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Maize silage on a pasture-based system

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Maize silage may also be used to “dilute” the high protein content of pastures. Typically, grass proteins run between 24 and 30% crude protein (CP) in spring and summer. Too much protein in the diet is not desirable as it has a negative impact on fertility (embryotic death), normally when milk urea nitrogen levels are above 20 mg/dl. Cows use up energy when getting rid of excess nitrogen in their diet. This has a negative impact on the production and body condition of the animals. Ideally the target crude protein levels in the total diet are between 15 and 17% CP, depending on the stage of lactation. In spring, we run into the mid-twenties. Even with these high protein levels, we still see a milk response when extra bypass protein is added to the ration. The reason is that a high proportion of the protein in the grass is soluble nitrogen or rumen-degradable protein and not bypass protein. Bypass protein stimulates milk production.

Maize silage plays an important role in a transition/fresh cow ration, especially in spring as it increases the energy level of the ration, helps increase DMI and results in higher crude fibre levels which slow down the rate of passage. This allows the cows to utilise more nutrients from the ration. The digestibility of an early season ryegrass can be as high as 87%. This, in combination with the low dry matter (12–13%) and low crude fibre of the grass, make the rate of passage extremely fast.

Pasture substitution

There is almost always a degree of pasture substitution when maize silage is fed in a pasture-based system. The overall response to the maize silage depends on how well the substituted pasture is utilised by the dairy cows for milk solids production or improving body condition at a later stage (Macdonald 1999; Cooper & Austin 2000*)

Fed silage strategically

Maize silage can be fed strategically in order to control pasture residuals and keep the ryegrass in its most productive growth stage. Slowing down your grazing rotation in order to bulk up grass for winter or because of slower growth rates will require additional dry matter from sources such as maize silage which are off the milking platform. Maize silage also acts as a bit of an insurance policy in a drought situation when water for irrigation is limited and there is therefore less pasture growth.

The correct timing for cutting maize is critical as 10 days could mean the difference between poor quality (low starch and low dry matter) and good quality maize silage – the cost of harvesting will remain the same, yet quality may vary significantly. Figure 1 shows the positive correlation between starch and dry matter content of maize silage.

Figure 1 The correlation between the starch content and the dry matter content of maize silage

Aim to grow the best quality maize silage you can, as this will have a positive impact on your production and bottom line. The VEM (energy available for milk production) difference between the top 25% and bottom 25% of maize silage samples taken by De Heus in 2017 is 67 VEM/kg DM. If the silage was fed at a rate of 7 kg DM/cow, there is a difference of around one litre between the two.

2017 Maize silage results

To summarise, maize silage is a very valuable feed in a pasture-based system as it is used strategically at different times of the year for various applications. Without maize silage in a pasture-based system, the carrying capacity would be significantly lower unless you bought in additional feed to fill the gaps.

*Reference: Cooper, C.; Austin, G. 2000. Using maize silage to increase economic farm surplus. Dairying Research Corporation Field Day: 10 – 12.

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