A study of diurnal changes in cortisol and glucose levels and FDPA activity in foals during the first 13 weeks of life and in their lactating mothers

1. In six standard-bred mares and their foals diurnal changes in the cortisol and glucose levels and in FDPA activity were studies for 13 weeks of foal life. 2. In the cortisol level diurnal rhythm was found in the 3rd, 7th and 11th week of foal life and in the 11th week of lactation in mares. 3. In mares the mean diurnal cortisol level changed from 32 ng/ml in the first week to 57 in the 11th week and in foals from 24 in the first week to 16 ng/ml in the 11th week. 4. In the glucose level no diurnal rhythm was observed. 5. In mares the mean diurnal glucose level after parturition was about 58 mg/100 ml and increased to 83-85 mg/100 ml. In foals it changed from 105 to 128 mg/100 ml. 6. In the activity of FDPA no diurnal rhythm was observed. 7. The mean activity of FDPA changed in mares from 3.3 to 4.4 U and in foals from 5.7 to 7.5 U.     

Influence of pregnancy on diurnal and seasonal changes in cortisol, T3 and T4 levels in the mare blood serum.

1. The diurnal changes in the level of total protein, cortisol, T3 and T4 were studied in four barren and four pregnant standard-bred mares, kept and examined under the same conditions. 2. Blood samples were taken every 4 hr. for one day each month, throughout one year. 3. In barren mares, a diurnal rhythm in cortisol level (acrophase at 0530 hr in summer and at 0830 hr in winter) and in T3 level (acrophase at 1330 hr in summer and at 1800 hr in winter) was found. 4. In pregnant mares, a diurnal rhythm in cortisol level only till 5th month of pregnancy was observed. 5. A diurnal rhythm in T3 level was found throughout the pregnancy, with acrophase always at 1400 hr. 6. No diurnal rhythm in the total protein content and in the T4 level was observed. 7. In both groups of mares the seasonal cyclicity in T3 and T4 levels were found. A seasonal cyclicity in cortisol level was found only in pregnant mares. 8. Pregnancy abolished seasonal cyclicity in total protein and showed it in cortisol level. 9. Pregnancy in mares modifies diurnal rhythms as well as seasonal cycles in secretion and metabolism of the hormones studied.     

Influence of pregnancy on diurnal and seasonal changes in glucose level and activity of FDPA, AlAT and AspAT in mares.

1. The diurnal changes in the glucose level and in activity of FDPA, A1AT and AspAT in four pregnant standard-bred mares were studied. 2. As a control four barren mares, were kept and examined in the same conditions. 3. Blood samples were taken every 4 hr for one day, each month, throughout pregnancy, or one year. 4. A diurnal rhythm in activity of A1AT and AspAT in barren mares was found. The pregnancy masked diurnal rhythm in activities of both transaminases. 5. No diurnal rhythm in glucose level and FDPA activity in both groups of mares was observed. 6. Seasonal cyclicity was found in all indices studied, in both groups of mares. 7. The pregnancy did not abolish cyclicity in parameters studied but modified their behaviour--causing a shift of acrophases (glucose, FDPA, AspAT) and lowering the amplitudes (FDPA, A1AT, AspAT).     

Diurnal changes in lactic and pyruvic acid levels and pH values in foals during the first 13 weeks of their life and in their lactating mothers.

1. The diurnal changes in the levels of lactic (LA) and pyruvic (PA) acids and values of pH were studied in standard-bred mares and their foals, for 13 weeks of foal life, throughout 2 years. 2. The studies began when a foal was 7 days old and were repeated every 2 weeks until foals reached 13 weeks of age. 3. Blood samples were taken every 4 hr for one day, each second week. 4. In the LA, PA levels and pH values no diurnal rhythm was stated in lactating mares during study periods. 5. In foals the diurnal rhythm in LA and PA occurred in the 3rd month of their life, with the acrophase at night hours. 6. The significant correlations between foal and their mother metabolites studied were observed. 7. The environmental factors (air temperature, humidity) influence fluctuations of the amplitude in parameters studied in the horse blood.     

