Progesterone Concentration in the Peripheral Plasma of Galway and Finnish Landrace Sheepduring the Oestrous CycleAuthor(s): J. F. Quirke and J. GoslingSource: Irish Journal of Agricultural Research, Vol. 14, No. 1 (Apr., 1975), pp. 49-53Published by: TEAGASC-Agriculture and Food Development AuthorityStable URL: http://www.jstor.org/stable/25555754 .

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Ir. J. agric. Res. 14: 49-53, 1975

PROGESTERONE CONCENTRATION IN THE PERIPHERAL PLASMA OF GALWAY AND FINNISH LANDRACE SHEEP

DURING THE OESTROUS CYCLE

J. F. Quirke

An Foras Taluntais, Ballinrobe, Co. Mayo

J. Gosling

Biochemistry Department, University College, Galway

ABSTRACT

The progesterone concentration in the peripheral plasma of Galway and Finnish Landrace ewes

throughout the oestrous cycle was determined by radioimmunoassay. The progesterone concentration

during the luteal phase of the cycle was significantly greater in the Finnish Landrace than in the

Galway ewes. There was a sharp drop in the level of progesterone in both breeds before the onset of the next oestrous period. The Finnish Landrace ewes tended to come into oestrus more quickly than the Galway ewes when the progesterone level fell below 1.0 ng per ml.

INTRODUCTION

The changes which occur in the level of progesterone in the peripheral blood plasma of the ewe during the oestrous cycle have been documented in a number of studies

(1, 2, 3, 4, 5). The progesterone concentration in the peripheral plasma of ewes

throughout pregnancy has also been reported (5, 6, 7) and has been used to diagnose pregnancy with a very high degree of accuracy (8, 9, 10). The present paper reports on the changes in the plasma progesterone level during the oestrous cycle in Galway and Finnish Landrace sheep.

EXPERIMENTAL

Animals Four Galway and two Finnish Landrace ewes, aged 3 to 5 years, were used in the

study. A raddled vasectomised ram was run continuously with the ewes to detect

49

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50 IRISH JOURNAL OF AGRICULTURAL RESEARCH, VOL. 14, NO. 1, 1974

oestrus. The ewes were checked daily for raddle marks at 9.00 hours. All animals were housed and fed a pelleted diet, which consisted of barley and grassmeal in equal pro

portions, ad libitum. One normal oestrous cycle was observed before the start of the

experiment.

Blood collection Blood samples were collected daily from the 6 ewes over two cycles. Sampling

commenced in the period November 20 to 26, 1973, and all samples were taken be tween 9.00 and 10.30 hours each day. The first sample was taken as soon as the ewe

was observed to be in oestrus following the daily check for oestrus (day 0). Blood was taken from a jugular vein and collected into 10-ml vacutainers containing EDTA

(Becton, Dickinson). Immediately after collection the blood was centrifuged for 20 minutes at 3000 rpm and the resulting plasma was aspirated off and stored at ? 20?C until assay.

Estimation of progesterone Plasma progesterone was estimated by means of a conventional radioimmunoassay.

Plasma samples (0.5 ml) were extracted with 5.0 ml petroleum spirit, 40? to 60?C

boiling range. The assay buffer was 0.1 % (w/v) gelatin in 0.14 m NaCl, 0.1 % NaN3, 0.01 m NaP04

? NaOH, pH 7.0. The assay volume was 0.2 ml and contained 1/8000

sheep antiserum to progesterone-11-hemisuccinate-bovine serum albumin (kindly sup

plied by Dr. Brian Cook, Department of Steroid Biochemistry, Royal Infirmary, Glasgow) and tritiated progesterone (93,000 dpm, 160 pg). A charcoal separation pro cedure was used to prepare the bound fraction. During the trial repeated assay of

pooled bovine plasma containing about 4 ng progesterone per ml gave a coefficient of variation of less than 10%.

RESULTS AND DISCUSSION

Oestrous cycle lengths ranged from 17 to 20 days (mean 17.8 days) in Galway ewes

and from 15 to 18 days (mean 17.0 days) in Finnish Landrace ewes. We have chosen to refer the daily plasma progesterone levels for each ewe throughout the cycle to the number of days before and after the first day of oestrus (day 0). The daily plasma progesterone levels (means and standard errors) for eight oestrous cycles from four

Galway ewes and for four oestrous cycles from the two Finnish Landrace ewes are

shown in Figs. 1 and 2 respectively. In the Galway ewes the concentration of progesterone in the peripheral plasma

was very low at oestrus (mean values ?se for days 0 and 1 were 0.22?0.05 and 0.15? 0.04 respectively). The level rose slowly through the 3rd and 4th days, after which the rate of increase was accelerated until a plateau was reached which persisted from the

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QUIRKE AND GOSLING: PROGESTERONE CONCENTRATION 51

2'51

_2?- '- 'It

?? LTT H []

r?- it ]

I0.5. I J

0"T ' f" I ' I I I I I I I I 'I ' . 6 -4 -2 0 2 4 6 8 10 12 14 16

N'888888897778866788888888 Day of oestrous cycle

Fig. 1: Peripheral plasma progesterone concentrations (ng per ml) in Galway ewes

throughout eight oestrous cycles; the vertical lines represent the standard errors

of the means; the number of observations (N) are shown beneath each day of the cycle

40

1 3-0- I 1 Illr r'T I [ j I I1

"R t

i1 .0- T x1 a.

