Estrogen induces estrus unaccompanied by a preovulatory surge in luteinizing hormone in suckled sows

The objective was to determine if progressive changes occurred in incidence of estrus and patterns of luteinizing hormone (LH) after estradiol benzoate (EB) administration at three stages of lactation. Estradiol benzoate (800 micrograms) was injected at the beginning of the second (7.8 +/- 0.3 days, range 7-8, n = 4), third (15.6 +/- 0.3 days, range 15-16 days, n = 5), or fourth (23.3 +/- 0.5 days, range 22-24, n = 4) wk of lactation. Interval to estrus (h) and proportion in estrus (in parentheses) were 72 (1/4), 88.5 (4/5), and 99 (4/4; pooled SEM = 3.5) for the second, third, and fourth weeks, respectively. Only one animal ovulated during lactation (third week). This animal had a progesterone concentration of 17 ng/ml 1 wk after estrus and an LH concentration above 2.0 ng/ml for 72 through 90 h after EB. In other sows, LH remained less than 1.0 ng/ml after EB. Patterns of LH after EB in sows treated during the fourth week of lactation were increased to a maximum of 0.76 ng/ml by 120 h after EB, which was greater than for those treated during the second or third week (maxima of 0.38 and 0.32 ng/ml, respectively; pooled SEM = 0.07; p less than 0.05). Concentrations of LH in sows that exhibited estrus were greater both before and after treatment than in sows that did not exhibit estrus after EB (p less than 0.05). By 2 wk after weaning, 8 sows had ovulated (6 of these exhibited estrus), and there were no effects of stage of lactation on these responses. We concluded that the behavioral responsiveness to EB increased as lactation progressed. The increased LH in sows treated during the fourth week indicated a partial recovery of the positive feedback response to EB. These data suggested that separate mechanisms caused behavioral and gonadotropin responses to EB in lactating sows.     

Changes in the hypothalamic-hypophyseal-ovarian axis of primiparous sows following weaning or pulsatile gonadotropin releasing homrone administration and weaning

Lactating primiparous sows were used to examine relationships among hypothalamic gonadotropin releasing hormone (GnRH), serum, and anterior pituitary gonadotropins and follicular development after weaning or after administering GnRH pulses (1.5 ug) once hourly for 72 h before weaning. Control sows were either slaughtered at 0 or 72 h after weaning or were cannulated for collection of blood samples until 24 h after estrus. Sows pulsed with GnRH were either slaughtered 72 h after beginning of GnRH treatment or were cannulated for collection of blood samples until 24 h after estrus. Exogenous GnRH pulsed hourly during 72 h prior to weaning stimulated follicular growth as demonstrated by an increase in number of surface follicles >5 mm in diameter and a decrease in number of follicles <5 mm in diameter. Interval (h) from weaning to an increase in estradiol (>16 pg/ml) was less in GnRH-pulsed than in control sows (P < 0.05), but hours from weaning to estrus were similar between groups. Amounts of GnRH in the medial basal hypothalamus (MBH), stalk median eminence (SME), and hypophyseal portal area (HPA) were similar among control sows killed at 0 or 72 h and sows pulsed with GnRH. Serum concentrations of luteinizing hormone (LH) and frequency of release of LH were similar between GnRH-pulsed and control sows, but concentrations of LH and follicle stimulating hormone (FSH) in anterior pituitary were lower in GnRH-pulsed sows than control sows. Administration of GnRH for 72 h prior to weaning in primiparous sows stimulated follicular growth as manifested by increased secretion of estrogen; however, the amount of follicular growth was apparently inadequate to hasten the onset of estrus after weaning.     

