Masters Theses

Date of Award

5-2019

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Agustin Rius

Committee Members

Gina Pighetti, Peter Krawczel

Abstract

Quantity and quality of pastures are significantly impacted by irregular weather patterns in the Southeastern US. Predominate forage types observed in Kentucky and Tennessee are cool season (CS) species which grow best in atmospheric temperatures ranging from 8-24°C. However, in this area, temperatures can reach above 32°C during the summer months. With average temperatures higher than required for CS species, growth and quality decline during the summer. Therefore, an increase in summer forage performance would benefit pasture-based organic dairies to help sustain milk production. Warm season (WS) forages flourish in atmospheric temperatures from 25 to 35°C, which reflect summer temperatures observed in the Southeast. This led to our first hypothesis that incorporation of WS forages would increase forage yield and quality in summer. To test this, four forage mixtures were designed with one mixture containing only CS species, while the remaining three contained CS and WS species: Mixtures contained a combination CS legumes and grasses, WS legumes and grasses, and/or brassicas. Compared with the CS mixture, mixtures containing WS species did not increase yields of DM in summer. Yields of legume were significantly greater in the CS mixture, with this mixture also maintaining the highest quality. First-year results indicated that the inclusion of WS forages might not increase pasture quality and yield and CS forages may be best for pasture-based organic dairy farms in Tennessee and Kentucky.The second hypothesis of this work was that the forage mixtures used to test the first hypothesis would affect predictions of milk production. Using observed forage yield and quality from the previous hypothesis, a whole-farm model (FARMAX, New Zealand) predicted milk production of pasture-based dairy farm systems. Inputted forage content of crude protein and energy was the highest for the CS mixture throughout the simulated grazing season and these levels affected predictions of milk and milk component yields. Therefore, the CS mixture predicted the highest average milk and milk component yields. With results from conditions experienced in this study, incorporation of WS forages with CS forages did not help promote increased forage yield and quality, or average milk production during the summer season.

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