Background and Objective: Slow-growing broilers are well adapted to tropical climate but have poor growth performance and feed efficiency. This study aimed to evaluate the effect of feeding strategy on production efficiency and welfare behavior of slow-growing broilers in the tropics. Materials and Methods: A total of 390 Sasso broiler chickens of 14 days old were divided into three groups of five replicates with 26 chicken per replicate: birds in group A (as control) fed complete diet, birds in group B fed diets with variation in energy content and in group C birds fed diet with energy and protein contents. Feeding behavior at 10 weeks of age and carcass evaluation, abdominal fat and meat pH at 11 weeks of age were evaluated. Results: Results showed that feed intake, energy intake, growth rate and body weight were higher (p<0.05) in broiler chickens of group A compared to those of groups B and C. Protein intake, thigh weight, mortality, feed cost per chicken were similar among all treatment groups (p>0.05). However, birds fed sequentially showed lower abdominal fat, feed conversion ratio and higher economic feed efficiency (p<0.05). In addition, they showed positive welfare behavior under tropical condition. Moreover, carcass weight increased (p<0.05) in birds of groups A and B. The meat pH decreased more rapidly in groups A and C compared to group B. Conclusion: It was concluded that the variation of the energy level of diet can be used as a feeding strategy for slow growing broilers in the tropics.
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Fast growing broilers, genetically selected for production efficiency, are very sensitive to tropical climatic conditions and therefore less thermotolerant compared to slow growing strains1,2. Their rapid growth is associated with several metabolic disorders such as sudden death, lameness and myopathies. Also, enteric diseases and other troubles have been reported3-5. However, the benefits of using slow growing breeds are numerous: Thermotolerance, welfare and meat quality (less tender and less juicy meat compared to that of fast-growing breeds)6,7. Moreover, because they take longer time to mature, slow-growing broilers have fewer problems with muscle abnormalities and therefore can be used as free-range chicken in rural areas8. Despite this, they present lower growth performances and poor feed efficiency9. The poor feed efficiency of birds is a major challenge resulting in an increased feed intake10. This makes them less economical and profitable for farmers8. Improving these chickens’ ability to convert feed intake into meat is a primary objective11. But, because of the negative correlation between thermotolerance and growth rate, feeding practices are the most appropriate way to address the problem12. Feeding is a key factor which must be controlled in order to improve feed efficiency and profitability13. According to Kpomasse et al.14, intestinal length and carcass yield weight of Sasso chickens was improved by the distribution of diet with low energy and high protein contents in the morning followed by high energy and low protein contents diets in the afternoon under hot climate. Nevertheless, such feeding method did not improve feed efficiency of Sasso broiler and since then, very few studies have focused on improving feed efficiency of slow-growing broilers through the use of feeding strategies. The observations reported in the previous studies are extended in this study. It aimed to evaluate the effect of feeding strategy on production efficiency and welfare behavior of slow-growing broiler in the tropics.
MATERIALS AND METHODS
This study was carried out in strict accordance with the recommendations of the Guide for the Care and Use of Experimental Animals of the University of Lome, Togo. The protocol was approved by the Ethics of Animal Experimentation Committee of the same University. All efforts were made to minimize discomfort to the birds (ref: 008/2021/BC-BPA/FDS-UL).
Experimental design: A total of 390 chickens (14 days of age) were allotted to three treatments of five replicates of twenty-six chicken. The treatments were: A: served as control (broiler chickens fed complete diet)’ B: Birds fed sequentially low energy diet (E- diet) in the morning and high energy diet (E+ diet) in the afternoon] and C [birds fed sequentially low energy and high protein (EP+) diet in the morning and high energy and low protein (E+P) diet in the afternoon. All the chickens were reared on a deep litter with wood shavings having a density of 5 birds per m2 during the experiment. Feed was provided twice a day: 07:00 and 13:00 (UTC). Birds of sequential group received alternated diets during the day (Table 1). Lighting program of 23 hrs of light and 1 hr of darkness was used and water was supplied ad libitum.
Management of chicken: Feed intake in the morning and afternoon was recorded weekly and the difference between the feed supplied and the left-over was used to calculate total feed intake. Mortality was recorded daily. Also, body weight and weight gain (difference between body weight at the end of the week and body weight at the beginning of the week) were evaluated weekly and feed conversion ratio was calculated as feed intake per weight gain. At 11 week of age, six broiler chickens per replication were slaughtered for the determination of carcass traits. Physiological organ weights, intestinal length and weight and carcass weight were determined.
