The effect of different levels of early and late feed restrictions on commercial performance and ascites index in broiler chickens

Growth performance of broiler chickens has been increased mainly due to the genetic progress, improvements of nutrition and controlled environment (Dastar et al. 2014). The increase in growth rate of modern broiler chickens has been associated with certain metabolic disorders such as ascites (Aftab and Khan 2005). These situations most commonly occur in broilers that had ad libitum feed consumption. It seems possible to reduce these problems by using feed restriction. Feed restriction is a technique of feeding where time, duration and amount of feed offering are limited, with expectation that the bird is able to reach the same body weight with ad libitum feeding (Yu and Robinson 1992). In general, feed restriction included of quantitative and qualitative restriction that is in quantitative to limiting the amount of offered daily feed to the birds; whereas, a qualitative restriction is related to nutrient dilution in the diet (Sedghi et al. 2018). Therefore, compensatory growth after feed restriction may have positive effects on feed efficiency and have more economical benefits (Zamani et al. 2013). This experiment was carried out to evaluate the effects of different levels of early and late feed restriction and consequently, compensatory gain, on performance and ascites index in broiler chickens. Total number of 1000 one-day boiler chicks were used in a completely Randomized Design (CRD) and allocated to 8 experimental groups with 5 replicates per each group. Experimental groups included: 1) control group with no feed restriction (con), 2) 8 hours (8 h) daily feed restriction from 9 to 24 days of age (d), 3) 16 h feed restriction from d 9 to 21, 4) 24 h (every other day) feed restriction from d 9 to 18, and other groups: 5) 10 percent (10%) feed restriction, 6) 20% feed restriction, 7) 30% feed restriction, and 8) 40% feed restriction (from d 22 to 35). Feed consumption, body weight, FCR (feed conversion ratio) and EPF (European productivity factor) were measured weekly from 21 to 49 days of age. Blood sampling and sacrificing were carried out at day 49 of age and carcass segments and lactate dehydrogenase (LDH) and hematocrit of blood samples were evaluated. Ascites index as an indicator of cardiac function, was calculated by the cardiac right ventricular mass ratio to sum of the cardiac left ventricular and ventricular septum masses (Julian 1993). All data were analyzed based on a completely randomized design using proc GLM of SAS software and means were compared by Duncan multiple range test. Statistical analysis of 3 weeks of age indicated lower feed intake (FI) and body weight gain in 16 and 24 h feed restriction groups versus control group (p<0.05). There was no substantial difference between group 8 h feed restriction and control group; it seems that in spite of 8 hours feed restriction, birds compensate feed consumption in remained time and this result is in agreement with Mahmood et al. (2007) study. Also, lower feed consumption in these groups led to lower body weight at 3 weeks of age is consistent with Cornejo et al (2007) experiment. Feed intakes were lower in 20, 30 and 40% feed restriction groups at 4 weeks of age and lower in 20 and 40% groups at 5 week of age versus control group (P<0.05) that induced lower body weights than control group; but there was no significant difference in body weight at end of 6 and 7 weeks of age (P>0.05). The lowest total FI was observed in 24h group (P<0.05); whereas, 24 h group had the highest European performance factor (EPF). Though, there were no significant differences among experimental groups in total body weight, feed conversion rate (FCR) and EPF at 49 days of age (P>0.05). In consistent with Jalal and Zakaria (2012), relative liver weights were lower in groups with 24 h and 40% feed restriction than control group (P<0.05); but present study was contradictory regarding relative heart weight with no significant differences among experimental groups. Also, there were no significant differences in carcass traits, hematocrit, LDH and ascites index between experimental groups (P>0.05). Previous studies have expressed feed restriction in broiler chickens led to lower body weight and consequently lower ascites index (Dastar et al. 2014), while that is inconsistent with the present study. it seems that 24 h daily (every other day) feed restriction from 9 to 18 days of age, resulted in lower feed intake, compensatory growth and proper EPF broiler chickens.