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Medicated Salt-Mineral Mixtures for Cow-Calf Pairs Grazing Native Range Pastures

D. G. Landblom and J. L. Nelson

Medicated feeds have been used by livestock producers for many years in all classes of livestock. One such compound that has been used under feedlot conditions is chlortetracycline. This compound is a broad spectrum antibiotic sold by American Cyanamid Company under the registered tradename Aureomycin. American Cyanamid has been doing field grazing studies in conjunction with universities to ascertain the effectiveness of medicating salt-mineral-vitamin mixtures for about 10 years. Research under grazing conditions done with ranchers under the direction of Kansas State University has shown a positive cost effective response favoring increased weight gains and a lower incidence of pink eye and foot rot. In Kentucky, where the medication was used with cow-calf pairs over a two year period on fescue-clover pastures, calves were 31 pounds heavier, and pregnancy rates in the treatment groups were 10-13% higher. Since the geographical region where these studies were conducted is quite different from southwestern North Dakota it is important to investigate the usefulness of this antibiotic under our conditions.

Angus X Hereford first calf heifers and their Milking Shorthorn X Angus X Hereford calves were allotted to graze native range pastures and receive either a chlortetracycline medicated mineral mix or an unmedicated control mixture. Fed free choice in covered mineral feeders, the salt mineral mix contained two parts trace mineral salt and one part dicalcium phosphate. Chlortetracycline was added at the rate of 312.5 mg. per ounce of mineral mix.

The mineral blend was kept fresh by adding small amounts at frequent intervals. Results for the 1984 grazing season, which ran for 151 days from June 1st to October 30th are shown in Table 1.

Summary: Chlortetracycline fed in the salt mineral mixtures resulted in 5.9% faster calf gains and cow weight gains were 17% better at the end of the 151 day grazing period. Although a gain advantage was shown for medication, the cost for the medicated mixture was $11.23 more per cow-calf pair than for the control. Using .70 per pound for value of the additional gain, the 18.1 pounds of calf obtained by using the medication would amount to $12.68. Any advantage for the medication in the form of weight gain would be eliminated by the cost of medication.

Table 1. Summary of cow-calf pairs supplemented with Chlortetracycline medicated and unmedicated salt mineral mixtures.
  Control Medicated
Cows   Calves Cows   Calves
No. cow/calf pairs 15   15 15   15
Starting weight June 1 950   199 954   192
Final weight Oct. 30 1020   486 1039   497
Days grazing 151   151 151   151
Avg. daily gain .46   1.89 .56   2.01
Total pounds salt/ mineral mix consumed   450     700  
Avg. consumption/pair1 daily, ounces   3.10     4.82  
Salt mineral mixture cost/pound,   10     31.1  
Avg. mineral cost/pair daily   .0193     .0936  
Total cost/pair, $   2.91     14.14  
1Herd bull included in average daily consumption.

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