Date of Award
MS in Agriculture - Animal Science
COMPLETION OF AN IN VIVO DIGESTIBILITY TRIAL IN HORSES AND IN VITRO DIGESTIBILITY ASSAY DEVELOPMENT
Cassandra Renee Sweeney
In vivo analysis of equine feed digestibility has been the gold standard since the late 1800's, although it can be time consuming, costly, and labor intensive. In vitro digestibility analysis may be more economical and beneficial to both feed manufacturers and consumers. The availability of accurate in vivo data is crucial for critical evaluation and validation of any potential in vitro method (Coles et al., 2005). Ten adult American quarter horse geldings were used in the in vivo digestibility evaluation of two complete pelleted feeds fed as 100% of intake. The ingredients of the two treatments were similar: wheat middlings, rice hulls, alfalfa and beet pulp. The treatments differed in added mineral sources, yeast, direct fed microbials, and Yucca schidigera extract, added to enhance dry matter digestibility of the test diet. The in vivo evaluation consisted of two phases in a randomized crossover design. Total daily dry matter intake (DMI) and daily dry matter excretion (DME) were measured. Apparent digestibility (aDig) of % DM, % NDF, % ADF, % ADLom, and % OM (DM) were also calculated. No differences were seen in aDig of NDF, ADF, ADLOM or OM between the two experimental diets (P > 0.05). There was also no difference in DMI or DME, as a percentage of body weight (BW), between the two experimental diets. The effect of phase was not significant for all tests run on aDig, DMI, and DME (P > 0.05). BW was not significantly different (P > 0.05) between diets, however there was a trend for v heavier BW during phase 2 (P = 0.073). In vitro digestibility assay development followed the in vivo evaluation. A three-stage batch system as briefly described by Boisen and Fernandez (1997) was utilized. Through literature review, trial and error, personal communication with other labs and product and chemical manufactures, careful documentation of the methods were detailed. Using the control feed from the in vivo evaluation, variation in the methods was significantly reduced, and estimations of DML began to approach those seen in vivo throughout method development. Although further method development may be needed for species-specific use, the methods described here can provide the foundation for future in vitro digestibility studies.