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Feed restriction in broilers has aimed in the past at preventing metabolic disorders, such as sudden death syndrome and ascites. Rising feed costs drive the interest in interventions such as feed restriction to improve feed efficiency and reduce abdominal fat accretion. There are 2 main methods to apply feed restriction. Qualitative feed restriction is defined as limiting (specific) nutrient intake through dilution of the diet. Quantitative feed restriction is defined as reducing nutrient intake through reducing the amount of feed consumed. The aim of this research was to investigate the effects of feeding 90, 80, or 70% of ad libitum during the second wk of life, or 95, 90, 85, or 80% of ad libitum during the third wk of life on broiler growth performance, feed efficiency, and allometric growth till 35 d of age. It was hypothesized that the BW of chickens restricted for the starter or the grower period would catch up after restriction, show a lower cumulative FCR, and show a lower abdominal fat pad weight. It was also hypothesized that allometric growth curves differ between the treatments.
The current study was conducted to determine the effect of level of feed restriction during d 8 to 14 or d 15 to 21 on BW, feed efficiency, and allometric growth. Eight treatments were used in a completely randomized design. In the control treatment, broilers were provided ad libitum access to feed. Feed restriction treatments provided 90, 80, or 70% of the expected daily intake of the starter diet from d 7 to 14, or provided 95, 90, 85, or 80% of the expected daily intake of the grower diet from d 14 to 21. One-day-old Ross x Ross 308 broiler chickens (n = 314) were allocated in 32 wood shavings covered floor pens (around 10 chickens per pen, approximately 5 females and 5 males). Pens were randomly assigned to one of the 8 different treatments, with 4 replicates per treatment. Except during the respective feed restriction treatment periods, all chickens received ad libitum access to feed. Feed intake and BW were determined at d zero, 7, 14, 21, 28, and 35. The coefficient of variation (CV) for BW was determined for each pen at each age. Feed intake was recorded per pen; BW was recorded individually. Feed conversion ratio was calculated as ADFI/ADG, based on feed intake and average BW of each pen. At d zero, 7, 14, 21, and 28, one randomly chosen chicken per pen was dissected. At d 35 all remaining chickens were killed and dissected. At each dissection, abdominal fat pad, filled gastro-intestinal tract (GIT), breast muscle (total weight of pectoralis major and pectoralis minor), heart, legs without skin, and liver weight were recorded. Allometric growth curves were estimated for each treatment to predict abdominal fat pad, GIT, empty GIT, breast muscle, heart, legs, and liver weight.
No treatment differences in mortality were observed. The realized ADFI during the second wk of life was approximately according to the prediction, 87, 83, and 73% for the treatments fed 90, 80 and 70% of ad libitum, respectively. During the third wk of life, the realized ADFI was still about 10% lower than the intended levels, but this is most likely the result of the fact that the ad libitum group had a higher ADFI than was expected, on average 8% more (100 g). As expected, during the period of feed restriction ADG tended to be lower with increasing degrees of feed restriction. However, only the treatments fed 70% of ad libitum during the second wk of life and 80% of ad libitum during the third wk of life significantly differed in ADG from the ad libitum fed control group. Apparently, feeding 80 or 90% of ad libitum during the second wk of life was not severe enough to show a significant decrease ADG or BW. The differences in BW disappeared within a wk after the feed restriction period, both for wk 2 and wk 3 restricted chickens, so chickens displayed prompt compensatory growth. Finally, there was no difference in the CV of BW among treatments (data not shown). Heart growth maturation rate was significantly lowered in chickens fed 70% of ad libitum during wk two compared to ad libitum fed chickens, but no significant effect of the treatments on heart weight was seen at 35 d of age. Moreover, the fat pad allometric growth curve was significantly lower for the group fed 70% of ad libitum from d 8 to 14. The current study suggests that feeding 90, 80, or 70% of ad libitum during the second wk of life might improve the carcass quality by reducing abdominal fat pad. Breast muscle weight at d 35 was not affected by any of the restriction treatments. An interaction was found between sex and treatment for GIT weight. Feeding 80% of ad libitum during the third week of life decreased GIT weight in females at d 35, but males did not show a difference between different restriction levels.
From this study it can be concluded that moderate feed restriction (down to 70% of ad libitum intake in wk 2, and down to 80% of ad libitum intake during wk 3) can be applied in the broiler industry without compromising BW. The expected reduction in FCR following feed restriction was not shown by the current study. However, feeding 70% of ad libitum during wk 2 could decrease abdominal fat pad weight without reducing breast muscle growth. Feed restriction during the third wk of life seems undesirable, as breast muscle growth curve was lowered. More research is required to elucidate the cause of sex-dependent effects of feed restriction on broiler growth development.