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The Veterinary Journal 169 (2005) 322–325
TheVeterinary Journal
Fast track
Effect of prolonged use of altrenogest on behaviour in maresq
David Hodgson a,*, Stephanie Howe a, Leo Jeffcott b,d, Stuart Reid c,Dominic Mellor c, Andrew Higgins d
a Faculty of Veterinary Science, University of Sydney, Private Mailbag 4, Narellan Delivery Centre, Narellan, NSW 2567, Australiab Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, UK
c Comparative Epidemiology and Informatics, Department of Veterinary Clinical Studies, University of Glasgow Veterinary School,
Bearsden Rd, Bearsden, Glasgow G61 1QH, UKd Federation Equestre Internationale, Avenue Man Repos 24, 1000 Lausanne, Switzerland
Abstract
Oral administration of altrenogest for oestrus suppression in competition horses is believed to be widespread in some equestrian
disciplines, and can be administered continuously for several months during a competition season. To examine whether altrenogest
has any anabolic or other potential performance enhancing properties that may give a horse an unfair advantage, we examined the
effect of oral altrenogest (0.044 mg/kg), given daily for a period of eight weeks, on social hierarchy, activity budget, body-mass and
body condition score of 12 sedentary mares. It was concluded that prolonged oral administration of altrenogest at recommended
dose rates to sedentary mares had no effect on dominance hierarchies, body-mass or condition score.
� 2005 Elsevier Ltd. All rights reserved.
Keywords: Altrenogest; Regumate; Anabolic; Behaviour; Competition
Altrenogest, a progestagen, is the 17a-allyl derivativeof the potent anabolic agent trenbolone which is struc-
turally similar to the male sex hormone, testosterone.
Altrenogest is reputedly used widely, and for long peri-
ods, in female competition horses. This occurs in an at-
tempt to ameliorate reproductive cyclicity, thus making
them more tractable and suitable for training and com-
petition. However, prolonged administration is not in
accordance with manufacturers� recommendations. Inmost countries, the drug is registered only for oral
administration to mares for 10 days for the purpose of
induction of ovulatory oestrus in the late transitional
stage of the oestrus cycle. Altrenogest suppresses behav-
1090-0233/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tvjl.2005.03.003
q PII of original article: S1090–0233(04)00126-1.* Corresponding author. Tel.: +61 2 4655 0743/0777; fax: +61 2 4655
6942/1212.
E-mail address: [email protected] (D. Hodgson).
ioural oestrus in mares within 2–3 days of commence-ment of administration. The effects of long-term
administration to mares of altrenogest are largely un-
known, particularly with reference to those used in com-
petition. Additionally, it is not clear whether the drug
has any anabolic or significant behavioural effects in
horses.
A study was therefore designed to provide a prelimin-
ary assessment of prolonged administration of altreno-gest to sedentary mares in terms of social hierarchy,
body-mass and body condition score (BCS). Twelve
mares of mixed breed (Thoroughbred and Standard-
bred) were acquired from a local horse dealer. The ani-
mals were kept at pasture as a single group for a total of
20 weeks. Following acquisition, all mares underwent
routine health care procedures, including de-worming,
dental prophylaxis, hoof care and vaccination. Mareswere allowed to acclimate to the new environment for
D. Hodgson et al. / The Veterinary Journal 169 (2005) 322–325 323
four weeks during which time they stabilised as a social
group, and became accustomed to routine management
procedures, e.g., being caught, weighed, placed in a
crush, administration of oral medication by syringe.
Throughout the entire period of study supplementary
lucerne hay was fed. Mares were weighed and conditionscore was recorded twice weekly.
A summary of the study protocol is given in Table 1.
Following acclimation, at the beginning of week 5,
mares commenced the pre-treatment assessment period,
which ran for four weeks. The hierarchy of the group,
was established using a modification of standard tech-
niques (Houpt and Wolski, 1980; Keiper and Sambraus,
1986). This assessment was made at regular intervalsthroughout each of the periods in the study. Briefly,
dominance was determined using a paired feeding test.
