Thermal manipulation of the embryo modifies the physiology and body composition of broiler chickens reared in floor pens without affecting breast meat processing quality1

Abstract

Selection in broiler chickens has increased muscle mass without similar development of the cardiovascular and respiratory systems, resulting in limited ability to sustain high ambient temperatures. The aim of this study was to determine the long-lasting effects of heat manipulation of the embryo on the physiology, body temperature (Tb), growth rate and meat processing quality of broiler chickens reared in floor pens. Broiler chicken eggs were incubated in control conditions (37.8°C, 56% relative humidity; RH) or exposed to thermal manipulation (TM; 12 h/d, 39.5°C, 65% RH) from d 7 to 16 of embryogenesis. This study was planned in a pedigree design to identify possible heritable characters for further selection of broiler chickens to improve thermotolerance. Thermal manipulation did not affect hatchability but resulted in lower Tb at hatching and until d 28 post-hatch, with associated changes in plasma thyroid hormone concentrations. At d 34, chickens were exposed to a moderate heat challenge (5 h, 32°C). Greater O2 saturation and reduced CO2 partial pressure were observed (P < 0.05) in the venous blood of TM than in that of control chickens, suggesting long-term respiratory adaptation. At slaughter age, TM chickens were 1.4% lighter and exhibited 8% less relative abdominal fat pad than controls. Breast muscle yield was enhanced by TM, especially in females, but without significant change in breast meat characteristics (pH, color, drip loss). Plasma glucose/insulin balance was affected (P < 0.05) by thermal treatments. The heat challenge increased the heterophil/lymphocyte ratio in controls (P < 0.05) but not in TM birds, possibly reflecting a lower stress status in TM chickens. Interestingly, broiler chickens had moderate heritability estimates for the plasma triiodothyronine/thyroxine concentration ratio at d 28 and comb temperature during the heat challenge on d 34 (h(2) > 0.17). In conclusion, TM of the embryo modified the physiology of broilers in the long term as a possible adaptation for heat tolerance, without affecting breast meat quality. This study highlights the value of 2 new heritable characters involved in thermoregulation for further broiler selection.

Heritability of body surface temperature in hens estimated by infrared thermography at normal or hot temperatures and genetic correlations with egg and feather quality

“…Of the three body areas analysed, the shank surface temperature may be a reliable trait for introduction of heat dissipation ability in selection programmes. The heritability values obtained in this study for body surface temperatures are consistent with the previous estimates of 0.06 to 0.19 for internal body temperature (Tixier-Boichard et al, 1995;Loyau et al, 2013) in broilers and adult layers and with those obtained for comb surface temperature in broilers (0.12 at thermo-neutrality and 0.33 in hot conditions, Loyau et al, 2013). Tixier-Boichard et al (1995) found much higher heritability of internal temperature in adult males than in females (0.49 ± 0.03 v. 0.19 ± 0.02), which suggests that measurement of temperature in adult females can be affected by daily variations due to the ovulatory cycle.…”

Heritable variation in maternally derived yolk androgens, thyroid hormones and immune factors

“…Yolk THs enter the ovum from the female circulation and are assumed to reflect circulating THs (although possibly with some control, suggested by their nonlinear correlation; McNabb and Wilson, 1997;. There is evidence for heritability of thyroid function and circulating TH levels in adult vertebrates, including chickens (for example, McLachlan et al, 2011;Loyau et al, 2013). Thus it remains an open question whether heritability of yolk THs simply reflect consistent variation in female circulating T3 levels, or whether yolk T3 levels can evolve independently.…”

Cyclic variations in incubation conditions induce adaptive responses to later heat exposure in chickens: a review

“…The longer period of development and maturation of thermoregulatory mechanisms, including the hypothalamus-pituitary-thyroid and -adrenal axes, has recently been proposed as the critical period for TM to achieve efficient thermotolerance 2009a). Results obtained from Cobb broiler chickens Loyau et al, 2013) indicated that the critical period for improvement of thermotolerance is between days E7 and E16 of embryogenesis, a period which covers the setting up of both regulatory axes. TM during this period has a long-lasting positive effect on body temperature until day 70 of age (Piestun et al, 2013a), resulting in improvement in thermal resistance by reducing mortality during heat challenge by 50% in male chickens .…”

“…Second, the level of increase in incubation temperature during embryogenesis has to be accurately tuned. Thermal treatment during incubation of eggs has in many studies been based on repeated increases in incubation temperature up to 39.5°C to improve thermotolerance (v. 37.8°C; Moraes et al, 2004;Collin et al, 2007;Piestun et al, 2008;Loyau et al, 2013). A treatment temperature of 41°C appeared to be too high to maintain hatchability as good as in controls (Yahav et al, 2004a).…”

“…Improvement of embryo's heat thermotolerance has been the goal of many studies during recent decades (Iqbal et al, 1990;Piestun et al, 2008;Yahav, 2009;Druyan et al, 2012;Loyau et al, 2013). The hypothesis on which these studies were based highlighted the positive effects of increasing incubation temperature on the long-lasting improvement of thermotolerance.…”