Swine responses to constant and modified diurnal cyclic temperatures

Ad libitum fed and individually penned crossbred gilts (39 ± 2 kg) were exposed to a constant air temperature of 30.8*" C (CON) and equal-mean diurnal cyclic temperatures cycling from 26° to 33* C (RPK) and from 23.4° to 40° C (RNT). Fluorescent lighting with an intensity of 800 to 1100 L/m/m2 was provided from 0600 h to 2100 h. Measurements of feed intake, heat loss rates, water usage, growth, and ingestion behavior were made for a five-day period and replicated six times. Daily average heat loss rates, water usage, and feed conversion of the RPK and RNT pigs could be predicted with those of the CON pigs. However, daily feed intake and growth of the RNT pigs, 1.56 kg and 0.70 kg, respectively, were reduced (p < 0.01) compared to the CON pigs (1.71 and 0.82) and the RPK pigs (1.78 and 0.84). Ingestion patterns of the pigs for all treatments were characterized by a meal size of 160 to 170 g/meal-pig, drink size of 250 to 270 g/drink-pig, meal frequency of 9 to 11 meals/day, drink frequency of 36 drinks/day-pig, meal duration of 13 to 14 min/meal, and drink duration of 0.6 min/drink. Hourly feed intakes of the pigs were unevenly distributed throughout the 24-h period. Total heat production generally increased about two to three hours after an increase in feed intake and declined accordingly.