Effect of maternal treatment with altrenogest on age at puberty, hormone concentrations, pituitary response to exogenous GnRH, oestrous cycle characteristics and fertility of fillies

Pregnancy monitoring in mares: Ultrasonographic and endocrine approaches

Methods to diagnose and monitor equine pregnancy continue to advance with improved instrumentation enabling the development of novel, non-invasive approaches to assess fetal well-being and viability using ultrasound and endocrine testing. From early embryonic loss to placentitis, that is typically encountered later in gestation, fetal viability and development as well as placental function can be evaluated using two fundamentally different, structural and functional, approaches. Ultrasound provides structural information on embryonic and fetal growth using such parameters as combined thickness of the uterus and placenta (CTUP), visual assessment of fetal fluids, activity, heart rate and multiple biometrics involving the fetal head and eyes, limbs and joints among many others, depending on the stage of gestation. Endocrine profiles that include progesterone and 5α-dihydroprogesterone, other metabolites, androgens and estrogens can be evaluated simultaneously using liquid chromatography-tandem mass spectrometry (LC-MS/MS) providing more functional information on fetal and placental competence and development. Endocrine information can be used in making clinical decisions including the need for progestin supplementation or when it can cease, and even estimating gestational stage in mares that cannot be easily palpated or scanned, as with mini-breeds or rancorous animals most notably. When used together, monitoring gestation by ultrasound and hormonal analysis provides unusual insight into feto-placental well-being and the progress of pregnancy, helping to identify problems needing therapeutic intervention.

Alteration of the mare's immune system by the synthetic progestin, altrenogest

PROBLEM

Progestins are immunomodulatory in a variety of species. In the horse, the most commonly administered synthetic progestin is altrenogest (ALT), but its effect on the immune system of the non-pregnant mare is unknown.

METHODS

Peripheral blood mononuclear cells (PBMCs) from diestrous mares were incubated with varying concentrations of progesterone (P4) or ALT to assess intracellular production of IFNγ and the expression of select cytokines. Additionally, ten mares received either ALT or VEH daily utilizing a switchback design beginning on the day of ovulation and continuing for 7 days. Circulating PBMCs and endometrial biopsies were obtained to assess the production and expression of the same cytokines.

RESULTS

In vitro, both P4 and ALT caused a dose-dependent decrease in intracellular IFNγ in PBMCs. P4 caused a dose-dependent decrease in the expression of IFNγ, IL-10 and IL-4, while ALT caused an increase in the expression of IL-6 and IL-1β in PBMCs. In vivo, ALT suppressed the intracellular levels of IFNγ in PBMCs on d6. While control mares experienced a decrease in IL-1β expression from d0 to d6, ALT-treated mares did not. In the endometrium, ALT increased the expression of IL-1RN and IFNγ in comparison with VEH-treated mares.

CONCLUSION

P4 and ALT appear to alter the immune system of the non-pregnant mare both systemically in addition to locally within the endometrium. Further research is necessary to determine the pathways through which this synthetic progestin functions on the immune system of the horse, and the consequences it may have.

Efeito da categoria reprodutiva sobre a fertilidade de éguas inseminadas com sêmen asinino diluído e resfriado a 5ºC por 12 horas de armazenamento

Estudou-se o efeito da categoria reprodutiva sobre a fertilidade de éguas inseminadas com sêmen asinino diluído, resfriado e armazenado. Os ciclos foram acompanhados por palpação retal e rufiação, sendo as inseminações realizadas às terças, quintas e sábados, a partir da detecção de um folículo de 3,0 a 3,5cm de diâmetro, em um dos ovários, até a ovulação. O sêmen de cinco jumentos da raça Pêga foi diluído nos diluidores de leite em pó desnatado-glicose ou glicina-gema de ovo, resfriado a 5ºC e armazenado por 12 horas, sendo a dose inseminante de 400 x 106espermatozoides móveis (no momento da diluição final, pré-resfriamento) depositada no corpo do útero. O diagnóstico de gestação foi realizado por meio de palpação transretal, rufiação e ultrassonografia, realizada a cada 14 dias. Os resultados de 195 ciclos, referentes a 141 éguas, foram agrupados de acordo com a categoria reprodutiva a que pertenciam: potra, égua solteira, égua parida e no "cio do potro". As taxas de concepção, ao primeiro ciclo, foram de 60,00%, 48,28%, 75,00% e 47,17% e, após quatro ciclos, de 61,54%, 47,13%, 54,76% e 47,17%, na mesma ordem para as categorias descritas anteriormente. A categoria reprodutiva não teve efeito (P>0,05) sobre a fertilidade das éguas inseminadas com sêmen asinino resfriado, sendo as potras, éguas solteiras, éguas paridas e no "cio do potro" igualmente eficientes para o uso na reprodução.

