Efficacy and safety of dietary N,N-dimethylglycine in broiler production

Important objectives in the meat-type broiler industry remain to improve feed conversion ratio (FCR), mortality rate and carcass yield. Moreover, alleviating welfare problems is currently considered essential in enhancing animal production systems. Metabolic disorders may give rise to a compromised animal welfare next to financial losses due to deterioration of production efficiency as a result of increased mortality rate, less efficient utilisation of nutrients, or to condemnation of carcasses. Potential means to achieve the above mentioned goals comprise genetic improvement and refinements in rearing conditions, next to optimising nutrition, including development of new feed additives. The main objective of the current research was to evaluate the potential of N,N-dimethylglycine (DMG), a naturally occurring metabolite in living organisms, as a new feed additive in broiler diets. A first aim was to examine if DMG alleviates pulmonary hypertension syndrome or broiler ascites syndrome, whereas a second aim was to investigate if DMG enhances nutrient digestibility. A third aim included determination of the dose-response relationship of DMG on technical performance traits and health in broilers and the effect of dietary fatty acid profile. A fourth aim was to evaluate persistency of DMG effects in different rearing conditions, basal diets and broiler strains. The final objective was to evaluate tolerance, safety and bioaccumulation of dietary DMG in the target species. The first two aims were addressed in a challenge trial in which a total of 64, 14-day-old broiler hens (Ross-308) were randomly assigned to two groups of eight replicate pens of four birds each. Test diets contained 0 or 167 mg Na-DMG per kg feed. The broilers were raised under cold environmental temperature conditions and fed a high energy diet in order to incite pulmonary hypertension syndrome. The main objectives of this study were to evaluate the effect of dietary supplementation with a low dosage of DMG on incidence of pulmonary hyper¬tension syndrome and on nutrient digestibility in broilers. The results showed an important protective effect of DMG on progres¬sion towards broiler ascites syndrome as demonstrated by a reduction in incidence of pulmonary hypertension from 44.8% in the control group to 14.6% in the DMG group. This effect is likely related to an effect of DMG on the fat metabolism through which plasma non-esterified fatty acids (NEFA) increased significantly less with age in the DMG groups. This hypothesis is based on the noxious effect of NEFA on the pulmonary vasculature, which eventually leads to endothelial dysfunction and progression towards pulmonary hypertension. As DMG strongly diminished plasma NEFA level in the finisher phase of broilers, this likely coincided with an equivalent reduction in NEFA-mediated damage to the pulmonary vasculature through which pulmonary hypertension was abated. Next, dietary DMG supplementation resulted in a significant increase in apparent faecal digestibility of crude protein from 81.4 to 86.5% and nitrogen-free extract from 62.5 to 70.6%. The most likely working mechanism to explain these findings is the surfactant potential of DMG, through which nutrients become less insulated by fat droplets, rendering them more available for digestive enzymes and the absorptive brush border of the small intestine. Concomitantly to improved protein digestibility, nitrogen emission was significantly reduced by dietary supplementation with DMG. A second trial addressed the third aim and entailed 10 dietary treatments, which were tested in a complete block design with 5 replicate pens of 30 1-day old broilers (Cobb-500) per treatment. Herein, 5 dosages of DMG, ranging from 0 to 1,000 mg Na-DMG were tested in broiler diets with one of two fat sources: animal or vegetal. The main conclusions were that dietary supplementation with DMG can improve technical and slaughter performance, and may reduce oxidative stress and pulmonary hypertension, but the degree of the effect is modulated by fatty acid profile of the diet. In this respect, effects are more pronounced in a diet rich in polyunsaturated fatty acids (PUFA) compared to a diet rich in saturated and monounsaturated fatty acids (SFA and MUFA). A recommended dosage of 1,000 mg Na-DMG per kg feed was suggested based on this trial. The next trials intended to assess persistence of efficacy of DMG at the recommended dosage to improve broiler performance over a range of broiler strains, rearing conditions and basal flock efficiency. Three trials were conducted at 3 European locations: trial 1 in Settimo Torinese, Italy, trial 2 in Kraig, Austria and trial 3 in Berlin, Germany. In all trials, 1-day-old chicks were randomly divided over several pens with birds having ad libitum access to one of two diets during the entire rearing period. The test diets were either a control diet or the same diet supplemented with the recommended dosage of DMG. Control diets, broiler strain, and rearing conditions as well as period were according to standard practices of the respective region. Technical performance (feed conversion ratio [FCR], finishing bodyweight [BWfin] and production value [PV]) and carcass traits were determined. In each trial, two of three tested technical performance traits were significantly improved by DMG. Moreover, meta-analysis showed an overall, significant improvement in FCR, BWfin and PV by -2.8%, +2.3% and +4.3%, respectively. Organoleptic quality was similar between treatment groups and, irrespective to trial site, DMG supplementation resulted in an overall increase in breast meat yield and meat to fat ratio by +2.2 and +12.6%, respectively. The final study included a tolerance and safety trial to investigate eventual deleterious effects of DMG on broiler health and performance traits at the recommended or ten times the recommended dosage. Furthermore, bioaccumulation of DMG was examined. The trial consisted of 3 treatment groups with each 8 replicate pens of 20, 1-day old broiler chicks (Cobb, Avimex GmbH) that were fed 1 of 3 test diets until slaughter age at 39 days. The treatment groups were: control (0 mg Na-DMG per kg), the recommended dosage of 1,000 mg Na-DMG per kg and a tolerance dosage of 10,000 mg Na-DMG per kg. Technical performance parameters were recorded at pen level and 12 replicate blood samples were obtained at slaughter age for determination of cell counts, hemoglobin, electrolytes, enzymes and metabolites in plasma. Liver, heart and kidney samples of the 12 replicate chicks were histopathologically examined. The recommended DMG level showed a significant improvement in BWfin, FCR and PV compared to the control, similar to the results found in the previous trials. Technical performance of the chicks fed the tolerance dosage was not further improved but was in between those of the control and recommended DMG groups. Neither of the assessed blood parameters showed a significant difference between treatment groups. Pathological changes in target organs were absent in either treatment group. Bioaccumulation occurred in blood at both doses, and in meat, liver and kidney at the tenfold dose. Nevertheless, DMG content in raw meat at the tenfold dose was comparable with wheat bran and much lower than uncooked spinach. In conclusion, the experimental results showed dietary DMG to be well-tolerated and safe in broilers. As a general conclusion, the trials revealed DMG to be a valuable feed additive in broiler diets that is safe and well-tolerated in the target species and does not accumulate in consumer parts at a recommended dosage of 1,000 mg Na-DMG per kg feed. This new feed additive effectively abates progression towards broiler ascites syndrome, which is a metabolic disease that causes large financial losses as well as impaired animal welfare. In addition, DMG improves nutrient digestibility and lowers nitrogen load of poultry manure. Finally, DMG enhances feed utilisation, even in high performing birds, and may improve slaughter performance.