Effect of cycle stage on immunoglobulin concentrations in reproductive tract secretions of the mare.

The effect of cycle stage on immunoglobulin and albumin levels in serum, follicular fluid, oviductal, uterine and vaginal secretions was measured. There was no variation in serum immunoglobulin levels during the oestrous cycle, although IgM levels were elevated in cyclic mares compared to non-cyclic (immature and anoestrous) animals. Similarly, there was no cyclical variation in follicular or oviductal protein concentrations. In the uterus, IgG and IgA levels relative to total protein were higher in oestrogenic than in progestagenic secretions, while the trend in relative IgM concentrations was reversed. Albumin levels were unchanged. In mares sampled repeatedly from the uterus and vagina during a single oestrous cycle, protein levels in secretions were affected by the collection technique. However, there was variation in absolute IgG, IgA, albumin and total protein concentrations, with maxima during dioestrus and minima at oestrus. Protein concentrations were higher in vaginal than in uterine secretions, although IgA relative to total protein was higher in the uterus than the vagina.