BY PROVIDING grazing livestock with a variety of plants and encouraging them to try novel foods, farmers can help animals be healthier, more resilient to changes in feed conditions and productive, scientist Dean Revell (pictured) said.
Having options allows individual animals to choose what they need in terms of energy, protein, minerals, vitamins and even plant secondary compounds that can be medicinal in appropriate (often small) doses, Dr Revell told delegates at the Grassland Society of Southern Australia conference last week.
In many managed landscapes, animals are fed to the average requirement of the group or are forced to eat a limited array of plants that inevitably have insufficient amounts of some nutrients and excessive amounts of others that can limit their performance, he said.
"Given the flexibility and adaptability of animals in choosing what to eat, you may be asking, why do animals tend to eat the same thing over time and why don't I see them mixing and matching?"
"Although grazing livestock are aiming to match nutrient supply to their needs, they also tend to avoid the unknown."
Livestock managers need to first understand diet selection by grazing livestock and can then use it to their advantage, Dr Revell said.
Diet selection is the choice by an animal to consume particular parts of what is on offer – it is not a conscious decision as humans make, but neural and hormonal responses to what an animal's body needs triggers changes in feeding behaviours.
Experiences strongly shape the dietary choices an animal makes, so the relative preference for or against a plant, commonly referred to as its palatability, is not a fixed trait but a combination of plant characteristics and animal experiences, he said.
"If animals encounter a new plant or food, how do they know it is of value to them as a food source?
"They need to learn the nutritional characteristics of the new plant, so if they are not encouraged to explore the potential food source, the new plant can remain an object of no desire."
Research shows short, repeated encouragement to try a novel plant or feed can have persistent effect over an animal's life, including during tough times such as drought, he said.
Farmers can also help animals learn to eat a wider variety of plants by tapping into the multiple ways animals learn: in utero, from their mother (after birth), from peers and by trial and error themselves.
Dr Revell has been involved with experiments in which animals have used new plants by 'teaching themselves' with the support of grazing management, for example in Western Australia, a team had sheep graze a diverse shrub-pasture system and moved them into a fresh strip of forage every week.
"Initially, a few of the shrub species were eaten cautiously but, with each successive move (which could be thought of as a 'lesson'), their intake increased and broadened," Dr Revell said.
"Their growth rate increased concomitantly with intake. A new pattern of diet selection was created after about four 'lessons'."
In another recently completed study, sheep grazed diverse pasture-shrub forage system and were moved to fresh forage on a weekly basis.
The animals gained about 200 grams/head/day during the autumn feed gap of south-western Australia, he said.
"This was achieved without supplementary hand-feeding as the shrubs supplemented the pasture and the pasture supplemented the shrubs, and because grazing management encouraged diet diversity."