Diurnal changes in the haemoglobin level, red blood cell number and mean corpuscular haemoglobin in foals during the first 13 weeks of life and in their lactating mothers

1. In six foals and their mothers (of Standard breed) diurnal changes in the haemoglobin level, red blood cell number and mean corpuscular haemoglobin during the first 13 weeks of foal life were studied. 2. Studies begun when a foal reached 7 days of age and were repeated every two weeks till 13 weeks of foal life. Blood was taken every 6 hr in foals and every 4 hr in mares. 3. No diurnal rhythmicity in parameters studied either in foals or in mares was found. 4. Decrease of haemoglobin level in lactating mares (14.0-12.5 g/100 ml) without changes in red blood cell number were observed. Mean corpuscular haemoglobin changed distinctly from one study day to another. 5. In foals were stated: significantly higher haemoglobin level and erythrocyte number and lower mean corpuscular haemoglobin than in mares.     

Influence of pregnancy and lactation on diurnal and seasonal changes in lactic acid and pyruvic acid levels and in values of pH, pCO2 and pO2 in the mare blood.

1. The diurnal changes in the levels of lactic (LA) and pyruvic (PA) acids and in values of pH, pO2 and pCO2 were studied in the blood of barren and later on in pregnant and lactating mares, throughout three subsequent years. 2. Blood samples were taken every 4 hr, for one day, each month, throughout 3 years. 3. The mares were kept and fed in the same conditions, lighting was natural. 4. In barren mares, diurnal rhythm in LA, PA, pO2 and pCO2 was found. 5. The pregnancy as well as lactation masked diurnal rhythms in parameters studied, except the LA level during lactation but then the acrophase was shifted by 3-4 hr. 6. Seasonal cyclicity was found in the values of LA, PA and pCO2 in barren mares. The pregnancy abolished cyclicity in LA level and modified the behaviour of PA and pCO2 values causing a shift of acrophases and lowering the amplitudes of the indices. 7. In the pO2 tensions no seasonal cycles were observed. 8. In the values of pH neither diurnal rhythms nor seasonal cycles throughout study years were observed.     

Circadian and seasonal changes of the inducer:suppressor ratio (OKT4+:OKT8+) in venous blood of healthy adults

Circadian and seasonal variations in the T helper: T suppressor-cytotoxic ratio were investigated in peripheral blood from five healthy young men. Mononuclear cells were isolated on Ficoll-Paque gradient, then incubated with OKT4 and OKT8 monoclonal antibodies. Plasma cortisol was determined in four of these seven time series. Large interindividual differences were documented and statistically validated for the 24-hr.-means of total lymphocytes, OKT4+:OKT8+ ratio, and of plasma cortisol (both total and free). For a pooled data, a circadian rhythm was demonstrated by cosinor (p less than 0.001) for total lymphocytes (acrophase at 1.00 hr.), total plasma cortisol (acrophase at 10.30 hrs.) and free plasma cortisol (acrophase at 9.50 hrs.), but not for OKT4+:OKT8+ ratio. This index however exhibited a statistically significant circadian rhythm in April and August, but not in November. Its double-amplitude exceeded 80% of the 24-hour-mean and its acrophase was localized at 6.40 hrs. in April and at 22.30 hrs. in August. Its 24-hr-mean was higher in August as compared to April and November. The circadian rhythm in the OKT4+:OKT8+ ratio did not seem to be related to that of plasma cortisol. Both circadian and seasonal variations need to be taken into account when investigating the regulations of immune variables such as T helper: T suppressor-cytotoxic ratio.     

Induction of parturition in the mare with prostaglandin F2α

Thirty-one mares of Quarter Horse and Thoroughbred breeding were utilized in two experiments to evaluate the efficacy of prostaglandin F₂α (PGF₂α)_for induction of equine parturition and to monitor the effects of this treatment on viability of the resulting foals.Three of five mares given 5 mg PGF₂α (im) on day 338 of gestation foaled 19.6 ± 8.2 hr postinjection. In the second experiment immediately following 3 daily injections of 10 mg estradiol cypionate (ECP) given on days 326, 327 and 328 of gestation, seven mares were infused (iv) with PGF₂α at the rate of 1.3 mg/hr for 24 hr or until parturition occurred. Four of the seven mares foaled in 8.8 ± 1.8 hr after the start of infusion. Side effects including sweating, hypothermia, increased respiration rate and diarrhea were evident in both injected and infused mares, but effects were transient. Neither the injection, nor infusion route of administration of PGF₁α adversely affected the viability of foals. However, some mares induced to foal 12 days prior to expected parturition had foals with slightly weaker pasterns than those of control mares.     

