Abrupt change from pasture to hay results in decreased body weight.
The use of the horse as a recreational and competitive animal often necessitates management changes that are challenging to the normal behavior and physiological well-being of the horse. In some instances, it is necessary to remove a horse from a free-choice pasture diet and impose an all hay diet (i.e. seasonal changes in MN).
When such changes are made, a loss in body weight (BW) has been observed. It has been speculated that the BW loss is the result of a decrease in a full gut (digestive track), as pasture forage tend to have higher moisture contents related to hay.
However, dry matter intake is correlated to water intake, thus hay-fed animals should be able to maintain a full gut and BW as a result of increased water consumption. This study was undertaken at Michigan State University to examine the effect of an abrupt diet change from pasture to a hay diet on BW and abdominal circumference (AC).
BW decreased immediately following a change from pasture to a hay diet, yet BW was not significantly different than the starting value by day 5.
The immediate decrease was likely a result of decreased feed intake by the horse due to the sudden diet change.
This data is not surprising, but supports that abrupt change from pasture to a hay diet results in a persistent decrease in BW, likely due to a decrease in gut fill.
The research also reinforces the need to change horse diets slowly. Horse owner are frequently reminded to gradually introduce horses to pasture (from hay) in the spring, but should also gradually remove horses from pasture (to hay) in the fall, especially if a reduction in body weight is a concern.