Mathematical modelling of digesta passage rate, mean retention time and in vivo apparent digestibility of two different lengths of hay and big-bale grass silage in ponies.

The research article discusses an experiment on Welsh-cross pony geldings to determine the rate of passage and apparent digestibility of certain types of feed. The study used mathematical modelling to ascertain that silage has higher digestibilities than hay but the length of the chop does not affect it.

Objective of the Research

• The primary objective of the research was to study the digestibility rate and passage rate of different types of feed (grass silage and hay) in Welsh-cross pony geldings. They specifically compared unchopped big-bale grass silage, chopped big-bale grass silage, unchopped grass hay, and chopped grass hay.
• Furthermore, the research aimed to determine whether the length of the chop affected the digestibility of the feed.

Methodology

• The experiment used a 4×4 Latin square design and the feed was offered at about 15 g/kg body weight per day.
• To track the passage rate, the ponies were fed with ytterbium chloride hexahydrate-marked feed and total faecal collection was done 8 hours later, continuing for a total of 168 hours.
• Apparent digestibilities of various components like feed DM (Dry Matter), organic matter (OM), crude protein (CP, Nx6.25), acid-detergent fibre (ADF) and neutral-detergent fibre (NDF) were determined.
• The researchers used the models of Pond et al. (1988) and the algebraic method of Thielmans et al. (1978) to calculate and interpret the data.

Findings

• The research concluded that silage had significantly higher digestibilities of DM, OM, CP, ADF and NDF than hay. This indicates that ponies can more effectively digest silage than hay.
• However, the results showed that the chop length of the feed had no significant effect on its digestibility.
• The different models accurately described the pattern of faecal marker excretion, indicating that the retention time varied for different feeds.
• The research also found that big-bale grass silage and chopped hay diets had longer mean retention time (MRT) in the time-dependent compartment, whereas chopped big-bale grass silage and unchopped hay had longer MRT in the time-independent compartment.

Conclusion

• The research concluded that both unchopped and chopped big-bale grass silage are readily accepted and digested by the ponies.
• The use of Ytterbium chloride hexahydrate as an external marker was effective for determining total tract MRT and for modelling faecal excretion curves in horses.
• Despite the considered approach, the results did not allow any definite conclusions to be drawn on the digesta MRT within the different compartments of the equid gut.