Levels of progesterone and changes in prostaglandin F

Animal Reproduction Science 59 Ž2000. 87–97
www.elsevier.comrlocateranireprosci
Levels of progesterone and changes in
prostaglandin F2 a release during luteolysis and early
pregnancy in llamas and the effect of treatment with
flunixin meglumine
M.A. Aba a,b,d,) , H. Kindahl c,d , M. Forsberg a,d , M. Quiroga b,
N. Auza b
a
Department of Clinical Chemistry, Faculty of Veterinary Medicine, Swedish UniÕersity of Agricultural
Sciences, P.O. Box 7038, S-750 07Uppsala, Sweden
b
Department of Physiopathology Campus UniÕersitario, Faculty of Veterinary Sciences, UNCPBA, Paraje
Arroyo Seco sr n, Tandil, 7000Buenos Aires, Argentina
c
Department of Obstetrics and Gynaecology, Faculty of Veterinary Medicine, Swedish UniÕersity of
Agricultural Sciences, P.O. Box 7039, S-750 07Uppsala, Sweden
d
Centre for ReproductiÕe Biology, SLU, Uppsala, Sweden
Received 19 March 1999; received in revised form 7 December 1999; accepted 7 December 1999
Abstract
The secretory patterns of progesterone in relation to concentrations of 15-ketodihydro-PGF2 a
ŽPGFM. during the period of luteolysis or of maternal recognition of pregnancy were determined
in the blood of llamas mated either with an intact or a vasectomized male. The ability of flunixin
meglumine ŽFM. to postpone luteolysis in non-pregnant llamas was investigated by injecting the
drug intravenously every 6 h at a dose of 2.2 mgrkg from days 6 to 12 post-copulation into a
group of non-pregnant llamas. A pulsatile pattern of prostaglandin release was recorded during
luteolysis in non-pregnant llamas, giving further support to the hypothesis that PGF2 a is the
luteolytic agent in llamas. The mean number of peaks per animal rose from 0.3 on day 7 to 3.8 on
day 10 and then declined to 1.1 on day 12 with corresponding mean peak amplitude changing
from 465 to 1234 and 566 pmol ly1, respectively. In pregnant llamas, prostaglandin pulsatile
release also occurred. The mean number of peaks per animal rose from 0.4 on day 7 to 0.8 on day
10 and then declined to 0.2 on day 11 and 0.6 on day 12, with corresponding mean peak
)
Corresponding author. UNCPBA Faculty of Veterinary Sci, Dept. of Physiopathology, Campus Universitario, Paraje Arroyo Seco, 7000 Tandil Buenos Aires, Argentina, Tel.: q54-293-26667; fax: q54-293-28485.
E-mail address: [email protected] ŽM.A. Aba..
0378-4320r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 4 3 2 0 Ž 0 0 . 0 0 0 6 8 - 3
88
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
amplitude changing from 494 to 676, 388 and 547 pmol ly1, respectively. The transient decrease
and subsequent recovery in progesterone concentrations was observed to occur in connection with
prostaglandin release during early pregnancy. Oestradiol-17b plasma peak concentrations attained
after luteolysis were significantly higher than those recorded in early pregnant animals Žaround 30
pmol ly1 and ll pmol ly1 .. Concentrations of PGFM decreased rapidly after the first administration of FM and remained low throughout the first 2 days of treatment. Thereafter, pulsatile release
of prostaglandins started, and luteolysis proceeded; but a delay of 1–1.5 days in the progesterone
decline was observed. Thus, it might be suggested that a higher dose andror a more intensive
injection schedule is required in llamas than in other ruminants to prevent luteolysis. q 2000
Elsevier Science B.V. All rights reserved.
Keywords: Llama; Progesterone; Prostaglandins; Flunixin meglumine; Corpus luteum; Pregnancy
1. Introduction
In non-pregnant llamas Ž Lama glama. a dramatic fall in progesterone concentrations
is observed between days 9 and 11 post-mating, in connection with repeated surge
release of PGF2 a from the uterus ŽSumar et al., 1988; Aba et al., 1995.. In pregnant
animals, a transient decrease and subsequent recovery in progesterone concentrations has
been reported during the period when maternal recognition of pregnancy is expected to
occur ŽAdams et al., 1991; Aba et al., 1995.. In these studies, no pulsatile release of
PGF2 a has been reported in association with the transitory decline in progesterone
concentrations in llamas, but in the closely related alpaca Ž L. pacos ., prostaglandin
metabolite peaks have been detected from days 8 to 13 of pregnancy, indicating a
temporal relationship between the progesterone decline and PGF2 a pulsatile release
ŽAba et al., 1997..
