Effect of short-term dietary protein restriction before slaughter on meat quality and skeletal muscle metabolomic profile in culled ewes

•The effect of dietary protein restriction on meat quality was evaluated in ewes.•The tenderness of meat aged for 1 and 7 days decreased with protein restriction.•Ewes subjected to protein restriction require more time for meat tenderization.•Collagen content increased in meat in response to dietary protein restriction.•The muscle valine and asparagine content reduced with dietary protein restriction. Tenderness is one of the most important meat quality traits. It has been suggested that a short-term dietary protein restriction prior to slaughter could change muscle protein turnover and improve meat tenderness without affecting animal performance. Therefore, the aim of this study was to evaluate the effect of a short-term dietary protein restriction in the end of the finishing phase on skeletal muscle metabolome and meat quality traits of culled ewes. Fourteen crossbred ewes (3 years of age) averaging 39.3 ± 9.4 kg of body weight (BW) were enrolled in this study. Culled ewes were grouped (n = 7) and randomly assigned to one of the following treatments, consisting of: continuously fed the control diet with 13.3% of crude protein (CTRL); fed the control diet to reach the target body weight (45 kg) followed by 14 days feeding a low protein diet (4.33% crude protein; STR). The experiment lasted 46 days. Short-term dietary protein restriction increased meat shear-force at 1 day postmortem (3.67 vs. 3.02 kgf; P = 0.04), which could be partially explained by the higher total collagen content (P = 0.02) in STR compared to CTRL group (2.35 vs. 2.05 mg/g). The protein restriction did not affect final body weight nor carcass weight (P > 0.05), but decreased backfat thickness (3.19 vs. 5.10 mm; P = 0.04). Excreted and retained nitrogen were respectively 80.4% and 70% lower in STR (P < 0.01) than in the CTRL group. A lower abundance of valine (P = 0.02) and asparagine (P = 0.01) was observed in skeletal muscle of STR ewes compared to the CTRL group. Of the muscle metabolites identified, progesterone, succinic acid, and tartronic acid were positively correlated with meat shear-force (toughness), while lysine was negatively correlated (P < 0.05) with the same trait. Collectively, our data shows that despite the changes observed in the skeletal muscle for the abundance of metabolites involved in energy and protein metabolism, the short-term dietary protein restriction near maintenance level prior to slaughter did not improve quality of ewes’ meat quality traits.