The Fertility of Heifers Inseminated at Predetermined Intervals Following Treatment With Mga and HCG to Control Ovulation

The influence of Gn-RH, hCG and a PMSG-hCG mixture (PG600) on the time of ovulation, ovulation rate and on the occurrence of oestrus in ewes treated with progestagen-impregnated sponges for 12 days examined. The effects of Gn-RH analogues on plasma LH, oestrus, ovulation and conception rate were also investigated. Six separate experiments were carried out. When 50 micrograms Gn-RH were given 24 h after sponge removal ovulation occurred in 44--46% of ewes within 24 h and in all ewes by 34 h. Gn-RH was a more potent ovulation synchronizer than hCG. Both hCG and PG600 reduced the incidence of overt oestrus. Gn-RH also had this effect in ewes treated during February and May but not in August and September. Gn-RH analogues given 2 days before sponge removal significantly increased ovulation rate. The display of oestrus was not affected in ewes treated 2 days before sponge removal but was suppressed in 43-69% of ewes treated with an analogue at the time of sponge removal. Ovulation occurred in 50-62% of ewes within 30-35 h of injection of Gn-RH analogues, regardless of the time of their administration. The release of LH in response to one analogue was not influenced by the presence of the progestagen-impregnated sponge in the vagina. When given a Gn-RH analogue 2 days before sponge removal or at the time of sponge removal 63 and 62% of mated ewes became pregnant compared with 70% of control ewes.

Section: Discussionsupporting

confidence: 74%

Oestrus, time of ovulation, ovulation rate and conception rate in progestagen-treated ewes given Gn-RH, Gn-RH analogues and gonadotrophins

Quirke¹,

Jennings²,

Hanrahan³

et al. 1979

“…Oestrus and ovulation can be synchronized in cows with progestagens but the conception rate to matings at the controlled oestrus is lower than normal (Hansel, 1967;Mauléon & Chupín, 1971; Jochle, 1972;Roche & Crowley, 1973). When the period of progestagen treatment is reduced to 10 days, by giving an injection of oestrogen on the 1st day of progestagen treatment to induce premature regression of the CL, the conception rate has been reported to be normal (Wiltbank & Kasson, 1968;Wiltbank, Sturges, Wideman, Le Fever & Faulkner, 1971; Chupín, Le Provost, Mauléon, Ortavant, Parez & Petit, 1972;Roche, 1974a).…”

Section: Introductionmentioning

confidence: 99%

Effect of Short-Term Progesterone Treatment on Oestrous Response and Fertility in Heifers

Roche¹

1974

Self Cite

The reasons for a reduced oestrous response in heifers following a 9-day treatment with implants of progesterone were determined. Progesterone implants were inserted into Hereford cross heifers for 9 days at different stages of the oestrous cycle. Oestradiol benzoate (5 mg) was also given at the time of insertion of implants. The oestrous response obtained was low in animals receiving implants on Days 3 or 17 but was high in those receiving implants between Days 5 to 15. Injecting 50 mg progesterone with the 5 mg oestrogen increased the oestrous response in animals receiving implants on Day 17 but the onset of oestrus was more variable following this treatment in animals receiving implants on Day 3 or between Days 5 and 15. Removing the implants after 12 days instead of 9 days, however, gave a precise onset of oestrus. The conception rate to A.I. was not different in heifers synchronized with a 9or 12-day treatment from that of the controls but it was lower in heifers synchronized with implants of progesterone removed after 18 or 21 days. The high conception rates obtained at slaughter 30 to 40 days after the last insemination were substantiated by allowing a group of heifers to calve after synchronization with a 9-day progesterone treatment.

“…Long-term progestagen treat¬ ments have resulted in reduced fertility levels at the controlled oestrus (Jochle, 1972). The use of oestrogens (Ulberg & Lindley, 1960;Hansel et al, 1961) and Oestrous cycle control in heifers 369 gonadotrophins (Graves & Dziuk, 1968;Boyd & Tasker, 1971;Roche & Crowley, 1973) in association with long-term progestagen treatments and fixedtime insemination procedures have generally resulted in further reductions in conception rates. Recent reports have indicated that if the period of progestagen treatment is reduced to about 10 days, fertility levels are normal at the con¬ trolled oestrus (Wiltbank & Kasson, 1968;Wishart & Young, 1974;Roche, 1974;Sreenan, 1975).…”

mentioning

confidence: 99%

The Application of Long- And Short-Term Progestagen Treatments for Oestrous Cycle Control in Heifers

Sreenan¹,

Mulvehill²

1975

Progestagen-impregnated pessaries were inserted into 205 heifers on eight farms. Treatments were either pessaries only for 20 days or pessaries for 10 days combined with an intramuscular injection of 250 mg progesterone+7-5 mg oestradiol benzoate on the day of insertion. Pessary retention was low (86.7%) over the 20-day period, but high (93-6%) during the 10-day period. Calving rates of heifers inseminated in oestrus following the 20-day treatment were low, while those of heifers inseminated on a fixed-time basis with the 10-day treatment were slightly higher than those of control heifers.