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

Abstract

Summary The aims of this study were to monitor electromyographic (EMG) activity of masseter muscle in healthy horses fed (i) different types of roughage and (ii) maize after different hay allocations. Four horses were offered the following three diets ad libitum: hay, haylage or straw/alfalfa chaff (SAC). In a second trial, four horses were fed cracked maize (CM) and hay in three different orders: (i) CM after a 12‐h overnight fast; (ii) CM immediately after restricted hay intake (0.6 kg hay/100 kg BW); or 3) CM after hay intake ad libitum. The activity of the masseter muscle was determined by EMG (IED®), and the following were measured: amplitude (muscle action potential = MAP, maximum voltage) and duration of MAP (s). The intake of hay or haylage was associated with intense masseter muscle activity (MAP: hay, 10 ± 1.7 V; haylage, 11 ± 3.3 V; and duration of MAP: hay, 0.31 ± 0.04 s; haylage, 0.30 ± 0.04 s). Similar intense chewing was measured for SAC (MAP 13 ± 3.8 V), although duration of the chewing cycle was relatively short (0.22 ± 0.03 s, diet p < 0.05), which is possibly related to the shorter fibre length. CM was consumed rapidly, with less intense masseter muscle activity (MAP 6.0 ± 1.5 V). Hay intake before CM did not affect chewing force of CM, but duration of chewing cycle was significantly prolonged by feeding hay ad libitum before CM was fed. The consumption of hay, haylage or SAC was associated with intensive masseter muscle activity that was likely to stimulate salivary flow rate. In contrast to roughage, concentrates like CM are consumed rapidly with less intensive masseter muscle activity. This situation is associated with a low salivary flow that may have an adverse effect on gastric function.

Silage and haylage for horses

“…Eating time is regarded as an important equine welfare issue as short eating times may increase the risk of development of oral stereotypies in horses (e.g ., McGreevy, Cripps, French, Green, & Nicol, ; Redbo, Redbo‐Torstensson, Ödberg, Hedendahl, & Holm, ). In a study (Vervuert et al., ) where equine intake time of forage DM was compared between haylage (745 g DM per kg, 384 g crude fibre (CF) per kg DM) and hay (891 g DM and 345 g CF per kg DM) fed ad libitum, both forages were found to give similar DM intake times (52 ± 10.4 and 39 ± 15.3 min per kg DM, respectively, p > 0.05). By monitoring masseter muscle activity in the horses, it was also found that number of chews per kg DM, amplitude of muscle action potential (V) and duration of muscle action potential (sec) was similar between hay and haylage diets, implying that intake and chewing behaviour did not differ between the hay and haylage used in the study (Vervuert et al., ).…”

Can Strain Dependent Inhibition of Cross-Bridge Binding Explain Shifts in Optimum Muscle Length?

“…It is a major input into musculoskeletal models (Delp et al 2007;Dick et al 2017), and has been used to draw the broad conclusion that muscles tune their operating length to maximize some aspect of performance (Rome and Sosnicki 1991;Herzog et al 1992;Burkholder et al 2001;Tu 2004;Azizi and Roberts 2010;Rubenson et al 2012;Arnold et al 2013;Azizi 2014;Holt and Azizi 2016;Foster and Higham 2017;Nikolaidou et al 2017). However, the variation in activation level with mechanical demand (Lieber and Brown 1992;Gorassini et al 2000;Hodson-Tole and Wakeling 2007;Morris and Askew 2010;Vervuert et al 2013;Seven et al 2014), and the activation-dependent shift in optimum length (Rack and Westbury 1969;Close 1972;Stephenson and Wendt 1984;Balnave and Allen 1996;Holt and Azizi 2014), suggest these predictions and interpretations may be subject to systematic errors.…”

The effect of activation level on muscle function during locomotion: are optimal lengths and velocities always used?

“…Activation level has been observed to vary as a function of speed during locomotion [31][32][33], substrate type during feeding [34] and gas composition during breathing [35]. Hence, if muscles always perform optimally, operating lengths and velocities should change with activation level in order to track the changes that occur in optima [25][26][27][28][29].…”