Attenuation of PGF2alpha release in ewes infused with the oxytocin antagonist L-368,899

We have investigated the effects of systemic administration of the oxytocin antagonist (OTA) L-368,899 on luteolytic PGF(2alpha) release in ewes. In the first study, carried out in four ovariectomized ewes primed with progesterone to induce responsiveness to oxytocin, 3-h i.v. infusions of 3, 10 and 30 microg/kg/min OTA, carried out on days 12, 14, 16 and 18 in a Latin Square design, resulted in a significant attenuation of the oxytocin induced increase in PGFM concentration at all doses (OTA 139+/-8.3% of pre-oxytocin baseline; control 206.8+/-18.7%; P<0.005). In a further study, continuous infusion of cyclic ewes (n=6) with 10 microg/kg/min OTA from day 13 to day 17 of the cycle resulted in a reduction in both the frequency (OTA 1.0+/-0.4/ewe; control 2.2+/-0.2/ewe; P<0.05) and amplitude (OTA 31.8+/-11.0 pg/ml; control 68.8+/-10.4 pg/ml; P<0.05) of endogenous PGFM episodes compared to control ewes (n=5) measured during daily 8-h sampling windows on days 14-17. This reduction in PGFM concentrations was accompanied by a modest extension in the day of luteolysis (progesterone <0.5 ng/ml) to day 17.5+/-0.4 in the OTA treated group compared with day 16.4+/-0.5 in the control group (P=0.07). The results demonstrate that treatment with OTA caused a significant reduction in episodes of increased PGFM concentration during the period of luteolysis and may provide an approach by which to reduce early pregnancy failure.     

Repetitive abortion in Neospora-infected ewes.

Pregnant ewes inoculated with cultured Neospora caninum tachyzoites in 1995, 1996, or 1995 and 1996 aborted or delivered weak or clinically normal lambs in 1996. Nine of 11 ewes in the study had previously produced infected lambs or fetuses after being experimentally infected in 1995. Fetuses and lambs produced in 1996 showed histologic lesions and zoites indicative of Neospora. Serologic responses and production of infected fetuses/lambs indicated systemic neosporosis in the ewes during gestation, although tachyzoites could not be cultured from maternal tissues. The repetitive infection of fetuses, and resulting clinical and histopathologic findings in the present study are similar to those reported in naturally infected cattle, adding to the already established similarities of neosporosis between sheep and cattle.     

Elimination of tilmicosin in lactating ewes.

Tilmicosin was injected subcutaneously to lactating ewes once at a dose of 10 mg kg-1 b.wt. to determine its plasma, milk, urine and ruminal juice concentrations. Tilmicosin could be detected in all those fluids 30 minutes after injection. Milk and urine concentrations were higher than those of plasma and ruminal juice. The drug was detectable in milk, urine and plasma for 9, 4 and 3 days after injection, respectively. No amount of tilmicosin could be detected in ruminal juice 12 hours following administration. The mean peak concentration of tilmicosin in plasma and milk (Cmax) were 1.29 and 9.5 micrograms ml-1 and were obtained at (Tmax) 5.235 and 15.093 hours, respectively. The drug was slowly eliminated from plasma and milk as indicated by its long half-life (t1/2el) of 15.4 and 26.2 hours, respectively. The mean binding of tilmicosin to plasma and milk proteins in vitro was 16.8% and 26.8%, respectively. The drug was not bound to ruminal juice at any extent. The rate of tilmicosin renal clearance revealed that it was correspondingly increased with higher blood concentrations. While creatinine clearance showed no significant change after tilmicosin administration. The ratio (fractional clearance) between tilmicosin renal clearance to creatinine clearance was less than one indicating that the glomerular filtration is the main pathway of elimination through kidneys. The rate of ruminal gas fermentation in ewes was inhibited after subcutaneous injection of tilmicosin at a dose of 10 mg kg-1 b.wt. The tested samples taken at different time intervals from the rumen of ewes showed a subsequent reduction in the rate of fermentation as compared to control samples. The reduction was correspondingly increased with the increase of tilmicosin concentration in ruminal juice and returned to normal thereafter.     

PGFM response to exogenous oxytocin and determination of the half-life of oxytocin in nonpregnant mares.

