Immunization of sheep against GnRH early in life: effects on reproductive function and hormones in ewes.

Groups of Merino ewe lambs were immunized against GnRH either soon after birth (prepubertal) or around puberty (peripubertal) with a prototype commercial preparation and were studied over the following 2 years to determine the long-term effects on reproductive development, function and hormone concentrations. At least 60% of the GnRH-immunized ewes in either treatment group did not experience oestrus and possessed small uteri and small ovaries that lacked follicular development. Growth rates of immunized and control ewes were similar throughout the study. Compared with the increase in plasma LH and FSH concentrations with age in control ewes, the concentrations of these hormones in immunized animals were lower and remained relatively constant from 46 to 90 weeks of age. Plasma FSH concentrations were particularly suppressed in immunized ewes and were significantly (P < 0.05) lower than the control values of 61 and 90 weeks of age. LH release after injection of 1 microgram GnRH at 90 weeks of age was either absent or suppressed in immunized ewes compared with controls. The findings suggest that the lack of GnRH stimulation and consequent deprivation of gonadotrophins, early in the life of ewes, may result in some degree of permanent impairment of hypothalamic and/or pituitary function.

Immunization of sheep against GnRH early in life: effects on reproductive function and hormones in rams.

Groups of Merino ram lambs were immunized against GnRH either soon after birth (prepubertal) or around puberty (peripubertal) with a prototype commercial preparation and studied over the following 2 years to determine the long-term effects of such immunization on reproductive development, function and hormone concentrations. The treatment was equally effective in suppressing reproductive function and hormones when given at either time. Growth rates of immunized and controls rams were similar throughout the study. Prepubertal immunization delayed testicular growth until the rams were at least 27 weeks of age and some rams had subnormally sized testes even at 115 weeks of age. After peripubertal immunization, the mass of the testes declined and remained regressed until the rams were from 51 to 90 weeks old. There was a significant correlation between total testicular mass at 115 weeks of age and duration (weeks) of suppression of testicular growth (prepubertal, r = -0.7375; peripubertal, r = -0.7132, P < 0.001). Prepubertal immunization markedly delayed separation of the penis from the prepuce. The immunized rams did not display sexual activity until their total testicular mass reached at least 70 g. In control and immunized rams with testicular mass > 100 g, the semen did not differ in the percentage of spermatozoa that were unstained (live), of normal morphology, or showed progressive movement. Compared with the increase in plasma LH and FSH concentrations with age in control rams, the concentrations of these hormones in the immunized animals were lower and remained relatively constant from 46 to 90 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Vaxstrate: an anti-reproductive vaccine for cattle.

This paper describes the development of a vaccine for the prevention of pregnancy in female cattle. The vaccine is based on the established principle that antibodies to the hypothalamic releasing hormone, gonadotrophin releasing hormone (GnRH) block the action of GnRH on pituitary secretion of luteinizing hormone and follicle stimulating hormone, leading to gonadal atrophy in mammals. The vaccine comprises an immunogenic GnRH:ovalbumin conjugate formulated in a novel double adjuvant system and is administered in a two-dose treatment regimen. Field trials have confirmed efficacy and the product, Vaxstrate, has now been registered and commercialized.

Effect of mouse epidermal growth factor on plasma concentrations of LH, FSH and testosterone in rams.

Two experiments were conducted to examine the effects of mouse epidermal growth factor (EGF) on the concentrations of testosterone, LH and FSH in jugular blood plasma and on the pituitary responsiveness to LHRH. In 20 rams treated with subcutaneous doses of EGF at rates of 85, 98 or 113 micrograms/kg fleece-free body weight, mean plasma LH and testosterone concentrations were significantly reduced (P less than 0.05) at 6 h after treatment but not at 24 h. EGF treatment at 130 micrograms/kg fleece-free body weight suppressed the plasma content of these hormones for up to 48 h. Mean plasma FSH concentrations decreased significantly (P less than 0.05) for up to 48 h after EGF treatment, the effect being most pronounced in rams with mean pretreatment FSH values greater than or equal to 0.5 ng/ml. Intravenous injections of 1.0 micrograms LHRH given to each of 5 rams before and at 6 h, 24 h and 72 h after EGF treatment produced LH and testosterone release patterns which paralleled those obtained in 5 control rams similarly treated with LHRH. These results suggest that, in rams, depilatory doses of mouse EGF temporarily impair gonadotrophin and androgen secretion by inhibiting LHRH release from the hypothalamus. Such treatment appears to have no effect on the responsiveness of the pituitary to LHRH.

Reproductive hormone secretion and testicular growth in bull calves actively immunized against testosterone and oestradiol-17 beta.

