Electromyographic evaluation of masseter muscle activity in horses fed (i) different types of roughage and (ii) maize after different hay allocations.

This research investigated the effect of different diets on the activity of the masseter muscle (a major jaw muscle) in horses, with the aim of understanding the influence of diet on the horse’s chewing function and potentially, their salivary flow rate. The study found that the consumption of hay, haylage, or straw/alfalfa chaff was associated with intensive masseter muscle activity. On the contrary, concentrates like maize were consumed rapidly with lower muscle activity.

Objective of the Study

• The study aimed to determine the impact of different types of roughage and the timing of maize consumption after different hay allocations on the activity of the masseter muscle in horses.

Methodology

• The trial used four healthy horses consuming three different diets in large quantities: hay, haylage or straw/alfalfa chaff (SAC).
• In a second trial, four horses were fed cracked maize (CM) and hay in three different sequence: CM after an overnight fast of 12 hours, CM immediately after restricted hay intake, and lastly CM after unrestricted hay consumption.
• The electromyographic (EMG) method was used to monitor masseter muscle activity, particularly focusing on the amplitude (muscle action potential or MAP, essentially the signal strength of the muscle’s activity) and duration of MAP.

Findings

• The study concluded that intake of hay or haylage was associated with significant masseter muscle activity, as was straw/alfalfa chaff, although the duration of SAC chewing was shorter, possibly linked to its shorter fibre length.
• In contrast, cracked maize was consumed more quickly, with lower intensity of masseter muscle activity.
• Unrestricted hay intake before feeding cracked maize did not affect the intensity of masseter muscle activity during maize consumption, but it significantly prolonged the duration of the chewing cycle.

Implications

• The intensive masseter activity associated with hay, haylage, and SAC consumption is believed to stimulate salivary flow, unlike concentrates like cracked maize, which are consumed quickly with less intensive muscle activity.
• This situation could lead to lower saliva production, potentially impacting gastric function in horses — a consideration for both the health and performance of horses in various settings.