Phosphorus supplementation for cattle |

Phosphorus supplementation for cattle

Professor Emeritus, University of Nebraska Panhandle Research and Extension Center
Ivan Rush |

Cost of mineral supplements has increased considerably this past year which has caused some to question how much is actually needed without sacrificing performance. The majority of the price increase was due to the increased price of the sources of phosphorus. This was supposedly due to the high price of oil, so hopefully phosphorus prices will decrease for both cattle and crops as petroleum prices have decreased. Considerable differences in opinion and actual supplementing of minerals exist in the beef industry. Some recommend producers feed a phosphorus containing minerals year-round while other cattlemen only feed salt. Perhaps somewhere in the middle is most advisable.

Theoretically, it should be relatively simple. The cow has a requirement for phosphorus – all feedstuffs contain a level of phosphorus – and one’s goal would be to get the two to match as economical as possible. Several grey areas exist however; seldom do we know the phosphorus content of the forages consumed. Even though we can analyze harvested forages and we can determine the level fed I know of few cow/calf producers that actually make the calculation as to the level of supplementation needed, if any. In addition, grazed forages can vary greatly in quantity consumed and the content of phosphorus, leading to wide estimates of supplemental needs.

Requirements were established by the National Research Council, published in 1996, which should serve as a starting place. In general, the cow’s phosphorus requirements before calving is in the range of 0.15 percent of the diet, or 13-18 grams daily, and 0.25 percent or 20-25 grams after calving.

Analysis of high quality forages such as early spring grass, hay with more than 10 percent protein and alfalfa, will often contain phosphorus levels in the 0.2 percent range or in some cases higher. The more mature forages and often crop residues will be less than 0.2 percent and in some cases close to 0.1 percent indicating a definite need for phosphorus supplementation. In good quality native ranges in the inter-mountain region, in most cases, the spring and summer forages will meet the cow’s phosphorus needs, but as the forages mature in the fall the phosphorus level may drop below the cow’s requirement even though in spring calving the cow’s requirement will decrease also.

Another problem in meeting the cows’ needs is that under range conditions we rely on free choice feeding to supply the supplemental phosphorus, as well as other minerals, and we have tremendous variation in intake from region to region, pasture to pasture and from one mineral source to another. In some cases they will consume very high quantities due to formulation, availability and other available feeds. In other cases they will not voluntarily consume a sufficient amount for the same reasons. They will not have the ability to just eat what they need and nothing more. They are intelligent but don’t have that much nutritional wisdom – just as the kid in the candy store with $20 in his pocket. I find it interesting that in many cases, even though it is easy to determine, producers do not actually know the consumptions level of the mineral they are feeding and yet it is critical in determining if the mineral program is balanced. I also find it interesting that the feed industry devotes a lot of resources to determine the proper level of nutrients to include in a mineral product and when it is delivered to the cattle it is blended with various levels of salt, diluting out the nutrients included in the mineral formulated.

We also need to consider the level of phosphorus in other supplements that are fed, if any. Many protein supplements offer a relative high level of phosphorus. Most byproducts that are used in protein supplements are relatively high in phosphorus plus often supplements are fortified to supply 0.75-1.0 percent phosphorus. If a 1,300 pound cow (remember when we used to use a 1,000-1,100 pound cow) requires 25 grams of phosphorus daily 2-3 months after calving and is consuming forage at 2.5 percent (dry matter) of her weight and if the forage contains 0.15 percent phosphorus then she will only need three grams of supplemental phosphorus. One pound of a protein supplement containing 0.75 percent phosphorus would supply that three grams leaving no need for additional phosphorus in a self-fed mineral. Mineral supplements should not just consider phosphorus as other minerals may be needed such as copper, zinc, vitamin A and in some cases may be used to deliver additives to aid in fly control, enhance performance, etc… and may justify the use of a commercial supplement.

In summary, phosphorus is the major source of expense in mineral supplementation. Often times the feeds consumed will meet the cow’s needs. There are times when the forage is very mature or in crop aftermath grazing the cow’s requirements may not be met and some supplementation may be needed but other times when the level consumed is adequate, some cost savings can be realized without hurting performance. The best starting point is to determine or at least estimate the level of phosphorus consumed and compare that to the level required.

Hope all goes well during calving.

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