Ovulation rate and embryo survival in Damline ewes after treatment with bovine follicular fluid in the luteal phase of the oestrous cycle

Treatment of Damline ewes with twice daily i.v. injections of bovine follicular fluid during the luteal phase for 10, 6 or 2 days before prostaglandin-induced luteolysis resulted in an increase in ovulation rate. This was associated with a large rebound increase in plasma concentrations of FSH after the last injection of bovine follicular fluid. While conception rate was not affected by bovine follicular fluid treatment, a higher percentage embryonic loss was observed between Days 3 and 34 of pregnancy in the 10-day treatment group only compared to controls. This reflected the increase in ovulation rate above the optimum for embryonic survival in this breed. The present results suggest that the increase in ovulation rate induced by bovine follicular fluid treatment in the luteal phase of the cycle before mating would result in a significant increase in the number of lambs born.     

The effect of exposure to oestrous ewes on rams' sexual behaviour, plasma testosterone concentration and ability to stimulate ovulation in seasonally anoestrous ewes

Ruminants eat a variety of foods from different locations in the environment. While water, cover, social interactions, and predators are all likely to influence choice of foraging location, differences in macronutrient content among forages may also cause ruminants to forage in different locations even during a meal. We hypothesized that lambs forage at locations containing foods that complement their basal diet and meet their nutritional needs. Based on this hypothesis, we predicted that lambs (n=12) fed a basal diet low in protein and high in energy would forage where a high-protein food (Food P) was located, and that lambs (n=12) fed a basal diet low in energy and high in protein would forage where a high-energy food (Food E) was located. Food P was a ground mixture of blood meal (50%), grape pomace (30%), and alfalfa (20%) that contained 47% crude protein (CP) and 2.211 Mcal/kg digestible energy (DE). Food E was a ground mixture of cornstarch (50%), grape pomace (30%), and rolled barley (20%) that contained 6% CP and 3.07 Mcal/kg DE. Food P provided 212 g CP/Mcal DE, whereas Food E provided 20 g CP/Mcal DE. Lambs growing at a moderate rate require 179 g CP and 3.95 Mcal DE. During Trial 1, we determined if lambs foraged to correct a nutrient imbalance, and if they preferred a variety of foods (Foods P and E) to only one food at a location (Food P or E). During Trial 2, we determined if nutrient-imbalanced lambs foraged in the location with the food that corrected the imbalance when the location of the foods changed daily. During Trial 3, lambs were offered familiar foods (Foods P and E) at the location furthest - and novel foods (wheat and soybean meal) at the location nearest - the shelter of their pen. During all three trials, lambs foraged most at the location with the food that contained the highest concentration of the macronutrient lacking in their basal diet, but they always ate some of both foods. Lambs did not feed exclusively at the location with a variety of foods (P and E). Rather, they fed at the location nearest the shelter that contained the macronutrient lacking in their diet. As availability of the food with the needed macronutrient declined in one location, lambs moved to the nearest location that had food with the needed macronutrient. When food that complemented their basal diet was moved to a different location, lambs foraged in the new location. Collectively, these results show that lambs challenged by imbalances in energy or protein selected foods and foraging locations that complemented the nutrient content of their macronutrient imbalanced basal diets.     

Melanin concentrating hormone (MCH) in the cerebrospinal fluid of ewes during spontaneous oestrous cycles and ram effect induced follicular phases

The melanin-concentrating hormone (MCH) is a neuropeptide synthesized by neurons of the lateral hypothalamus and incerto-hypothalamic area that project throughout the central nervous system. The aims of the present report were: (1) to determine if MCH levels in cerebrospinal fluid (CSF) of ewes vary between the mid-luteal and the oestrous phase of spontaneous oestrous cycles; and (2) to study if MCH levels in CSF of ewes vary acutely during the follicular phase induced with the ram effect in anoestrous ewes. In the first experiment, CSF was collected from 8 adult ewes during spontaneous oestrous and during the mid-luteal phase (8-10 days after natural oestrus). In the second experiment, performed during the mid non-breeding season, a follicular phase was induced with the ram effect. After isolating a group of 16 ewes from rams, CSF was obtained from 5 of such ewes (control group). Three rams were joined with the ewes, and samples were obtained 12h (n=6) and 24h (n=5) later. In Experiment 1, there were no differences in MCH concentrations in CSF measured during the mid-luteal phase and spontaneous oestrus (0.14 ± 0.04 vs. 0.16 ± 0.05 ng/mL respectively). In Experiment 2, MCH concentrations tended to increase 12h after rams introduction (0.15 ± 0.08 vs. 0.35 ± 0.21 ng/mL, P=0.08), and increased significantly 24h after rams introduction (0.37 ± 0.15 ng/mL, P=0.02). We concluded that MCH concentration measured in the CSF from ewes increased markedly during the response to the ram effect but not during the natural oestrous cycle of ewes.     

