REPETITION OF PROGESTOGEN (FGA) AND OTHER GONAD STIMULATING HORMONE (FSH AND LH) TREATMENTS IN LATE LACTATING LACAUNE EWES - EFFECTS ON PRODUCTION AND MILK-COMPOSITION AND ON ALVEOLAR AND CISTERNAL DISTRIBUTION

After a brief nursing period (48 h), 132 Lacaune ewes were machine mil ked for a preexperimental period of 7 weeks (S1-S7). At the end of thi s period, the ewes were divided into three groups of 44 ewes each that were balanced with respect to production and milk composition. During the experimental period of 16 weeks (S8-S23), the first group underwe nt a superovulation treatment (six injections of FSH and LH) every 4 w eeks (S8, S12, S16, S20). These injections occurred at the same time a s the removal of a sponge (FGA 40 mg) which had been placed in the vag ina 14 d earlier (S5 S10, S14, S18). The second group of ewes received the same sponges at the same times and for the same intervals, but di d not have the FSH and LH injections. The third group did not receive either the sponges (FGA) or the injections (FSH and LH). The results i ndicated that the milk production increased during the period of the s ponge implantation, The increase was most noticeable during Be first 7 days. It then decreased regularly as the sponge became discharged. In the sheep that received the injections of FSH at the moment when the sponge was removed (first group), the milk production again increased to a peak 7 or 8 d after the injections, During the 16 week experiment al period, the ewes from the three groups (values are for groups 3, 2 and 1, respectively) produced a daily average of 955.3, 983.8 (+3.0%) and 1 063.0 (+11.3%) mL of milk: 68.1, 68.6 (+0.7%) and 74.1 (8.8%) g of fat: 47.1, 48.1 (+2.1%) and 52.3 (+11.10%) g of protein, for fat co ntents of 72.8, 71.0 and 70.8%, and protein contents of 49.9, 49.4 and 49.8 %. This study suggests that milk secretion may be stimulated by i) exogenous progestagens (FGA) or endogenous ones (progesteron), but the precise mechanism is, as yet, unclear; and ii) that luteal oxytoci n avoids the inhibiting consequences of stagnant milk on the metabolis m or the epithelial cell lining the walls of the acini, by facilitatin g the transfer of the aveolar milk to the cistern.