ULTRASONOGRAPHIC ASSESSMENT OF POSTPARTUM UTERINE INVOLUTION AND ONSET OF OVARIAN ACTIVITY IN THE OSSIMI EWE

A .Ali¹, Anas A.Salem² and A. El-Din Zain¹

¹Dept. Theriogeology, Faculty of Vet.  Med., Assiut University

²Dept. Animal Production, Faculty of Agriculture, Assiut University

ABSTRACT

The postpartum fertility is based primarily on two main factors, the involution of the uterus and the resumption of ovarian activity. This study was planned to clarify the time of complete uterine involution using ultrasound examination and the onset and patterns of postpartum ovarian activity as detected by hormonal analysis in Ossimi ewes. A total of 13 maiden Ossimi ewes were synchronized to give birth in May. After parturition, the animals were examined once weekly using a 6/8 MHz transrectal transducer. Maximum diameter of the previous gravid horn was taken on a fixed screen. Complete uterine involution was considered when there was no further reduction in the uterine horn diameter for 3 successive examinations. Blood samples were obtained from each ewe once weekly for 3 months after parturition. The blood-serum was analyzed for the progesterone hormone. The onset of ovarian activity was considered by the first increase in the progesterone hormone (> 2 ng/ml) followed by normal cyclic activity. The obtained results indicated that, complete uterine involution occurred on an average of 16.27 ± 5.1 days (range 12-30 days) after parturition, while the ovarian activity started on an average of 43.91 ± 15.0 days (range 23-73 days) after parturition. Out of the examined animals, 7 ewes showed normal progesterone profile, 3 revealed a prolonged luteal activity, 2 did not show any ovarian activity during the examination period and one ewe entered in a cessation period after a normal luteal activity. It could be concluded that, uterine involution in Ossimi ewes was completed within two to three weeks after birth, while ovarian activity started about six weeks after parturition. It is important to check ewes for the start of ovarian activity 4-6 weeks postpartum so as to treat the cases with abnormal ovarian activity.

INTRODUCTION

Sheep can contribute to provide meat, milk and fiber for a growing world population (Shelton, 1995). One of the most important advantages of sheep lies in its rapid reproductive rate. Twice-yearly lambing or three lambing in two years is the ideal goal of sheep production (Gordon, 1997). To lamb twice a year, ewes need to conceive about one month after lambing. Ossimi ewes is one of the most common breed in Egypt. It show estrous activity throughout the year (Aboul-Naga et al., 1991). So, the aim of  twice-yearly lambing might be possible in this breed if the postpartum period is short.

The postpartum fertility  is based mainly on two factors, the involution of the uterus and the resumption of ovarian activity. For lambing more freguently than once a year, the postpartum interval to the resumption of sexual activity must be reasonably short so that the ewes could become pregnant again with a minimum of delay. To plan an effective lambing protocol, the time of complete postpartum uterine involution and the onset of ovarian activity must be known.

Real-time ultrasound evaluation of small ruminant offers an unparalleled range of information (Haibel, 1990). However, the ultrasonic characterization of the postpartum uterus in sheep is very scanty in the literature.

This work was planned to clarify the time of complete uterine involution and the onset and patterns of postpartum ovarian activity in Ossimi ewes using ultrasound examination and hormonal analysis.

MATERIAL AND METHODS

A total number of 13 maiden Ossimi ewes were used in the current work. Their age and weight at the beginning of the experiment ranged from 15-17 months and 33-35 kg, respectively. They were clinically free from any infectious, parasitic or genital diseases. The ewes were housed in the Agriculture Farm of Assiut University. The animals were kept in a shed attached with an open yard. Each animal was given daily 2 kg. concentrated ratio, in addition to a green food (Trifolium alexandrium) during the green season..

The ewes were synchronized with a double doses of Prostaglandin F₂a analogue (0.300 mg tiaprost^â , i.m.[1]). They were mated in the induced estrous with a fertile ram and examined for pregnancy one month later using a transrectal ultrasound technique (Pie Medica 100 LC, 6/8 MHz linear transducer). All ewes gave their birth in May after normal gestation period and normal parturition. They were allowed to nurse their lambs for two months, thereafter the lambs were weaned.

