Pregnancy-associated glycoprotein profile in milk and its relationship with the circulating level during early pregnancy in goats

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The level of pregnancy-associated glycoprotein (PAG) in milk and its relationship with the concentration in peripheral circulation during early pregnancy remain uncertain in goats. Therefore, the objectives of present study were to investigate temporal profile of PAG in milk (whole and skim milk) and blood, and to determine the relationship between milk and circulating PAG level during early pregnancy in goats. Milk and plasma samples were collected from multiparous goats (n = 5) on alternate day from d 26 to 30, and thereafter weekly till d 51 of gestation to estimate PAG level using commercial ELISA tests. Pregnancies were confirmed at d 37 of gestation by transrectal ultrasonography (USG). The eff ;ects of days of pregnancy and animal status (pregnant vs. non-pregnant) on PAG levels in milk and plasma were analyzed using linear mixed model. Compared to USG, assay accuracy were 94.4%, 88.9% and 93.3% for whole milk, skim milk and plasma ELISA tests, respectively. Maternal PAG level in milk (both whole and skim milk) and circulation progressively increased with the days of pregnancy during early gestation (P < 0.001). On the contrary, the PAG level of corresponding milk and plasma samples of non-pregnant goats remain unchanged (P > 0.05) and below to cut-off values throughout the experiment. PAG levels in whole and skim milk samples of pregnant goats were similar (P > 0.05) at all-time points with approximately 2-folds lower PAG compared to the plasma samples. A strong positive correlation and high agreement of plasma PAG with PAG levels in whole and skim milk were detected. By using milk, the ELISA showed sensitivity of 100% after d 28 of gestation. In conclusion, the PAG level in milk and peripheral circulation is affected by the day of gestation during early pregnancy and the optimal time to carry out first pregnancy diagnosis using milk or plasma based ELISA is on and after d 28 of gestation. The strong relationship and high agreement of milk PAG with its level in peripheral circulation supports that milk (both whole and skim milk) is a good alternative to plasma for early pregnancy diagnosis from d 28 to d 51 and can effectively be used as a marker of placental functions and fetal health in goats.