| Popis: |
A total of 216 Single Comb White Leghorn pullets were divided into three equal groups and individually caged in environmentally controlled chambers. The environments imposed were: (1) 21°C. constant (21° Co); (2) 31°C. constant (31° Co); (3) 26.7–35.6° cyclic with an average of 31°C. (31° Cy). Relative humidity was maintained at 50% in all environments. The hens in each environment were fed either a typical corn-soy laying diet or a “High Nutrient Density” (HND) diet (25% more of all nutrients except energy which was increased 10%). The data collected over 12 weeks showed that the following parameters were reduced by both heat stress conditions, but that the values for 31°Cy were intermediate between 31° Co and 21° Co: (1) egg production; (2) specific gravity of eggs; (3) shell thickness; (4) serum thyroxine levels. Factors which were lowered by heat stress, but which were not greatly different between cyclic and constant 31°C. included: (1) food consumption; (2) egg weight; (3) plasma calcium; (4) hematocrit values; (5) bone ash. Feed conversion was improved with high temperature, and the best conversion was noted in the 31° Cy environment. The HND diet increased egg production only at high temperatures, and egg production of hens fed the HND diet at elevated temperatures approached normal. Food consumption was decreased, egg size was increased, feed efficiency was improved and plasma calcium was increased by feeding the HND diet regardless of environment. However, diet had no effect on the various measures of shell quality (specific gravity, shell thickness, percent true shell). |
