ROUND bale forage sorghum silage has proven a very popular option for beef producers this year in anticipation of inevitable declining pasture quality levels later in the year.
Following good rain earlier in summer, sorghum silages have been around 45-55 per cent dry matter, 9-12pc crude protein and 8-10 megajoules of metabolisable energy on a DM basis.
An important advantage is that the harvesting, storage and feeding of silage can be completely mechanised. Innoculants with a guaranteed bacterial strain such as Lactobacillus Buchneri 40788 will ensure aerobic stability of silage.
However, as the costs of machinery, fuel, and labor have increased, the cost of harvesting silage has increased more rapidly than harvesting as grain.
The costs of urea fertiliser, planting and herbicide combined being about $270/hectare.
Yields can be good at 12 tonnes/hectare but additional costs of cutting, wrapping and carting mean total baling costs will be about $80 for a 500kg bale from start to finish. That makes the dry matter basis about $320/tonne, assuming the bale is 50pc dry matter.
Silage can be used as the major feedstuff for growing steer calves from 150-350kg for daily gains of 0.5-1kg. Heifer gains can match steers if a live yeast is added.
Protein will be needed in all weight groups for 0.75kg of gain. To produce gains greater than 0.75kg in 180-300kg cattle, the ration will need to contain 11-11.5pc crude protein.
Silage can be low in energy. For 0.75kg gains, 1-1.5kg of grain is needed along with protein, mineral and vitamin supplements. For 0.8-1kg gains, about 2-2.5kg is required. Calcium, phosphorus and trace minerals in chelated form are also necessary.
There is little need to add dry roughage to a high silage ration. Dry matter intake, and consequently rate of gain, tends to be lower for cattle fed high moisture silage in growing rations.
If you're feeding a wet silage, adding grain to reach the desired energy intake may be the most economical method of increasing gains. On the other hand, slower gains may result in the most economical total gain to marketing since compensatory gain usually occurs during the following finishing period.
Silage can be used for a large part of the ration when gains as low as 0.5kg/day or less are acceptable.
Silage also provides the roughage needed in high concentrate finishing rations. Intermediate rations or rations with medium levels of grain and silage tend to be less efficient than either a high silage ration or a high grain ration, or programs involving a high silage phase followed by a high grain feeding period.
The best explanation for this is that starch depresses fibre digestion, resulting in forage being poorly utilised when moderately high roughage.
For high grain finishing rations, the suggested minimum is about 10pc silage DM with about 13pc protein, 0.5-0.7pc calcium and 0.3pc phosphorus. After the cattle are well adjusted and weigh more than 350-400kg, the protein level can be reduced to 11.5pc.
Silages contain more energy than needed by dry heifers or cows. When restricted amounts of silage are fed to meet energy needs of the gestating cow, protein supplements should be limited. Additional vitamins and minerals should be fed for the last 60 to 70 days before calving as well as a high (10-15pc) phosphorus mineral supplement.
Silages will provide supplemental energy for cows and heifers carrying calves during the first few months of lactation, but it will be advantageous to feed additional grain and protein supplement with this.
- Toby Doak is a livestock nutrition advisor with Alltech Lienert Australia.
