If you can understand cow nutrition you can understand farming and, why farmers do what they do. It’ll also be useful to explain just how important the by-products of the human food chain are to agriculture.

Animal feed

Animal feed is measured in kilograms of dry matter (KGDM). Dry matter is what is left when all the water is removed.

The energy component of a feed is measured in megajoules of metabolisable energy, MJME for short.

And the other main metric farmers are interested in is crude protein (CP).

There are other important components such as fat, carbohydrates, starch, etc. But we’ll ignore those for now.

Leafy spring pasture is almost the perfect feed for cows. It has an 18% dry matter content. That means it’s 82% water.

Farmers don’t measure feed by its wet weight rather they use its dry matter content. If a farmer said they are feeding 1 kg of grass, they are meaning 1kg of dry matter. The actual wet weight of the grass is more like 5.5 kgs.

The table below shows that 1 kg of leafy spring pasture contains 11.7 Megajoules of metabolisable energy (MJME) and has a crude protein percentage of 26%.

Leafy grass is high in energy and high in protein.  It’s the perfect cow feed and it’s also the cheapest form of feed to grow.

What does a cow need to eat?

A cow’s daily needs:

• 63 MJME to just maintain her body.
• 65 MJME for every 1 kg of milk solids or 11.5 litres of milk produced.
• 39 MJME to gain 1 kg of live weight over time.
• 1 MJME for every km she walks.

And lastly, she needs energy to sustain her pregnancy:

• 6 mths pregnant =  5 MJME
• 7 mths pregnant =  10 MJME
• 8 mths Pregnant =  20 MJME
• 9 mths pregnant =  30 MJME

The other main component is the crude protein content of the feed.

The diet of a cow producing 18 litres per day needs to have a protein content of at least 18%.

A cow producing 28 litres per day will require 24% protein.

For this example, we’ll take an average 500 kg cow who is 6 months pregnant, is putting 0.5 kg of body weight, walks 2 km and is producing 1.8 kgms per day or 20.7 litres. She will require 205 MJME per day and a crude protein content of 19%.

What the above table shows is that the cow is eating a target of 18 kgdm of grass per day.

The total feed that the cow is eating has 210 MJME and 26% protein content.

This means that the leafy spring grass is meeting all the cow’s needs and more.

But, look what happens when the season changes and the cow is now eating summer leafy pasture. The MJME of the summer grass has reduced by just 0.5 MJ.

The cow is now in a slight energy deficiency.

This small deficit will likely eat into her live weight gain. So she won’t be gaining as much weight but her milk production will not be impacted as much.

In reality, the farmer feeding summer pasture will also have to decrease the amount of grass they are feeding the cows.

This is because the grass is not growing as fast as it did in the spring.

Farmers have excess grass growth in the spring. They cut that excess grass and make it into silage or baleage.

They can feed this to the cows when there is a feed deficit.

The table below shows the cow eating a diet where the pasture quantity has been reduced and replaced with baleage. As you can see below there is still a slight energy deficit with this diet.

This is where by-products can be useful to farmers. The table below shows some by-products that are commonly fed to cows. Take note of the energy and protein content of each feed.

Dried distiller’s grain is maize that has been fermented. The ethanol is removed via distillation and the residue that is left behind is then dried. It’s very high in crude protein and energy.

Molasses is made from sugar cane and is a by-product of the sugar manufacturing process. It’s a thick liquid often mixed with dried feeds. It has high energy content but almost no protein.

Palm kernel expeller (PKE) is a feed that gets a lot of media attention in NZ. Palm oil is extracted from the fruit of oil palms. The palm fruit is surrounded by a husk. This husk is dried and milled into a powder. Palm kernel has slightly lower energy than summer grass and low to moderate protein content.

Soy hulls are pellets made from the husk that surrounds the soybean. It’s essentially the soy version of palm kernel. They have similar nutritional values too.

Tapioca pellets are made from the Manihot Esculenta plant. It has a very high energy content (ME) and very low crude protein. It can actually encourage cows to eat more feed.

In the above table, the farmer has reduced the baleage by 1 kg DM and added 1 kg DM of distiller’s grain.

This has solved the energy deficit problem.

Generally the higher the protein content the more expensive the feed is.

The farmer is paying $770/ tonne for the distiller’s grain which has a protein content of 30%.

In this example, the farmer has more protein than is needed.

The table below shows a better option of using tapioca pellets instead of the distiller’s grain. This solves the energy issue and it’s cheaper.

But what if the farmer is experiencing a dry summer and they don’t have enough baleage?

This is a very common issue for farmers.

In this situation, a farmer would have to reduce the pasture content of their feed even further. They could use the cheapest by-product, palm kernel, and increase the tapioca pellets by 1 kg DM.

As you can see the cow is still receiving 18 kg DM but the energy and protein content is a little low.

By reducing the palm kernel by 1 kg DM and replacing it with distiller’s grain. The energy and protein deficit has been solved. As you can see there are lots of options and ways of feeding a cow. Some are more expensive than others.

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New Zealand context

It’s important to note that in the New Zealand context, farmers would love to only feed grass.

It’s the perfect feed and it’s the cheapest feed by far.

If you look at the tables at the top of this article, you will see that the cost to feed a cow for a day was only $1.80 when fed 100% pasture.

As soon as the farmer added baleage, the cost increased to more than double. Taking the total cost to $1.88.

That’s because, the farmer had to pay for a tractor to cut the grass, bail, and wrap the grass in plastic.

Then when we added a very small percentage of the cow’s diet to include by-products, the cost jumped to $3.18. In the final table, 44% of the cow’s diet was made up of by-products and the daily cost of feeding that cow is $5.68.

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Carbon footprint

Another aspect to consider is the carbon footprint of each of these feeding scenarios.

The 100% grass scenario involves the cow walking to the paddock, and harvesting the grass herself.

There’s no transport or tractors involved.

As soon as the baleage is added, there are now tractors, fuel, and labour. All of which create emissions. But when by-products are added, we’re now transporting feed to a port, shipping to NZ and then trucking it to a depot, and then transporting it to the farm. Then often times the farmer needs to use their tractor to feed it to the cows.

How cows are fed is the core issue around how dairy farming is conducted.

Dairy NZ has a useful document called The 5 Production Systems.

In New Zealand, a good cow’s milk production will peak at 27 litres/day in October and slowly decrease over the following months.

In Saudi Arabia, a cow’s average production is 40 litres/day over the whole season.

This is mainly due to feeding.

It’s a simple and predictable formula. Energy in = Milk out. New Zealand farmers have always come to the conclusion that lower milk production, produced on cheap grass is the most profitable model.