Abstract

MINDY, a mechanistic and dynamic dairy cow model was used to explore strategic feeding managements in early (EL) and late lactation (LL), with the aim of reducing enteric methane (CH4 g d-1) emissions and urinary N (UN g d-1) excretion, while maintaining milk production. Strategies explored were a factorial arrangement of (1) herbage allowances (20, 30, 40, or 50 kg d-1), (2) times of herbage allocation (AM or PM), (3) supplement types (barley grain, maize grain and silage) and (4) times of supplement allocation (AM, PM, or both). A Pareto front analysis was conducted to identify ‘best compromise’ treatments. Increasing herbage allowance increased consumption of fermentable carbohydrates and N, resulting in greater CH4 and UN emissions per cow. Allocating herbage in the PM rather than the AM increased dry matter intake by 1.9 and 1.7% and milk solids (MS) by 2.3 and 0.7% in EL and LL, respectively. Afternoon forage allocation produced more CH4 (5.1 and 3.6%) and less UN (4.7 and 7.8%) in EL and LL, respectively. Morning supplement allocation on average yielded the lowest CH4 and UN emissions. Results indicate that feeding management can mitigate both UN and CH4 however, MS production can be compromised depending on stage of lactation.

K, Garrett, MR Beck, and P Gregorini

New Zealand Journal of Animal Science and Production, Volume 79, Palmerston North, 20-25, 2019