Date of Graduation

Fall 2019


Master of Science in Agriculture


College of Agriculture

Committee Chair

Gary Webb


Previous research indicates equine fecal inoculates produce comparable results to cecal fluid when used for in vitro procedures to analyze dry matter digestibility (DMD). Equine hindgut microbial populations represented in fecal samples have been shown to be affected by diet. The objective of this study was to determine the effect of diet on in vitro DMD when fecal samples from horses on varying starch and fiber diets were used as inoculates. Six mature Quarter Horses (BW 522 ± 45kg) were used in a crossover repeated measures design to compare the effects of a grain vs. all forage diets on the in vitro digestion of forages ranging: CP 7.7 to 16.4 %DM, NDF 53 to 72 %DM. Treatments were a grain diet of corn chops and mixed grass hay with alfalfa cubes and a forage only diet of mixed grass hay with alfalfa cubes. Horses were divided into two groups of three and assigned an initial start diet. Fecal samples were collected from each horse on days 0,11, 22, 33, and 44, with groups switching treatments on day 22. Inoculum prepared from samples were used in the Ankom Daisy II Incubator® to compare DMD after fermentation. Digested NDF (NDFD) and digested ADF (ADFD) of forage samples were analyzed using the Ankom2000 Fiber Analyzer®. Data were analyzed using the MIXED procedure of SAS using covtest to evaluate digestibility differences in the diet by forage parameter interaction. After the 22d adaptation period, fecal samples from horses on the grain diet promoted higher NDFD of forages with high NDF and low CP when CP and NDF were used as covariates (P=0.04 and 0.03, respectively). Dry matter digestibility tended to be higher (P=0.08). There was a significant horse effect on DMD and NDFD (P≤0.05). Findings suggest diet may influence hindgut microbial population to the extent of effecting fiber digestion and should be considered when selecting equine fecal samples for in-vitro digestion procedures. Increased digestibility of lowquality forage was seen when horses were fed a grain diet. In addition, pooling fecal samples from more than one donor consuming various diets may yield more precise results for in vitro digestibility trials. Further investigation of forage digestibility using a broader spectrum of forage types may elucidate a more distinct pattern of the dietary impact on fiber digestion.


Equine, microbial population, fermentation, digestion, NDF, ADF

Subject Categories

Animal Sciences


© Taylor N. Godwin

Open Access