Flunixin meglumine ŽFM., a non-steroidal anti-inflammatory drug, has the ability to
reduce prostaglandin biosynthesis by inhibiting the enzyme cyclo-oxygenase. In consequence, when used intensively, the drug has shown the ability to inhibit the synthesis of
PGF2 a to the extent that luteolysis is prevented in cattle, without interfering irreversibly
with the pulsatile mechanism of prostaglandin ŽAiumlamai et al., 1990..
The objective of the present study was twofold: first, to investigate the plasma
concentrations of progesterone in relation to concentrations of 15-ketodihydro-PGF2 a
ŽPGFM. during the period of luteolysis and maternal recognition of pregnancy in llamas
and, second, to evaluate the ability of FM to inhibit luteolysis in non-pregnant llamas.
2. Materials and methods
2.1. Animals
Eleven sexually mature female llamas Ž L. glama., 3–5 years old with an average
weight of 105 kg Žrange 95–120., were used. The animals were kept in a natural pasture
at the Faculty of Veterinary Sciences, UNCPBA, Tandil, Argentina, Ž37817X S.L., sea
level. and were supplemented with hay twice a day. Since several animals were assigned
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
89
to successive trials, a complete rest period of 2 months was provided to the animals
between treatments in order to circumvent possible carry-over effects of the previous
treatment to the outcome of the following.
2.2. Treatments
Intra-vaginal sponges containing medroxyprogesterone acetate ŽMPA. Ž120 mg,
Syntex, Buenos Aires, Argentina. were inserted and left in the vagina for 9 days. Six
days after removal of the sponges Žday 15., 10 animals were bred with an intact male,
while 11 llamas were mated with a vasectomized male. Five of the animals mated with
the vasectomized male were treated with FM ŽFinadyne w vet., Schering-Plough, Union,
NJ, USA.. FM was injected intravenously every 6 h Ž06:00, 12:00, 18:00 and 24:00 h. at
a dose of 2.2 mgrkg from days 6 to 12 post-copulation.
2.3. Blood sampling
Blood samples were collected daily from days 3 to 6 post-mating. Thereafter, samples
were obtained every second hour during the day Ž08:00–20:00 h. and every fourth hour
during the night Ž20:00–08:00 h. until day 16 post-mating. In animals treated with FM,
the first sample was collected on day 5 post-mating, and the following samples were
collected at 2-h intervals from 06:00 to 24:00 h from days 6 to 12 after mating. All
blood samples were collected by venipuncture and immediately drawn into heparinized
tubes. Plasma was separated by centrifugation and stored at y208C until analysed. In
order to minimise possible damage to the jugular veins from the sampling protocol,
puncture was performed according to a schedule at high, medium and low positions, on
both the left and right sides of the neck.
2.4. Hormone assays
Progesterone was assayed with an enhanced luminescence immunoassay technique
ŽAmerlite; Kodak Clinical Diagnostics, England. previously validated for llama plasma
ŽAba et al., 1995.. The intra-assay coefficient of variation calculated from the precision
profiles was below 8% for concentrations between 2 and 160 nmol ly1 . The inter-assay
coefficients of variation, for three quality-control samples were 7% Ž2 nmol ly1 ., 8%
Ž18 nmol ly1 . and 6% Ž54 nmol ly1 .. The sensitivity of the assay was 0.2 nmol ly1 .
The plasma metabolite of PGF2 a , PGFM, was analysed by RIA according to Kindahl
et al. Ž1976. and Granstrom
¨ and Kindahl Ž1982.. The intra-assay coefficients of variation
were below 8% for samples containing 240 and 485 pmol ly1 . The corresponding
inter-assay coefficients of variation were 5.5% and 8.4%, respectively. The practical
detection limit of the assay was 30 pmol ly1 .
