Studies on dietary methionine efficiency and requirement in naked neck and normally feathered growing chickens

A total of five experiments were conducted with naked neck and normally feathered chickens. The experiments were conducted for the estimation of nitrogen deposition potential, modeling of methionine (Met) requirement in naked neck chicken. On the other hands, the normally feathered chickens were evaluated for the ideal dietary Met to Lys ratio, ileal amino acid digestibility and whole body and feather AA composition. Estimation of nitrogen deposition potential (Experiment I) Introduction of naked neck gene (Na) in modern meat type chicken was observed helpful in tolerating the high ambient temperature (AT). The daily N maintenance requirement (NMR) and the threshold value of daily N retention (NRmaxT) were determined using graded dietary protein supplies and exponential regressions between N intake (NI) and N excretion (NEX) or N deposition (ND), respectively. The study utilized 144 average weighed homozygous (Na/Na) and heterozygous (Na/na) naked neck chickens (50% each genotype and gender) in N balance experiments involving both starter (d10-20) and grower period (d25-35). Birds were randomly allotted to 5 diets with graded dietary protein supply and Met as identified first limiting amino acid in each diet. The observed estimates depending on genotype, sex and age varied for NMR and NRmaxT from 224 to 395 and 2881 to 4049 mg N/BWkg0.67/day, respectively. Modeling of Methionine requirement (Experiment II) In the second experiment the Met requirement for the naked neck chickens were estimated based on model parameters and N balance data derived from 1st experiment. On average, 0.47% (Na/Na) and 0.45% (Na/na) dietary Met was derived as adequate in the starter diet, whereas, 0.37% (Na/Na) and 0.36% (Na/na) in grower diet for both of the sexes. In conclusion, Met requirement for the naked neck chicken are not quite different from normally feathered counterparts. Ideal Met to Lys ratio in growing chicken (Experiment III) The optimal dietary Met to Lys ratio in the presence of adequate dietary Cys level was estimated in meat type growing chicken through the N balance experiments. Twelve averaged weighed birds (each male and female) were utilized in N balance trials at starter (d10-20) and grower period (d25-35). Total of five and six dietary treatments were used in starter and grower periods respectively. First three diets were having graded dietary Cys to Met ratio at 85:100, 95:100,105:100. Fourth diet with added betaine (Bet), fifth was a Lys limiting diet, whereas, the sixth diet was balanced for ideal AA ratio. All the dietary treatments were Met limited. Individual N-balance data per treatment group was utilized for assessing the dietary CP efficiency by use of an approved N utilization model. Elevated dietary Cys levels including Bet supplemented diet did not improve the CP quality and ultimately efficiency. The established optimal Met to Lys ratios were 33:100 for males and 35:100 for females for both the age periods. Ileal digestibility in growing chicken (Experiment IV) The study was conducted to evaluate the effect of a mono-component protease (Ronozyme®) in a finisher chicken diet on apparent ileal digestibility (AID) of CP, AAs and total protein utilization. Male broiler chickens (ROSS 308) were raised under standard feeding and management conditions for 30 days. On d31 a total of 36 average weighed birds (12 per treatment) were transferred into metabolic cages for N balance studies. An AA balanced control diet (CD) with a marginal undersupply of Met was fed. Graded enzyme level (CD = no protease added; EL-I = +15,000 PROT/kg; EL-II = 30,000 PROT/kg) were applied as treatment factor. At the end of the balance trial the birds were euthanized and ileal contents were collected by direct sampling method withTiO2 as indigestible marker. The AID of CP was significantly improved in diets EL-I and EL-II (82.08 and 83.37%) compared to CD (78.64%). The AID of individual AA gradually increased from diet CD to EL-II, but this effect was statistically insignificant. Likewise, the model parameter (b) indicating the final dietary protein quality was not improved by protease supplementation (p>0.05). Whole body and feather amino acid composition (Experiment V) Growth experiments were performed for the evaluation of whole body and feather composition of the naked neck and normally feathered chickens at specified age. The birds (males and females separately) were raised in 24 floor pens (L: 70 × 150 cm W: 108 × 120 cm). Each pen has capacity of sustaining five birds and is supplied with feeder and nipple drinkers. Whole body was collected for analysis after 24h fasting and hand plucking the feathers. Body CP and AAs contents at d-0 were found higher than in starter and grower periods. Statistically non-significant (p>0.05) difference was found in feather AAs at every age and sex.