Nutrient restriction induces failure of reproductive function and molecular changes in hypothalamus–pituitary–gonadal axis in postpubertal gilts

People on a diet to lose weight may be at risk of reproductive failure. To investigate the effects of nutrient restriction on reproductive function and the underlying mechanism, changes of reproductive traits, hormone secretions and gene expressions in hypothalamus–pituitary–gonadal axis were examined in postpubertal gilts at anestrus induced by nutrient restriction. Gilts having experienced two estrus cycles were fed a normal (CON, 2.86 kg/d) or nutrient restricted (NR, 1 kg/d) food regimens to expect anestrus. NR gilts experienced another three estrus cycles, but did not express estrus symptoms at the anticipated fourth estrus. Blood samples were collected at 5 days’ interval for consecutive three times for measurement of hormone concentrations at the 23th day of the fourth estrus cycle. Individual progesterone concentrations of NR gilts from three consecutive blood samples were below 1.0 ng/mL versus 2.0 ng/mL in CON gilts, which was considered anestrus. NR gilts had impaired development of reproductive tract characterized by absence of large follicles (diameter ≥ 6 mm), decreased number of corepus lutea and atrophy of uterus and ovary tissues. Circulating concentrations of IGF-I, kisspeptin, estradiol, progesterone and leptin were significantly lower in NR gilts than that in CON gilts. Nutrient restriction down-regulated gene expressions of kiss-1, G-protein coupled protein 54, gonadotropin-releasing hormone, estrogen receptor α, progesterone receptor, leptin receptor, follicle-stimulating hormone and luteinizing hormone and insulin-like growth factor I in hypothalamus–pituitary–gonadal axis of gilts. Collectively, nutrient restriction resulted in impairment of reproductive function and changes of hormone secretions and gene expressions in hypothalamus–pituitary–gonadal axis, which shed light on the underlying mechanism by which nutrient restriction influenced reproductive function.     

Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 and diestrus: 1.6-10.8 ng mL(-1); P<0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2+/-3.1 ng mL(-1)h(-1)) followed by estrus (25.1+/-2.7) and anestrus (21.0+/-0.4 ng mL(-1)h(-1); P<0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations (R=0.5; P<0.05), but it did not correlate with the interval from PRID removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6+/-28.6 ng mL(-1)h(-1)) when compared to estrous and diestrous mares (349.7+/-53.3 and 370.5+/-40.3 ng mL(-1)h(-1); P<0.05). Follicular size at PRID insertion had no effects on the intervals from PRID removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID were significantly correlated with the interval from coil removal to estrus (R=-0.55, P<0.05) and ovulation (R=-0.72, P<0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.     

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.     

Progesterone profiles in postpartum Holstein dairy cows as an aid in the study of retained fetal membranes, pyometra and anestrus

This study was carried out to investigate the utility of enzymeimmunoassay (EIA) - derived progesterone profiles in the investigation of postpartum reproductive abnormalities and the effect of their use on reproductive performance in Holstein cows. Whole milk samples, collected twice weekly from parturition until confirmation of pregnancy or removal from the herd, were assayed for progesterone (P4) concentration using a commercially available microtitre plate EIA. The sensitivity, specificity, precision and accuracy were satisfactory to distinguish cyclic changes of P4 reflecting ovarian activity. The P4 profiles indicated that retained fetal membranes and anestrus were associated with increased mean intervals to first ovulation and first estrus (P < 0.05). The first luteal phase of cows with pyometra was prolonged compared with that of normal herdmates (P < 0.05). Anestrus cows had an increased number of ovulations before first service and before pregnancy (3.9 and 5.9) in comparison with normal herdmates (2.1 and 3.5; P < 0.05). Calving to pregnancy interval was increased above normal (74.8) for pyometra (125.0) and anestrus (152.7) (P < 0.05). Pregnancy rate for anestrus cows (82%) was lower than for normal cows (100%) and more anestrous cows were culled (27%) than normal cows (5%) (P < 0.5). The P4 profiles indicated that the major problem in the herd studied, anestrus (32% incidence rate), was most likely due to the failure to observe estrus rather than acyclicity.     