Oestradiol-17b concentration was determined using RIA kit ŽDiagnostic Products,
Los Angeles, CA, USA., reported for use with bovine plasma ŽSirois and Fortune,
1990., and validated for use with llama plasma after minor modifications ŽAba et al.,
1995.. The intra-assay coefficients of variation calculated from the precision profiles
were 18% at 6 pmol ly1 , and below 11% for concentrations between 19 and 180 pmol
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
90
ly1 . The inter-assay coefficients of variation for three control samples were 22% Ž13
pmol ly1 ., 6% Ž39 pmol ly1 . and 10% Ž84 pmol ly1 .. The lowest amount of
oestradiol-17b detectable Ždefined as the intercept of maximal binding y2 SD. was 4
pmol ly1 .
Hormone concentrations are expressed in SI units. To convert from pmol ly1 to pg
y1
ml
and from nmol ly1 to ng mly1 the following factors should be used: PGF2 a
metabolite: 2.8; oestradiol-17b: 3.7 and progesterone: 3.2.
2.5. Analysis of data
Basal concentrations of PGF2 a metabolite were calculated by averaging the values
obtained on each particular day and removing values higher than two standard deviations from the mean value, until the baseline remained unchanged. Concentrations that
exceeded the baseline by more than two standard deviations between days 7 and 12 were
defined as peaks. The amount of PGF2 a released during each peak was estimated by
calculating the areas under the release curve according to the formula:
PGF2 a release s Ý Ž Ž PGFM i q PGFM iq120 . r2 . = 120 min,
where i s 0, 120, 240, . . . , min and where PGFM i s basal concentration was considered equal to 0. Daily progesterone concentrations were estimated by averaging the
concentrations measured in the sample collected at 08:00, 16:00 and 24:00 h for each
individual animal. Analysis of variance, using a repeated measures Žwithin-SS. design,
was applied to detect differences in hormone concentrations. In all cases, a least-significant difference test ŽLSD. was used to determine differences between means. Because of
variations in the time required to attain peak progesterone concentrations in pregnant
animals, values were normalised against the highest concentration during days 7, 8 and
9. The mean peak value was further compared with mean concentrations attained during
the following days. All statistical analyses were carried out using the StatisticarW,
release 4.0, software package Statsoft, USA ŽStatistica for Windows, 1993.. Results are
expressed as mean " SEM.
3. Results
The progesterone profiles showed that all animals ovulated in response to copulation.
Increasing concentrations of progesterone were recorded by day 4 post-mating. Five out
of 10 llamas mated with an intact male became pregnant Ž50%.. By day 10–11 after
mating, all non-pregnant llamas showed progesterone concentrations close to the detection limit of the assay.
Visual examination of the results for each individual confirmed that a pulsatile
pattern of prostaglandin release occurred during luteolysis in non-pregnant llamas. Fig.
1Ža. shows the mean Ž"SEM. plasma progesterone concentrations in non-pregnant
animals mated with an intact male and the PGFM secretory pattern in a representative
llama from days 3 to 16 after mating. Although only statistically significant in three
animals, slight increases in plasma PGFM were observed as early as day 7 after mating
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
91
Fig. 1. Plasma concentrations of progesterone Žmean, dotted line, "SEM, shaded area. in non-pregnant Ža.
and pregnant Žb. llamas and a prostaglandin metabolite secretory profile Žsolid line. in a representative animal
from days 3 to 16 post-mating. Values identified as significant pulses of PGF2 a metabolite are indicated by
asterisks. Note the logarithmic scale for the prostaglandin metabolite values.
in most of the animals. PGFM pulses were registered between days 8 and 9 and day 13
after mating in non-pregnant animals. Since no significant differences in the hormonal
secretory patterns were registered between non-pregnant llamas, whether mated with an
intact or a vasectomized male, all animals were considered as one group for further
analysis of PGFM profiles. Table 1 shows the characteristics of luteolytic pulses of
Table 1
Characterisation of normal luteolytic release of PGF2 a as determined by PGFM analysis in llamas Ž ns11..
Numbers within parentheses in the second column represent the mean number of peaks detected on each
particular day. M s 08:00 h, As16:00 h, N s 24:00 h
Days
after
mating
Cumulative
number
of peaksr
animal
Area under
curve Žpeaks.
Žpmol ly1 .
Ž%.
Peak-to-peak
interval Žh.
7
8
9
10
11
12
0.3
1.4 Ž1.1.
4.3 Ž2.9.
8.2 Ž3.8.
10.5 Ž2.3.
11.6 Ž1.1.
