Topic:Comparative Study
Comparative studies in equine research involve the systematic analysis of different horse breeds, management practices, or physiological responses to identify variations and similarities. These studies are instrumental in understanding how different factors influence health, performance, and behavior in horses. Common areas of comparison include genetic traits, nutritional requirements, disease resistance, and response to training. By evaluating these differences, researchers can develop targeted strategies for breeding, healthcare, and training. This page aggregates peer-reviewed research studies and scholarly articles that focus on the methodologies, findings, and implications of comparative studies in the context of equine science.
Androgens and oestrogens in normal and cryptorchid stallions. Total androgens, testosterone and total oestrogens were measured in twenty-one intact, nine unilaterally cryptorchid, three bilaterally cryptorchid stallions and four geldings. Total oestrogens were significantly higher (P less than 0-005) and total androgens significantly lower (P less than 0-05) in the bilateral cryptorchid compared to other groups. There was a significant (P less than 0-025) day and night variation in total androgen levels. Thyroidectomized and intact animals showed a marked decrease in total androgen as well as testosterone levels during the winter period thus showing an e...
Gonadal dysgenesis in the mare. Five phenotypically normal but infertile mares were studied; four had karyotypes of 63XO, and one was a 25,64XX/13,63XO mosaic. The mares exhibited small uteri and has small ovaries that lacked germ cells and consisted primarily of undifferentiated ovarian stroma. These cases demonstrate that chromosome analysis is an important technique for the diagnosis of some forms of equine infertility.
Some aspects of endometrial cup formation and PMSG production. Two females of heterosexual pairs of chimaeric horse twins were fertilized by their co-twin brother and PMSG production examined during gestation. Four pregnancies developed in one mare and two in the other. The levels of PMSG were high in both mares and remained detectable in the peripheral blood until 220 and 265 days of gestation. The fetal membranes of one mare contained remnants of cup secretion with PMSG activity at term. The findings support the thesis of Allen & Moor (1972) that the endometrial cups are of fetal origin and that they are destroyed by immunological mechanisms.
Duration of oestrus and time of ovulation in mares treated with synthetic Gn-RH (AY-24,031). Synthetic Gn-RH, administered during oestrus, stimulates the release of pituitary LH in the cyclic mare. Duration of oestrus was significantly reduced by 1 mg Gn-RH given on Day 2 of oestrus; the time of ovulation, measured in days from the onset of oestrus, also tended to be reduced. An injection of 2 mg Gn-RH had nor further effect, but daily injections from Day 2 until ovulation significantly shortened the duration of oestrus and the time to ovulation. The profiles of LH were found to be variable from mare to mare, but in all mares, treated and control, elevation of LH was detected close to...
Induction of parturition in mares. Thirty-seven induced parturitions involving thirty-one mares were studied over a 2-year period using various doses of oestrogen and oxytocin. The time of appearance and degree of expression of the major clinical signs of parturition, and the time for completion of delivery and the passage of the placenta were significantly influenced by increasing doses of oxytocin. Oestrogen was useful in softening and relaxing the cervix when it was tight, but was not essential to induction when the cervix was already soft and dilating. Fertility was not adversely affected by induced parturition.
Carbonic anhydrase isozymes in American ponies and riding horses: a new polymorphic high-activity type isozyme. A study of the erythrocyte carbonic anhydrases of 219 American ponies and 76 riding horses has revealed the presence of five variants of the low-activity CA B isozyme and two variants of the high-activity CA C isozyme. The previously undetected variant of CA C was found only in the pony population and had an allele frequency of 8.9%. A family study of animals possessing the CA B variant A2 showed an unexpected high frequency of inheritance.
A survey of eggs in the oviducts of mares. A total of 424 eggs was recovered from flushings of 176 pairs of oviducts. Of these eggs, 324 were in a state of advanced degeneration (Type 4) and ten appeared to have been recently ovulated (Type 1). The number of eggs/oviduct varied from 0 to 13, most being up to 3 eggs, but fifty oviducts contained no eggs. It is widely believed that unfertilized ova are selectively retained in the oviducts but an alternative explanation for their presence is put forward.
Surfactant studies in the fetal and neonatal foal. Phospholipids in embryonic lung tissue, pulmonary washings and amniotic fluid were measured to study the development of lyng surfactant in the horse. A significant increase in the concentration of total phospholipids in lung tissue and a concomitant rise in the amount of dipalmitoyl lecithin in amniotic fluid between 100 and 150 days of gestation indicated the initial formation of surfactant in the fetal lung during this period.
Comparison of the methods of rectal palpation and haemagglutination-inhibition assay for diagnosis of pregnancy in mares. The diagnostic value of rectal palpation and immunological assay of PMSG was tested at different stages of pregnancy in mares inseminated with frozen semen in three separate studies. The results were based on foaling success and particular attention was paid to the numbers of inconsistent results obtained by the two tests. Generally, the number of false positive diagnoses was lower for the immunological assay than for palpation in early pregnancy (Days 40 to 60) and the relationship became reversed later in gestation.
