Posparto y amamantamiento en ovejas: efecto sobre el desempeño reproductivo a una IATF con re-sincronización en otoño

The sheep sector in the country has been undergoing transformations, the most notable of which is production specialization, with the production of fine and super fine wool located mainly in the north of the country. On the other hand, producers with flocks of medium and thick wool, saw difficulties in selling for several harvests, accompanied by attractive values ​​in the price of meat, found themselves in the need to look for new alternatives to increase income. This is how the production of heavy lamb for export emerged, and the production of sheep meat as an attractive item for the sector. For this productive option, obtaining a greater number of lambs per year, and the search for tools that promote an increase in the reproductive results of the flocks, seems to be a priority. Having followed a technological path that, among other things, decreased the perinatal mortality of lambs and increased the prolificacy of flocks, some researchers in the country have focused their interest on accelerating the interval between calving, although they have found limitations in reproductive results when serving ewes giving birth and suckling. This experiment compares the reproductive results of synchronization and subsequent resynchronization of oestrus and ovulation using fixed-time artificial insemination (FTAI) in the reproductive season of multiparous ewes calving in early autumn and suckling (PAR group), with that of multiparous ewes that calved in spring and had been weaned 3 months earlier (Group CON). In general terms, the PAR group ewes had a worse performance, mainly in synchronization and first IATF than those of the CON group. They had a lower (P ≤ 0.05) presentation of estrus (39.4%), percentage of ewes that at 17 days presented a vascularized corpus luteum indicator of early pregnancy (21.2%), and at 42 days none of them was diagnosed pregnant. In comparison to the CON group in which 71.7% of ewes were observed to be in heat and a pregnancy at 42 days of almost 60% of the ewes. However, at resynchronization and second FTAI, no differences were observed in the percentage of oestrus between groups (62.5% and 65.2% PAR and CON groups, respectively), and although at 42 days a tendency was found for pregnancy percentage was lower in PAR ewes than in CON ewes (20.8% vs 43.4%; P = 0.06), the percentage of lambing was not different between groups (20.8% and 34.7 %, PAR and CON group, respectively). As a result of both FTAI, calving results were higher in the CON group than in the PAR group (71.7% vs 15.1%; P = 0.005). Based on the results obtained, it is concluded that the technique used is not recommended in ewes 30 days postpartum and nursing a lamb.