Objective: This study aimed to determine the appropriate ratio of energy and protein to maintain optimal growth of pullet chicks that will lead to optimum layer performance. Materials and Methods: A total of 270 day-old chicks (Isa Brown), were distributed in a completely randomized design in a 3×3 factorial arrangement forming 9 treatments with 30 birds per treatment. Each treatment was replicated three times. The chicks were fed diets containing 3 energy (2500, 2700 and 2900 ME (kcal kg1) and 3 crude protein (CP) levels (18, 20 and 22%) from 2-7 weeks of age. Results: Feed intake of chicks increased with increase in E:P-ratio (from 124.97-139.60 g bird1 week1) while at 20 and 22% CP, feed intake of chicks decreased with increase in E:P-ratio. Body weight gain increased with increase in protein levels at the three energy levels. Birds fed on 2500, 2700 and 2900 ME kcal kg1 showed increased body weight gain (281.17-524.17 g, 282.50-325.83 g and 362.00-492.33 g, respectively) with increment in CP levels from 18, 20 and 22%. Similarly, lower feed conversion ratio was observed in birds fed 18, 20 and 22% CP. Conclusion: The results of this study showed that starter chicks fed low energy-high protein diet (2500 ME (kcal kg1) at 22% CP level grew significantly faster and had lower cost kg1 gain (₦ 194.25) as compared to other combinations (₦ 204.15 to ₦ 234.57), therefore it is recommended that, starter chicks could be fed on 2500 ME (kcal kg1) diet at 22% crude protein.
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In most parts of the world, protein is the major nutrient deficiency1. This is more visible in developing countries where animal protein has been insufficient to meet the demands of the rapidly growing population of about 5.814 billion2. FAO3 reported that consumption of poultry products in developing countries has increased by 5.8% per annum, over the last decade and this is faster than the human population growth, and has created a great increase in demand. Ojo4 reported that animal protein consumption in Nigeria is 5 g caput1 day1 which is below the FAO3 recommended level of 35 g caput1 day1. In USA, Denmark and UK, it is 64, 57 and 54 g, respectively5. Nutrition is perhaps the most important consideration in livestock management. Inadequate supply of feeds, nutritionally imbalanced rations, adulterated ingredients or stale feeds are some of the factors responsible for low productivity of livestock in the tropics6. In poultry nutrition, energy is used for the provision of body heat, maintenance, growth and production7, while protein is a vital nutrient for poultry. In virtue of its amino acid constituents, protein play a significant role in growth, egg production, immunity, adaptation to the environment and in many other biological functions. Dietary energy and protein is mainly associated with the production cost of meat. While the importance of energy cannot be over-emphasized, dietary protein are essential for normal growth and reproduction of animal. The cost of protein and energy components used in commercial poultry diets make up approximately 90% of total feed cost8. In considering any material as component of feeds, its nutritive values, availability, price and ease of processing should be considered. Many energy and protein sources of both plant and animal origins have been used by researchers with the view of minimizing cost of production and improve or at least maintaining performance. Pond et al.9 stated that feed accounts for about 60-80% of the total costs of poultry production out of which energy constitute 40-60% and protein 30-40%. Aremu et al.10 stated that the provisions of energy and protein in the diet account for 90% of the total cost of the ration. With that in mind, there is need for judicious use and application of these resources to reduce cost of production and maximize profit. Therefore, maximizing the efficiency of energy and protein (amino acids) utilization is very important for the reduction of feed cost, ultimate profit and maximization of lean meat production with minimum intake of diet. The concept of energy: protein ratio (EP ratio) or calorie: protein ratio (CP ratio) is very important in poultry feeding. It ensures adequate protein intake at all possible dietary metabolisable energy levels. This stud was conducted to makes possible formulation of high energy diets for maximum growth rate and feed conversion efficiency of chickens.
