Thursday, 28 March 2019 08:48

Will maize cover for grass?

Written by  Ian Williams, Pioneer genetics specialist

The summer dry has resulted this autumn in less-than-ideal quantities of grass being available to cows.

And, typically, at this time of year we get a lot of questions about feeding maize in autumn when there often isn’t much grass in cows’ diets. Let me cover some typical questions.

I have just harvested my maize; how long do I need to wait before feeding it? 

You can begin feeding maize as soon as you have harvested it. We recommend you wait for 4-20 days because this gives the maize time to become oxygen-free and therefore ensile. If you have used a proven inoculant (e.g. Pioneer 1132), the maize will have reached pH 3.6-4.0 in four days. If you haven’t used a proven inoculant, it can take up to 20 days to ensile. If you have used an inoculant with L. buchneri in it, ideally you should wait 20 days before opening the stack, as it simply takes longer for the bacteria to do their job.

How much maize silage can I feed? 

This is a ‘how long is a piece of string’ type question because many factors go into the answer. The amount you can feed depends on the class of stock you are feeding and what you want to achieve. When I visited France, some farmers were feeding 90% of the cows’ diet in maize silage; the other 10% was a very high protein-and-mineral pellet. If you are feeding late lactation cows, you will require an average of 14% crude protein in the diet. Maize is only about 7% crude protein (CP). If you need a total of, say, 14kgDM to achieve the milk production you are aiming for and you only have maize and grass, then if the grass is 18% and maize is 7% you will need to feed about 9 kgDM pasture and 5kgDM maize silage. This calculation will be different for each farm so if you feel uncomfortable about calculating this yourself, give your farm consultant or vet a call.

What is the most profitable use of maize silage in late lactation? 

This is one of those ‘it depends’ questions. The data shows that very high milk response rates to maize silage -- and therefore returns -- can be achieved by bridging a feed gap and, instead of drying off, you would able to keep cows milking. Likewise, if your cows are thin (i.e. below BCS 4.0 at calving), using maize silage to put weight on cows to achieve BCS 5.5 for first and second calvers and BCS 5.0 for mixed age cows can also result in high milk response rates.

Should I save my maize silage and only feed it to dry cows? 

I sometimes hear “maize silage is no good for milking off therefore I should only feed it to my drys”. Nothing is further from the truth. While it is true that dry cows fed maize silage put on weight very efficiently, it is not true that cows will not milk on maize silage. As long as the cow’s total diet is adequate in protein, at 11 mjme/kgDM maize silage is a great milking feed. It is often better than grass silage (average energy content 9.5 mjme/kgDM) and in some regions with pastures plagued by summer grass (10-10.5mjme/kgDM) it can be higher energy than pasture. So, if you need energy to keep your cows milking, and there is enough protein in the diet, feed maize to milkers.

Do I need to add minerals to my maize and if so, how much?

The best person to answer this question for your farm is your vet or animal nutritionist. However, a rough rule of thumb is that as maize silage is low in Ca, Na, Mg and P, if you are feeding more than one third of the cow’s diet as maize silage, you will likely need to add these to the diet. 

A good guide is the DairyNZ website

• Ian Williams is a Pioneer genetics specialist.

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