Effect of physical restriction of feed and re-feeding on growth performance, carcass characteristics and chemical composition of Lori lambs

Compensatory growth is the overweight that is achieved by providing the animal with access to adequate food after a period of nutritional restriction. Therefore, a livestock that is affected by a period of feed restriction after re-feeding, especially at the beginning of this period, has less maintenance requirements compared to a livestock that has not been affected by the feed restriction period. Considering the feedlot of 320,000 fattening lambs in Lorestan province per year and the possibility of using feed restriction to promote the use of compensatory growth in lamb fattening, the project was carried out aims to investigate the possibility of process changing the growth rate, fattening and physical and chemical composition of carcass lambs Lori breed by short-term strategies of feed restriction.

Twenty male Lori lambs with a mean live weight of 30±1.45 kg were selected for the experiment. The four experimental diets included 1) the control group (fattening diet without restriction and ad libitum); 2) 80% ad libitum group 3) 70% ad libitum group 4) 60% ad libitum group. At the end of experiment, daily weight gain, final weight, feed conversion ratio, feed efficiency and feed intake were calculated and then three lambs were slathered from each treatment. Carcass characteristics were calculated with the cost of production per kg of weight gain, carcass and lean meat. Percentage of dry matter, ash, crude fat and crude protein were determined for meat chemical composition. Performance data, carcass traits and chemical composition of carcass were completely randomized design with four replications (each replication including six lambs and three for carcass traits and carcass chemical composition) by analysis of covariance means of mixed model procedure. Comparison of mean treatments was performed by Tukey test.

Results showed that there were significant difference between the final weight of lambs at the end of feed restriction period (p < 0.05). At the end of the re-feeding, no significant differences were observed among the control treatment with 70% and 80% feed restriction groups (P>0.05). There were significant difference among intake dry matter of lambs at the end of feed restriction period (p < 0.05). At the end of compensatory growth, no significant difference was observed between control and restraint groups. During the re-feeding period, feed conversion ratio was lower in feed restraint treatments compared to control treatment. Feed efficiency was similar to feed conversion during feed restriction and re-feeding period in the experimental groups. Results of physical composition of carcass during re-feeding showed that the average of most carcass traits in control and 80% of feed restriction treatments had no significant difference and were higher than 70 and 60% of feed restriction. Meanwhile, the fat tail weight and percentage and total carcass fat were higher in the control group than in all control groups. The results showed that the percentage of cold carcass lean meat in the compensatory groups was higher than the control treatment. Percentage of carcass chemicals in feed restriction period showed that dry matter, percentage of crude protein and fat in control treatment were higher than feed restriction treatments and there were significant difference among treatments (P <0.05). The percentage of crude protein in the re-feeding period was higher than the control group.

This study showed that lambs with 80% restriction of feed due to higher weight gain, feed conversion ratio were more favorable in terms of fattening condition than control lambs who consumed feed during whole period. Also, this treatment was the total carcass fat percentage lower and lean meat higher and ultimately, the production costs per kg carcass and lean meat were lower than other treatments.