Seasonal modulation of luteinizing-hormone secretion in female rhesus monkeys

The seasonal restriction of ovulations in rhesus monkeys is thought to be due to enhanced estradiol (E2)-negative feedback suppression of luteinizing hormone (LH) during the spring and summer anovulatory months. This hypothesis was examined in seven ovariectomized monkeys housed in an outdoor environment and treated with various doses of E2 in a counterbalanced design during both the anovulatory season (May-Jul) and the breeding season (Sep-Nov). Subcutaneous implants of E2 produced levels that mimicked late follicular (LF-100 pg/ml) or periovulatory concentrations (PO-190 pg/ml). Analyses of twice weekly serum samples revealed that during the period of no E2 treatment (NT), basal levels of bioactive LH were significantly lower in the summer than the fall. Although treatment with both doses of E2 lowered basal LH levels during both seasons, the decrease in LH was significantly greater during the summer. Samples collected at 15-min intervals for 2 h revealed that during NT, LH pulses were significantly slower during the summer than in the fall, whereas pulse amplitude did not differ between seasons. Treatment with both doses of E2 either abolished or significantly reduced both LH pulse amplitude and frequency in the summer. In contrast, LH pulses during the fall were not affected by E2 treatment. Response to treatment with LH-releasing hormone (5 micrograms/kg i.v.) revealed that release was significantly reduced during E2 treatment in the summer. These data indicate that seasonal changes in the environment influence both nongonadal control and E2-negative feedback inhibition of LH secretion. The reduced ability of E2 to maximally suppress LH release in the fall can thus account for the seasonally delimited pattern of ovulations observed in rhesus monkeys.     

Seasonal differences in function of the hypothalamic-hypophysial-ovarian axis in weaned primiparous sows

Primiparous sows were fed to appetite during lactations that occurred during winter or summer, and 11.4 +/- 0.4 pigs per litter were weaned at 23.5 +/- 0.1 days of age. Sows were slaughtered at 0 or 72 h after weaning or blood samples were collected until 24 h after onset of oestrus. Sows that lactated during summer consumed less food and lost more (P less than 0.05) weight, heartgirth and backfat than those that lactated during winter. Weaning-to-oestrus interval was greater (P less than 0.05) in summer (224 +/- 25 h) than in winter (93 +/- 13 h). Content of GnRH in the hypothalamus and concentrations of LH in the anterior pituitary and serum were lower (P less than 0.05) after weaning in summer than winter. The numbers of visible ovarian follicles less than 5 mm in diameter at weaning were lower (P less than 0.05) in summer than in winter. In contrast to LH, FSH concentration in serum was higher (P less than 0.10) in summer than winter, but FSH values in the anterior pituitary were lower (P less than 0.05) in summer than in winter. Post-weaning patterns of secretion of oestradiol and follicular development differed between winter and summer. For example, in some sows weaned during the summer, transient surges of oestradiol occurred repeatedly during 0 to 280 h after weaning without provoking surges of LH. These results indicate that the period of post-weaning anoestrus in summer is prolonged because of altered activity of the hypothalamic-pituitary axis, possibly because of changes in sensitivity to the feedback of oestradiol. Lower feed intake during lactations that occur during summer may predispose the endocrine system to the aberrations.     

Treatment of long-term anestrous sows with estradiol benzoate and GnRH: response of serum LH and occurrence of estrus

Seventeen primiparous sows, anestrous for 41 +/- 4 days after weaning, received i.m. injections of 500 mug estradiol benzoate (EB) or corn oil. At 48 hr after treatment, LH averaged 12.1 +/- 2.6 ng/ml in EB-treated sows and 0.7 +/- 0.1 ng/ml in corn oil-treated sows. At 55 hr after EB or corn oil, each sow was given 50 mug gonadotropin releasing hormone (GnRH). Average LH 1 hr after GnRH was 5.7 +/- 1.1 and 5.1 +/- 0.9 ng/ml in EB- and corn oil-treated sows, respectively. All EB-treated sows exhibited estrus 2.3 +/- 0.2 days after treatment and were mated. None of the corn oil-treated sows exhibited estrus and all were slaughtered two weeks after treatment. Examination of reproductive tracts revealed that the ovaries of corn oil-treated sows were small and did not contain corpora lutea. In mated sows, progesterone concentrations in blood two weeks after mating indicated luteal function in eight of the nine animals. Positive pregnancy diagnoses were made in all eight animals; however, only three sows farrowed, with litter sizes of four, five and seven, respectively. Results of the present experiment indicate that the hypothalamus and anterior pituitary of long-term anestrous sows are capable of responding to endocrine stimuli (i.e. estradiol and GnRH). Moreover, estradiol induced estrus and ovulation, but subsequent farrowing rate was only 33 percent and size of litters was small.     