Meat pH evaluation at different times: Meat pH measurements were carried out on pectoralis major muscle from slaughtered birds. The pHu values after 15 min and 24 hrs (pHu 15 min and pHu 24 hrs, respectively) were measured by inserting a glass electrode directly into the thickest part of the muscle using a pH meter OARTON pH 700 (with precision of 0.01). Muscles were stored in a cooler at 4°C during assessment15-17.
Chicken behavior assessment through kinetics of feed and nutrients intake: During a short period in the morning and in the afternoon (2h30), feeding behavior of 10 week aged broiler chickens of different treatments were evaluated. A one-day adaptation period to human presence was performed before data collection on three consecutive days18. The chickens were deprived of feed for 8 hrs before the beginning of the observations which started from 7 am in the morning and at 1 pm in the afternoon18,19. The amount of feed remaining was weighed every 30 min during each observation period.
Evaluation of production efficiency: For different calculations, the values for each phase (starter and growing phase) were calculated and then summed. Feed cost per chicken per treatment and economic feed efficiency were calculated using the following equation as described by Houndonougbo et al.20:
Feed cost per chicken per treatment (€) = Starter diet cost + price per kg of feed × FCR × Body weight gain (kg) per chicken from 3-11 weeks of age
where, FCR is feed conversion ratio
For a given rearing phase, the economic feed efficiency was calculated using the following equation:
where, BWG is body weight gain and feed cost is the amount invested in feeding.
Statistical analysis: The software Graph Pad Prism 8.0.2 (GraphPad Software, San Diego, CA, USA) was used for data analysis. One way analysis of variance was used to compare the sample means. The generalized linear regression model was used to analyze the effects of feeding strategy on feed consumption, growth rate, feed conversion ratio, carcass characteristics, abdominal fat weight, digestive organs weights, production efficiency and feed and nutrients consumption. When significant, further analyses were performed using Tukeyʼs test21. Mortality was analyzed with a χ2 test. Tested parameters were considered as significantly different if p<0.05.
Effect of feeding strategy on feed and nutrients intake, weight gain, final body weight and mortality: Table 2 shows the effect of feeding strategy on feed, energy and protein consumed by Sasso chickens during the experimental period. In the morning, feed consumption of broiler chicken in group C was higher (p<0.05) than those of groups A and B while in the afternoon, feed intake of control group (group A) was higher (p<0.05) than those of groups B and C. Overall, broiler chickens of group A fed complete diet consumed daily more feed than those of group B and C (p<0.05) (Table 2). Similarly, these birds consumed more energy (p<0.05) than those of groups B and C. However, the amount of protein consumed did not differ (p>0.05) across all treatment groups (Table 2).
As shown in Table 3, weight gain and final body weight of broiler chicken of group A were higher (p<0.05) than those of groups B and C. Also, mortality was not significantly different in all treatment groups (Table 3).
Effect of feeding strategy on digestive organ weights: The effect of feeding method on gizzard, liver, heart weights, small intestine weight and length are presented in Table 4. Broiler chickens in group B [birds fed sequentially low energy diet (E diet) in the morning and high energy diet (E+ diet) in the afternoon] had a heavier gizzard weight (p<0.05) than those of groups A (control group) and C [birds fed sequentially low energy and high protein (EP+) diet in the morning and high energy and low protein (E+P) diet in the afternoon]. However, birds in group C had a higher (p<0.05) liver weight compared to those of the other treatment groups. No significant difference was noticed in heart and small intestine weight (p>0.05) among all treatment groups. But an increase in the length of small intestine (p<0.05) was observed in birds of groups A and B (Table 4).
Effect of feeding strategy on meat yield, abdominal fat and meat pH at different times: As indicated in Table 5, broiler chickens of groups A and B showed higher carcass yield and lower breast yield compared to that of group C (p<0.05). Thigh weight was similar among all treatment groups (p>0.05). Also, birds in groups B and C showed a reduction in abdominal fat (p<0.05) (Table 5). Broiler chicken in groups A and C showed higher meat pH at 15 min while those of groups A and B showed a decrease in meat pH at 24 hrs (p<0.05) (Table 5).