|  |
Maintaining the Proper Cation-Anion Balance in Dry Cow Rations 1
Barney Harris, Jr.2Dietary electrolyte balancing is a new concept that has received some attention in recent months as a nutritional tool for reducing milk fever in early lactation as well as improving health and production. The dietary electrolytes are balanced according to the charges they contain. Since cations are positively and anions are negatively charged, the ration is balanced to be either negative or positive. A slightly negatively balanced ration favors prepartum dry cows and reduced incidence of milk fever whereas a strongly positive balanced ration favors lactating cows. Minerals considered in the electrolyte balancing are usually sodium, potassium, chlorine and sometimes sulfur (Table 1 ).
PREPARTUM RATIONS
Prepartum cows are identified as those cows in the last 3 to 4 weeks of the dry period. Since they are approaching calving, changes are frequently needed in their feeding and management programs. Also, cows can be fed more liberally during the late dry period and introduced to the lactating cow ration. This is especially true where lactating cows are receiving feedstuffs not in the dry cow ration. It is important that prepartum cows receive adequate amounts of long hay in their diet in order to avoid metabolic problems. The objective is to reduce stress by feeding more liberally a balanced ration that contains adequate amounts of long fiber and is similar to the lactating cow ration. By feeding more liberally the last 3 weeks, the cow is adjusted to eating more feed at the time of calving.To balance a seemingly well-balanced ration using the cation-anion approach, use about 200 grams of compounds such as ammonium chloride, ammonium sulfate and magnesium sulfate starting about 21 days before calving. Because anionic diets stimulate losses of calcium from bone, they must not be fed the entire dry period. The ammonium compounds are fairly expensive and quite unpalatable to dairy cows. As a result, they should be used with caution and mixed thoroughly in the dry cow ration.A cation-anion balance is calculated by subtracting anion milliequivalents from cation milliequivalents (mEq.). While several formulas have been used, the following is suggested for dry cows. It is best to use a combination of at least two of the compounds.Suggested Equations:* 1. Cation-anion balance = mEq. (Na + K) - mEq. (Cl + S) * 2. Cation-anion balance = mEq. (Na + K) - mEq. (Cl).Here is a sample calculation for a dry cow ration containing 1.0% potassium, 0.30% sodium, .30% chlorine and .28% sulfur. The percentage of an element in a compound may be expressed as pounds per hundred pounds or grams per hundred grams. Note that the results are expressed as mEq. per hundred grams. To calculate the ration balance, divide the percent of the element in the ration by the milliequivalent for the element (Table 2 ).
The cation-anion balance would be the summation of the above charges: +13, +25.6, -8.5, -17.5 = +12.6. In this case, the ration contains a greater amount of cations than anions.Studies to date report less milk fever when cows are fed low-cation or high-anion balanced diets during the late dry period. Three such studies are summarized in Table 3 . The reduction in incidence of milk fever appears to be primarily due to the greater absorption of calcium from these anionic rations. Research has shown that cows fed anionic diets have higher blood calcium levels at calving.
Present research indicates that watching the cation-anion balance may have potential for improving milk yield and reducing the incidence of milk fever. Research is underway at the University of Florida to help in defining the parameters needed in making recommendations.
LACTATION RATIONS
Lactating cows seem to respond more to a positively balanced ration whereas the opposite appears to be the case for dry cows. Kentucky workers reported that milking cows fed a ration containing a positive 20.0 mEq. per 100 grams produced 8.6% more milk than cows having a negative 10.0 cation-anion balanced ration.The principle of evaluating dairy cattle rations in terms of the anion-cation balance is fairly straightforward. Most of the available research indicates that diets which are acidogenic (negative cation-anion balance) are beneficial to calcium absorption and in the reduction of the incidence of milk fever. The feeding of such rations should be during the last 3 weeks of the dry period. While specific guidelines and recommendations are not yet available, some nutritionists are recommending a slightly negative cation-anion balanced ration in herds where milk fever is a problem. Even so, dairymen are encouraged to look at other approaches in reducing milk fever problems whenever possible.
Footnotes
1. This document is DS49, one of a series of the Animal Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date June 1992. Reviewed June 2003. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.