Plasma concentration of insulin-like growth factor I (IGF-I) in growing Ardenner horses suffering from juvenile digital degenerative osteoarthropathy

Degenerative osteoarthropathy resulting in a reduced active lifespan was observed in Ardenner horses. In the context of joint biology, insulin-like growth factor I (IGF-I) is a potential candidate to affect the anabolism of cartilage matrix molecules. A group of 30 Ardenner horses reared under standardized conditions from weaning were evaluated periodically from 15 to 28 months of age to detect the early manifestations of the disease. At the end of this period, horses were classified in two pathological groups related to the degree of interphalangeal degenerative osteoarthropathy based on clinical and radiographic evaluations: healthy (46.7%) and pathological (53.3%) horses. Seven sequential blood samples were taken from each horse (during the evaluation period) to study the variation of IGF-I plasma concentration. We tested the variations of the IGF-I plasma concentration during growth, and the effect of sex and of pathological classes. Significant variations were observed during the research period, with a maximum value corresponding to spring and a minimum in autumn. A significant reduction of the IGF-I plasma concentration was also observed in the pathological horses (433.5 +/- 19.5 ng/ml) compared to the healthy horses (493.9 +/- 18.2 ng/ml). An alteration in the level of this growth factor could induce a disregulation of the mechanisms involved in the local control of joint and bone tissue development.

Onset of puberty in pasture-raised Thoroughbreds born in southern hemisphere spring and autumn

REASONS FOR PERFORMING STUDY

There is little information on age, weight and time of year of puberty in Thoroughbred horses, and the interpretation of such data is difficult due to the wide variety of descriptions of the onset of puberty.

OBJECTIVES

To examine the age, bodyweight and date of onset of puberty in Thoroughbreds born in spring and autumn.

METHODS

Bodyweight data and blood samples were collected in 59 pasture-raised Thoroughbred horses. Five autumn-born and 18 spring-born colts and 3 autumn-born and 33 spring-born fillies were examined from birth to age 13 and 17 months. A testosterone concentration >2 s.d. above the baseline concentration was indicative of onset of puberty in colts; and progesterone concentration >2 ng/ml and at least 3 times greater than the previous progesterone concentration was indicative of a first ovulation in fillies.

RESULTS

Spring-born fillies and colts were older and heavier than autumn-born fillies and colts at puberty. The age at onset of puberty in spring- and autumn-born foals was 291-408 days and 212-270 days, respectively. The weight at puberty in spring-born foals was 302-409 kg, and in autumn-born foals was 277-344 kg. However, the mean date at onset of puberty was not significantly different between spring- and autumn-born horses, with puberty occurring in October (New Zealand spring).

CONCLUSIONS AND POTENTIAL RELEVANCE

Seasonal changes in photoperiod affect the timing of onset of puberty, provided a minimum threshold bodyweight has been reached. Spring-born horses reached this threshold weight during the winter months and remained reproductively inactive until after the stimulus of increasing day-length occurred. The autumn-born horses reached the threshold weight to support puberty at the same time as stimulatory photoperiod and, therefore, reached puberty significantly younger and lighter than the spring-born horses.

Dynamics of follicle populations and gonadotropin concentrations in fillies age two to ten months

Follicle populations and concentrations of circulating gonadotropins were studied during age 2-10 months in 10 spring-born pony fillies. Blood sampling and ultrasound scanning were done every 4 days and daily for four 30 day periods. During 5-12 weeks, FSH concentrations were lower in 6 fillies with follicles > or = 6 mm (mean +/- s.e. 1.4 +/- 0.1 ng/ml) than in 4 fillies with follicles < 6 mm (2.8 +/- 0.3 ng/ml). The diameters and numbers of follicles and gonadotropin concentrations increased progressively during age 2-4 months. A plateau in follicle activity and reduced levels of gonadotropins occurred during 5-7 months. During 8-10 months, follicles grew to > 10 mm and gonadotropin concentrations increased. Waves of follicular growth were identified during the 30 day periods by significant increases in the diameter of the 10 largest follicles. The waves did not partition into dominant and subordinate follicles. Results indicated an initial postnatal period of negative ovarian feedback, temporally related changes in gonadotropins and follicles for months 3-10, and development of follicles in waves.