Factors affecting methane production of composite and crossbred cattle grazing tropical and subtropical pastures in Northern Australia

Abstract

Understanding the factors affecting variation in methane (CH4) production rate among individual animals is an essential step in developing methane phenotypes to enable genomic selection for lower CH4 emissions. GreenFeed units (C-Lock inc., Rapid City, SD, USA) are an increasingly popular method for recoding methane production of grazing cattle. GreenFeed units take short-term breath measurements (of several minutes duration) when visited by cattle. Our aim was twofold 1) understand the factors associated with variation in CH4 production records from grazing beef cattle across tropical and sub-tropical cattle grazing regions and 2) given these factors and frequencies of visitation, determine trial length necessary to derive accurate phenotypes for genomic prediction. In total 5 trials were conducted across 3 locations resulting in repeated measurements on 328 mixed sex cattle. Factors including test day, trial location, hour of visit and pipe temperature had a significant effect on CH4 production. GreenFeed unit contributed a significant proportion of the total variation in methane emissions, across both intraday and daily methane production (P < 0.05). Testing the effect of trial length ranging from 5 and 52 days, showed that within-animal variation slightly decreased with repeated observations. However, the addition of cattle not previously recorded increased between animal variation, this slowed post 30 days. The optimal trial length balancing maximising cattle recorded, and repeated observations, was 28 days resulting in 20,440 visits from 324 cattle.