The Ovariectomized Ewe: Its Contribution to Controlled Breeding

Nw, Moore

doi:10.1071/bi9880015

Cited by 4 publications

(3 citation statements)

References 32 publications

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“…Therefore, as puberty is normally preceded by a luteal phase (Ronayne, Fitzsimons, Hanrahan, Quirke and Roche, 1991) a deficiency at this time might account for the infertility observed in group A in experiment I. This cannot explain the subfertility of the animals given a single oestrogen and progestagen therapy prior to mating because this treatment would have simulated endocrine changes similar to those that occur during a normal oestrous cycle (Moore, 1988). Furthermore, the subfertility observed in this group was similar to that recorded for pubertal ewes given progestagen/PMSG treatment (Quirke et ah, 1983).…”

Section: Discussionmentioning

confidence: 69%

The effect of stage of breeding season or pre-mating oestrogen and progestagen therapy on fertility in ewe lambs

Beck

Davies

1994

Anim. Sci.

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An investigation was conducted to determine the effect of mating at puberty or third oestrus or after pre-mating oestrogen and progestagen therapy, designed to mimic the changes that occur in plasma oestrogen and progesterone concentrations during the 1st, 2nd or 3rd oestrous cycles, on fertility in ewe lambs. Twenty-five ewe lambs were mated at puberty on mean date of 18 October and 21 were mated at third oestrus on 3 December. Of these, 28% and 81% of animals mated at puberty and third oestrus lambed, respectively (P < 0-05). A similar number of ewe lambs were mated within 24 h of ram introduction in the groups given one, two or three consecutive applications of oestrogen and progestagen (25 fig oestradiol benzoate followed 48 h later by a progestagen pessary left in situ for 12 days). Of the 43 corpora lutea, 21 were represented by viable embryos in the 37 animals holding to service after one application compared with 34 out of 46 corpora lutea in 40 animals given three applications (P < 0-05). Furthermore, embryo crown-rump length, embryo weight and amniotic sac width was greater (P < 0-05), on day 32 of pregnancy, in animals given one compared with three applications of oestrogen and progestagen. These results demonstrate that fertility is improved in ewe lambs mated on third oestrus or after progestagen and oestrogen therapy designed to simulate three oestrous cycles.

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Section: Discussionmentioning

confidence: 69%

The effect of stage of breeding season or pre-mating oestrogen and progestagen therapy on fertility in ewe lambs

Beck

Davies

1994

Anim. Sci.

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“…Exogenous MAP (Ricketts and Flint, 1980) and progesterone (Moore, 1988) have been used to maintain pregnancy in ovariectomized or otherwise luteally impaired ewes. Parr et al (1992) showed that post-mating supplementation increased the proportion of pregnant ewes only when the ewes were subjected to a nutritional regime which promoted peripheral plasma progesterone deficit through an increased metabolic clearance rate (Parr et al, 1993).…”

Section: Discussionmentioning

confidence: 99%

Ram-induced reproduction in seasonally anovular Corriedale ewes: MAP doses for oestrous induction, ram percentages and post-mating progestagen supplementation

