Grazing Management: Animals as Grazers

Pub 19: Pasture Production > Chapter 4: Grazing Management > Animals as Grazers

 

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Excerpt from Publication 19, Pasture Production, Order this publication

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Table of Contents

1. Introduction
2. Sheep
3. Goats
4. Horses
5. Cattle
6. Other Grazing Management Recommendations
   • Effects of Grazing on Plants
   • Grazing Management Systems
   • Designing a Rotational Grazing System
   • Stocking Rate
   • Introducing Livestock to Pasture
   • Clipping Paddocks
   • Nutritional Supplement
7. Related Links
   
   

Introduction

Animals affect pastures and pasture productivity by trampling, spreading seeds, recycling nutrients and by grazing.

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Animals generally graze 7–12 hours a day, and within a livestock class, stays the same day to day. The peak periods of grazing are after daybreak, in the late afternoon and around midnight. When the weather is hot, animals spend more time grazing at night. The amount they eat a day depends on their bite size and the rate at which they eat. When forage supply and quality is good, they take fewer, larger bites than when forage is in short supply. When the grazing is good, cattle and sheep take approximately 36,000 bites a day.

Animals maintain their feed intake as the pasture gets shorter by increasing the number of bites per minute and by grazing longer. However, a point is quickly reached when animals cannot eat enough small mouthfuls of forage in a day to meet their nutritional needs.

When forage supply is plentiful, animals select the highest quality forage present. They prefer leaves over stems, and try to avoid eating dead plant material, trampled plants contaminated with soil, and plants growing near dung. Different animals prefer different plant species, or a different proportion of those plants species in their diet.

Animals use sight, smell, texture and taste to choose the plants to eat and, if given the chance, eat only what they like. This can result in spot grazing. Plants in the grazed areas are kept in a short, immature, leafy condition and have a high feed quality. Usually there is not enough quantity in these overgrazed areas to satisfy the nutritional requirements of the animals and the plants eventually die from being overgrazed.

Plants that are not grazed become mature, are less attractive to the animals, and are wasted. With time, the less attractive plants become the dominant plant species in the pasture. As the forage supply per animal decreases, the degree of selectivity decreases. Ideally, stocking rates should be high enough to eliminate most, but not all, of the selective grazing. Animals perform better when there is some opportunity for selective grazing.

Animals have different abilities to be selective grazers. Sheep and goats are the most selective, followed by horses and then cattle. The ability of animals to be selective grazers and to graze plants at different heights depends on their mouth parts.

Sheep

The structure of sheep lips and the way they use their tongues allows sheep to be very selective grazers. They can easily choose individual leaves over other leaves from the same plant. They prefer to graze plants in the following order: forbes, broadleaved grasses, fine-leaved grasses, sedges, and dwarf shrubs. Their relatively mobile upper lip allows them to graze pastures closely. They are much better at maintaining forage intake on short pastures than cattle. However, in order to perform well, ewes need at least 550 kg of dry matter per hectare available for grazing at all times. Lamb production is very sensitive to forage availability and quality, as they have high nutrient requirements. Finishing lambs needs 1,000 kg of dry matter per hectare. Sheep pastures should be no lower than 6 cm in height. If the pasture is thin, increase this minimum height.

Goats

Goats are similar to sheep in their ability to selectively graze, but prefer a wider range of plants in their diet. They are quite adaptable and browse more easily than sheep or cattle. Up to 80% of their diet can be from small trees and shrubs. Graze milking goats, with their high protein and energy requirements, on pastures with high quality forage.

Horses

Horses are selective grazers and can bite plants off closer to the ground than cattle. They tend to be spot grazers, grazing one area close to the ground and leaving other areas for droppings. Under low stocking rates the field develops a pattern of heavily and lightly grazed areas. They spend a longer time grazing than ruminants. A mature horse needs up to a hectare of productive pasture for the entire grazing season; heavy horses require an additional hectare. Horses need space to run. Keep this in mind when designing paddocks. They need relatively large areas, and long rectangular paddocks are preferable to small, square paddocks.

Cattle

Cattle use their tongues to pull plants into their mouth. This means they are unable to graze as selectively as sheep, goats or horses. They are also less able to maintain feed intake when grazing short plants. Graze cattle in pastures 10–30 cm tall.

The ideal height ranges from 12–15 cm. At this range, mature animals graze at a rate of 70–80 bites per minute and eat 70 kg of forage a day. Cattle eat at this quick pace because they easily form a food bolus, swallowing the feed without lifting their heads. When pasture plants are tall (30 cm (%) cattle have difficulty forming a food bolus. They must lift their heads up to form the bolus and swallow. This reduces the number of bites they take per minute, reducing feed intake to 30–40 kg/ day. When grazing short plants, less than 8 cm, cattle eat only 15–20 kg of forage/day. Cattle grazing plants shorter than 10 cm cannot get enough energy or protein to meet their daily requirements.

Cattle prefer to graze fine grasses over broadleaved grasses or legumes. They like to change the area they graze frequently; rotational or strip grazing suits cattle. Do not keep milking dairy cows longer than 2 days in the same paddock. Ideally give milking cows fresh pasture at least once a day. Top producing pastures can support 2 milking cows per hectare for the grazing season. Dairy heifers and dry cows do not have to move as frequently as the milking herd, and can stay a maximum of 5 days in a paddock or field. Beef cattle benefit from being moved every 3–4 days; do not leave them longer than 5 days in a paddock or field.

Related Links

... on forages and pastures, visit Forages and Pastures (OMAFRA)
... on weed control, order Publication 75 Guide to Weed Control: Forage Crops
... on agronomy for field crops, order Pub. 811 Agronomy Guide for Field Crops: Chapter 3 Forages
... on field crop protection, order Publication 812, Field Crop Protection Guide
... on livestock, visit Livestock (OMAFRA)