2.6
49.7
358.9
520.8
227.2
23.3
–
19.6
7.5
7.1
9.1
11.7
0.1
3.6
28.6
45.7
19.9
2.1
Mean peak
amplitude
Žpmol ly1 .
Progesterone
Žpmol ly1 .
M
A
N
465
748
1112
1234
779
566
7.9
8.9
4.9
1.0
0.5
0.5
9.3
6.5
1.9
0.6
0.5
0.5
8.3
7.6
3.3
0.7
0.7
0.5
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
92
Table 2
Mean Ž"SEM. plasma progesterone concentrations from days 10 to 16 after mating in pregnant llamas
compared with the mean maximum concentration between days 7 and 9
Mean days 7–9
13.00
"1.90
Plasma progesterone concentrations Žnmol ly1 .
Day 10
Day 11
Day 12
Day 13
Day 14
Day 15
Day 16
9.00UU
"0.72
8.93UU
"0.61
9.26UU
"0.70
8.83UU
"0.63
8.38UU
"0.64
9.66
"0.94
9.15U
"0.83
U
P - 0.05
P - 0.01
UU
PGFM during luteolysis Ždays 7–12 after mating. in non-pregnant animals Ž n s 11.. In
all cases, the initial pulses were lower in amplitude Ž525.9 " 36.7 pmol ly1 . than those
recorded later Ž P - 0.01.. The mean peak concentration of the luteolytic pulses was
1019 " 48.5 pmol ly1 . On average, 11.6 Žrange 10–14. peaks per animal were recorded
between days 7 and 12 post-mating. Decreasing concentrations of progesterone were
already registered by the afternoon of day 8, when only one or two prostaglandin
metabolite peaks were recorded in each individual animal. Although all animals had
reached basal plasma concentrations of progesterone on day 10 after mating, PGFM
peaks were recorded during the following 2 days.
In pregnant animals, plasma concentrations of progesterone remained high until the
end of the experiment ŽFig. 1Žb... Peak plasma progesterone concentrations were
attained between days 7 and 9. When the mean progesterone concentrations registered
on those days were compared with the mean concentrations registered from days 10 to
16, a significant drop in progesterone was seen after day 9 ŽTable 2.. In connection with
the progesterone decline, PGF2 a pulsatile release was observed in all pregnant animals
from days 7 to 15 after mating. Fig. 1Žb. shows the PGFM concentrations in a
representative llama. The characteristics of prostaglandin release during early pregnancy
Ždays 7–12 after mating. are shown in Table 3. The overall mean frequency of PGF2 a
Table 3
Characterisation of PGF2 a release during early pregnancy in llamas as determined by PGFM analysis Ž ns 5..
Numbers between parentheses in the second column represent the mean number of peaks detected on each
particular day. M s 08:00 h, As16:00 h, N s 24:00 h
Days
after
mating
Cumulative
number
of peaksr
animal
Area under
curveŽpeaks.
Žpmol ly1 .
Peak-to-peak
interval Žh.
Ž%.
7
8
9
10
11
12
0.4
1.0 Ž0.6.
1.4 Ž0.6.
2.2 Ž0.8.
2.4 Ž0.2.
3.0 Ž0.6.
11.1
6.0
11.0
69.3
7.3
28.8
0.1
3.6
28.6
45.7
19.9
2.1
–
–
28.0
35.3
38.0
99.0
Mean peak
amplitude
Žpmol ly1 .
Progesterone
Žnmol ly1 .
M
A
N
494
443
488
676
388
547
7.6
9.1
10.0
10.0
8.7
8.0
8.7
8.2
7.3
8.0
8.4
9.4
6.2
11.3
8.0
9.0
9.8
10.4
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
93
Fig. 2. Plasma concentrations of oestradiol-17b Žmean"SEM, shaded area. in non-pregnant Ža. and pregnant
Žb. llamas from days 3 to 16 post-mating.
metabolite peaks detected in pregnant animals was 0.64 peaksranimalrday, while the
mean peak amplitude was 503.8 " 49.1 pmol ly1 .
Oestradiol-17b plasma concentrations increased slowly from days 3 to 8 after mating
in all lamas. Thereafter, concentrations sharply increased in non-pregnant llamas, until
peak concentrations Ž30.9 " 3.8 pmol ly1 . were attained on day 15. Conversely, a slow
oestradiol-17b rise was recorded in pregnant animals in which the highest concentrations Ž11.2 " 4.9 pmol ly1 . were observed 12 days after mating ŽFig. 2Ža. and Žb.
respectively..
