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Roe deer are seasonal breeders with a complete yearly testicular cycle. The peak in reproductive activity is recorded during summer, the rutting period, with the highest levels of androgens and testicular weight. Melatonin plays a pivotal role in seasonal breeders by stimulating the hypothalamus–pituitary–gonads axis and acting locally, in different species, its synthesis within testes has been reported. The aim of this study was to evaluate the physiological melatonin pattern within roe deer testes by comparing data obtained from animals sampled during pre- and post-rut periods. Melatonin was quantified in testicular parenchyma, along with the genetic expression of enzymes involved in its local synthesis (AANAT and ASMT) and function (UCP1). Melatonin receptors, MT1-2, were quantified both at protein and gene expression levels. Finally, to assess changes in reproductive hormonal profiles, testicular dehydroepiandrosterone (DHEA) was quantified and used for a correlation analysis. Melatonin and AANAT were detected in all samples, without significant differences between pre- and post-rut periods. Despite DHEA levels confirming testicular involution during the post-rut period, no correlations appeared between such involution and melatonin pathways. This study represents the first report regarding melatonin synthesis in roe deer testes, opening the way for future prospective studies in the physiology of this species.

Steroids, providing information regarding several biological patterns including stress and sexual behavior, have been investigated in different matrices in laboratory mice. Data regarding hair quantification, indicative of longer timespans when compared to blood and saliva, are lacking. The aim of the work was to analyze the hormonal hair profile of laboratory male mice and to investigate potential relationships with age and housing, as a potential tool for welfare assessment. Fifty-six adult male C57BL/6J and C57BL/6OlaHsd substrain mice were included in the study, housed in pairs or groups. Testosterone (T) and dehydroepiandrosterone (DHEA) were quantified by radioimmunoassay, corticosterone (CORT) by ELISA. Mean hormone levels were 6.42 pg/mg for T, 23.16 pg/mg for DHEA and 502.1 pg/mg for CORT. Age influenced all hormones by significantly increasing T and DHEA levels and decreasing CORT, only DHEA, significantly higher in grouped mice, was influenced by housing conditions. The influence of age indicates the need for accurate age-related reference intervals, while the higher levels of DHEA in grouped animals suggests that such housing practice may be beneficial for social interactions. In conclusion, it seems that hair hormones quantification may be a good tool for welfare assessment in laboratory mice and may help in refining husbandry.

The red deer (Cervus elaphus L., 1758) is one of the largest deer species in the world. Females are seasonal polyestrous, with negative photoperiod: the increase of the night peak of melatonin determines the secretion of GnRH and, therefore, LH and FSH. To date there is little information regarding the hormonal control during pregnancy for this species; this could be due to the difficulty of sampling wild subjects, while farmed animals’ hormonal concentrations may not reflect the physiology of the animal in a natural state. In this study we evaluated the concentration of cortisol and progesterone, extracted from blood and hair, on 10 wild and pregnant red deer females. Belonging to the population of the Bolognese Apennines (Italy), the hinds were sampled in the January−March 2018 period, according to the regional selective hunting plan. Plasma progesterone (P4) ranged from a minimum of 1.9 to a maximum of 7.48 ng/mL; while hair P4 concentrations varied from 41.68 to 153.57 pg/mg. The plasma and hair cortisol ranges are respectively 0.4−2.97 ng/mL and 0.03−0.55 pg/mg; the only significant correlation was found between hair concentration of P4 and the date of death. The results of this preliminary study represent a small step towards a better knowledge of this species’ physiology during pregnancy.

