Date of Award:

2015

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Animal, Dairy, and Veterinary Sciences

Advisor/Chair:

Jong-Su Eun

Abstract

Forages containing condensed tannins (CT) have potential to reduce the environmental impact of dairy farming. In 3 studies, I hypothesized that feeding CTcontaining birdsfoot trefoil (Lotus corniculatus, BFT) would result in improved nutrient utilization and lactational performance of dairy cows compared with control forages of the respective experiments.

Improved milk components, reduction in waste N, and overall improved N efficiency were hypothesized for BFT-fed cows compared to those cows fed alfalfa hay (Study 1) or grass-based diets (Study 2). In addition, a decrease in in vitro methane production and improved rumen fermentation due to diets based on BFT pasture and concentrate supplementation compared with grass pasture-based diets was the hypothesis of the third study.

Study 1 showed BFT-hay diets improved lactational performance through increased energy-corrected milk yield and increased milk protein yield, resulting in improved N utilization efficiency compared with the alfalfa hay diet. Total volatile fatty acids concentration tended to increase, and greater microbial protein yield was exhibited by cows fed BFT compared to other diets tested. Therefore, BFT can replace alfalfa hay in dairy diets and showed improved feed and N utilization efficiencies and lactational performance.

Study 2 determined that pasture nutrient content increased for BFT pasture compared to the mixed grass control, contributing to increases in milk yield most weeks during the 2-year study. Energy-corrected milk yield increased most weeks by BFT-grazed cows due to increased milk yield, although milk protein concentration was similar between treatments. Cows grazing BFT pasture increased N efficiency coupled with decreased milk urea N secretion in the first, but not the second year, suggesting an environmental advantage over traditional grass-based pastures depending on the effect of growing conditions on pasture quality at time of grazing.

Study 3 showed that offering BFT pasture to continuous cultures without or with barley grain or total mixed ration supplements reduced methane production and altered rumen microbial populations. The reduced methane production on the continuous cultures was likely due to direct and/or indirect effects of CT on rumen microbiota.

Overall, diets including BFT showed improved nutritive, lactational, and environmental benefits by decreasing N waste and methane production over typical alfalfa hay-based dairy diets and grass pastures.

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