EFFECT OF REPEATED USE OF PROGESTAGEN-PMSG TREATMENT FOR ESTRUS CONTROL IN DAIRY GOATS OUT OF BREEDING-SEASON

In order to analyze the effects of repeated use of progestagen-PMSG treatment, estrus and pregnancy results have been analyzed for 1989 in a Saanen dairy goat herd in which breeding takes place each year out of season after FGA/PMSG treatment. After the first 1989 treatment (169 goats), percentage of goats showing estrus and kidding have been lower for 59 multiparous than for 46 primiparous and 64 nulliparous females. Moreover, when 38 goats are treated for a second time in 1989, 44.7% exhibited estrus vs 71.0% after the first treatment (P < 0.05). The PMSG binding level before the lst 1989 treatment is higher for multiparous (17.5+/-23.1%) than nulli and primiparous (-0.06+/-0.7 and 1.2+/-1.9%) and is increased for all parities after treatment (23.2+/-26.4 after vs 5.7+/-15.0% before, P < 0.01). For nulliparous and primiparous females; PMSG binding levels are not different for pregnant or not pregnant nulliparous and primiparous goats. On the opposite, PMSG binding rates are higher in non pregnant (25.7+/-23.3) than in pregnant multiparous goats (6.5+/-15.9) (P < 0.01). However, when the binding rate is less-than-or-equal-to 5.12% (computerized distributions) multiparous goats exhibit estrus and pregnancy at levels not different from nulliparous or primiparous females (% estrus 95.8 vs 100 or 97.8%, % pregnancy 66.7 vs 70.3 and 63.0% respectively). Repeated use of PMSG during the female life or during one given year leads to active immunization against PMSG (as measured by percentage of binding of PMSG in plasma) decreasing the efficiency of ovarian stimulation out of breeding season.