Donkey jenny's corpus luteum (CL) response to PGF2α analogues has not been investigated in depth. Aim of this study was to evaluate the donkey jenny's corpus luteum (CL) ultrasonographic characteristics (diameter, area and vascularized area) by B-Mode, Color Doppler and serum progesterone concentration ([P4]) after treatment with the prostaglandins F2α analogue alfaprostol at day 3 or day 6 after ovulation (groups PG3 and PG6, respectively). [P4] was positively correlated (P

Inclusion of sustained-release androgen implants into fertility treatment regimes of female freshwater eels has been proposed to benefit artificial maturation outcomes. This study sought to test whether co-administration of the androgen 17-methyltestosterone (17-MT) in combination with ‘traditional’ hypophysation of female European silver eels would affect egg quality and subsequent larval survival. Implants, containing 1 mg 17-methyltestosterone (17α-methyl-4-androsten-17β-ol-3-one in a matrix of cholesterol:cellulose = 95:5), were administered twice, at 1 and 5 weeks after onset of experimentation (MTA- and MTB-groups); control eels (Ctrl) were given a blank implant. Female eels received weekly injections with carp pituitary homogenates (CPH) from either Week 1 (MTA- and Ctrl groups) or Week 5 onwards (MTB-group). First 4 injections were made with 10 mg CPH/kg body weight (BW) in sterile physiological saline (0.9% NaCl); the subsequent 12 injections with 30 mg/kg CPH and thereafter, 40 mg/kg CPH was injected until fish were considered ready for induction of final maturation. Bi-weekly blood samples were collected (Day 0 onwards) and analyzed for levels of testosterone (T) and estradiol-17β (E2) by radioimmunoassay. After reaching maturity, fertilized eggs were obtained upon spontaneous spawning of co-housed breeders and egg performance (fertilization, hatching, survival rates) was recorded. No differences were observed between eels from the MTA- and MTB-groups; however, egg performance was notably better in eels treated with 17-MT + CPH compared to eels receiving CPH only, with hatching rates reaching mean values as high as around 70% for both 17-MT and CPH co-treated groups, but only averaging 21.0 ± 8.4% for eggs from the Ctrl-group. Furthermore, 17-MT treated eels displayed a more distinct pre-spawning peak for levels of plasma T and E2 and for body weight, the latter being indicative of increased batch fecundity. We conclude that androgen co-treatment holds promise for future development of eel captive breeding technologies. Statement of relevance Artificial propagation of the European eel is increasingly urgent to release the strain on natural populations. This study presents a novel approach to artificial maturation of female eels: centered around the incorporation of androgens during fertility treatment. Accordingly, increased performance was observed in terms of fertilization, hatching and survival rates, which contributes to completing the life cycle of this fish in captivity. © 2017 Elsevier B.V.

Hair analysis has been proposed as a minimally invasive technique capable of furnishing information regarding the stress response during medium- and long-term periods. Bristle samples were collected from the rump region of sows at three key physiological phases (before delivery - BD; weaning time - WT; pregnancy diagnosis - PD) during consecutive reproductive cycles in order to test swine hair as a reliable matrix of cortisol evaluation. Cortisol was extracted from the bristles and assayed using radioimmunoassay. The highest mean hair cortisol concentrations were demonstrated (p

Summary This study evaluated the carry-over effects of ewe body reserves during early pregnancy on peri-partum adipose tissue metabolism. Forty-nine multiparous ewes were divided in three categories according to their body condition score (BCS) at day 30 of pregnancy (BCS 3, 3.25–3.5). Live-weight (LW) and BCS gains from 1st to 4th month of pregnancy were greater in ewes with BCS 3 animals. In contrast, in the last month of pregnancy, there was BCS decrease in all groups, although LW continued increasing. There were no differences in LW or BCS across ewe categories during this period. Peripheral leptin levels throughout the three last weeks of pregnancy were greater in ewes with BCS > 3 than in the rest, but this difference did not persist after lambing. Plasma metabolites related to energy metabolism, milk yield and lamb growth were not affected by ewe BCS in early pregnancy. Long-chain saturated milk fatty acids (FA) (C16–C24) were greater in ewes with lowest BCS (

