Enteric Methane Mitigation Interventions with a Specific Focus on Current Literature and On-Farm Research

The objectives of the present thesis are to 1) review the current literature on enteric methane (CH4) mitigation interventions and 2) report the results and limitations of providing a feed additive to individual dairy cattle on a commercial farm. Chapter 1 considers the mode of action, efficacy, and moderating variables of anti-methanogenic interventions, as well as associated impacts on rumen fermentation, animal health and productivity, and net greenhouse (GHG) emissions. Selective breeding has the potential to produce lasting, cumulative CH4 emission reductions while dietary reformulation and feed additives generally offer immediate and reversible effects. Limited interventions are currently available for commercial use, and more on-farm research is needed before widespread implementation. Chapter 2 delves into an on-farm study, where the Agolin Ruminant (EOB) feed additive was pulse-dosed to dairy cows through GreenFeed (GF) units (C-Lock, Inc., Rapid City, SD). The primary parameters of interest included 1) enteric gases, particularly CH4 production (g/d) and CH4 intensity (g/kg milk or energy-corrected milk (ECM)), and 2) lactation performance. Seventy-two multiparous, mid-lactation cows were blocked by days in milk (DIM), parity, and milk yield and housed in a single pen. After a 2-wk covariate period, cows within each block were randomly assigned to one of two treatments for 10 weeks: Control (blank pellets) and EOBP (blank pellets + EOB pellets). Hopper 1 of each GF unit contained the EOB pellets, formulated to provide ~1g EOB from the first daily drop of pellets for each EOBP cow. Hopper 2 dispensed blank pellets to EOBP cows for their remaining daily drops and to Control cows for all drops. Enteric gases were measured via the GF units through open access and additional encouragement. Milk yields and components were obtained twice weekly, and individual dry matter intake (DMI) was modeled on a weekly basis using milk data, body weight, and body condition score. Overall, no significant differences were observed between treatments for any parameters, except for a tendency towards lower milk lactose concentration in cows receiving EOB. However, in week 7, the EOBP cows outperformed the Control cows in milk yield, ECM, yields of milk protein, lactose, and solids-non-fat, modeled DMI, and CH4 intensity (considering weekly CH4 production measurements from ≥ 2 time points). The lack of significant differences overall might be attributed to inherent limitations of administering EOB through the GF units, as well as a low average number of CH4 measurements (<20/week per cow) that predominantly occurred after peak emissions. The study's attempt to deliver a feed additive to individual cows, while considering the impact of farm management, contributes to the advancement of on-farm enteric CH4 mitigation research