The effect of level of feed intake on progesterone clearance rate by measuring faecal progesterone metabolites in grazing dairy cows

摘要

The objective of the present study was to determine the effect of level of feed intake of pasture on P4 clearance rates in dairy cows. Twelve non-lactating Holstein-Friesian cows aged 4-9 years were randomly allocated to a restricted or ad libitum group. The ad libitum group had unrestricted access to irrigated pasture, whereas the restricted group had access for only 2h per day. Each animal was drenched orally twice daily with a chromic oxide capsule to allow daily feed intake to be estimated from faecal output (FO). Endogenous progesterone (P4) production was eliminated by subcutanously implanting a capsule containing 6 mg of a potent GnRH-agonist (deslorelin) into the ear of each animal 3 weeks before inserting a CIDR device containing 1.9 g P4 into the vagina. Two luteolytic PGF2 alpha were given 10 days later. Each device was removed after 11 days and residual P4 measured. Daily plasma samples were assayed for P4. Faecal samples were also taken daily and assayed for pregnanes (FP4M) containing a 20-oxo-, a 20 alpha- or a 20 beta -OH group with EIAs.