Many hormones are involved in the regulation of male reproductive functions, controlling sexual behavior, and influencing sexual arousal, the onset of erection and ejaculation, and the post-ejaculatory detumescence. The aims of this study were to analyze the plasma concentrations of 15-ketodihydro-PGF 2α (PGFM), LH, testosterone (T), oestrone sulphate (OS), and cortisol (C) in relation to sexual stimulation and to evaluate the possible correlations among circulating hormones and between hormones and semen characteristics in the donkey stallion. Thirteen sexually experienced Martina Franca jackass of proven fertility were enrolled and semen was collected through an artificial vagina. Plasma samples were collected at 12, 9, 6 and 3 min before oestrous jenny exposure, at the first erection in the mating arena in the presence of an oestrous jenny, during ejaculation, at dismounting, 3, 6, 9 and 12 min after ejaculation in box, and then every 10 min during the following 50 min. PGFM showed an increasing trend with significant differences between the pre-ejaculatory and post-ejaculatory period, suggesting a role of this hormone in the control of ejaculation. LH showed a significantly higher concentration at ejaculation compared to last samples, while T showed significantly higher levels at erection, ejaculation and dismounting, probably for its influence on these processes and on sexual behavior. Finally, OS did not show any difference in the period of observation, while C presented a significant increase only 22 minutes after erection. The only hormonal correlation found was a positive one between LH and T at erection and dismounting, while T and OS were positively correlated with total and progressive motility, respectively.

The transition from intra- to extrauterine environment represents a very delicate phase, in which the successful coordination of maturation is strictly connected with several hormonal changes during the last weeks of gestation and at parturition. While the peripartal endocrinology in the mare has been deeply investigated, the peripartal hormonal changes in the jenny need further evaluation. The aim of this study is to evaluate the mean 15-ketodihydro-PGF2α (PGFM), cortisol (C), progesterone (P4), and 17β-estradiol (E2) levels during the peripartal period in this species. Ten Martina Franca jennies, with normal gestational length and parturition, were enrolled. From each jenny, blood was collected twice a day from 10 d before to 7 d after parturition and from the plasma obtained PGFM, C, P4 and E2 were analyzed by RIA. Higher, constant PGFM concentrations were observed in the pre-foaling days compared to the decreasing levels detected the days after delivery, as previously observed in the mare. During the whole period of observation no significant differences in plasma C levels were detected. In contrast to the mare, P4 has always been detectable and the highest level found at −2.5 days was significantly different compared to samples obtained between −10 and −4.5 days and between 1.5 and 7 days after foaling. Finally, E2 showed higher concentrations before foaling, with the highest values between −3 and −1.5 days, decreasing only one day before foaling. A positive correlation was found between PGFM and P4, during the last 4 days of gestation, while a positive correlation between PGFM and E2 was observed during the prepartum. Despite some similarities with the mare exist, differences have been found in P4 and E2 profiles, underlining once more the differences in the physiology of this two species.

Hormonal changes during early neonatal life play a major role in the physiological processes underlying the maturation of several organs. Since prostaglandins and cortisol are associated with fetal organ system maturation, the aim of this study was to evaluate 15-ketodihydro-PGF2a (PGM) and cortisol plasma concentrations during the first 21 days after birth in foals born by either spontaneous (24 foals) or low-dose oxytocin (OT)-induced parturition performed after at least 320 gestational days (25 foals) since induction is often considered to be a cause of prematurity. After spontaneous birth, the PGM concentration was significantly (P < 0.05) higher at 20 and 30 min compared to samples taken several hours or days later, while induced foals showed significantly (P < 0.05) higher concentrations at 10, 20, and 30 min. Regarding differences between the two groups, the plasma concentration of PGM was significantly higher 10 (P < 0.01), 20 (P < 0.05), and 30 (P < 0.05) min and 3 h (P < 0.05) after birth in induced foals compared to foals born by spontaneous parturition. It is difficult to determine whether the higher initial PGM concentrations in induced foals is related to higher uterine or fetal PGM release induced by exogenous OT stimulation. Cortisol plasma levels in both groups were higher at birth (P < 0.05) compared to the later sampling times. No differences were observed between the two groups indicating that the induction protocol used does not seem to result in premature foals.

