Induction of fertile oestrus in seasonally anoestrous ewes with low doses of Gn-RH

Oestrus, conception and lambing performance were assessed in progesterone-primed seasonally anoestrous ewes induced to ovulate with gonadotrophin-releasing hormone (Gn-RH), which was administered intravenously for 48 h as either injections of 250 ng at 2-h intervals (n = 15) or as a continuous infusion at the rate of 125 ng/h (n = 12) or 250 ng/h (n = 12).In $\text{14}\text{15}$ of the ewes injected with Gn-RH, a preovulatory LH peak was recorded at a mean time interval of 33.9 ± 1.8 h after the start of treatment. All ewes displayed oestrus and all ovulated, with a mean ovulation rate of 1.67 ± 0.13. Eleven ewes were diagnosed as pregnant and subsequently lambed. Following infusion of Gn-RH, preovulatory LH peaks were recorded in $\text{21}\text{24}$ ewes at a mean time of 36.1 ± 2.9 h (125 ng/h) and 34.7 ± 2.0 h (250 ng/h). All but two of the ewes displayed oestrus and $\text{23}\text{24}$ ovulated. The group mean ovulation rates of 1.27 ± 0.14 (125 ng/h) and 1.75 ± 0.22 (250 ng/h) were not significantly different. Eleven of the 22 ewes mated were diagnosed as pregnant and produced live lambs.These results suggest that fertility of Gn-RH-induced ovulations in seasonally anoestrous ewes is comparable to that apparent in ewes ovulating spontaneously during the breeding season.     

Effect of monensin and suckling on the GnRH induced luteinizing hormone surge and the effect of monensin on the postpartum interval in Brangus cows

Twenty-seven fall calving Brangus cows were randomly allotted to one of four treatment groups: nonsuckled monensin (NSM), suckled monensin (SM), nonsuckled control (NSC), and suckled control (SC). Cows were group fed 1.82 kg/hd/day concentrate and Coastal bermuda grass hay $\text{ad}$$\text{libitum}$. Monensin cows received 200 mg monensin/hd/day in the concentrate. At 0800 hr on day 21 postcalving, the calves were separated from the cows. Suckled monensin and SC cows were allowed to suckle their calves for 30 min at 6-hr intervals. Nonsuckled monensin and NSC cows were not suckled. Calves were given free access to the cows after 1400 hr on day 22 postpartum. At 0800 hr on day 22 postpartum, a blood sample was collected. A 100 μg GnRH challenge was administered IM at 0801 hr. Blood samples were collected at 15-min intervals for 6 hr postinjection. Changes in body weight and body condition from day 21 postpartum to the day of first estrus were not different (P>0.10) by dietary treatment. Monensin cows consumed 10.7% less hay than did the control cows. Serum luteinizing hormone (LH) following GnRH was greater (P<0.005) in suckled than nonsuckled cows. Control cows released more (P<0.005) LH in response to GnRH than did the monensin cows. The postpartum interval (to first estrus) for the monensin cows (92.4±14.7 days) was shorter (P<0.025) than the controls (138.5±9.5 days). A greater proportion (P<0.005) of the monensin cows (8 of 14) exhibited estrus by 90 days postpartum compared to the control cows (0 of 13). Monensin and suckling appear to exert independent and agonistic influences on pituitary function in the postpartum beef cow.     

The continuous presence of ewes in estrus in spring influences testicular volume,testicular echogenicity and testosterone concentration,but not LH pulsatility in rams

