-red (p < 0.05), and ewes had a higher percentage of alpha-white fibers (p < 0.05). Intramuscular fat cells were larger (p < 0.10) in ewes than in wethers. Lambs in the group fed 12.5% protein had larger subcutaneous fat cells at the sacral vertebrae location. Overall, both sources and levels of dietary protein had significant effects on lamb muscle and fat histological features, suggesting the potential of modulating muscle or fiber types through dietary protein strategies.