Oxytocin-induced release of prostaglandin F2 alpha in postpartum beef cows: comparison of short versus normal luteal phases.
The first postpartum ovulation after early weaning of calves (30 35 days of age) from cows is normally followed by a short luteal phase (6 10 days) unless the animals are pretreated with a progestogen (e.g. norgestomet). Reduced luteal lifespan in cattle is reportedly due to the premature release of a luteolysin (presumably prostaglandin F2 alpha [PGF2 alpha]). Therefore, the objective was to determine if oxytocin-induced release of PGF2 alpha (measured by the stable PGF2 alpha metabolite, 15-keto-13,14-dihydro PGF2 alpha [PGFM]) was greater for cows having a short compared to a normal luteal phase on Day 5 following the first postpartum estrus (Day 0). Thirty postpartum beef cows were randomly assigned into three groups (n = 10 per group) expected to have short (Short d 5) or normal (Norgestomet d 5 and Norgestomet d 16) luteal phases. Cows in Norgestomet d 5 and d 16 groups received Norgestomet (progestogen) implants for 9 days beginning 21 23 days postpartum. On Day 5 (Short d 5 and Norgestomet d 5) or Day 16 (Norgestomet d 16) following first postpartum estrus, each animal was injected (i.v.) with 100 IU oxytocin. In addition, cows in the Short d 5 group were subdivided into two groups following second estrus (normal luteal phase, n = 5 per group) to receive 100 IU oxytocin on Day 5 (Normal d 5) or 16 (Normal d 16), respectively. Estrous cycle length (means +/- SE) for cows in the Short d 5 group (8.7 +/- 0.4 days) was shorter (p less than 0.01) than for cows in all other groups (21.1 +/- 0.3 days).(ABSTRACT TRUNCATED AT 250 WORDS)
Zollers
W G
WG
Department of Dairy, University of Missouri, Columbia 65211.
Garverick
H A
HA
Smith
M F
MF
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D015237:Dinoprost / Q000378:metabolism*; D005260:Female; D008183:Luteal Phase; D010121:Oxytocin / Q000494:pharmacology*; D049590:Postpartum Period / Q000378:metabolism*; D011247:Pregnancy; D011282:Pregnenediones / Q000494:pharmacology; D011374:Progesterone / Q000097:blood; D045167:Progesterone Congeners / Q000494:pharmacology; D011897:Random Allocation
D011282:Pregnenediones; D045167:Progesterone Congeners; C100284:norgestomet; D011374:Progesterone; D010121:Oxytocin; D015237:Dinoprost