MATERIALS AND METHODS
The research was conducted at the University Poultry Research Farm, Modibbo Adama University Yola, Adamawa State, Nigeria. Yola is Located between latitude 7° and 11°N of the equator and longitude11° and 14°E of the Greenwich Meridian with altitude of 185.9 m above sea level and lies within the Northern Guinea Savannah Zone of Nigeria. Maximum temperature in the state reaches 40°C particularly in April while minimum temperature is 18°C between December and January. Mean monthly temperature in the state ranges from 26.7°C in the South to 27.8°C in the Northeast part of the state11.
Experimental animals, treatments, design and management: A total of 270 day-old chicks (Isa Brown) were purchased from ECWA Farm, Jos with an average body weight of 31.25 g on arrival. The chicks were provided with heat during the first two weeks of age using kerosene-heated stoves and 200W electric bulbs. The chicks were randomly allocated to nine treatments, replicated three times in a Complete Randomised Block Design involving 3×3 factorial arrangement, after two weeks of brooding. Each replicate of ten chicks were reared on concrete floor, measuring 1.2×2.0 m covered with wood shavings of 5 cm thick as bedding material. The low-medium and high-energy diets, contained 18% CP (low protein), 20% CP (medium protein) and 22% CP (high protein), respectively. The dietary metabolisable energy (ME) levels were 2500 kcal kg1 diet (low energy), 2700 kcal kg1 diet (medium energy) and 2900 kcal kg1 diet (high energy). The three energy levels and three protein levels were used to produce the nine treatment diets namely: Low energy-low protein (LELP), Low energy-Medium protein (LEMP), Low energy-high protein (LEHP), Medium energy-low protein (MELP), Medium energy-medium protein (MEMP), Medium energy-high protein (MEHP), High energy-low protein (HELP), High energy-medium protein (HEMP) and high energy-high protein (HEHP). The starter diets (Table 1) were formulated using maize, maize bran, groundnut cake, fish meal, bone meal, limestone, lysine, methionine, salt and chick premix. Feed intake was recorded on daily basis, while body weights and body weight gains were recorded weekly. Feed conversion ratios were calculated on weekly basis.
The chicks were fed the various treatment diets for a period of seven weeks (from 2-9 weeks of age). Feed and water were provided ad libitum. Birds were vaccinated against Gumboro (1st and 2nd vaccination), New castle disease, Fowl pox, Fowl cholera and Fowl typhoid as described by NVRI12.
Chemical analysis: Proximate analysis for dry matter, moisture, crude protein, crude fibre, ether extract, ash and nitrogen free extract of the starter chicks’ diets were carried out as described by the AOAC13.
Statistical analysis: Data collected on feed intake, body weight, body weight gain, feed conversion ratio and water intake of the starter chicks were subjected to two-way analysis of variance (ANOVA) as described by Steel and Torrie14 using the general linear model. Where significant difference was found among the treatment means, duncan multiple range test (DMRT) was used to separate the means15.
RESULTS AND DISCUSSION
Feed Intake: The interaction and main effects of dietary energy and protein are shown on Table 2-4. Birds fed on 2500, 2700 and 2900 ME (kcal kg1) diets, showed increase in feed intake from 124.97-205.31 g, 127.70-143.80 g and 139.60-171.50 g (Table 2), respectively with increase in crude protein levels from 18, 20 and 22%, respectively. This result showed that feed intake increase with decrease in energy-protein ratio (Table 3), which is in agreement with a previous study conducted by Nahashon et al.16 who reported that at hatch to 8 weeks of age, the Pearl Grey guinea fowl pullets fed diets containing 24% CP diet consumed more feed (p>0.05) than those fed 20 and 22% CP diets. The present study also in agreement with the findings of Leeson et al.17 who reported that low-CP diets significantly depressed appetite in poultry (Table 4).
Birds fed diets containing 18% CP showed increase in feed intake (124.97 g, 127.70 g and 139.60 g) per energy level. At higher CP (22%) feed intake decreased (205.31 g, 143.80 g and 171.50 g) per energy level (2500, 2700 and 2900 kcal kg diets), respectively. This result agrees with the findings of Nahashon et al.16 and Golian and Maurice18, who reported that birds on lower caloric diets will tend to consume more feed to meet their energy needs than those birds fed diet containing higher calories.