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Snider, Miriam Allison

Animal and Veterinary Sciences

2023

Ph. D.

The organic, grassfed (OGF) dairy sector has been growing for the past 10 yr with expansion rapidly outpacing other dairy sectors. Unique management approaches are needed for OGF systems, but research to support said approaches is lacking. The objectives of this dissertation were to 1) survey OGF dairy producers to better understand producer knowledge and practices, as well as identify areas of needed research to support this farmer population, 2) determine in vitro rumen performance of energetic supplements commonly utilized on OGF dairy farms in the Northeastern (NE) United States (U.S.), and 3) identify and evaluate forage combinations using in vitro continuous culture fermentation, focused on rumen energetic status and environmental output. While Chapter 1 reviews the published literature relevant to OGF dairy systems with a focus on their nutritional management, Chapter 2 utilized a survey questionnaire that was mailed to 351 OGF dairy farms throughout the U.S. with a 46.8% response rate. This survey confirmed the need for further forage-related research, as producers indicated that agricultural-related challenges, such as forage quality and milk production, were the largest limitations to farm success followed by economic factors. In Chapter 3, we evaluated rumen fermentation metrics of red clover + orchardgrass harvested at first and second cuttings, and further investigated the impacts of dietary apple cider vinegar (ACV) supplementation in combination with first cut forages on fermentation metrics using two in vitro batch culture experiments (Objective 2). In Experiment 1, tubes were supplemented with either 1) 50% red clover + 50% orchardgrass harvested at first cut (CUT 1) or 2) 50% red clover + 50% orchardgrass harvested at second cut (CUT 2). In Experiment 2, tubes received either 1) CUT 1 substrate only or 2) CUT 1 substrate + ACV. Tubes receiving CUT 1 produced more methane (CH4) and had higher DM (dry matter) disappearance and mean pH compared with those receiving CUT 2. Fermentation metrics of CUT 1 tubes were not affected by ACV. Ultimately, this trial confirmed that forage cut, and chemical profile, is a more impactful variable driving rumen function. Objective 3 of this dissertation was addressed in Chapters 4 and 5 in which fermentation metrics of mixed forage diets were compared using dual-flow continuous culture fermenters. Chapter 4 focused on forage diversity using cool-season forages. Four diets were mixed (on a DM-basis) to include 40% red clover plus: 1) 60% orchardgrass (OG); 2) 30% orchardgrass + 30% meadow fescue (MF); 3) 20% orchardgrass + 20% meadow fescue + 20% Kentucky bluegrass (KYBG); or 4) 15% orchardgrass + 15% meadow fescue + 15% Kentucky bluegrass + 15% perennial ryegrass (PRG). Diets including 20% Kentucky bluegrass were more digestible but produced higher amounts of CH4. Other forages, such as perennial ryegrass and meadow fescue, may be just as nutritionally beneficial as Kentucky bluegrass with the additional advantage of decreased CH4 emissions. Chapter 5 focused on warm-season annual (WSA) inclusion, complemented by a simple cost analysis. Dietary treatments (on a DM-basis) included 1) 50% orchardgrass + 50% alfalfa (OG-ALF); 2) 25% orchardgrass + 25% alfalfa + 50% red clover (RC); 3) 25% orchardgrass + 25% alfalfa + 50% pearl millet (MIL); and 4) 25% orchardgrass + 25% alfalfa + 50% sorghum x sudangrass (SUD). Diets with WSA showed marked decreases in CH4 output but were similar in digestibility to other diets.