Karen Trebilcock

“Cow advocate” Andrea Murphy says nutrition should be looked at from the paddock-up and not supplement-down.

At the New Zealand Association of Ruminant Nutritionists’ (NZARN) conference in Gore in November, nutritionist Murphy said farmers should look at what was making up the main part of their cows’ diet and then work out what was lacking.

“Don’t think you have to radically change anything.”

She said a cow’s rumen needed a stable environment with a balance of protein and energy.

“That means the same feed every day at about the same time.”

Leibig’s 19th century Law of the Minimum was still relevant – if one essential nutrient is deficient, performance will be poor even when all other essential nutrients are abundant.

Farmers needed to plug the gaps, to bring up the nutrients that were at the lowest in the diet to where they needed to be, she said.

“We’re asking our cows to run an ironman race everyday so if they’re lacking in something it is going to affect their performance.”

But farmers also had to focus on profitability and work out the cheapest way of supplying the nutrients that were lacking in pasture or in forage crops.

“When cows are eating as much pasture as they can fit in, and that pasture is high in protein as it is in spring, then the limiting nutrient is usually starch.

“Palm kernel is usually used to plug the hole because per tonne, it is a lot cheaper than barley, but it is only 4% starch while barley is 55% starch.

“So palm kernel works out about $7.22/kg of starch while barley is only 85c/kg starch (palm kernel $290/tonne, barley $410/t).

“When pasture proteins are high and the rumen bugs are looking for a readily available source of carbohydrates to complement high-soluble protein, on a cost per kg starch basis, palm kernel is way too expensive.”

Murphy also used the analogy of a glass jar filled with rocks with the jar representing the rumen and the rocks representing pasture.

“But there are gaps in the jar and you can fill those with smaller rocks or with sand and water and that is the supplements.

“Don’t just look at the drymatter requirements, or the energy requirements of the animal. You have to look also at the protein and the starch and the minerals.”

Farmers should do pasture walks to measure cow intake and test the pasture to see what is lacking, she said.

“Also ask the animals. They will tell you if they’re not getting what they need.

“Cows don’t make milk from pasture, they make it from nutrients.”

Farmers also had to consider the different nutrient requirements for their different stock classes – a calf needed different nutrients to a yearling to a lactating, fully grown cow.

While fodder beet was an excellent diet for steers needing to put on weight in the last month before they were killed, it was far from ideal for growing yearlings because of its lack of protein and minerals, she said.

“The correct nutrition and the management of cows is not simple but it’s got to be made simple otherwise it gets too scary and no one wants to know about it.”

She echoed other speakers at the conference saying “if you don’t need it then don’t feed it”.

NZARN is a network of experienced ruminant nutritionists which exchanges ideas and experiences to understand and improve the health and productivity of ruminant livestock.

More? Visit www.nzarn.org.nz