Three hundred straight-run ‘Cobb 400’ day-old broiler chicks were randomly distributed into five treatment groups having three replicates containing 20 chicks in each and reared up to 6 weeks of age. The dietary treatment groups were the threonine deficient diet-Negative Control (A), Control diet containing threonine level as per NRC (B), diet containing L- threonine 10% (C), 20% (D), 30% (E) above NRC, (1994) recommendation. At the end of 3rd week, antibody titres against New Castle Disease (ND) were significantly (P<0.05) higher in treatment group C as compared to other treatment groups, whereas, there was non-significant difference in 6th week of age. At the end of 3rd and 6th week of age the Infectious Bursal Disease (IBD) antibody titers were numerically higher in L-threonine supplemented groups but, differences were non-significant among all treatment groups. The edible carcass yield was slightly higher in l-threonine supplemented groups. The abdominal fat percentage in L-threonine supplemented group C at 10% above NRC level was numerically lower than control and other treatment groups. The results of the present trial suggested that the dietary supplementation of L-threonine at 10% above NRC were found to be beneficial in term of improved immune response and carcass traits in broiler chickens.
Feed is the major input accounting 70-75% of the cost of broiler production and feed cost is the major constraint but a major mean for manipulating production cost and making poultry enterprise profitable. Broilers have high dietary CP needs. Dietary protein level, therefore, has major effect on growth performance and overall cost of finished product. Dietary CP level could possibly be reduced if there were adequate of the minimum levels of amino acids needed to support growth and muscle of broilers (Firman and Boling, 1998). An important objective of the least cost formulation of broiler diets is to provide sufficient amounts of most limiting amino acids to support the needs of tissue maintenance and growth (Kidd, 2000). Marginal dietary deficiencies of threonine may result in economic losses from increased feed conversion and reduced breast meat accretion. It is therefore, important to meet the minimum level of threonine in a broiler diet. As threonine has its role in optimal growth, therefore, meeting the threonine requirement in least cost formulation with the supplementation of crystalline L-threonine (L-Thr.) may reduce dietary crude protein, which ultimately can reduce the feed cost (Khan et al., 2006). In poultry nutrition, the essential amino acids are of great concern and of which threonine is the third limiting amino acid after methionine and lysine in diets of broiler chickens (Han et al., 1992). Adequate digestible Threonine levels are needed to support optimum growth (Kidd et al., 1999) because it serves as important component of body protein and plays an important role as precursor of lysine and serine (Ojano and Waldroup, 2002). Threonine improves the livability of heat stressed broilers (Kidd, 2000). Increased dietary threonine concentration is known to improve nitrogen retention in broiler chicks; therefore changing level of threonine concentration is an important tool to improve nitrogen utilization (Dozier et al., 2001). Broilers fed inadequate threonine had decreased live performance but no effects were apparent on carcass fat. Therefore, it is necessary to balance threonine in broiler diet by adding L-Threonine supplementation or use of soybean meal and meat meal as most important ingredients which supply threonine in the chick diets (Rezaeipour and Gazani, 2014). The threonine requirement of broiler chicken at various ages is variable and factors such as dietary crude protein breed, sex, age and main bird forming diet can affect the threonine requirements (Ciftci and Ceylan, 2004). Keeping above facts in view, the present study was conducted to investigate the effect of L-threonine supplementation in diets on immune response and carcass traits in broiler chickens.
Materials and Methods
The experiment was carried out on 300 day-old Cobb-400 straight run commercial broiler chicks for a period of 42 days (from 7th May, 2016 to 17th June, 2016) at Poultry Research Centre, Department of poultry Science, Post Graduate Institute of Veterinary and Animal Sciences, Akola, Maharashtra Animal and Fishery science University Nagpur (MS), India.
Experimental Design and Management of Birds
Three hundred straight run ‘Cobb 400’ day-old broiler chicks were randomly distributed into five treatment groups having three replicates containing 20 chicks in each and reared up to 6 weeks of age. The diets were formulated as per BIS (2007), while threonine level was maintained as per NRC (1994). The dietary treatment groups were the threonine deficient diet-Negative Control (A), Control diet containing threonine level as per NRC (B), diet containing L- threonine 10% (C), 20% (D), 30% (E) above NRC recommendation. All the diets were isocaloric and isonitrogeneous. The experimental design used for housing the broilers is presented in Table 1.
