Effects of constant or intermittent high temperature on egg production, feed intake, and hypothalamic expression of antioxidant and pro-oxidant enzymes genes in laying ducks

Abstract

Heat stress is a major environmental factor contributing to lower production of poultry. The objective of present study was to evaluate the influence of constant or intermittent high temperature on the production performance and redox status of plasma and hypothalamus in laying ducks. A total of 288 weight- and laying-matched laying ducks were randomly assigned to 1 of 4 treatments (each with 6 replicates of 12 birds): control, pair-fed, constant high temperature (24 h, 34 ± 1°C), and intermittent high temperature (10 h, 34 ± 1°C). Blood and hypothalamic tissue samples were collected on days 1, 21, and 55 to determine redox status. Average daily feed intake and egg weight was reduced (P < 0.001) during imposition of both high-temperature treatments but was not different (P > 0.05) among the treatments during the recovery period. Lower (P < 0.05) egg mass was observed in pair-fed and intermittent high-temperature treatment during high-temperature period and in constant high temperature during the recovery period. Haugh units from high temperature-treated ducks were significantly lower than those from control or pair-fed ducks (P < 0.05) during the high-temperature period. Both models of heat exposure decreased plasma concentrations of glutathione (GSH) at day 1, and constant high temperature decreased plasma activity of GSH peroxidase (GSH-PX) at day 21 (P < 0.05). Hypothalamic expression of antioxidant genes GSH reductase (GR) and mitochondrial NADH dehydrogenase subunit (Complex Ι) were decreased by both high-temperature treatments at day 1. Hypothalamic expression of genes for pro-oxidant enzymes cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX), and cytochrome P450 7A1 (CYP7A1) were decreased (P < 0.05) by both models of high temperature but transcripts of cyclooxygenase-1 (COX-1) of ducks that were pair-fed or were exposed to constant high temperature were increased at day 21. The transcripts of NADPH oxidase 1 (NOX-1) were decreased at day 1 by both high-temperature treatments (P < 0.05) but increased during the recovery period. These results indicate that, for laying ducks, intermittent high temperature caused much greater negative production performance effects than constant high temperature during high-temperature period, but laying ducks exposed to constant high temperature tend to take longer to recover their production performance. High-temperature stress, either constant or intermittent, altered hypothalamic expression of antioxidation and pro-oxidation genes.

Figure 1.

Feed intake of laying ducks during the period of high temperature and recovery. (A) Daily feed intake changes; (B) statistical results of feed intake among treatments. Data are means ± SEM, n = 6 for each treatment. Different uppercase letters indicate significant difference at the 0.001 probability level, different lowercase letters indicate significant difference at the 0.05 probability level.

Figure 2.

Egg weight and egg mass of laying ducks during the period of high temperature and recovery. (A) Changes in egg weight; (B) statistical results of egg weight among treatments; (C) changes in egg mass; (D) statistical results of egg mass among treatments. Data are means ± SEM, n = 6 for each treatment. Different letters indicate significant difference at the 0.001 probability level.

Figure 3.

Egg production (A) and feed conversion ratio (B) in laying ducks during the period of high temperature and recovery. Data are means ± SEM. n = 6 for each treatment. Different uppercase letters indicate significant difference at the 0.001 probability level, different lowercase letters indicate significant difference at the 0.05 probability level.

Figure 4.

Redox metabolites and antioxidant enzyme activities in plasma of laying ducks during the period of high temperature (days 1 and 21) and recovery (day 55). (A) The leve of malondialdehyde (MDA); (B) The activity of superoxide dismutase (SOD); (C) The level of glutathione (GSH); (D) The activity of GSH peroxidase (GSH-Px). Data are means ± SEM, n = 6 for each treatment at each time points. Different letters indicate significant difference at the 0.05 probability level.