Everglades Station iMimeo Report EES67-5 October, 1966
THE VALUE OF THIABEIDAZOLE TO STEERS ON PASTURE
2. E. Hainesl/ 2
There is much evidence that the livestock industry needs more effective
anthelmintic agents which show a wider range of anti-parasitic action, greater
efficacy and a reasonable margin of safety. One of the newer anthelmintic
materials that appears to merit consideration in meeting these requirements is
thiabendazole. A summary of the results of many studies with this drug has been
compiled by the Ierck Sharp and Dohme Research Laboratories (1).
Brown et al. (2) describes thiabendazole as a stable, white crystalline
compound that has an empirical formula of C10H7N3S and a molecular weight of
201.3. Studies by Tocco and Bowers (3) found that "thiabendazole was almost
completely metabolized to its 5-hydroxyl derivative and excreted as such and as
the glucuronide and sulfate ester of this metabolite". These research workers
also reported that 75% of the dose was recovered in the urine and 14% in the
feces of lambs in a 96-hour post-administration period.
A few studies indicate that thiabendazole has a wide margin of safety. Leiper
and Crowley (4) reported there was no evidence of toxicity when the drug was given
to cattle, pigs, sheep, chickens, and horses. Reinecke and Rossiter (5) found
that only mild toxicity symptoms'developed in calves given as much as 20 times
the therapeutic dosage rate. A report by Green et al. (6) indicated that a
favorable response was obtained when calves were treated as frequently as six
times in a 140-day period with thiabendazole. In this latter study, the anthelmintic
also improved weight gains.
A summary by Allen et al. (7) of several studies indicates that thiabendazole
has been effective against at least nine genera of cattle gastro-intestinal
parasites. Activity was noted against"both immature forms of nematodes and the
adults. Effective dosage rates have ranged between 3 and 4.5 gms. per hundred
pounds of body weight. The material may be administered by drench, capsule or
mixed with feed as it is very palatable.
In view of the many possible advantages of thiabendazole, it seemed desirable
to investigate its effectiveness with steers in south Florida. Each of the two
studies reported herein involved four groups of yearling steers that received
different rates of concentrate mixture while on pasture. One-half of the animals
in each nutritional treatment were treated with thiabendazole.
1/ Associate Animal Husbandman, Everglades Experiment Station, Belle Glade, Florida.
2/ F. R. Fields, Field Representative, M-erck Sharp and Dohme Research Laboratories,
Rahway, New Jersey provided the thiabendazole used in this study, assisted in
the administration of this material and in the collection of experimental data.
F. G. Martin, Department of Statistics, Gainesville, conducted the statistical
analysis of data presented.
The steers in the first trial were crossbred yearlings that had been secured
at weaning in south Florida. They consisted of a mixture of Hereford, Angus, and
Brahman breeding. Eighty of these steers were selected and equally divided into
four groups on the basis of breed composition, weight, and market grade. Each
group of 20 steers was kept on a 10-acre block of Roselawm St. Augustinegrass until
ready for slaughter or the feedlot, depending upon the nutritional treatment to
which they were subjected.
For the second trial, the yearling steers were predominately Hereford
crossbreds which had been purchased in central Florida. In order to allow for
adjustments in pasture stocking rates caused by the four nutritional levels, 104
steers were selected for this trial. This resulted in groups of 20, 24, 28, and
32 steers on 10-acre pastures of Roselawn St. Augustinegrass. Similar to the
first trial, the groups of steers were kept on their pasture blocks until ready
for slaughter or the feedlot.
The four nutritional treatments in each year were as follows:
Ration 1 No supplemental feed.
Ration 2 5 lbs. of concentrate, mixture per head daily.
Ration 3- 10 lbs. of concentrate mixture per head daily.
Ration 4 Full feed of concentrate mixture.
Since a constant average slaughter weight was desired in each year, the four
groups required different lengths of time to reach the termination point.
One-half of the steers in each of the nutritional treatments received
thiabendazole while the other half served as controls and were not treated. In
the first trial, thiabendazole was administered to the treated steers in November,
December, January, and February. However, in the second trial, steers were
treated only with a single dose in February. The thiabendazole was administered
as a drench at the rate of three grams per hundred pounds of body weight. Changes
in parasitic populations, as determined by fecal samples, and changes in body
weight during a six-month post-treatment period were compared for treated and
non-treated steers. Differences in weight gains due to treatments were analyzed
for statistical significance.
The average initial weight of all sub-groups.within each study year were
practically identical, thus' it was convenient to use differences in weight gains
between treatments as a comparison. In the first year the thiabendazole improved
the gains of steers receiving no concentrate, five pounds of concentrate and ten
pounds of concentrate; however, the full fed group did not show a benefit from
thiabendazole. The same trend was evident in the second year but the differences
in weight gains between the treated and untreated groups, within each nutritional
treatment, were smaller. The average weight gains for each sub-group are shown
in Table 1 along with the combined average for both years of study.
Table l.--Average gains in pounds during a six-month post-treatment period.
