Pregnancy-associated glycoprotein (PAG) concentration in plasma and milk samples for early pregnancy diagnosis in Lacaune dairy sheep

•PAG profiles were established in milk along the first trimester of pregnancy in sheep.•PAG concentrations were compared in ewes carrying single or multiple fetuses.•In milk, pregnancy diagnosis could be performed 32 days after fertilization.•Milk concentrations were generally 10 times lower than in plasma.

In the present study, four RIA systems (RIA-1 to -4) based on two antisera raised against ovine pregnancy-associated glycoproteins (ovPAGs), combined with an ovine or a bovine PAG tracer were used to measure PAG concentrations in plasma and milk samples of dairy ewes. Blood and milk samples were collected on different days of gestation: 0, 18, 20, 22, 25, 28, 32, 42, and 49. From day 20 onward, the PAG in plasma could be detected in all pregnant ewes using the four RIA systems. By using milk, except for RIA-1, the other systems showed a sensitivity of 100% from day 28 of gestation onward. In plasma, PAG concentrations were higher in multiple than in single pregnancies, while no clear relationship was observed in milk. In conclusion, milk is a good alternative to plasma for early pregnancy diagnosis in sheep from day 28 to day 42.