Plasma progesterone profiles and fertility status of anestrus Zebu cattle treated with norgestomet-estradiol-eCG regimen

Zebu cattle are notorious for poor fertility characterized by late maturity and long intercalving intervals attributed to a variety of factors, including genetic, nutritional and climatic. The aim of the present investigation, therefore, was to induce fertile estrus in acyclic pubertal heifers and postpartum anestrous Zebu cows by hormonal intervention. Pubertal Hariana and Sahiwal anestrous heifers (n=51) and postpartum cows (n=55) were either assigned a placebo (controls, N=6 for each breed and parity) or treated with 10-d norgestomet (3 mg) subcutaneous ear implants, with an initial injection of 3 mg, im norgestomet + 5 mg estradiol valerate, followed by 500 IU eCG at implant withdrawal (NOR-treated groups). Jugular venous plasma samples were obtained from a total of 28 animals (controls : 4 heifers and 4 cows; NOR-treated : 12 heifers and 8 cows) on Days 0 (implant insertion), 3, 7, 9 and Day 10 (implant withdrawal), every 12 h on Days 11 and 12, and then once daily on Days 17, 24 and 31. All the samples were assayed for progesterone. Almost all (97%) heifers and 81% cows were induced to estrus, the majority (92% heifers and 79% cows) within 120 h of implant removal. Synchrony of the induced estrus was better in cows, but interval to estrus and estrus duration were significantly longer in heifers (P<0.05). Post-treatment fertility, based on Day 28 nonretum rate, first service, and overall conception rates, was better in heifers (78.9, 60.5 and 73.7%, respectively) than cows (77.1, 48.6 and 62.9%, respectively), but the differences were significant only for the overall pregnancy rate (71.8% for heifers and 51.2% for cows; P<0.05). Low pre-treatment plasma progesterone values (<0.5ng/mL) were consistent with ovarian inactivity, confirming the true anestrus status of experimental animals. Controls failed to exhibit estrus and maintained low progesterone concentrations throughout the study. In treated animals, high progesterone values from Day 17 onwards suggested ovulatory estrus. These early luteal phase progesterone concentrations in nonpregnant (P=0.06) and nonpregnant, nonretum (P<0.05) animals were low in comparison with those of pregnant animals. Good fertility resulting from breeding according to estrus, inspite of variable intervals to estrus and estrus duration, advocates its advantage over fixed-time insemination in norgestomet-treated anestrous Zebu cattle.     

Milk progesterone profiles in various reproductive states in dairy buffaloes under field conditions

Fifty-one dairy buffaloes in the last two months of gestation were selected at seven private peri-urban farms in the Peshawar district. Observations were recorded in buffaloes during normal (NBS, August to January) and low breeding seasons (LBS, February to July). After parturition, rectal examination of reproductive organs was carried out. Estrus detection was made through visual observation and the use of intact bull. Postpartum ovulation was confirmed by ovarian palpation per rectum and milk progesterone levels (MPL), determined through radio-immunoassay. MPL was higher (p < 0.01) at various intervals in NBS calves (1.97 +/- 0.30 ng/ml) as compared to LBS calves (0.68 +/- 0.08 ng/ml). During LBS, MPL remained < 0.30 ng/ml up to the third fortnight and started rising later, reaching a peak of 1.27 ng/ml during the sixth fortnight. During NBS, there was a sharp rise in MPL during the second fortnight, reaching 3.64 ng/ml during the sixth fortnight. MPL was significantly different on different experimental farms (p < 0.01). MPL reached the lowest levels on the day of estrus (0.10 ng/ml), reached it's peak on day 7 and started declining on day 17 of estrus. MPL showed two postpartum elevations. In true anestrus buffaloes, MPL remained consistently low. However, in the anestrus period, silent ovulations were also noted, as reflected by increasing MPL without estrus signs. In pregnant buffaloes, MPL remained > 1 ng/ml. Results of the study showed that the low postpartum reproductive performance in dairy buffaloes during LBS was primarily due to inadequate functioning of the corpus luteum in secreting optimum concentrations of progesterone. The higher incidence of silent estrus during LBS indicated improved management for the detection of estrus.     

