Tropical grass digestibility assessed by the mobile bag and in vitro methods in horses.
Authors: Silva A H, Lucena J E C, Taran F M P, Cunha D S, Almeida J A T, Lima R S, Dias W S, Santiago J M
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Tropical Grass Digestibility Assessment in Horses Evaluating forage quality through digestibility measurement is essential for formulating appropriate rations for horses, yet traditional in vivo methods using mobile nylon bags are labour-intensive and costly. Silva and colleagues (2024) compared digestibility values obtained from the mobile bag technique—where nylon bags containing grass samples are placed directly in the horse's digestive tract—against an in vitro method using horse faecal inoculum across five tropical grass species, including Tifton 85 hay, Sabi grass, Alexandergrass, and two native grasses. Results demonstrated that the in vitro method produced comparable digestibility estimates to in vivo measurements for Sabi grass and sixweeks threeawn (P>0.05), but significantly underestimated nutrient digestibility in Tifton 85, Alexandergrass, and capim-de-raiz, with particular discrepancies in crude protein and fibre fractions. Importantly, mobile bags remained in the equine gastrointestinal tract for an average of 43.69 hours, with retention time varying by grass type and influencing digestibility outcomes. For nutritionists and feed advisors working with tropical forages in resource-limited settings, the in vitro method offers a practical alternative for some grass species, though validation remains necessary for cultivated varieties such as Tifton 85 that demonstrate systematic method bias.
Read the full abstract on PubMed
Practical Takeaways
- •For nutritionists and veterinarians: The in vitro digestibility method offers a faster, non-invasive alternative to mobile bag testing for certain tropical grasses, specifically sixweeks threeawn and Sabi grass, potentially reducing study costs and animal handling stress
- •When evaluating Tifton 85 hay for horses, mobile bag results will differ from laboratory in vitro predictions—field-based digestibility assessment may be more reliable for this commonly used forage
- •Understanding grass-specific retention times (43.7 hours average) helps predict nutrient availability and plan feeding schedules for horses consuming different tropical grass species
Key Findings
- •In vivo mobile bag and in vitro methods showed no significant difference for Sabi grass and sixweeks threeawn digestibility (P>0.05)
- •Tifton 85 hay showed significant differences between in vivo and in vitro methods for all nutrient digestibility parameters (P<0.05)
- •Mobile bag retention time in equine digestive tract averaged 43.69 hours, with sixweeks threeawn and Sabi grass having shorter retention times than other grasses tested
- •In vitro method using equine fecal inoculum can reliably replace mobile bag method for digestibility assessment of sixweeks threeawn and Sabi grass