Ovarian capillary blood flow in seasonally anoestrous ewes induced to ovulate by treatment with GnRH

The microsphere technique was used to obtain estimates of ovarian capillary blood flow near ovulation, in 8 seasonally anoestrous ewes, which were induced to ovulate by GnRH therapy. Plasma progesterone concentrations were monitored in jugular blood sampled between Days 4 and 7 after the onset of the preovulatory LH surge. The ewes were then slaughtered. Three of the ewes were treated with a single injection of 20 mg progesterone before GnRH therapy. In these ewes and 1 other, plasma progesterone values increased after ovulation and reached 1.0 ng/ml on Day 7 following the preovulatory LH surge (normal, functional CL), whilst in the other 4 ewes progesterone concentrations increased initially then declined to 0.5 ng/ml by Day 7 (abnormal CL). In the ewes exhibiting normal luteal function, the mean ovarian capillary blood flow was significantly greater (P less than 0.01) than that for ewes having abnormal luteal function. Irrespective of the type of CL produced, capillary blood flow was significantly greater (P less than 0.05) in ovulatory ovaries than in non-ovulatory ovaries. These findings indicate that the rate of capillary blood flow in ovaries near ovulation may be a critical factor in normal development and maturation of preovulatory follicles and function of subsequently formed CL.     

Treatment with progesterone affects follicular steroidogenesis in anoestrous ewes

Ovaries were recovered from two groups (n=6/group) of anoestrous Romney Marsh ewes, one group of which had been treated with progesterone implants prior to slaughter. A comparison was made between the maturational characteristics of the follicles > 2 mm diameter recovered from both groups and some significant differences were noted. In particular, the large follicles (> 4 mm diameter) recovered from the progesterone-treated ewes had a significantly (P<0.01) reduced capacity to secrete oestradiol, but enhanced (P<0.01) ability to bind hCG when compared to follicles recovered from control ewes. There were also differences in the relationships between follicular characteristics in the two groups of animals including a significant (P <0.05) correlation between follicular fluid progesterone and hCG binding to theca tissue in large follicles from progesterone-treated animals which did not exist in the control animals. Conversely, in the control animals a significant (P<0.05) relationship existed between oestradiol production and hCG binding to granulosa cells, but there was no such relationship in the follicles from progesterone-treated ewes. These results demonstrate that the treatment of ewes with progesterone during the anoestrous period clearly affects oestradiol synthesis and hCG binding and thus modifies follicular development.     

Ovulation rate in ewes after single oral glucogenic dosage during a ram-induced follicular phase

A 2-factor factorial array with three replicates (N = 280) was used to simultaneously assess the effects on ovulation rate of two alternative doses of medroxy-progesterone acetate (MPA) (10 or 60 mg), applied during a 6-day priming period, and the effect of a single dosage of a glucogenic formulation, administered immediately before ram exposure to groups of adult seasonally anovular Corriedale ewes. The glucogenic formulation contained 1,2,3-propanetriol (glycerol; 70% $\text{v}\text{v}$), 1,2-propanediol (propylene glycol; 20% $\text{v}\text{v}$) and distilled water (10% $\text{v}\text{v}$). At sponge withdrawal, a single oral dose of 100 ml of this formulation or the same volume of distilled water was administered to treated and control groups, respectively, and ewes were immediately exposed to rams and hormonally-induced oestrous ewes. Data from an ancillary experiment (n = 10) showed significantly (P < 0.005) above normal plasma glucose levels in treated animals at 3 and 6 h after dosage. A significant interaction (P = 0.0006) between MPA priming doses and glucogenic supplementation was detected. Supplemented ewes, among those exposed to the lower dose of MPA, exhibited a higher (P = 0.0098) mean ovulation rate (1.56 ± 0.076) than ewes that did not receive glucogenic treatment (1.31 ± 0.060). In contrast, ovulation rate was significantly decreased (P = 0.021) from 1.30 ± 0.058 to 1.13 ± 0.042 after glucogenic treatment in ewes that were primed with sponges containing 60 mg of MPA. Ewes exposed to 60 mg of MPA were marked by the rams at a significantly later (P < 0.00001) mean time (54.8 ± 1.44 h) than ewes receiving 10 mg sponges (43.6 ± 1.08 h). These results reveal the potential for modifying ovulation rate through short-term glucogenic manipulations, at least during the compressed follicular phase typical of ram-induced ovulations.     

