Laying hens have physiological responses that affect their productive performance when given different ambient temperatures. The objectives of this study were, first, to quantitatively describe the relationship between different constant environmental temperatures and egg production characteristics of laying hens by a statistical analysis and assessment of the published literature. Second, to compare the effect of different cycling environmental temperatures on the egg production characteristics of laying hens. Twenty-nine experiments were selected that had compared different constant temperatures and that included 21°C within their range. Differences in egg production were expressed as a proportion of the treatment group given 21°C within that experiment. An exponential curve with the addition of a linear trend gave the best (P<0.001) description of egg numbers, weight and mass, feed intakes and egg composition variables. There was a linear decrease (P<0.001) in measures of shell strength with increasing temperature. A second statistical analysis compared eight published experiments that had described the egg laying responses of laying hens kept in daily fluctuating temperatures and had been compared to a treatment group kept at 21°C within the same experiment. The results indicated that the egg laying responses of the hens were best predicted by computing the mean of the predicted responses to each of the temperatures that occurred during the day. However, information on the low temperature, the proportion of the day at the low temperature and the amplitude of the temperature cycle were required to give a precise prediction of the egg laying responses.

The interaction between essential dietary components and changes in tissue nutrient reserves, egg quality and egg composition, were studied from 60 d before and during the spawning of Sparus aurata broodstock. Fish were given isonitrogenous (550 g/kg dry weight) and isolipidic (100 g/kg dry weight) diets, based on protein and lipid extracts of squid meal. Diets differed in the levels of n−6 (10–30 mg/g dry weight) and n−3 (0–10 mg/g dry weight) essential fatty acids. The effects of these diets on biochemical and fatty acid composition of body tissues, and the subsequent effects on egg composition and egg viability were measured. Dietary essential fatty acids were mostly incorporated into the liver, ovaries, digestive tract and associated adipose tissues. The lipid composition of these tissues reached an equilibrium with dietary lipid composition within 15 d of feeding on any given diet. Muscle and gill cartilage tissues did not show any significant changes in their biochemical and fatty acid composition, even after 60 d feeding. Egg viability decreased significantly within 10 d of feeding the broodstock with a diet deficient in n−3 highly unsaturated fatty acids (n−3 HUFA). The levels of n−3 HUFA in both polar and neutral fractions of egg lipid were directly correlated with their levels in the broodstock diet. When the total amount of egg n−3 HUFA dropped below 17 mg/g dry weight, egg viability and larvae hatching rate decreased by 53% and 47 % respectively. These results suggest that the biochemical composition of organs involved in S. aurata reproduction are highly sensitive to the nutritional value of the diet, which affects egg and larval quality rapidly.