During the 15 min test two horses were in a 3 m · 3 m
yard and had access to one bucket of grain. The domi-
nant horse ate from the bucket for the greater part of
the 15 min. The horses received no food for 16–18 h be-
fore the test. The yard in which the tests were carried out
was familiar to all horses. No horse was tested morethan once a day. Each horse in the herd was paired with
every other horse in the herd with each pair being tested
once. Within the herd, the horse dominant to all other
Table 1
Flow chart of activities
Week 0 Mares acquired
Weeks 1–4 Acclimation (routine health care, acclimation to
scales, weigh and BCS)
Weeks 5–8 Pre-treatment assessment period (weigh, BCS,
determine hierarchy)
Weeks 9–16 Treatment period (weigh, BCS, determine
hierarchy)
Weeks 17–20 Post-treatment assessment period (weigh, BCS,
determine hierarchy)
Table 2
Hierarchies for mares throughout the period of study
Order in
hierarchy
Horse no:
wk 5 (pre)
Horse no:
wk 8 (pre)
Horse no:
wk 12 (treat)
1 10 10 10
2 3 3 3
3 4 4 4
4 2 2 2
5 11 11 11
6 5 5 7
7 6 6 5
8 7 7 6
9 12 12 1
10 1 1 12
11 8 8 8
Key:
� Bold, treatment group; italic, control group.
� Horse 1 in the hierarchy is the dominant mare, whereas 11 is the least d
� Horse 9 died as a result of an intestinal crisis in week 7. Results for this
horses was given the rank of 1 (see Table 2). The horse
which failed to dominate any other horse was given the
highest numeric rank (11 in a herd of 11). It was possible
for two or more horses to be dominant over the same
number of animals. In that case, the lower rank (domi-
nance) was ascribed to the horse that was the dominantmember of that particular pair.
During the test of hierarchy the aggressive actions of
each horse were recorded. The aggressive actions were
scored as follows:
(1) threat to bite (the aggressor laying its ears back
and moving its head towards the opponent);
(2) threat to kick (the aggressor turning the hindquar-ters towards the opponent with ears laid back and
one hind leg lifted);
(3) bite;
(4) kick;
(5) chase (the aggressor moving at least three steps
away from the bucket and towards the opponent).
The aggressive scoring system is an arbitrary one inwhich a threat is considered the mildest form of aggres-
sion and given a score of 1 each time it occurs and a
chase, the most severe type of aggression, is given a
score of 5 each time it occurs.
Attempts to assess the activity budget (time spent eat-
ing, non-eating activity and resting) for each mare as de-
scribed by Boyd et al. (1988) was attempted in week 5
However, this proved too difficult and was thus not con-tinued throughout the study.
At the beginning of week 9 (treatment period) mares
were randomly divided into two groups with six mares
treated daily with altrenogest (Regumate, Hoechst
Roussel) at the recommended dose rate of 0.044 mg/kg
body weight per os by syringe. One of the mares in the
Horse no:
wk 16 (treat)
Horse no:
wk 18 (post)
Horse no:
wk 20 (post)
10 10 10
4 4 4
3 3 3
2 2 2
11 11 11
7 7 7
5 5 5
6 6 6
1 1 1
12 12 12
8 8 8
ominant.
mare were discarded from the analyses.
Table 3
Weights of horses (kg)
Horse no. Wk 1: (accl) Wk 5: (pre) Wk 8: (treat) Wk 12: (treat) Wk 8: (post) Wk 20: (post)
1 568 584 576 556 550 556
2 572 574 548 542 542 530
3 530 536 528 530 534 530
4 466 475 464 463 456 458
5 548 554 536 536 544 556
6 558 560 552 554 556 556
7 544 542 534 539 540 546
8 522 522 516 516 520 526
9 534 534 DECEASED DECEASED DECEASED DECEASED
10 546 552 554 550 554 556
11 520 528 529 528 526 528
12 495 499 500 499 498 496
Key as for Table 2.
324 D. Hodgson et al. / The Veterinary Journal 169 (2005) 322–325
treatment group died as a result of an intestinal crisis in
week 10 and results for this animal were excluded from
analyses. The remaining six mares acted as controls and
were administered a placebo (yogurt) per os q 24 h. The
treatment protocol was continued for eight weeks.
Again observations to determine the dominance hierar-chy of the group were made weekly. Routine determina-
tion of body-mass and BCS were continued as
described. A similar protocol of observation and mea-
surement was followed for the four weeks following ces-
sation of therapy (post-treatment assessment period).