Ovulation rate and oocyte numbers in ewes after prolonged exposure to oestrogenic pasture.

Ewes which had been exposed to oestrogenic clover for 3 years showed an elevated ovulation rate but no difference in numbers of primordial follicles compared with normal ewes.     

Ovulation in the merino ewe in the breeding and anoestrous seasons

The pattern of ovulation of Merino ewes was studied by repeated laparoscopy each 14 days in the anoestrous (n = 97) and breeding (n = 87) seasons. In the anoestrous season the proportion of ewes ovulating did not decrease below 11%, 42% of ewes never ovulated and the remainder fluctuated between the two states. On 20 occasions a clear anovulatory period was interrupted by an isolated spontaneous ovulation. In the breeding season the overall mean proportion of ewes with corpora lutea or albicantia at laparoscopy was 87%, 54% of ewes ovulated regularly throughout while in another 31% absence of corpora lutea or albicantia coincided with the follicular phase of an oestrous cycle as evidenced by an appropriately aged corpora lutea at the next laparoscopy. Of the remaining 15% of the flock 3% had anovulatory periods greater than 14 days while the remainder experienced irregular ovulatory cycles--the majority due to short periods of anovulation but some ewes retained corpora lutea for longer than 14 days while others ovulated twice between successive laparoscopies.     

Effect of FSH on ovarian inhibin secretion in anoestrous ewes

In Exp. 1, 7 Finn-Merino ewes which had one ovary autotransplanted to a site in the neck had jugular and timed ovarian venous blood samples collected at 10-min intervals for 2 h before and 3 h after injection of 5 micrograms NIAMDD-oFSH-S16. In Exp. 2, 8 Finn-Merino ewes with ovarian autotransplants had jugular and timed ovarian venous blood samples collected at 15-min intervals for 2 h before and 12 h after bolus injection of 40 micrograms NIAMDD-oFSH-S16 and infusion of oFSH-S16 at 6 micrograms/min for 4 h. In Exp. 2 the follicular population of the ovary was assessed by real-time ultrasound at the beginning and end of the experimental period. In both experiments the secretion rates of inhibin (1-3 ng/min) and oestradiol (0.5-8 ng/min) were similar to those observed during the luteal phase of the cycle in the breeding season, indicating significant follicular development in these animals. In Exp. 1 there was no change in the secretion of oestradiol or inhibin after the injection of FSH which resulted in a 25% increase (P less than 0.05) in the concentration of FSH in plasma. Inhibin secretion was pulsatile but there was no difference in inhibin pulse frequency before (1.6 +/- 0.2 pulses/h) or after (1.2 +/- 0.5 pulses/h) injection of FSH. In Exp. 2 injection of FSH resulted in an increase (P less than 0.001) in plasma concentrations of FSH in the sample taken 10 min after injection from a baseline of 1.2 +/- 0.2 ng/ml to a peak of 10.6 +/- 1.0 ng/ml (mean +/- s.e.m.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ram-seeking activity associated with oestrous behaviour in ewes

Ram-seeking activity associated with oestrous behaviour was studied in entire and oestrogentreated spayed ewes. In spayed ewes, the incidence of both oestrous behaviour and ram-seeking activity increased with dose of oestrogen. All ewes could be induced to show ram-seeking activity, but only when injected with a dose of oestrogen greatly in excess of that needed to induce oestrous behaviour. The incidence of ram-seeking activity in entire ewes remained about 25 per cent lower than the incidence of oestrous behaviour at all stages of the breeding season. All ewes were capable of ramseeking activity, but normal levels of endogenous oestrogen probably were too low to induce a full response. In the absence of rams, spayed ewes injected with a dose of oestrogen sufficient to induce ram-seeking behaviour showed no increase in random walking activity. Ram-seeking behaviour appeared to depend not only on the internal stimulus of oestrogen, but also on the external stimulus provided by the presence of rams.     

