Effect of replacing urea with fish meal in finishing diet on performance of Awassi lamb under heat stress

An in situ trial and a finishing trial were conducted to evaluate replacing urea (U) with fish meal (FM) in finishing lamb diet. Three ruminally canulated Awassi ram lambs were used in situ trial to determine rumen undegraded intake protein (UIP) of U and FM containing diets fed to lambs in finishing trial. Twenty Awassi lambs (3-4 month old) were randomly allotted to dietary treatments into equal numbers for each diet containing either U or FM as a supplemental protein source in a completely randomized design. In finishing trial, diets were available on an ad libitum basis (105% of actual intake) during 60 d under heat stress condition (average daily temperature 31.6 °C with lowest 24.4 °C and highest 38.3 °C). According to in situ trial, UIP value of urea and fish meal diets were determined 2.70 and 6.18% of DM diet, respectively. In finishing trial, replacing U with FM in diet increased average daily gain (0.236 kg/d versus 0.268 kg/d; P = 0.05). DMI of lambs was not affected by the protein source (P < 0.05). Feed efficiency (kg gain/kg DMI) was better (0.226 kg/d versus 0.252 kg/d) for FM containing diets for only the first 40 d of trial (P = 0.03). Dietary protein source did not alter rectal body temperature, blood glucose, urea, and total protein levels (P > 0.05). As a result, UIP source of FM can improve the finishing performance of Awassi lambs especially first 40 d of the finishing period under heat stress.