We investigated the half-life of oxytocin in reproductively normal mares and the prostaglandin response after oxytocin administrations. Mares were given oxytocin, 10 or 25 iu, i.v., on the day of, or 2 days after, ovulation, and frequent jugular blood samples were collected for analysis of oxytocin and Prostaglandin F metabolite (PGFM) by RIA. Neither dose of oxytocin nor day of treatment affected the half-life of the exogenous oxytocin, which was determined to be 6.8 min. A significant increase in PGFM was observed within 6 min of oxytocin administration and peak values were observed within 10 min. PGFM response after oxytocin administration on the day of ovulation appeared elevated compared to the response 2 days after ovulation.     

Measurement of histological changes in the cervix of ewes after prolonged exposure to oestrogenic clover or oestradiol-17β

Morphometric methods were used to measure abnormalities in histological architecture of the endocervix in ewes with infertility after prolonged exposure to oestrogenic clover pastures. Similar measurements were made on the cervix of ewes exposed to oestradiol-17 beta for 6 months. In both cases the changes in histological appearance were essentially similar, and were most easily measured by counting the number of cervical crypts. Ewes treated with either phyto-oestrogens or oestradiol also had significantly wider cervical folds, greater areas of lamina propria, and more cervical glands. The results provide a basis for measuring the severity of permanent oestrogenic change in different flocks or after different experimental treatments.     

Experimental Brucella ovis infection in pregnant ewes.

Forty yearling Brucella-free ewes were inoculated with Brucella ovis by the conjunctival route in mid or late first pregnancy. Only a few ewes excreted B ovis during pregnancy and gave birth to stillborn lambs, but most of them excreted the organism at lambing or during lactation. One of the 11 lambs which were born alive but died before they were weaned was found to be infected postmortem. In contrast, none of the 46 surviving lambs which were reared in isolation until adulthood, was found to be infected. At weaning, the 40 ewes were mated again with five Brucella-free rams. Although many of the ewes excreted B ovis, none of the rams was found to be infected when necropsied after mating. Most of the ewes that became pregnant, all having excreted B ovis during their first pregnancy, cleared the infection during the second pregnancy. However, three remained persistently infected and excreted B ovis in their milk throughout the second lactation. None of the lambs born to these three ewes was found to be infected when necropsied at weaning.     

Actions of oxytocin and a long-acting carba oxytocin analog on the porcine myometrium in vitro and in vivo.

The contractile actions of oxytocin and its analog 1-desamino-1-monocarba-[2-Tyr(OMe)]-oxytocin were compared on in vitro (experiment 1) and in vivo (experiment 2) preparations of porcine uterine horns. In both experiments, sows in estrus were selected for maximal sensitivity. Despite the loss of peak amplitude associated with the substitution at sequence position 2 of O-methyltyrosine for tyrosine, the two remaining alterations (N-terminal desamination and replacement of the 1-6 S-S bridge by CH2S) prolonged the action of single-dose presentations. Thus, instead of having a response lasting minutes when the parent hormone is given, an IV dose of about 5 micrograms of the analog/kg of body weight in the intact anesthetized sow resulted in a response lasting two hours.     

Combined treatment with oestradiol benzoate,d‐cloprostenol and oxytocin permits cervical dilation and nonsurgical embryo recovery in ewes

This study examined the feasibility of transcervical embryo recovery after the hormonal treatment to induce cervical dilation, following the 7‐day oestrous synchronization protocol in multiparous Santa Inês ewes. A total of 23 cyclic ewes received two doses of 37.5 μg of d‐cloprostenol by latero‐vulvar route 7 days apart. After the second injection of d‐cloprostenol, the ewes were checked for oestrus (every 12 hr) and then mated by fertile rams throughout the oestrous period. All ewes received 37.5 μg of d‐cloprostenol (latero‐vulvar) and 1 mg of oestradiol benzoate by either intramuscular (EBim group; n = 12) or intravaginal (EBivg group; n = 11) route 16 hr before embryo flushing. Twenty minutes before the flushing, 50 IU of oxytocin were administered intravenously. The oestrous response (i.e., the percentage of ewes that showed signs of oestrous behaviour after the second d‐cloprostenol injection) was 91.3% (21/23). The proportion of successfully penetrated ewes (81.8% compared with 80.0%), the mean duration of embryo flushing (24.7 ± 2.0 min compared 26.2 ± 1.9 min), the flushing fluid recovery rate (94.8 ± 1.3% compared with 91.0 ± 2.9%) and the average number of structures recovered per ewe (0.5 ± 0.4 compared with 0.8 ± 0.4) did not vary (p > 0.05) between the EBim and EBivg groups. Viable embryos were recovered from 41.2% (7/17) of successfully penetrated ewes. It can be concluded that nonsurgical (i.e., transcervical) embryo collection can be performed in oestrous‐synchronized Santa Inês ewes pretreated with d‐cloprostenol, oxytocin and oestradiol benzoate, with the latter hormone administered by either the intramuscular or intravaginal route.     

