A comparison between chromium-mordanted hay and acid-insoluble ash to determine apparent digestibility of a chaffed, molassed hay/straw mixture.

This study investigates the accuracy of using either chromium-mordanted hay or acid-insoluble ash to measure the apparent digestibility of a particular hay/straw mix in horses. The results suggest that although both methods yield similar estimates, chromium may underestimate and acid-insoluble ash may overestimate the figure, and amongst these two, acid-insoluble ash is the preferred method due to less variation.

Research Methodology

• The study was carried out on four mature horses individually stalled and kept on rubber mats. The mean weight of the horses used for the experiment was 606 kg.
• The horses were given a preliminary feeding period of 18 days followed by a collection period of ten days. The feeding schedule was fixed at four hours intervals: 08.00 hrs, 12.00 hrs, 16.00 hrs, and 20.00 hrs.
• The feed used in the experiment was a chaffed, molassed hay/straw mixture. The first feed also included chromium-mordanted hay.
• During the collection period, the horses’ faeces were sampled over a 24-hour period on days 3 and 10. Additionally, faecal material was also sampled at 10.00 hrs and 16.00 hrs throughout the ten-day period.

Results and Findings

• The average chromium recovery from faecal samples was found to be 96.5% with a standard error (se) of 0.76. The hay/straw mixture contained 7 MJDE/kg dry matter and 15.1 g DCP/kg dry matter.
• No significant difference was observed between the chromium and acid-insoluble ash methods for estimating the apparent digestibility of the feed. However, it was noted that chromium measurements tended to underestimate the digestibility values, while acid-insoluble ash seemed to overestimate them.
• Furthermore, the researchers found that there was a significant variation in faecal chromium concentration for each horse over a 24-hour period when compared to acid-insoluble ash concentrations. Thus, it was concluded that indirect estimates of apparent digestibility of nutrients in the equine could have large errors if chromium is used as a marker.

Conclusion

• If total faecal collection is impractical, the study recommends using acid-insoluble ash as the preferred indirect marker for estimating apparent digestibility coefficients for nutrients in horses, as it produced more consistent results compared to chromium.