Table 1: Experimental design used for housing of broilers
|Treatment groups||Treatment group details||No. of birds/ replicate||No. of replicates /treatment||Number of birds|
|A||Threonine deficient diet (Negative Control)||20||3||60|
|B||Diet with threonine level as per NRC (Control)||20||3||60|
|C||Diet with L-threonine level 10% above NRC||20||3||60|
|D||Diet with L-threonine level 20% above NRC||20||3||60|
|E||Diet with L-threonine level 30% above NRC||20||3||60|
|Total number of birds||300|
The standard and uniform managemental practices were followed for all treatment groups throughout the experimental period. The birds were offered ad-lib fresh and clean drinking water throughout the experiment. The immunization against Ranikhet disease (B1 strain) and Infectious Bursal Disease (IBD Intermediate Strain) vaccination was carried out on 7th and 14th day, respectively, followed by booster doses on 21st day and 28th day through drinking water.
Procurement of Ingredients and Feed Formulation
The good quality feed ingredients were procured from local market for preparation of experimental diets. The L-threonine was supplied by Evonik India Pvt. Ltd. Andheri East, Mumbai, Maharashtra, India. The feeding of broilers was done in three phases as pre-starter (300 g/bird), starter (700 g/bird) and then finisher for all treatment groups. As per the plan of experiment, the composition of broiler feed for pre-starter, starter and finisher have been presented in Table 2.
Two birds from each replicate and a total of six birds from each treatment group were randomly selected for the blood collection at the end of 3rd and 6th week of age. The serum samples were used for Haemagglutination Inhibition (HI) test to detect the antibody titer against New Castle Disease Virus by Beta procedure (Allan et al., 1978). The ND antibody titer @ 8 HAU and specific antibody titer against IBD as quantified by enzyme-linked immunosorbent assay (ELISA). The total six birds from each treatment i.e. two birds from each replicate were randomly selected at the end of 6th week of age and slaughtered to study carcass traits.
Table 2: Ingredient (%) and nutrient composition of treatment Groups A (negative control group) and B (control group)
|Group A||Group B||Group A||Group B||Group A||Group B|
|Maize gluten meal (60%)||7.00||6.00||3.50||3.00||3.000||2.000|
|Meat cum bone meal (MBM)||5.00||5.00||4.50||4.00||4.500||3.700|
|Dicalcium phosphate (DCP)||0.70||0.70||0.75||0.85||0.850||1.000|
|Limestone powder (LSP)||0.80||0.80||0.90||0.90||0.900||0.900|
|Trace mineral premix*||0.15||0.15||0.15||0.15||0.150||0.150|
|Nutrient Composition on dry matter basis|
|Metabolizable energy (kcal/kg)||3007.14||3002.93||3102.34||3100.36||3204.70||3203.87|
|Crude protein (%)||23.02||23.01||22.01||22.05||20.05||20.06|
|Ether extract (%)||4.69||4.85||6.91||6.97||8.20||8.38|
|Total phosphorus (%)||0.73||0.73||0.70||0.70||0.70||0.69|
|Available phosphorus (%)||0.47||0.47||0.46||0.45||0.47||0.46|
|Crude fiber (%)||4.03||3.92||3.99||3.87||3.77||3.70|
|Total lysine (%)||1.30||1.30||1.20||1.20||1.03||1.04|
|Total methionine (%)||0.50||0.50||0.50||0.50||0.45||0.45|
|Total Threonine (%)||0.76||0.80||0.76||0.80||0.69||0.72|
The diets C, D and E were formulated by adding L-threonine at 10, 20 and 30% above NRC (1994) recommendation to control diet group B; *Trace Mineral Mixture: – Each kg contains: Copper-15g, Iodine-2g, Iron-90g, Manganese-100g, Selenium-0.3g and Zinc-80g; ** Vitamin Premix: -Each 500g contains: Vit. A12.50MIU, Vit. D3-2.50 MIU, Vit. E-12g, Vit. K-1.50g, Thiamine (B1)-1.50g, Riboflavin (B2)-5g, Pyridoxine (B6)-2g, Cyanocobalamin (B12)- 0.015g, Niacin-15g, Cal D Pantothenate-10g and Folic acid-0.50g.
Data was subjected to statistical analysis by using Complete Randomized Design as described by Snedecor and Cochran, (1994).
Results and Discussion
ND Antibody Titers
The statistical analysis of data pertaining to ND antibody titer and IBD antibody titer at the end of 3rd and 6th weeks of age was presented in Table 4. At the end of 3rd week, antibody titers against ND were significantly (P<0.05) higher in treatment group C as compared to other treatment groups (Table 3).