The continuous presence of active male small ruminants prevents seasonal anestrus in females, but evidence of the same mechanism operating from the females to the males is scarce. This study assessed the effects of the continuous presence of ewes in estrus in spring on ram sexual activity, testicular size and echogenicity, and LH and testosterone concentrations. On 1 March, 20 rams were assigned to two groups (n = 10 each): isolated (ISO) from other sheep, or stimulated (STI) by 12 ewes, which were separated from the rams by an openwork metal barrier, allowing contact between sexes. Each week, four ewes were induced into estrus by intravaginal sponges. Live weight, scrotal circumference, testicular width (TW) and length (TL) were recorded at the beginning and at the end of the experiment, and testicular volume (TV) was calculated; at the same time, testicular ultrasonography and color Doppler scanning were performed. Blood samples (March to May) were collected once per week for testosterone determinations, and at the end of the experiment, blood samples were collected for 6 h at 20-min intervals for LH analysis. Rams were exposed to four estrous ewes in a serving-capacity test. Scrotal circumference, TW and TL were higher in the STI than in the ISO rams (P < 0.05) in May, and TV was higher (P < 0.05) in the STI (391 ± 17 cm³) than in the ISO rams (354 ± 24 cm³). In ISO rams, the number of white pixels was higher (P < 0.01) in May (348 ± 74) than in March (94 ± 21) and differed significantly (P < 0.01) from that of the STI rams in May (160 ± 33). In ISO rams, the number of grey pixels was higher (P < 0.05) in May (107 ± 3) than it was in March (99 ± 1). Stimulated and ISO rams did not differ significantly in mean LH plasma concentrations (0.8 ± 0.5 v. 0.9 ± 0.4 ng/ml), LH pulses (2.1 ± 0.5 v. 2.2 ± 0.2) and amplitude (2.0 ± 0.4 v. 3.2 ± 0.7 ng/ml, respectively). Stimulated rams had significantly higher testosterone concentrations than ISO rams from April to the end of the experiment. Stimulated rams performed more (P < 0.05) mountings with intromission (3.0 ± 0.4) than did ISO rams (1.5 ± 0.5). In conclusion, after 3 months in the continuous presence of ewes in estrus in spring, rams had higher TV and some testicular echogenic parameters were modified than isolated rams. Although exposed rams also had higher levels of testosterone after 2 months in the presence of estrous ewes, their LH pulsatility at the end of the study was not modified.     

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.     

Effect of monensin on postpartum interval to first estrus and serum LH response to 0, 1, 2 or 4 mg estradiol-17β at 21 days postpartum

A 2×4 factorial design was used to evaluate the effects of monensin (0 vs 200 mg) and estradiol-17β (E2) dose (0, 1, 2 vs 4 mg) on postpartum interval (PPI) to first estrus and on serum LH release at 21 days postpartum. Forty-eight spring calving Brangus cows were randomly stratified by calving date and sex of calf into two feeding groups within 24 hr of calving. Each group received 2.7 kg/head/day of a milo:cottonseed meal (4:1) mixture containing either 0 or 200 mg monensin. Coastal bermuda grass hay and water were available $\text{ad}$$\text{libitum}$. During the period of E2 treatment and bi-hourly blood sampling, suckling was controlled at 6-hr intervals.Mean cow weight and body condition score within cell changed less than 23 kg and 0.5 points, respectively, from day 1 to day 21 postpartum and were unaffected by treatment (P>0.10). PPI was reduced (P<0.01) and proportion of cows exhibiting estrual behavior by 85 days postpartum was increased (P<0.05) by treatment with 200 mg monensin and unaffected by E2 dose. Monensin fed cows had a longer (P<0.05) interval to LH response (ILH) and to peak LH (ILHP) at the 4 mg E2 dose. Monensin had no effect (P>0.10) on LH variables at 0, 1 or 2 mg E2.     