For estimating the time of complete uterine involution, the animals were examined ultrasonographically once weekly, starting one week after parturition until there was no further reduction in the uterine diameter for three successive examinations.  For ultrasonic examination, the ewe was restrained in a standing position with the help of an assistant. The rectum was evacuated from feces and air with the aid of the lubricated fingers of the operator. Thereafter, the transducer with some ultrasonic jell and one finger of the operator (the index) were introduced into the rectum. The transducer was moved with the index a little bit medially and laterally to get the best view of the examined uterus. Maximum diameter of the previous gravid horn was taken on fixed screen of the scanner (fig 1 and 2).

Resumption of the ovarian activity was considered by the first increase (> 2 ng/ml) in the serum progesterone followed by a normal cyclic activity (Campell et al., 1994). Therefore, blood samples were taken from all ewes once weekly for 3 successive months after parturition starting 7 days after birth. The samples were centrifuged at 3000 rpm for 10 minutes and the separated serum was kept at –20 ^oC till analyzed for progesterone. The progesterone hormone was estimated by ELISA-technique. The Kits were supplied by Biosource, Europe S. A., Belgium. The assay was carried following its produced instruction. Coefficient of variance of intra- and interassay were 10.7 and 12.5%, respectively.

The data were analyzed statistically using SPSS-program version 0.6. Differences in uterine horn diameters at the successive examinations were compared with paired t-test.

 1] Ilieren Hoechst Veterinar Gmbh, D-85716 Unterschleissheim b. Munchen.

RESULTS

All included ewes showed  normal gestation period of 149-150 days and they showed no disturbances during parturition or during the postpartum period.

The average postpartum uterine diameters, as estimated ultrasonography, at the different postpartum periods is shown in table1. The uterus completed its involution on an average of 16.27 ± 5.1 days (range 12-30 days) after birth. Reduction of the uterine diameter was more faster between the first and second weeks (1.49 ± 0.7 cm) than between the second and third weeks (0.49 ± 0.3 cm) and between the third and fourth weeks (0.46 ± 0.2) (p< 0.01).

Table 1: Postpartum uterine horn diameters as determined by ultrasound examination

Values with different superscript letters in the same column were significantly differ (a-b, a-c p<0.01, b-c p<0.05).

           The postpartum ovarian resumption, as indicated by the first increase in the serum progesterone hormone (> 2 ng/ml), occurred on an average of 43.91 ± 5.1 days (range 23-73 days) after birth. Distribution of the onset of ovarian resumption on the postpartum period is illustrated in table 2. Ovarian resumption was delayed up to the third week after birth. Large proportion of ewes (5/13) showed ovarian resumption between 5^th and 7^th weeks of parturition. Most of the ewes (10/13) showed the ovarian activity during the suckling period. Only one ewe showed this activity directly after removal of her lamb.

Table 2: Onset of ovarian activity at the different postpartum periods

Out of the examined ewes, 7 showed normal progesterone profile (fig. 3), 3 revealed a prolonged luteal activity (fig. 4), 2 did not show ovarian activity during the examination period (fig. 5), while one entered a cessation period after a normal luteal activity (fig. 6).

DISCUSSION

            The ability to achieve maximum reproductive efficiency in ewes depends upon understanding postpartum changes of uterus, ovaries and pituitary (Lewis and Blot, 1983).

The advantages of real-time ultrasonography are its sensitivity, accuracy, speed and safety. It provides a safe, non-invasive method for direct visualization of ovaries, uterus and conceptus. However, the authors could not locate literature illustrating ultrasonographically the postpartum changes in the uterus of ewes. Ultrasound examination provided not only  a precise dimensions of the postpartum uterus, but it gave also information about the nature of the uterine content.

