Ovarian stimulation following repeated injections of LH or LH + FSH in Ile-de-France sheep in early and mid-seasonal anoestrus

Variations between years in the ram effect when Coopworth or Poll Dorset rams are introduced to seasonally anovular Coopworth ewes

“…Because time of onset of the breeding season (spontaneous oestrus) varies between years (Montgomery et al 1988), depth of anoestrus at any fixed time of the year could also be expected to vary. In support of this view, two types of anoestrus have recently been distinguished (Oussaid et al 1993). Type 1 is characterised by a slight anoestrus with high plasma levels of folliclestimulating hormone (FSH) and presence of normal follicles.…”

Induction of fertile estrus during seasonal anestrus in ewes and fall born ewe lambs

“…Although some reports suggest there is little change in the secretion of FSH between the estrous and anestrous seasons Bister and Paquay, 1983;Bartlewski et al, 1998;, others have observed lower concentrations of FSH in the ewe (Findlay and Cumming, 1976;Legan and Karsch, 1980) and at a time equivalent to anestrous in the ram (Lincoln et al, 1977;1982). Oussaid et al (1993) observed a higher concentration of FSH during early than mid-anestrous and suggested that the contrasting results obtained in comparisons between seasons may be a result of the time (early vs mid vs late) within anestrous when samples were taken. Suppression of LH pulse frequency that is needed to drive final stages of follicular maturation and lower concentrations of FSH may reduce the number of ovulatory follicles during seasonal anestrous.…”

“…Long-term GnRH administration maintained cyclic activity during anestrous in Romney ewes (McNatty et al, 1982) but LH alone failed to do so beyond two consecutive cycles (McNatty et al, 1984b). A decrease in the responsiveness to LH also occurs from early to middle anestrus (Oussaid et al 1993). During early anestrus repeated LH administration alone (10 ug i.v.…”

“…However, during mid-anestrus treatment with FSH (50 µg i.v. every 2 h for the first 24 h) was also necessary to induce ovulation in response to LH administration (Oussaid et al, 1993). The authors thus suggested that an increase in estradiol negative feedback on FSH occurs gradually during anestrus and this is associated with a gradual decline in responsiveness to LH.…”

“…Cahill (1984) suggested therefore that gonadotropins are more useful in super-ovulating ewes rather than increasing twin ovulations. With respect to increasing ovulation rate and prolificacy during the seasonal anestrous, the response to a given dose of gonadotropins may be lower and more variable due to a decreased and variable sensitivity of the ovarian follicles (Oussaid et al, 1993;Noël et al, 1999). An ovulation rate of between 2.3-3 (1-5 range)…”