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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., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Fifty crossbred cows (38 multiparous and 12 nulliparous) were used to evaluate in utero androgenization of heifer calves with trenbolone acetate. Three 200-mg trenbolone acetate (Finaplix-H) implants were implanted in the ear of treated cows (n = 24) on d 214 +/- 11 of gestation; the remaining animals (n = 26) were used as controls. Cows' rate of gain, serum levels of trenbolone acetate, gestation length, degree of dystocia, percentage bred back, days until conception, and 24-h milk production were evaluated. Fourteen-day weigh periods until parturition indicated that trenbolone acetate-treated dams had an increased (P < .05) average daily gain (1.05 +/- .1 kg) compared with control cows (.55 +/- .1 kg). Serum concentrations of trenbolone acetate were higher (P < .01) in treated cows with a peak at 9 d after implantation and returned to basal concentrations by d 77. Treatment did not affect degree of dystocia among all cows (P > .05) but seemed to increase (P < .01) the incidence of dystocia in nulliparous cows compared with nulliparous control cows. Gestation length and subsequent fertility were not affected by treatment (P > .05). Similarly, there was no difference in 24-h milk production (P > .05) between treated and control cows. Calf birth weight, phenotypic measurements at birth, vigor, average daily gain, carcass characteristics, and heifer reproductive tract and ovarian weights did not differ with treatment (P > .05). These data showed that late-gestation treatment with 600 mg of trenbolone acetate significantly increased weight gain of dams without demonstrating any androgenizing effects on the growth or physical characteristics of heifer calves.