Effects of feed restriction on performance, diet digestibility, blood metabolites and slaughter characteristics in fattening Sanjabi male lambs

Compensatory growth is usually considered as an integral part of studies on feed restriction and there is little information about ruminant’s fattening performance under continuous long term feed restriction (throughout all fattening period), especially in high concentrate diets. The aims of this study were, therefore, to evaluate the effects of quantitative feed restriction on growth performance, serum metabolites concentration, diet chemical components digestibility and the weights of offal components in male Sanjabi lambs. This study was conducted based on a completely randomized design, including three treatments and seven replicates using 21 male Sanjabi lambs (90±9 days old; 29.5±3.25 kg). Experimental diet was formulated based on NRC (2007) recommendations. After weaning, lambs were randomly distributed between 3 treatments. Treatments were: 1) ad libitum consumption of diet throughout the fattening period (control); 2) restricted feeding at 90 % of ad libitum intake, and 3) restricted feeding at 80 % of ad libitum intake throughout the fattening period. The amount of feed consumption for each lamb was recorded daily and body weight gain and feed conversion ratio were recorded and calculated triweekly. To Blood samples were collected from jugular vein at days 1, 42 and 84 to measurement serum metabolites concentration. The digestibility of diet’s chemical components was determined using acid-insoluble ash marker. Upon completion of the 84-day recording period, 4 lambs from each treatment were slaughtered and weights of noncarcass components and carcass percentage were measured. Average daily weight gain decreased significantly and in a linear manner by reduction in feed intake level (P<0.01) and feed conversion ratio did not affect by feed restriction. Body and empty body weights, hot carcass weight and weights of head, fat tail, kidneys, omental fat and empty gastrointestinal tract reduced significantly by 20% reducing in feed consumption comparison to lambs in control group (P<0.05). With the exception of significant decrease in serum insulin and glucose concentrations (P<0.05), feed restriction had no significant effect on concentration of other measured blood serum metabolites including total protein, creatinine, urea, cholesterol, non-esterified fatty acids and also thyroxine and triiodothyronine hormones. Digestibility of dry matter and other diet chemical ingredients, regardless significant reduce in ether extract digestibility (P<0.05), were not affected by restricting feed consumption. Results showed that slight feed restriction caused downfall in fattening male lambs growth performance. Thus, restriction the feed offered to fattening lambs during the total fattening period is not recommended.