The present work indicated that complete uterine involution occurred mostly between the 2^nd and 3^rd weeks of parturition (average 16 days). Van Niekerk (1976) recorded that uterine involution and regeneration of the epithelium in ewes may not be completed until the 26^th day in the breeding season, while during anestrous involution was delayed until the 30^th day in the dry sheep and the 63^rd day in the nursing ewes. Elsewhere, uterine involution has been estimated to be completed within 24 days (Call et al., 1976) or from 35 days for non-lactating to 60 days for lactating ewes (Honmode, 1977). Tian and Noakes (1991), using radio-opaque markers, recorded involution to be completed by about 29 days after lambing. Akinbami et al. (1992) assessed uterine involution in ewes between day 30 and 50 after lambing using vascular permeability and leukocyte concentrations as markers. They concluded that the low fertility and conception rates observed in sheep mated before day 50 after lambing was probably a consequence of incomplete uterine invoultion.

Difference between data of the present work and that of previous ones may be due to breed difference and that animals in the present study were purely primiparous ewes. In cattle, uterine involution was faster in primiparous than pluriparous cows (Ali, 1992). Indeed, the effect of parity, season, nutrition, lactation on uterine involution in ewes needs further investigation.

In the present work the mean interval from parturition to the resumption of the ovarian activity was about 44 days. In mature Marino ewes the interval from parturition to the first cycle was 59 in lactating and 45 in non-lactating (Bostedt et al., 1981). In Ossimi ewe onset of ovarian activity occurred 58 days postpartum (Hussein, 1996).

All the examined ewes showed a state of ovarian inactivity during the first three weeks after parturition, as indicated by the low serum progesterone level. This is identical to the reports of Shevah, et al.,(1975), Wright et al., (1980), Lewis and Blot, (1983) that stated that, the plasma progesterone level remained minimal (< 1 ng/ml) during the first three weeks after birth. The endocrine basis of postpartum ovarian inactivity is not fully understood. The immediate postpartum period in the ewe is characterized by a gradual recovery of ovarian activity, high prolactin level which gradually decreases after the first week (Lamming, et al., 1974) and a low tonic of LH level which increases slowly (Restall and Starr, 1977). Lack of ovarian activity was thought to be due to an alteration in the response of the hypothalamic-pituitary axis to the negative feedback effect of estrogen, similar to that shown by ovariectomized ewes during anestrus (Legan et al., 1977). The authors suggested that both seasonal anestrus and postpartum anestrus may involve suppression of tonic LH due to increased inhibition by estradiol. It is known that the percentage of ewes responding to estrogen injection with an LH surge increases with the time postpartum (Smart et al., 1994). Bartlewski, et al. (2000)  suggested that during the postpartum period in ewes, suppression of follicular growth was seen in all ovaries that had corpora lutea during pregnancy. Follicular growth to the ovulatory sizes initially resumed in ovaries that did not have corpora lutea and then ,around 4 weeks after parturition, in ovaries that had corpora lutea.

About half of the examined ewes (7/13) revealed a normal postpartum progesterone profile, while the other half showed abnormal forms including prolonged luteal activity, delayed onset of the ovarian activity and cessation of  cycle. The same forms of abnormal postpartum luteal activity were recorded in 35% of postpartum cows (Ali, 1992). Moreover, about 40% of ewes with induced estrous 21 days postpartum were found to exhibit abnormal luteal function (Wallace et al, 1989). Prolonged postpartum luteal activity might be the result of the high prolactin hormone observed in the first few weeks postpartum (Lamming, et al., 1974). There is evidence that both LH and prolactin contribute to the maintenance of the sheep corpus luteum. Delayed onset of the ovarian activity and cessation of cycle might be due to a negative energy or protein balance. Ewes nursing lambs were often in negative energy balance during the first month of lactation (Robinson et al., 1979).

It could be concluded that, complete uterine involution in primiparous Ossimi ewes occurred between the 2^nd and 3^rd weeks of parturition, while the ovarian activity started on an average of 6^th week after birth. The above observations about uterine involution and ovarian resumption would suggest that the time taken for the ovarian resumption may be long to permit a continuous six-month lambing interval on a flock basis, a more realistic minimum interval is probably about 7-8 month interval. 

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