INTRODUCTION
Poultry population in Nigeria is put at 140 million and it is a major contributor to the economy (FMAWR, 2008). There is also a consistent rise in intensification of production and a growth rate of 306.6% between 1999 and 2004 (Glipha, 2007). The importance of these statistics is that Nigeria inadvertently contributes to environmental issues currently debated world - wide vix air and water pollution, greenhouse gas (GHG) emission, climate change etc. Owing to the poverty level of the average Nigerian commercial poultry farmer, profitability rather than sustainability has been the major thrust of poultry production.
Environmental considerations are major current issues world - wide in every human endeavour. Climate change and its associated effects has been the major discussion and it is thought to be a future moderator of human economic activities. Agricultural activities have been reported to contribute about 60% non-carbon greenhouse gases. In France, 74% nitrous oxide emission was from agricultural activities in the year 2000 (Jean-Marc, 2004). About 50% greenhouse gas emission of intensive livestock production is from production units and 25% from waste disposal. Poultry production releases nitrous oxide into the atmosphere via biodegradation and denitrification of faecal materials. Faecal materials have been analyxed to contain 2 - 4% nitrogen (Costello, 2007). Nitrous oxide has been on the increase (15%) since 1750 and to have a global warming potential (GWP) of 298 and a carbon equivalent of 81.27 (GWP x 0.2727) (Hopwood and Cohen, 1998). This greenhouse gas production is further compounded by imbalance of dietary amino acid and deep litter system (Eberhard, 2007). Reduction of nitrogen contribution from poultry production units can be achieved through scientific feed manipulation. This is achieved by feeding the required level of amino acid to reduce faecal nitrogen available for denitrification (Misselbrook, 1998).
Environmental efforts in Nigeria geared towards reducing greenhouse gas from livestock production for sustainable production system (balance between production economics and environment) is still a novel study direction. Currently, a typical commercial broiler starter feed contains about 23 - 24% crude protein, which has been considered a waste both to profit and environment. Commercial feeds are produced using National Research Council (NRC) recommendations for overall protein while the balance of amino acid is generally not adhered to. The resultant effect is the increased faecal nitrogen available for denitrification and other associated environmental concerns. The present study employed feed manipulation (appropriate amino acids vis - a - vis crude protein requirements) to determine the sustainability of broiler production by considering performance and relative nitrogen economy.
MATERIALS AND METHODS
Two hundred (200) day - old and mixed sex ANAK 2000 broiler chicks were purchased and randomly allocated to electrically heated metabolism cages. Birds were given water and feed (Table 1) ad libitum for a study period of four (4) weeks. Different crude protein levels (formulated for specific amino acid requirements) were the treatments in this study. The levels of crude proteins were 22.0, 22.5, 23.0, 23.5 and 24% (Table 1). Birds were randomly allocated to these treatments in five (5) units (replicates) of eight (8) birds each.
Birds were vaccinated against Newcastle disease at 1 week and 3 weeks of age as well as infectious bursa disease at 2 weeks of age. The required medications were also administered as at when due. The study was conducted for four weeks.
Data were collected daily on feed intake and weight gain. Feed : gain was computed from the data of daily feed intake as a ratio of weight gain. At the end of the third week of study, a nutrient retention study was conducted. Feed was weighed and given to birds and faecal samples collected over a period of 72 hours employing total collection method. Faecal samples collected were oven- dried, ground and analyxed for proximate composition. Anthropogenic potential (AP) of each treatment was calculated as:
Anthropogenic propensity = 2((y1y2)/y3) x K Where:
y1 =% faecal nitrogen, y2=faecal dried weight, y3= mass of nitrogen,
K= GWP of nitrous oxide (0.2727)
At the end of the study, four birds per treatment were starved for 12 hours prior to slaughtering by head decapitation. After evisceration of the carcass, a carcass characteristic assessment was conducted. Histological sample of the liver was cut, freed of adhering fat and blood and preserved in 10% formalin solution. The tissue sample was trimmed, fixed in bouin fixative for 24 hrs, embedded in wax, sectioned at 5 - 6µ with microtome (Leitx and Wetxair) and stained in haematoxylin and eosin (H and E) King et al (1980). At four weeks of age, blood samples were taken from the wing veins of four (4) birds from each treatment into bijou bottles containing EDTA (anticoagulant). PCV, haemoglobin concentration, total RBC and WBC were evaluated according to Dacie and
Lewis (1997). Serological samples were taken from collected blood (without anticoagulant), centrifuged at 4000 rpm for 3 minutes and the supernatant sera harvested in bijou bottles for the determination of specific serum biochemical indices. Enxyme assay for serum aspartate amino transferase (AST, EC 2.6.1.1) and alanine amino transferase (ALT, EC 2.6.1.2) were determined by the colorimetric method of Reitman and Frankel (1957), while alkaline phosphatase (AP < EC 3.1.1.3) was determined by the kinetic method of Frajola et al. (1965). Proximate compositions of feed and faecal samples were carried out using the methods of AOAC (1990). Response criteria were subjected to analysis of variance and treatment means separated by Duncan Multiple Range Test using the SAS statistical package (SAS, 1985).
