Genetic selection modulates feeding behavior of group-housed pigs exposed to daily cyclic high ambient temperatures

Abstract

This study was conducted to evaluate the effect of genetic selection (Lines A and B; Line A pigs have a greater proportion of Pietrain genes than those from Line B and therefore, selected for improved lean tissue accretion) on the feeding behavior of group-housed pigs exposed to daily cyclic high ambient temperatures. Feeding behavior of 78 barrows housed together in a single room was recorded in real time by five automatic feeders. The feeders registered each visit of each pig (day, hour, min, and second) and the amount of feed requested. Daily cyclic high ambient temperature was induced exposing pigs at 22°C from 18.00 to 10.00 h and 30°C from 10.01 to 17.59 h. From this temperature variation, day-period was divided into: 22°C(06-10h), from 6.00 to 10.00 h; 30°C(10-18h), from 10.01 to 17.59 h; and 22°C(18-06h), from 18.00 to 5.59 h. Meal criteria was estimated based on the probability of animals starting a new feeding event within the next minute since the last visit (Pstart). After defining the meal criteria, the number of meals (n), feed intake rate (g/min), feed intake (g/meal), feeder occupancy (min/meal), and interval between meals (min) of each animal were calculated. Greatest probability of starting to feed was observed at 22°C(06-10h), followed by 30°C(10-18h) and then 22°C(18-06h). Regardless of time period, pigs from line A had greater feed intake rate and lower feed intake, feed occupancy per meal and probability of starting a meal when compared with line B pigs. Only line A pigs had greater feed intake and feeder occupancy per meal at 22°C(18-06h) than remainder of the day. This indicates that pig feeding pattern is strongly related to the circadian rhythm. However, the genetic selection for improved lean tissue accretion may modulate pigs feeding behavior under daily cyclic high ambient temperatures.

Feeding Behavior of Finishing Pigs under Diurnal Cyclic Variation in Ambient Temperature

“…Alternatively, as long as pigs became more adapted to the CHS condition, they normalized their feed intake rate over the day, which resulted in a lack of period effect in the EP2. Our outcomes agree with Fraga et al [8], who also did not observe changes in feed intake rate throughout the day for pigs (22 kg to 105 kg of body weight) raised under a similar cyclic AT protocol. To maintain a constant feed intake rate throughout the day under cyclic AT, pigs increase the meal size, which implies an increase in meal duration [25].…”

“…Feeding behavior is affected by animal-related factors such as sex [22], breed [8], body weight [23], circadian rhythm [21], ambient temperature [7], type of heat challenge (warm constant × cyclic temperatures; [4]), origin, age [24], diet, and handling. Therefore, a single experiment with pigs with similar characteristics, differing only in the AT condition, as described in the present study, seems to be more suitable to evaluate the impact of AT on FB.…”

“…Based on the data grouped into meals, the number of meals (n/pig), meal size (feed intake, g/meal), meal duration (feeder occupancy, min/meal), feed intake rate (defined as the feed intake for each minute spent feeding over a meal, g/min/meal), and the interval between meals (min) of each animal were calculated. It should be noted that pig FB changes throughout the 24-h day occur regardless of AT [8,20]. In addition, the circadian rhythm may also change FB [21].…”

“…For this purpose, the probability of the pigs starting a new feeding event within the next minute (pstart) was calculated over the day (all dataset) and for the TN period, as well as for the HS period, and plotted against the interval between visits to the feeder. The meal criterion was estimated as the first point that minimizes the pstart curve as previously described [18] and had been recently used in this type of dataset [8,19]. To reduce the effect of random variation in the pstart function, a simple moving average over 21-minute intervals was used.…”

“…However, the impact on VFI is smaller for daily CHS compared to constant HS. This is because pigs show specific behavioral adaptations, such as reducing VFI during the warm periods of the day and increasing it during fresh periods, especially in the nocturnal period [5,8]. Since pigs are sensitive to their environment [9], lighting programs may also alter the feeding pattern of pigs.…”