Effect of exogenous gonadotropins on the weaning-to-estrus interval in sows

The efficacy of PG 600 (400 IU PMSG and 200 IU hCG) for accelerating the onset of estrus was determined for sows weaned during the summer. Yorkshire sows (average parity = 4.6), nursing 8.6 +/- 0.2 pigs (mean +/- SEM) were weaned after 27.7 +/- 0.4 d of lactation and were treated intramuscularly with either PG 600 (n = 35) or with 0.9% saline (n = 35). Sows were checked for estrus once daily in the presence of a mature boar. Treatment with PG 600 increased (P < 0.05) the percentage of sows in estrus within 7 d after weaning (97.1 vs 82.9%). Relative to controls, sows given PG 600 expressed estrus sooner (3.8 +/- 0.1 d vs 4.5 +/- 0.1 d; P < 0.01). Sows exhibiting estrus within 7 d after treatments were artificially inseminated 0 and 24 h after first exhibiting estrus. The percentage of inseminated sows that farrowed tended to be higher (P < 0.07) for control than for PG 600-treated sows (96.6 vs 82.3%). The number of pigs born live was similar (P > 0.1) for sows treated with PG 600 and with saline, and was 12.7 +/- 0.6 and 11.7 +/- 0.7, respectively. Pigs farrowed by saline-treated sows, however, tended to be heavier (P < 0.09) than pigs farrowed by sows treated with PG 600 (1.49 +/- 0.06 kg vs 1.34 +/- 0.06 kg). In summary, PG 600 accelerated the onset of estrus in sows weaned during the summer. Sows mated during the induced estrus, however, tended to have a lower farrowing rate and farrowed lighter pigs than control sows inseminated during a natural estrus occurring within 7 d after weaning.     

Hypersecretion of follicle-stimulating hormone (FSH) on estrous afternoon in rats treated with RU486 in proestrus

Summary 1. Intact or ovariectomized (OVX) cyclic rats injected or not with RU486 (4 mg/0.2 ml oil) from proestrus onwards were bled at 0800 and 1800h on proestrus, estrus and metestrus. Additional RU486-treated rats were injected with: LHRH antagonist (LHRHa), estradiol benzoate (EB) or bovine follicular fluid (bFF) and sacrified at 1800 h in estrous afternoon. LH and FSH serum levels were determined by RIA.2. RU486-treated intact or OVX rats had decreased preovulatory surges of LH and FSH, abolished secondary secretion of FSH and hypersecretion of FSH in estrous afternoon. The latter was decreased by LHRHa and abolished by EB or bFF. In contrast, EB induced an hypersecretion of LH in RU486-treated rats at 1800h in estrus.3. It can be concluded that in the absence of the proestrous progesterone actions, the absence of the inhibitory effect of the ovary in estrus evoked a LHRH independent secretion of FSH.     

Factors affecting temporal relationships between estrus and ovulation in commercial sow farms

