Effects of reduced dietary crude protein supplemented with crystalline amino acids on productive performance, egg quality, nutrient utilization, and cecal microbiota of Jinding laying ducks.

A total of 216 healthy 40-week-old female Jinding laying ducks were used in an 8-week feeding trial to evaluate how far dietary crude protein (CP) could be reduced when multiple limiting amino acids were supplemented. Three dietary CP levels, 17.5, 16.5, and 15.5%, were tested, with 6 replicates per treatment and 12 ducks per replicate. Lysine, methionine, threonine, tryptophan, arginine, leucine, isoleucine, and valine were added to the diets containing 16.5 and 15.5% CP. Reducing dietary CP from 17.5 to 16.5% did not significantly affect laying rate, average daily feed intake, average egg weight, daily egg mass, or feed-to-egg ratio, but decreased eggshell weight and eggshell proportion. A further reduction to 15.5% CP impaired laying performance, as shown by a lower laying rate and a higher feed-to-egg ratio. As dietary CP decreased, fecal CP content declined, whereas apparent CP utilization did not differ significantly among treatments. Serum biochemical indicators and intestinal trypsin and chymotrypsin activities changed little across treatments. The alpha diversity of the cecal bacterial community remained unchanged, whereas the overall community structure showed a tendency to differ among treatments; LEfSe analysis identified differences in several bacterial genera. Overall, under the condition of supplementing these amino acids, dietary CP could be reduced from 17.5 to 16.5% without impairing laying performance in Jinding laying ducks, whereas a further reduction to 15.5% adversely affected egg production and feed efficiency.