Page 119 - The Welfare of Cattle

96 the WeLfare of CattLe

relationship, thus reducing stress and enhancing productivity (Hemsworth et al., 2000). Resistance to
Bovine Respiratory Disease, the most prevalent and costly disease in feedlot cattle (USDA-APHIS,
2013), is a trait that may be enhanced through genetic selection (Snowder et al., 2006; Schneider
et al., 2010; Cockrum et al., 2016) and would be beneficial to cattle welfare, yet more research is
needed to elucidate this relationship. Laying hens housed in aviary systems are being selected for
bone strength to reduce keel bone damage in commercial settings (Stratmann et al., 2016) which
is painful (Nasr et al., 2012b), and is associated with increased mortality (McCoy et al., 1996)
and reduced egg production (Nasr et al., 2012a). By evaluating the heritability of species-specific
behavioral, physical, and physiological traits that may enhance animal welfare, animal managers
may be able to harness the genetic potential of animals that are optimized mentally, physically, and
emotionally for food production systems.
Feed additives. Direct-fed microbials (DFMs) (i.e., probiotics) and β-agonists have been
developed to promote rumen health, productivity, and efficiency of both beef and dairy cattle.
In young calves, probiotics are administered to stabilize the gut microbiota, reduce the risk of
pathogen colonization, and reduce the risk and severity of diarrhea. Thus, administration of probi-
otics during stressful events may mitigate some of the consequences of the stressor. In adult beef
and dairy cattle, many probiotics are given to stabilize rumen pH and improve fiber digestion by
rumen microorganisms, and probiotics increase milk-fat yield in dairy cows (Chiquette et al., 2008).
Investigations into the impact of probiotics on average daily gain, final weight, feed intake, and feed
efficiency have yielded contradicting results (Uyeno et al., 2015). β-Agonists fed to cattle during
the final phase of the growing period promote muscle growth and feed efficiency. Research oppor-
tunities to better understand the impact of directly fed microbials and β-agonists on cattle health
and productivity are abundant, as their impact on cattle productivity can be influenced by multiple
factors including diet, age, stress, management practices, and adaptive response of the rumen.
The gut microbiome component of the gut–brain axis is an untapped resource for harnessing its
ability to influence behavior, stress responsivity, and productivity in animals (Wiley et al., 2017).
The field of microbial neuroendocrinology is in its infancy, and recent discoveries into the brain–gut
axis suggest behaviors are influenced directly by communication from the gut microbiome (Rhee
et al., 2009; Ezenwa et al., 2012). The gut microbiome is beginning to be considered an endocrine
organ capable of influencing behavior (O’Callaghan et al., 2016) and physiology, including milk-fat
yield (Jami et al., 2014), ADG, and feed efficiency (Myer et al., 2017). By increasing our understand-
ing of the impact the gut microbiome has on animal physiology and emotion, we expect to identify
biotechnologies that enhance the mental and physical aspects of animal welfare.
The gut microbiome influences anxiety, depression, and stress-induced corticosterone release
in mice and humans (Desbonnet et al., 2008; Rao et al., 2009; Bravo et al., 2012; Cryan and Dinan,
2012; Foster and McVey Neufeld, 2013). The villi of the small intestine have a high concentration
of enteric nerves which connect directly to the vagal nerve and the brain. This direct connection
between the gut and the brain suggests that brain activity is influenced by gut contents, and poten-
tially biotechnologies developed to enhance gut health and promote productivity. DFMs are being
utilized in poultry production to promote productivity, decrease morbidity, and enhance profitabil-
ity (Flint and Garner, 2009). Probiotic supplementation in mice stimulates the gut immune system
and protect against infection during a stress challenge (Martin Manuel et al., 2017). Therefore, the
gut microbiome has the potential to be used as a management tool designed to reduce the stress
response in animals to a known stressor (e.g., weaning, transportation, handling).
However, the brain–gut axis is a two-way street. Not only can intestinal microbiota influence
behavior but also the intestinal microflora can be influenced by the experiences of the host (Bailey
et al., 2011). Therefore, understanding the temporal relationships between microbiome stability and
behavior is an important component of this development in biotechnology. Because the relationship
between the intestinal microflora and host appears to be symbiotic and egalitarian (Rhee et al.,