296 Short-Term Diurnal Heat Stress Modulation of Growing Gilt and Barrow Growth and Feed Intake

Abstract

Abstract During summer months, the increase in temperature and humidity can lead to heat stress conditions that have negative impacts on the growth performance of pigs. The objective of this study was to characterize the effects of diurnal heat stress (dHS) on gilt and barrow growth, day-time and night-time feed intake. Twelve gilts and 12 barrows (46.5 ± 2.47 kg BW) were individually housed in metabolism crates over two experimental periods. For Period 1, all pigs were housed in thermoneutral (TN) conditions (20-21°C and 40-60% humidity). Following the TN period, period 2 consisted of four days of dHS (6 h at 32°C, 18 h at 27°C, 40-60% humidity). The conditions in the dHS period were designed to replicate summer, industry-applicable cyclical heat stress conditions. In each period lasting 4 days, pig BW and feed disappearance were recorded and ADG, ADFI and G:F calculated. Additionally, within each day, 0700 to 1700 h (day-time) and 1700 to 0700 h (night-time) feed intake was recorded. Changes in pig body temperatures (BT) and respiration rates (RR) were measured daily at 0800, 1200 and 1800 h. Pig was considered the experimental unit, and all data were analyzed for the fixed effects of period (TN vs. HS), sex, and period-by-sex interaction. There were no period-by-sex interactions observed for any analyzed variable (P > 0.05). As expected, dHS markedly increased pig 3-day average BT and RR compared with their TN values (P < 0.05). Compared with TN, dHS BT measurements at noon, PM, and overall were on average 1.0°C greater (P < 0.0001). The RR was also increased by 200 to 300% for AM, noon, PM, and overall, for the dHS period as compared with TN (P < 0.001). Within the dHS period, BT was highest at the noon and PM recordings, and RR was highest at the noon recording (P < 0.0001). Pigs tended to have reduced ADFI during dHS compared with TN period (1.54 vs 1.70 kg/d, P = 0.051). During the TN period, pigs consumed 61% (1.03 kg) of daily total feed consumption during day-time and 39% (0.67 kg) in the PM period (P < 0.0001). The opposite effect was found during dHS, in which pigs consumed 33.3% (0.52 kg) of their total daily feed during the peak heat conditions (day-time) and 66.7% (1.02 kg) consumed in the cooler night-time period (P < 0.0001). Compared with barrows, gilts tended to have greater overall ADFI (1.61 vs. 1.48 kg/d; P = 0.079). Within both the TN and dHS period, gilts had a lower average noon BT (P < 0.05), and lower morning RR (P < 0.05). Altogether, three days of dHS increased pig RR and BT, and decreased ADFI. However, day- and night-time feed intake patterns changed compared with the TN period. Diurnal heat stress has similar impacts to both gilts vs. barrows.