For every mammal, the digestion of food starts in the mouth. The oral cavity in cattle has evolved into a very specialised part of their anatomy which has helped them to master the art of mastication and rumination. Their specialised digestive system is designed to digest plant materials with cell walls.
This article will discuss the unique features of the oral cavity of cattle and discuss the anatomy of their teeth.
Mastication and rumination
A healthy ruminant spends a lot of time masticating. Chewing reduces the particle size of the food, which makes the nutrients in plant materials easier to absorb by the rest of the digestive system. Most mammals chew, although in herbivores, it aids the digestive process more than in meat-eating species.
How much initial mastication is carried out by a cow depends on the food (Bailey and Balch, 1961). Typically, forage takes longer to eat and needs more chewing than concentrates. Forages with a higher water content, such as grass silage, are chewed less and swallowed more quickly than straw or hay. This means that the particle size of masticated and swallowed straw/hay is smaller than that of grass silage. When food has arrived in the rumen, particles will be broken down further before continuation to the omasum and abomasum takes place (Beauchemin, 2018).
Saliva production
The other function of chewing is the production of saliva, which contains large amounts of potassium and bicarbonate. These products act as a buffer in the rumen when the food bolus is swallowed. Depending on what they are fed, cattle can produce an enormous amount of saliva: 100 litres or more a day (Dyce et al., 1996). When saliva is not reabsorbed in the digestive system, a cow will lose vast amounts of electrolytes, which can quickly cause imbalances in blood electrolytes.
Saliva is produced by the parotid, mandibular, sublingual and many minor salivary glands in the head. The parotid gland lies ventral to the ear, along the caudal border of the masseter; this gland continuously produces saliva, with variation in the amount. In contrast, the mandibular gland is larger and situated below the jaw, secreting mixed saliva when a cow is eating or ruminating. This means the total amount of saliva produced during the day is not constant.
When saliva is not reabsorbed in the digestive system, a cow will lose vast amounts of electrolytes, which can quickly cause imbalances
The salivary ducts of the different glands enter the mouth in different spots: the parotic gland duct enters the mouth between the molars, while the mandibular gland duct runs below the oral mucosa and into the mouth by the sublingual caruncle. There are two caruncles below the apex of the tongue, just caudal to the incisors. Many more drainage points for the different salivary glands are present on the floor of the mouth (Dyce et al., 1996).
Saliva production depends on the dry matter content of the feed and the speed at which food is eaten (which, in turn, depends on the amount of neutral detergent fibre (NDF), or cell wall, in the food) and less so on particle size.
Further anatomy of the oral cavity of cattle
The mouth cavity is long and narrow, and the tongue is its main feature. The vestibule between the cheeks and the margin of the jaws has a fair amount of space. Buccal papillae that point backwards cover the inside of the lips and cheeks. The mouth does not open very wide, which means cattle can only take relatively small bites at a time. The hard palate contains ridges and is mostly in front of the cheek teeth, while the soft palate is situated in between and caudal to the cheek teeth.
In contrast to other herbivores, the maxillae of ruminants do not have incisors. Instead, there are two dental pads. These pads are crescentic elevations with a horny surface that are pliant when compressed. To reduce the risk of injury to the dental pads, the lower incisors are quite loosely and flatly implanted in the bone; therefore, the incisors can easily be manipulated in a healthy cow. Also, the incisor arcades of cattle (grazers) are wider and flatter than those of ruminant browsers such as goats (Gordon and Ilius, 1988).
Cattle do not graze by edge-to-edge biting; they mostly use their tongue. In contrast to sheep and goats that have flexible lips, cows’ lips are quite rigid. While sheep use their lips for grazing, cattle pull a bunch of grass into the mouth with the tongue and the dental plate, then the incisors cut the grass off the stems. Specifically, they use the point of their tongue to grasp the food. This grazing method means that cattle cannot graze meadows completely down.