Ovarian activity and peripheral plasma levels of oestrogens and progesterone in the lactating sow

Ten gilts were examined for peripheral plasma levels of progesterone and oestrogens 3 weeks before and up to 8 weeks after parturition. The sows were slaughtered at different intervals after parturition and the ovaries were examined. Peripheral plasma levels of progesterone decreased dramatically from about 8ng/ml two days before parturition to about 2 ng/ml on the day before parturition. After parturition the mean progesterone level was about 1.5 ng/ml. Maximum oestrone levels of about 7 ng/ml were obtained two days before parturition. After parturition the level dropped to below 0.1 ng/ml. Three sows showed high levels of oestradiol (75–440 pg/ml) without signs of heat during the lactation. In no case were ovulated follicles or periodic corpora lutea registered.     

Effect of repeated injections of GnRH on reproductive parameters in postpartum anestrous dairy cows

To induce cyclicity in dairy cattle with prolonged postpartum anestrous, repeated dosages of gonadotrophin releasing hormone (GnRH) were administered. Twenty-one (21) Holstein dairy cows and heifers calving between October 1, 1989, and January 1, 1990, at the Louisiana State University Dairy were used in the study. The animals were defined as anestrous if their plasma progesterone remained < 1.0 ng/ml until 32 to 36 days post partum. They were randomly assigned to one of two treatment groups. Group 1 (n=6) received two injections 1 hour apart of a GnRH analogue (50 mug) (i.m.). The treatment was repeated twice weekly at 3- to 4-day intervals. Group 2 controls (n=6) received saline (1 ml, i.m.) on the same schedule as Group 1. A maximum of 12 to 13 treatments were given. Cattle that had plasma progesterone >1.0 ng/ml by 32 to 36 days post partum were identified as Group 3, or cyclic contemporaries (n=9). Postpartum anestrous in the herd was 46.2% (18 39 ). Cows in Group 1 had significantly fewer days to first plasma progesterone > 1.0 ng/ml than those in Group 2 (P < 0.05), but more days than Group 3. Cows in Group 1 also had significantly fewer treatments to induce plasma progesterone > 1.0 ng/ml than those in Group 2 (P < 0.05). There were no significant differences among treatment groups in the number of days from calving to first observed estrus or the number of days open (P > 0.05).     

Induction of estrus in cows by a new analogue of PGF2α(alfaprostol)

A new analogue of PGFα, alfaprostol, was used to induce estrus in normally cycling and anestrous cows.Five groups of six animals were treated with single injections of different doses of the drug (4, 5, 6, 7 or 8 mg/animal) on day 10–11 of the estrous cycle. Six cows in anestrus, with palpable corpora lutea, were treated i.m. with 8 mg/animal. The luteolytic properties of alfaprostol were assessed by measuring milk progesterone by RIA for 96 h after treatment and by checking for the subsequent signs of estrus. The dose of 4 mg caused a slight fall in progesterone but did not induce heat; the 5 and 6 mg doses induced estrus in animals and the 7 mg dose was effective in animals. The 8 mg dose produced a sharp reduction in milk progesterone within 24 h, followed by estrus in both the normally cycling and the anestrous groups in animals. No clinical signs of drug intolerance were seen. The present results show that alfaprostol might be of great use for both cycle synchronization in normally cycling cows and for treatment of anestrus caused by a persistent corpus luteum.     

Effects of melatonin supplementation prior to Ovsynch protocol on ovarian activity and conception rates in anestrous Murrah buffalo heifers during out of breeding season