Year 1 + Year 2
No cone. 27 .59 76 86 51 73
5 lbs. cone. 157 168 238 243 201 209
10 lbs. conc. 193 237 294 304 252 275
Full fed cone. 309 306 368 366 345 343
Average 172 193 262 267 222 235
Each value represents an..average of ten steers.
TBZ is an abbreviation for thiabendazole.
Each value in No cone., 5 ib. cone., 10 Ibs. cone., and
represent 10, 12, 14, and 16 .steers, respectively.
Full fed groups
The difference in gains between the treated and control groups, when no
concentrate feed was provided, was significant at the one percent level; while
the difference in the groups on the ten-pound rate of concentrate was significant
at the five percent level. With the other two nutritional treatments, the
difference between the treated and control groups was not statistically signi-
ficant. When the gains of all treated groups were combined, these steers aver-
aged 12.2 pounds more than the non-treated steers. This difference was
significant only at the ten percent -level. The year-treatment interactions were
not significant within each nutritional treatment which suggests that the
difference between the treated and non-treated group was similar for both years.
The average initial number of eggs per gram of feces (EPG) indicated that
there was a low level of parasitic infestation present in these steers. This
means that responses to anthelmintic treatments in studies of this type would be
difficult to measure under these conditions. However, to illustrate the low level
of parasitism, the average EPG counts at the terminal examination are shown in
Table 2. Each figure represents five steers in the sub-groups and shows that the
EPG counts are too low in both treated and control groups to be considered of
Table 2.--Average final EPGI/ counts for steers with and without thiabendazole.
Pasture Year 1 Year 2 Year 1 + Year 2
Supplement Control TBZ=/ Control TBZ Control TBZ
No cone. 52 26 140 320 96 173
5 lbs. cone. 78 65 40 100 59 83
10 lbs, cone. 0 26 0 80 0 53
Full fed cone. 156 13 0 20 78 17
EPG refers to eggs per gram of feces.
TBZ is an abbreviation for thiabendazole.
It was obvious that the plane of nutrition had an effect on the response of
these steers to thiabendazole treatments and this difference due to nutritional
levels was statistically significant at the one percent level. Under maximum
well-balanced nutrient intakes the beneficial effects of thiabendazole were of
doubtful value but when lower levels of nutrition were involved the performance
of the steers was improved. This improvement in gains should be converted to
economical aspects for cattlemen as the additional gains of some of these groups
Calculations can be based on a cost of $1.00 for a single dose of thiaben-
dazole and a market price of $0.20 per pound for standard grade feeder steers.
Since the producer of thiabendazole recommends two treatments this would be a
total cost of $2.00 for the drug. The steers receiving no supplemental food and
those receiving ten pounds of concentrate showed a monetary advantage for the
use of thiabendazole. The treated non-supplemented group returned $2.40 per head
over the cost of the drug (22 lbs. @.20 = $4.40 $2.00) while the treated steers
receiving ten pounds of concent:-ate had a $2.60 per head return over their non-
treated counterparts (23 lbs. @ .20 = $4.60 $2.00). The difference of eight
pounds between the treated and control steers in the five pound level of concentrate
supplementation was not quite enough to pay for the cost of two doses of thia-
bendazole. Thus, the thiabendazole was of economic value to groups of steers
under certain nutritional levels on pasture.
Thiabendazole was administered to groups of yearling steers on pasture under
four levels of concentrate supplementation in two consecutive years. Steers that
received no supplemental concentrate showed the greatest response to thiabendazole
while those on the highest level of nutritional intake showed no benefit from the
anthelmintic agent. Steers feed limited amounts of concentrate exhibited an inter-
mediate response when thiabendazole was administered.
1. Thibenzole*, Annotated Bibliography. Compiled by Animal Science Research,
Merck Sharp & Dohme Research Laboratories, Merck & Company, Inc., Rahway,
N. J. 1963.
2. Brown, H. D., A. R. Matzuk, I. R. Ilves, L. H. Peterson, S. A. Harris, L. H.
Sarett, J. R. Egerton, J. J. Yakstis, W. C. Campbell and A. C. Cuckler.
Antiparasitic Drugs IV. 2(4'-Thiazolyl)-Benzimidazole, A new anthelmintic.
Jour. Am. Chem. Soc. 83:1764-1765. 1961.
3. Tocco, D. J. and W. Bowers. Metabolism of thiabendazole, a new anthelmintic.
Federation Proc. 21: 180. March-April, 1962.
4. Leiper, J.
W. G. and J. Crowley. Thiabendazole tested against the gastro-
nematodes of British farm animals (excluding sheep). J. Helminthol.
5. Reinecke, R. K. and L. W. Rossiter. Anthelmintic trials with thiabendazole.
J. South African Vet. Med. Assoc. 33:193-199. June, 1962.
6. Green, D. F., S. E. Park, R. L. Kilgore and 0. H. Siegmund. Effects of
thiabendazole on pastured cattle. Jour. An. Sci. 23:856. 1964.
7. Allen, P. H., S. E. Park, E. R. Ames, A. Ziessig and D. F. Green. Preliminary
report on thiabendazole in cattle. Jour. An. Sci. 21:1038. 1962.