Endogenous transplacental transmission of Neospora hughesi in naturally infected horses

Over a 2-yr study period, we investigated possible endogenous transplacental transmission of Neospora hughesi in 74 mare and foal pairs following the diagnosis of neuronal neosporosis in a weanling foal. Presuckle and postsuckle serum of each foal, serum and colostrum of each periparturient mare, and serum of each mare and foal pair, collected at 3-mo intervals thereafter, were tested for N. hughesi using an indirect fluorescent antibody test (IFAT). Furthermore, whole blood and colostrum samples and placentae were tested for the presence of N. hughesi by real-time PCR. The mares' seroprevalence at foaling based on IFAT (titer ≥ 160) was 52 and 6% in 2006 and 2007, respectively. Colostral antibodies against N. hughesi were detected in 96 and 11% of the mares in the 2-yr study. With the exception of 3 foals, all remaining foals were born seronegative to N. hughesi. Passive transfer of colostral antibodies to N. hughesi was documented in 15 foals. Three foals born from 2 different mares had presuckle antibodies at a titer ranging from 2,560 to 20,480. All 3 foals were born healthy. Two foals were born to the same dam that also gave birth to the weanling diagnosed with neuronal neosporosis in 2005. The third foal was born to a second mare with no previous foaling history at the farm. Seroconversion was documented in 10 foals and 9 mares over the 2-yr study. All blood and colostrum samples tested PCR negative for N. hughesi. Only 1 placenta collected in 2007 from the mare with the 2 congenitally infected foals tested PCR positive for N. hughesi. In conclusion, N. hughesi persisted in this population via endogenous transplacental infection.     

Maternal care and foal social relationships in a herd of Sorraia horses: Influence of maternal rank and experience

The influence of maternal rank and experience on patterns of maternal care and social relationships of foals were investigated in a managed herd of Sorraia horses, Equus caballus. Social interactions and spatial relationships of 13 foals (seven females and six males) born to seven mares were examined from birth to 10 months of life, within the three major periods of foal development. Conflict over suckling between dam and foal was not generally affected by rank and experience, but higher-ranking mothers allowed more suckling during late lactation than lower-ranking mothers. Foals of higher-ranking mares spent more time in proximity to the mother during socialization. Maternal rank and experience did not significantly affect maternal protectiveness, foal independence from the mother or the development of affiliative relationships between foals and group members. Foals of higher-ranking mares received lower frequencies of aggression from other horses only in the first month of life. Dominance relationships among foals depended mainly on aggressiveness and were not associated with maternal rank. The large variability in maternal behaviour, the absence of a significant association between maternal rank and body condition at parturition and the stable social environment within this herd may partly account for the reported results.     

Use of prostaglandin E2 to ripen the cervix of the mare prior to induction of parturition

