Passage rate of digesta through the equine gastrointestinal tract: A review

Passage rate through the equine gastrointestinal tract is best described by mean retention time (MRT). Transit times of digesta differ greatly between the different parts of the gastrointestinal tract. Passage through the stomach and small intestine is rapid (5 h on average), whereas a longer retention time is recorded in the cecum and colon (35 h on average).Important considerations in estimating MRT have been the use of a solute phase and a fluid phase marker and calculations applied, especially when sampling frequency is reduced.A number of animal and feed related factors influence MRT: body weight, pregnancy and lactation may increase passage rate, whereas the impact of exercise, the most important animal related factor, will depend on the exercise type and the fluid/particle ratio.Information on the effect of the main feed related factors is lacking. Smaller particles and feed with a higher water-holding capacity move slower through the gut, but reduced fibre length, increased feeding level and increased forage/concentrate ratio will accelerate passage rate. Feeding frequency seems not to affect passage rate.Sometimes, conclusions are contradictory as effect of animals, feeds and methods are confusing.