Feed processing usually means altering the physical (and sometimes chemical) nature of feed commodities to optimise utilisation by animals and to enhance mixing and stability of the diet. The major components of any diet, roughage and grain, are the feeds most likely to be processed. However, in some cases, the minor components of the diet (additives) are processed into pellets to help mixing and to maintain the stability of the diet.
The common grains fed in feedlots are barley and sorghum, although maize, wheat and triticale are fed when prices are competitive. Processing of grain improves digestibility by 8% to 15%, with the methods utilised being categorised as either ‘dry’ or ‘wet’. Common dry processing methods are, roller milling and milling plus pelleting. Wet processing methods include steam flaking, high moisture storage plus roller milling and reconstitution plus roller milling.
Sorghum has the lowest digestibility of the grains (unprocessed) and benefits greatly from processing, which breaks up the (endosperm) structure of the seed. A recent, significant research finding was that although steam flaking of barley had little advantage over dry rolled barley, steam flaking of sorghum did have a significant advantage over dry rolled sorghum. It would appear that wet processing of sorghum is important when this grain is being fed in feedlots.
Processing improves digestibility of grains which means less material passes through the animal for subsequent fermentation and odour production on the feedlot pad. Lot-feeders claim that wet processing reduces feedlot odour, although this has not been proven experimentally.
With dry processing, it is best to coarsely mill grain, ideally into three to five pieces. Fine grinding lowers animal performance and can cause digestive upsets. Small feedlots tend to use roller mills. Many of the bigger commercial feedlots have installed wet processing systems.
Steam flaking has the effect of gelatinising the starch, whereas high moisture treatment disrupts the protein matrix in the peripheral endosperm improving protein and starch digestibility.
Rolled, high moisture grain produces weight gains equal or superior to gains of cattle fed rolled dry grain. Additionally, rolled high moisture grain produces better feed conversion efficiency than ‘traditional’ dry rolled grain.
High moisture grain usually refers to grain with a moisture content of 25% to 30% compared to normal grain, with a moisture content of about 12%. This higher moisture content can be achieved by harvesting at 25% to 30% moisture or by adding water (reconstituting).
In both cases, the grain must be stored in the absence of air during the processing method. Ideally, the high moisture grain must be stored for at least 10 days prior to feeding. The storage process is an ensilage process which changes the nature of the endosperm thus improving digestibility.
Commodities categorised as roughages, more commonly include hay, straw, hull, whole cottonseed and silage. In some opportunity feedlots, grain and additives are fed in self feeders, whilst roughages are often fed in separate hay racks. In this situation, it is not necessary to process the roughage. However, in most commercial feedlots, regardless of their size, feed roughages are mixed with the grain and additives and fed-out in open troughs/bunks, as it is processed. This is achieved by either utilising a rotation-mixer, vertical mixer or tub grinder. Silage is the exception to the rule, and is fed ‘as is’ from the silo. Silage is usually chopped into small pieces, during harvest with the forage harvester, prior to being ensiled.
Roughage should be processed to obtain a particle length of approximately 2cm in length. If processed too fine, the physical attributes of the roughage are lost and rumen function can be diminished. If processed too long, animals can separate the roughage from the grain, leading to ‘selective sorting’ and the subsequent increased risk of grain poisoning.
Contact the Department of Agriculture and Fisheries Customer Service Centre on 13 25 23 (Queensland residents) or 07 3404 6999 between 8am and 6pm weekdays, or email firstname.lastname@example.org.
Sarah-Jane Forster, formerly Queensland Government.