Eleven light-breed pregnant mares (335 to 347 d gestaton) were used to evaluate the use of prostaglandin E2 as a cervical ripening agent prior to induction of parturition during the months of April and May. Six hours prior to induction, each mare's cervix was examined per vagina for softness and dilation. Each mare was then assigned to 1 of 2 treatment groups: Group PGE mares (n = 7) received 2.0 to 2.5 mg prostaglandin E2 deposited intracervically; Group SAL mares (n = 4) received 0.5 mL of sterile NaCl deposited intracervically. Six hours later, the mares were readied for parturition by wrapping the tail, scrubbing and rinsing the perineum and udder, and examining the cervix as previously described. Each mare was then administered 15 U, i.v. oxytocin at 15-min intervals until the chorioallantois ruptured. Intervals from initial oxytocin injection until rupture of the chorioallantois, from initial oxytocin injection until delivery of the foal, from delivery of the foal until the foal stood unassisted, and from delivery of the foal until the foal suckled were recorded. Mean cervical dilation immediately prior to induction of parturition tended to be greater in Group PGE mares (3.9 +/- 1.7 cm) than in Group SAL mares (1.9 +/- 1.9 cm; P = 0.10). Mean change in cervical dilation over the 6-h period prior to induction (3.4 +/- 1.9 cm vs 1.5 +/- 2.1 cm), mean number of injections of oxytocin required until the chorioallantois ruptured (1.9 +/- 0.7 vs 2.5 +/- 1.0), and mean intervals from initial injection of oxytocin to rupture of the chorioallantois (20 +/- 10 min vs 28 +/- 19 min) and delivery of the foal (28 +/- 7 min vs 34 +/- 22 min) were not different between Group PGE and SAL mares, respectively (P > 0.10). The proportion of foals that stood within 1 h of birth also did not differ between Group PGE foals (6/7; 86%) and Group SAL foals (3/4; 75%; Chi-square = 0.17; P > 0.10). The proportion of foals that nursed within 2 h of birth was higher in Group PGE foals (6/7; 86%) than in Group SAL foals (1/4; 25%; Chi-square = 4.02; P < 0.05). Premature separation requiring manual rupture of the chorioallantois at the vulvar labia occurred in 1 Group PGE mare (cervical dilation of 1.5 cm at time of induction) and 1 Group SAL mare (cervix closed and firm at time of induction). Foals born from the 2 mares with premature placental separation had the longest intervals from initial oxytocin injection to delivery, delivery to ability to stand unassisted, and delivery to suckling within their respective treatment groups. In summary, it appears that cervical ripening prior to induction of parturition favors shorter deliveries and foal vigor. Intracervical administration of prostaglandin E2 may prove useful for ripening the cervix of the mare prior to induction of parturition. Further studies are indicated to determine optimal dosage and method of administration of prostaglandin E2.     

Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses

Despite a large body of safety data, concern exists that porcine zonae pellucidae (PZP) immunocontraception--used to manage wild horse populations--may cause out-of-season births with resulting foal mortality. Our study at Assateague, Maryland indicated the effects of immunocontraception on season of birth and foal survival between 1990 and 2002 on wild horses from Assateague Island. Among 91 mares never treated, 69 (75.8%) of foals were born in April, May, and June (in season). Among 77 treated mares, 50 (64.9%) were born in season. Of 29 mares foaling within 1 year after treatment (contraceptive failures), 20 (68.9%) were born in season. Of 48 mares treated for greater than 2 years then withdrawn from treatment, 30 (62.5%) of 48 foals were born in season. There were no significant differences (p <.05) between either treatment group or untreated mares. Survival did not differ significantly among foals born in or out of season or among foals born to treated or untreated mares. Data indicate a lack of effect of PZP contraception on season of birth or foal survival on barrier island habitats.     

Effects of Moderate Amounts of Barley in Late Pregnancy on Growth,Glucose Metabolism and Osteoarticular Status of Pre-Weaning Horses

In stud management, broodmares are commonly fed concentrates in late pregnancy. This practice, however, was shown to correlate with an increased incidence of osteochondrosis in foals, which may be related to insulin sensitivity. We hypothesized that supplementation of the mare with barley in the last trimester of pregnancy alters the pre-weaning foal growth, glucose metabolism and osteoarticular status. Here, pregnant multiparous saddlebred mares were fed forage only (group F, n=13) or both forage and cracked barley (group B, n=12) from the 7^th month of pregnancy until term, as calculated to cover nutritional needs of broodmares. Diets were given in two daily meals. All mares and foals returned to pasture after parturition. Post-natal growth, glucose metabolism and osteoarticular status were investigated in pre-weaning foals. B mares maintained an optimal body condition score (>3.5), whereas that of F mares decreased and remained low (<2.5) up to 3 months of lactation, with a significantly lower bodyweight (-7%) than B mares throughout the last 2 months of pregnancy. B mares had increased plasma glucose and insulin after the first meal and after the second meal to a lesser extent, which was not observed in F mares. B mares also had increased insulin secretion during an intravenous glucose tolerance test (IVGTT). Plasma NEFA and leptin were only temporarily affected by diet in mares during pregnancy or in early lactation. Neonatal B foals had increased serum osteocalcin and slightly increased glucose increments and clearance after glucose injection, but these effects had vanished at weaning. Body measurements, plasma IGF-1, T₄, T₃, NEFA and leptin concentrations, insulin secretion during IVGTT, as well as glucose metabolism rate during euglycemic hyperinsulinemic clamps after weaning, did not differ between groups. Radiographic examination of joints indicated increased osteochondrosis relative risk in B foals, but this was not significant. These data demonstrate that B or F maternal nutrition has very few effects on foal growth, endocrinology and glucose homeostasis until weaning, but may induce cartilage lesions.     