Aspects of respiration in anaesthetized newborn foals. The arterial oxygen tension (PaO2) in clinically normal newborn foals at 1300 m above sea-level is considerably lower (less than 60 mmHg) than in similarly aged foals at lower altitudes. This figure is further reduced to less than 50 mmHg without adverse effect in newborn foals at 1300 m maintained under pentobarbitone anaesthesia for prolonged periods. Measurement of O2 dissociation curves indicates that haemoglobin becomes saturated at a lower blood O2 tension in newborn foals than adult horses.
Embryological studies on the dartmoor pony during the first third of gestation. A sequence of ten known-age embryos recovered from Dartmoor Ponies during the first 4 months of gestation is described. Changes in size, shape and vascularity of the conceptus are recorded, as well as the growth and decline of the yolk-sac and the succeeding establishment of the allantochorion. The progress of equine somatogenesis is compared with that of the pig which it lags on average of about 4 days. Some quantitative data are presented.
Plasma progestagens in the pregnant mare in the first and last 90 days of gestation. Plasma progestagens were measured in eighteen pregnant mares to establish normal levels in the first and last 90 days of gestation. Progestagens increased from 25 ng/ml at 90 days before birth to 60 ng/ml at 10 days before birth, decreased to 58 ng/ml at 5 days before, and were 3 ng/ml or less by 5 days after perturition. During the first 90 days of pregnancy, progestagens reflected luteal activity with an increase in plasma levels from Day 30 to Day 60.
Immunoglobulins produced by the antigenized equine fetus. The foal is born without detectable antibody and except for small amounts of IgM is devoid of immunoglobulins. Intrafetal administration of either Venezuelan equine encephalomyelitis virus (VEE-TC83) or ovine erythrocytes elicited IgGa, IgGb and a trace of IgG(T). The fetal blood VEE-TC83 neutralization titre was higher than the neutralization titre elicited by the same preparation in older horses.
Oestrogen excretion in mares in relation to various reproductive states. The rate of urinary oestrogen excretion was studied in four ovariectomized mares. In two animals ovariectomized when urinary oestrogen concentration was high, levels fell to a minimun within 48 hr. Intramuscular injection of oestradiol-17beta produced maximum urinary oestrogen levels within 3 to 6 hr and a return to minimum detectable levels within 24 hr. The major urinary oestrogen in mares was oestrone. In nine maiden mares studied between September and June, the cycle, the durations of dioestrus and oestrus, and the time of ovulation were similar in autumn (September to December) and spring...
Experimental studies on equine herpesvirus type 1 infections. The EHV-1 viruses of fetal origin grew better and had a wider tissue culture host range than those isolated from horses with respiratory diseases. Comparisons of a fetal isolate (F/304) and a respiratory disease isolate (R/NM-3) in partly immune horses showed that the F/304 virus infected horses more readily, grew better in the nasopharynx, was more likely to cause abortion, and was excreted to a greater extent into the environment.
Ontogeny of equine haemoglobins. Studies were made of the O2 affinities of fetal and maternal haemoglobins in the horse, and correlations were found with erythrocytic levels of 2,3-diphosphoglycerate.
Anatomy of the placental barrier in the mare. The study of the equine placenta, which began in Venice in 1598, has a long but discontinuous history. Early observations were purely morphological, but new techniques have stimulated a broader and more functional approach. Histological and ultrastructural observations at various stages of pregnancy have shown that the fetal side of the placenta comes to acquire certain features in common with the air-blood barrier of the mammalian lung. These changes may reflect the increasing O2 requirements of the fetus as gestation proceeds.
Follicular and luteal development in pregnant mares. Examination of the ovaries of mares at various stages of pregnancy and after hysterectomy, together with measurement of progesterone concentrations in the peripheral plasma of pregnant and hysterectomized mares and in uterine and ovarian venous plasma of pregnant mares, demonstrated that the primary CL of pregnancy remains functional until at least Day 160 of gestation. The results showed that primary and secondary CL, and the placenta or uterus, all contribute to the total progesterone pool in mares during pregnancy. Similarities and differences in ovarian function observed between pregnant a...
Relationship between luteal function and metabolic clearance and production rates of progesterone in the mare. The functional activity of the equine CL was measured by its ability to convert [4-14C]3beta-hydroxy-5-en-20-one to [4-14C]pregn-4-en-3,20-dione. The capacity of homogenates of CL of different ages followed the temporal pattern of plasma progestagen concentrations. In ten mares which ovulated twice at intervals of 0 to 9 days in the same cycle, the conversion capacity of the CL from the second ovulation was similar to that from the first ovulation. After adjusting for age, the CL from the first of two ovulations had a similar conversion capacity as that resulting from a single ovulation. Plasm...