The main objective was to examine effects of season, parity, genotype, lactation length, and weaning-to-estrus interval on duration of estrus (DE) and onset of estrus-to-ovulation interval (EOI) in three sow farms. Detection of estrus and ovulation by the back-pressure test and transabdominal ultrasonography, respectively, were performed every 6 h from day 2-10 postweaning in 535 sows (approximately 89 per farm per season). The average weaning-to-estrus interval, DE, and EOI of the 501 sows that returned to estrus by day 10 postweaning were 4.6+/-0.1 days, 55.2+/-0.5 h, and 41.8+/-0.5 h, respectively. Farm x season (P<0.01), parity x season (P <0.05), and farm x weaning-to-estrus interval (P<0.05) interactions for DE and EOI were detected. Sows weaned in the summer had an 8 h longer (P<0.001) DE and EOI than those weaned in the spring on farms 1 and 3. On farm 2 however, DE and EOI did not differ (P=0.09) in sows weaned in summer versus spring. On each farm, parity 3 and > or =4 sows had a 4.5 h longer (P<0.05) DE and EOI than parity 1 and 2 sows in the summer, but there were no differences (P>0.11) in DE or EOI among parity classes in the spring. There was a linear decrease of DE (P<0.001) and EOI (P<0.05) as weaning-to-estrus interval increased from the 3 to the > or =7 day class on each farm. However, the range of weaning-to-estrus interval that exhibited a stepwise decrease of DE and EOI was narrower on farm 1 (3-5 days) than farms 2 and 3 (3-6 days). Only farms 1 and 3 had multiple genotypes. Genotype did not affect (P>0.14) DE on either farm, but the EOI of genotype B was 4 h shorter (P<0.05) than genotype C on farm 1. On each farm, DE decreased linearly (P<0.01) as lactation length increased from < or =13 to > or =20 days. In general, factors that affected EOI also affected (P<0.05) the percentage of inseminations that occurred within 24 h pre- to 3h post-ovulation. These data indicate that factors other than weaning-to-estrus interval, such as season and parity, can significantly alter DE and EOI. However, the effects of season and weaning-to-estrus interval on DE and EOI can be inconsistent among different farms.     

Influence of season and estradiol on secretion of luteinizing hormone in ovariectomized cows

The hypotheses that secretion of luteinizing hormone (LH) varies with season and that estradiol may modulate the seasonal fluctuation in secretion of LH in cows were investigated. Seven mature cows were ovariectomized approximately 30 days before initiation of the experiment. Three of the ovariectomized cows (OVX-E2) were administered a subcutaneous estradiol implant that provided low circulating levels of 17 beta-estradiol. The remaining 4 cows (OVX) were not implanted. From December 21, 1982, to September 20, 1984, blood samples were collected sequentially (at 10-min intervals for 6 h) at each summer and winter solstice, and each spring and autumn equinox. In addition, from March 17, 1983, to March 17, 1984, sequential samples were collected midway between each solstice and equinox. Concentration of LH was measured in all samples, and concentration of estradiol was measured in pools of samples. An annual cycle in mean serum concentration of LH and amplitude of LH pulses was detected in both groups of cows. The seasonal pattern did not differ in the two treatment groups. Serum concentration of LH and amplitude of LH pulses were highest around the spring equinox, decreased gradually to the autumn equinox, and then increased and peaked again during the following spring equinox. Frequency of LH pulses and concentration of estradiol in serum did not vary with season. Circulating concentrations of LH and amplitude of pulses tended to be higher in OVX-E2 than OVX cows throughout the experimental period. Frequency of pulses of LH was lower in OVX-E2 than OVX cows throughout the experiment. Concentrations of estradiol were higher in the implanted cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variation in LH pulsatility during 24h after a postweaning altrenogest treatment in relation to follicle development in primiparous sows

This study assessed pulsatile release of LH during altrenogest treatment after weaning in primiparous sows and related this to follicle development, estrus and ovulation rate. Weaned sows (n=10) received altrenogest 20mg/day from D-1 to D13 (weaning=D0) at 0800 h. On D13, blood samples were collected every 12 min from 1000 until 1900 h (1st sampling period) and from 2300 h until 0800 h (2nd sampling period). During the 1st sampling period, LH concentrations remained low and no LH pulses were detected in 8/10 sows. During the 2nd sampling period, average and basal LH concentrations (P<0.04) and frequency of pulses (P<0.0001) were higher than during the 1st sampling period. Sows with short vs. long intervals to estrus (<5 days vs. ≥5 days) had higher basal and average LH concentrations during the 2nd sampling period (P≤0.004) and showed more follicular growth during treatment (P=0.007), generating larger follicles at D14 (P=0.005). Sows with high ovulation rate (≥25) displayed more LH pulses in total than sows with low (<25) ovulation rates (P=0.03). In conclusion, this study showed that altrenogest efficiently prevented LH pulsatility during the first bleeding period and that low frequency/high amplitude LH pulses were generally present during the second bleeding period. This variability in LH release in between two altrenogest administrations (24h) may explain why follicular growth progresses to 5mm during altrenogest treatments. LH pulsatility was related to length of the follicular phase and ovulation rate, which signifies its relevance.     