RESULTS
Feed intake and mortality were not significantly different (P > 0.05) for the different crude protein levels. However, weight gain and feed:gain were influenced (P < 0.05) by the dietary treatments. Broiler chicks fed 22.5% crude protein level had better daily weight gains (24.44 g/bird/day) and feed : gain (1.85) (Figure 1; Table 2).
Percentage faecal nitrogen was significantly influenced (P < 0.05) and directly related to dietary protein levels. Birds fed 22.0% had the lowest percentage faecal nitrogen (1.76%) though it was not significantly different from the value for broiler chicks fed 22.5% CP.
Dietary protein level was significantly affected (P < 0.05) and directly related to serum total protein, albumin, uric acid and serum creatinine (Table 3). From this study, lower levels of dietary crude protein containing the recommended amino acid profile by NRC (1994) guaranteed sustainable broiler production, recording lower N output and consequently, lower anthropogenic potential compared to higher CP levels (Figure 2). Serum total protein was different (P < 0.05) for the various dietary protein treatments.
Broilers fed 24% CP had the highest serum protein value measured (63 g/l), while those fed 22.0% CP recorded the lowest (44 g/l). Serum albumin was significantly affected (P < 0.05) by the varying dietary crude protein. Chicks fed 22.5%, 23.5% and 24% CP had statistically similar values for serum albumin; however, the lowest value (13 g/l) was observed for birds fed 22.0% CP. Uric acid values varied significantly (P < 0.05) among birds fed the various dietary treatments. Chicks fed 23.0%, 23.5% and 24% CP had similar values of uric acid compared to birds fed lower levels of crude protein. Serum creatinine was significantly affected (P < 0.05) and directly related to varying levels of crude protein. Generally, dietary levels of protein did not influence (P > 0.05) the enxyme profiles of the fed bird.
Haematological values, carcass characteristics and serum enxymes obtained for broiler chicks in this study were not significant (P > 0.05) and were within the range for birds of the ages used in this study (Tables 4 and 5).
DISCUSSION
The feed intake of the broiler chicks showed similarity as all the diets were all accepted. This observation corroborates the report of Fara Filho (2003) that modulation of feed intake is not just a consequence of the amount of crude protein alone but of protein quality. However, observations from this study suggest that lower dietary proteins favour daily weight gain and feed : gain ratio. This report supports the findings of Odunsi et al. (1999) that there is the possibility of feeding diets containing 17% crude protein with a balance amino acid profile without affecting broiler chicken performance. This observation is further corroborated by the relative nitrogen retained and faecal nitrogen observed for broilers chicks fed 22.5% CP; while the faecal nitrogen increased as the protein level increased. Nitrogen, an elemental component of protein, is essential for growth. Ward et al. (1975) have shown that the excretion of nitrogen increased as protein level increased. Low crude protein diets containing synthetic amino acids have been shown to reduce nitrogen excretion in pigs which can lead to potential reduction in ammonia emission (Pahl et al., 2001). As dietary levels of protein decreased in the poultry diets, greenhouse gases, especially nitrous oxide produced from denitrified feacal nitrogen, are expected to decrease (Eberhard, 2007). Faecal nitrogen levels reported in this study are different from values obtained by Costello (2007). Misselbrook (1998) reported that feeding required levels of amino acids rather than overall crude protein level reduced faecal nitrogen available for denitrification. Faecal nitrogen is a major contributor to the anthropogenic potential in animals, especially poultry. Intensification of production further increases the anthropogenicity of poultry production through the emission of non - carbon greenhouse gas (Jean-Marc, 2004). As observed in this study, feeding higher levels of crude protein constitute a waste in terms of economic returns because dietary protein level has significant effect on feed cost. Hence, reduction of dietary protein levels will not only mitigate concerns from nitrogen released to the environment (Aletor et al., 2000; Bergendahl et al., 2002), but will also, reduce cost of production. Poor nitrogen economy resulting in relatively high faecal nitrogen contributed to the higher anthropogenic propensity observed in this study.
Serum protein is an index of dietary protein intake (Annongu, 1997). The quality and quantity of protein in any diet are factors influencing blood protein concentration. Higher values of uric acid and serum creatinine were observed in birds fed higher levels of dietary crude protein. These values are a measure of amino acid degradation (Shukla and Pachaurii, 1995) and may also be an early pointer to depressed liver and kidney functions (Annongu, 1997). Low values of uric acid and creatinine for birds given lower protein level corroborates the data on weight gain. Enxyme profile of broiler chicks observed in this study falls within acceptable ranges. A lower serum value of uric acid and creatine, in this study, in birds fed 22.5% crude protein suggest a normal liver and kidney functions (Reitman and Frankel, 1975; Bolu et al., 2006). In this study, no treatment effect was observed in the haematological parameters obtained.
CONCLUSION
The results of this study suggest that feed manipulations in terms of feeding the required level of crude protein and amino acid can go a long way in reducing the amount of faecal nitrogen available for denitrification. This in turn will reduce the anthropogenic propensity of intensive chicken broiler production. For sustainable broiler production, crude protein level of 22.5% in broiler starter diet may be suitable in terms of performance and environmental stability and mitigation of climate change.
This article was originally published in Journal of Applied Agricultural Research 2011, 3: 133-139, and it is reproduced here with permission from the author.