The tongue itself also contains different kinds of papillae: harsh, caudally directed filiform papillae are on the tip of the tongue, and conical and flat lenticular papillae are found towards the pharynx. All these papillae aid in moving the food towards the rumen. Fungiform and vallate papillae have taste receptors. However, the fungiform papillae are at the rostral end of the tongue, while the vallate papillae are at the base. About two-thirds of the way down the tongue, there is a lingual fossa where food can collect. This is a hazard and a potential place for infection as the epithelium within the fossa is relatively delicate and can be easily damaged by sharp particles; this is the reason why infections in the tongue are relatively common.
Complications of cattle’s unique anatomy
Cattle easily swallow foreign bodies. These foreign bodies can cause obstructions or diseases such as hardware disease. It is thought that the combination of an insensitive mouth with the focus of many anatomical parts in the oral cavity on the backward movement of feedstuffs and the large production of saliva means cattle are more likely to miss foreign bodies than other herbivores such as equids (Dyce et al., 1996).
The combination of an insensitive mouth with the focus of many anatomical parts in the oral cavity on the backward movement of feedstuffs […] means cattle are more likely to miss foreign bodies
Dental anatomy of cattle
Dental formula
Adult cattle do not have any canines. During evolution, the two canines moved rostrally in the mandible and became incisors. This means that there are eight incisors in total. The first premolars in the upper and lower arcades do not develop, which means adult cattle have three premolars and three molars in each arch (Dyce et al., 1996).
Deciduous teeth
Calves have all their temporary teeth either at birth or within the first couple of weeks of life. In total, these consist of eight incisors and six premolars. The deciduous premolars are bigger and more complicated than their permanent successors because they initially have to do all the masticating.
From six months onwards, the first molar comes through. By about three years of age, all permanent premolars and molars are present. The permanent incisors take four years to erupt and replace the temporary incisors (Dyce et al., 1996).
Hypsodont versus brachydont teeth
Humans and, for example, dogs have brachydont teeth. These are so-called “low-crowned teeth”. Brachydont teeth do not keep growing so the enamel is restricted to the tooth crown. Ruminants, on the other hand, have hypsodont teeth. Generally, these teeth have enamel that is invaginated into the dentin to form infundibula and reaches far down the root. The hypsodont teeth of herbivores (except the mandibular premolars of ruminants) are covered by cementum, which more or less fills the infundibula.
Ruminant incisors are brachydont but have enamel covering part of the root dentin and cementum covering the root enamel (Grant Maxie, 2015). The permanent incisors initially have sharp edges and ridges. Over time, dentine is exposed and the teeth “level off”. This means that the occlusal surface increases and the lingual edge of the occlusal service becomes smooth.
When the animal is young, the cheek teeth surfaces have raised enamel ridges that are very specific to ruminants. Over time, however, the enamel ridges wear down
The hypsodont cheek teeth of cattle have a reserved crown below the gingiva that slowly comes through while the top of the crown wears down. After a while, the whole crown comes through and the roots are formed. After this, the teeth will still be pushed out from below, but the crowns will reduce in size. If the animal reaches an advanced age, the whole crown can be worn down, which greatly reduces chewing efficacy.
In cattle, the upper rows of teeth are more widely separated than those of the lower jaw, meaning only narrow strips of opposing teeth are in contact when the mouth is closed. The tables of the teeth also slope transversely. When the animal is young, the cheek teeth surfaces have raised enamel ridges that are very specific to ruminants. Over time, however, the enamel ridges wear down (Eubanks, 2012); short-term wear will expose dentin, which means that the variation of harder and softer materials creates an uneven surface that is very efficient in reducing the particle size of the foodstuffs (Dyce et al., 1996).
Conclusion
The highly specialised mouth of cattle has evolved to consume large amounts of plant materials. The ability of cattle to digest cell walls and produce milk has helped humanity to breed a domesticated animal capable of converting large amounts of plant materials into copious amounts of milk, which is quite extraordinary.