Effect of zearalenone and estradiol benzoate on serum concentrations of LH, FSH and prolactin in ovariectomized gilts

Six ovariectomized gilts were given zearalenone (Z), estradiol benzoate (EB) or vehicle in a replicated 3 x 3 Latin square design. Zearalenone was added to 2.3 kg of a corn-soybean ration at a dose of 1 mg Z/kg body weight; EB was given intramuscularly at 0.1 mg EB/kg body weight. Control gilts received vehicle solvent for both Z and EB. Blood samples were collected from indwelling jugular cannulas at 6-h intervals for 48 h before Z, EB or vehicle was given. After treatment, blood samples were drawn at 6-h intervals for an additional 84 h. Serum concentrations of luteinizing hormone (LH) decreased (P<0.001) from 4.67 ng/ml to 0.29 ng/ml within 6 h of EB. From 54 to 84 h after EB, serum concentrations of LH rose to 15.60 ng/ml (P<0.001). Serum concentrations of LH were reduced (P<0.001) in a similar pattern after Z (3.70 ng/ml to 0.49 ng/ml), but a rise in serum LH was not observed 54 to 84 h after Z (1.30 ng/ml). Serum concentrations of LH remained unchanged (P=0.55) in gilts given vehicle. Serum concentrations of follicle stimulating hormone (FSH) were suppressed (P<0.03) at 6 h in EB (19.10 vs 11.35 ng/ml) and Z gilts (16.16 vs 11.41 ng/ml) but remained unchanged in vehicle gilts. Serum concentrations of FSH did not change in EB or Z gilts during the next 36 h. These data indicate that the suppressive action of Z on serum concentrations of LH and FSH was similar to that of EB, while the biphasic stimulatory effect of EB for LH was not manifested by Z.     

Two days of pulsatile GnRH infusion beginning 4 days before weaning in sows initiates a wave of follicular growth that is not sustained after weaning

Intervals to estrus and ovulation in weaned sows depend partially on the diameter of ovarian follicles at weaning. The objective was to determine if follicular diameter in sows could be increased by a 48h period of GnRH infusion before weaning and whether this pre-weaning growth would advance follicular development after weaning. The posterior vena cava was cannulated in eight sows at 10+/-1 day after farrowing. Sows were randomly assigned to receive intravenous treatment with either 2mL of GnRH (1microg/mL; n=4) or 2mL of saline (n=4) every 0.5h for 48h beginning 94h before weaning. The average follicular diameter and the number of follicles within diameter classes were determined daily by ultrasonography. Serum LH concentrations increased on the first infusion day but serum LH was equal to control on the last infusion day (P<0.077). The GnRH infusion increased the average diameter of ovarian follicles (P<0.001). Serum estradiol increased (P<0.001) and serum FSH decreased (P<0.016) coincident with GnRH-induced follicular development but these changes were reversed within 24h after the end of the infusion period. Follicles that grew in response to GnRH regressed and were replaced by a new population of follicles within 4 days after weaning. Within the experimental model for the present study, a GnRH infusion increased follicular growth in lactating sows but follicles could not be sustained beyond the end of GnRH infusion.     