The aims of this study were to study the effects of fasting on progesterone (P4) production in the pig and to verify whether fasting influences luteal expression of PGF(2alpha) receptor (FPr) and prostaglandin secretion. Superovulated prepubertal gilts were used; half of them were fasted for 72h starting on day 2 (F2) or 9 (F9) of the induced estrous cycle, respectively, while two groups (C2 and C9) served as respective controls. Plasma P4 and PGFM concentrations were determined by RIA while FPr mRNA expression in CLs collected at the end of fasting period was measured by real-time PCR. In experiment 1, plasma P4 concentrations in fasted gilts were significantly (P

Contents Ghrelin, the endogenous ligand of the growth hormone (GH) secretagogue receptor, is considered a pleiotropic regulator involved in a large array of functions, including control of energy balance, regulation of food intake and, more recently, modulation of the reproductive axis. The present study was aimed at determining the changes in plasma concentrations of acyl-ghrelin in pregnant and lactating sows, with special emphasis on the relationship with the levels of GH, leptin, non-esterified fatty acids (NEFA) and insulin-like growth factor (IGF-1). Blood samples were collected via jugular venipuncture from 22 multiparous sow 30, 60 and 90 days after artificial insemination, 7 and 21 days after farrowing and at first oestrus post-weaning. Plasma concentrations of acyl-ghrelin, leptin, GH and IGF-1 were quantified by validated radioimmunoassay; NEFA were determined using a colorimetric procedure. Plasma acyl ghrelin levels were highest at 30 days of pregnancy and decreased thereafter and during lactation. At the beginning of lactation, GH, IGF-1 and NEFA concentrations significantly increased, while a significant reduction occurred in leptin. In conclusion, ghrelin concentrations in sow maternal circulation does not seem to play an important role in maintaining circulating GH levels during lactation; moreover, ghrelin is not associated with leptin, NEFA and IGF-1 levels.

Ghrelin is a peripheral circulating hormone, mainly released from the stomach, which can stimulate food intake. We studied fed, fasted and fasted-refed prepuberal gilts in order to outline possible changes in gastric mucosal ghrelin cells and in plasma ghrelin profiles in reponse to food deprivation. Acyl-ghrelin-immunoreactive cells were numerous in oxyntic glands, less abundant in cardiac glands and least frequent in pyloric glands, with the addition of a minor population of labelled cells in the gastric pit mucosa. When fed and fasted animals were compared (72-h fast versus fed; n=4 each), no clear-cut differences were revealed in labelled cell numbers, nor in their staining intensity. An RIA for plasma porcine acyl-ghrelin (n-octanoylated at Ser-3), not recognizing des-acyl-ghrelin, was validated. Plasma acyl-ghrelin progressively increased upon fasting (over 6, 12, 24 and 48 h); ghrelin levels significantly (P

This study was designed to verify whether fasting influences vascular endothelial growth factor (VEGF) production and VEGF, VEGF receptor-2 (VEGFR-2) as well as endothelin (ET) system members (endothelin converting enzyme-1, ECE-1; ET-1; endothelin receptor type A, ET-A) mRNA expression in pig corpora lutea; furthermore, we wanted to assess whether fasting affects steroidogenesis in luteal cells. Eight prepubertal gilts were induced to ovulate and were randomly assigned to two groups: (A) n = 4, normally fed; and (B) n = 4, fasted for 72 h starting 3 days after ovulation. At the end of fasting, ovaries were removed from all the animals and corpora lutea (CLs) were collected. VEGF and steroid levels in luteal tissue were determined by ELISA and RIA, respectively; VEGF, VEGFR-2, ET-1, ET-A and ECE-1 mRNAs expression was measured by real-time PCR. VEGF protein levels were similar in the two groups, while all steroid (progesterone, testosterone, estradiol 17beta) concentrations were significantly (P < 0.001) higher in CLs collected from fasted animals compared with those from normally fed gilts. VEGF, VEGFR-2, ET-1 and ECE-1 (but not ET-A) mRNA expression was significantly lower (P < 0.05) in fasted versus normally fed animals. The overall conclusion is that all the parameters studied are affected by feed restriction, but the mechanisms activated at luteal level are possibly not fully adequate to compensate for nutrient shortage.

