Chewing rates among domestic dog breeds

Functional significance and welfare implications of chewing in dogs (Canis familiaris)

Dogs chew on both nutritive and non-nutritive items as part of their food acquisition, ingestive behaviour, self-care, and social interactions. Various definitions distinguish chewing from related oral activities, such as gnawing, masticating, and biting. Surprisingly, despite chewing being a ubiquitous behaviour in dogs, its relevance to a dog's comfort, health, and purpose remains unclear. Additionally, the risk of dental fractures or other injuries may lead veterinarians to advise against feeding bones to dogs. This article explores the literature on chewing in dogs through the ethological framework of "Tinbergen's Four Questions" and the Five Domains framework for animal welfare assessment. Evidence is gathered from wild and domestic canids and from human and animal models where shared physiological or biological processes provide insight. Chewing appears to promote biological fitness, providing benefits such as dental and oral hygiene, digestive health, bone strength, psychological health, and stress management. Furthermore, this article discusses the evolutionary importance of chewing, the mechanisms underlying bite force, chew rate and morphology, and the development of chewing throughout a dog's life, from primary teeth eruption to senescence. Application of the Five Domains framework for animal welfare helps assess the impact of chewing, or lack thereof, on a dog's welfare. A dog's preference for chew items is primarily driven by odour, taste, and mouthfeel. Macronutrient proportions may also play a role in food preferences, which, in turn, can affect the selection of chewable items. A lack of preferred chew items may result in redirected chewing toward less appropriate items, such as non-food chews that could be harmful to dentition or the gastrointestinal tract (GIT). Chewing on such inappropriate items may also lead to the adoption of alternative oral behaviours or reduced their contentment by impeding telos. Overall, chewing positively impacts a dog's physical and psychological health, contributing to its welfare and appearing essential as a regular part of a dog's daily life. However, the significant benefits of chewing must be carefully weighed against potential risks.

Computer simulations of food oral processing to engineer teeth cleaning

Oral biofilm accumulation in pets is a growing concern. It is desirable to address this problem via non-invasive teeth cleaning techniques, such as through friction between teeth and food during chewing. Therefore, pet food design tools are needed towards optimising cleaning efficacy. Developing such tools is challenging, as several parameters affecting teeth cleaning should be considered: the food’s complex mechanical response, the contacting surfaces topology as well as the wide range of masticatory and anatomical characteristics amongst breeds. We show that Finite Element (FE) models can efficiently account for all these parameters, through the simulation of food deformation and fracture during the first bite. This reduces the need for time consuming and costly in-vivo or in-vitro trials. Our in-silico model is validated through in-vitro tests, demonstrating that the initial oral processing stage can be engineered through computers with high fidelity.

Oral care based foods are of great interest for increasing the dental health of animals. Here, the authors report on computer simulations to optimise the texture and geometry of food in order to maximise tooth abrasion and enhance cleaning efficiency.

Physics of chewing in terrestrial mammals

Previous studies on chewing frequency across animal species have focused on finding a single universal scaling law. Controversy between the different models has been aroused without elucidating the variations in chewing frequency. In the present study we show that vigorous chewing is limited by the maximum force of muscle, so that the upper chewing frequency scales as the -1/3 power of body mass for large animals and as a constant frequency for small animals. On the other hand, gentle chewing to mix food uniformly without excess of saliva describes the lower limit of chewing frequency, scaling approximately as the -1/6 power of body mass. These physical constraints frame the -1/4 power law classically inferred from allometry of animal metabolic rates. All of our experimental data stay within these physical boundaries over six orders of magnitude of body mass regardless of food types.

Fracture investigation in starch-based foods

The study of oral processing and specifically cutting of the food piece during mastication can lead towards optimization of products for humans or animals. Food materials are complex biocomposites with a highly nonlinear constitutive response. Their fracture properties have not been largely investigated, while the need for models capable of predicting food breakdown increases. In this study, the blade cutting and the essential work of fracture (EWF) methodologies assessed the fracture behaviour of starch-based pet food. Tensile tests revealed rate-dependent stiffness and stress softening effects, attributed to viscoplasticity and micro-cracking, respectively. Cutting data were collected for 5, 10 and 30 mm s(-1) sample feed rates, whereas the EWF tests were conducted at 1.7, 3.3 and 8.3 mm s(-1) crosshead speeds corresponding to average crack speeds of 4, 7 and 15 mm s(-1), respectively. A reasonable agreement was achieved between cutting and EWF, reporting 1.26, 1.78, 1.76 kJ m(-2) and 1.52, 1.37, 1.45 kJ m(-2) values, respectively, for the corresponding crack speeds. These toughness data were used in a novel numerical model simulating the 'first' bite mastication process. A viscoplastic material model is adopted for the food piece, combined with a damage law that enabled predicting fracture patterns in the product.