Effect of stage of maturity of grass at harvest on intake,chewing activity and distribution of particle size in faeces from pregnant ewes

This study was conducted to investigate the effect of stage of maturity at harvest on the intake of grass silage, eating and ruminating activity and the distribution of faecal particle size in ewes during late pregnancy. A total of 18 Swedish Finull × Dorset 85 ± 8 kg (mean ± s.d.) ewes bearing twins were randomly assigned to three dietary treatments 6 weeks before lambing. The treatments included ad libitum feeding with early harvested (EH), medium harvested (MH) or late harvested (LH) primary-growth grass silage with 45%, 58% and 63% NDF on a dry matter (DM) basis, respectively. Intake and chewing activity were recorded and faeces were sampled over 4 continuous days for each individual ewe. The faeces samples were washed in nylon bags, freeze dried and sieved with pore sizes from 2.4 mm to 0.1 mm; particles less than 0.1 mm in size were also collected. Subsamples of each sieving fraction were scanned and the dimensions of the individual particles in each sieving fraction were measured by image analysis. In addition, the number of particles longer than 7 mm was counted from the particles retained on a sieve with a pore size of 2.4 mm using a simple wet sieving technique. The time spent eating and ruminating per kg of DM intake was affected by the stage of maturity at harvest; it was shorter in ewes fed EH compared with ewes fed MH and LH (P < 0.05). In comparison with feeding LH, feeding EH resulted in the retention of a larger proportion of particles in the lower and upper sieve fractions (<0.2 mm and >1 mm, respectively, P < 0.01), a smaller mean particle size (P < 0.05) and a smaller mean particle width in faeces (P < 0.01). The results from the simple wet sieving technique confirmed the results from dry sieving and image analysis, showing a higher number of large particles in faeces from ewes fed the EH compared with the ewes fed the MH and LH (P < 0.001). In conclusion, the distribution of faecal particle size might be considered as a footprint of the characteristics of forage fibre eaten by ewes.     

Pulsatile infusion of luteinizing hormone-releasing hormone: Effects on luteinizing hormone secretion and ovarian function in prepuberal gilts

Ten intact and hypophysial stalk-transected (HST), prepuberal Yorkshire gilts, 112–160 days old, were subjected to a pulsatile infusion regimen of luteinizing hormone-releasing hormone (LHRH) to investigate secretion profiles of luteinizing hormone (LH) and ovarian function. A catheter was implanted in a common carotid artery and connected to an infusion pump and recycling timer, whereas an indwelling external jugular catheter allowed collection of sequential blood samples for radioimmunoassay of LH and progesterone. In a dose response study, intracarotid injection of 5 μg LHRH induced peak LH release (5.9 ± 0.65 ng/ml; mean ± SE) within 20 min, which was greater (P < 0.001) than during the preinjection period (0.7 ± 0.65 ng/ml). After HST, 5 μg LHRH elicited LH release in only one of three prepuberal gilts. Four intact animals were infused with 5 μg LHRH (in 0.1% gel phosphate buffer saline, PBS) in 0.5-ml pulses (0.1 ml/min) at 1.5-h intervals continuously during 12 days. Daily blood samples were obtained at 20-min intervals 1 h before and 5, 10, 20, 40, 60 and 80 min after one LHRH infusion. Plasma LH release occurred in response to pulsatile LHRH infusion during the 12-day period; circulating LH during 60 min before onset of LHRH infusion was 0.7 ± 0.16 ng/ml compared with 1.3 ± 0.16 ng/ml during 60 min after onset of infusion (P < 0.001). Only one of four intact gilts ovulated, however, in response to LHRH infusion. This animal was 159 days old, and successive estrous cycles did not recur after LHRH infusion was discontinued. Puberal estrus occurred at 252 ± 7 days in these gilts and was confirmed by plasma progesterone levels. These results indicate that intracarotid infusion of 5 μg LHRH elicits LH release in the intact prepuberal gilt, but this dosage is insufficient to cause a consistent response after HST.     