Use of PMSG in the prevention of seasonal post-weaning anestrus in sows

PMSG (500 I.U.; administered I.M.) prevented post-weaning anestrus when given to sows weaned during the months of August, September and October compared to untreated controls during the same months. During winter and spring months, there was no difference in the post-weaning return to estrous rate for treated and control sows. Control sows had a greater degree of estrous synchrony following weaning during winter and spring months compared to summer months. PMSG-treated sows were in estrus earlier (frequently Day 3) than controls. Results indicate that PMSG, given at weaning, is effective in preventing summer-early fall post-weaning anestrus.     

Pulsatile secretion of luteinizing hormone and follicle stimulating hormone and their relationship to secretion of estradiol and onset of estrus in weaned sows

The objective of this experiment was to characterise temporal changes in estradiol and pulsatile secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) during the interval between weaning and estrus in the sow. Five multiparous sows were sampled at 10-min intervals for 3 h beginning 8 h after weaning and continuing every 12 h until estrus. Interval to estrus was 102 ± 2 h (range 96–108) after litters were weaned, and interval to preovulatory LH and FSH surges was 109 ± 5 h (range 92–116). With the exception of the period of the preovulatory surge, neither average nor basal concentrations of LH or FSH changed over time. Number of LH peaks per 3 h reached a maximum of 2.8 at 48 h before the preovulatory surge, then declined to 0.8 at 12 h before the surge. Peak amplitude for LH and peak frequency and amplitude for FSH also declined with time before preovulatory surges. Relative ranks were computed for individual sows based on the mean concentration of LH or FSH for each bleeding period. Rankings were consistent over the periods, but were not correlated with interval to estrus. Estradiol concentrations peaked (88 ± 7 pg/ml) at 36 h before preovulatory surges, coincident with the decline in peak frequency of LH. We conclude that pulsatile secretion of LH and FSH changes during the interval between weaning and estrus but secretion of these two hormones may be controlled by different mechanisms.     

Effect of estrogen administration on endogenous and luteinizing hormone-releasing-hormone-induced luteinizing hormone secretion and follicular development in the lactating sow

The objectives of this study were to investigate whether estradiol treatment during lactation modifies 1) the patterns of endogenous LH, FSH, and prolactin (PRL) release; 2) the sensitivity of the pituitary to exogenous injections of LHRH; and 3) the responsiveness of the ovarian follicles to gonadotropin. Plasma LH, FSH, and PRL were determined in samples taken repeatedly from 18 sows on Days 24-27 of lactation. Ovaries were then recovered, and follicular development was assessed by measuring the follicular diameter (FFD) and follicular fluid estradiol-17 beta concentration (FFE) of the ten largest follicles dissected from each ovary. Sows were randomly allocated to one of four treatments: 1) Group C (4 sows) received no treatment; 2) Group LHRH (5 sows) received 800 ng of LHRH every 2 h throughout the sampling period; 3) Group E2 (4 sows) received subcutaneous implants containing estradiol-17 beta 24 h after start of sampling; 4) Group LHRH + E2 (5 sows) were administered a combination of LHRH and estradiol-17 beta implants. Between-animal variability for plasma LH, FSH, and PRL was considerable. LH concentration and LH pulse frequency increased (p less than 0.05) after LHRH treatment in the LHRH and LHRH + E2 groups; however, an acute inhibition of LH secretion was observed in the latter group immediately after estradiol implant application. In the absence of LHRH treatment, estradiol caused chronic inhibition of LH secretion. Follicular development was greater in the LHRH and LHRH + E2 groups compared to the C and E2 groups (p less than 0.05 for both FFD and FFE).(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors of importance when selecting sows as embryo donors

