Muscle pH is a measure of acidity and alkalinity, measured on a scale of 0-14. The pH of muscle in a live animal is almost neutral at 7.1. The optimum pH of meat is less than 5.70, which is slightly acidic.
When an animal is slaughtered, brain function and circulation are stopped but muscle continues to metabolise energy (known as glycolysis). The process of glycolysis produces lactic acid and energy that cause pH to decline. Once the pH decline has ceased, the ultimate pH is achieved and measured during grading.
The amount of energy stored as glycogen in muscle affects the ultimate pH. If there is only a small amount of muscle glycogen present pre-slaughter, then only a small amount of lactic acid can be formed which may not be enough to reduce the pH to the required level.
To prevent high pH levels, stress should be minimised.
Animals can be stressed by factors such as exposure to harsh weather conditions, poor transport and excessive periods without feed or water. Pre-slaughter stress, including on property handling, transport and abattoir (lairage) stresses, also affect glycogen levels. When an animal is frightened or put under excessive pressure, the energy or glycogen in the muscles is rapidly used in a ‘flight or fight’ response.
Once glycogen levels are depleted, only a small amount of lactic acid can be formed, resulting in higher pH levels. The animal must eat high energy feed again to restore the glycogen levels in the muscle, which can take up to 14 days.
Tips for improving muscle pH include:
- Handle and train cattle from birth to ensure they are used to human contact and yarding.
- Muster and handle cattle gently to reduce stress and preserve muscle glycogen levels.
- Feed cattle on high energy feed for sufficient periods before dispatch. The 30 days prior to slaughter are most important.
- Keep cattle together a single mob (prevent mixing and drafting) within 14 days of dispatch.
- Remove females observed in oestrus.
- Cattle should be loaded quietly with minimal use of electric prodders.
- The use of dogs should be minimized particularly if cattle haven’t been previously worked by dogs.
- Remove flighty, poor temperament animals. It is not always the flighty animal that produces a high pH carcase, rather the quiet animals that are stirred up by the unsettled behaviour of the flighty animal.