Achieving satisfactory glycogen levels

Glycogen (animal sugar) 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.

The muscle glycogen bucket

Good nutrition results in a high and normal 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, aim for a weight gain of at least 100g/day for crossbred lambs and 150g/day for Merinos. The other important factor in maintaining glycogen levels is management of animals for minimum stress. Merino sheep have a higher pre-slaughter growth target because they are more stress sensitive during the pre-slaughter period. 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 contamination of the truck with manure and associated soiling of animal pelts and likely processor discounts. Stock grown on green pasture, fodder crops, lucerne, legume stubbles or in a feedlot may require a longer curfew.

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

Health management affecting carcase and offal quality

Healthy animals grow faster and are more efficient at converting pasture into product. Specific problems affecting carcase and offal quality and yield (especially in older sheep) are cheesy gland abscesses (see tool 11.12 in Healthy and Contented Sheep) and grass seed penetration into the wool, skin and carcase.

Achieving fat scores

As a general rule, when finishing lambs on high energy diets, such as high-quality pasture or grain, in the 35–45kg liveweight range a gain of 7kg liveweight will increase the fat score by 1. Genetic merit for muscle and leanness of the breeding flock (see tool 9.9 in Gain from Genetics), 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 from 5% to 20% of the value paid for lambs and sheep. A number of management factors affect skin quality and value. Applying best management practices in the production system improves skin quality and financial returns.