Tool 3.6 Factors affecting carcase quality and value

Achieving satisfactory glycogen levels

High levels of glycogen (animal sugar) in the muscle at slaughter is essential for optimal meat quality. Meat with high levels of glycogen will be tenderer, juicier, lighter in colour, have better flavour and keeping quality.

Glycogen is used as the primary energy source as muscle turns into meat. Glycogen is held in reserve for vigorous muscular activity or times of stress.

Source: MLA

Good nutrition results in a high (normal and desirable) concentration of glycogen in muscle tissue and reduces the risk of slaughter animals developing high pH meat. A muscle glycogen bucket less than half full at slaughter leads to meat that has a high pH, poor flavour and poorer keeping quality. It is visually unattractive, tougher, and takes longer to cook than low pH meat.

To ensure the glycogen bucket is full:

1. aim for weight gain of at least 100g/day for crossbred lambs and 150g/day for Merinos.
2. manage animals for minimum stress. Merino sheep are more stress sensitive during the pre-slaughter period so additional care should be taken.

Short-term fasting has little effect on glycogen levels.

Managing pre-sale liveweight - carcase weight loss

Animals lose weight rapidly during the first 12 hours held off feed (there is a 5% and 7.5% decline in liveweight at 12 and 24 hours respectively) due mainly to emptying of the gut and faecal expulsion. Most processors require at least 24–36 hours off-feed before trucking (the on-farm feed curfew period) to reduce the risk of injury or bruising to stock whilst in transport and contamination of the truck with manure and associated soiling of animal pelts and likely processor discounts.

Carcase weight loss in lambs starts at 12 hours off-feed at a rate of 0.1%/hour for the next 36 hours. For example, on a 20 kg carcase weight, reducing the total time off feed in the pre-slaughter period from 48 to 36 hours will improve carcase weight by 0.24 kg (20 kg {carcase weight} x 0.001 {carcase weight loss per hour} x 12 {reduction in time off feed in hours} = 0.24 kg).

Dehydration in slaughter lambs causes a reduction in both dressing percentage and carcase weight. If possible, train lambs to drink from troughs so they may be more inclined when in lairage to drink from the stock water points in the pens.

Health management affecting carcase and offal quality

Healthy animals grow faster and are more efficient at converting feed into liveweight gain. Specific problems affecting carcase and offal quality and yield (especially in older sheep) are cheesy gland and abscesses.

Achieving fat scores

As a general rule, when finishing lambs on high energy diets (such as high-quality pasture or grain) an increase of 7 kg liveweight in a 35–45 kg liveweight lamb will increase the fat score by 1. Genetic merit for muscle and leanness of the breeding flock (see tool 9.9 in MMFS Module 9 Boost Business with Breeding), sex and level of nutrition all have an influence.

Managing skin quality and value

Skins can be a valuable product in the sheepmeat enterprise and can contribute to the value paid for lambs and sheep. Several management factors affect skin quality and value and applying best management practices in the production system improves skin quality and financial returns.