Influence of dietary slow‐release urea on growth performance, organ development and serum biochemical parameters of mutton sheep

Summary Eighty Dorper × thin‐tailed Han cross‐bred non‐castrated male lambs [mean body weight ( BW ), 25.87 ± 1.06 kg] were randomly allocated to one of five different concentrations of slow‐release urea (urea phosphate, UP ). The feed consisted of an equal amount of concentrate diet and roughage; the concentrate feed was formulated to be isoenergetic and isonitrogenic and contained 0%, 1%, 2%, 4% and 8% UP ( UP 0.0, UP 1.0, UP 2.0, UP 4.0 and UP 8.0, respectively) as a replacement for soya bean meal. Feed intake, BW , average daily gain ( ADG ), feed utilisation efficiency ( FUE ), absolute and relative organ weights and biochemical and histopathological parameters were measured. Feed intake, BW , ADG and FUE significantly decreased in the group receiving UP 8.0 (p   <   0.05), but no difference was found among the other groups (p   >   0.05). Quadratic equations were developed between the UP dosage in the concentrate feed and ADG or FUE ( r 2  = 0.973 for ADG and r 2  = 0.761 for FUE ) to determine the appropriate dosage of UP given the desire to maximise either ADG or FUE , the appropriate dosage (feed concentration) was calculated as 2.01% UP to achieve the greatest ADG or 2.13% UP to achieve the best FUE . The relative weight of the liver (% BW ) in the UP 2.0 groups was significantly greater than that of UP 0.0 (p   <   0.05), and the relative weight of the intestine in the UP 8.0 was significantly greater than that of UP 0.0 (p   <   0.05); the relative weight of the carcass, heart, spleen, lung, kidney, rumen, reticulum, omasum and abomasum did not differ among treatments (p   >   0.05). The UP 8.0 treatment significantly increased serum phosphorus levels (p   <   0.05) and decreased the levels of alkaline phosphatase, glucose and calcium (Ca) compared with the lower UP dosage (p   <   0.05). No histopathological differences were found in either hepatic tissues or renal tissues among treatments. Dietary UP as a replacement for soya bean in concentrate feeds for mutton sheep should not exceed 4%, as higher dosing may cause malnutrition and mineral disorders.