Bushfire exposure is associated with darker color of beef loin at grading

The effect of bushfires (also known as wildfires) on the Australian livestock industry extends beyond the direct loss of animals and farming assets, with anecdotal reports of increased incidence of dark meat color defects in beef carcasses at grading (AUSMEAT color score >3) from bushfire affected cattle. To understand the association between bushfire exposure and meat color, an investigation using historical MSA (Meat Standards Australia) grading data, pasture data and bushfire data over two bushfire seasons (2018–2019, 2019–2020) was conducted. For bushfire affected beef cattle (n = 451 299), predictive models were developed to estimate the association between bushfire exposure and (1) loin color at grading, and (2) the incidence of ‘dark color’ defects. Both models incorporated bushfire exposure, production, and animal variables, with hierarchical random effects specified as plant/processing date/consignment. For the two predictive models, distance of the animal's originating property from closest bushfire (km), the days the animal was exposed to bushfire, feed type (grass, grain), the use of hormone growth promotants (HGPs; no, yes), the interaction of distance of property from closest bushfire and feed type, and days of bushfire and HGP treatment, were all significant predictors of loin color outcomes (P < 0.05 for all). Model 1 indicated that as distance from closest bushfire decreased, loin from grain-fed animals had darker color (P < 0.001), and that as days of bushfire exposure increased, HGP treatment exacerbated dark color outcomes for grain-fed animals but had little effect on the consistently high color scores of grass-fed HGP treated animals (P = 0.001). For model 2, the highest predicted proportion of dark color defects (11.8 %) was for grass-fed, HGP treated cattle, 10 km from the closest bushfire and exposed to 150 days of bushfire. The lowest predicted proportion of dark colour carcasses (1.3 %) was for grain fed, non-HGP treated cattle, 30 km from the closest bushfire, with no change associated with increasing days of bushfire. Cattle can be categorized in order of increasing susceptibility to dark color defects as a result of being exposed to bushfires; grain-fed cattle with no HGPs were the least susceptible to dark color defects, and grass-fed cattle with HGP treatment were the most susceptible. Remediation strategies are discussed in relation to cattle susceptibility to adverse loin meat color outcomes associated with bushfire exposure.