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Daily progesterone fluctuations during the estrous cycle in the bitch
Daily progesterone fluctuations during the estrous cycle in the bitch.
Linde Forsberg C, Ström Holst B, Forsberg M.
Department of Clinical Sciences, Division of Reproduction, P.O. Box 7054, Swedish
University of Agricultural Sciences, SE-750 07 Uppsala, Sweden. +46 18 67 21 63; Fax: +46
18 67 35 45.
The use of progesterone assays to determine the optimal time during estrus for mating or
artificial insemination (AI), and during late pregnancy for a planned Cesarean section, have
become routine procedures. Both quantitative and qualitative assays are being used, and the
results may vary considerably depending on the reliability of the assay, and also with the
individual bitch. The aim of the present study was to define the daily physiological variation
in progesterone in bitches during the non-pregnant and pregnant estrous cycle using an
immunoassay (Amerlite) validated for the dog, with an intra-assay coefficient of variation
(CV) of <4%, an inter-assay CV of <8.1% and a detection limit of 0.20±0.06nmol/L(1).
Six bitches, 2 to 8 years old, were used. Four bitches were followed during a non-pregnant
cycle, and 2 during a pregnant cycle. Blood samples were collected from the cephalic vein
three times daily, at 8.00-9.30, 13.00-14.00 and 15.00-16.00 in heparinized tubes that were
centrifuged and the plasma stored frozen until analyzed. During proestrus and estrus the
bitches were sampled three times per week and during metestrus once a week.
Mean progesterone levels per week and the CVs are show in Table 1. Progesterone variations
in one of the non-pregnant cycles are shown in Figure 1, and in one of the pregnant cycles in
Figure 2. The large variation in progesterone between the three sampling times each day
found in this study is of a considerable clinical importance. In three of the individual bitches
the difference in progesterone in one day during the optimal period for mating or AI was as
large as 7.9 nmol/L (20.4 – 28.3 nmol/L), 8.3 nmol/L (23.6 – 31.9 nmol/L) and 12.7 nmol/L
(36.7 – 49.4 nmol/L). During metestrus the daily individual variation was up to 49.1 nmol/L
(77.1-126.2 nmol/L). No diurnal variations were found using this 3 times daily sampling
regimen, which is in contrast to some earlier studies using a twice daily sampling model (2,3).
Table 1. Progesterone values (means) and coefficients of variation (CV) in pregnant and non-
pregnant bitches during the different weeks of the estrous cycle.
5 99.7 18.1 76.7 12.0 6 79.4 30.9 60.2 17.0 7 37.3 27.5 39.8 18.0 8 19.8 26.5 25.4 6.7 9 8.6 43.7 12.3 21.0
Days of the estrous cycle
Figure 1. Variations in progesterone in the three daily samples in one of the non-pregnant cycles.
Days of the estrous cycle
Figure 2. Variations in progesterone in the three daily samples in one of the pregnant cycles. Also when using a well validated assay for progesterone in the dog, with a high sensitivity, accuracy and precision, large fluctuations in progesterone over the day were discovered depending on a rhythmic secretion of this hormone. Further studies should be performed to determine whether a diurnal pattern of secretion of progesterone occurs in the dog. References: 1.Forsberg M, Linde-Forsberg C, Karlsson Å et al. Progesterone and oestradiol in canine plasma monitored by enhanced luminescence immunoassays. J Reprod Fert. Suppl. 47, 1993; 127-132. 2.Steinetz B, Goldsmith L, Syed H et al. Diurnal variation of serum progesterone, but not relaxin, prolactin, or estradiol-17β in the pregnant bitch. Endocrinology 1990; 127:1057-63. 3.Thuróczy J, Wölfling A, Tibold A et al. Effect of anticoagulants and sampling time on results of progesterone determination in canine blood samples. Reprod Dom Anim 2003;8:386-9.
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