Effects of nitrogen source on the performance and feeding behavior of lambs fed a high concentrate diet containing pomegranate peel

Abstract

This experiment was conducted to investigate the effects of protein degradability on the performance, nutrient digestibility, rumen fermentation and behavior of lambs fed diets containing pomegranate peel (PP). Twenty-four male Iranian Arabic lambs (mean ± standard deviation; 16.3 ± 1.3 kg BW) were assigned randomly into four groups of six lambs each in a completely randomized design for 94 days. Treatments were: 1) control diet (CON); 2) diet containing PP with lower Rumen Degradable Nitrogen (RDN) (Soybean meal, PSOY); 3) diet containing PP with higher RDN (Urea, PUREA) and 4) free choice between diet 2 and 3 (PFREE). Forage to concentrate ratio of the diets was 20:80. The final body weight and dry matter intake were unaffected by treatments (P < 0.05), but there was a tendency to lower final body weight in PP groups compared to the CON (P = 0.09). A total replacement of soybean meal with urea negatively affected feed conversion ratio and OM digestibility. Daily weight gain was highest in lambs when offered CON (0.221 kg) and lowest in PUREA (0.182 kg), with lambs receiving PSOY (0.210 kg) and free choice (0.196 kg) having intermediate values. Apparent total tract digestibility of dry matter, organic matter, crude protein and ADF showed a decrease in PP containing diets (P < 0.05). Animals fed by urea containing diet showed higher mean rumen pH, rumen NH3-N concentration and blood urea nitrogen than CON and PSOY. Differences in volatile fatty acids concentrations were limited to valerate, which was lower for PP diets (P < 0.01). Providing lambs with PP diets increased time spent eating (190.7 vs. 166.5 min. d; P < 0.05) and intake per visit (70.5 vs. 50.1 g DM; P < 0.01), however, eating rate (7.56 g of DM/min) remained unchanged among treatments. Similarly, there was an increase (P < 0.01) in rumination and chewing activities with PP diets. In the free-choice treatment, lambs showed an increase in rumination and chewing time compared to the CON and PSOY groups. PP-fed lambs showed lower time spent self-grooming, social behavior, and lying, compared with the CON. The results suggest that in PP containing diets, the replacement of soybean meal with urea can be achieved with some adverse effects on performance, with the feed conversion being improved when free choice was given between protein sources. The inclusion level of 21.0% PP was probably too high for fattening lambs fed by high concentrate diets to ensure optimal growth performance and nutrient digestibility.