The aim of the present study was to verify how repeated ovum pick-up (OPU), performed in anestrous and cyclic mares, affect ovarian activity, measured by progesterone (P4) and 17ß-estradiol (E2) plasma levels. Ovum pick-up of all visible follicles was performed every 9 to 12 days, and four sessions were carried out during anestrous (A) and breeding season (BS). The number of aspirated follicles per mare at each session was not significantly different between the two periods (BS: 6.1 ± 2.4; A: 7.5 ± 4.4; P0.05), but the mean follicular diameter was significantly higher during BS (16.0 ± 7.1 vs. 10.2 ± 5.1 mm; P0.05); during A the number of aspirated follicles less than 15 mm in diameter resulted significantly higher than that registered in BS (5.1 ± 2.7 vs. 3.0 ± 1.8; P0.05). The total mean value of P4 was higher in BS than in A (6.3 ± 4.4 vs. 0.3 ± 1.8 ng/mL; P0.05), whereas the total mean level of E2 was not different between the two periods (3.8 ± 3.4 vs. 2.5 ± 2.7 pg/mL; P0.05). Estradiol plasma values resulted positively correlated, in A and BS, with diameter of follicles detected on the ovaries (R = 0.345 and R = 0.331, respectively), whereas a negative correlation was observed between P4 and follicular diameter in BS (R = -0.162). Both E2 and P4 presented a high individual variability during BS; in particular, in three of seven mares, P4 trend was compatible with a normal estrous cycle, and the interval between two consecutive peaks was 21 days. In two of seven mares, with CL at first OPU, P4 concentrations remained more than 3 ng/mL throughout the entire treatment period. Finally, in two of seven animals, P4 levels initially showed a similar pattern to that of a normal estrous cycle, then, after the second aspiration, they remained consistently higher than 3 ng/mL. When the procedure was carried out in cyclic animals, the influence of this technique on ovarian activity seemed to be related to individual variability although, according to progesterone values, structures observed on the ovaries after aspirations presented luteal function. Furthermore, the resumption of normal ovarian activity, after repeated OPU sessions, occurred in a period not much longer than the duration of a normal estrous cycle (25.4 ± 5.2 days). Data recorded during nonbreeding period showed that repeated OPU in anestrous mares do not affect ovarian activity and do not anticipate the resumption of ovarian cyclicity. However, based on the number of aspirated follicles in anestrous and cyclic mares, both types of subjects could be considered as oocyte donors.

Embryo transfer (ET) in the donkey resulted in a very low recipient pregnancy rates. The aim of these studies was to investigate if nonsurgical transfer techniques or donkey embryo quality affect donkey recipient pregnancy failure. In Study 1, the impact of transfer technique was investigated by evaluating if cervical catheterization is associated with prostaglandin release and suppression of luteal function and if donkey recipients would become pregnant after nonsurgical transfer of horse embryos. Four jennies, from 5 to 8 d after ovulation, were submitted to a sham transcervical ET and to evaluation of PGFM and progesterone plasma concentrations. Five 8 d horse embryos were nonsurgically transferred into synchronized donkey recipients (HD). Cervical stimulation caused a transient PGF(2α) release in two of four jennies in the absence of a significant decrease in progesterone plasma concentration. All transferred horse embryos resulted in pregnancies in the jenny recipients. In Study 2, donkey embryo viability was investigated by 1.2 meters, 6-diamidino-2-phenylindole (DAPI) staining of 10 embryos and by the transfer of 6 and 12 donkey embryos in synchronized mare (DH) and donkey (DD) recipients, respectively, of known fertility. The estimated proportion of dead cells in DAPI stained embryos was 0.9% (range 0-3.9%) and below what is considered normal (20%) for horse embryos. Three of six and six of 12 of the DH and DD ETs, respectively resulted in pregnancies at 14 and 25 d (50%), a higher pregnancy rate than previously reported after DD ET. The overall results of this study suggest that the transcervical technique for ET and donkey embryo viability are not the reasons for the low pregnancy rates that have previously been described in donkey recipients, and that nonsurgical ET in donkeys can result in acceptable results.