Groups of bull calves received a primary immunization against testosterone (Group T; N = 7) or oestradiol-17 beta (Group E; N = 9) at 3 months of age and booster injections on four occasions at approximately 2 month intervals. Controls (Group C, N = 7) were immunized against human serum albumin alone using the same protocol. Immunity was achieved against both steroids as judged by the secondary antisteroid antibody titres in Group T (730 +/- 231; reciprocal of titre) and Group E (12,205 +/- 4366) bulls; however, peak antibody titres generally declined with successive booster injections. Mean plasma concentrations of LH, FSH and testosterone during the period from 3 to 10 months of age were higher (P less than 0.05) in Group T bulls than in Groups C and E. Group T bulls had larger testes compared with controls from 6 months of age onwards. At castration at 14 months of age, testes of Group T bulls were heavier (P less than 0.05) than those of Groups C and E (179 +/- 13, 145 +/- 8 and 147 +/- 6 g, respectively). At 10 months of age, there were no differences among treatment groups in LH responses to LHRH, but the testosterone responses were greater (P less than 0.05) in bulls in Group T (26.2 +/- 4.9 ng/ml) and Group E (16.6 +/- 1.8 ng/ml) compared with those in Group C (6.9 +/- 0.6 ng/ml). Testosterone responses to hCG determined at 13 months of age were also greater (P less than 0.05) in Groups T and E relative to controls. At 14 months of age daily sperm production rates per bull (X 10(-9)) were higher (P less than 0.10) in Group T bulls (2.2 +/- 0.1) than those in Groups C (1.6 +/- 0.2) and E (1.6 +/- 0.1). These results indicate that early immunity against testosterone is associated with increased gonadotrophin secretion and accelerated growth of the testes in prepubertal bulls. Also, chronic immunity against testosterone or oestradiol-17 beta enhances the steroidogenic response of bull testes to gonadotrophic stimulation. If the above responses observed in young bulls are shown to be sustained, then immunity against gonadal steroids early in life may confer some reproductive advantage in mature animals.

Capillary blood flow in the endometrium and myometrium of conscious sheep: effect of catheterization of uterine arteries.

Measures of capillary blood flow in the uterine tissues of conscious ewes were obtained by the use of microspheres. Total uterine capillary blood flow was significantly greater (P less than 0.01) at oestrus than at day 8 of the oestrous cycle [69.5 +/- (s.e.m.) 11.9, cf. 15.3 +/- 1.2 ml min-1, n = 7], reflecting increases of a similar order in both the endometrium and the myometrium. At these stages of the oestrous cycle, endometrial capillary blood flow constituted 83.6 and 80.5%, respectively, of the total uterine capillary flow. Following the placement of indwelling catheters in each middle uterine artery there was a decrease in the ratio of endometrial to myometrial capillary blood flow for 3-5 days.

Effects of ovarian hormones on ovarian capillary blood flow in anoestrous ewes.

The indicator fractionation technique with [86Rb]rubidium chloride as the indicator was used to determine the relative blood flow (RBF) as a measure of capillary blood flow in the ovaries of conscious, hormonally treated, anoestrous ewes. Treatment of ewes with either progesterone only or oestradiol only had no effect on ovarian RBF, but treatment with oestradiol subsequent to progesterone caused a significant increase (P less than 0.001). Consequently, it appears that progesterone-induced sensitivity of the ovarian vasculature to the vasodilatory effects of oestradiol may be responsible for increased ovarian blood flow around oestrus in cyclic ewes.

Measurements of endometrial blood flow in anaesthetized ewes by xenon-133 clearance and microsphere techniques.

In six anaesthetized, non-pregnant ewes, uterine blood flow rates measured by monitoring the clearance of xenon (133Xe) from the lumen of the uterus were compared with estimates of endometrial and myometrial capillary blood flow obtained by the use of microspheres of 15 micron diameter (eleven comparisons). On analysis, seven of the 133Xe clearance curves indicated the occurrence of both a fast and a slow compartment of flow with flow rates approximating to the rate of capillary blood flow in the caruncular and inter-caruncular portions of the endometrium, respectively. In each of the remaining four curves which provided a single estimate of flow, the derived blood flow rate was similar to the rate of capillary blood flow in both the caruncular and inter-caruncular portions of the endometrium. No relationship existed between myometrial capillary blood flow and the flow rates derived from the 133Xe clearance curves.

Evidence for functional arterio--venous anastomoses in the ovaries of sheep.

Vessels with histological features characteristic of arterio--venous anastomoses were found in the stroma but not in CL. In 5 conscious ewes at the mid-luteal stage of the oestrous cycle, ovarian blood flow was significantly greater (P less than 0.025) with microspheres of 50 than of 15 micrometers diameter in ovaries without CL (0.23 +/- 0.04 (s.e.m.) and 0.11 +/- 0.02 ml/min, respectively), but not in ovaries with CL (4.42 +/- 0.86 and 3.73 +/- 0.70 ml/min, respectively). In 5 similar but anaesthetized ewes, the portion of each ovarian artery within the ovarian vascular pedicle was bypassed with re-entrant catheters through which microspheres were perfused. A greater proportion (P less than 0.01) of 50 than of 15 micrometers microspheres was retained in ovaries with (90 and 79%) or without (82 and 45%) a CL. It is concluded that functional arterio--venous anastomoses are present in sheep ovaries.

Ovarian arterial blood velocity measured with Doppler ultrasonic transducers in conscious ewes.

