Opinion: A "varied diet" is in response to food availability and an attempt to restrain our own inclinations to indulge. Imposing this recent and muddled human concept on animals is inappropriate, Dr Jacqueline Rowarth writes.
Children like lollies. Not always, but generally. Sweet-free aisles at the supermarket are in place to avoid trouble.
Watch what happens at a children's party and the energy foods will be eaten first – icecream, cake, chips. Not always, but generally.
In adulthood, doughnuts are a popular choice to meet the need, and research involving bagels has shown that the most popular choice has the combination of sugar for instant energy and fat for long-term calorie maximisation.
Energy has been the priority during most of human history when we have eaten whatever we could hunt, gather, scavenge, barter or steal.
The advent of modern agriculture and trade has replaced "Is there anything to eat?" with "what would you like to eat?"
And while children might still respond "icecream", most of us know that focusing on sugar and fat for energy that we aren't going to use, will lead to weight gain (already linked to many of our current health problems).
The concept of "varied diet" is in response to food availability and an attempt to restrain our own inclinations to indulge.
Despite this, most of our actual purchasing decisions are still based on taste.
The International Food Information Council (USA) states that purchasing decisions haven't changed for a decade: taste remains number one, followed by cost and convenience and then health.
In Europe most people think that a varied diet is "healthier" than a non-varied diet. They also appear to think that a sustainable diet is one with variety.
In this context, sustainability is more about their own health than that of the environment.
The European Commission published "Making our food fit for the future – Citizens' expectations" in December.
The research involved more than 27,000 people in 27 European countries. Almost 60 per cent of people responded that eating a variety of foods and having a balanced diet with "more fruit and vegetables" constituted a healthy and sustainable diet.
Breaking down the results by country, it appeared that the higher the GDP per capita, the greater emphasis on variety (perhaps an excuse to eat more) lower GDP per capita was associated with "more fruit and vegetables".
Consideration of impact on the environment was similarly associated – richer countries being more aware of environmental footprints than other countries.
However, even the most concerned country, Sweden, reported only 27 per cent of respondents being influenced by environmental impact when making purchasing decisions.
People make choices based on taste, not environment.
So do animals.
In the productive sector, farm animals are still focused on energy. A New Zealand herd or flock let on to new grass will very rapidly identify the highest energy patches and deter all others by marking territory in very basic ways.
Put a trolley of carbohydrate into the paddock and animals will gravitate quickly to the source of energy.
Despite this basic instinct, there is increasing noise about mixed pastures and varied diets, even to the extent that animals will "self-medicate" by picking and choosing herbs in the sward.
Self-medication implies some sickness and should be of concern. A well-fed cow or sheep living outside on mostly pasture shouldn't need to self-medicate.
But of more importance is that the human construct of "varied diet" (which many people don't actually follow), is being super-imposed on animals. We've turned house-pets into pseudo-children and now we're embracing farm animals under the same umbrella.
Doing this will result in unintended consequences, such as weight gain, just as it has in humans and pets. It will also increase waste because it is difficult to manage different foods optimally, whether weekly from the supermarket or within a grazing rotation.
Mixed species pastures have been investigated in New Zealand since the 1930s.
Sir Bruce Levy, a DSIR Grasslands scientist, reported in the mid-1930s that whatever the number of species sown, simplicity produces the maximum quantity and quality of edible herbage.
This is because a few species can be managed optimally, and the rest die out through inevitable competition.
This decade, research by Dr Al Black and Professor Derrick Moot, forage specialists at Lincoln University, has shown that sowing up to three species of different functional groups (grass, legume, herb) provides increased yields and weed suppression.
Listen to Jamie Mackay interview Dr Jacqueline Rowarth on The Country below:
Any further increase in species number changes the botanical composition but not the total yield and quality of the pasture.
Quality is important in this debate because it affects animal performance and greenhouse gas production. High-quality pasture allows the genetic potential of the animal to be fulfilled for least impact on the environment.
For farm animals managed optimally for intake, health and low environmental impact, the research is clear. Grass, legume and herb is the recipe for high quality and optimal animal performance. Imposing the human concept of varied diet, which is recent and muddled, is inappropriate.
Farmers in New Zealand have worked with scientists and followed the research for almost 100 years, constantly evaluating their pastures to provide animals with the maximum opportunity to express their genetic potential.
The result, again shown by research, is low environmental impact per unit of production.
The same cannot be said of most humans in their own dietary choices.
• Dr Jacqueline Rowarth is an adjunct professor with Lincoln University and a farmer-elected director on the Boards of DairyNZ and Ravensdown. The analysis and conclusions above are her own. firstname.lastname@example.org