Plasma luteinizing hormone and prolactin in normothermic and hyperthermic ovariectomized ewes

The effect of bromocriptine on concentrations of luteinizing hormone (LH) and prolactin (PRL) as well as the rhythmicity of episodic profiles of plasma LH were investigated in twelve ovariectomized ewes exposed to 3-day trials during which ambient temperature/humidity conditions maintained either normothermia or induced an average of 1.4°C increase of rectal temperature (hyperthermia). In 24 of 48 trials, ewes received twice daily subcutaneous injections of 1 mg bromocriptine beginning at 1900 hr on day 1. Plasma PRL and LH were measured at 10-min intervals for 4 hr on days 2 and 3. Bromocriptine significantly decreased plasma PRL (65 ± 6 vs 5 ± 1 ng/ml), mean plasma LH (11.0 ± 0.2 vs 6.5 ± 0.2 ng/ml) and tended (P < 0.1) to decrease LH rhythmicity. In hyperthermic placebo-treated ewes, plasma PRL was increased (65 ± 6 vs 212 ± 20 ng/ml) and mean LH was decreased (11.0 ± 0.2 vs 8.2 ± 0.2 vg/ml) compared to normothermic, placebo-treated ewes, but there was no effect of hyperthermia on LH rhythmicity. Bromocriptine treatment of hyperthermic ewes decreased mean PRL (212 ± 20 vs 32 ± 9 ng/ml) on both days of sampling although mean levels were significantly higher on day 2 than on day 3(54 ± 14 vs 10 ± 6 ng/ml). Perhaps because mean LH was already inhibited in hyperthermic ewes, bromocriptine did not further decrease mean LH (8.2 ± 0.2 vs 6.6 ± 0.2 ng/ml), but LH rhythmicity was decreased (P < 0.01). There was no significant difference in mean LH between normothermic ewes receiving bromocriptine and hyperthermic ewes receiving bromocriptine (6.5 ± 0.2 vs 6.6 ± 0.2 ng/ml). These results indicate that bromocriptine inhibits PRL and LH secretion in normothermic ewes. In hyperthermic ewes, the inhibitory effect of bromoriptine on PRL was even more pronounced, but the effect on LH release was minimal perhaps because LH was already inhibited by hyperthermia.     

The effect of microsomal enzyme inducing drugs on reproductive function in the ewe.

A number of drugs cause marked increases in the steroid hydroxylase activity of hepatic microsomes. Beginning 2 days after estrus, 117 mature ewes were each given 14 injections over a 27-day period of phenobarbital sodium, diphenylhydantoin, chlorcyclizine HCl or phenylbutazone. Blood samples for luteinizing hormone (LH) and progesterone determination by radioimmunoassay (RIA) were taken on day 10 of the first estrous cycle (day 18 if no heat was observed) and on days 5 and 10 of the second cycle. On day 10 of the second cycle, the ewes were given an intravenous injection of 1 ml of 6% solution of pentobarbitol sodium anesthetic per 4.5 kg body weight, and the length of anesthetic sleep time was measured. The ewes were then killed and corpora lutea and liver were weighed.In 33 ewes treated with either phenobarbitol sodium or phenylbutazone, sleep time was shortened (18 min $\text{vs}$ 29 min in untreated controls, P<.01), indicating that enzyme induction had occurred. For 41 ewes treated with either chlorcyclizine HCl or diphenylhydantoin, sleep time was lengthened to 93 min (P<.01 $\text{vs}$ controls), indicating impaired liver function. Electron micrographs of liver cells verified that enzyme induction or hepatic degeneration had occurred.     

Plasma follicle stimulating hormone,ovulation rate and fertility in Merino ewes treated with bovine follicular fluid

Charcoal-treated bovine follicular fluid (bFF) given as four 5-ml subcutaneous injections to 13 Merino-Border Leicester ewes around the time of natural luteolysis suppressed (P<0.01) plasma levels of follicle stimulating hormone (FSH) [from 1.08 ± 0.05 to 0.41 ± 0.03, mean ± s.e.m. of log_e (ng+ 1) /mlplasma]. This was followed (P < 0.01) by hypersecretion or a rebound of FSH (to 1.46 ± 0.11) lasting 32 h in 10 of the treated ewes, and then by a further fall (to 0.73 ± 0.03, P < 0.05) before the surge (1.21 ± 0.07, P < 0.05) associated with the preovulatory surge of luteinizing hormone (LH).Plasma FSH at 56–72 h before the LH surge (i.e., at the time of the FSH rebound) was correlated with the subsequent ovulation rate (n=13, r= + 0.73, P < 0.01). Fewer ewes treated with four injections of 2 or 5 ml of bFF than control ewes (injected with bovine plasma) became pregnant (28 of 41 vs. 38 of 41, χ² = 4.05, P < 0.05), although plasma progesterone was similar at Day 11 in treated and control ewes. It is concluded that plasma FSH during such a rebound influences the subsequent ovulation rate in sheep.     