Synchronization of oestrous cycles in sable antelope

Techniques for manipulating the oestrous cycle of sable antelope, Hippotragus niger, were evaluated in a captive population of 24 females maintained at the Smithsonian Institution's Conservation and Research Center in Front Royal, VA, USA. A secondary objective was to demonstrate the effectiveness of fecal steroid monitoring techniques as a non-invasive method of tracking experimental manipulations. Controlled Internal Drug Releasing (CIDR) devices designed for cattle (type B, reduced in length by 5 cm to fit the sable antelope's smaller reproductive tract) were more effective than CIDR devices designed for goats (type G) at delivering progesterone into circulation, and maintained serum progesterone at levels up to 86.1+/-7.8% of normal luteal concentrations in females whose spontaneous ovarian activity had been inhibited with melengestrol acetate. Serum progesterone and fecal progestagen measurements were highly correlated (P<0.05). Synchronization treatments of prostaglandin (PG) F2alpha alone and in combination with modified CIDR-B devices (12-day insertion interval) were both effective in inducing synchronized ovulation, however the PGF2alpha/modified CIDR-B treatment resulted in more precise synchrony and a shorter latency to ovulation than did PGF2alpha alone. In a separate experiment to characterize the temporal relationship between synchronization treatment, behavioral oestrus and ovulation, onset of behavioral oestrus occurred 34.1+/-5.7 h following PGF2alpha/modified CIDR-B treatment. Mean duration of the induced oestrus was 24.9+/-4.3 h. The first detectable rise in fecal progestagens occurred 5.1+/-1.0 and 4.1+/-1.0 days following PGF2alpha/modified CIDR-B treatment in groups of females housed with and without an adult male, respectively, indicating that the presence of a male did not accelerate the onset of the induced cycle.     

Ram-induced growth of ovarian follicles and gonadotrophin inhibition in anoestrous ewes

Southdown ewes in mid-seasonal anoestrus were exposed to rams for 0 h (control group), 2 h, 24 h, 40 h, 3 days, 10 days or 20 days. Serial blood samples were then taken to determine LH and FSH levels. Ewes with greater than 24 h ram exposure were ovariectomized immediately after bleeding, and all follicles greater than 1 mm diameter were dissected from the ovaries and measured. LH basal concentrations and pulse frequency increased significantly within 2 h of ram introduction, but by 24 h fell, and then remained low. FSH concentrations fell within 2 h of ram introduction and remained low. Control group ewes (isolated) had no follicles greater than 4 mm diameter, whereas all ewes exposed to rams had large follicles, with CL or preovulatory follicles present at 40 h after ram introduction. Ram introduction was also associated with follicle recruitment (antrum formation to less than 2 mm). Follicular recruitment and development to the large follicle stage therefore occurred during a period of low plasma gonadotrophin levels and suppressed LH pulsing.     

Plasma FSH concentrations in seasonally anoestrous ewes induced to ovulate with repeated injections or continuous infusion of GnRH

Plasma FSH concentrations were monitored in 34 seasonally anoestrous ewes in which ovulation was induced by the administration of low doses of GnRH, given as either a series of i.v. injections (75, 125, 250 or 500 ng/2 h) or as a continuous i.v. infusion (125 or 250 ng/h). Fifteen of the animals had been pretreated with progesterone for 14 days. Before the start of GnRH treatment, mean FSH concentrations did not differ between progesterone-pretreated and non-pretreated ewes (23 ± 3.0 and 20 ± 2.0 ng/ml, respectively). In a significant (P < 0.01) proportion of animals mean FSH concentrations were elevated for the first 2 h of GnRH treatment, but thereafter they declined progressively and were significantly (P < 0.001) lower than pretreatment levels over the second 12 h of GnRH treatment. These changes in FSH concentrations were not related to dose of GnRH, the mode of administration or to progesterone priming. These results demonstrate that the pattern of FSH secretion associated with GnRH-induced ovulation in the seasonally anoestrous ewe is similar to that observed from the time of luteal regression in the naturally cycling ewe. In addition, although pretreatment with progesterone has a marked effect on subsequent luteal function, this is not mediated through changes in plasma FSH concentrations.     

Laparoscopy in the ewe: A photographic record of the ovarian activity of ewes experiencing normal or abnormal oestrous cycles

Daily observation of ovarian activity in cycling ewes by laparoscopy shows that visual estimation of the age of corpora lutea must be primarily related to changes in their colour rather than to changes in either their shape or size. The shape and size of corpora lutea varies widely depending upon their depth of origin within the cortex of the ovary.A 36-day oestrous cycle in one ewe was found to be associated with the maintenance of a mature corpus luteum rather than with a silent ovulation. By contrast, a 6-day oestrous cycle in another ewe was associated with the premature regression of the corpus luteum.