Ingestive mastication in horses resembles rumination but not ingestive mastication in cattle and camels

Abstract

Horses achieve a higher degree of particle size reduction through ingestive mastication than functional ruminants. We characterized mastication using chew-monitoring halters (RumiWatch) in six domestic horses, cattle, and Bactrian camels each. All animals were offered grass hay of the same batch for 15 min. In cattle and camels, measurements were continued after eating until rumination was observed. Except for one horse, 96% of the horses' ingestive mastication data were identified as "rumination" by the proprietary RumiWatch algorithm, whereas ingestion and rumination by cattle and camels were mostly classified correctly. There were no systematic differences between cattle and camels. In cattle and camels, ingestive mastication was less regular than rumination, indicated by significantly higher standard deviations of chewing peak intervals, peak heights, and peak breadths in intraindividual comparisons. The average standard deviations of these measures were lower in horses than in cattle and camel ingestive mastication, indicating a more consistent chewing pattern in horses. Horse values were similar to those of rumination mastication, suggesting equally regular chewing motions. Regular, rhythmic chewing represents a common feature of horses and functional ruminants, but the less uniform ingestive mastication in functional ruminants represents a deviating pattern, the adaptive value of which remains unclear. In particular, it does not appear to promote a higher ingestion rate. A potential cause may be the avoidance of high tooth wear rates by delaying a more regular, systematic mastication until ingesta has been softened and the grit has been washed off in the forestomach.

Dust and grit matter: abrasives of different size lead to opposing dental microwear textures in experimentally fed sheep (Ovis aries)

“…In ruminants, the majority of masticatory particle size reduction occurs not during ingestion but during rumination (Trudell-Moore and White, 1983;McLeod and Minson, 1988). During ingestion, ruminants chew less consistently than during rumination (Dittmann et al, 2017), which might also lead to less pronounced wear effects due to ingestive versus rumination mastication. Prior to rumination, the ingested material is subject to peristaltic movements in the rumen liquid, which washes off external abrasives; those rumen contents from which material is recruited for regurgitation and rumination are therefore depleted of external abrasives compared with the ingested diet (Hatt et al, 2019).…”

Comparative selective retention of particle size classes in the gastrointestinal tract of ponies and goats

“…In contrast, when feeding the same marker set to a domestic horse ( Figure 2b), no difference in the excretion pattern between the different-sized markers was evident. However, in horses, the more intensive ingestive mastication (Dittmann, Kreuzer, Runge, & Clauss, 2017;Janis, Constable, Houpt, Streich, & Clauss, 2010), together with their particularly efficient dental design (Rensberger, 1973), could reduce labelled long particles that are fed to the animals to such a degree that the result no longer represents different-sized particles. This concern is supported by the mean particle size observed in horse faeces of 0.5-1.9 mm (Carmalt, Cymbaluk, & Townsend, 2005;Clauss et al, 2014;Fritz et al, 2009;Gunnarsdottir et al, 2014;Zwirglmaier et al, 2013), which, due to the absence of rumination, can be used as a proxy for their chewing efficiency during ingestion (Carmalt & Allen, 2008).…”

Increasing food intake affects digesta retention, digestibility and gut fill but not chewing efficiency in domestic rabbits (Oryctolagus cuniculus)

“…studies (Findeisen et al, 2021). The difference between ruminants and nonruminants might stem from the fact that in ruminants, ingestive mastication is less systematic and consistent, and hence possibly less 'fixed', than in nonruminants (Dittmann et al, 2017). The effect of intake on faecal particle size then stems from the fact that at high fill of the reticulorumen, larger particles may escape retention and re-mastication (Hummel et al, 2018), rather than a reduction in rumination chewing efficiency itself (Findeisen et al, 2021).…”