Maternal influence on feeding site selection of male and female lambs

We conducted an experiment to determine whether early-life social learning of feeding site selection in lambs was sex-specific. Sixteen ewes and their new born lambs were used in a controlled experiment. Eight ewe–lamb pairs included a male lamb and the remaining eight a female lamb. All pairs were individually exposed to an experimental arena containing a safe and unsafe artificial feeding site (SFS, UFS) each consisting of nine bowls which contained either ground Bermuda grass hay (SFS) or ground alfalfa hay (UFS). The bowls in UFS were surrounded by bright orange traffic cones (visual cues). Half the ewes were trained with controlled electric shock to avoid UFS. Thus, pairs were randomly assigned to: (1) shock aversion training (SAT) to mothers of male lambs (MS); (2) SAT to mothers of female lambs (FS); (3) no aversion training (NAT, control) to mothers of male lambs (MC); and (4) NAT (control) to mothers of female lambs (FC). None of the lambs were subjected to SAT. During training, testing, extinction, and retraining ewe–lamb pairs were exposed to the arena together. Ewes were then removed from the experiment and two additional extinction phases were conducted with weaned lambs alone. Fear conditioning elicited UFS avoidance of both the trained ewes (means±s.e.m. % times observed in UFS during testing phase: FC=95.3±1.70; MC=94.4±4.87; FS=1.6±1.63; MS=0 ±0; P<0.01) and their naïve lambs (FC=83.8±6.07%; MC=76.6±6.56%; FS=30.4±7.90%; MS=33.9±9.23%; P<0.01). UFS avoidance in lambs occurred regardless of sex and tended to persist after weaning (% times observed in UFS during 1st post-weaning extinction phase: FC=92.6±4.50%; MC=89.8±6.09%; FS=45.1±10.57%; MS=43.5±10.42%; P=0.06). Fear conditioning in mothers appeared to alter sex-related differences in mother–infant behavioral synchrony by increasing and decreasing feeding synchrony of male and female lambs, respectively (FC: r=0.52, P<0.01; MC: r=−0.02, P=0.86; FS: r=0.14, P=0.26; MS: r=0.46, P<0.01). During the extinction phase mothers of ram lambs were observed feeding more often (FC=85.0±2.33%; MC=92.7±1.45%; FS=47.3±8.81%; MS=72±5.68%; P=0.02) and standing less often than ewes with daughters (FC=7.3±2.40%; MC=2.7±0.83%; FS=39.3±9.04%; MS=18.0±5.29%; P=0.06). This study suggests that social conditioning at an early age could be a viable tool to induce learning of feeding site avoidance in female and male lambs alike.     

Serum luteinizing hormone levels in cattle under various reproductive states

Serum lutinizing hormone (LH) levels in cattle during various reproductive states were measured by radioimmunoassay. A sharp LH peak observed at estrus (22.72 ± 5.68 ng/ml) was about 26 times higher than at other stages of the cycle (0.87 ± 0.06 ng/ml). LH levels during the first 90 days of pregnancy (0.75 ± 0.15 ng/ml) were similar to those of the estrous cycle, except during estrus, while those during the second (0.22 ± 0.07 ng/ml) and third trimesters of pregnancy (0.22 ± 0.08 ng/ml) were significantly lower. Higher levels than those of the cycling cows, except during estrus, were seen in ovariectomized cows (2.21 ± 0.56 ng/ml). Levels of LH in cows with cystic follicles (2.00 ± 0.49 ng/ml) were higher than the levels in the cycle. LH levels in bulls (1.29 ± 0.39 ng/ml) were comparable to that of estrous cows. Serum LH of calves increased with age from 1.00 ± 0.32 ng/ml (less than 30 days of age), to 2.30 ± 0.83 ng/ml (181 to 210 days of age), and the level after 151 days was significantly higher than that of the cyclic cows, except during estrus.     