Changes in the mean velocity of ovarian arterial blood flow during the oestrous cycle were monitored in 5 ewes by the use of doppler ultrasonic transducers chronically implanted around the ovarian arteries. In arteries supplying ovaries with a corpus luteum (CL), the velocity was minimal from Day -1 to Day 2 inclusive (Day 0 = day of oestrus), increased steadily until Day 13 (-4) and then declined precipitously. In contralateral arteries supplying ovaries without a CL, the velocity remained at a consistently low level throughout the oestrous cycle. In each ewe, arterial blood velocity to the ovary with a CL and progesterone levels in peripheral plasma were highly correlated; within-individual correlations falling between r = 0.830 (P < 0.001, n = 15) and r = 0.936 (P < 0.001, n = 15). The changes in the velocity of the arterial supply to the ovulatory ovary and the pattern to that for weight of luteal tissue in similar ewes.

Endometrial blood flow in anaesthetized sheep as measured with krypton-85 clearance and microsphere techniques.

Uterine blood flow rates were obtained with a Krypton (85Kr) clearance technique and with radio-active microspheres in six anaesthetized, non-pregnant ewes (a total of ten comparisons). 85Kr was administered, via a catheter, into the abdominal aorta and beta-emissions were detected with a catheter-type semi-conductor detector probe situated in the lumen of a uterine horn. In seven instances, the 85Kr clearance curve had only one component while in the remaining three instances the curves could be resolved into two components. The flow rates derived from the single component curves and the mean flow rates calculated from the curves with two components were of the same order as, and highly correlated with, estimates of capillary blood flow obtained with microspheres for either the caruncles, the inter-caruncular endometrium or the total endometrium (r = 0.832, r = 0.822 and r = 0.841, respectively, P less than 0.005). There was no correlation between the flow rates obtained with the 85Kr technique and estimates of myometrial capillary blood flow obtained with microspheres.

The relation between patterns of ovarian follicle growth and ovulation rate in sheep.

The number and growth rate of follicles within classes based on granulosa volume were determined for ovaries taken from groups of 4-5-year-old, fine-wool Merino ewes drawn at different times of the year from a single strain flock maintained at Armidale, N.S.W. The breeding season of the flock normally extends from February to October and the mean ovulation rate rises from about 0.5 in February to about 1.8-1.9 during April-May. Ewes sampled when they were anoestrous or had one (single-ovulatory) or two (twin-ovulatory) recent corpora lutea did not differ in respect to the mean total number of ovarian follicles, the mean number of follicles in individual classes, the time for follicles to complete their rapid growth stage, or the incidence of follicle atresia. However, the ovaries of twin-ovulatory ewes contained significantly more follicles in the two terminal classes within the rapid growth stage than did the ovaries of single-ovulatory or anoestrous ewes (2.2 v. 0.9 and 1.0). This difference was attributed to the differing numbers of follicles per day entering into the rapid growth stage (5.2, 4.5 and 3.7 respectively in twin-ovulatory, single-ovulatory and anoestrous ewes).

Ovarian function in suckling and non-suckling beef cows post partum.

Two groups, each of 7 crossbred beef cows, which were suckling or not suckling calves, were fed a high quality food ad libitum for 3 months post partum. The non-suckling cows experienced regular ovarian cycles from 10--33 days post partum while the suckling cows did not do so until at least 14 weeks post partum. There was little difference between the groups in growth rate or in plasma glucose concentration. The plasma prolactin concentrations in the non-suckling cows showed a seasonal trend which paralleled ambient temperature and daylight hours; in the suckling cows this trend was less evident. Plasma LH concentrations were lower in suckling cows before Day 30 post partum but were similar thereafter. Most suckling cows also failed to experience oestrus or to exhibit LH release in response to an injection of oestradiol benzoate at about 6 weeks post partum. This failure, together with the earlier lower levels of LH in the suckling cows, is considered to be indicative of malfunction of the hypothalamic mechanism normally responsible for the establishment and maintenance of cyclic ovarian function.

Capillary blood flow in the genital tracts of conscious ewes: cyclic changes and the effect of ovarian hormones.

The indicator fractionation technique with [86Rb]rubidium chloride as the indicator was used in conscious animals to determine the relative blood flow (RBF) as a measure of capillary blood flow in regions of the genital tract of cyclic ewes and of hormonally treated ovariectomized ewes. The RBF values in the ampulla, isthmus, uterus and cervix of cyclic ewes were markedly raised at pro-oestrus and declined thereafter to low levels during the remainder of the oestrous cycle. On Day 4 a small secondary rise in flow occurred in the ampulla and isthmus. In ovariectomized ewes, oestradiol induced high levels of RBF in the ampulla, isthmus, uterus and cervix whether the animals had been treated previously with progesterone or given concurrent small doses of progesterone. Though progesterone given alone caused a significant rise in RBF in the uterus, this effect appeared to be one occurring only during active re-growth of regressed tracts. The findings are discussed in relation to oestradiol inducing a stimulatory effect on RBF in the genital tract of the ewe around oestrus but not at Days 3-4 of the oestrous cycle.