No abstract

Ovarian follicle selection is a natural biological process in the pre-ovulatory hierarchy in birds that drives growing follicles to be selected within the ovulatory cycle. Follicle selection in birds is strictly regulated, involving signaling pathways mediated by dietary nutrients, gonadotrophic hormones and paracrine factors. This study aimed to test the hypothesis that dietary Ca may participate in regulating follicle selection in laying ducks through activating the signaling pathway of cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/extracellular signal-regulated kinase (ERK), possibly mediated by gonadotrophic hormones. Female ducks at 22 weeks of age were initially fed one of two Ca-deficient diets (containing 1.8% or 0.38% Ca) or a Ca-adequate control diet (containing 3.6% Ca) for 67 days (depletion period), then all birds were fed the Ca-adequate diet for an additional 67 days (repletion period). Compared with the Ca-adequate control, ducks fed 0.38% Ca during the depletion period had significantly decreased (P < 0.05) numbers of hierarchical follicles and total ovarian weight, which were accompanied by reduced egg production. Plasma concentration of FSH was decreased by the diet containing 1.8% Ca but not by that containing 0.38%. The ovarian content of cAMP was increased with the two Ca-deficient diets, and phosphorylation of PKA and ERK1/2 was increased with 0.38% dietary Ca. Transcripts of ovarian estradiol receptor 2 and luteinizing hormone receptor ( LHR ) were reduced in the ducks fed the two Ca-deficient diets (P < 0.05), while those of the ovarian follicle stimulating hormone receptor ( FSHR ) were decreased in the ducks fed 0.38% Ca. The transcript abundance of ovary gap junction proteins, A1 and A4, was reduced with the Ca-deficient diets (P < 0.05). The down-regulation of gene expression of gap junction proteins and hormone receptors, the increased cAMP content and the suppressed hierarchical follicle numbers were reversed by repletion of dietary Ca. These results indicate that dietary Ca deficiency negatively affects follicle selection of laying ducks, independent of FSH, but probably by activating cAMP/PKA/ERK1/2 signaling pathway.

This study was aimed at studying use of reduced dietary crude protein ( CP ) level supplemented with additional amino acids in laying ducks. A total of 720 Jingjiang ducks (50 wk) were randomly assigned to 5 treatments and fed 5 basal diets with CP levels at 17.5, 16.5, 15.5, 14.5, or 13.5%, with additional amino acids added to each diet for 12 wk. Each treatment had 6 replicates of 24 ducks each. Dietary CP levels affected ( P < 0.05) egg production and mass of laying ducks, and there was a linear and quadratic decrease with decreasing CP levels ( P < 0.05). Dietary CP levels did not affect egg weight and feed conversion ratio ( FCR ), but egg weight decreased linearly ( P < 0.05); FCR increased linearly and quadratically ( P < 0.05) with decreasing CP levels. There were no significant differences in egg quality among the different CP levels ( P > 0.05). Ovarian weight, total and mean weight of preovulatory follicles, and total weight of small yellow follicles ( SYF ) were decreased by dietary CP levels (linear, P < 0.01 and quadratic, P < 0.05). The oviductal weight decreased linearly ( P < 0.05), and the number of SYF decreased linearly and quadratically with decreasing CP levels ( P < 0.05). The serum estradiol content decreased linearly with dietary CP levels ( P < 0.05). The serum contents of luteinizing hormone, prolactin, and progesterone decreased ( P < 0.05), linearly and quadratically (both P < 0.01) with decreasing CP levels. The serum contents of creatinine ( CRE ), triglycerides ( TG ), total cholesterol ( TC ), and alanine aminotransferase ( ALT ) activity were affected ( P < 0.05) by different dietary CP levels. The total protein content increased linearly ( P < 0.05), TC content increased quadratically ( P < 0.05), and contents of albumin, CRE, TG, and phosphorus, and activities of aspartate aminotransferase and ALT increased linearly and quadratically (both P < 0.05) with decreasing CP levels. Overall, reduced dietary CP levels with addition of amino acids affected the laying performance, the development of reproductive organs and ovarian follicles, serum hormones, and biochemical indices of laying ducks. Dietary CP levels can be reduced to 14.5% with additional amino acid supplementation for 12 wk in laying ducks without negative effect on laying performance and egg quality.