Feeding motivation and plasma metabolites in pregnant sows fed diets rich in dietary fiber either once or twice daily

The present study investigated the effects of source and level of dietary fiber (DF) and feeding frequency (once vs. twice daily) on feeding motivation and plasma metabolites at 4 different time points post feeding. Sixty pregnant sows (Sus scrofa, 4 blocks of 15 sows) were allocated to 1 of 5 diets within blocks. Four diets were restricted (approximately 35 MJ ME/d): a barley and wheat control diet (171 g DF/kg DM; 12 g DF/MJ ME), and 3 fiber diets formulated to contain 35% DF by including pectin residue (323 g DF/kg DM; 25 g DF/MJ ME), potato pulp (404 g DF/kg DM; 29 g DF/MJ ME), or sugar beet pulp (367 g DF/kg DM; 25 g DF/MJ ME). The fifth diet was a mixture including an equal amount of the 3 fiber diets offered semi ad libitum (ad libitum access to feed during 6 periods of 1 h starting at 0300, 0600, 1100, 1500, 1800, and 2300; 354 g DF/kg DM; 25 g DF/MJ ME). The experimental period included 2 periods of 4 wk each. Restricted-fed sows were fed once daily (0800 h) during the first period and twice daily (0800 and 1500 h) during the second period, or vice versa. Semi ad libitum fed sows had access to feed 6 times a day in both periods. In each period, the feeding motivation was assessed in an operant conditioning test, and samples of peripheral blood were taken in a balanced design, at 0900, 1200, 1900, and 0700 h, corresponding to 1, 4, 11, and 23 h after feeding for restricted sows fed once daily. No differences in the feeding motivation were found between the 4 restricted diets at any of the time points post feeding, but semi ad libitum fed sows had a decreased feeding motivation (P < 0.001). Among the restricted-fed sows, feeding twice daily resulted in decreased feeding motivation at 1900 h (P < 0.001) and at 0700h (P < 0.05) compared with feeding once daily, but not at 0900 and 1200 h, indicating that feeding twice daily reduced feeding motivation during the night compared with feeding once daily. Among restricted-fed sows, plasma concentrations of short-chain fatty acids (SCFA) were greater in sows fed high-fiber diets compared with the control (P = 0.02). Nonesterified fatty acid was least in sows on the control diet and greatest in sows on the potato diet, whereas sows on the pectin and sugar beet diets were intermediate (P < 0.001). Less diurnal variation in glucose (P < 0.001) was seen in sows on high-fiber diets. In spite of the found effects on plasma metabolites, the applied level of fiber in the diet of restrictedly fed sows did not reduce their feeding motivation irrespective of fiber source.