Buffalo heifers have tendency to show anestrus during summer season. Melatonin has been used for correcting summer dependent anestrous via inducing resumption of ovarian activity. Therefore, the investigation was conducted to compare efficacy of melatonin for induction of estrus and conception rate with Ovsynch protocol in summer anestrous Murrah buffalo heifers. Thirty, summer anestrous Murrah buffalo heifers were selected and divided into two groups- treatment (n?=?20; 12 melatonin implants) and control (n?=?10; no treatment). On day 28 post-implant insertion, animals of both the groups were subjected to Ovsynch protocol. Blood sampling and ovarian ultrasonography were conducted to measure plasma melatonin, progesterone concentration and ovarian dynamics, respectively. No animal in either group showed estrus during first 28?days post-implant insertion. However, estrus induction rate was 100% after Ovsynch protocol in both groups. As compared to controls, treatment group exhibited higher (p?<?0.05) plasma melatonin on days 1, 4, 8, 15, 22 and 28 post-melatonin, with highest concentration on day 4. The progesterone concentration increased (p?<?0.05) on days 15 and 22 post-melatonin treatment. The treatment group had larger (p?<?0.05) preovulatory follicle on day of AI, subsequently developed larger (p?<?0.05) corpus luteum and higher plasma progesterone concentrations by day 12 post-AI as compared to the control group. The overall conception rate was 50 and 20% in treatment and control groups, respectively. In conclusion, melatonin treatment along with Ovsynch protocol improved the luteal profiles as well as the conception rate in buffalo heifers when compared with animals treated with Ovsynch protocol alone during summer season.     

Autoclaved, previously used intravaginal progesterone devices induces estrus and ovulation in anestrous Toggenburg goats

Intravaginal progesterone devices are used worldwide for estrus induction in goats. Reused devices are able to induce estrus; however, this can be a health risk within a flock. The objective was to compare new and previously used (and autoclaved) progesterone-releasing intravaginal devices for induction of estrus and ovulation in seasonally anestrous Toggenburg goats. Anestrous goats (n=42) received new intravaginal devices containing 0.3g progesterone (CONTROL), or similar devices previously used for either 6 (USED6) or 12d (USED12) and subsequently autoclaved. All goats received 5mg dinoprost at device insertion and 200 IU eCG 5d later, and all devices were removed after 6d. After device removal, estrus was monitored and females displaying signs of estrus were mated by fertile bucks. Transrectal ovarian ultrasonography was performed after device removal until detection of ovulation. Blood samples were collected for determination of plasma progesterone concentration at different times. There was no difference (P>0.05) among groups CONTROL, USED6 or USED12 for: estrus response (87, 100 or 100%, respectively); duration of estrus (32.3±2.3, 25.2±3.4 or 27.3±4.1h); ovulation rate (100, 88 or 100%); number of ovulations (1.5±0.2, 1.9±0.3 or 1.7±0.3); and pregnancy rate (60, 58 or 67%). Plasma progesterone (P4) concentrations were greater (P<0.05) in CONTROL than in USED6-treated and USED12-treated goats (7.2±1.2, 4.7±0.7 and 4.3±0.6 ng/mL, respectively) at 6h after device insertion; these differences were maintained until 4d after device insertion (3.4±0.4, 2.3±0.2, and 2.5±0.2 ng/mL). Overall, plasma progesterone concentrations were greater (P<0.05) in nulliparous than in lactating goats (3.1±0.8 compared to 2.4±0.6 ng/mL, respectively). In conclusion, autoclaved, previously used intravaginal progesterone-releasing devices resulted in significant lesser plasma progesterone concentrations than new devices, but were similarly effective in inducing estrus and ovulation in anestrous goats.     

Efficacy of a prostaglandin analogue in reproduction in the anestrous mare

A prostaglandin F analogue was studied in anestrous mares: a dose-response study; a study in mares presumed pregnant; and a field evaluation of effective doses in breeding establishments. A dose of 2.0mg given by single subcutaneous injection to mares with initial plasma progesterone levels greater than 1.0ng/ml, caused luteolysis on the basis of decline in plasma progesterone concentrations. Follicle maturation leading to ovulation, accompanied by estrus, was observed, and fertility at mating either by natural service or artificial insemination was satisfactory. A dose of 1.0mg was generally effective for luteolysis, but pregnancy rates were lower than after 2.0mg. A proportion of mares which had less than 1.0mg of plasma progesterone at the time of injection ovulated and became pregnant.     

