Diet digestibility, nitrogen balance, growth and carcass composition of barbarine lambs as affected by nitrogen source and rosemary residues substitution in concentrate

The study aimed to determine the effect of the inclusion of rosemary residues (RR) associated with two nitrogen sources in the concentrate fed to Barbarine lambs on nutrient digestibility, nitrogen balance, growth and body composition. According to BW, 24 male Barbarine lambs (3 months old, 17.83±2.6 kg) were divided into three groups namely, CON, RRS and RRF. All lambs received 600g of oat hay as a basal feed in addition to 600g each of the standard concentrate for the control group (CON). The concentrate of the CON group was replaced with pellets containing ~30% RR along with either soybean meal or faba-bean as nitrogen supplement in the RRS and RRF groups, respectively. The feeding trial lasted 65 d. Dry matter and CP intakes were similar among groups; however, intake of phenolic compounds and tocopherols was significantly higher for RR groups. Neither the RR intake nor the nitrogen source did change (P>0.05) the digestibility of DM, CP and fibre. Animals were in positive nitrogen balance showing higher values for RRF and RRS than CON group. The final BW, BW gain and conversion rates were similar (P>0.05) for all lambs regardless of the dietary treatment. Consequently, the cost of gain was reduced by the use of RR with both protein sources. The dietary treatments affected neither the final muscle and fat weights nor their daily gains. It is concluded that rosemary residues may substitute the standard concentrate without affecting animal health, resulting in similar performances due to the similar utilization of nutrients and without altering the body composition while reducing the feeding cost.