Date of Award:

8-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee

Jennifer W. MacAdam

Committee

Jeanette M. Norton

Committee

Juan J. Villalba

Abstract

Despite the increasing worldwide demand for beef as a protein source, consumers are concerned about the sustainability of ruminant production systems. Their main concerns are animal welfare for feedlot-fed animals, greenhouse gas (GHG) emissions, global warming and worker safety. Traditional feedlot-based beef production systems have been associated with locally greater levels of soil, water and air contamination, as well as the overuse of antibiotics and growth hormones. The use of legume pastures such as cicer milkvetch (CMV) and birdsfoot trefoil (BFT), which fix their own nitrogen (N) and often contain beneficial secondary compounds such as tannins and provide for rapid gain and improved meat quality, holds promise as an alternative strategy to feedlots for beef finishing. These legumes can mitigate GHG emissions without reducing beef productivity and improve enterprise profitability when sold locally as natural or organic pasture-finished meat. Tannins can be beneficial to ruminants or some types, especially in high concentrations, can have anti-herbivore properties. The condensed tannins synthesized by BFT are known to prevent bloat and to enhance the production of ruminants. More generally, tannins are beneficial not only to the plants that accumulate them, but can also slow soil mineralization of organic matter, better matching N release to plant uptake. Ruminants can convert fibrous feedstuffs not suitable for human consumption, such as corn stalks, into sources of high-quality protein for human consumption, and thrive without grain on pastures and hay produced on marginal land that is not suitable for cultivation. Legumes pay a key role in the mitigation of environmental impacts of beef production, because their elevated forage quality increases digestion rate, intake and animal gain, their tannins improve the efficiency of rumen N utilization, and their quality and tannin concentrations both tend to reduce enteric CH4 emissions and N losses. Likewise, plant litter and manure from tannin-containing species would help to sequester N and carbon in the production system, helping to achieve sustainable beef production. Evaluation of the sustainability of ruminant production systems should be based on their environmental impact, the nutritive value of the food produced, the appropriate use of agricultural land, and the economic sustainability of producers and their rural communities.

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