Effect of heat load and other factors on the incidence of dark cutting carcasses of feedlot cattle

Summary

Stress, poor nutrition and processor factors can affect the 'dark cutting' of beef, which occurs when high pH levels affect the colour and eating quality of the meat.

Three comprehensive experiments were conducted to examine the effect of production, transport, heat load, climate, environmental conditions, time in lairage and time to grading on the rate of dark cutting carcases of feedlot cattle in Australia.

The results of this project demonstrate that environmental conditions have a statistically significant (but small compared to other factors) impact on the incidence of dark cutting meat, compared to the larger effects caused by animal and carcase management factors measured at the feedlot and processing plant.

Objectives

The aim of each experiment was to:

• conduct an analysis of historical Meat Standard Australia (MSA) carcase data in combination with Bureau of Meteorology data, to assess the impact of climatic conditions on the rate of dark cutting beef (experiment 1)
• evaluate the effect of production, climate, animal handling, transport and processing factors on the rate of dark cutting beef (experiment 2)
• determine whether the time from slaughter to grading influences dark cutting, which carcase characteristics influence meat colour and pH and the effect of re-grading beef at later time intervals and any economic impacts of re-grading (experiment 3).

Key findings

• Minimising time in lairage and maximising time to grading can reduce pH and improve meat colour, which reduces dark cutting meat.
• Experiment 1 indicated that climatic conditions have a statistically significant, but small, impact on the incidence of dark cutting. Specifically, high humidity and temperatures in the 48 hours prior to transport increased dark cutting.
• Experiment 2 demonstrated that there are several factors that affect cuts that are 'pH non-compliant'. Feedlot conditions, processing (transport and slaughter) fat colour had the largest negative effects on pH compliant MSA grading.
• Experiment 3 included re-grading 'pH non-compliant' carcases 12 hours after initial grading. This method reduced the incidence of dark cutting and demonstrated that processors can save $5,129 over 1,000 carcases through an increase in MSA pH compliant cuts.

Benefits to industry

This study has generated a greater understanding of the factors that influence the incidence of dark cutting in grainfed beef, which aids the development of effective management strategies to improve the welfare of feedlot cattle and the eating quality of their beef.

MLA action

The results of this project were presented to industry stakeholders at the 'ALFA SmartBeef' conference and the 'ALFA-MLA Vets and Nutritionist' meeting at Dalby in October 2019.

As a first step to instigating positive impact to the industry and improving lot feeder profitability, the Australian Lot Feeders' Association (ALFA) has on-going meetings with key stakeholders to extend the main findings of this project.

Future research

To further reduce dark cutting beef, it is important for producers to manage feed quality and intake, as well as reduce the stress on cattle during the pre-slaughter period. Strategic assessment and manipulation of individual supply chains and processing conditions (time in lairage and time to grading) will most likely achieve the greatest reductions in dark cutting in the feedlot sector.