Fig. 3. Plasma concentrations of progesterone Žmean, dotted line, "SEM, shaded area. in non-pregnant llamas
mated with a vasectomized male Ža. and in non-pregnant llamas treated with FM Žblack bar. four times a day
Žb., and a prostaglandin metabolite secretory profile Žsolid line. in a representative animal from days 5 to 12
post-mating. Values identified as significant pulses of PGF2 a metabolite are indicated by asterisks.
94
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
Prostaglandin metabolite concentrations decreased rapidly in all animals after the first
administration of FM from about 450 pmol ly1 to concentrations of around 180 pmol
ly1 Ž P - 0.01.. Concentrations of the metabolite remained low throughout the first 2
days of FM treatment Ždays 6 and 7 post-mating.. Thereafter, pulsatile release of PGF2 a
started, and concentrations similar to those recorded during the first 2 days of treatment
were recorded between peaks.
Fig. 3 shows the changes in hormone concentrations in non-pregnant llamas mated
with a vasectomized male during normal luteolysis Ža. and during FM treatment Žb.. In
llamas treated with FM, the cumulative number of peaksranimal were 1 Žday 8., 2.2
Žday 9., 4.4 Žday 10., 5.8 Žday 11. and 6 Žday 12.. The mean peak prostaglandin
metabolite amplitudes were 261 pmol ly1 Žday 8., 547 pmol ly1 Žday 9., 561 pmol ly1
Žday 10., 993 pmol ly1 Žday 11. and 864 pmol ly1 Žday 12.. Increasing concentrations
of progesterone were recorded from days 5 to 7 post-mating in both groups. Thereafter,
progesterone concentrations declined and were close to the detection limit of the assay
by day 9 post-copulation in untreated animals. Progesterone concentrations remained
high until day 8 post-mating, after which, they started to decrease until basal concentrations were attained by day 10 or 11 post-mating.
4. Discussion
The PGFM, pattern registered during luteolysis, correlates well with previous reports
showing the close temporal association between pulsatile release of PGF2 a and termination of the corpus luteum function in llamas ŽSumar et al., 1988; Aba et al., 1995.. The
sampling schedule used in this study, allowed a more detailed study of the luteolytic
pulses of PGF2 a in llamas, although some peaks could have been missed. As has been
shown in cattle, sheep and goat ŽFredriksson et al., 1984; Basu and Kindahl, 1987; Zarco
et al., 1988b., the first peaks Žregistered on days 7 and 8. had consistently lower
amplitudes than those recorded during the following days. Calculating the area under the
peaks revealed that about 35% of the total release of PGF2 a occurred during days 8 and
9, when luteolysis was at its highest, while about 65% of the total release was seen after
progesterone levels had decreased below 1 nmol ly1 . Sampling was not frequent enough
to permit an accurate estimation of the duration of pulses. However, based on the
observation that increased PGFM concentrations were registered in two successive
samples in most cases during the period of maximum secretion, an estimate of 4–5 h for
peak duration may be suggested. Moreover, it was observed during this period that in
several cases, concentrations did not reach basal values between two consecutive peaks,
indicating that the interval between the end of one peak and the beginning of the next
could be shorter than 2 hours. This suggestion is supported by the observation that most
of the animals had at least four peaks during 1 day Žday 10.. The overall secretory
pattern of PGF2 a appears to be similar to that observed in other ruminants. However,
PGF2 a pulses during the period of luteolysis seemed to be somewhat shorter in duration
and to be produced at a higher frequency in llamas than those reported in cattle ŽBasu
and Kindahl, 1987..
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
95
The luteolytic release of PGF2 a starts on day 7 or 8 post-mating Žapproximately day
5–6 after ovulation. and is completed by day 9 or 10 after mating in non-pregnant
llamas. It has also been shown that in South American camelids, the first significant
increase in progesterone concentrations is observed 3–4 days after mating ŽSumar et al.,
1988; Bravo et al., 1996.. Exposure to an environment characterised by high progesterone concentrations is claimed to play a key role in the regulation of uterine oxytocin
receptors and, consequently, of prostaglandin pulsatile release in ruminants ŽSilvia et al.,
1991; Lamming and Mann, 1995.. Such a period lasts only 3–4 days in llamas, while it
lasts around 3 and 5 times longer in the sheep and in the cow, respectively. In addition,
it is apparent that luteal activity after a sterile mating in llamas, is considerably shorter
than that observed in other induced ovulators. Thus, using the length of the normal
pregnancy for each specie as 100%, the lifespan of the CL in non-pregnant animals
varies from 100% in mink and ferret ŽMøller, 1973; Heap and Hammond, 1974., to
approximately 55–60% in rabbit and cat ŽPaape et al., 1975, Rowlands and Weir, 1984.
