Dietary self-selection of laying hens inadequate to overcome the effects of high environmental temperature

Diet selection by Japanese quail (Coturnix coturnix japonica) in relation to ambient temperature and metabolic rate

1. A choice between a high-energy, wheat-based, low protein mixture and a lower-energy, soya-based, high protein mixture offered to growing Japanese quail at ambient temperatures of 20 degrees, 25 degrees, 30 degrees and 35 degrees C. 2. the quail were kept in open-circuit respiration calorimeters, so that diet selection could be related to energy requirement. 3. Increasing ambient temperature had no significant effect on food intake by weight, but the proportion of the high energy choice decreased and, conversely, the proportion of the lower-energy but higher-protein choice increased. 4. Energy intake was therefore negatively correlated with ambient temperature, but protein intake per unit of energy intake increased, allowing the birds to gain weight at about the same rate at all temperatures. 5. Heat production decreased as ambient temperature increased. Respiratory quotient decreased with increasing temperature, which indicates a reduced utilisation of carbohydrate as an energy source. 6. Water intake increased with temperature but there were no overt signs of heat stress and there was no significant change in body temperature. 7. Japanese quail selected a dietary mixture which maintained similar growth rates over a wide range of ambient temperature, by sustaining protein intake but altering energy intake in line with thermoregulatory energy demands.

Effect of diet and natural variations in climates on the performance of laying hens

1. Laying hens raised in 3 natural tropical environments were fed on 2 series of diets with a view to defining the optimum combination of climate and dietary energy. 2. A combination of 3 growing climates, 3 laying climates (temperate, hot dry, hot humid), and 2 dietary energy concentrations (10.03 and 11.70 MJ ME/kg with protein concentrations proportional to energy) were tested for 46 weeks using 432 point-of-lay pullets. 3. Both growing and laying climates significantly affected most traits measured during the laying period. The patterns of egg production showed good persistency in all environments and differences observed reduced with age. 4. The difference between the high and low energy intake reduced at high ambient temperatures. Feeding low energy diets did not affect mean age at first egg, rate of lay or the egg output in the hot dry environment, nor egg weight in either hot dry or hot humid climates. Rather, feeding low energy diets resulted in improved body weight change in all 3 laying environments. 5. The growing climate and diet interacted significantly on body weight change, while highly significant interactions between laying climate and diet occurred on rate of lay, food and energy intake and egg weight during the laying period.

Climatic adaptation of laying hens

Three hundred Warren Isabrown female day old chicks were raised for 18 weeks in 3 distinct artificial climates described as temperate (20 degrees C, 60% RH), hot dry (32 degrees C, 40% RH) and hot humid (32 degrees C, 90% RH). At 18 weeks each group was divided into 3 and re-allocated to 3 similar air-conditioned laying rooms as during the growing period. Different diets were fed to the 3 groups up to 18 weeks. The energy needed in order to produce the same average live body weight at 18 weeks was similar in all the 3 climatic chambers. The effect of treatments in the growing period was not significantly different (P > 0.05) for most of the parameters subsequently measured during the laying period. The exception was the body weight gain between 18 and 38 weeks and the food and energy intakes. However, apart from the sexual maturity, all these parameters were negatively influenced (P < 0.05) by the effect of hot climates during the laying period irrespective of method of rearing. The results of this study seem to indicate that ambient temperature experienced during the first 18 weeks after hatching has little effect on subsequent productivity and that rearing birds at high ambient temperature does not acclimatise them to these conditions better than rearing them under temperate conditions.

Protein and energy self-selection by turkey hens: reproductive performance

1. The influence of protein and energy self-selection on the reproductive performance of turkey hens was investigated. Large White turkey hens were fed on either a complete diet (185 g CP/kg, 11.30 MJ ME/kg) or were provided with a choice between a high protein-low energy diet (348 g CP/kg, 7.74 MJ ME/kg) and a high energy-low protein diet (81 g CP/kg, 13.39 MJ ME/kg). 2. Egg production, egg weight, and the fertility and hatchability of eggs produced were not significantly affected by the dietary treatments (P greater than 0.05). 3. While energy intake was not significantly different between groups, protein consumption decreased by approximately 40% (P less than or equal to 0.001) among self-selecting hens compared to hens fed on the complete diet. This resulted in a 10% (P less than or equal to 0.05) reduction in the food intake in the self-selecting birds.