Best options for milling maize grain supplements for grazing dairy cows

Date: 24 Dec 2004 Author: Brad Granzin

Research conducted at Wollongbar in spring 2002 looked at whether there is an optimum method of processing maize grain supplements for cows grazing ryegrass and prairie grass pastures.

Background

Research conducted at Wollongbar Agricultural Institute during 1999 showed that feeding supplements based on coarsely rolled maize, as opposed to rolled barley, resulted in higher milk-fat and milk-protein concentrations when fed to cows grazing ryegrass and prairie grass pastures. There was a problem encountered during this experiment in that significant amounts of undigested maize grain were lost in dung.

An option for reducing grain loss in dung is to finely roll or hammermill grains. Although we were confident that this would reduce grain loss in dung, we were unsure what effects this would have on milk yield and composition.

Experimental details

Forty mature Holstein-Friesian cows grazing ryegrass and prairie grass pastures from early September to late October were fed maize-based concentrates (6 kg/cow/day), where the grain was processed in one of five ways:

Grain-processing method Average particle size (mm)
Fine hammermilled 0.5
Coarse hammermilled 0.7
Fine rolled 1.3
Average rolled 1.5
Coarse rolled 2.1

Preparing the concentrate:

  • To prepare the fine hammermilled concentrate, a 3.2 mm (1/8 inch) screen was used.
  • To prepare the coarse hammermilled concentrate, a 4.8 mm (3/16 inch) screen was used.

Results

Figure 1. The fine-rolled maize concentrate fed in this experiment

  • Of the treatments evaluated, fine rolling (Figure 1) resulted in the high milk yield (Figure 2) and high protein yield.
  • Coarse hammermilling resulted in the highest fat yield.
  • There were no real advantages in reducing grain loss in dung by milling maize grain finer than ‘average rolled’.
  • Milk fat concentrations were low in this experiment (2.80% to 3.26%). Milk from cows that were fed fine-rolled maize concentrate had the lowest fat concentration. These low milk-fat percentages were because the cows used in the experiment were in early lactation, being fed high-quality pastures and producing high volumes of milk.
  • Milk protein concentrations were similar across treatments (2.96% to 3.01%).

Figure 2. Daily milk yield of cows grazing ryegrass/prairie grass pastures<br /> and supplemented with 6 kg of maize-based concentrate

Costs and benefits

Assuming a milk price of 31c/L (with deductions of 0.335c per 0.1% below 3.95% fat and per 0.1% below 3.15% protein), returns ($/cow.day) were highest when maize was fine rolled ($8.94), followed by coarse hammermilled ($8.85), fine hammermilled ($8.65), average rolled ($8.45) and coarse rolled ($8.31).

It should be noted that the low milk-fat concentration (2.80%) of cows fed fine-rolled maize would cause this milk to be downgraded to second class on some payment schemes. However, in an all-year calving herd, this should not be an issue, as late-lactation cows would have higher milk-fat concentrations. This would keep vat milk-fat levels above 3.0%.

In terms of electricity, there is about 5 kilowatt hours difference (or about 40c) per tonne between the different types of processing used here, for example in the change from coarse rolling to fine rolling. Although dependent on mill capacity, it usually takes a longer time to process grain more finely, so there may also be changes to labour costs.

Practical implications

The results of this experiment show that in order to maximise milk yields of early-lactation cows fed a maize grain and ryegrass / prairie grass diet, then:

  • a large screen should be used on hammermills;
  • roller mills should be adjusted to provide a fine particle size.

Further research is needed to determine the best way to process maize-based supplements for cows in late lactation grazing ryegrass and prairie grass paddocks.

Acknowledgment

The financial support of the Far North Coast Subregional Team of the Subtropical Dairy Program, and of Norco Ltd, is acknowledged.