Table 3: Immune response and carcass traits in broilers fed different levels of L-threonine
|A (Thr. deficient diet)||B(Control)||C (10% L-thr. above NRC)||D (20% L-thr. above NRC)||E (30% L-thr. above NRC)|
|(Thr. as per NRC)|
|ND antibody titer- 3rd week||4.0±1.3b||4.6±0.9b||10.3±2.6a||5.3±0.4b||5.6±1.1b||4.320*|
|ND antibody titer- 6th week||4.3±0.8||5.3±0.8||5.0±0.8||5.6±1.1||5.0±0.4||NS|
|IBD antibody titer-3rd week||225.5±152.08||226±88.04||304.8±33.96||282.8±34.42||297.5±74.61||NS|
|IBD antibody titer-6th week||1886.5±441.04||2136.8±287.36||2324.1±159.41||2287.5±211.50||2156.6±196.91||NS|
|Edible carcass yield (%)||76.89±0.95||76.61±0.62||75.39±0.49||76.80±0.28||77.03±0.58||–|
|Abdominal fat (%)||1.70±0.10||1.47±0.06||1.21±0.15||1.26±0.15||1.36±0.10||–|
Means bearing similar superscript within a row do not differ significantly from each other. * P<0.05, NS – Non-Significant, CD – Critical Difference.
Table 4: Analysis of variance for immune response in broilers fed different levels of L-threonine
|Source||DF||ND antibody titer- 3rd week||ND antibody titer- 6th week|
|SS||MSS||F ratio||SS||MSS||F ratio|
|IBD antibody titer-3rd week||IBD antibody titer-6th week|
DF- Degrees of freedom, SS- Sum of squares, MSS- Mean sum of squares
The L-threonine supplemented groups C, D and E above NRC levels were numerically higher ND antibody titers as compared to control group B and threonine deficient group A, but the difference was non-significant in all treatment groups. At the end of 6th week of age the data revealed that ND antibody titers were non-significant in all treatment groups, whereas, ND antibody titers were improved in L-threonine supplemented groups and control group as compared to threonine deficient group. The results are in agreement with Abbasi et al. (2014) who reported that supplementation of dietary L-threonine upto 110% in Ross strain improved antibody titers. Similarly, Maroufyan et al. (2010) observed that ND antibody titers of broilers receiving the highest level of methionine and threonine were significantly higher than that of other treatment groups.
IBD Antibody Titers
At the end of 3rd and 6th weeks of age the IBD antibody titers were non-significantly higher in treatment group C (Table 3). L-threonine supplemented groups showed numerically higher IBD antibody titres as compared to control group B and threonine deficient group A. These finding are in agreement with Mehdi et al. (2013) reported that the threonine supplementation has great effect on antibody titers against IBD., the broilers receiving threonine levels of higher than NRC recommendations have a numerically higher IBD antibody titer than those received lower level of threonine. The best level of threonine was 0.81% which supported immune function. In contrast, Maroufyan et al. (2010) reported that IBD antibody titers of broilers receiving highest level of methionine and threonine were significantly higher than that of other treatment groups.
The edible carcass yield was slightly higher in threonine supplemented groups (Table 3). The present findings are in accordance with Corzo et al. (2003) reported carcass as well as breast meat improved in linear manner with increasing dietary threonine. However, Mazraeh et al. (2013) also reported that positive beneficial effect of L-threonine on development of carcass of broiler chicken. Similarly Dozier et al. (2000) also reported that increasing dietary threonine did not alter carcass yield.
It was observed that the abdominal fat percentage in L-threonine supplemented group C at 10% above NRC level was numerically lower than control and other treatment groups. The present finding is in comparable with Estalkhzir et al. (2013) reported that the highest percentage of abdominal fat related to 115% treatment and the lowest its percentage is related to threonine 105% treatment. Similarly, Nadeem et al. (2004) reported that abdominal fat was significantly affected by higher concentration of threonine.
The results of the present experiment suggested that the dietary supplementation of L-threonine at 10% above NRC were found to be beneficial in terms of improved immune response and carcass traits in broiler chickens.
The authors are highly grateful to Director of Research, MAFSU, Nagpur and Associate Dean, Post Graduate Institute of Veterinary and Animal Sciences, Akola for providing necessary facilities and for his help at various stages of the experiment. The authors are also thankful to M/s. Evonik India Pvt. Ltd. Sakinaka, Andheri East, Mumbai, India for providing the L-threonine for research.