by Dale Engstrom, M.Sc., P.Ag
I am often asked about using free-choice loose and block minerals. Are they needed? Do they do a good job of providing essential nutrients to sheep? Are they cost effective?
Let’s start by reviewing what minerals are. Minerals fit into two classes: major (or macro) minerals and trace (or micro) minerals.
Major minerals are those that are measured in feedstuffs and reported in requirement tables as percentages (parts per hundred). For example: alfalfa hay may contain calcium in the amount of 1.6% of the dry matter, and a mineral supplement may contain 16% calcium.
Trace (or micro) minerals are measured or required and reported in milligrams per kg (mg/kg), parts per million (ppm) or parts per billion (ppb). For example: grass hay may contain copper in the amount of 5 mg/kg (or ppm), and a trace-mineralized salt may contain 250 mg/kg.
The table below shows the major and trace minerals required in specific amounts in all sheep diets.
So these minerals are ‘essential’ and needed in sheep diets. Does that mean you have to provide supplemental sources of these minerals to your sheep? Not necessarily. Most feeds contain a wide variety of these minerals. The question is: do they contain enough to meet your sheep’s requirements? The only way to know for sure is to find out what is in the feeds (by feed sampling and testing), and then balance rations for each stage of production.
The minerals in the table are the ones that may be deficient to some extent in sheep feeds. When we don’t know how much the sheep are getting, we have to fall back on general recommendations. Here are my rules of thumb for mineral supplementation:
Have major feeds that are going to be used in critical periods (flushing, late gestation, early lactation) tested, and balance rations to determine how much mineral supplementation is required.
Mix required minerals with the grain or silage portion of the ration. This may not be possible; grain is not always being fed and minerals don’t stay evenly distributed in a dry hay mix. One producer I know adds a liquid mineral supplement to his hay/grain rations to get over this problem.
If you can’t mix your mineral supplement effectively with your sheep rations, free-choice mineral feeding is a practical alternative. This is better than not feeding minerals at all when they are needed in the diet. But it pays to actively manage the free choice mineral program:
a. Select the mineral supplement that best fits your rations. Grass and legume forages are often short of phosphorus, so using a mineral relatively high in phosphorus will get you going in the right direction. Look for a salt-free mineral that contains at least 12% phosphorus. Greenfeed and grain rations are typically short of calcium. In this case, select a salt-free mineral that contains about twice as much calcium as phosphorus (e.g., 18% calcium and 9% phosphorus).
b. Always feed a trace-mineralized salt, as most feeds grown in Canada are deficient in copper, manganese, zinc, selenium, cobalt and iodine. A modest level of copper (less than 500 mg/kg) is my recommendation for sheep, while much higher levels are required for cattle and horses. You should not feed cattle and horse minerals to sheep without checking the copper level.
c. Another option is to buy a complete product, one that contains salt (sodium chloride), other major minerals (such as calcium and phosphorus) and trace minerals. The salt level should be around 40 to 60%. The sheep’s natural appetite for salt will encourage consumption of the complete mineral mix, if you don’t feed any additional salt. You can make your own complete mineral by mixing a bag of salt with a bag of salt-free mineral. This will give you 50% salt in the final mix.
d. Have a target level of mineral consumption in mind, and monitor the flock intake to get close to the target. For example, if the ewes need 20 grams (.044 lb.) of mineral mix per day, 100 ewes should then consume 14 kg (30.8 lb.) per week.
e. Keep minerals fresh by feeding two or three times per week, and feed only the amount the sheep will clean up between feedings. Use a feeder that keeps manure and rain out.
f. You can vary the salt content to increase or decrease the consumption of the overall mix. Less salt should result in more intake, and vice versa.
g. Put the mineral feeder near the water source or an area where the sheep spend time.
h. Recognize the limitations of a free-choice system. If there are high sodium levels in your water, the sheep may not eat much mineral that contains salt. Intake of free-choice mineral varies considerably between individual sheep. Deficiencies in some trace minerals, such as selenium, may need custom formulations rather than off-the-shelf products.
Consumption of blocks is usually much lower than that of loose mineral, and a block may not make a significant contribution to the nutrition program. The exception would be blocks that are high in molasses, and intake of these products is hard to predict. Blocks are generally more expensive than loose minerals, but they are also more convenient and usually have less waste. If you use blocks, be sure to monitor intake.
Mineral supplements often come fortified with vitamins ADE. If using a custom-made mineral, specify the amount of vitamins you want included. That way all of the mineral and vitamin requirements for your sheep can be met in a single product. If you are feeding the right vitamin/mineral supplements, and have achieved the right amount of intake, then there would be no need to worry about injecting vitamins or minerals (e.g., selenium) into newborn lambs or other sheep. Prevention of deficiencies through a balanced feeding program is always preferred over treatment later on.
In summary, mineral supplementation needs to be addressed when designing balanced feeding programs. While mixing minerals with grain or TMR’s (total mixed rations) is preferred, free-choice mineral feeding programs are used effectively on many sheep farms. Free choice systems will be more useful and cost-effective when managed by the shepherd, rather than by the sheep alone.
Questions and comments are welcome and can be directed to firstname.lastname@example.org.
Dale Engstrom is a retired former sheep farmer and ruminant nutritionist living in Lake Isle, Alberta, who now consults on sheep nutrition.