This experiment was designed to determine the effects of sexual stimulation on plasma concentrations of oxytocin (OT), vasopressin (VP), 15-ketodihydro-PGF(2alpha) (PG-metabolite), luteinizing hormone (LH), testosterone (T), estrone sulfate (ES), and cortisol (C) in stallions. Semen samples were collected from 14 light horse stallions (Equus caballus) of proven fertility using a Missouri model artificial vagina. Blood samples were collected at 15, 12, 9, 6, and 3 min before estrous mare exposure, at erection, at ejaculation, and at 3, 6, and 9 min after ejaculation. Afterwards, blood sampling was performed every 10 min for the following 60 min. Sexual activity determined an increase in plasma concentrations of OT, VP, C, PG-metabolite, and ES and caused no changes in LH and T concentrations. The finding of a negative correlation between C and VP at erection, and between C and T before erection and at the time of erection, could be explained by a possible inhibitory role exerted by C in the mechanism of sexual arousal described for men.

Since results with using sulpiride and domperidone are conflicting and since both have not been tested at the same time, the aim of this study was to compare the efficacy of these substances for the induction of ovulation in deep anestrous mares in the same experimental conditions and to determine their fertility after artificial insemination (AI) at the induced estrus. Twenty-six non-pregnant, non-lactating standardbred anestrous mares were randomly assigned to three groups and treated daily for 25 days (from February 3rd to February 28th) with either sulpiride (1mg/kg of body weight im SID, n=10), or domperidone (1mg/kg po SID, n=10); 6 animals were used as control. The beginning of the transition period and the first ovulation were hastened in sulpiride (16.4+/-0.8 days) but not in domperidone (46.0+/-3.3 days) treated mares (P0.05). It was concluded that sulpiride is effective in advancing the beginning of transition period and the first ovulation whereas domperidone is successful only in some mares.

Seventeen adult and cyclic Moxoto goats were synchronized using 60 mg MPA vaginal sponge for 11 days and 50 lg cloprostenol, 48 h before sponge removal, and superovulated with 120 mg pFSH i.m. in decreasing doses at 12 h intervals for three consecutive days. In seven goats, 0.2 IU/kg BW/day of long acting insulin was subcutaneously injected at same time as pFSH, and in the other five goats, the same dose of insulin was injected for three consecutive days starting 24 h after mating. Finally, five goats were supplemented with an oral dose of 80 ml/goat/day of propylene glycol continuously during the experiment. The animals were flushed at 7 days after mating and the embryos were classified based on International Embryo Transfer Society criteria. Blood samples were collected every 3 days for insulin assay. Administration of insulin raised the insulin levels of the goats (p < 0.05), whereas in the group treated with propylene glycol, insulin rate was different only between FSH treatment and after mating (p < 0.05). Similar rates of recovery for total (80.05 ± 9.78%) or transferable structures (61.03 ± 15.13%) were obtained. Treatment was not influenced (p > 0.05) by responsiveness to superovulation, which averaged 64%. By contrast, insulin treatments were shown to increase the number of embryos considered excellent with respect to goats supplemented with propylene glycol (p < 0.05). When insulin was given before mating, a strong relationship (r ¼ 0. 90) (p < 0.05) between number of transferable embryo and ovulations was observed in the animals. In conclusion, superovulated goats treated with low doses of exogenous insulin resulted in an enhancement in embryo quality, which was related to changes in circulating insulin concentrations.

