Robustness to chronic heat stress in laying hens: a meta-analysis

Abstract

Chronic heat is a major stress factor in laying hens and many studies on the effect of heat stress have been published. It remains difficult, however, to draw general conclusions about the effect of chronic heat stress on performance and its relationship with genetic and environmental factors, as these studies have been done under varying experimental conditions and using various experimental designs. A meta-analysis enabled us to make a quantitative review of the results from 131 published papers. The relative effects of four factors (genotype, age, group size, and amplitude of temperature variation) and their interactions with temperature were analyzed for 13 traits. After pre-correcting the data for a random study effect, the best model for each trait was selected in a stepwise procedure based on its residual sum of squares. Shell strength, daily feed intake, egg mass, and hen-day egg production were found to be more sensitive to heat stress than the other traits as they dropped by 9.0 to 22.6% between thermo-neutrality (15 to 20°C) and heat stress (30 to 35°C) while yolk and albumen proportions or Haugh units showed nearly no variation with temperature (<1.2% between thermo-neutrality and heat stress). Many interactions (17) were found between temperature and one or more factors in the 13 traits studied here, which reinforces the interest of using a meta-analysis to summarize data from the literature. This study highlighted that the impact of heat stress in laying hens depends on the genotype, age, and group size, some of which have rarely been investigated.

How heat stress (continuous or cyclical) interferes with nutrient digestibility, energy and nitrogen balances and performance in broilers

“…Moreover, the pair-feeding experimental schedule showed that 70% of the reduced body weight gain in continuously stressed birds was due to the reduction in feed intake and 30% due to temperature exposure per se. These numbers confirm the hypothesis raised by the meta-analysis carried out by Mignon-Grasteau et al (2015) that the reduction in feed intake is the main cause of the effect on the other performance traits in heat stressed laying hensis also true for broilers. On the other hand, cyclical heat stress only affected growth due to the reduction in feed intake.…”

Effects of chronic heat exposure on growth performance, intestinal epithelial histology, appetite‐related hormones and genes expression in broilers

“…Moreover, it was found that the ADG and the ratio of feed gain of the HS group were significantly reduced compared with the PF group, although both groups received the same feed intake, which is in line with the study of Yunianto et al 23 Similarly, compared with birds raised under a continuous heat environment, the PF group at the same level of feed intake gained more body weight. 24,25 These results indicate that heat stress could not only inhibit appetite but also could induce some subsequent stress to reduce growth and this subsequent stress may influence nutrients digestibility or absorption.…”

Heat Stress Impairs the Physiological Responses and Regulates Genes Coding for Extracellular Exosomal Proteins in Rat

“…Heat stress is a nonspecific body response resulting from the pathological increase in core body temperature without an increase in the temperature set point [5]. In livestock, HS can lead to a decrease in fertility, as well as reduced milk and meat production resulting in great economic losses [6][7][8]. Management measures for preventing HS, such as improvement of housing conditions, application of different nutritional regimens, or breeding heat tolerant breeds rats were used in a HS timed selection experiment at 42 °C for 30 min (H30, n = 9), 60 min (H60, n = 9), or 120 min (H120, n = 18) (Step 2).…”