Managing cows in a drylot can be a way to maintain the herd when forage production is reduced due to drought or as a part of a system when pasture is unavailable for other reasons.
When cattle are managed in a drylot over an extended period of time, minerals and vitamins that need to be supplied can vary significantly from those needed when cows are grazing. The most common vitamins and minerals to be impacted by deficiencies or antagonisms when feeding production cows in confinement are Vitamin A, Calcium (Ca), Magnesium (Mg), Copper (Cu), Manganese (Mn), and Zinc (Zn).
Micronutrient considerations when using stored feeds
Vitamin A is typically low in stored forages and concentrates and these feeds usually will not meet the requirements of the cow. Brown forages are basically devoid of vitamin A. Of the stored forages, green silage contains the most vitamin A. However, high quality corn silage, that is still green, contains 2 to 3 times that of high quality green hay and is still 5 times less than fresh green grass. Cows grazing green grass can meet their needs and will build up vitamin A storage in the liver. These stores can help meet their needs when consuming stored feeds short term (3 to 4 months). However, when feeding stored feeds over longer periods (more than 4 months), greater vitamin A supplementation is needed. Commonly, it is suggested to supplement 42,000 IU/day for a 1300 lb non-lactating cow, and when lactating, her requirement increases to 59,000 IU/d. Therefore, 4 oz of free choice mineral would need to contain 168,000 IU/lb for a dry cow and 234,000 IU/lb for a lactating cow. However, these recommendations likely assume that cows will have body stores to use in addition to what is found in the diet. In long term drylot situations, a few herds have experienced significant calf health issues and losses. When the vitamin A status of the cows and calves were evaluated, they were deficient in vitamin A. The amount of vitamin A needed to maintain status of cows when managed on stored feeds long term is not currently well known. Observational data would suggest at least 100,000 IU/d or 400,000 IU/lb in a 4 oz mineral is needed to maintain adequate vitamin A status when managing cows solely in the drylot. This is especially true for cows consuming diets with little to no green forage.
Low quality forage plus distillers diets
Low quality forages such as corn residue, straw, and mature hay are low in micronutrients. This means that when these feed resources are staples of a cow diet, particular attention to the mineral supplement program is needed.
In many confined production cow diets, the most inexpensive diets include limit feeding low quality forage and distillers grains. These diets may contain 20 to 50% of the diet dry matter as distillers. Distillers has a high phosphorus (P) content and will supply all that is needed by the cow. In fact, additional calcium is needed to balance the P. When 20% distillers is being fed, a minimum of 12% Ca in a 4 oz mineral is needed. When the diet consists of 50% distillers, the 4 oz mineral needs at least 26% Ca.
Distillers have a relatively high sulfur content, which can increase the need for Cu but also Mg. Some lactating cows limit fed distillers and low quality forage have exhibited signs of “grass tetany”, such as muscle twitching, irritability/aggressiveness. Blood samples in some of these cows indicated low blood Mg. In a forage based diet, elevated sulfur can negatively impact absorption of Mg from the rumen. The solution to this problem is just to feed more Mg. When feeding these type of diets to lactating cows, having 10% Mg in a 4 oz mineral mix should be sufficient.
When feeding distillers plus low quality forage (corn residue/straw) based diets, it seems a minimum of 2000 ppm of Cu, 4000 ppm of Zn and 2000 ppm Mn is needed in a 4 oz mineral to maintain adequate status of cows.
Special consideration with silage
Using silage can result in a need for additional supplemental Mn, if the silage is high in iron. In the past few years, several cases of Mn deficiency have been observed in cow herds that were fed silage as a major component of the diet. Calves born to Mn deficient cows can be weak and small and develop enlarged joints and/or laxity in joints, which makes it hard for them to stand. While these situations are not common, it is good to be aware and take preventive measures if needed. The culprit is dirt contamination of the silage resulting in high iron. During the ensiling process, the iron in dirt is converted into an available form that can be absorbed by the cow and will compete with Mn for absorption into the animal. The best thing to do is to test your silage for iron. If the iron is 200 ppm or above, then feeding higher amounts of Mn is needed. For a 4 oz mineral, 3000 to 5000 ppm of Mn may be needed depending on the amount of iron.
Custom mineral mixes can be helpful
Given that the needs of cows drylotted long term can be unique, it is hard to find a commercial mineral that checks all the boxes. Using a “co-product balancer” when feeding these high distillers diets can provide the high Ca, Cu, Mn and Zn that the cows need. However, they often fall short on Mg and vitamin A. It can be worth checking with local mills to see if they can custom mix a mineral. If their minimum batch size fits with your operation’s needs, this can often be a great way to meet the cows’ needs and lower costs. Many of the prepackaged minerals have added features and the associated added costs. Some of these features, such as weatherization may not be needed, when adding mineral to the diet each day. Shopping around with the mills in the area can also pay, as there can be considerable differences in what they charge for mixing and handling.
Having a good mineral and vitamin program can have a huge impact on calf health. A good mineral program does not have to be expensive, nor is cost correlated with effectiveness. It is worth taking some time and evaluating your program to determine if changes would be beneficial. These guidelines are not one size fits all. Testing feed and water sources can always help determine supplementation needs. Consulting with a local nutritionist or someone from your local extension office can help you develop a program that will work best for you.
（October 11, 2021. From “ The Cattle Site”）
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Post time: Oct-11-2021