1997

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Exploiting the 'ram effect' is an inexpensive alternative for out-of-season breeding in moderately seasonal breeds. For maximum efficacy in Corriedale sheep, oestrous ewes have to be introduced together with the teaser rams. Successful applications depend upon timely manipulation of the animals to induce oestrus in most ewes and to minimize the likelihood of successfully induced non-pregnant ewes returning to anoestrus during the mating period. In the first of two experiments, the effects of two alternative ram : ewe ratios (1 : 6 or 1:12) and five different doses (0, 15, 30, 45 or 60 mg) of medroxy-progesterone acetate (MAP) applied in intravaginal sponges for 9 days were assessed on seasonally anovular adult Corriedale ewes. Control ewes (0 MAP) did not receive sponges, but were injected with 20 mg progesterone at ram introduction. A second experiment tested the efficacy of post-oestrus intravaginally applied MAP (30 mg; 7-day treatment starting on days 3 to 6 after oestrus) for improving reproductive variables of successfully induced ewes exposed to entire rams. Proportions of ewes ovulating and ovulation rates (assessed through laparoscopy) did not differ significantly (P > 0-05) in ewes treated with various MAP doses (213/220 = 96-8% and 1-26 (s.e. 0-031) respectively) or injected with progesterone (56/58 = 96-6% and 1-21 (s.e. 0-058) respectively). The MAP content of the sponges did not affect (V > 0-05) the proportion of ewes ovulating (269/278), marked by the rams (197/213), returning to oestrus (81/197) or lambing among those not returning to first oestrus (87/119). More ewes were marked in the groups exposed to a higher ram percentage (79-7 to 70-6%; P < 0-001) but no other reproductive variable was affected by the ram: ewe ratio at ram introduction (P > 0-05). In the second experiment, post oestrus progestagen supplementation reduced the proportion of ewes returning to first oestrus from 27% to 16% (P < 0-05) but failed to improve lambing rate or the number of lambs born per ewe lambing. Thus, MAP doses as low as 0-25 of the commercial formulation (60 mg) induced oestrus in seasonally anovulatory Corriedale ewes exposed to rams and oestrous ewes. Increasing the ram : ewe ratio augmented the proportion of marked ewes but did not affect any other reproductive variable. Supplementing MAP after oestrus did not improve reproductive rate in Corriedale ewes induced to ovulate during the seasonal anoestrus.

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“…Given their stimulatory (kisspeptin and NKB) and inhibitory (dynorphin) roles in GnRH/LH secretion, we hypothesized that chronic undernutrition, which we have shown suppresses LH secretion in young, castrated male sheep, 49 would inhibit expression of kisspeptin and NKB at the same time as stimulating dynorphin expression in the ARC and within KNDy neurons of OVX sheep. In the present study, we used OVX sheep, a longstanding animal model in reproduction, 50 to directly examine the nutritional effects on LH secretion apart from changes in sensitivity to gonadal steroids. In addition, in the present study, we used maintenance fed females as controls.…”

Section: Introductionmentioning

confidence: 99%

The impact of undernutrition on KNDy (kisspeptin/neurokinin B/dynorphin) neurons in female lambs

Harlow

Griesgraber

Seman

et al. 2022

J Neuroendocrinology

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Undernutrition limits reproduction through inhibition of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) secretion. Because KNDy neurons coexpress neuropeptides that play stimulatory (kisspeptin and neurokinin B [NKB]) and inhibitory (dynorphin) roles in pulsatile GnRH/LH release, we hypothesized that undernutrition would inhibit kisspeptin and NKB expression at the same time as increasing dynorphin expression. Fifteen ovariectomized lambs were either fed to maintain prestudy body weight (controls) or feed-restricted to lose 20% of pre-study body weight (FR) over 13 weeks. Blood samples were collected and plasma from weeks 0 and 13 were assessed for LH by radioimmunoassay. At week 13, animals were killed, and brain tissue was processed for assessment of KNDy peptide mRNA or protein expression. Mean LH and LH pulse amplitude were lower in FR lambs compared to controls.We observed lower mRNA abundance for kisspeptin within KNDy neurons of FR lambs compared to controls with no significant change in mRNA for NKB or dynorphin.We also observed that FR lambs had fewer numbers of arcuate nucleus kisspeptin and NKB perikarya compared to controls. These findings support the idea that KNDy neurons are important for regulating reproduction during undernutrition in female sheep.

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The Ovariectomized Ewe: Its Contribution to Controlled Breeding

Cited by 4 publications

References 32 publications

The effect of stage of breeding season or pre-mating oestrogen and progestagen therapy on fertility in ewe lambs

The effect of stage of breeding season or pre-mating oestrogen and progestagen therapy on fertility in ewe lambs

Ram-induced reproduction in seasonally anovular Corriedale ewes: MAP doses for oestrous induction, ram percentages and post-mating progestagen supplementation

The impact of undernutrition on KNDy (kisspeptin/neurokinin B/dynorphin) neurons in female lambs

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