| How to Determine How Many Head of Cattle Per Acre Are Required for Your Pastures Dec 22nd 2012, 08:00 Knowing how many head of cattle are allowed or required per acre for your pasture is important to prevent overgrazing via over-stocking, or even under-stocking. There are many variables that determine number of head of cattle per acre, from the difference between grazing pressure, stocking rate and stocking density to the arithmetic required to calculate carrying capacity, stocking rate, stocking density and grazing pressure. Note: This article is also applicable to those keeping horses, goats, sheep and other grazing animals. - Understand the factors involved with determining how to stock your pasture. Simply assuming that the standard stocking rate for all farms is one cow per acre is going to get you in a lot of trouble, because many factors make this "rule of thumb" the complete opposite of reliable. There are many factors involved which need to be taken into account when judging the topic of this very how-to article. Questions to be answered that are associated with these factors are as followed:
- Location: Where in what country (USA, Canada, Australia, India, etc.) do you live? Remember that simply stating the state or province of that particular country is not the answer to solving your problem of number of head/acre. For instance in Alberta, there is much variation from the north to the south and from east to west when determining stocking rate.
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Soil quality and type: What type of soil do you have and what of its quality? Your soil has much to do with how many cattle you can stock per acre. - Get your soil tested to determine the type, quality and nutrient level that your soil possesses. If you know what type of soil you have already, then the test will be a great tool to determine quality or nutrient level to determine whether and what fertilizing it needs.
- Vegetation quality and quantity: What is the quantity and quality of vegetation in your pastures? The amount of forage (as in forage yield in terms of lb/acre or kg/hectare) and the quality of that forage is a crucial part of judging how many cattle per acre on your pastures. The general principle is that higher the forage yield, the more cattle you can have per acre. Forage yield is measured by calculating the total mass of forage that is produced per unit of land area (acres or hectares) over a period of time.
- Forage mass is obtained by taking all the forage from a 1 ft by 1 ft square (or 1 ft diameter ring) and cutting it four to six inches above ground, weighing it as as-fed matter, then drying it out in a Koster Tester, Vortex Dryer, or similar equipment specially used for evaporating moisture from the feed or sward collected, then weighing it again. The weight obtained can be used to calculate the average forage yield of your pastures--but only after you have obtained a number of samples to base this average on, and not just one!
- Vegetation quality and quantity is always subject to change throughout the year, and is what determines pasture health. The poorer the health of the pasture, the less strain that should be put on by the animals grazing on it. In other words, the poorer the pasture, the less number of head per acre required for your pastures. As such, are the grasses in your pasture just starting to emerge, or are they reaching maturity (i.e., seed heads emerging)?
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Vegetation type: What type of vegetation are you having your cattle graze in: forest, crop field (i. - Precipitation: What is the annual precipitation level for your area? Usually measured in millimeters (mm) or inches (in), the precipitation or moisture that you get in your area determines the number of animals to stock per acre. Higher precipitation generally is associated with greater biomass, and less precipitation with less biomass.
- Type of cattle: Are you grazing dairy or beef cattle? Dairy cattle tend to consume more than beef cattle do due to the requirements for lactation on their bodies. Dairy cattle also require higher-quality pasture than beef cattle do, which can heavily influence cattle/acre and even when to best graze them.
- Class of your cattle: What class of cattle do you have to graze your pastures? Do you have just one class or more than one that can be combined or need to be grazed separately? Class refers to the age (relatively speaking), gender and physiological/reproductive stage of livestock. If you have:
- Cows, are they bred or open (not bred), and if bred, what trimester of pregnancy are they in? Are they young or old? Lactating/suckling a calf or dry?
- Bulls, are they growing or fully mature? Young or old? Coming off breeding season or not?
- Steers, are they being backgrounded/stockered or finished?
- Heifers, are they being grazed as replacements or as stockers? Are you fattening them up for slaughter?
- Calves, are they on their mothers, raised as veal calves, just weaned, or bottle babies? If they're on their mothers, often the stocking rate is determined by the weight of the cow and calf together as one unit. But not if they're raised as weanlings, veal calves or bottle calves.
- Weight of your cattle: What is the average weight of your animals, particularly those divided into classes and averaged out as a herd? Weight should be measured in pounds (lbs) or kilograms (kg) and is often rounded to the nearest 10 to 100 lbs. Weight is a huge factor in number of cattle allowed per acre, because the general rule is that the larger the animal, the more they will eat, and thus the greater area needed for them to graze or, less time in a particular area is required for them to graze.
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Use any and all of these factors to determine carrying capacity, grazing pressure, stocking rate or stocking density for your pastures. - Stocking rate refers to the number of animals on a pasture during one month or a grazing season, and is expressed as animal unit months (AUMs) per acre.
- Stocking density is the number of animals on a particular piece of land at a certain point in time, usually measured as number of animal units (AUs) per acre.
- One AU is equivalent to a 1000-lb (450-kg) cow with or without a calf that consumes around 25 lbs per day of dry-matter forage or 2.5% of its body weight on dry-matter ration. However, some sources define an animal unit differently. For instance, according to Forages: An Introduction to Grassland Agriculture, Vol. 1 (2003), "[an] animal unit is defined as an 1100-lb (500-kg) nonlactating mature cow (Bos taurus) fed at maintenance or its equivalent in other kinds and classes of livestock." At maintenance refers to the average 2.5% of body weight in dry matter ration.
