Modeling energy requirement for layer-type chicks reared at different ambient temperatures

Precision feeding of poultry depends on the dynamic estimation of nutrient requirement, which is related to the physiological stage and rearing temperature. The objective of this study is to determine the effect of temperature on the net energy requirement of layer-type chicks in the periods from 1 to 14 d of age. In trail 1, the energy requirement for maintenance (MEm) of chicks at different temperatures was measured. A total of 160 one-day old Jingfen layer-type chicks were selected and divided into five groups with four replicates of eight chicks. The chicks were randomly subjected to one of five temperature treatments: 30, 32, 34, 36, and 38 °C. After 4-days adaptation, the oxygen consumption and CO₂ production were measured at 6-days of age for 72 h with open-circuit negative pressure respiratory thermometry device. n trial 2, the growth performance of chicks reared at different temperatures was determined to evaluate the NE requirement for body weight (BW) gain. A total of 480 1-day-old chicks were divided into five groups and each group had 12 replicates of eight chicks. The rearing temperatures were 32-30-29 °C, 33.5-32-30.5 °C, 35-34-32 °C, 36.5-36-34 °C, and 38-38-35 °C in the periods from D 1 to D 3, D 4 to D 7, and D 8 to D 14, respectively. During the 14-days experimental period, all the chicks had free access to feed and water. The body weight and feed intake were measured weekly. Body composition and energy content were determined at the beginning and end of the experiment. The result showed that the fasting heat production (FHP) was decreased with increasing temperature (P < 0.001). The FHP of chicks at 30, 32, 34, 36, and 38 °C was 519.70, 710.80, 493.50, 361.70, and 437.90 kJ/kg W^0.75/day, respectively. The BW gain and feed intake were decreased (P < 0.001) when temperature increased, whereas the feed conversion ratio was changed by temperature only in the period of D 1 to D 7 (P < 0.01). The relative weight of heart (P < 0.05), liver (P < 0.001), and breast muscles (P < 0.001) were decreased with increased temperature. The NE requirement for BW gain was not altered (P > 0.05) by temperature. The NE requirement of Jingfen layer-type chicks in the periods from 1 to14 days of age is: NE (kJ/bird·day^-1) = (505.93 - 162.78T - 38.87T² + 194.41T³)·kgW^0.75 + 7.16·BW gain (g/d).