Two trials were conducted to study the effects of heat stress during rearing (trial 1) and crating (trial 2) on broiler stress parameters and fear, breast meat quality, and nutrient composition. The relationships between stress parameters and meat quality traits were also determined. Trial 1 consisted of 3 temperature treatments from 3 to 7 wk: control (temperature was 22 degrees C); diurnal cyclic temperature (temperature was 28 degrees C from 1000 to 1700 h and 22 degrees C from 1700 to 1000 h); and constant high temperature (34 degrees C; temperature was 34 degrees C). In trial 2, broilers from the control and 34 degrees C groups in trial 1 were used. Broilers in each group were placed in transport cages. The 9 cages from the control group were divided into 3 groups and placed into 3 rooms at 15, 22, or 34 degrees C for 2 h. The 3 cages from the 34 degrees C group were also held in the room at 34 degrees C (34-34 degrees C). Diurnal cyclic temperature had no effect on BW up to 5 wk of age. The effect of 34 degrees C constant temperature on BW of broilers increased with age. Plasma levels of glucose and albumin increased by 34 degrees C, but no dramatic change in levels occurred when those broilers were crated at 34 degrees C. The heterophil:lymphocyte (H:L) was higher for the 34-34 degrees C broilers and the control broilers in the 34 degrees C room than those from the 22 and 15 degrees C room. Breast muscle glycogen level decreased in broilers reared under diurnal cyclic or high temperatures. A lower pH and higher lightness (L*) and redness values and redness:yellowness were found in meat for broilers from both 34 degrees C and 34-34 degrees C groups. Higher H:L was associated with breast muscle pH according to first-order polynomial regression. The H:L had a significant effect on L* values, which were described by a second-order polynomial regression. Blood glucose level was positively correlated with L* and redness values. Duration of tonic immobility was neither influenced by rearing and crating temperatures nor associated with meat quality parameters.

A study was conducted to evaluate the effect of genotype by environment (G x E) interaction on the performance of commercial broilers. Temperate and hot environments were established by making use of the natural climatic differences between spring and summer in western Turkey. The experimental population was produced by a full-pedigree, randomly assigned mating scheme consisting of 29 sires and five dams per sire. The sires were considered genotypes, and the G x E interaction was evaluated by regressing sire breeding values in summer on those estimated from their spring offspring. The correlation between the two seasons for weight gain from 0 to 4 wk of age was r = 0.26, significantly lower than rho = 1 (the expectation when there is no G x E interaction). This correlation was even negative (although not significantly lower than rho = 0) for weight gain (WG) from 4 to 7 wk of age and BW at 7 wk of age. Genotype by season ANOVA also revealed highly significant G x E interaction effects on all traits. These interactions suggest the presence of substantial genetic variation in the magnitude of heat tolerance. It appeared that this variation was not random, but rather related to growth potential, where genotypes that gain more weight in the spring tended to gain less weight under the hot conditions of summer.

Hot climate is a major limiting factor of broiler production in tropical and subtropical regions. The use of standard stocks in hot climates may result in large economic losses because genotypes selected in temperate climates may respond differently to the high ambient temperatures in hot regions or seasons. The summer and fall in Izmir, Turkey, provided the natural hot and temperate climates, respectively, for this study. Broiler chicks were obtained from three commercial stocks, all bred in temperate climates. Male and female chicks, 60 per pen, were housed in four pens per stock per season. Individual BW was determined at hatch, and at 4 and 7 wk of age. Feed consumption and efficiency were determined per pen. Feathering was scored at 4, 5, and 6 wk of age. Body temperature was measured twice on three birds per sex per pen, 16 h and immediately before slaughter, and feather weight was determined for each of these birds. The two seasons clearly differed in ambient temperature at the broiler house, and consequently, BW at 7 wk was significantly lower in the summer than in the fall in all stocks, with an average reduction of 23%. The season effect was largest (33.5%) on BW gain from 4 to 7 wk, along with 23 and 15% reductions in feed consumption and efficiency, respectively, during these 3 wk. A significant season by stock interaction was detected for BW gain from 0 to 4 wk and 4 to 7 wk. The three stocks exhibited similar 4- to 7-wk BW gains under the temperate fall climatic conditions, but differed significantly in the summer. These differences were not related to normal differences in feather coverage or body temperature, suggesting that standard broiler stocks must be tested in hot climates in order to find the one most suited to these conditions.

Injurious pecking (IP) represents a serious concern for the welfare of laying hens (Gallus gallus domesticus). The risk of IP among hens with intact beaks in cage-free housing prompts a need for solutions based on an understanding of underlying mechanisms. In this review, we explore how behavioural programming via prenatal and early postnatal environmental conditions could influence the development of IP in laying hens. The possible roles of early life adversity and mismatch between early life programming and subsequent environmental conditions are considered. We review the role of maternal stress, egg conditions, incubation settings (temperature, light, sound, odour) and chick brooding conditions on behavioural programming that could be linked to IP. Brain and behavioural development can be programmed by prenatal and postnatal environmental conditions, which if suboptimal could lead to a tendency to develop IP later in life, as we illustrate with a Jenga tower that could fall over if not built solidly. If so, steps taken to optimise the environmental conditions of previous generations and incubation conditions, reduce stress around hatching, and guide the early learning of chicks will aid in prevention of IP in commercial laying hen flocks.

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