Observations on the genital tract of cull ewes.

Genital tracts were collected from non-pregnant cull ewes in early April and examined for macroscopic abnormalities. An assessment was made of the possible effect of any abnormality on the ability of the animal to become pregnant. It was found that 23.2 per cent of the tracts had abnormalities and it was considered that 16.8 per cent had abnormalities likely to interfere with the establishment of pregnancy.     

Abattoir survey of acquired reproductive abnormalities in ewes.

Abnormalities of the reproductive tract of female sheep were studied by examining 9970 reproductive tracts from cull ewes and 23,536 tracts from nulliparous sheep (prime lambs) over a period of 12 months in abattoirs in south-west England. Overall, 3.37 per cent of the tracts were pregnant (8.11 per cent of cull ewes, and 1.36 per cent of nulliparous sheep), with a peak incidence between September and December. A total of 655 ewes (6.57 per cent) and 459 nulliparous sheep (1.95 per cent) had acquired abnormalities of the reproductive tract. Within these totals, abnormalities of the ovaries accounted for 3.51 per cent (for the ewes) and 10.68 per cent (for the nulliparous sheep) of all the abnormalities, and abnormalities of the ovarian bursa and uterine tube accounted for 42.1 per cent (for the ewes) and 5.23 per cent (for the nulliparous sheep). In addition, uterine lesions (hydrometra and metritis) accounted for 9.92 per cent (for the ewes) and 13.51 per cent (for the nulliparous sheep); lesions of the cervix and vagina (total of 1.44 per cent) and Cysticercus tenuicollis cysts associated with the reproductive tract (total of 3.05 per cent) were less common. Among the ewes the most common ovarian lesions were ovulation tags, and follicular cysts were the most common in nulliparous animals. Lesions such as bursitis, parametritis and abscesses of the reproductive tract were much more common in cull ewes than in nulliparous sheep, probably having arisen from peripartum infections. Hydrosalpinx and hydrometra, in which the intraluminal fluid was clear, were present at relatively high incidence in nulliparous animals, but not in cull ewes. The proportion of tracts containing macerated fetal remnants (2.14 per cent of all abnormalities in cull ewes) was lower than expected. It was considered that the functional significance of many of the lesions, such as ovulation tags and C tenuicollis cysts, was likely to be low, although in some cases of the latter calcification of the cyst had occluded the uterine tubes. Other lesions, notably hydrosalpinx, bursitis and metritis were likely to have made the affected animals sterile. The acquired abnormalities were therefore more significant in terms of individual animal infertility than as a major cause of infertility in flocks.     

Concentration of manganese in the tissues of cycling and anestrous ewes.

A wide range of variation in concentration of manganese was found in the blood of 51 cycling ewes although no significant differences were evident (P less than 0.05) between days 4, 11 and 15 (day 0 = day of estrus) of the estrous cycle. In addition, no differences (P less than 0.05) were found in the manganese concentrations of various soft tissues of 15 ewes, killed on day 4 (five animals), day 11 (five animals) or during anestrus (five animals). The highest concentration of manganese was present in the liver, pancreas and kidney cortex, tissues which are rich in mitochondria. Among the tissues of the reproductive tract, the corpus luteum showed the highest manganese concentration and the level increased significantly (P less than 0.01) between days 4 and 11 suggesting that this trace element may be closely related to the metabolic and possible functional characteristics of this endocrine gland. Uterine horn and caruncles contained greater manganese concentrations than other components of the reproductive tract. The significance of these findings in relation to the effect of manganese intake on ewe fertility remains to be assessed.     

Real-time ultrasonography for determining the gestational age of ewes.

Seven Swedish peltsheep ewes were examined weekly by transabdominal ultrasound scanning from one-and-a-half to two months of gestation until parturition. By means of a simple regression analysis, the heart rate, the biparietal diameter of the skull and the diameter of the body trunk were correlated with fetal age, and it was concluded that these measurements could be used to estimate the age of the fetus.     

Hard udders in ewes

Extract

Sir,—D. P. Sinclair, Superintendent, Manutuke Research Station, has drawn my attention to a condition of ewes' udders which may cause many of the lamb deaths due to starvation or exposure which are noted in perinatal Iamb death surveys in New Zealand.