Orthosiphon stamineus and rosmarinic acid reduce heat stress in laying hens

Abstract

Heat stress is a great concern in the layer industry because it decreases egg production and egg quality. Orthosiphon stamineus extract (OE) has the potential to relieve heat stress, and rosmarinic acid (RA) is the main effective constituent of OE. However, the effects and mechanisms of OE and RA on heat stress in commercial laying hens remain unclear. In the current study, four hundred eighty 56 wk old hens were divided into 2 hen houses, one maintained at the low temperature and other maintained at a high temperature. Hens in each house were assigned to 3 dietary treatments (basal, basal + 0.4% OE, and basal + 0.02% RA) with 20 cages per treatment and 4 hens per cage. Performance traits were recorded, and 1 egg in 4 cages were collected randomly each day (35 eggs per treatment/wk) for egg quality assay. The excreta were collected by mixed every 5 adjacent cage at the end (28 d) of the experiment for apparent digestibility analysis, and then 1 hen from each 2 cages were sacrificed for blood and intestinal samples. The OE and RA supplementation increased the egg production rate (P < 0.05) and improved the eggshell strength and haugh unit (P < 0.05). The analysis of digestibility of basic nutrients showed OE or RA supplementation improved protein (OE: P = 0.074; RA: P = 0.037), fat, and Ca digestion (P < 0.05) in laying hens. To explore the mechanisms associated with the improvements of performance traits and egg quality, serum biochemical indices and related gene expression and intestinal villi integrity were measured. Supplementing the diet of the laying hens with OE or RA increased superoxide dismutase (P < 0.05) activities in both the serum and jejunum, decreased the malondialdehyde contents (P < 0.05), and also decreased the caspase-3 activity (P < 0.05) in jejunum of laying hens. Intestine sections showed RA supplementation improved the jejunum villus height (P = 0.007). The OE or RA supplements up-regulated nuclear factor erythroid 2-related factor 2 (Nrf2) and occludin gene expressions, and down-regulated caspase-3 gene expression in hens (P < 0.05). In conclusion, The OE and RA supplements may increase nutrient digestibility, stimulate the antioxidant defense mechanism system through the Nrf2-mediated pathway, decrease intestinal epithelial cell apoptosis, and protect the intestinal barrier. This study indicated that dietary supplementation with OE or RA is beneficial for laying hens under heat-stress conditions.