PROTEIN-SPARING EFFECT OF DL-METHIONINE AND CHOLINE SUPPLEMENTATION OF LOW-PROTEIN DIETS ON PRODUCTIVITY IN LAYING HENS

An experiment was conducted to investigate the sparing effect of Dl-methionine and choline in lowprotein diets offered to laying hens on productivity performance, egg quality, immune response, and nutrients digestibility; and in reducing pollution of the environment due to lowering ammonia nitrogen in the excreta. Two levels of dietary protein (18 and 15% CP) were investigated in laying hens. The control diet contained 18% CP, 0.40% methionine and 400 mg choline/kg. The experimental diets that contained 15% CP were supplemented with two levels of methionine, 0.30 and 0.40 %, and three levels of choline, 400, 800, and 1600 mg/kg diet, for a total of six dietary treatments. The control and six experimental diets were studied in Seven hundred Bovans White hens, at 27-week of age. Each experimental group consisted of 100-hens, which were sub-divided into 4 replicates of 25-hens each. Results showed that a significant increase in hen-day egg production (P<0.0001) and egg weight (P<0.05) in hens fed diet that contained 15% protein, 0.30% methionine and 1600 mg choline/kg. Hens receiving the low-CP diets consumed significantly more (P<0.05) feed than those receiving the control diet. Moreover, the combination of 15% protein at different levels of methionine and choline supplementation significantly improved (P<0.0001) feed conversion ratio and protein conversion ratio compared to the control group which contained 18% CP. However, average live body weight gain was not affected by protein, methionine and choline interactions. Shell thickness and serum total immunoglobulin titers were significantly improved with all the diets that contained 15% CP at different levels of methionine and choline, compared to the control group. Nevertheless, no significant effects on egg shell weight and Haugh unit were observed due to protein, methionine and choline combinations. However, there was a significant increased (P<0.0001) in yolk and albumen weight due to interaction among low-protein diets which contained 0.30 or 0.40 % methionine, and 800 or 1600 mg choline/kg. It was also noted that crude protein digestibility, nitrogen excreted (NE) and nitrogen balance (NB) were significantly improved by dietary protein, methionine, choline, or their interaction; while, dry matter, organic matter, ether extract, crude fiber and nitrogen free extract digestibilities were not affected by studied same nutrients. It appears that laying hens fed low protein diet supplemented with methionine excreted less nitrogen in their excreta, hence less pollution to the environment compared to the group fed control diet. The economic study was affected by different combinations of protein, methionine and choline levels, where increasing level of choline supplementation to the low-protein and low-methionine diets increased economic efficiency. In conclusion, the dietary combination of 15% CP, 0.30 methionine, and 1600 mg choline/kg diet was adequate in meeting the birds dietary requirements, without adversely affecting hen's productivity performance, egg quality, immune response and nutrient digestibility, and with the added benefit of reducing environmental contamination with ammonia nitrogen. Also, choline can spare part of the methionine supplementation in layer's diets, and was as effective in improving performance, egg quality and immunity of the birds.