Induced breeding in anestrous milking ewes of dairy breeds: Comparison of norgestomet,medroxyprogesterone and fluorogestone in two regimes of PMSG

The present investigation compares the suitability of norgestomet versus medroxyprogesterone and fluorogestone in inducing breeding in anestrous lactating ewes. Six hundred lactating ewes of two local dairy breeds were randomly divided into three equal groups during the spring. Ewes in group I were treated with 60 mg of medroxyprogesterone and in group II with 40 mg of fluorogestone using impregnated polyurethane vaginal sponges for 14 days. Ewes in group III were treated with 1.3 mg of norgestomet in impregnated mini-implants, placed subcutaneously in dorsal pinnae of the ear. The day the sponges and implants were removed, the ewes in each group were randomly allocated in two subgroups, a and b, and received 500 I.U. and 1,000 I.U. of PMSG, respectively. Vasectomized rams were used for estrus detection and fertile rams for hand mating. The percentage of estrus exhibition and subsequent mating was similar among groups (98 and 84%, subgroups Ia and Ib $\text{vs}$ 100 and 100%, subgroups IIa and IIb $\text{vs}$ 100 and 96%, subgroups IIIa and IIIb). The meantime of estrus exhibition ranged between 40.1h ± 6.2h to 42.3h ± 4.1h in IIIa and IIIb, 46.4h ± 6.1h to 49.2h ± 3.9h in Ia and Ib, and 48.3h ± 6.1h to 50h ± 4.6h in IIa and IIb, respectively. The lambing percentage ranged between 59 to 49% in IIIa and IIIb, 62 to 39% in Ia and Ib, and 71 to 28% in IIa and IIb, respectively. The percentage of subsequent estrus returns was ranged between 39 to 50% in IIIa and IIIb, 38 to 59% in Ia and Ib, and 26 to 70% in IIa and IIb, respectively. The lambing percentage of the returns ranged in the same level (86 to 100% in group I $\text{vs}$ 92 to 96% in group II $\text{vs}$ 91 to 90% in group III, respectively) as well as the prolificacy (178 to 209 in group I $\text{vs}$ 187 to 176 in group II $\text{vs}$ 200 to 188 in group III, respectively). It was concluded that induction of breeding in anestrous lactating ewes of dairy breeds, using implants containing only 1.3 mg norgestomet, might be a useful tool to improve efficiency of sheep production.     

Serum profiles of luteinizing hormone,progesterone and total estrogens during the canine estrous cycle

Serum levels of LH, total estrogen and progesterone were measured daily by radioimmunoassay during proestrus, estrus and early diestrus in five beagle bitches. Occurrence of the LH peak relative to the onset of estrus was quite variable ranging from 3 days before to 7 days after the onset of estrus. Serum LH levels were elevated for 3 days with a peak value of 25 ± 2 ng/ml reached 2.4 days after the start of estrus. LH levels were ≤ 2 ng/ml when measured at other times during the estrous cycle. Estrogen titers ranged from 84 ± 39 pg/ml at 9 days before the LH peak to 175 ± 15 pg/ml coincident with the LH peak. A broad estrogen peak was evident beginning 5 days before and continuing for 5 days after the LH peak. An estrogen surge was seen in 4 of 5 dogs immediately preceding or coincident with the LH peak suggesting that LH release in the bitch is triggered by a sharp elevation in estrogen levels. Serum progesterone levels rose from ≤ 5 ng/ml before the LH peak to 46 ± 6 ng/ml 6 days afterwards.     

