Page 98 - The Welfare of Cattle

sense and sensIbILItY 75

determinations, sometimes rather quickly (Fraser, 1983). Both wild and domesticated cattle spend
varying amounts of time scanning their environments for predators (Partan & Marler, 2002), i.e.,
engaging in vigilance behavior, a behavior that is motivated by fear (Grandin, 2014). Their sensory
systems have evolved to enable cattle to collect information from their surrounding environment
as a means of survival. Although normally humans do not instill as much fear in domesticated
cattle as a predator in the wild does, such as a wolf or a mountain lion, a human handler can be
perceived as a predator/intruder in the environment of a cow. It is this (often muted) prey response
that enables trained individuals to skillfully move cattle through handling facilities. The concept of
the flight zone and point of balance are foundational components of animal handling and are based
upon the animal’s response to people in their environment (Grandin, 2014).

SeNSOrY reCePtOrS aND theIr CONNeCtION tO the BOVINe BraIN

Each of the five major senses of cattle, olfaction, gustation, vision, hearing and touch, have
specialized cells that respond to the different types of sensory information received and transduce
that information into electrical signals that communicate with the brain. There are two different
types of sensory receptors, chemoreceptors and mechanoreceptors. Although these receptor cells
respond to different types of stimuli, chemical vs mechanical, they have morphological and func-
tional similarities. Chemoreceptors, found in the olfactory (smell) and gustatory (taste) systems,
respond to chemicals that are either airborne in the case of olfaction or dissolved in a liquid as in
the case of gustation. Mechanoreceptors, found in the vision, hearing and somatosensory (touch)
systems, respond to mechanical stimuli, including sound waves, photons, and pressure. The sensory
systems have evolved to capture the chemical and mechanical stimuli through a specialized system
that ultimately transforms the information so it is understandable to the brain and the recipient can
use it. For example, vision begins when a photon is absorbed by a photopigment found in a special-
ized photoreceptor cell within the eye. The photopigments initiate an electrical change that sends a
message to the visual cortex of the brain. The other sensory systems all function in a similar man-
ner. There are two different types of sensory receptors: one type of receptor cell is an afferent nerve
fiber containing a specialized region that captures sense information. The other type of receptor
synapses with the afferent nerve fiber to send the electrical message to the central nervous system.
The subsequent sections describe the specialized sensory cells within system.
Simply, each of the sense systems is connected via nerve fibers to a particular part in the brain’s
cerebral cortex that processes the information. In the parietal lobe, located in the cortex from the
middle to the back of the skull, the somatosensory cortex is responsible for processing information
about touch. In the occipital lobe, located in the cortex at the back of the skull, the visual cortex
processes visual information. In front of the occipital lobe, the temporal lobe, the auditory cortex is
responsible for processing hearing. The gustatory cortex and the olfactory cortex are found under
the frontal, temporal and parietal lobes.

Fear and Sensory Inputs

When thinking about sensory processing of cattle, it is also important to understand how sen-
sory stimuli interact with fear processing in the brain. The amygdala is a brain structure that is
anatomically complex made up of distinct regions called nuclei and is responsible in complex
vertebrates, such as cattle, for processing fear. From an evolutionary perspective, the growth and
differentiation of the amygdala and the mammalian cortex have occurred in parallel (Stephan &
Andy, 1977). The neural network that is involved in fear processing is complex and involves many
different circuits that process different types of fear; it has been suggested that there are actually
distinct circuits for fear of pain, fear of predators, and fear of conspecifics (Gross & Canteras, 2012).