Date of Award:

12-2019

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

J. Earl Creech

Co-Advisor/Chair:

Blair L. Waldron

Third Advisor:

Michael D. Peel

Abstract

Pasture-based dairies have become more prevalent in recent years due to a higher proportion of organic milk demand and production. Organic certification requires that animals must graze at least 120 days in each growing season. However, dry matter intake is often limited when dairy animals receive most of their herbage from pasture, resulting in lower animal performance and milk production. The purpose of this study was to analyze the complimentary effect of high energy grasses with birdsfoot trefoil (BFT) tannins to improve intake of dairy heifers. Jersey heifers were rotationally grazed for 105 days in 2017 and 2018 on eight different pasture treatments, which included monocultures of perennial ryegrass (PR), orchardgrass (OG), meadow bromegrass (MB), and tall fescue (TF), with each respective grass also planted in mixture with BFT. Intake was measured by sampling herbage before and after each seven-day grazing period and was from greatest to least as follows: MB+BFT, OG+BFT, OG, MB, PR+BFT, TF+BFT, PR, TF. Physical characteristics such as pasture bulk density, herbage height, herbage allowance, leaf pubescence, leaf softness, and birdsfoot trefoil content as well as nutritional properties such as fat, non-fibrous carbohydrates, fiber, and energy were all associated with intake. Crude protein and ash were also associated with intake. While PR+BFT did not have the greatest overall intake, it was the only treatment that consistently had greater intake than its respective grass monoculture (PR). Since it had more energy and tannins than all other grasses, a complimentary effect between energy and tannins to increase intake was likely. The fact that both physical and chemical herbage characteristics were associated with intake shows the importance of planting the right species in pasture as well as making proper management decisions to maximize nutritive value and herbage intake.

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