SmallRuminant Research, 8 (1992) 47-53 47 Elsevier Science Publishers B.V., Amsterdam

Progesterone concentrations in peripheral plasma of Menz sheep during gestation and parturition

E. MukasaoMugerwa and P. Viviani Animal Reproduction and Health Section, International Livestock Centre for Africa (ILCA), Addis

Ababa, Ethiopia

(Accepted 26 September 1991 )

ABSTRACT

Mukasa-Mugerwa, E. and Viviani, P., 1992. Progesterone concentrations in peripheral plasma of Menz sheep during gestation and parturition. Small Rumin. Res., 8: 47-53.

Progesterone concentrations were monitored weekly during gestation, averaging 151 + 2 d, in pe- ripheral plasma of Menz ewes using enzyme immunoassay. Mean hormone concentrations were basal, ~< 1.0 ng/ml at service, but increased to 4.7 ng/ml on d 14 and remained elevated throughout preg- nancy, differing significantly between ewes and stage of gestation (P< 0.01 ), but not due to number or sex of foetuses (P> 0.10). Progesterone production was also lowly related to weight of lambs at birth (r = 0.24). Progesterone level increased to 8.4 + 0.3 ng/ml by d 35 (first trimester), 13.2 + 0.4 ng/ml by d 75 (second trimester) and 13.8 + 1.0 ng/ml by d 126 (third trimester). This was followed by a gradual decline during the last three weeks which accelerated 3 d prepartum to reach below 1.0 ng/ml 2 to 4 d after lambing. It was concluded that elevated progesterone levels 18 to 22 d after mating indicate continued luteal function and/or pregnancy in Menz sheep.

INTRODUCTION

Changes in blood or milk progesterone have been used to monitor ovarian function and pregnancy in cows (Heap et al., 1973; Mukasa-Mugerwa et al., 1989), sheep (Gadsby et al., 1972; Shemesh et al., 1973; Tyrrell et al., 1980; Yenikoye et al., 1982) and goats (Thorburn and Schneider, 1972; Mavro- genis, 1988). Progesterone concentration may be affected by season, nutri- tion, breed and ovulation rate (Cahill et al., 1981; Rhind et al., 1985 ). More- over, embryonic losses in sheep may result from low peripheral progesterone concentration (Cumming et al., 1971 ).

The endocrinology of reproductive cycles in African sheep is not widely reported (Yenikoye et al., 1981, 1982; Lahlou-Kassi and Boukhliq, 1989), especially in the tropics (Mukasa-Mugerwa et al., 1990). This study aimed to

Correspondence to." E. Mukasa-Mugerwa, Animal Reproduction and Health Section, ILCA, P.O. Box 5689, Addis Ababa, Ethiopia.

0921-4488/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.

48 E. MUKASA-MUGERWA AND P. VIVIANI

characterize progesterone profiles of Menz ewes during gestation with intent to gain insight into applied clinical endocrinology in early pregnancy diagno- sis and monitoring of prenatal reproductive wastage.

MATERIALS AND METHODS

Ten Menz ewes aged 3-4 yr, averaging 30.7 +_ 4.7 kg BW and ranging from 3 to 4 in body condition (Russell et al., 1969) were used. The study was lo- cated at the ILCA Debre Berhan research station, 120 km north of Addis Ababa and at 2850 m altitude. Area climatic data have been described (Mu- kasa-Mugerwa et al., 1990). Animals grazed during the day from natural pas- tures dominated by Andropogon, Festuca and Penisetum spp..grasses and Tri- folium semense legumes. They were penned overnight and fed 250 g natural grass hay per head per day. The nutritional composition of pastures and hay are given in Table 1. Animals were watered daily and mineral licks were avail- able in the pens. In April 1988, ewes were run with harnessed vasectomised rams to detect oestrus (Day 0). Jugular blood samples ( 10 ml) were taken daily between 0900 and 1100 a.m. over an entire oestrous cycle. Heparinised plasma was recovered by centrifugation at 2500 rpm within 15 minutes and stored frozen until assayed for progesterone. Progesterone concentration was determined by enzyme-linked immunosorbent assay (ELISA) using com- mercial kits from Cambridge Veterinary Sciences (UK). Procedural details of the method were given in Mukasa-Mugerwa et al. (1989). The intra-assay