Periodic fluctuations in FSH concentrations during the ovine estrous cycle

Heterologous radioimmunoassays for ovine LH and ovine FSH were validated and used to examine the concentrations of gonadotropins during the estrous cycle. Concentrations of LH were maximal on the day of estrus as previously reported. Concentrations of FSH were minimal 1 or 2 days before estrus, increased markedly during estrus, and fluctuated widely during diestrus. Most ewes ($\text{11}\text{13}$) had periodic waves of FSH occurring at short intervals (3.5–6 days, $\text{3}\text{13}\text{ewes}$), long intervals (10–18 days, $\text{3}\text{13}\text{ewes}$), or at both long and short intervals ($\text{5}\text{13}\text{ewes}$).     

Treatment with recombinant bovine somatotrophin enhances ovarian follicle development and increases the secretion of insulin-like growth factor-I by ovarian follicles in ewes

To investigate the effect of recombinant bovine somatotrophin (rGH) on ovarian folliculogenesis in sheep, 18 mature Scottish Blackface ewes were assigned randomly to two treatment groups. Starting from day 5 of the synchronised oestrous cycle, animals were injected daily with either vehicle (control group) or 12.5 mg rGH (rGH-treated group) for 7 days. Blood samples were collected once daily during the experimental period for the measurement of growth hormone (GH), insulin-like growth factor-I (IGF-I), insulin, follicle-stimulating hormone (FSH), luteinising hormone (LH) and progesterone. At the end of treatment animals were killed and ovaries collected. All follicles at least 1.0 mm in diameter were dissected out and diameters measured to assess follicular populations for individual animals. Five small follicles (1.0–3.4 mm in diameter) and all the large follicles (at least 3.5 mm) from each animal were incubated in 1 ml of Medium 199 for 1 h. Medium was then changed and incubation continued for a further hour. All medium samples were assayed for IGF-I, oestradiol, testosterone and progesterone.Treatment of ewes with rGH had no effect on the total number of follicles at least 1.0 mm in diameter (control, 34.4 ± 2.6; rGH-treated, 31.3 ± 1.4; P > 0.2). However, when follicles were further classified into different size categories (1.0–2.0, 2.1–3.0, 3.1–4.0, 4.1–5.0, 5.1–6.0 and over 6.0 mm in diameter), the population of follicles 2.1–3.0 mm in diameter was significantly increased by rGH treatment (control, 9.2 ± 0.7; rGH-treated, 13.8 ± 1.1; P = 0.02). The number of follicles of 3.1–4.0 mm diameter in the rGH-treated group tended to be increased (P = 0.09), whilst the population of follicles 1.0–2.0 mm in diameter was reduced (P = 0.07). Treatment of ewes with rGH significantly increased peripheral concentrations of GH (P < 0.01), IGF-I (P < 0.01), insulin (P < 0.01) and progesterone (P < 0.05). There was no effect of rGH treatment on circulating concentrations of FSH and LH. Both large and small follicles from rGH-treated ewes secreted significantly (P < 0.001) more IGF-I (37.8 ± 2.2 ng ml h⁻¹, n = 50) than follicles from the control group (26.7 ± 1.6 ng ml⁻¹ h⁻¹, n = 73). However, there was no significant effect of rGH treatment on the secretion of oestradiol, testosterone and progesterone by either large or small follicles.It is concluded that treatment of mature ewes with rGH can enhance the development of ovarian follicles to the gonadotrophin-dependent stages. Furthermore, rGH appears to act through increased secretion of ovarian IGF-I, as well as increased peripheral concentrations of IGF-I and insulin.     

