Reproductive responses associated with ram introduction in mature tropical Menz ewes after a period of isolation

doi:10.1016/0378-4320(94)90071-X

Animal Reproduction Science

Volume 36, Issues 3–4, September 1994, Pages 243-251

https://doi.org/10.1016/0378-4320(94)90071-X Get rights and content

Abstract

This study was undertaken using 48 mature Menz ewes (3–6 years of age) and averaging 31.5 (standard deviation (SD) = 4.9) kg body weight, to evaluate oestrus synchronization, conception and lambing rates after ram introduction following a period of isolation (n = 24) or constant exposure to vasectomized rams (n = 24) on a low or high level of nutrition.

The overall level of oestrus synchrony was low (27%), but was higher for animals previously isolated (38 vs. 17%). The mean interval from ram introduction to oestrus was 12.2 (SD = 7.3) days, but this was significantly shorter for isolated ewes (9.4 ± 1.2 vs. 14.8 ± 1.7 days, P < 0.05). Animals previously better fed were heavier at mating (P < 0.01), but this had no relationship to the response to ram stimulation (P > 0.05). Oestrus after ram introduction included two peaks (at 6 and 13 days) which were influenced by the behaviour of previously isolated animals. Conception rates to first and second service of 86% and 14%, respectively, were confirmed by plasma progesterone determinations. Subsequent lambing rate was only 72%, suggesting high prenatal reproductive wastage. Lambing was compacted, except for ewes conceiving at their second oestrus. There were as many twins born to isolated ewes as to exposed ewes but substantially more to ewes that were heavier at mating. These data suggest that, although ram introduction after a period of isolation will not increase ovulation and twinning rate in isolated Menz sheep as judged by litter size, it is a natural tool that could be useful to match events of the reproductive cycle of tropical sheep with feed and other management resources.

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Cited by (3)

