LAUSR

ABSTRACT This study was conducted to examine five lysine (Lys) levels (0.75, 0.80, 0.85, 0.90, and 0.95%) to estimate the optimal level of Lys for Longyan laying ducks from 22 to 38 wk of age. Nine hundred Longyan ducks aged 22 wk were assigned randomly to the 5 dietary treatments, where each treatment comprised 6 replicate pens with 30 ducks per pen. Lys had no effects on egg production, egg mass, feed conversion ratio, shape index, Haugh unit, yolk colour, yolk weight, or albumen weight, but the egg weight was improved significantly (P < 0.05) by dietary Lys supplementation, whereas the eggshell thickness, eggshell weight, and eggshell proportion decreased significantly as the Lys levels increased. Dietary supplementation of Lys did not affect the reproductive organ indices or the plasma levels of estradiol, luteinizing hormone, or follicle-stimulating hormone, whereas the plasma level of progesterone declined significantly (P < 0.01) as elevation the concentrations of Lys in the diets. In conclusion, the results indicate that the optimal Lys level in Longyan laying ducks diets is 0.80% to produce eggs with normal egg weight without adverse effects on the eggshell weight, eggshell proportion, or eggshell thickness.