Friday, October 26, 2012

The Value of Increasing Pasture Numbers

Historically pastures have been seen as low yielding land and little, if anything, was done to increase their productivity. In recent years management intensive rotational grazing has done much to change this perspective and high yielding, high quality pastures now form the backbone of many profitable livestock farms. This blog entry will describe one of the management practices that has greatly increased pasture yields--managing a larger number of pastures.

Increasing Harvest Efficiency

Farmers that practice rotational grazing manage many paddocks (small pastures 2-5 acres in size) instead of a smaller number of large pastures. This practice results in very large increases in harvest efficiency.  The traditional pasture typically had cows continuously grazing throughout the whole growing season. Under this system only 30% of the potentially available feed is harvested by the cows. However, as graziers add pastures, cow harvest efficiency greatly increases up to 75% of available feed when at least 24 pastures/paddocks are grazed in rotation. Figure 1 demonstrates this by using 5 tons DM of available feed per acre for a single growing season multiplied by the appropriate harvest efficiency as pasture numbers increase. Harvest efficiency data was taken from the USDA grazing stick. For more information about the USDA grazing stick see the instructional video and availability.

Figure 1: Increasing Pasture Number Increases Feed Grazed

Generally once a pasture is grazed, farmers wait 25-40 days before returning their cows to that pasture. This rest period allows enough regrowth in order for the grass and legume root carbohydrate reserves to be resupplied. Additionally rotational graziers don't graze their pastures until the soil is bare, but rather they tend to "take half and leave half" . Leaving at least 4 inches of grass is necessary in most cases to maintain desired  species in the pasture. Clipping the pastures once a year helps maintain an even stand without unpalatable clumps of dead plants. In many areas graziers will harvest a number of their pastures for hay or silage in the spring because often there is more feed than can be grazed. They then feed the spring harvests during the summer or winter in order to supplement or replace the pastures.

Increasing Feed Quality

Increasing pasture numbers not only increases the quantity of pasture that cows eat, but it also increases the quality of the pasture. In management intensive rotational grazing, grasses and legumes are grazed when they are in the vegetative growth stage. Pastures grazed at this time are more palatable, higher in protein, higher in fiber digestibility, higher in starch and sugar content, and lower in fiber content. Figure 2 outlines generally how forage quality declines with increasing plant maturity.  As pasture plants age they lose leaves and gain more stems resulting in lower forage quality.

Figure 2: Declining Forage Quality with Increasing Plant Maturity
From page 4 in Understanding Forage Quality

Grazing generally begins when the pastures are at least 8 to 12 inches tall. If pastures are grazed too soon in the spring cattle will often get diarrhea and will need supplemental fiber from low quality hay.  Having many pastures allows for staggered plant maturity across the farm. This allows cows to continuously graze high quality feed. Grass heading date determines how long grass will be in the high quality vegetative growth stage in the spring. Different grass species and different grass varieties have heading dates from a week to a month apart. By planting different grass species and/or varieties with different heading dates in separate pastures graziers can more effectively maintain pastures constantly in the vegetative growth stage. When using rotational grazing beef producers will generally move their animals every one or two days, while dairy farmers will move their animals to new pasture after every milking during the growing season. Maintaining high levels of pasture fertility, selecting proper plant species and varieties, building appropriate fences, supplying adequate water, sheltering animals from extreme weather conditions, and other factors are also necessary in order have a well managed, profitable rotational grazing farm.

Bottom Line

1. Dividing one large pasture into two dozen or more paddocks can double the amount of feed that cows will be able to graze over the course of growing season.

2. Having many pastures enables grazers to have the highest feeding quality through the growing season, because plants are constantly in the vegetative growth stage.

Understanding Forage Quality
Don Ball, Mike Collins, Garry Lacefield, Neal Martin, David Mertens, Ken Olson, Dan Putnam, Dan Undersander, and Mike Wolf

USDA Grazing Stick Availability
Debra Heleba, University of Vermont Extension

USDA Grazing Stick Instructional Video 
Sarah Flack, Sarah Flack Consulting & Amanda Gervais, University of Vermont Extension