Effect of different dietary energy on collagen accumulation in skeletal muscle of ram lambs1

Tenderness is one of the most appreciated characteristics of meat quality. The objective of this trial was to investigate the effect of different energy diets on collagen deposition and meat tenderness. Twelve one-half Dorper × one-half small thin-tailed sheep crossed ram lambs (20 ± 0.5 kg of BW) were randomly selected and divided into 2 groups in a completely randomized design. Animals were offered identical diets at 100 or 65% of ad libitum intake. Lambs were euthanized when BW in the ad libitum group reached 35 kg, and the semitendinosus (ST) muscle were sampled. The results showed that Warner–Bratzler shear force (WBSF) was significantly increased when lambs were fed an energy-restricted diet (P < 0.05). Masson trichrome stain and hydroxyproline assay demonstrated increased collagen content in ST muscle of feed restriction lambs. Both collagen I and fibronectin mRNA contents were significantly increased when lambs were fed an energy-restricted diet (P < 0.05), whereas no difference for collagen III mRNA expression was observed (P > 0.05). Expression of prolyl 4-hydroxylase α (P4HA) was greater in the feed restriction group (P < 0.01), and no differences were observed for both lysyl oxidase (LO) and lysyl hydroxylase 2b (LH2b) mRNA contents (P > 0.05). In addition, matrix metalloproteinase 1, 2, 9, and 13 (MMP1, MMP2, MMP9, and MMP13) did not change with the feed restriction, whereas both tissue inhibitor of matrix metalloproteinase 1 and 2 (TIMP1 and TIMP2) were increased. Feed restriction did not alter TGF-β and SMAD protein contents, but phosphor-p38 protein content was elevated. In summary, feed restriction enhanced collagen accumulation in ST muscle, which may negatively affect the lamb tenderness, and was associated with the upregulated p38 signaling pathway.