Age at puberty, fertility and litter size of ewe lambs reared under different photogegimens

Effect of stimulation with a gonadotropin mixture on reproductive outcome in nulliparous ewes bred during seasonal anestrus and early breeding season

“…However, ram-induced gonadotropin secretion might not stimulate production of sufficient quantities of estrogen to induce estrus in most ewe lambs during seasonal anestrus. Supplementation with estrogen directly (Knights et al, 2002) or with gonadotropins (Ainsworth and Shrestha, 1987;Ainsworth et al, 1991 and current study) improved reproductive performance in fall-born ewe lambs exposed to rams during mid-anestrous. Gonadotropic supplementation of yearlings bred during seasonal anestrus may be necessary (Robinson and Smith, 1967;Burfening and Van Horn, 1970) or of little benefit (current study) depending on the extent to which the ram effect response is maximized.…”

“…Treatment with equine chorionic gonadotropin (eCG) after progestogen priming induced fertile estrus in fallborn ewe lambs (Ainsworth and Shrestha, 1987;Ainsworth et al, 1991;Stellflug et al, 1993) and yearlings (Robinson and Smith, 1967;Burfening and Van Horn, 1970) bred during seasonal anestrus. Additionally, a small dose of estrogen increased the proportion of progesterone-primed fall-born ewe lambs expressing estrus during anestrus (Knights et al, 2002).…”

Effects of a Gonadotropin Mixture on Reproductive Success in Progesterone- Treated Non-Lactating Anestrous Ewes

“…Attempts to breed fall-born ewe lambs out-of-season have not been successful. Approaches used to evaluate the response have included ram introduction alone (Lopez-Sebastian et al, 1985), manipulation of the photoperiod (Ainsworth and Shrestha, 1987;Ainsworth et al, 1991), and use of gonadotropins in combination with progesterone and estradiol (Foote and Bennett, 1968). With ram introduction alone, fall-born ewe lambs exhibit "silent ovulations," where they are observed to ovulate, but often times do not exhibit estrus until the second or even third ovulation.…”

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

“…In order for the age at first lambing in fall and spring lambing systems to be comparable, fall born ewe lambs must be bred during the period of seasonal anestrous. Treatment with long days (from 5 to 20 weeks) followed by a period of short days (20-32 weeks) with progestogen-eCG treatments commencing towards the end of the short day photoperiod induced fertile estrus in fall born lambs during seasonal anestrous (Ainsworth and Shrestha, 1987;Ainsworth et al, 1991). The percentage of ewe lambs lambing and the litter size to two service periods after synchronization treatments were 58% and 1.6, respectively.…”

“…Photoperiodic manipulations (long day followed by short days) have also been used to induce puberty during the anoestrous period in fall born ewe lambs (Foster and Ryan, 1981;Ainsworth and Shrestha, 1987;Ainsworth et al, 1991).…”