Evaluation of methionine requirements in turkeys

In poultry nutrition and production, methionine (Met) is considered the first essential amino acid because birds do not produce it themselves. Aside from being part of protein synthesis, Met serves as a methyl donor for several critical metabolic reactions, as a precursor to other amino acids (AA) such as cysteine, serine, and taurine (Cys, Ser, Tau; non-essential AAs), and other metabolically active compounds. Based on these and several other key metabolic functions, Met plays a critical role in growth, development, and reproduction.

To meet the digestible sulfur amino acid (SAA) needs for growth and production, poultry must obtain Met and Cys from their feed. In feed formulation, the animals’ digestible Met (dMet) and dSAA requirements are balanced by blending ingredients that supply intact protein that is typically low in Met and Cys (ex. soybean meal, corn, wheat, meat&bone meal, etc.) with a pure source of Met (DL-Met, L-Met, or OH-Met; the hydroxy form of Methionine). In least-cost feed formulation, the level of dSAA (i.e., the requirement) is often defined and set as a proportion to the digestible Lysine (dLys) in the diet. In the literature, the dSAA requirement for turkeys is reported to be between 0.90 to 1.00% for the starter phase (0 to 28 d).

US trial with 3,200 turkeys

With increased production pressures due to high raw material costs, and with the growth and interest of the turkey sector, Adisseo took a closer look at the dSAA requirement of turkeys and the effects that dSAA have on animal performance when different Met sources are used.

In the controlled study that was conducted at the Missouri Contract Poultry Research in the US, a total of 3,200 male Hybrid Converter poults were used. The birds were fed increasing doses of either DL-Met (99% DL-Met) or OH-Met (88% OH-Met) from 0 to 28 days of age. It is important to note that both Met sources were formulated with 100% bioavailability so as not to bias any of the growth performance data.

7 different dSAA levels tested

In the study, the poults were raised from 0 to 28 days in floor pens and placed in groups of 20 birds per pen (with 16 treatments and 10 replicate pens/treatment, for a total of 160 pens). The animals were fed a corn-soybean meal-based diet, formulated to be low in dMet and dSAA (0.336% dMet; 0.700% dSAA).

Methionine in the form of DL-Met or OH-Met was added in increments to create 7 different levels of dSAA (0.78, 0.86, 0.94, 1.02, 1.10, 1.18 and 1.26%), of which 3 were below, and 3 were above the dSAA requirement that is cited in the literature. Additionally, a diet sufficient in dSAA was fed as a positive control to ascertain that maximal growth has occurred in the dSAA sufficient treatments; the formulated level of intact protein in this diet was completely different from the experimental Met treatments.

The diets were not changed throughout the 28-d period, and both feed and water were provided ad libitum. Birds and feed were weighed at hatch, at 14 days and at the end of the trial (28 days). Data collected included mortality, body weight, body weight gain, and feed/gain that was adjusted for mortality.

Both Met sources perform similarly

Mortality was low during the full trial period and showed no differences between treatments. Although zootechnical performances were all significantly affected by treatment in both analysed periods (i.e., changing the dietary level of dMet and dSAA), no significant performance differences were observed between DL-Met and OH-Met-supplemented treatments (P > 0.10).

From 0 to 14 days, weight gain (P < 0.001) and adjusted feed conversion ratio (P < 0.001) were improved with the increasing dSAA level; however, feed intake was not affected (P = 0.31). In the 0 to 28 d period, all performance criteria were significantly affected as the dSAA level changed (P < 0.05).

Regardless of the period measured (0-14 d or 0-28 d), no significant interaction was observed between the Met sources and the dSAA level for all variables (P > 0.10), demonstrating that DL-Met and OH-Met can equally sustain turkeys’ growth performance, as reported earlier in broilers and ducks. The 14-day growth rate and FCR improved in a dose-dependent manner until 0.98% dSAA was reached, with no difference seen after this level for both DL-Met and OH-Met.

For the 0-28 d period, the basal diet led to the worst performance, whereas a significant improvement was observed as the dSAA dose reached the positive control dSAA level. No further improvements were obtained beyond this total dSAA level.

Using the 0-28 d data, with dSAA levels as independent variable (Table 1), the dSAA requirement was determined by 2 models: Broken Line (BL; Tends to underestimate requirements) and Two Slope, segmented regression (TSSR; A hybrid between the BL and quadratic plateau models).

Looking at the responses for each model, the respective Broken Line dSAA requirements for DL-Met and OH-Met were 0.98% and 1.00% for weight gain and 0.95% and 0.99% for FCR. For the 2-Slope model, the respective dSAA requirements for DL-Met and OH-Met were 0.93% and 0.95% for weight gain and 0.93% for FCR. These results demonstrate how the dSAA can change based on the data and the models used. In this instance, the 2-Slope model gave the most consistent results for the 2 Met sources regarding the dSAA requirement for weight gain and FCR.

Financial success

As in turkey production, the least-cost formulation is used to optimise the use of dietary nutrients at the lowest cost possible, thereby not only maximising bird performance but also the business’ financial success. This can be achieved by having accurate data on the AA content and digestibility within feeds and understanding the animals’ AA requirements for optimal performance. This study evaluated the dSAA requirement for weight gain and FCR using 2 statistical models. Overall, feeding the 2 different methionine sources resulted in similar bird performance from 0 to 28 days. While differences were noted between the models, the estimated dSAA requirement for weight gain and FCR using the 2-Slope model were the most consistent, resulting in a dSAA requirement of 0.93% dSAA for both DL-Met and OH-Met.

References are available on request.