The cycle of oestrus, ovulation and plasma levels of hormones in the mare. The duration of the oestrous cycle and day of ovulation were recorded in six mares which were used for concurrent assay of plasma levels of sex steroids and pituitary LH concentration. Peak of progesterone were reached during dioestrus and those of oestradiol and androstenedione occurred 2 days before ovulation and were in decline on the day of ovulation. Plasma oestrone remained constant (between 9 and 12 pg/ml) throughout the cycle. Plasma LH rose to a maximum near to the time of ovulation, and thereafter decreased gradually until mid-dioestrus. The pattern of secretion is compared with that...
The ultrastructure of endometrial cups in pregnant mares. Electron microscopy and immunofluorescence techniques were used to study the various epithelial cells in the endometrial cups of ten pregnant mares, and in the uterine epithelium of one non-pregnant mare. Evidence was obtained which suggested that epithelial gland cells within the endometrial cups, as distinct from the hypertrophied decidual-like cells in the cup, may synthesize PMSG. The suggestion does not agree with the findings of other workers in the fetal origin (chorionic girdle cells) of this gonadotrophin.
Immunoglobulin metabolism in the neonatal foal. The proteins IgG and IgG(T) are the predominant immunoglobulins in equine colostrum. Their distribution and catabolism were studied in the newborn foal using an isotopic tracer technique. More precise quantitation of the absorption of these immunoglobulins from colostrum is now possible.
The site of ovulation in the mare. Serial photography of the ovary of a mare by periodic surgical exteriorization of the ovary and peritonescopy in situ revealed that the ovulatory fossa is the site of ovulation in this species.
A review of cytogenetics in equine reproduction. The karyotype of the horse consists of 64 chromosomes; 18 pairs have a terminal centromere and 13 pairs a non-terminal centromere. Identification of individual chromosomes is enhanced by the use of band-staining techniques which allow recognition of minor structural rearrangements of chromatin material. Seven previously reported cases of male pseudohermaphroditism with chromosome studies are reviewed. Three were genetic females, one was basically an XX/XY chimaera, one was an XX/XXY chimaera, and one was an XXXY. Also reviewed is an infertile mare with 63 chromosomes and no distinguishable sex...
Sperm transport and distribution in the mare. Fifty mares were inseminated on Days 2, 4, 7, 11 or 17 of the oestrous cycle with spermatozoa from one of three stallions to observe the distribution of the spermatozoa in various parts of the reproductive tract 12 hr later (Days 3, 5, 8, 12 and 18). Only 0-06 to 2-21% of inseminated spermatozoa were recovered from the tract. More (P less than 0-05) spermatozoa were recovered from the cervix and uterus on Day 12 than on Days 3, 5, 8 and 18. The mean number of spermatozoa recovered from either or both oviducts was significantly greater (P less than 0-10) on Days 5 and 8 than on Days 3, 12 and 1...
Plasma progestagens in pregnant mares. Peripheral plasma progestagens were quantified by a competitive protein-binding assay throughout pregnancy. The level of progesterone increased significantly between Days 0 and 8 (P less than 0-05) and again between Days 28 and 44 and reached a maximum on Day 64. Subsequently, it fell slowly until about Day 300 and then rose again during the last 30 days before reaching a minimum on the day after foaling. Very low concentrations of 17alpha-hydroxyprogesterone were found except between Days 40 and 120 and during the last 30 days before birth. Two unidentified compounds, one eluting slightly bef...
The effect of rectal palpation on the fertility of cyclic mares. The effect of rectal palpation of fertility of non-lactating, normal cyclic mares was studied over 3 years. During the first year (1971), the conception rates in mares after daily paplaption during oestrus only, and during oestrus and the first 50 days of pregnancy, were not significantly lower (P greater than 0-05) than the conception rates recorded in mares not palpated. No abortions could be attributed to palpation. Oestrus lasted longer (P less than 0-05) in non-palpated than palpated mares. During the second year (1972), first-cycle pregnancy rates in two groups of mares palpated daily du...
Plasma LH levels in the mare during the oestrous cycle. Plasma levels of LH were determined by heterologous radioimmunoassay utilizing highly purified equine LH as standard. Samples were taken regularly from eleven mares for twenty-six oestrous cycles over a period of 10 weeks. The mean cycle length was 20-5 +/- 3-1 (S.D.) days, and ovulation occurred on average 4-3 +/- 1-6 (S.D.) days from the time heat was first detected. Levels of LH were persistently low from Days 5 to 16 of the cycle (ovulation = Day 0). They then increased slowly over a number of days and continued to rise beyond the levels observed at any time during the immediate preovulato...