There are a number of things that occur when stock are moved onto winter crops. Firstly, there is the time for the rumen to change over to this new feed. This is generally quick only taking a few days depending on what feed the animals have come off. What is not as quick is the fact that when animals are put on a high quality from poorer quality feed there is a reduction in the size of their rumen and liver.

Secondly, changes in gut fill and bladder fullness will have the greatest influence on liveweight. In grown livestock, gut fill and bladder fullness accounts for 12-22 per cent of an animals liveweight and hence anything you see on the livestock scales.

There are a number of factors that affect gut fill and the weight of the gut fill. These include the quantity of water the animal has drunk, the feed eaten (both quantity and quality), the type of feed (grain, crop or pasture) and also the time since the stock last ate or drunk.

In a practical situation we find the biggest loss of liveweight is when livestock are on very high quality pasture or crops. This is all to do with the rate of passage of the feed and also the high moisture content of the feed. We would expect livestock on actively growing winter cereal crop will lose 10-14 per cent of their liveweight in the first 16 hours off feed and water. On the other hand cattle which are on a feedlot diet, high in grain will only lose between 3-4 per cent of their liveweight in the same period. This is due to the smaller over all quantity/weight that they are eating and also its lower moisture content.

Anything that has an effect on the rate of passage through the gut will have an effect on the liveweight. So the type of plant (legumes for the same quality will move through the gut quicker than grass) and the stage of growth, therefore the digestibility of the plant, will affect liveweight.

Another factor that influences gut fill is the time of day when you weigh your stock. Stock will do a 70 per cent – 30 per cent graze in the day.

Stock taken off feed and weighed early in the day will have less gut fill then those weighed later on in the day.

An example of this is cattle at a feedlot in a research trial that were walking over weigher. These cattle had up to a 30kg variation in liveweight in the one day. This is up to a 6 per cent variation on these 500kg steers.

So next time you weigh your stock think about the type of feed they have been on and are your scales telling you the whole truth of their performance.

For further information please contact Brett Littler, Senior Land Services Officer – Livestock at the Mudgee Local Land Services office on 6378 1708.