- Despite the differences, the most widely accepted definition of an AU is the former definition above the author of this article has provided.
- Please note that it is incorrect to assume all cattle are 1000 lbs. Cattle vary in weight from 300 lbs to well over 1800 lbs, and this would consequently affect stocking rate and density of your pastures.
- Animal units are not just applied to pasturing cattle; it is a system also widely accepted for pasturing various types of stock as grazing animals as well. See the Tips below for how animal units can be calculated for these other types and classes of livestock.
- Carrying capacity is the number of animals that can be placed on a pasture or rangeland for an entire season without harming it, such as that with overgrazing or desertification. Carrying capacity is expressed in AUMs and is the measure of a pasture or rangeland's ability to produce enough forage to meet the requirements of a herd of grazing animals such as cattle, bison, elk, deer or even horses.
- An AUM is the amount of forage required by a one animal unit (AU) for one month. Thus one AUM is equal to 762.5 lb (30.5 days x 25 lb/day) of dry matter forage that one AU consumes per month.
- Grazing pressure is defined as the ratio of animal units to forage mass. This term is used to define undergrazing and overgrazing. Undergrazing is when grazing pressure is low, or there are few animal units per unit of forage mass (the amount of forage in dry matter per unit of land area at a single point in time), and is when forage supply exceeds animal needs. Overgrazing is the opposite of this: it is when grazing pressure is high, and is when animal needs exceeds forage supply.
- This type of calculation does not state how many animals to stock per acre (or per hectare), but really gives you an idea as to whether you have too many, too few or just the right number of animals on your pastures.
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Stock your pastures accordingly. - Monitor pasture conditions (in terms of forage quality), the weight of your animals (especially if you are grazing growing young animals, not mature ones), grazing pressure and forage quality to keep up to date with the number of animals you need to stock per acre per day, week or month. If it's possible, change your stocking rate or stocking density accordingly.
- Make use of local farmers or the county extension office to get information on local vegetation and soil and precipitation rates.
- Use a scale or weight-tape to judge the weight of your cattle. Some veteran cattlefolk are really good at judging how much a bovine weighs just by looking at it, but not everyone. Even those who can guess a bovine's weight aren't always accurate themselves!
- Don't be afraid to do some math! Math is good, and it's especially needed to figure out how many animals to stock your pastures with. If you don't do the math and simply assume, there's a much higher chance that you will overstock your pastures than find out you have the perfect number or are just under the optimum range as far as grazing pressure is concerned.
- Try to first understand the difference between stocking rate and stocking density. Stocking rate is more for continuous grazing or grazing where cattle are on a large piece of land for over a month, and stocking density is more applicable towards mob-grazing or managed intensive grazing.
- There are various grazing methods available for you to choose from. These include rotational and continuous stocking, creep grazing, first-last grazing, sequence grazing, strip grazing, buffer grazing, frontal grazing, mob-grazing, intensive cell-grazing, and many others. What you choose is up to you and your management practices.
- If you are reading this article and wondering about other livestock and how to determine how many head of these other livestock besides cattle per acre (or hectare) are required for your pastures, this article actually still applies to them as well. It also applies to cattle that are not exactly 1000 lbs per head. In order to determine the exact number of livestock required per acre, a more accurate way to equate livestock is based on metabolic body size--a mathematical approach to equate animals based on their body surface area than true body weight--generally accepted and calculated as the animal's weight in pounds (or kilograms) to the 0.75 power (BW^0.75).
- One AU is (1000 lb)^0.75 = 191. So, let's take a 450 lb ewe for example to find out what she equates to in terms of animal units: (450)^0.75 = 97.7, or (97.7/191) = 0.51 AU.
- This calculation can be used for all classes and types of livestock of various weights, from mature bulls that are over 2200 lbs to weaned goat kids under 50 lbs and everything else in between.
- Remember most calculations are based on Dry Matter, unless otherwise specified. Dry Matter means when a sample of forage is, essentially, cooked until all the water is removed, and it is weighed as "dry matter." As-fed refers to forage that is fed as it is without going through the oven to dry it out.
- Everything in nature is subject to change and will never stay the same. So don't assume that pasture conditions or the weight of your animals will stay the same throughout the grazing season.
- It is indeed feasible to do your own dry-matter calculations and measurements yourself on your farm without having to send feed to a facility to get your feed tested, especially if all your interested in is the dry matter content of your feed and not anything else. All you need is a piece of equipment used for this, such as a Vortex Dryer, Koster Tester, Forced-Air Oven (most commonly used in laboratories, but quite expensive to purchase), food dehydrator, or even your own microwave oven. There are also electronic testers on the market to determine moisture content but these are primarily used for grain, hay (in bale and swaths) and silage, not for standing pasture forage that is about to be grazed by your animals.
- As mentioned above in the steps, make sure you get more than one sample (at least 10 in different areas of the pasture or paddock is best) to calculate your average forage mass and forage yield. You will also need to remember to weigh the container the forage will be in first in order to calculate just the mass of the forage, not the forage and container together. If you don't do this you will skew the results.
Edit Warnings - Never get stocking rate nor stocking density confused with the other. The best way to remember which is which is that "rate" is more towards "continuous" and "density" is equivalent to "mob" or "intensive" as in managed intensive grazing or mob grazing.
- Never assume that a forage or pasture stocking calculation is based on an as-fed basis. Your calculations may be incorrect and far off the mark to what is the correct answer.
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