The effect of dairy herd management on environmental pollution

: methane emissions and nitrogen use efficiency

Abstract

Recent global initiatives to reduce the effect of livestock farming on environmental pollution have necessitated negotiating a balance between production and pollution outputs. Knowledge of animal weight is important to assess growth, and the commercially available Animeter weigh tape is equally as accurate in estimating body weight in absence of electronic scales, compared with some previously published equations. Optimising heifer growth is fundamental in successfully rearing a replacement herd, however key to this is supplying the right nutrition, particularly in terms of dietary crude protein. Feeding protein in excess of animal requirements (which can be assessed by modelling) decreases the nitrogen use efficiency of farms as assessed by the CNE model, with no benefit on growth, but contributes to nitrogen pollution (ammonia and nitrous oxide). Diet composition can influence heifer performance, but potential effects on methane emissions (another potent greenhouse gas) need to be considered. The inclusion of a novel low-lignin breeding line of oats in dairy cow diets was shown to have no negative effects on methane emissions or diet digestibility, as assessed in vitro, or on growth assessed in vivo as part of a pre-weaning calf starter diet. Changing global climates threaten the ability of growing crops to sustain livestock agriculture, and one example is the problem of bush encroachment in Namibian grasslands that reduces forage production. To study the potential use of bush encroachment plants as potential feeds or dietary additives, turning a problem into an opportunity, several Namibian plant species were investigated in combination with grass silage using in vitro analyses to assess digestibility and methane production potential, highlighting Rhigozum trichotomum as a potential forage inclusion. Managerial decisions related to the rearing of a replacement dairy herd have been shown to be beneficial in balancing maintaining animal growth with not increasing pollutant outputs

Date of Award	2023
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Jon Moorby (Supervisor) & Ruth Wonfor (Supervisor)