TABLE1

Chemical composition (DM basis) of pastures and hay

Pasture Hay

Dry season ~ Wet season 2

Dry matter (%) 93.2 91.9 94.3 Ash 6.7 10.1 9.4 NDF (%) 76.6 64.1 71.3 ADF (%) 42.3 34.1 40.9 Lignin 6.6 3. l 6.9 In-vitro digestibility 56.2 72.1 57.4 Calcium (%) 0.3 0.6 0.6 Phosphorus (%) 0.2 0.3 0.2 Nitrogen 0.9 1.8 0.7 Crude protein (%) 5.8 11.6 4.6 Digestible protein, g/kg 3.3 8.4 2.6 ME, Mcal/kg 1.0 0.9 1.3

June-Sept and February-May. 2October-January.

PROGESTERONE CONCENTRATIONS IN PERIPHERAL PLASMA 49

and inter-assay coefficients of variation were 0.18 and 0.27, respectively at 8 ng/ml.

During June and July ewes were mated to fertile rams, and blood plasma was collected weekly throughout pregnancy. Samples were taken daily during the last week of gestation and first week post partum. Lambing was predicted from a gestation of 147 to 153 d. Litter size, lamb birth weight and sex were recorded at birth. Data were analysed by least squares procedures (SPSS, 1988).

RESULTS

Seven ewes conceived at first service but two returned to oestrus after 18 and 27 d. The tenth was a repeat breeder displaying erratic oestrous behav- iour and progesterone values continuously less than 2.5 ng/ml. It failed to conceive despite 13 matings. Remaining ewes lambed after 151 _+ 2 d produc- ing 12 lambs (mean litter size= 1.3 ).

Ewes exhibited congruent progesterone patterns up to d 14 of the pregnant and non-pregnant cycle. Up to that stage absolute values were higher in preg- nant animals and, after conception, progesterone concentration tended to be higher in ewes with twins. Differences were however non-significant (P > 0.10 ) and data were pooled to generate the composite graph in Fig. 1.

Progesterone levels were basal, -<< 1.0 ng/ml, from d 2 before oestrus to d 4 after oestrus, but rose to peak levels of 4.7 ng/ml by d 14 post oestrus. This was followed by a rapid decline to less than 1.0 ng/ml by d 17, prior to the

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Fig. 1. Mean ( _+ SEM) plasma progesterone concentrations during pregnancy in Menz ewes.

50 E. MUKASA-MUGERWA AND P. VIV1ANI

next oestrus following unsuccessful mating. In contrast, progesterone values remained above 4 ng/ml after d 14 in pregnant animals with three phases. First, a steady increase to 8.3 _ 0.3 (mean _ s.e.m.) ng/ml or 78% of the d 14 luteal phase value (Mukasa-Mugerwa et al., 1990) was observed by d 35 (wk. 5, first trimester). Second, there was a slow rise to 13.2_ 0.4 ng/ml by d 75 (wk. 11, second trimester) which was maintained during the last trimester; 13.8+ 1.0 ng/ml at d 126, 3 times the luteal phase maximum at d 14. Lastly, there was a gradual decline during the last three weeks of pregnancy. The rate of decline accelerated during the last 2 to 3 d of pregnancy when mean con- centration dropped to between 75 and 47% of the 11.8 +_ 0.7 ng/ml observed 7 d before lambing. Progesterone concentration averaged 3.3 ng/ml at par- turition and was less than 1.0 ng/ml on d 4 post partum when sampling stopped.

Mean weekly progesterone values varied significantly (P< 0.01 ) between ewes but not due to number of foetuses or their sex (P> 0.10). Further, though ewes with twins tended to produce more progesterone, the relationship be- tween estimated progesterone production and final lamb birth weight was low (r=0.24).