The improvement in porcine embryo preservation and non-surgical embryo transfer (ET) procedures achieved in recent years represents essential progress for the practical use of ET in the pig industry. This study aimed to evaluate the effects of parity, weaning-to-estrus interval (WEI) and season on reproductive and embryonic parameters at day 6 after insemination of donor sows superovulated after weaning. The selection of donor sows was based on their reproductive history, body condition and parity. The effects of parity at weaning (2 to 3, 4 to 5 or 6 to 7 litters), season (fall, winter and spring), and WEI (estrus within 3 to 4 days), and their interactions on the number of corpus luteum, cysts in sows with cysts, number and quality of viable and transferable embryos, embryo developmental stage and recovery and fertilization rates were evaluated using linear mixed effects models. The analyses showed a lack of significant effects of parity, season, WEI or their interactions on any of the reproductive and embryonic parameters examined. In conclusion, these results demonstrate that fertilization rates and numbers of viable and transferable embryos collected at day 6 of the cycle from superovulated donor sows are not affected by their parity, regardless of the time of the year (from fall to spring) and WEI (3 or 4 days).     

Seasonal variation in the activity of the Leydig cells in Egyptian Nubian goat (Zaraibi) bucks

Ten Egyptian Nubian goat bucks were used to evaluate the effect of season on testicular hormonal activity and ultrastructure. Parameters were recorded for 7 consecutive weeks in the middle of the four seasons, with blood samples being collected weekly. At the end of each of these seasons, testicular biopsies were obtained surgically for histological and cytological studies. Season had a significant effect on plasma testosterone concentration, being at its lowest level (P < 0.01) during winter and spring (1.2 and 2.6 ng/ml, respectively), while at its highest during summer (10 ng/ml). The effect of season on plasma LH concentration was higher (P < 0.01) in autumn (2.9 mIU/ml) and less in spring and summer (0.4 mIU/ml). Season of the year influenced the percentage of sectional tissue area occupied by the seminiferous tubules and interstitial tissue. Seminiferous tubules occupied the majority of the testicular tissue during winter (76.6%), with the least being occupied during spring (49.8%). The thickness of the seminiferous tubules was maximal during autumn, followed by summer (53 and 36 μm, respectively). In summer the Leydig cells contained abundant smooth endoplasmic reticulum (sER), while some areas of the cytoplasm were occupied exclusively by tubular sER, arranged in parallel—indicating the highest activity of these cells. A characteristic multivesicular structure with numerous large lipid droplets and vacuoles was recorded in the Leydig cells during spring and winter, denoting low or even arrested activity of the cells. It could be concluded that season influences the activity of the Leydig cells of Egyptian Nubian bucks, and this is reflected by their ultrastructure and secretive activity.     

The use of oxytocin in liquid semen doses to reduce seasonal fluctuations in the reproductive performance of sows and improve litter parameters—a 2-year study

The objective of the present research was to eliminate seasonal fluctuations in year-round reproductive performance of sows and to improve litter parameters by administration of oxytocin into liquid semen insemination doses. A 2-year experiment was performed on crossbreed sows, Polish Large White × Polish Landrace, which were partitioned into two groups: control, insemination without any modification with 100 mL semen doses and oxytocin, insemination with 100 mL semen doses to which 5 IU of oxytocin was added just before insemination. A total of 10,486 inseminations were made. The farrowing rate and obtained litter parameters, including the effect of season, were analyzed. For each litter, the following factors were defined: average litter size, percentage of fetal death and mummified piglets, average piglet birth weight, percentage of piglet mortality, fecundity index, average number of piglets weaned, weaned piglet weight, and daily gain. Sows presented a positive reaction to the experimental factor. A statistically higher farrowing rate for oxytocin group in summer and autumn seasons was confirmed (P ≤ 0.01). Regardless of the season, a higher average litter size was observed in the oxytocin group with the most evident differences for winter, spring (P ≤ 0.01), and summer (P ≤ 0.05). The effect of oxytocin on the percentage of fetal death and mummified piglets born was not confirmed statistically except for winter. Analyzing the fecundity index, higher values were obtained for the oxytocin group in all seasons (P ≤ 0.01), including the lowest difference between groups for winter (51.43) and the highest for summer (100.61). A higher average birth piglet weight and weaned piglet weight were recorded for the oxytocin group in all seasons. The highest differences in birth piglet weight between groups were noted for spring (0.22 kg; P ≤ 0.01) and winter (0.17 kg; P ≤ 0.05) and in weaned piglet weight for winter and spring (0.58 kg and 0.52 kg; for both, P ≤ 0.01). The greatest daily gains were observed in the winter season (P ≤ 0.05) in favor of oxytocin. On the basis of the presented results, it should be noted that the use of oxytocin into insemination doses improves the farrowing rate and other parameters of the reproductive performance of sows. In the absence of negative effects, year-round insemination with oxytocin addition into seminal doses is recommended, which effectively improves the production performance and reduces the problem of seasonality in reproduction.     

