Comparison of In Vivo and In Vitro Digestibility in Donkeys

SIMPLE SUMMARY: Traditional in vivo methods of determining digestibility of feeds are expensive and time-consuming, and very few data are available for donkeys. The aim of this study was to verify if the in vitro method developed for the Ankom Daisy(II) Incubator could produce accurate estimates of the in vivo dry matter and neutral detergent fiber digestibility of diets fed to donkeys. Four donkeys and four diets were used in the trial, and the experiment was repeated four times. Buffered donkey feces were used as an inoculum source for the assessment of digestibility in vitro, with an incubation time of 60 h. The obtained results showed that the Ankom Daisy(II) Incubator ranked the diets in the same order as the in vivo method. However, in vitro values were lower than those obtained in vivo. The regression analyses used to predict in vivo estimates from in vitro data gave poor results and low precision. In conclusion, further studies, using different sample size and digestion times in vitro, are needed to verify if accurate prediction of in vivo feed digestibility can be obtained using the Ankom Daisy(II) Incubator and donkey feces as inoculum. ABSTRACT: We compared in vivo and in vitro dry matter (DM) and neutral detergent fiber (NDF) digestibility in donkeys using feces as microbial inoculum. Four donkeys were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. The animals were fed two types of hay, with or without flaked barley. For the in vivo procedure, total feces were collected for 6 days from each donkey; digestibility was calculated as the difference between ingested and excreted DM and NDF. For the in vitro procedure, donkey feces were buffered and used as microbial inoculum in an Ankom Daisy(II) Incubator; digestibility was estimated after 60 h of incubation. In vivo results showed that the addition of barley to hays did not change the digestibility values. In vivo estimates were higher than in vitro ones. The equations used to predict in vivo estimates from in vitro data were not reliable (R(2) = 0.47 and 0.21; P = 0.003 and 0.078 for NDF and DM digestibility, respectively). Further studies need to evaluate different sample size and digestion times.