Intrauterine injection of recombinant ovine interferon-tau extends the interestrous interval in sheep

The ability of recombinant ovine interferon-tau (roIFNτ) to extend the interestrous interval (IEI) in sheep was studied. Ewes were fitted with bilateral uterine catheters 7 or 8 days post estrus and were assigned to receive either 10 or 20 million antiviral (AV) units/day i.u. (∼100 or 200 ug) of roIFNτ or ovine conceptus secretory proteins containing equivalent AV units of native oIFNτ (noIFNτ; 4 ewes/treatment). Four control ewes received ovine serum proteins (SP). Total protein injected was 6 mg per day, half at 0700 hours and half at 1730 hours. The treatments were administered from Day 11.5 (estrus=Day 0) to Day 16. Blood samples were collected by jugular vienipuncture daily from Day 11 until ewes returned to estrus. Concentrations of progesterone (P) in plasma were determined by RIA. Treatment with either noIFNτ or roIFNτ extended IEI beyond that of SP-treated ewes (19.1 vs 31.2±3.4 days P<0.03). Of the ewes receiving 100 μg/day of oIFNτ, 2 of 4 receiving noIFNτ (23.6±5.2 days) and 3 of 4 receiving roIFNτ (34.2±5.2 days) had an extended IEI. All ewes receiving 200 μg/day of noIFNτ or roIFNτ had an extended IEI (28.8 and 38.5±5.2 days. respectively). Ewes receiving roIFNτ had a longer IEI than those receiving noIFNτ (36.7 vs 26.2±3.4 days; P=0.07). Ewes with an extended IEI had functional corpora lutea, as assessed by P production. The results demonstrate that 10 or 20 million AV units (∼100 or 200 ug) of roIFNτ extends the IEI and that the length of the IEI is longer for ewes receiving roIFNτ than noIFNτ following injection of equivalent AV units.