Quantitative Evaluation of Stress in Pregnant Sows in Response to Time Restricted Feeding and Meal Frequency Under Limit Feeding Regime.

The objective of the study was to quantify stress in pregnant sows in response to time restricted feeding and meal frequency. Thirty-seven pregnant focal sows [(Landrace X Yorkshire); initial BW 226.10±3.10 kg; parity 3.1±0.42; from 2 cohort groups of sows were blocked by parity and BW and randomly assigned to 1 or 5 treatments in completely randomized design. Sows were fed corn-soybean meal-based diet once [0730 (Control, T1), 1130 (T2), or 1530 h (T3)], twice [half ration at 0730 and 1530 h (T4)], or thrice [a 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. On average, sows received 6934.5, kcal ME day^-1 from d30 to d60 of gestation. The gestation diet was formulated to contain SID Lys:ME of 1.71 g/Mcal. Saliva sampling with synthetic swab was done on d52 of pregnancy from 0630 to 1830 h, every 2 hours in stalls. Saliva was extracted, stored at -20℃, and subsequently assayed for cortisol concentration by ELISA technique. Sensitivity of the assay and the intra-assay CV of samples were 0.04 ng/mL and 8.7% respectively. Data was analyzed using PROC MIXED REPEATED MEASURES, (SAS 9.4). Sow was the experimental unit. Cortisol total area under the curve (AUC) was determined by trapezoidal summation method. Response to treatments was conducted via pre-planned contrast statements. Significance was set at P-values ≤0.05 while P-values >0.05 and ≤0.10 considered a trend. Results are presented as least squares means ± SE. Cortisol AUC for sows fed once daily around noon tended to be lower compared to the control group (319.35±46.2 vs 269.34±46.2 ng*min/ml; P=0.100) but lower than sows fed at 1530 h (349.10±45.2 vs 269.34±46.2 ng*min/ml; P<0.001). Feeding sows twice daily led to significant reduction of cortisol AUC relative to both the control group (319.35±46.2 vs 246.52±46.17 ng*min/ml; P<0.021) and sows fed three times daily (355.09±45.4 vs 246.52±46.17 ng*min/ml; P<0.001). Cortisol AUC was similar in the control sows and the group fed thrice daily (355.09±45.4 vs 319.35±46.2 ng*min/ml; P=0.209). The results provide evidence of the influence of time restricted feeding on the diurnal saliva cortisol secretion, but no clue was found as to why feeding the same amount of feed at different time of the day tended to affect the pituitary-adrenal axis differently. In conclusion, feeding of pregnant sows around mid-day had synchronizing role by reducing the normal saliva cortisol oscillations. Additionally, feeding sows twice daily minimizes stress compared to once or thrice daily feeding under limit-feeding regime.