Clinical evaluation of a new prostaglandin analog in pigs: 2. Prophylaxis and therapy of anestrus after weaning in sows and first litter gilts

Alfaprostol, a new prostaglandin F(2alpha) (PGF) analog was given in a first trial at two dose levels known to be luteolytic (1 and 2 mg) to 200 sows and first litter gilts at the day of weaning after a 21-day lactation period; 189 controls received saline only. The treatment with alfaprostol shortened the interval to heat (6.0 vs 11.3 days; p<0.01) and increased the percentage of animals coming into heat within 10 days (84.0 vs 65.5%; p<0.01). Fertility to a.i. and litter size at the subsequent parturition were normal. In a second trial, 100 first litter gilts and 100 sows received alfaprostol, 1 or 2 mg, respectively, during July and August when high environmental temperatures tend to increase the rate of anestrus. Again, treatment with alfaprostol shortened effectively the interval to heat (5.9 vs 17.4 days in gilts, p<0.001; 5.6 vs 9.7 days in sows; p<0.01) and greatly increased the number of animals in heat (81 vs 47% in gilts, 83 vs 62% in sows; p<0.001). The effect on the seasonal incidence of clinical anestrus was marked; it was more pronounced in gilts than in sows, expressed by the length of time it took to resume cyclic functions and the lower percentage of animals coming into heat (p<0.001). The effect of alfaprostol was equally well expressed in first litter gilts and sows. In a third trial, 295 anestrous sows and gilts were treated on day 22 after weaning with either 2 mg alfaprostol, or 400 I.U. PMSG+200 I.U. hCG, or saline. Within five days after weaning, 38% of the alfaprostol treated, and 78% and 23% of the animals treated with PMSG/hCG and saline came into heat.     

Postpartum reproductive management of dairy cows in a large Florida dairy herd

Dairy cows (n = 199) were assigned randomly at Day 14 post partum to a control group or a programmed reproductive treatment group (PRT). Cows in the PRT group received 8 ug of GnRH on Days 14 and 50 post partum and 25 mg of PGF2alpha injected on Days 21, 34 and 57 post partum. Cows in the PRT group had a greater frequency of progesterone (P4) concentrations > 1 ng/ml (50% vs 30%; P < 0.01). Frequency of cows having P4 > 1 ng/ml at both Days 21 and 34 post partum was greater in the PRT group than in the control group (39% vs 20%; P < 0.01). Accumulation of days with a palpable cystic ovary was lower in the PRT than the control group (11.4% vs 6.5%; P < 0.05). The frequency of anestrous cows through Day 57 post partum was not different between the 2 groups. Cows that were anestrous had a lower body condition score throughout the postpartum period than the cyclic cows (2.7 vs <3.0; P < 0.01). Conception rate to first service, conception rate to all services, services per conception and days open were not different between the groups. Intensity of estrus detection was low for the study based on a low estrus detection rate (42%) and a low palpation pregnancy rate index (below 68%) throughout the study period. Accuracy of estrus detection was low based on the distribution of normal interestrus intervals for the study (19 to 23 d; 13.5%). It is concluded that programmed reproductive treatments during the postpartum period are functionally effective relative to altered ovarian activity; however, potential advantages to such a system are not evident without good estrus detection practices in a large commercial herd.     

Monitoring ovarian cyclicity in postpartum Murrah buffalo through milk progesterone enzyme immunoassay

Milk samples were collected from Murrah buffalo between Day 30 and Day 120 post partum and analysed for progesterone concentration to monitor ovarian cyclicity. Progesterone levels were low (1 to 5 ng/ml) during the anestrous period. Levels were also low around estrus, but they began to increase at Day 6 postestrus; high levels (15 to 32 ng/ml) were maintained for different periods. There was a marked drop in progesterone level after Day 16 to 18 of the estrous cycle in those animals which returned to estrus. Progesterone levels remained high in buffalo which did not return to estrus, indicating that these animals were pregnant. Some of the progesterone cycles were not associated with the expression of estrus. This study indicated that a milk progesterone enzymoimmunoassay can be used to detect early pregnancy as well as conditions such as silent estrus and anovulatory estrus; it can thus help reduce the long intercalving period in buffalo.     

