Page 102 - The Welfare of Cattle

sense and sensIbILItY 79

behavior of cattle: looking for food, eating the meal, and digesting it; gustation plays an important
role in all components of cattle feeding behavior.
Taste can be influenced by the other senses; think about when someone has a head cold and he
complains about not being able to fully taste his food. It is likely that the future approach of study-
ing gustation will take into consideration the role of other senses in determining taste (Spector &
Glendinning, 2009). When studying humans, taste sensations are categorized by the subjects into
specific classifications, traditionally sweet, sour, bitter, salty or umami (and the taste of fat, the sixth
taste modality?; Bernard, 1964; Besnard, Passilly-Degrace, & Khan, 2016) and when studying ani-
mals, researchers are ultimately looking at acceptance, selection, rejection, aversion and/or indif-
ference (Bernard, 1964). Studying taste alone can be somewhat misleading as olfaction and even
somatosensation (temperature of food in the mouth and texture) can impact how something “tastes.”

a Cow’s tongue

The tongue is the cow’s main vehicle for tasting. A cow’s tongue is also used for prehension,
mastication, and food manipulation. The tongue is covered with lingual papillae, projections on
the surface of the tongue of different shapes and sizes by function and species. Papillae are catego-
rized as mechanical (filiform, conical, and lenticular papillae) or gustatory (circumvallate and fun-
giform) based on their function (Chamorro, De Paz, Sandoval, & Fernandez, 1986; de Paz Cabello,
Chamorro, Sandoval, & Fernandez, 1988). If you have ever been licked by a cow you have likely seen
and felt the filiform papillae, the rougher projections on the surface of the cow’s tongue that help with
prehension. Along the surface area of the gustatory papillae are taste buds, onion-shaped structures
which are made up of clusters of taste cells (usually 50–100 taste cells per cluster; Bachmanov &
Beauchamp, 2007; Lindemann, 2001), the gustatory receptor cells or chemoreceptors. [Interesting
fact: the chemoreceptors of fish, similar to taste buds in humans, are on the outside of their body,
helping to chemically scan their environment for food (Kare, 1971).] In order to “taste” something,
the chemical molecule must be liquid or be dissolved in saliva so that it can be transported to the
taste cell microvilli positioned at taste pores on the papillae. Once in contact with the chemical, the
taste cell transduces a signal to the gustatory neural pathway; there are different theories regarding
how the taste is encoded in this neural pathway (Chandrashekar, Hoon, Ryba, & Zuker, 2006).
On the cow’s tongue, the highest concentrations of taste buds are found on the posterior por-
tion of the tongue on the circumvallate papillae (Davies, Kare, & Cagan, 1979; Kare, 1971). The
circumvallate papillae on a cow’s tongue contain approximately 90% of all the taste buds (Davies,
Kare, & Cagan, 1979). The fungiform papillae which contain taste buds as well but significantly
fewer per papilla are found in high concentration on the tip of the tongue with few scattered on the
mid-section (Davies, Kare, & Cagan, 1979). The size, number, distribution on the papillae, and
number of taste receptors vary greatly between species (Kare, 1971). To provide some comparison
of the range of number of taste buds identified in several studies in the 1940s to the 1960s, calves
have 25,000 taste buds (Weber, Davies, & Kare, 1966), compared with 9,000 in humans (Cole, 1941)
and 24 in the chicken (Lindenmaier & Kare, 1959). It is necessary to note that the total numbers of
taste buds do not correlate to the gustatory abilities of the species, i.e., some species have a relatively
low number of taste buds but can differentiate certain chemicals at levels imperceptible to species
with a larger number of taste buds (Kare, 1971).
It has been suggested that domestication has impacted the function of taste and an animal’s
ability to taste (Belyaev, 1969). Some studies in animals have explored preference for and intake of
sugary or toxic solutions. Maller and Kare (1965) conducted a study in which they provided wild
and domestic rats with nonnutritive and potentially toxic sugar solutions (different experimental
treatments) in addition to a nutritive balanced diet. Although both the wild and domestic rats pre-
ferred the sugar solutions, the domestic rats almost doubled their fluid intake by drinking the sugar
solution and the wild rats did not. The results of their study suggested that the wild rats were more