Comparisons of chewing rhythm, craniomandibular morphology, body mass and height between mothers and their biological daughters

OBJECTIVE

To study and compare the relationships between mean chewing cycle duration, selected cephalometric variables representing mandibular length, face height, etc., measured in women and in their teenage or young-adult biological daughters.

DESIGN

Daughters were recruited from local high schools and the University of Michigan School of Dentistry. Selection criteria included healthy females with full dentition, 1st molar occlusion, no active orthodontics, no medical conditions nor medication use that could interfere with normal masticatory motor function. Mothers had to be biologically related to their daughters. All data were obtained in the School of Dentistry. Measurements obtained from lateral cephalograms included: two "jaw length" measures, condylion-gnathion and gonion-gnathion, and four measures of facial profile including lower anterior face height, and angles sella-nasion-A point (SNA), sella-nasion-B point (SNB) and A point-nasion-B point (ANB). Mean cycle duration was calculated from 60 continuous chewing cycles, where a cycle was defined as the time between two successive maximum jaw openings in the vertical dimension. Other variables included subject height and weight. Linear and logistic regression analyses were used to evaluate the mother-daughter relationships and to study the relationships between cephalometric variables and chewing cycle duration.

RESULTS

Height, weight, Co-Gn and Go-Gn were significantly correlated between mother-daughter pairs; however, mean cycle duration was not (r(2)=0.015). Mean cycle duration was positively correlated with ANB and height in mothers, but negatively correlated with Co-Gn in daughters.

CONCLUSIONS

Chewing rate is not correlated between mothers and daughters in humans.

Relationships between masticatory rhythmicity, body mass and cephalometrically-determined aesthetic and functional variables during development in humans

OBJECTIVE

We studied the relationship between chewing rhythmicity, craniomandibular morphology, and age in humans.

DESIGN

Sixty subjects (10M:10F/group×three age groups, viz., 4-8, 10-14, and 17-21 years) participated. Subjects chewed gum for 2min while jaw movements in the frontal plane were videorecorded. Mean and variation in mean chewing cycle duration (TC) were quantified using maximum opening to maximum opening as cycle boundaries. Five "aesthetic" cephalometric variables (e.g., ANB) and seven "functional" variables (e.g., jaw length) were quantified from subjects' lateral cephalographs. Simple linear regression models and several multivariate analyses were used in comparisons.

RESULTS

Mean TC increased and variation in TC decreased significantly with age. Body mass correlated with age, height, TC, all seven "functional" variables and only two "aesthetic" variables. Mean TC was correlated significantly with jaw length, distance from condylion to first molar point, distance from gonion to zygomatic arch, and distance from hyoid to menton.

CONCLUSIONS

TC appeared to adapt with age. Although TC scaled most significantly with age, it is more likely that TC is mechanistically linked to jaw length or size. The decrease in TC variation with age suggests improved efficiency. TC did not scale with "aesthetic" variables, suggesting that these do not impact chewing rate; however, clinical procedures that impact jaw length may. The negative allometric scaling of TC with "functional" variables may reflect the pedomorphic jaw and face of humans. Further human studies will provide insights into the nature of scaling and adaptation of rhythmic chewing during development.

Intraspecific scaling of chewing cycle duration in three species of domestic ungulates

In mammals, chewing cycle duration (CCD) increases with various measures of size, scaling with body mass0.13–0.28 and jaw length0.55. Proposed explanations for these scaling relationships include the allometry of body size, basal metabolic rate and tooth size, on the one hand, and pendular mechanics treating the jaw as a gravity-driven pendulum, on the other. Little is known, however, about the relationship between CCD and size within species. Recent research in dogs demonstrates altogether different scaling exponents and weaker correlations. This research suggests that breed-specific growth rates influence the maturation of the neural networks generating chewing rhythm, which may be altered because of changes in jaw mass during early postnatal growth. Here, we explored the intraspecific scaling of CCD within a sample of adult horses ranging from miniatures to draft breeds and an ontogenetic sample of goats and alpacas from infants to adults. In horses, CCD scales with body mass0.19 and jaw length0.57, although in neither case is the correlation significant. In the ontogenetic samples of goats and alpacas, CCD is significantly correlated with body mass, scaling as CCD∝body mass0.37 in both species. In goats, but not alpacas, CCD is also significantly correlated with jaw length, scaling as jaw length1.032. As in dogs, the scaling of CCD in horses may reflect the influence of selective breeding on growth trajectories of different breeds, resulting in reduced body and jaw size differences among infants, when CCD is established, compared with adults. However, the allometric scaling of tooth size in horses of different breeds may be a potential influence on the scaling of CCD. The scaling of CCD with body and jaw size in goats, and to a lesser extent in alpacas, also suggests that the development of peripheral masticatory structures such as the teeth and occlusal relations may play a role in changes in CCD during the earliest stages of postnatal ontogeny.