Date of Award:

8-2020

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Kara J. Thornton-Kurth

Committee

Kara J. Thornton-Kurth

Committee

Kerry A. Rood

Committee

S. Clay Isom

Committee

Blair Waldron

Abstract

Raising dairy heifers in a certified organic setting can be difficult for producers. Conventionally, heifers are raised in a confined setting, and fed a total mixed ration (TMR) that is balanced daily to contain all the needed nutrients for developing heifers. Organic producers can use a TMR in their operations, but due to high organic feed costs, many choose to raise their heifers in pasture-based systems. While pasture-based systems may lower costs, heifers on pasture commonly have lower rates of gain, which can be financially burdensome to producers. Grass-legume pastures may help improve rates of gain in heifers on pasture-based systems. In this study, yearling Jersey heifers received one of nine different treatments: eight pasture treatments or a conventional TMR control, for a 105-d period. Pasture treatments included four grass pastures: tall fescue (TF), meadow bromegrass (MB), orchard grass (OG), perennial ryegrass (PR) and four mixed pastures with each individual grass interseeded with the legume birdsfoot trefoil (BFT). To determine the effects of different pastures on heifer growth, heifers were sampled every 35 days over a 105-d period. During sampling, weight and hip-height were measured, and blood and fecal samples were taken from each heifer. Blood samples were analyzed for blood urea nitrogen (BUN), an indicator of protein status, and insulin-like growth factor-1 (IGF-1), an indicator of energy balance. Fecal samples were analyzed to determine the parasite load of each heifer. At day 105 of the study, heifers were bred, and conception rates were determined 35 days after breeding. Heifers on mixed pasture tended to have increased body weights compared to heifers on grass pastures. Heifers fed on mixed pastures had a similar weight gain to those fed a TMR, except for heifers on TF+BFT were lower. Heifers fed on mixed pastures also had higher BUN concentrations than heifers fed on grass pastures. Heifers fed grass and mixed pastures had similar IGF-1 concentrations, parasite load and conception rates. Adding the legume BFT to grass pasture helped dairy heifers grow faster and more efficiently. Interseeding grass pastures with BFT may be a sustainable method to improve growth of developing jersey heifers being raised in a pasture-based system, although additional research is needed.

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