عنوان مقاله [English]
Introduction: Compensatory growth is actually a physiological process in which the animal's potential, after a period of dietary restriction, can be exploited to increase growth and growth efficiency during the free feeding period (Hornick et al 2000). Compensatory growth is widely used today in various countries. Another specific management approach (short-term strategies) in lamb fattening is appropriate weight at the beginning of fattening (Santos Silva et al 2002). The benefits of applying a compensatory growth mechanism during the breeding period can be improved feed efficiency during the compensatory growth period (Abouhif et al 2013 and Sami et al 2016), reduced feed cost throughout the breeding period, also improved weight gain during the breeding period (Clark et al 2007; Abuhif et a l 2015) and reduced energy maintenance needs (Kamalzadeh et al 2009; Shadnosh et al 2011). 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.This study was conducted to investigate the effect of different weight start of feed restriction on growth performance and carcass lambs traits Lori breed lambs.
Material and methods: Fifty four male Lori lambs with a mean live weight of 26 kg were selected for the experiment. Treatments were consisted of 6 feed restriction treatments (60,80%) and ad libitum(fattening diet without restriction) for two weights (30 and 35 kg). At the beginning of expriment, 54 experimental lambs were fed the same diet.After a 14 day pre-feed restriction period, a group of 27 individuals that had reached an average weight of 30 kg were separated from the rest and subjected to feed restraint treatments. The remaining 27 lambs were fed the former diet for 35 days until reaching a weight of 35 kg. Upon reaching this group, an average of 35 kg dietary restriction was applied.The feed restriction period for both groups was 30 and 35 kg for 35 days. Then the 30 kg group for 49 days and the 35 kg group for 28 days until the end of the fattening period were re-fed the control diet (fattening ration without restriction and ad libitum). 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. Analysis were done by repeated measurements basis on a completely randomized design with a mixed model procedure. Comparison of mean treatments was performed by Tukey test. The statistical model was as follows:Yijk= μ + Ti+ Dk + Aij+ (T*D)ik + εijk.
Results and discussion: The results of Table 2 showed that the effect of the experimental diets had no significant effect on all the traits of lambs weighing 30 and 35 kg over the pre-feed restriction period. 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 (30 and 35kg) with 60 and 80% feed restriction groups. In the present study, at the beginning of the re-feeding period in the respective treatments, the daily weight gain in the feed restriction treatments was significantly higher than the control groups at 30 and 35 kg. 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, there was observed no significant difference between control and restriction groups. During the re-feeding period, feed conversion ratio was lower in feed restriction treatments compared to control treatment (30 and 35 kg). Compensated feeding reduced FCR in lambs with prior feed restriction compared to control. The results showed that feed efficiency and feed intake needed to maintain live weight are affected by the animal feeding program. Results of physical composition of carcass during re-feeding showed that the average of most carcass traits in the control treatment (30 and 35kg) and 80% of feed restriction treatment for 30kg lambs had no significant difference and were higher than other groups. Also in the compensatory growth experiment, there was no significant difference between the number of empty body weight, hot carcass and cold carcass weight sa well as dressing percentage due to no difference in the final live weight between the 30 and 35 kg control groups with 80% feed intake. Another study in other ruminants was consistent with feed restriction and compensatory growth.Meanwhile, the fat tail weight and percentage and total carcass fat were higher in the control treatment (30 and 35kg) than in all control groups. The results showed that the percentage of carcass lean meat in the compensatory groups was higher than the control treatments. This study showed that lambs with 80% feed restriction for 30kg lambs due to higher weight gain and FCR 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.