So you’re feeding supplements but aren’t certain if you’re doing it as successfully as you could. Figuring out what is making money, and not costing it, will make sure you, your cows, and your bank manager, are happy.

Feeding the right supplement for the right reasons is important and the gains will be seen in the vat, in the numbers of cows in calf, and the health of the calves when they’re born.

However, there is still a lot of discussion about the merits of grass-feeding only.

I have seen a photo, from memory taken in the United States, of what 18kg of grass drymatter looks like in spring. The pile towers over the cow in the picture. I would love to see it replicated in New Zealand.

We expect a cow to stick that much grass down its throat and ruminate it and on top of that go through peak production, deal with the changeable weather, recover from calving, and get pregnant again.

Supplementing spring pasture with its high moisture content and high protein with energy dense concentrates that take up little space in the rumen and are rapidly digested makes sense to many farmers.

But it’s just not about looking at the metabolisable energy (MJ ME) a supplement contains and costing it on that.

Many supplements also contain protein and that should be factored in as well.

And there are times when it is protein, not energy, you need for your cows.

Of the high energy supplements, maize grain is the top with 13.75MJ ME/kg DM (73% starch) along with 8% protein with wheat coming a close second with 13.5MJ ME (70% starch) and 12% protein.

Barley is just behind them with 13MJ ME (about 68% starch) and 11% protein and sugar beet is 12MJ ME and 8% protein.

Molasses, usually fed with grain in in-shed feeding systems, is a byproduct of the sugar industry and is high in energy mainly from sugars. It is also very palatable and can encourage the intake of less palatable feeds.

It has 12MJ ME and 4.5% protein.

Be careful feeding high energy supplements. While grass can be fed ad-lib, with the cows stuffing as much in as they can, don’t do the same with grain.

Energy dense feeds are usually high in starches and sugars, which can cause acidosis. The starches and sugars cause propionic acid to be made in the rumen, which reduces the pH and burns the stomach lining.

Give rumen microbes time to adapt to these feeds and limit how much they can eat.

When summer pasture matures or when the cow’s diet is mostly made up of whole crop silage, maize silage or poor-quality grass silage, protein dense concentrates is the answer.

Soya oilcake is the Rolls-Royce of plant protein sources with 13MJ ME and 50% protein. It is a high protein and high energy feed – supplying both high quality protein and energy. It is very different from soya hulls, as reflected in the price.

Canola oil cake is a byproduct from the canola (rape seed) oil industry and is 11.5MJ ME and 38% protein.

Dried distiller’s grain (DDG) is a byproduct of making alcohol or ethanol. It is relatively high in both energy and protein, but low in starch, making it less of an acidosis risk.

It’s also highly palatable, so helps with getting cows eating in spring, when pasture may be low in protein such as in dry periods and when high levels of silage are being fed.

You need to know whether the DDG is from wheat or maize as this affects both the protein and energy content. Maize DDG is 12.5MJ ME and 28% protein and wheat DDG is 12MJ ME and 32% protein.

The third class of concentrates are those with high fibre. Because they are low in starch or sugars, they contain less energy per kilogram of DM and are safer to feed in larger quantities or ad-lib in trailers.

Palm kernel (also known as PKE) is the byproduct of palm oil production and has 11.5MJ ME and 16% protein. It is high in neutral detergent fibre (NDF) and short-chain fatty acids, which can be a problem when processing milk. The amount fed has to be limited (usually to 2-3 kg) to avoid FEI grades.

Soya hull pellets (not to be confused with soya oil cake) is 10.5MJ ME and 12% protein, and so contains less energy and protein than pasture. It is more of a concentrated roughage at best, or pasture replacer, than a performance enhancer.

Brewers grains is a beer byproduct – the remains of the barley after brewing. The starch has been fermented (and gone into the beer), which reduces the energy content of the product. It does have a higher protein content because the starch has been removed, concentrating the protein. It can also have a high moisture content, making it difficult to handle and store.

With 11.5MJ ME and 22% protein it is similar to quality pasture.

Knowing the energy and protein of each feed lets you figure out the best value for money. Barley may be more expensive than palm kernel, but if it’s the energy from the barley your cows need, then the maths works.

If palm kernel is $290/t and has 4% starch, then it works out as $7.22 per kilogram of starch. Barley, at $410/t and 55% starch, is a mere 85 cents per kilogram of starch.

But if your pasture is seeding out and mature, starch is not the limiting factor for your cows; it’s protein. Invest instead in a high protein feed and again work out the dollars and cents.

Always start with your pasture – know what you are feeding your cows and add to their diet what they are not getting from the grass – energy or protein?

Also remember the trace elements such as calcium and phosphorous and all of the rest.

If you’re not sure, ask your cows. Do they look full? Do their sides almost touch the bales in the rotary? What does their poo look like? Are they producing their live weight in milk? Are their blood and liver tests what they should be? Are they getting in calf easily and staying in calf?

But don’t forget your grass is always your cheapest food. Feeding concentrates should make you a better grass farmer, not a lazy one.

Maintain grass quality as much as possible by shifting fences and pregraze mowing.

When your cows can’t keep up with grass growth, make sure surpluses are not wasted but turned into silage or balage for feeding later.