Page 101 - The Welfare of Cattle

78 the WeLfare of CattLe

Genetics and Olfaction

Traditionally, olfactory research has not been as common as research in some of the other senses
like vision. In the early 1990s, two scientific accomplishments changed the approach to olfactory
research: (1) the discovery of genes encoding odorant receptors (Buck & Axel, 1991) and (2) the
completion of sequencing of human and other animal genomes (Glusman, Yanai, Rubin, & Lancet,
2001; Keller & Vosshall, 2008; Zozulya, Echeverri, & Nguyen, 2001). Genomic and genetic tools
have enabled researchers to begin to identify how smell evolved to fit the specific needs of a variety
of species (Keller & Vosshall, 2008). Understanding species differences is interesting but also help-
ful to provide perspective on the physiological and genetic reasons the animals under human care
perceive and behave the way they do when exposed to certain stimuli.
Odor perception is mediated by OR genes and the number of OR genes, both functional genes
and pseudogenes, varies greatly between species (Keller & Vosshall, 2008). (Note: Pseudogenes,
gene copies that have coding deficiencies but resemble functional genes, were once thought to be
“junk” but now are considered to be important for gene regulation although their mechanism is still
not well understood) (Niimura & Nei, 2007; Tutar, 2012). The cow has approximately 1,000 func-
tional OR genes, the range between species quite broad being approximately 300 functional genes
in humans and other microsmatic species and approximately 1,500 functional genes in mice and
other macrosmatic species (Niimura & Nei, 2003; 2007). The number of OR genes has changed sig-
nificantly during mammalian evolution, OR genes both gained and lost, perhaps due to mammals’
need to adapt to their environment for survival, i.e., needing to be able to identify many odors vs
relying more heavily on other senses, respectively (Fleischer, Breer, & Strotmann, 2009; Niimura &
Nei, 2007). Although in most cases this seems highly likely, there are some instances in which the
survival factor and the number of genes are not congruent, i.e., the dog which has approximately
800 functional genes, less than the mouse, for example, but a highly sensitive sense of smell.

Olfaction and human–Cattle Interaction

Recognizing odorous substances is essential to cattle survival, to recognize predators, food, and
mating partners. As mentioned, pheromones are an important component in cattle communication
influencing social and sexual responses. Cattle have many odiferous glands suggesting the impor-
tance of olfaction in social structure. Interestingly, cattle can be trained to recognize conspecifics
from olfactory cues (the urine) alone (Baldwin, 1977). Cattle behavior associated with pheromone
communication, i.e., the Flehmen response, is often observed as a reproductive management tool
at production facilities. In specific relation to cattle handling, smell may impact how cattle move
through their environment but the chemical signals they receive are more difficult for humans to
control, alter and even recognize, as compared with visual and auditory cues, and therefore often
times less of a focus.

that taSteS GOOD, DOeSN’t It?—GUStatION

Taste, or gustation, is another chemical sense. Spector and Glendinning (2009) assert that there
are three categories of taste processing: (1) stimulus identification, (2) ingestive motivation, and
(3) digestive preparation. Stimulus identification refers to the animal’s ability to differentiate tastes
and ultimately link that information to other outcomes, i.e., at a basal level, those outcomes that
influence survival. Ingestive motivation encompasses things like palatability and reward that can
activate physiological pathways that can positively and negatively impact ingestion. Digestive prep-
aration includes activation of physiological components that aid in the digestive processes and help
maintain homeostasis. This categorization of taste can be applied when thinking about the foraging