Growth Performance, Blood Metabolites, Carcass Characteristics and Meat Quality of Lambs Fed Diets Containing Different Energy Levels Supplemented with Rumen-Protected Choline

Simple Summary Simple Summary: Supplementation with rumen-protected choline (RPC) can reduce dietary metabolizable energy (ME) while maintaining optimum performance, thus contributing to reducing production costs by saving grain which is the primary source of energy in the diet. Previous papers have reported on the interaction effects of ME level and RPC supplementation on production outcomes in dairy cattle and growing goats. The objective of this study was to examine the effects of ME level and RPC supplementation on the growth performance, carcass characteristics, meat quality, serum energy, lipid, and protein profiles of Karayaka lambs. In conclusion, the supplementation of RPC at 0 and 5 g/kg did not affect lamb growth performance and carcass characteristics. Given the lack of significant improvements in performance metrics, RPC supplementation would not result in net cost savings. However, it may play a role in modulating nitrogen metabolism under different dietary energy conditions, as indicated by the significant reduction in serum urea-N levels. The results of the current study indicate that there is no benefit to be gained from the supplementation of RPC in the low-energy diet of fattening lambs. Abstract This study aimed to examine the effects of metabolizable energy (ME) level and rumen-protected choline (RPC) supplementation on the growth performance, carcass characteristics, meat quality, serum energy, lipid, and protein profiles of Karayaka lambs. Twenty-eight Karayaka lambs, with an initial body weight (BW) of 26.85 ± 0.26 kg, were randomly assigned (2 × 2 factorial design) to one of four dietary treatments with two levels of ME (optimum: 2750 or low: 2500 kcal ME/kg dry matter) and two levels of RPC (0 or 4 g/d/lamb). Lambs of each group were housed in individual pens. The experiment lasted 66 d, with the first 10 d consisting of acclimation and the next 56 d of the formal experimental period. The data on BW, dietary matter intake (DMI), and serum glucose concentrations confirm that our model successfully induced low energy using 250 kcal/kg less energy than the optimum level. RPC supplementation did not significantly affect average daily DMI, total average daily gain (ADG), or feed conversion ratio (FCR) at any energy level. Additionally, there was no substantial effect on carcass characteristics, meat quality, serum lipids, energy metabolism indicators, and liver function parameters. There was also no interaction effect of RPC × ME on the parameters tested. However, at 56 d into the experiment, the interaction effect of RPC × ME on serum urea-N was highly significant, and RPC supplementation led to lower serum urea-N levels (p = 0.001). These results suggest that while RPC supplementation did not enhance overall performance and carcass characteristics in Karayaka lambs, it may play a role in modulating nitrogen metabolism, as indicated by the significant reduction in serum urea-N levels.