Response and Meat Yield of Broiler Chickens fed Different Levels of Digestible Methionine

Introduction

The carcass yield of commercial broilers is an important factor in the poultry industry. Studies have indicated that an increase in dietary protein content will result in increased carcass protein content and decreased carcass fat content (BEDFORD & SUMMERS, 1985). An increase in protein retention and decrease in fat retention with increasing dietary lysine content have been reported by SIBBALD & WOLYNETZ (1986). Similarly, increasing dietary methionine levels have been shown to increase breast meat yield (HICKLING et al., 1990; HUYGHEBAERT et al., 1994). It is demonstrated that methionine supplementation to diet increases the accretion and synthesis of protein in skeletal muscle. Methionine is involved in many metabolic processes in the body e.g. methylation and protein synthesis. Its insufficiency has adverse effects on metabolic process and eventually on bird’s performance. The requirements for methionine by poultry at various phases of growth have not been adequately assessed in recent years. It is likely that such requirements would have changed as bird genotypes change. Nutrient requirements need to be updated with the constant improvement in performance and carcass yield of commercial broiler chickens. Therefore, the primary objective of the current research was to assess the gross response and meat yield of broiler chickens when raised on diets varying in methionine levels at the starter, grower and finisher phases.

Materials and methods

The experiment was a completely randomized design, with four treatments, eight replicates per treatment and ten birds per replicate. Wheat-soybean-corn gluten-meat meal based experimental diets were formulated to consist of different levels of digestible methionine –4.0, 5.8, 6.7 and 7.6 g/kg; 3.5, 5.1, 6.0 and 6.8 g/kg; and 3.2, 4.6, 5.4 and 6.1 g/kg in the starter, grower and finisher diets, respectively. Digestible methionine+cystine contents were 7.2, 9.0, 9.9 and 10.8 g/kg (starter); 6.4, 8.0, 8.8 and 9.6 g/kg (grower); and 6.0, 7.5, 8.3 and 9.0 g/kg (finisher). The three dietary phases contained 12.0, 10.5 and 10.0 g digestible lysine /kg diet, respectively. Dietary treatments were equal in ME, CP, minerals and other amino acids, as recommended in the Ross breeder specifications. Diets were fed to broilers in 3 phases from 1 to 10, 11 to 23 and 24 to 35 days of age. All diets were mixed and coldpelleted.

Three hundred and twenty day-old male Ross broiler chicks (38.45 ± 1.49 g) were randomly assigned to thirty-two cages in four-tier battery brooders set up in an environmentally controlled house. At 23 days of age, chickens were transferred into larger metabolic cages in other climate-controlled rooms. Initial brooding temperature was 33 ^oC, which was gradually reduced to 24 ± 1^oC at 19 days of age. Except for the first day (24h light), 18 hours of lighting per day were provided throughout the trial period. Birds had access to feed and water ad libitum over the trial period. Body weight (BW) and feed intake (FI) were measured on a cage basis at 10, 23 and 35 days of age. Mortality was recorded when it occurred and feed conversion ratio (FCR, feed intake/weight gain) was corrected for mortality. Two birds were selected on day 35, weighed and killed by cervical dislocation, for assessment of carcass yield. Data were subjected to linear and quadratic regression (Minitab, 2010), to evaluate the effects of digestible methionine. Mean values were considered to be significant at P ≤ 0.05. This study was approved by the Animal Ethics Committee of University of New England, Australia (Approval No. AEC12-069).

Results

There were numerical, but not statistically significant, increases in feed intake to 10, 23 and 35 days for different levels of digestible methionine (Table 1). Body weight to days 10, 23 and 35 was numerically increased with increasing digestible methionine. Improvement in FCR to days 10 (Linear, P < 0.010, R² = 0.203) was observed with increasing digestible methionine level. There were also numerical improvements in FCR up to a dietary digestible methionine content of 6.7 g/kg (23 days of age) and 5.8 g/kg (35 days of age).

Dressing % was increased (non-significantly) with increase in digestible methionine up to 6.7 g/kg (Table 2). There was a linear increase (P < 0.013, R2 = 0.188) in breast meat weight of broilers with rising digestible methionine levels up to 6.7, 6.0 and 5.4 g/kg in the starter, grower and finisher stages, respectively. Similar linear responses were observed for thigh weight (P < 0.008, R2 = 0.215), drumstick weight (P < 0.000, R² = 0.405) and wing weight (P < 0.008, R2 = 0.214).

Discussion

In general, there were numerical increments in feed intake, body weight and reduction in FCR with increasing digestible methionine concentrations in diets. This is partially in agreement with the findings of MULAYANTINI et al. (2010), who showed that an increase in digestible methionine numerically increased gross response between 1 and 21 days of age. The significant increase in the weight of breast meat, thigh, drumstick and wing may be explained by decrease fat with increasing dietary digestible methionine levels (SCHUTTE &PACK, 1995b; AHMED & ABBAS, 2011). SCHUTTE & PACK (1995a) also reported that the requirement for sulphur amino acids, including methionine, for breast meat yield is higher than requirement for body weight gain. In the present study, when related to live weight at 35 days, the increase in dressing % as digestible methionine rose from 4.0 to 7.6 g/kg diet is about 12 %, which is higher than the actual change in live weight on its own.

Conclusions

It was revealed in this study that increasing digestible methionine concentrations in diets could improve meat yield without a significant increase in feed intake, body weight and FCR of broiler chickens. Further studies are required to understand the mechanisms behind the improvement in meat yield, particularly breast meat.

References

AHMED, M.E., T.E. ABBAS, 2011: Effects of dietary levels of methionine on broiler performance and carcass characteristics. International Journal of Poultry Science, 10(2):147-151.

BEDFORD, M.R., J.D. SUMMERS, 1985: Influence of the ratio of essential to nonessential amino acids on performance and carcass composition of the broiler chick. British Poultry science, 26:483-491.

HICKLING, D., W. GUENTER, M.E. JACKSON, 1990: The effects of dietary methionine and lysine on broiler chicken performance and breast meat yield. Canadian Journal of Animal Science, 70:673-678.

HUYGHEBAERT, G., M. PACK, G. DE GROOTE, 1994: Influence of protein concentration on the response of broilers to supplemental DL-methionine. Archiv Fur Geflugelkunde, 58:23-29.

MULYANTINI, N.G.A., R.L. ULRIKUS, W.L. BRYDEN, X. LI, 2010: Different levels of digestible methionine on performance of broiler starter. Animal Production, 12(1):6- 11

SCHUTTE, J.B., M. PACK, 1995a: Sulphur amino acid requirement of broiler chicks from fourteen to thirty-eight days of age. 1. Performance and carcass yield. Poultry Science, 74:480-487

SCHUTTE, J.B., M. PACK, 1995b: Effects of dietary sulphur-containing amino acids on performance and breast meat deposition of broiler chicks during the growing and finishing phases. British Poultry Science, 36:747-762. 

SIBBALD, I.R., M.S.WOLYNETZ, 1986: Effects of dietary lysine and feed intake on energy utilization and tissue synthesis by broiler chicks. Poultry science, 65:98-105