Oxytocin-Induced Release of Prostaglandin F2α in Postpartum Beef Cows: Comparison of Short Versus Normal Luteal Phases1

Abstract

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)

Factors Affecting Fertility According to the Postpartum Period in Crossbred Dual-Purpose Suckling Cows in the Tropics

“…This could be explained by the occurrence of short oestrous cycles accompanied by an irregular luteal phase or cycles with a normal duration but with a low progesterone level as reported in dairy breeds (Taylor and Rajamahendran, 1990;Garverick et al, 1992) and dual-purpose cows (González et al, 1988). Numerous reports indicate that an early release of PGF 2α from the uterus in response to an increased oxytocin concentration during this period (Zollers et al, 1989(Zollers et al, , 1993 could reduce the length of the luteal phase and the levels of circulating progesterone, increasing the estradiol concentration (Inskeep, 1995), which could lead to adverse conditions for establishing a new pregnancy and thus affect fertility during the early postpartum period.…”

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Harnessing basic knowledge of factors controlling puberty to improve synchronization of estrus and fertility in heifers1

“…Treatment with some progestins, before the first ovulation, was able to eliminate the occurrence of short-duration GL, but other progestins were not (Ramirez-Godinez et al, 1981;Smith et al, 1987;Zollers et al, 1989). For example, only 46% of anestrous beef cows fed MGA for 5 d before GnRH-induced ovulation had a normal luteal phase, compared with 100% of cows exposed to progesterone (i.e., in an intravaginal device) for the same 5 d .…”

Luteal function after intrauterine infusion of recombinant bovine interferon- I1 into postpartum beef cows expected to have short or normal luteal phases

“…In other studies, pulse amplitude and basal concentrations of plasma PGF2a were increased on days 4-9 for postpartum cows having a short rather than a normal length oestrous cycle (Cooper et al, 1991), and secretion of PGF2a in vitro from endometrial tissue from cows anticipated to have short (Zollers et al, 1991b). Injection of oxytocin on day 5 of the oestrous cycle induced a release of 13,14-dihydro-15-keto prostaglandin F2a (PGFM) in cows with a short, but not normal, oestrous cycle length (Zollers et al, 1989). Similarly, Hunter et al (1989) have demonstrated an association between pulses of oxytocin and PGFM on day 5 in ewes with short luteal phases similar to that observed during normal luteolysis.…”