Serum and milk progesterone concentrations with regard to milk yield and cyclicity in cows during progesterone administration

Abstract

Progesterone (P4) concentrations in serum and milk were investigated in lactating dairy cows during intravaginal P4 (CIDR®, Zoetis Animal Health, Turkey) administration. Cows (n=31) were randomly blocked based on milk yield (low: ≤ 30 L [20-30 L; n=15] vs. high: >30 L [34-49 L; [n=16]) and cyclicity (presence or absence of visible corpus luteum [average of length and width of CL > 19 mm; cyclic vs acyclic]) to generate four groups: high producing-cyclic (n=8), low producing-cyclic (n=7), high producing-acyclic (n=8) and low producing-acyclic (n=8). Immediately after collection of milk and blood samples, CIDR was inserted intravaginally to all cows. The other milk and blood samples were collected on days 1, 2, 4, 5 and 7 during CIDR insertion. Serum and milk P4 concentrations were maintained above physiological threshold levels (>1 ng or serum and ≥15 ng in milk) during CIDR insertion in acyclic cows. There were cyclicity (P<0.01) and cyclicity X day (P<0.01) effects for serum and milk P4 concentrations. In this regard, serum and milk P4 concentrations were lower (P<0.01) in acyclic cows (3.24 ± 0.48 ng/ml in serum; 13.67 ± 1.19 ng/ml in milk) then those in cyclic cows (6.49 ± 0.49 ng/ml in serum; 22.66 ±1.23 ng/ml in milk). There was a cyclicity X milk yield X day interaction effect (P=0.01) for milk P4 concentrations. In this matter, milk P4 concentrations did not differ between low and high producing acyclic cows; however, milk P4 concentrations were higher (P=0.01) in high producing-cyclic cows then those in low producing-cyclic cows. In conclusion, serum and milk P4 concentrations were lower in acyclic cows compared to those in cyclic cows; however, serum and milk P4 concentrations were elevated to physiological threshold levels following P4 administration in acyclic cows regardless of milk yield.