The World's Poultry Science Association (WPSA) is a long-established and unique organization that strives to advance knowledge and understanding of a

Commercial broilers are increasingly being subjected to environmental temperatures that are above their comfort zone. This is mainly because birds are growing faster than before and are therefore larger at any given age, but also because broiler production is being introduced as a farming system in environments that are unsuitable for such production. It is not economic for most producers to modify the environment within the broiler house to account for these problems and so it would be useful to know of nutritional strategies that could be used to reduce the effects of heat on broilers in the finishing stage.

1. As hens age, egg weight increases but the eggs contain proportionally more yolk and less albumen and shell. However, at a given age, larger eggs contain proportionally more albumen. When modelling the nutrient requirements of the hen over a production cycle, based on the daily outputs of each nutrient, egg weight needs to be predicted as the sum of the three components, since each has a unique chemical composition, and these proportional changes will therefore influence the nutrient requirements of the hen. 2. Yolk weight is related to hen age and may be calculated using a logistic or Gompertz function. Allometric functions are used to predict albumen weight from yolk weight and shell weight from the weight of the egg contents. 3. A mechanistic, stochastic population model for layers may be used to verify that these functions correctly reflect the proportional changes in the egg components with advancing hen age and at a given age, over a range of egg weights. 4. The various parameters used in the equations need to be defined for the available genotypes.

1. Various theories have been proposed to explain the reduced performance of broilers when given feeds excessively high in protein, but a satisfactory solution to this problem had, up to now, not been found. Three experiments were conducted to test the hypothesis that the efficiency of utilisation of protein (e_p) is a linear–plateau function of the ratio between the feed apparent metabolisable energy and digestible crude protein contents (AMEn:DCP) and that dietary protein quality, feed allocation and sex do not influence this relationship. 2. A ‘linear–plateau’ model successfully described the efficiency of protein utilisation (e_p) as a function of AMEn:DCP in all three experiments. In Experiment 1, with both sexes being both ad libitum and control fed, the breakpoint was at 58.6 MJ AMEn/kg DCP. In Experiment 2, both sexes were fed balanced and unbalanced protein series, and at different rates, the slopes of the ascending part of the linear–plateau relationships for the different treatments were the same for all treatments (0.0204), and the inflection point was at 71 MJ AMEn/kg DCP. Using similar treatments in Experiment 3, the breakpoint for the balanced protein was 72 MJ/kg and for the unbalanced, 64, with a combined slope of 68 MJ AMEn/kg DCP. 3. The three experiments provide adequate evidence that e_p is a linear–plateau function of the dietary AMEn:DCP ratio with a breakpoint of around 66.2 ± 1.98 MJ AMEn/kg DCP. Below this critical ratio, food intake declines as does protein and lipid retention. 4. That broilers, like pigs, exhibit an energy-dependent phase when high-protein feeds are offered is of practical importance when formulating pre-starter feeds for broilers and starter feeds for turkey poults as the e_p of such feeds may well fall below the maximum due to the lack of dietary energy required to process the high dietary protein contained in such feeds resulting in poorer performance than expected.

Poor uniformity in a broiler operation reduces revenue and increases waste. Uniformity in body weight at harvest is influenced by variation in genotype, environment and feed composition and form. Variation in growth in broilers within each sex is usually relatively small, but increases markedly when a poor quality feed is given. In attempting to grow to meet their potential when fed a diet low in protein, birds need to overconsume energy and then release excessive amounts of heat to the environment, although this ability is constrained by both feather cover and the ability to fatten. Consequently, as broiler genotypes have become faster growing and leaner, there is an increased need to feed higher levels of balanced protein in a cooler environment as a means of improving uniformity. Separating the sexes and reducing the range in day-old body weights will assist in achieving better uniformity at harvest.