DISCUSSION

Patterns of plasma progesterone concentration were similar to those re- ported for temperate sheep (Bassett et al., 1969; Bassett and Thorburn, 1973 ). Failure of progesterone to decline 14 to 17 d after conception agreed with Thorburn and Schneider( 1972 ); Shemesh et al. ( 1973, 1979) and Tyrrell et al. (1980), and indicated, that early pregnancy diagnosis can be undertaken in Menz sheep by monitoring progesterone 18 to 22 d after mating (Bassett et al., 1969; Shemesh et al., 1973, 1979). Plasma progesterone levels closely paralleled concentrations in milk or butterfat (Montigny et al., 1982), both of which can be used in milked sheep to reduce costs for field fertility man- agement purposes.

The relationship between circulatory progesterone and early pregnancy, lit- ter size, lamb sex or level of nutrition in sheep is not consistently reported. Corpus luteum is the major source of progesterone soon after conception. The tendency for higher progesterone in pregnant vs. non-pregnant ewes during the first 14 days agreed with Rhind et al. ( 1984, 1985 ) but was in contrast to Bassett and Thorburn (1973). Further, the trend towards higher progester- one in ewes with twins was consistent with Robertson and Sarda ( 1971 ), but its non-significant nature suggested that secretion may not be proportional to number of foetuses (Quirke et al., 1979). This, in addition to the limited relationship between total progesterone production and lamb birth weight, was interpreted to indicate that a threshold level of the hormone probably exists above which pregnancy is maintained irrespective of litter size or weight

PROGESTERONE CONCENTRATIONS IN PERIPHERAL PLASMA 51

of foetuses. Agarwal et al. ( 1988 ) suggested that the metabolic utilisation of progesterone in multiple pregnancies might just be faster. On the other hand, Bassett et al. (1969) found mean progesterone levels during the last 50 d to be twice as high in ewes with twins. Gadsby et al. (1972) predicted the num- ber of foetuses based on progesterone concentration with 69% accuracy even though from highly divergent litter sizes (0, 1-2, 3-4 ). Moreover, Bassett and Thorburn (1973) also reported a strong relationship between progesterone production and lamb birth weight.

The continuing rise in progesterone with advancing gestation confirmed the extraovarian source (placental synthesis) of the hormone also for tropical sheep. The extra amount appears to be additive and enough to maintain preg- nancy without that of luteal origin (Riera, 1984). We observed that gesta- tional progesterone values were already higher than peak luteal phase values by 40 d post conception. This suggests that the extraovarian source may al- ready be functional at that time, earlier than d 50 to 80 proposed by Bassett and Thorburn ( 1973 ). In contrast, among goats luteal function is maintained throughout gestation and interference with corpus luteum function through luteolysis, ovariectomy and hypophysectomy terminates pregnancy (Thor- burn and Schneider, 1972; Heap and Flint, 1984). Lastly, the gradual rather than abrupt decline in progesterone near lambing was in accordance with Thorburn et al. (1972) and Bassett and Thorburn (1973). It appears to occur because of cortisol and prostaglandin effects on the placenta.

In summary, these data show that elevated plasma progesterone 18 to 22 d after mating ( >/2 ng/ml using ELISA) is indicative of sustained corpus lu- teum function or early pregnancy in Menz sheep. This nevertheless requires knowledge of service dates. False positives may arise from irregularly cycling ewes, embryo or foetal losses and unobserved abortion. Thimonier et al. (1977) observed for example, that only 84% of ewes diagnosed pregnant at the early stage lambed subsequently. Such information along with the preva- lence of possible causes, is lacking in tropical sheep. Yet it will be vital in formulating cost-effective packages to improve the reproductive performance and overall production efficiency of regional sheep.

ACKNOWLEDGEMENTS

The authors are thankful to Mr. Tekeste Tibebu for animal management, Mr. Girma Abebe for laboratory technical analyses and Mr. Solomon Zewde for computer data analyses.

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52 E. MUKASA-MUGERWA AND P. VIVIANI

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