Supplementation of serine in low-gossypol cottonseed meal-based diet improved egg white gelling and rheological properties by regulating ovomucin synthesis and magnum physiological function in laying hens

This study examined the effect of dietary serine (Ser) on egg white quality, ovomucin content of laying hens fed low-gossypol cottonseed meal (LCSM)-based diet and sought to explore the regulatory mechanism underlying the effects. A total of 288 Hy-Line Brown layers were randomly assigned into 3 treatments and respectively offered soybean meal (SBM)-based diet, LCSM-based diet, and LCSM-based diet supplemented with 0.435% L-Ser. Dietary Ser supplementation reversed the decrease in quality indices of albumen, including the proportion of thick albumen (P<0.05), thick-to-thin ratio (P<0.05), albumen height (P<0.05), Haugh unit (P<0.05), and apparent viscosity that were caused by LCSM intake. Also, dietary Ser supplementation mitigated the LCSM-induced reduction in ovomucin content of the albumen (P<0.05). FT-IR analysis of ovomucin revealed differences in second derivative spectra at 1,200–800 cm–1 between birds received SBM- and LCSM-based diets, meanwhile, the α-helix of ovomucin was decreased by LCSM but increased by Ser addition (P<0.05). Furthermore, Ser addition up-regulated the mRNA expression of β-ovomucin in magnum mucosa at 2 and 7.5 h post-oviposition (P<0.05). Ser mitigated the LCSM-induced impairment of magnum epithelium, increased goblet cell counts (P<0.05), and up-regulated the expression of occludin, mucin 2, and the relevant glycosyltransferases for O-glycosylation in magnum mucosa (P<0.05). Conclusively, the alleviating effect of Ser on declining albumen quality due to dietary LCSM, could be explained by the efficacy of Ser in regulating ovomucin synthesis. This regulation occurred at the levels of transcription and post-transcriptional O-glycosylation modification of β-ovomucin, while positive effect on magnum morphology and barrier function could also in part account for the ovomucin content. This would provide a promising research direction on the adoption of nutritional interventions for manipulation of egg white quality from perspectives of albumen protein synthesis.