A comparison between each of the recording periods
used Spearman rank correlations. This compared results
for week 5 vs. week 8 (pre-treatment) to assess variationbefore treatment. Then, values for week 5 were dropped
and possible variations due to the treatment were as-
sessed, i.e., week 8 vs. week 12 vs. week 16 vs. week 18
vs. week 20. A post hoc two-way comparison was then
performed. Significance was ascribed at P < 0.05. Statis-
tical analyses revealed no differences in hierarchy in re-
sponse to treatment with altrenogest (Table 2). All
rankings were significantly correlated, even when cor-recting for multiple comparisons. Thus, given the pri-
mary hypothesis being tested that there is no difference
in the rankings in response to prolonged treatment with
altrenogest, the experimental data do not provide evi-
dence to reject the null hypothesis (P < 0.0001).
As shown in Table 3, statistical analyses also revealed
no differences in body weight in response to prolonged
treatment with altrenogest (P < 0.001). Similarly therewas no effect of altrenogest on BCS (P < 0.001) (data
not shown).
A search of the literature has revealed two papers
reporting the effect of altrenogest on growth (and other
variables) and these are in pigs by the same group (Klu-
ber et al., 1985, 1988). The data concluded that whereas
feeding altrenogest inhibited testicular growth and ste-
roidogenesis in boars it had no effect on body growth,carcass traits or back fat thickness. This is probably to
be expected as altrenogest�s 17a-C3 side chain
(–CH2CH@CH2), which provides the prostagenic activ-
ity, may well restrict binding to anabolic receptors.
When Johnson et al. (1997) looked at the effect of high
dose, prolonged oral administration of altrenogest on
sexual and aggressive behaviour and semen quality inyoung stallions, they found no differences in body
weight, BCS or metacarpal measurements between trea-
ted and control groups, although there was reduced libi-
do and decreased flehmen frequency and duration, a fall
in sperm production and a decrease in scrotal circumfer-
ence, all probably as a result of the effect of the drug on
the testes rather than any centrally acting effect. Re-
cently, Goolsby et al. (2004) reported the results of asurvey on the use of altrenogest in stallions. These
authors found that the agent was used in an attempt
to �create a more focused animal� during training and
competition.
In the present study, prolonged administration (eight
weeks) of altrenogest at recommended dose rates to sed-
entary mares caused no effect on dominance hierarchies,
body-mass or body condition score. We conclude thatthe evidence to date suggests that altrenogest when
administered in accordance with the manufacturer�sdata sheet, has no obvious anabolic or behavioural
effects that may affect the performance of a competition
mare.
References
Boyd, L.E., Carbonaro, D.A., Houpt, K.A., 1988. The 24-h time
budget of Przewalski horses. Applied Animal Behaviour Science
21, 5–17.
Goolsby, H.A., Brady, H.A., Prien, D., 2004. The off-label use of
altrenogest in stallions: a survey. Journal of Equine Veterinary
Science 24, 72–75.
Houpt, K.A., Wolski, T.R., 1980. Stability of equine hierarchies and
the prevention of dominance related aggression. Equine Veterinary
Journal 12, 15–18.
D. Hodgson et al. / The Veterinary Journal 169 (2005) 322–325 325
Johnson, N.N., Brady, H.A., Whisnant, C.S., LaCasha, P.A., 1997.
Effects of oral altrenogest on sexual and aggressive behaviors and
seminal parameters in young stallions. Journal of Equine Veteri-
nary Science 18, 249–253.
Keiper, R.R., Sambraus, H.H., 1986. The stability of equine domi-
nance hierarchies and the effects of kinship, proximity and foaling
status on hierarchy rank. Applied Animal Behaviour Science 16,
121–130.
Kluber, E.F., Pollman, D.S., Davis, D.L., Stevenson, J.S., 1985. Body
growth and testicular characteristics of boars fed a synthetic
progestogen, altrenogest. Journal of Animal Science 61, 1441–1447.
Kluber, E.F., Minton, J.E., Stevenson, J.S., Hunt, M.C., Davis,
D.L., Hoagland, T.A., Nelssen, J.L., 1988. Growth, carcass
traits, boar odor and testicular and endocrine functions of male
pigs fed a progestogen, altrenogest. Journal of Animal Science
66, 470–478.