Effect of active immunisation against testosterone-3-BSA on circulating levels of testosterone, LH, prolactin and testosterone antibody titre in the male rat

Male Sprague-Dawley rats were actively immunised against testosterone-3-bovine serum albumin (T-3-BSA) and on appearance of detectable anti-testosterone antibodies, elevated serum testosterone and LH concentrations were observed. These concentrations reached values of >28 μg/100ml testosterone and 16 μg/100ml LH in some animals after 5 months of immunisation. The corresponding prolactin values did not appear to differ significantly from controls. The circulating bound testosterone fraction as determined by equilibrium dialysis, rose from 65.0 ± 2.75% before immunisation to 98.7 ± 0.75% in those animals possessing high titre antisera. This entailed a nett $\text{decrease}$ in the concentration of unbound steroid from 144 ± 49 ng/100 ml to 78 ± 25 ng/100ml.     

The effects of prostacyclin (PGI2) and 6-keto-PGF1α on bovine plasma progesterone and LH concentrations

Injections of 1 mg PGI₂ directly into the bovine corpus luteum significantly increased peripheral plasma progesterone concentrations within 5 min. Concentrations were higher in the PGI₂-treated heifers than in saline-injected controls between 5 and 150 min and at 3.5, 4, 5, and 7 h post-treatment. Levels tended to remain elevated through 14 h. Saline and 6-keto-PGF_1α were without effect on plasma progesterone levels. The luteotrophic effect of PGI₂ was not due to alterations in circulating LH concentrations. An $\text{in vitro}$ experiment assessed the effects of either PGI₂ alone or in combination with LH on progesterone production by dispersed luteal cells. Progesterone accumulation over 2 h for control, 5 ng LH, 1 μg PGI₂, 10 μg PGI₂, and 10 μg PGI₂ plus 5 ng LH averaged 99 ± 42, 353 ± 70, 152 ± 35, 252 ± 45, and 287 ± 66 ng/ml (n=4), respectively. Thus PGI₂ has luteotrophic effects on the bovine CL both $\text{in vivo}$ and $\text{in vitro}$.     

Effects of systemic and intrafollicular injections of LH,prostaglandins, and indomethacin on the luteinization of rabbit Graafian follicles

The possibility that initiation of luteinization in ovarian follicles by luteinizing hormone (LH) is mediated by prostaglandins (PG's) was investigated in rabbits. Estrous rabbits, given an ovulatory dose of LH (50 μg) intravenously, were administered indomethacin (IM), an inhibitor of PG biosynthesis, by various routes. Progesterone levels in the serum and in the induced corpora lutea (CL) were subsequently measured by radioimmunoassay. Continued daily subcutaneous injections of IM from 2 days before through 2 days after LH treatment reduced the corpus luteal level, measured at 72 hours post-LH, of PGF from 208 ± 43 to 98 ± 20 pg/CL (P < 0.025) and that of PGE from 272 ± 31 to 115 ± 9 pg/CL (P < 0.005). At the same time, progesterone levels were 72 ± 12 and 93 ± 10 ng/CL (P > 0.05) in the oil-treated and IM-treated rabbits, respectively. Serum progesterone continued to rise in a linear fashion during the period from 24 to 72 hours following LH treatment, whether IM was injected or not. Intrafollicular treatment with LH (100 ng/follicle) raised the progesterone content in the treated follicles 72 hours later from 1.1 ± 0.5 to 50.1 ± 13.5 ng. (P < 0.01). This progesterone content reached 21.5 ± 15.8 ng (P < 0.05) in follicles similarly treated with PGE₂ (5 μg/follicle), but remained meagre at lower doses of PGE₂ (100 ng/follicle and 2 ng/follicle). Serum progesterone increased from 0.5 ± 0.1 to 1.2 ± 0.1 ng/ml (P < 0.005) within 72 hours in rabbits treated intrafollicularly with LH, but remained unaltered in those similarly treated with PGE₂ (P > 0.1). Intrafollicular injections with PGF_2α failed to induce changes in either level of progesterone. It is concluded that prostaglandins probably do not mediate the luteinizing action of LH in rabbit Graafian follicles, although some degree of luteinization can be induced by high levels of exogenous PGE₂.