Dose response to betaine dietary inclusion in broiler chicks up to 40 day of age

Betaine (tri-methyl glycine) is a methyl donor which supplies the methyl groups for methionine production. It therefore may be able to support higher levels of growth in diets based on vegetable protein sources, which tend to be deficient in glycine and serine. There is evidence that betaine can improve nutrient digestibility by supporting intestinal function and growth (Eklund et al., 2005)

Betaine is an osmoprotectant and commonly used to overcome heat stress in poultry due to its action as an osmolyte to increase water retention. It is also a compensatory solute which has the effect of enhancing protein stability and can counter the denaturing effect of urea (Yancey and Burg, 1990). Betaine has been shown to increase lean muscle mass and decrease fat in poultry (Zhan et al., 2006).

A trial was designed to determine the response to feeding diets with increasing levels of betaine supplementation up to 5kg/tonne, on performance characteristics, apparent metabolisable energy (AME), nitrogen retention and serum uric acid content in broiler chicks up to 40 days of age.

Methods

270 male Ross 308 chicks were fed one of 5 trial diets containing graded levels of betaine (0, 0.5, 1, 2.5, 5g/kg) from day of hatch until day 40. Two diet phases were formulated using a maize-soya bean meal base; starter crumb (D0-21) and finisher pellet (D21-40). Protein, fat, ash and energy were formulated to meet the requirements of the age and strain of the bird as follows for starter crumb – Protein 20%, Fat 4.5%, Ash 5.5% and Energy 16.5MJ/kg; and for finisher crumb – Protein 19%, Fat 5.4%, Ash 4.8% and Energy 16.8MJ/kg. Each diet was fed to 9 pens of 6 birds, with one pen considered one replicate. Birds were raised from day of hatch in wide mesh sided pens of 0.64m2 with wood shavings as bedding substrate and feed and water (from nipple drinkers) available ad libitum.

Birds and feed were weighed weekly to calculate bodyweight gain per bird (BWG) and feed intake per bird (FI), and subsequently feed conversion ratio (FCR). Excreta was collected per pen, over a 48 hour period from wire mesh topped floor trays from days 20 and 39, and the collected excreta was dried at 80oC for 5 days then ground before analysis. Excreta samples were analysed for energy (via bomb calorimetry), nitrogen content (via Dumas) and titanium dioxide content (via the method of Short et al., 1996) to calculate nitrogen retention and AME. Two birds per pen were culled at D21 and D40 by cervical dislocation and blood samples collected immediately post mortem by cardiac venepuncture, and pooled into one tube per pen. Blood tubes were allowed to clot before centrifugation to separate serum (2000g, 10 min). Serum was analysed for uric acid content using an Amplex red assay (Invitrogen) as per the kit directions. Statistical analysis was carried out using one way ANOVA with Bonferroni post hoc testing where appropriate after KS testing to confirm normality.

Results

No significant performance differences were recorded between the diets for any individual week or the whole trial period from D0-40 (Table 1).

Table 1: Bodyweight gain (BWG), Feed intake (FI) and Feed Conversion Ratio (FCR) of broiler chicks fed graded levels of Betaine at D40

 

AME and N retention were both significantly increased in the 5g/kg Betaine diet at D40 when compared to the control diet (no added Betaine) (Table 2).

Table 2: Apparent metabolisable energy and nitrogen retention of broiler chicks fed graded levels of Betaine from day of hatch to day 40.
 

No significant differences in serum uric acid were recorded at D40 (Table 3), although at D21 there was a trend that serum uric acid was greater in the 5g/kg Betaine supplemented diet compared with the control diet (0g/kg).

Table 3: Serum uric acid content of birds fed graded levels of Betaine at Day 21 and 40

Conclusions

Although several authors have found improvements in bodyweight gain and FCR with betaine supplementation in poultry (Hassan et al., 2005; Waldroup et al., 2006), these findings were not reproduced in this study. However, other studies have also found no effect with betaine supplementation (Rostagno and Pack, 1996), or positive effects only with diets containing inadequate methionine (Pillai et al., 2006). Also in methionine deficient diets, betaine supplementation has been shown to reduce serum uric acid concentration in 22 d old broilers (Zhan et al., 2006) which is the opposite of the results found at D21 in this study. However by D40 there was no effect on serum uric acid of betaine supplementation.

The improved energy metabolism and nitrogen retention described in this study may be due to higher amino acid availability for protein deposition (McDevitt et al., 2000), or improved osmotic support for intestinal cells (Eklund et al., 2005). Studies on piglets have shown improved ileal protein digestibility with betaine supplemented diets (Eklund et al., 2006).

It has been suggested that betaine may be advantageous when conditions are challenging physiologically, such as during high growth, disease or heat stress (Kidd et al., 1997), or when diets are low in supplemental methionine. However this study suggests a potential benefit for betaine supplementation in improving nutrient digestibility of chicks fed nutritionally adequate diets in a non-challenging environment.

References

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