I

A ^ml_ 0* i i1 i r i pi * i i "i -6-4 -2 0 2 4 6 8 1012 14

N> i i i i i i i i > i i r i t't i i i i i r i

4 4 3444 3 5 44 24 4 44 24 344 44

Day of oestrous cycle

Fig. 2: Peripheral plasma progesterone concentrations (ng per ml) in Finnish Landrace ewes throughout four oestrous cycles; the vertical lines represent the standard

errors of the means; the number of observations (N) are shown beneath each day of the cycle

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52 IRISH JOURNAL OF AGRICULTURAL RESEARCH, VOL. 14, NO. 1, 1974

9th to the 13th day of the cycle. The rate of the subsequent decline was greatest between the 3rd and 2nd days before the onset of oestrus.

In the Finnish Landrace ewes the levels of progesterone around the time of oestrus

tended to be slightly lower (p<0.20) than those observed in the Galway ewes (mean values ?se for days 0 and 1 were 0.11 ?0.04 and 0.11 ?0.04 respectively). The proges terone concentration rose sharply between the 4th and 7th days of the cycle, slowed in its rate of increase for 2 days and then rose again to a plateau which persisted from the 10th to the 13th day. The fall in the plasma progesterone level before the onset of oestrus was precipitous and oestrus was exhibited as soon as the level was low, which

was in marked contrast to the situation in the Galway ewes. The time interval between the drop in progesterone concentration to below 1.0 ng per ml and the onset of oestrus

was greater in the Galway (3.1 ? 1.1 days) than in the Finnish Landrace ewes (1.2? 1.0

days) and this difference was statistically significant (p<0.05).

TABLE 1: Mean plasma progesterone concentrations (ng per ml) in Galway and Finnish Landrace ewes in the luteal phase of the oestrous cycle3

Galway Finnish Landrace

Days post oestrus - Significance of

(inclusive) Mean?SE Mean?SE breed difference

10 to 12 1.99?0.15 2.84?0.27 p<0.05 (24)b (11)

9 to 13 1.94?0.11 2.61?0.20 p<0.05 (40) (19)

8 to 14 1.79?0.10 2.53?0.17 p<0.01 (55) (25)

a Because the luteal phase cannot be precisely denned the mean progesterone level was calculated for three increasing time intervals b Figures in parentheses represent the number of progesterone determinations comprising the mean

Progesterone levels during the oestrous cycle have not previously been reported in

the literature for either Finnish Landrace or Galway sheep. The levels observed

throughout the cycle in the Galway ewes agree with reports in the literature for a

number of breeds and crosses (1, 2, 3). The levels of progesterone recorded in the

luteal phase of the cycle in the present work were significantly higher in the Finnish

Landrace than in the Galway ewes (Table 1). This is undoubtedly a reflection of the

higher ovulation rate of the Finnish Landrace breed. The ewes which were used in the

present work were drawn from the same flocks in which Hanrahan and Quirke (11) recorded natural ovulation rates of 1.57 and 3.85 for the Galway and Finnish Land race breeds respectively. The breed differences observed in the interval between the

drop in plasma progesterone concentration and the onset of oestrus in the present work are consistent with the results of Hanrahan and Quirke (11), who have reported

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QUIRKE AND GOSLING: PROGESTERONE CONCENTRATION 53

that the time interval between the removal of progestagen-impregnated pessaries and the onset of oestrus is significantly shorter in Finn than in Galway ewes.

ACKNOWLEDGMENTS

The authors are indebted to Messrs. W. Parker, K. Brooks, and W. Loughnane for

skilled technical assistance. One of us (J.G.) acknowledges the receipt of a fellowship from An Foras Taluntais. This work was supported by a grant in-aid from An Foras Taluntais to the Biochemistry Department, U.C.G. We also wish to thank Professor P. F. Fottrell for his interest and advice.

REFERENCES

1. Thorburn, G. D., Bassett, J. M. and Smith, I. D., /. Endocr. 45: 459, 1969. 2. Stabenfeldt, G. H., Holt, J. A. and Ewing, L. L., Endocrinology 85: 11, 1969. 3. Allison, A. J. and McNatty, K. P., N.Z. Jl agric. Res. 15: 825, 1972. 4. McNatty, K. P., Revfeim, K. J. A. and Young, A., /. Endocr. 58: 219, 1973. 5. Sarda, I. R., Robertson, H. A. and Smeaton, I. C, Can. J. Anim. Sci. 53: 25, 1973. 6. Bassett, J. M., Oxborrow, I. J., Smith, I. D. and Thorburn, G. D., J. Endocr. 45: 449, 1969. 7. McNatty, K. P., Allison, A. J. and Thurley, D. C, N.Z. Jl agric. Res. 15: 831, 1972. 8. Robertson, H. A. and Sarda, I. R, /. Endocr. 49: 407, 1971. 9. Gadsby, J. E., Heap, R. B., Powell, D. G. and Walters, D. E., Vet. Rec. 90: 339,1972.

10. Shemesh, M., Ayalon, N. and Lindner, R. H., /. Anim. Sci. 36: 726, 1973. 11. Hanrahan, J. P. and Quirke, J. F., /. Reprod. Fert. (in press).

Received November 22,1974

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