Behavioral and stress responses to feeding time in pregnant sows under limit-fed regime

Abstract

We investigated the effect of feeding time on behavior and stress responses in pregnant sows under isocaloric conditions. Twenty-four sows were balanced for parity and randomly assigned to 1 of 3 feeding times. Corn-soybean meal-based diet was fed once at: 0730 (Control, T1), 1130 (T2), and 1530 h (T3). On average, sows received 7062 kcal ME/d from 2.20 kg of diet formulated to contain SID Lys/ME of 1.71 g/Mcal. The study was conducted for 28 days (21 d acclimation to the feeding regime and 7 days data collection). Saliva samples were collected every 2 hours for 12 hr in stalls on day 52 of pregnancy. Behavior data were collected 24 hr for 7 d from day 53 of gestating by affixing a remote insights ear tag to each sow. Each sow had 120,960 data points categorized into: "Active", "Feed" or "Dormant". Due to housing constraint, all sows were housed in individual stalls in the same barn presenting a potential limitation of the study. Data were analyzed using PROC MIXED and GLIMMIX procedures of SAS 9.4 for cortisol and behavior data, respectively. Sow was the experimental unit. The area under the curve (AUC) is quantitative evaluation of response as threshold varies over all possible values. A 12-hr cortisol total area under the curve (AUC) for sows fed once daily at 1130 h was reduced relative to sow group fed at 1530 h (P = 0.046) but similar compared with the control sows (P = 0. 323). The control sows (0730 h) had reduced total (P < 0.001) and feeding (P = 0.001) activity AUCs relative to sows on 1130 but did not differ compared with sows on 1530 h feeding schedules (P > 0.100). Sows on 1130 h feeding schedule had greater feed anticipatory activity (FAA), 24-hr total activity count, total (P < 0.001) and feeding (P < 0.001) activity AUC compared with sows fed daily at 1530 h. In conclusion, feeding pregnant sows earlier in the morning (0730 h) appears to minimize sows’ behavior but similar cortisol response. Sows on 1130 h feeding schedule had greater activities but reduced cortisol concentration, suggesting that elevated sow activity might not necessarily indicate activation of hypothalamic-pituitary-adrenal axis.