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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Minimal Mineral Supplementation
for Beef Cow Herds on MIG Pastures

Adequate intake of minerals by beef cattle is very important to insure expected growth and lactation performance. Most of us have been taught from an early age that mineral supplementation must not be overlooked. We decided to reexamine mineral supplementation of beef cows and their calves because of two experiences. First, the management- intensively grazed (MIG) pastures that we deal with have different availability and quality than many continuously grazed pastures. A major difference related to quality is the proportion of legumes found in many of our MIG pastures. Secondly, our work brings us in contact with people who supplement minerals at minimal rates or who even at times omit mineral supplements altogether. Others use products such as dried kelp, which contains a low mineral content. So the question becomes "How can these beef herd owners and managers be successful using minimal mineral supplementation?"

We collected data from a sizeable MIG research trial over a 4-year period, which enabled us to calculate mineral intake and compare that intake with accepted mineral requirements for lactating beef cows.

Materials & Methods: Four summer pasture systems were compared: Low Management (LMS), a 3-paddock rotation; Medium Management (MMS), a 6-paddock rotation; High Management (HMS), a 12-paddock rotation; and a complementary system which included big bluestem (CMP), 12-paddock rotation.

Data for this report included combined values for 1987, 88, and 89. The grazing period on these pastures was from late April through the end of September. Two replicates of each pasture system were used with a total of 52 cows and calves used in 1987 and 1989, and 50 cows in 1988. Within this project we evaluated milk production, weight gains, and reproductive performance of Polled Hereford cows, as well as growth rate of their Gelbvieh-sired calves. Milk production was determined every fourth week from April through September by mechanical milkout. Reported milk yields are 3.5%, fat corrected and adjusted for age of dam, using the adjustment factor for Polled Hereford cows. Cow and calf liveweight was recorded every 28 days throughout the grazing season. Forage measurements included determination of forage yield, quality, and stand persistence throughout the grazing season. The stocking rates for each system were based on prior research and experiences.

Calculations for pasture intake were based on energy requirements of cows and calves in this grazing trial,which in turn were based upon body maintenance, lactation, and gain or loss of weight. Forage samples clipped from random 0.25 mư areas were analyzed for minerals using plasma optical emission analysis.

Results: Average body weight, milk production, pasture intake, and gain or loss of body weight for the pasture season is shown in Table 1. Body weight of the cows gradually increased, and milk production and pasture intake decreased over the grazing season. Mineral content of the pasture samples are compared to the levels required by the cows in Table 2. Sulphur was not analyzed. Treatments LMS, MMS, and HMS are all diverse cool season pastures which contained significant amounts (30%) of legumes. Treatment CMP was big bluestem, which contained few legumes. Calcium, potassium, iron, and manganese were all adequate in the cool season pastures for the entire season. Sodium was markedly deficient, and phosphorus copper and zinc were borderline. Magnesium was deficient during the first two months, April and May, but adequate the remainder of the season. Big blue- stem was deficient or borderline during all or various periods of the pasture season for all minerals analyzed except manganese and iron. Molybdenum was far below any toxic or antagonistic level throughout the season.

Supplementation recommendation: The values observed in this study for well-managed cool season pastures indicate that a supplement containing 1/2 trace mineral (TM) salt and 1/2 dicalcium phosphate or steamed bonemeal which is fed free choice will adequately supplement the mineral intake for lactating beef cows & calves. In late winter and early spring magnesium oxide should be added to the mixture at a rate of 1/4 of the mix. Cows fed such a mixture free choice should consume an average of 1 to 2 oz of salt per day. With an intake of 1 oz TM salt or 2 oz total mix per day, the levels of sodium, phosphorus, magnesium and zinc should be adequate.

During grass tetany season, when magnesium oxide is fed, an appetizer may be needed in the mineral supplement mix because of the impalatability of the compound. Adding 1 part ground corn or cottonseed meal to 2 parts mineral mix will usually increase intake to needed levels. It is only necessary to feed additional magnesium oxide during late winter and early spring, usually up to mid-May. Missouri Agricultural Guide #G2081 contains a more thorough discussion of mineral supplements and their application.

Big bluestem pasture was only about 1/2 the mineral value of cool season pasture. Supplemental mineral intake will need to be 3-4 oz per day to make the dietary intake of minerals adequate.

In pasture settings, cattle may go for a period of time and consume little or no mineral supplement. This lack of intake over a period of a month or 6 weeks should not be of concern. Many minerals are contained in the body in fairly large pools which contribute to metabolism when needed. Calcium and phosphorus are examples. In times of short sup- ply, cattle use these body reserves to maintain body functions. At the same time, cattle may be able to conserve some minerals. In the case of phosphorus, cattle are able to recycle body-phosphorus and thus lower their normal required levels. Of course, in times of plenty, cattle will replenish their body reserves, and they need to be given that opportunity by either feeding mineral supplements or adequate supplies of mixed grass legume forages.

Summary: Diverse mixtures of well-managed cool season pastures need only minimal to no mineral supplementation when fed to lactating and/or dry beef cows. Only during periods of low pasture intake or during problem periods like grass tetany season, are mineral supplements needed in appreciable amounts. That is how some producers are able to get along on limited mineral supplementation and still maintain good productive performance in their beef cattle herds.

Table 1.  Average BW, milk production, DM intake and weight gain 
          or loss of beef cows grazing 4-pasture systems.
                       
Treatment      BW       Milk      DMI        Gain
               lb       lb/d      lb/d       lb/d
----------------------------------------------------
LMS, avg.     1121      15.1      26.5       .69
     range 1034-1176 12.7-21.3 20.9-29.6  -.33-3.29

MMS, avg.     1157      14.0      26.1       .69
     range 1069-1213 11.8-19.2 20.5-38.7  -.34-3.01

HMS, avg.     1144      14.2      26.4       .71
     range  1056-1193 11.9-24.2 21.2-41.2 -.56-3.36

CMP, avg.     1113      14.3      27.7       .45  
     range  1077-1147 10.7-18.2 24.0-30.1 -.24-.87
----------------------------------------------------
                                                             
                            
Table 2.  Average mineral content of pasture DM compared to
required amounts in diet DM.

Mineral                         Treatment                    Required
                                                             in Ration
                   LMS       MMS         HMS         CMP        DM  
----------------------------------------------------------------------
Calcium,   % DM   .49       .58         .61         .27         0.43
           range  .43-.64   .50-.65     .54-.72     .24-.30

Phosphor., % DM   .23       .24         .24         .15         0.28
           range  .19-.27   .21-.30     .21-.23     .14-.17

Potassium, % DM  1.60       1.66        1.87        1.09        0.90
           range 1.38-2.00  1.47-1.94   1.47-2.43  .83-1.27

Magnesium  % DM   .20        .22         .19         .19        0.20
           range  .15-.27    .16-.25     .16-.27     .18-.21

Sodium,    % DM   .019       .023        .016        .002       0.18
           range  .007-.029  .016-.028   .009-.032   .002-.003

Copper     ppm     12         12          13           9       10.00
           range  9-17      13-100      11-14         7-11

Iron       ppm    346        343         434          145       5.00
           range  250-536    239-500     299-640      112-183

Zinc       ppm    21         19          19           21       40.00
           range  17-28      17-22       17-20        17-25

Manganese  ppm    93         76          83           63       40.00
           range  81-115     67-85       61-96        53-71

Molybdenum ppm    .5         .8          1.0          trace   <10.00
           range  .2-.7      .5-1.2      .5-1.7       trace