Chewing Requirements and Glycemic Response of Fibrous Feedstuffs

Chewing duration is important for optimal horse health and welfare. The saliva produced during chewing buffers stomach acid, and longer chewing times can reduce the risk of boredom and stereotypies. Increased chewing may also result in lower glycemic responses, which could be important for certain horses. The study objectives were to determine whether there were differences in chewing and glycemic response among fibrous feeds. Five Thoroughbred geldings on a regular dental schedule participated in a 5 × 5 Latin square design over five 7-d periods. The treatments were soaked beet pulp shreds (BP; 41% NDF; 10.4% NSC; DM basis), fat-and-fiber pellet (FP; 39% NDF; 16% NSC), high-NDF long-stem timothy hay (HTH; 62% NDF; 16.2% NSC), and moderate-NDF long-stem timothy hay (MTH; 52% NDF; 7.6% NSC). Whole oats were included as the fifth treatment for glycemic indexing purposes only; no chewing data were collected for oats. Horses were fed 500 g of their treatment twice daily. Chewing halters were used to measure the number of chews taken and time spent chewing on d 4–6 of each period (3 observations/horse/period). A glycemic response test was conducted on d 7 over a 6-h period. Data were analyzed using repeated measures ANOVA, and relationships between chewing and glycemic response variables were measured using simple Pearson correlations. Horses consumed FP the fastest and the 2 hays the slowest, with BP consumed at an intermediate rate (P < 0.05). The number of chews per minute was lower in the HTH and MTH treatments compared with FP and BP (P < 0.05). Other research has demonstrated that long-stem hay requires larger jaw movements while chewing, which could slow down chewing rate. In addition to a slower chewing rate, the 2 hays and BP also required a greater number of chews per kg of DM compared with FP (P < 0.05), perhaps because the pellets broke apart the most easily during chewing. Due to differences in NDF among the feeds, chewing was expressed on an NDF basis, and there were no differences among feeds in chews per kg NDF (P > 0.10). Glycemic index was greatest for FP compared with BP and both hays, which were all similar to each other (P < 0.05). There were positive correlations between rate of intake and glycemic index (r = 0.81; P < 0.0001), and chews per minute and glycemic index (r = 0.45; P = 0.05). There was a negative correlation between glycemic index and chews per kg DM (r = −0.710; P < 0.01). Long-stem hay was chewed slower than smaller particle feeds. However, the amount of chewing per kg NDF is similar, suggesting that fiber content may also play a role in chewing requirements.

Fowler, A.L., C. Guinard, N.A. Imbeault, V.L. Erwin, I.N. Grayston, P. Sweetman, M. Winchester, and J.D. Pagan. 2025. Chewing requirements and glycemic response of fibrous feedstuffs. Journal of Equine Veterinary Science 148:105541.