Seasonal variations in characteristics of estrous cycles in pubertal Brahman heifers

A group of pubertal Brahman heifers (n = 16) was monitored from October through March to investigate the seasonal changes in estrous cyclicity. The heifers had a mean age of 16.7 +/- 0.3 mo at the initiation of the experiment. They were kept on pasture with vasectomized marker bulls. Supplemental feed to meet NRC requirements was provided. Estrus occurrence was checked once a day and blood samples were taken weekly by tail venipuncture from heifers that had been in estrus 7 to 14 d earlier. Samples were processed to yield serum and were assayed for serum progesterone by radioimmunoassay. A high proportion of heifers (88%) had abnormalities such as estrus without the formation of a functional corpus luteum (CL) or anestrus, with a distribution of the two abnormalities as follows: October 0 and 0, November 50 and 25, December 0 and 50, January 0 and 50, February 18 and 31 and March 0 and 7%, respectively. Mean serum progesterone concentrations during the luteal phase differed by month: 4.26, 1.50, 3.25, 2.27, 2.65 and 3.70 ng/ml for October, November, December, January, February and March, respectively (P<0.001). Heifers that went into anestrus had lower mean serum progesterone concentrations than heifers that had regular estrous cycles throughout the study period (1.35 vs 2.22 ng/ml; P<0.0005). The months with the shortest daylengths (December and January) had the highest incidence of anestrus. Transitional periods (November and February) seemed to occur before and after the months with the highest occurrence of anestrus. During this transitional period a high incidence of estrus without the formation of a functional CL was detected. Serum progesterone concentrations were lower in all heifers during the months with high occurrence of abnormal estrous cycles.     

The effects of stress and of ACTH administration in hormone profiles, oestrus and ovulation in pigs

Hormone concentrations and oestrous cycle patterns were studied in five chronically cannulated gilts. During oestrous cycles that were unaffected by stress, plasma oestrogen concentrations remained at basal luteal phase levels (10 to 30 pg/ml) until plasma progesterone had decreased to less than 2 ng/ml. The pre-oestrus surge of oestrogen ranged from 40 to 80 pg/ml. Plasma corticoid concentrations varied randomly and were not related to oestrogen, progesterone concentrations, or the stage of the oestrous cycle. There was, however, evidence of a positive relationship between elevated corticoid levels and observed stressful events. The stress of surgery or illness acting during the follicular phase of the oestrous cycle delayed the onset of oestrus, and corticoid levels were frequently elevated on these occasions. Elevated plasma corticoid concentrations in response to ACTH treatment were associated with either a change in the timing of or a suppression of the pre-oestrus LH peak. Altering the timing of the LH peak resulted in the formation of large partially luteinized ovarian cysts, while suppressing LH interfered with follicular development and led to small ovarian cysts. These experiments suggest that stress acting via the adrenal gland may play a role in the aetiology of infertility in sows.     

Influence of season and reproductive status on peripheral plasma progesterone levels in the lactating bovine

Data collected monthly for one calendar year from Holstein cows lactating under Louisiana ambient climatic conditions comprised a total of 264 cowmonths. The year was divided into seasons of cool, intermediate, and hot temperatures. A highly significant (P<0.01) relationship between plasma progesterone and animal age (r=–0.57) was observed. Plasma progesterone concentrations in the hot season (4.6 ng/ ml) were significantly (P<0.01) higher than concentrations in the cool and intermediate seasons (3.4 and 3.8 ng/ ml, respectively). Plasma cortisol concentrations were lower (P<0.01) in the hot season than in the cool and intermediate seasons and suggested the adrenal cortex did not contribute to the increase in progesterone concentrations which occured in the hot season. A significant (P<0.01) positive correlation (r=0.45) between cortisol and progesterone was observed. Reproductive status did not have a statistically significant effect on progesterone levels and the affect of season on progesterone concentrations was consistant across all reproductive status. Plasma progesterone levels in the anestrus animals (3.9 ng/ ml) suggested progesterone secretion was responsible for their failure to cycle. Similar progesterone levels were observed in normal (3.5 ng/ ml) and repeat breeders (3.6 ng/ ml).Presented at the Seventh International Biometeorological Congress, 17–23 August 1976, College Park, Maryland, USA.