QUANTITATIVE EVALUATION OF HUNGER IN PREGNANT SOWS: PHYSIOLOGICAL, BEHAVIORAL AND PERFORMANCE RESPONSES TO FEEDING TIME AND FREQUENCY UNDER LIMIT-FED REGIME

Abstract

The objectives of this dissertation were to determine the effects of feeding time and frequency on physiological and behavioral responses to hunger and investigate the impact on sow and litter performance under normal production conditions. Series of experiments were conducted to achieve these objectives. In exp. 1 and 2, a total of N = 300 sows (TN 70; Landrance X Yorkshire, Topigs Norsvin USA, Burnsville, MN) were used for the piglets and sow performance experiments. Sows were blocked by parity and farrowing date, balanced for BW, and randomly assigned to 1 of 5 treatments in a randomized complete block design. A subsample of n = 30, n = 40, (exp. 3) and n = 30 (exp. 4) sows were used for behavior, stress physiology, and hunger experiments, respectively. Treatments include sows fed corn-soybean meal-based diet once at [0730 (Control, T1), 1130 (T2), or 1530 h (T3)], twice [half ration at 0730 and 1530 h (T4)], or thrice [one third portion at 0730, 1130, and 1530 h (T5)], with daily feed quantity kept at 1.25× maintenance energy intake (100 × (BW)0.75) kcal ME/d. Treatments were imposed from d 30 to 109 of pregnancy for the performance exp. In the physiology and behavior exp., treatments were imposed from d 30 to 60 of gestation. Results showed that sows fed 2× daily during gestation had reduced incidence of stillbirth and improved the number of piglets weaned. Feeding time to elicit maximum insulin responses are 0730 and 1130 h but not at 1530 h. Elevated sow activity might not necessary indicate activation of hypothalamic-pituitary-adrenal axis (HPA). Feeding sows 2× daily reduced sows’ feed anticipatory activity, total activity, and feeding activity, and activation of the HPA axis. Consumption of 3 small meals (2311 kcal/meal) in 8 h resulted in 9.0% reduction in 23-h glucose total AUC. It is suggested that hunger in pregnant sows occurs at active ghrelin/total PYY ratio of 5.06 ± 0.20 and at a mean plasma glucose concentration of 70.37 ± 1.39 mg/dL and below. These studies provide insight to feed pregnant sows twice daily to improve their welfare and enhance pig productivity.