In the purpose to provide further information in respect of the relationship between metabolism and post partum (PP) ovarian activity resumption in dairy cows, the aim of the present study was to characterize the energy balance (EB) and leptin, NEFA and IGF-I plasma levels in Swedish Red and White (SRW) cows with and without ovarian activity re-initiation within 7 weeks PP. The study was conducted on 12 primiparous SRW cows fed the same diet as total mixed ration for ad libitum intake. The EB was calculated weekly from parturition until seven weeks PP. Blood samples were collected weekly from one week before until 7 weeks after calving for leptin, NEFA and IGF-I analysis. For progesterone (P4) analysis, blood samples were collected two times per week from parturition until the end of the study. P4 profile was used in addition to the clinical examination to detect cows with and without ovarian activity resumption. The clinical and ultrasonographic examination, coupled with P4 profile analysis showed the resumption of ovarian activity within 7 weeks after calving in 8 (group A) and no ovarian resumption in 4 cows (group B). No significant differences were detected in the whole period of observation in the amount of milk production between the two groups, while the mean milk protein content was significantly lower in group B at the third week PP. The calculated EB was negative in both groups in the first three weeks after calving, but more marked in group B. NEFA and Leptin plasma levels did not show significant differences between the two groups. In conclusion, the results of the present study showed that, when low milk producing primiparous cows are concerned, no significant differences in BW loss, milk yield, EB and leptin and NEFA plasma levels between the cows with and without resumption of ovarian activity within 7 weeks post partum were seen. However, significantly higher IGF-I levels in the first two weeks after calving were found in cows with post partum ovarian activity resumption, highlighting the important role of IGF-I as sensitive signal between metabolism and reproduction.

Leptin may play a role in the endocrine-metabolic processes that guarantee the physiological course of lactation in dairy cattle. This study was aimed at determining the changes in plasma concentrations of leptin and some of the main hormones and metabolites involved in the lactogenetic process in high-yielding dairy cows throughout lactation; we also wanted to assess whether leptin secretion is subjected to seasonal influences. Blood samples were collected from 23 Italian Friesian dairy cows from the end of a lactation to the ninth month of the subsequent one; in addition, blood was sampled from 47 dairy cows in different phases of lactation during February and July. Plasma concentrations of leptin, growth hormone (GH), insulin, prolactin (PRL), glucose, non-esterified fatty acids (NEFA) and urea were quantified by either validated radioimmunoassay (RIA) or enzymatic colorimetric methods. At the beginning of lactation, GH concentrations significantly increased, while a significant reduction occurred in leptin and insulin. This endocrine condition, such as the significant increase in NEFA plasma concentrations, is indicative of a marked lipid mobilization. In the more advanced stages of lactation, when both energy and protein balances become positive, leptin plasma concentrations increased, whereas GH and NEFA concentrations declined. During the summer months, a significant increase in leptin plasma concentrations, irrespective of the phase of lactation, was observed. Collectively, our findings suggest that, in dairy cows, leptin may represent a 'metabolic signal' of animal's status of fattening and nutritional level; in addition, leptin seems to be influenced by photoperiod and environmental temperature.

This study's aim was to examine whether fasting and refeeding would influence leptin levels in both plasma and follicular fluid from prepubertal gilts, and whether insulin affects leptin levels in fasting gilts. In experiment 1, four gilts were fasted for 72 h and then refed. Blood samples were withdrawn during normoalimentation, at the end of fasting, and for 4 h after refeeding. All samples were assayed for leptin; alternate samples were assayed for insulin, glucose and non-esterified fatty acids (NEFA). Fasting caused a decrease in leptin, glucose and insulin levels in plasma, while NEFA concentrations increased. In experiment 2, four gilts were given insulin as a bolus (0.2 IU/kg body weight) after 68 h of fasting. Blood samples were collected every 15 min around insulin administration and were assayed for leptin, insulin and glucose. This experiment shows that insulin administration increases leptin levels during fasting. In experiment 3, gilts were ovariectomized during normal alimentation (n=4), after 48 h of fasting (n=4), and after 48 h of realimentation following 48 h of fasting (n=4). Leptin levels in both plasma and follicular fluid collected after 48 h of fasting were significantly lower than those observed during normoalimentation or refeeding. In conclusion, a transient increase in insulin during fasting is effective in restoring leptin concentrations; in addition, leptin levels in follicular fluid parallel those in plasma.