Aggression and social spacing in light horse (Equus caballus) mares and foals

Aggression and social spacing were studied in 14 light horse mares and their foals living at pasture. Focal samples were collected on each mare-foal dyad for 6 to 10.5 h from 2 months of foal age until weaning at approximately 4 months of age. Observations on foals continued until approximately 6 months of age for 7.5 to 10.5 h per foal. Every 2 min the identities of all individuals within 5 m were recorded. All occurrences of agonistic behavior, and the participants, were recorded during the focal samples. In addition, during feeding of supplemental grain, all occurrences of agonistic behavior by all subjects were recorded. Significant correlations were found between mare rank and the rank of foals both prior to and after weaning. Before weaning, the rank of the foal was significantly correlated with birth order. No significant correlation between birth order and foal rank was found for the post-weaning hierarchy. An animal's gender had no significant effect on foal rank or the choice of preferred associate. Both prior to and after weaning, foals associated preferentially with the foal of their dam's most preferred associate. In addition, significant positive correlations were found between rank of mares and foals and the rate at which they directed aggression to other herd members.     

Maternal Lineage of Warmblood Mares Contributes to Variation of Gestation Length and Bias of Foal Sex Ratio

Maternal lineage influences performance traits in horses. This is probably caused by differences in mitochondrial DNA (mtDNA) transferred to the offspring via the oocyte. In the present study, we investigated if reproductive traits with high variability—gestation length and fetal sex ratio—are influenced by maternal lineage. Data from 142 Warmblood mares from the Brandenburg State Stud at Neustadt (Dosse), Germany, were available for the study. Mares were grouped according to their maternal lineage. Influences on the reproduction parameters gestation length and sex ratio of offspring were analyzed by simple and multiple analyses of variance. A total of 786 cases were included. From the 142 mares, 119 were assigned to six maternal lineages with n≥10 mares per lineage, and 23 mares belonged to smaller maternal lineages. The mean number of live foals produced per mare was 4.6±3.6 (±SD). Live foal rate was 83.5%. Mean gestation length was 338.5±8.9 days (±SD) with a range of 313 to 370 days. Gestation length was affected by maternal lineage (p<0.001). Gestation length was also significantly influenced by the individual mare, age of the mare, year of breeding, month of breeding and sex of the foal (p<0.05). Of the 640 foals born alive at term, 48% were male and 52% female. Mare age group and maternal lineage significantly influenced the sex ratio of the foals (p<0.05). It is concluded that maternal lineage influences reproductive parameters with high variation such as gestation length and foal sex ratio in horses. In young primiparous and aged mares, the percentage of female offspring is higher than the expected 1:1 ratio.     

Induction of ovulation during the postpartum period in the thoroughbred mare with a prostaglandin analogue,Synchrocept™

Breeding of mares at the foal heat is desirable, but the low pregnancy rate and the not infrequent occurrence of subsequent anestrus are a deterrent. A PGF_2a analogue, Synchrocept^? (prostalene), as a single 2 mg subcutaneous injection was used to induce ovulation, either during the corpus luteum phase subsequent to a foal heat (test group 1) or at a fixed interval of 20 days from parturition (test group 2) in mares that also had a foal heat. Mares with no signs of a foal heat were treated 20 days postpartum (test group 3). A total of 80, mostly Thoroughbred, mares were treated in more than 15 breeding centers in Northern Germany between mid-January and mid-May 1975. At the same locations and over the same time periods, 60 control mares (control group 1) were bred at the foal heat and 40 additional control mares (control group 2) were bred later than 25 days postpartum.In groups 1 and 2, treatment induced estrus in 95% of the mares and in group 3 estrus was induced in 68% of the mares. Of these animals, 92% were bred and 81% conceived on the average 28 days after parturition. The number of services per conception in mares treated was 25% lower (2.5) than in controls (3.2). Synchrocept acted as a luteolysin, but seems also to have induced heat and estrus in animals with plasma progesterone levels below 1 ng/ml, as has been reported previously. Neither mares nor foals showed detectable clinical signs of drug intolerance.     