Timing of sexual maturity in female rhesus monkeys (Macaca mulatta) housed outdoors

A comparison of the age and season at first parturition was made for spring-born female rhesus monkeys and for females born in the fall to mothers who had been laboratory-housed before being transferred outdoors. Females (N = 9) born during the fall had first parturition during the spring and summer, as did all spring-born females (N = 68), and not during the fall as would be predicted if age were the determining factor. A separate analysis of post-menarchial, spring-born females (N = 5) beginning in September at 29 months of age revealed that the ensuing 12 months were characterized by low serum levels of oestradiol (less than 50 pg/ml), progesterone (less than 1.0 ng/ml), LH (less than 7.0 ng/ml), and FSH (less than 5.50 micrograms/ml). First ovulation subsequently occurred in the fall in all subjects at a mean age of 41.9 +/- 0.1 months, and was preceded by significant elevations in basal LH and FSH, coincident in time with the transition of summer to fall (September). Female copulatory behaviour was restricted to the period surrounding first ovulation, beginning some 2 weeks before and ceasing within 3 days after the oestradiol peak. The most rapid gain in weight occurred during the summer months before first ovulation, and was associated with significant elevations in serum GH and prolactin. These data suggest that season may influence the timing of sexual maturation in rhesus monkeys kept outside in such a way that the occurrence of first ovulation is restricted to the fall and winter months.     

The relationship between electrical resistance of vaginal mucus and plasma hormonal parameters during periestrus in sows

Sixteen crossbred multiparous sows displaying estrus on Day 5 or 6 after weaning were used in this study. Jugular veins of sows were cannulated on Day 13 of the estrous cycle. Electrical resistance of the vaginal mucosa was measured twice daily on Days 17 to 19 of the cycle and at 4-h intervals (excluding 3 a.m.) during the periestrous period. Blood was sampled every 4 h beginning on Day 17 and continuing for 6 to 7 d. Blood samples were assayed for LH, P₄, E₂, androstenedione (A₄) and testosterone (T) by radioimmunoassay. All data were standardized to maximum LH concentration (0 h). The mean LH surge lasted about 28 h and its mean amplitude was 6.5 + 0.8 ng/ml of plasma. Vaginal electrical resistance (VER) decreased 4 d before the LH peak, remained low for 3 d and gradually started to increase after 0 h. The first signs of estrus were observed 16.9 + 17.8 h prior to the LH peak. The range of the interval was −44 h to +8 h. The increase in VER followed peak LH by 6.2 + 4.5 h. Intervals from peak LH to the beginning of the VER increase ranged from 0 to 16 h. Variation of the interval from the onset of estrus to the LH peak was significantly higher than that of the interval from LH peak to the beginning of the increase in VER (P < 0.005). The decrease in the VER observed during the follicular phase coincided with low levels of P₄ (<1 ng/ml) and increasing concentrations of E₂. Profiles of E₂ and both androgens (A₄ and T) were similar; these hormones increased gradually during the follicular phase of the cycle. The highest values of E₂, A₄ and T were observed before and during the first hours of the preovulatory LH surge. Sows with ovarian cysts (n = 3) had atypical patterns of electrical resistance and aberrant plasma hormone concentrations. These results indicate that measurement of VER can be utilized for detection of LH surges during estrus in sows. Moreover, the monitoring of VER changes provides a more reliable indication of the LH surge than detection of estrus.