RESPONSE OF LAYING HENS TO SOME DIETARY NUTRIENTS LEVELS

Abstract

Two experiments were conducted in a 3 x 2 x 2 factorial arrangement of treatments. Three levels of metabolizable energy 2600, 2800 and 3000 Kcal ME/kg diet, two levels of methionine (0.40 and 0.50%) and two levels of choline (300 and 900 mg/kg diet for experiment I) or two levels of folic acid (2.0 and 6.0 mglkg diet for experiment II) were used. The experimental diets were formulated to cover the nutrient requirements according to the recommended allowances of the breed, where 2800 kcal ME/kg, 0.40% methionine, 300 mg choline/kg and 2.0 mg folic acid/kg considered as a control. The diets were fed to 2400 ( 1200/experiment) Lohmann Drown (L.D.) laying hens, 28 weeks of age for 16 weeks. Hens in each experiment were randomly distributed into 12treatments, of 100 hens each, in 4 replicates. In both experiments, feed was given in all mash form and offered with water ad-libi/llm under a total of 16 hours light per day regimen. The resulls in experiment I and II indicated that hens fed the high energy diets produced more eggs than those fed the medium or low energy diets with no significant differences. Increasing energy, methionine, choline and folic acid levels did not affected egg weight. In both experiments, the amount of feed consumed decreased with increasing dietary energy level in the diet. The best feed conversion ratios were noticed with all diets containing 3000 kcal ME/kg, the ratio improved by 13.20 and 19.72% for experiment I vs. 11.68 and 19.82% for experiment II than the control diet and low ME diet, respectively. In the first and second experiments, the average live body weight gain increased gradually with increasing the energy level from 2600 lo 3000 kcal ME/kg with supplemental methionine, choline and folic acid. The resulls indicated that diet containing 2600 kcal ME/kg diet within 0.40% methionine and 300 mg choline or 2.0 mg folic acid proved to be adequate for good external (egg shape index, egg shell weight and egg shell thickness) and internal egg quality (egg yolk index, egg albumen index, yolk and albumen weights and Haugh units). The diets containing 2600 kcal ME/kg in both experiments tend to increase yolk total lipids and yolk total cholesterol compared to diets containing 2800 (control) and 3000 kcal ME/kg. Immune functions (serum total immunoglobulin titres) were significantly affected by energy levels in both experiments, but lillie affected by methionine and choline (experiment I) and folic acid (experiment II) supplementation in the diet. A slightly decrease was observed in serum total immunoglobulin titres with increased methionine and choline. In both experiments, the digestibility coefficients of the experimental diets revealed thai different energy levels, especially high energy diets which containing 3000 kcal ME/kg improved the digestion coefficient values of almost all the nutrients compared to.the control diet (2800 keal ME/kg) and diets containing 2600 kcal ME/kg. The addition of methionine, choline (experiment I) or folic acid (experiment II) showed different effects on nutrients digestibility coefficient based on energy level of the diet. Also, the diet containing 3000 kcal ME/kg gave the best metabolizability compared to other levels (2800 and 2600 kcal ME/kg). A significant difference in metabolizability was observed due to methionine, choline and folic acid supplementation with the effect depends on energy level. The economic study was affected by different energy, methionine, choline or folic acid levels, when..• increasing the dietary energy level increased economic efficiency in both experiments. Therefore, it may be generally concluded lhat: a diet containing 3000 kcal ME/kg would be ideal for the achieVement of optimum pcrfi1rmancc ouul revenue cost ratio of Lohmann Brown laying hens during 28-44 wk of age. The addition ofme1hionine, choline and folic acid up to 0.50%, 900 mg/kg and 6.0 mglkg to low energy diet (2600 keal ME/kg) improved egg quality and increased immune response compared to medium (2800 kcal ME/kg) and high energy levels (3000 kcal ME/kg), Therefore, we can decrease the usage ofyell<•w corn in diets. Obviously, very good egg production and economic efficit;ncy were obtained even whu1 the ratio of calories of metabolizable energy to amino acid (methionine) and vitamins (choline and I<'lie acid) in the diet, was I:1.67, I :0.30 and I :0.002, respectively. Added folic acid in layer diets increased egg shell thickness through estrogen hormone relations mechanism in which the estrogen reguli1tC the activity of osteoclasts and slow the process of bone dissolution. This lead lo increasing egg shell thickness and decreased the eggs broken percentage and therefore, increased economic eniciency.