and to about 3% in llamas. The mechanism behind this rapid increase in sensitivity and
the responsiveness of the developing CL to prostaglandins remains to be determined in
llamas.
In cows, no prostaglandin peaks are seen during maternal recognition of pregnancy
ŽBasu and Kindahl, 1987.. Similarly, there is no pulsatile pattern in pregnant goats
during this period, but PGFM concentrations in the peripheral circulation start to
increase on day 14 or 15 ŽFredriksson et al., 1984.. In pregnant sheep, although no
pulsatile pattern has been observed, two or three PGF2 a pulses of low amplitude,
separated by long intervals, can be distinguished during maternal recognition of pregnancy. However, no changes in plasma progesterone concentrations have been reported
in connection with these pulses ŽZarco et al., 1988a.. In the present study, prostaglandin
peaks were recorded in all pregnant llamas during the period when maternal recognition
of pregnancy was expected to occur. The magnitude and the frequency of the pulses
registered during days 7–12 of pregnancy were not comparable to those observed in
non-pregnant animals. The amount of PGFM recorded as peaks during early pregnancy
averaged about 3% of the total amount of prostaglandin released during luteolysis;
nevertheless, this prostaglandin production proved to be effective in inducing a decline
in progesterone concentrations. A similar transient decrease in progesterone concentrations during maternal recognition of pregnancy has been reported previously in llamas
and alpacas ŽAdams et al., 1990; Aba et al., 1995,1997.. Prostaglandin metabolite peaks
with relatively low amplitude have been observed in connection with the decline in
progesterone concentrations in pregnant alpacas ŽAba et al., 1997..
The mechanism by which the pulsatile release of PGF2 a from the uterus is depressed
Žbut not suppressed. in the pregnant llama is not known. Attempts to identify any
substance similar to ovine or bovine interferons in camel Žthe related Old World
camelids. conceptus incubates from days 10 to 33 after ovulation have been unsuccessful ŽSkidmore et al., 1994.. Moreover, no increase in oestrone sulphate concentrations in
urine or oestradiol-17b in plasma has been recorded during early pregnancy in South
American camelids ŽBravo et al., 1991; Aba et al., 1995..
The divergent pattern of oestradiol-17b plasma concentrations registered in pregnant
and non-pregnant llamas after day 9 post-mating further confirms the hypothesis that
96
M.A. Aba et al.r Animal Reproduction Science 59 (2000) 87–97
progesterone from the corpus luteum exerts a negative influence on follicular activity
during early pregnancy in llamas ŽAdams et al., 1990; Aba et al., 1995..
The dose of FM used here, proved to be effective in depressing prostaglandin
synthesis. This effect was clearly seen during the first 2 days of the treatment and during
the periods between peaks on the successive days. A negative influence on the pulsatile
pattern of PGF2 a was also observed. Thus, both the amplitude of the PGFM peaks and
the cumulative number of peaks per animal were significantly lower in llamas treated
with FM than in untreated animals; but this negative effect was not strong enough to
completely inhibit the occurrence of luteolytic pulses of PGF2 a , and luteolysis proceeded in these animals. However, the progesterone patterns indicated that luteolysis
was delayed for 1–1.5 days in treated llamas, as compared to untreated animals. A
similar dose of FM has been previously proven to be effective in other ruminants to
prevent luteolysis; however, earlier reports indicate that the FM half-life is shorter in the
related camel than it is in the cow. The authors concluded that, using the same dose
regimen in camels as has been used in cattle, would result in lower pharmacological
effectiveness ŽOukessou, 1994; Ali et al., 1996..
Acknowledgements
The International Foundation for Science ŽIFS., the Swedish Council for Forestry and
Agricultural Research ŽSJFR. and the Swedish Agency for Research Co-operation with
Developing Countries ŽSAREC., are acknowledged for financial support.
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