Date of this Version
The Author(s) 2019.
Many environmental and dietary factors affect ruminant livestock performance (Ames, 1980; Carberry et al., 2012). Energy used by ruminants is mainly derived from volatile fatty acids (VFA), including acetate, propionate, and butyrate, which are produced by bacterial fermentation of carbohydrates (Barcroft et al., 1944). With the importance of VFA production in ruminants (Bergman, 1990), it is essential to understand how various conditions livestock may be subjected to, such as ambient conditions and diet, can affect VFA production.
With the profound role of VFA production in energy status of the ruminant, and given that heat stress (HS) events can affect ruminal microbial populations (Tajima et al., 2007; Duffy et al., 2018) HS thereby may alter energy substrate available to the animal. Significant reductions in VFA levels have been reported during increased environmental temperature in both ad libitum and limit-fed animals (Weldy et al., 1964; Kelley et al., 1967; Freestone and Lyte, 2010).
We speculate that beta-adrenergic agonists (β-AA) may stimulate the production of VFA to increase the efficiency of nutrient digestion and provide more energy to the animal. However, the influence of HS and β-AA supplementation together on rumen VFA production has not been investigated. Researchers also have observed that β-AA reduce the frequency and intensity of ruminal contractions (Ruckebusch et al., 1983; Brikas et al., 1989; Leek, 2001), which are important to digestion, and others have shown that β-AA increase absorption in the digestive tract (McIntyre and Thompson, 1992). These changes in ruminant digestion attributed to β-AA may lead to changes in VFA production. In addition, β-AA may influence the production of VFA directly to increase the efficiency of digestion and provide more energy to the animal. The objective of this study was to determine the impact of β1 agonists, β2 agonists, and HS on rumen VFA production using lambs as a model for cattle. Our prior work showed that heat stress, but not β-AA alone, changed the overall composition of the ruminant microbiome (Duffy et al., 2018). These changes in the microbiome are postulated to change VFA production. Therefore, we hypothesize that heat stress, β-AA, and the associated interaction decrease the total level of VFA produced.