Effect of Non-structural Carbohydrate Intake from Forage on Hindgut Fermentation Parameters in Horses.

PEARSON, AMANDA CATHERINE. Effect of Non-Structural Carbohydrate Intake from Forage on Hindgut Fermentation Parameters in Horses. (Under the direction of Dr. Paul Siciliano, Dr. Vivek Fellner, and Dr. Gerald Huntington). Two experiments were conducted to determine the effect of nonstructural carbohydrate (NSC) intake on indicators of hindgut pH and fecal fermentation characteristics. Experiment 1 (EXPT1) was conducted to evaluate the effects of grazing fall pasture (relatively high NSC concentration) versus hay (low NSC concentration). Experiment 2 (EXPT2) was conducted to determine the effect of grazing spring pasture in the morning (low NSC concentration) versus afternoon (higher NSC concentration). In EXPT1 six geldings were randomly assigned to one of two dietary treatments in Period 1 (P1): pasture fed (PF; n = 3) or hay fed (HF; n = 3). PF horses had access to nontoxic endophyte infected tall fescue pasture from 1300 to 0700 the following d, followed by stall confinement from 0700 to 1300 each d for 14 d. HF horses were individually offered non-toxic endophyte infected tall fescue hay (2% of body weight, as-fed) one time per d at 1300. This continued for 14 d. Treatments were then switched for an additional 14-d period, Period 2 (P2), so that all horses received both treatments. Fresh fecal samples were collected from each horse on d-14 of each period to determine fecal pH and to inoculate fecal batch cultures. Pasture grass samples reflecting what the horses ate were taken on d4-7 and d11-14 of each period and analyzed for chemical composition using NIR. Differences in response variables (fecal pH, VFA profiles, body weight) between treatments within horses were analyzed using a paired t-test. Mean pasture NSC concentrations were 11.26 ± 1.4%. Mean hay NSC concentrations were 6.80% NSC. Overall mean fecal pH (±SEM) was 7.49 ± 0.07 for HF and 7.20 ± 0.06 for PF and was statistically different between treatments (P = .04). Mean batch culture media total VFA concentration ± SEM was 85.25 ± 3.39mM for PF and 73.43 ± 5.76 mM for HF, and were not statistically different between treatments (P = .18). In EXPT2 six geldings were randomly assigned to one of two treatments: morning turnout (AM; n = 3) or afternoon turnout (PM; n = 3). The AM and PM groups were turned out every d at 0700 and 1230h respectively, and allowed to graze for 8h. Following the first 14-d period, treatments were switched for an additional 14-d period, so that all horses received both treatments. The AM and PM horses grazed non-toxic endophyte infected tall fescue in separate, adjacent grazing cells. Horses were housed in individual stalls while not grazing. Fresh fecal samples were collected from each horse on d-12 to determine fecal pH inoculate batch cultures. Pasture grass samples reflecting what the horses ate were taken on d9-11 of each period and analyzed for chemical composition using NIR. Response variables (fecal pH and VFA) were analyzed using analysis of variance for cross-over designs and pasture NSC concentration was analyzed using analysis of variance for repeated measures design. Mean NSC increased (P < .01) from 15.2 ± . 7% at 800hr to 21 ± . 7% at 1400hr and did not change further at 2000hr during P1, and was not different between sampling times during P2, resulting in a significant period and treatment x period interaction. Mean batch culture media total VFA concentration was higher (P = .005) for AM (81.6 ± 1.4 mM) compared to PM (70.4 ± 1.4 mM); and higher (P = .004) in P1 (82 ± 1.4 mM) compared to P2 (70 ± 1.4 mM). Mean fecal pH was not affected by period (P = .5) or treatment (P = .72). Effect of Non-Structural Carbohydrate Intake from Forage on Hindgut Fermentation Parameters in Horses by Amanda Catherine Pearson A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science