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Oestrogen and seasonal effects on the production of an oestrus-associated glycoprotein in oviducal fluid of sheep

Summary. In 14 cyclic ewes, the oestrus-associated glycoprotein in the oviducal fluid was never detected between Days 7 and – 2 of the oestrous cycle and it was present in 5% of fluid samples collected on Day –1, 59% on Day 0, 96% on Day 1, 100% on Day 2, 79% on Day 3, 31% on Day 4, 16% on Day 5, and 4% on Day 6. Its presence generally coincided with the period of high flow rate of oviducal fluid which occurs around oestrus. The duration of detectable levels of the oestrus-associated glycoprotein did not vary significantly during the breeding season from a mean (± s.d.) of 3·9 ± 1·0 days. However, the peak flow rate of oviducal fluid dropped from 1·63 ± 0·50 (early) to 1·38 ± 0·40 (mid-) and to 0·85 ± 0·21 ml/day late in the season. Anoestrous ewes (3) induced to ovulate by treatment with progesterone implants and gonadotrophin showed low peak fluid flow rates (0·92 ± 0·30 ml/day) and the presence of the oestrusassociated glycoprotein for a shorter period (2·7 ± 0·7 days). Pregnancy (N = 3) did not appear to prolong the production of the protein. The injection of 25 µg oestradiol benzoate into 3 anoestrous, 2 mid-cycle and 9 ovariectomized ewes caused an increase in fluid flow rate and appearance of the glycoprotein 1–2 days later. The glycoprotein was present for a longer period in response to the exogenous oestrogen—6·8 ± 1 ·6 days in the ovariectomized ewes, 7·9 ± 1·3 days in anoestrous ewes, and 8·4 ± 0·8 days in the dioestrous ewes. In the ovariectomized ewes a seasonal effect was observed on fluid flow rates with lower peak values in response to oestrogen injection occurring later in the breeding season. The manipulation of progesterone alone did not cause production of the oestrus-associated glycoprotein.