Sex preferences in Jeju pony foals (Equus caballus) for mutual grooming and play-fighting behaviors

We investigated mutual grooming by Jeju pony (Equus caballus) foals to determine whether male foals preferentially interact with potential future sexual partners or competitors. We predicted that relative to female foals, male foals would exchange grooming more frequently with young mares and that in general, foals would mutually groom more frequently with the opposite sex rather than the same sex. Observing 53 foals between April and October 1998, we recorded 113 mutual grooming events. Male foals exchanged grooming with yearling mares more frequently than with their mother, while female foals exchanged grooming with their mother more frequently than with yearling mares. Contrary to the prediction, foals were not more likely to mutually groom with a foal of the opposite sex than with a foal of the same sex. In our study, 21 instances of play-fighting behavior followed mutual grooming between peers. Relative to intersexual grooming events, play-fighting was more likely to follow intrasexual mutual grooming, and male foals were much more likely to play fight than female foals. These results provide evidence that Jeju pony foals develop and maintain social relationships at the earliest stage of their lives. We suggest that early social experiences might influence social bonding later when the male foal begins to form a harem after separation from its mother.     

Effect of photoperiod on the diurnal rhythm of plasma testosterone, dihydrotestosterone and androstenedione in mature male chickens

1. The effects of different photoperiods on the concentrations of plasma androgens, testes weight and on the diurnal rhythm of plasma testosterone (T), dihydrotestosterone (DHT) and androstenedione (A) in mature, single comb White Leghorn male chickens were studied. 2. Birds were exposed to either 14 hr of light (lights on at 0600-2000 hr) or to 24 hr of light per day. 3. Blood samples were collected from birds in both groups at 3-hr intervals and plasma levels of T, DHT and A were measured using radioimmunoassays. Following blood collection, birds were weighed, killed and testis weights were recorded. 4. Under 14 hr of light, there was a diurnal rhythm of T and DHT with hormone concentrations peaking at the end of the dark period. There was no obvious rhythm for A. Exposure to 24 hr of light abolished the diurnal rhythm found under 14 hr of light. 5. There was an increase not only in testis weights but also in body weight and hormone concentrations under 24 hr of light. 6. It was concluded that photoperiod plays an important role in controlling the concentration and rhythm of androgens in mature male chickens.     

Spatial relations between mares and foals of the Welsh pony (Equus caballus)

Welsh pony mares and foals (Equus caballus) were usually found to be within 1 or 5 m of each other during the first week of the foal's life and gradually spent more time at greater distances as the foals became older. There was an overall levelling of the trend during the 9th–15th weeks of life of the foal, followed by a second period of change during weeks 16–24. Through weeks 21–24, mares and foals spent at least half of their time within 5 m of each other. Proximity was primarily due to foal activity except during foal recumbency. During the first 8 weeks of the foal's life, a mare remained close by when it was recumbent, either by grazing in a circle around it or by standing upright beside it. Mares and foals were most likely to be close together when they were resting upright with the other ponies in the herd and most likely to be far apart when the foal was playing. Similarities in patterns of spatial relationship between the foals of a given mare were demonstrated. There was no difference between colts and filies in the development of independence.     

Independence between Rhythms of Temperature and Progesterone in Mares

We investigated the ultradian and diurnal body temperature and plasma progesterone concentration rhythms and the temporal relationship between them in mares during the midluteal phase. Data were obtained from 6 mares at 3-h intervals for 3 consecutive days. Cosinor analysis showed that body temperature acrophases occurred in the evening, whereas the progesterone acrophases occurred in the early morning (3 mares) and at night (3 mares). The spectral analysis of the temperature data showed periods of 24 hr for all mares and of 8 hr for 1 mare. In contrast, the periods observed for plasma progesterone concentration were quite divergent (24 and 12 hr). The small variation in the rhythmic parameters of body temperature suggests that its oscillator system is stable. No phase relationship was detected between the rhythmometric parameters of body temperature and plasma progesterone concentration, suggesting that the physiological mechanisms of control of the 24 hr and ultradian rhythm of the two variables are not coupled during the midluteal phase.