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.