Investigation of ram effect and eCG usage in progesterone based oestrous synchronization protocols on fertility of ewes following fixed time artificial insemination
2020, Small Ruminant Research
Citation Excerpt :
It is however worth noting that studies which used short-term P4 and reported a higher proportion of ewes lambing to the first service period than what was obtained in the present study used PGF2α at the end of the treatment period (Martemucci and D’Alessandro, 2011; Fleisch et al., 2012) and intrauterine or natural methods of breeding (Fukui et al., 1994; Martemucci and D’Alessandro, 2011; Fleisch et al., 2012), which was possibly the reason for better lambing performance observed in these studies. Whereas other researchers who studied fertility following short-term P4 treatment did not report on the proportion of ewes which lambed to the first service period (Viñoles et al., 2001; Ali et al., 2009), suffice to say that benefits of oestrus synchronization using various protocols can only be fully realised when ewes which conceive carry their foetuses to term (Mukasa-Mugerwa et al., 1994). In conclusion, this study has shown that eCGshort, eCGlong, Ramshort and Ramlong oestrus synchronization protocols had similar effectiveness on oestrus synchronization and fertility, although the proportion of ewes lambing to the first service period in the Ramshort group was lower.
Improving oestrus synchronization protocols is important, particularly to ensure that protocols which guarantee reduced hormonal use and environmental safety also result in acceptable reproductive efficiency. The aim of this study was to compare the effect of long and short-term progesterone (P4) treatment and their combination with either equine chorionic gonadotropin (eCG) or the ram effect (Ram) on oestrous response and fertility of ewes. Seventy-eight South African Mutton Merino ewes were randomly allocated to four treatment groups in a 2 × 2 factorial design and primed with controlled internal drug release (CIDR) for a 9 (short) or 14 d (long) period. At CIDR withdrawal, ewes in each group received either a single intramuscular injection of equine chorionic gonadotrophin (eCG; 300 IU) or exposure to the ram effect; eCGshort (n = 19), Ramshort (n = 21), eCGlong (n = 19) and Ramlong (n = 19). Oestrous behaviour was monitored from 12−84 h post CIDR withdrawal. Ultrasound was performed at 48 h post CIDR withdrawal to examine number and diameter of follicles. Artificial insemination (AI) was performed twice at 48 and 60 h post CIDR withdrawal with fresh undiluted semen using the cervical method. Pregnancy diagnosis was performed by transrectal ultrasound at 35 d post AI and confirmed by lambing data. Oestrous behaviour was observed in 98.7% of all synchronized ewes, with no significant difference among treatment groups. Overall, conception rate (CR) and the proportion of ewes lambing to synchronized oestrus were (74.4% and 52.6%, respectively). There was no significant difference among treatment groups in oestrous response, onset of oestrus, number of follicles, diameter of the largest follicle, CR and AI to lambing interval (P > 0.05). When data were pooled, CIDR-14 d protocols showed a significantly shorter interval to onset of oestrus (24.9 ± 1.6 vs 30.8 ± 2.1, P < 0.05) than CIDR-9 d protocols but there was no difference (P > 0.05) between eCG and Ram protocols when data were pooled. CIDR-9 d protocols resulted in a significantly higher CR (85.0% vs 63.2%, P < 0.05) than CIDR-14 d protocols when data were pooled, but CR between eCG and Ram protocols was not statistically different (P > 0.05). Mean AI to lambing interval was 158.2 ± 1.2 d, ranging from 147 to 154 d and 166 to 186 d post AI. Ewes lambing to synchronized oestrus per treatment group were 52.6% (eCGshort), 42.9% (Ramshort), 63.2% (eCGlong) and 52.6% (Ramlong), respectively (P > 0.05). In conclusion, the 4 protocols investigated were effective in synchronizing oestrus with similar response to synchronization of oestrus and fertility among treatment groups. Of the 4 protocols, the Ramlong protocol offers the benefit of being less costly because of reduced hormonal use in addition to the adequate fertility obtained.
Reproductive performance and productivity of Menz and Horro sheep lambing in the wet and dry seasons in the highlands of Ethiopia
2002, Small Ruminant Research
Ewe reproduction and productivity were studied in the highlands of Ethiopia in Horro and Menz ewes mated to lamb in both the wet and dry seasons from June 1992 to May 1997. The data included a total of 4890 mating records of which 2516 were Menz ewes and 2374 Horro ewes, with 2360 matings in the wet season and 2530 in the dry season. Menz sheep had a significantly higher (P<0.001) weaning rate (lambs weaned per ewe mated) than the Horro ewes (0.73 versus 0.57, respectively) and ewes which lambed in the wet season had a significantly higher (P<0.001) weaning rate than those that lambed in the dry season (0.76 versus 0.53, respectively). Menz ewes showed their superiority in weaning rate over the Horro ewes more clearly when lambing in the wet season (0.85 versus 0.67, respectively) than when lambing in the dry season (0.59 versus 0.47, respectively). Overall flock productivity was expressed in terms of potential offtake of yearling sheep from flocks of Menz or Horro ewes lambing in either the wet or dry seasons. Both in terms of number of yearling sheep for sale and total live weight for sale, the offtake of a flock of Menz sheep in this environment was approximately three-fold greater than a flock of Horro sheep when they lambed in the wet season and approximately two-fold greater when they lambed in the dry season. Season had no effect on offtake in Horro ewes, but the Menz ewes lambing in the wet season had about a 1.5-fold greater offtake than Menz ewes lambing in the dry season.
In the first 3 years of the study (1992–1995), oestrous synchronisation was used at each mating. Oestrus was synchronised with intravaginal sponges containing 40 mg flugestone acetate (FGA). Most of the ewes (83%) came in oestrus after hormonal treatment and out of these 81% were synchronised and mated within 5 days after sponge removal. The percentage of ewes synchronised was 10% higher after treatment in the wet season than in the dry season (P<0.01) and 7% higher for Menz sheep than for Horro sheep (P<0.01). Of the ewes that eventually lambed, 73, 17 and 10%, respectively, conceived at the first, second and third or subsequent oestrus with an average 1.5 services per pregnancy.
Reproductive performance and productivity of Menz sheep in the Ethiopian highlands
1995, Small Ruminant Research
Ewe lambs attain puberty at 10 months and 16.9 ± 0.1 kg (56% of mature weight) and first lamb at 15 months. Postpartum anoestrus is 76 days, lambing interval is 8.4 months and 65% of ewes lamb three times in 2 years with a gestation period of 149 days. Ewes cycle year-round but oestrus activity declines from June to September due to increased silent ovulations. Fertilisation rates are high (⩾90%) but lambing rate is 72%, suggesting moderate embryonic mortality. Conception rates to first, second and third oestrus postpartum are 78%, 18% and 4%, respectively. Litter size (prolificacy) is 1.12 but can be increased by 10–40% through premating ewe nutrition management or treatment with gonadotropins. Ewe oestrus activity can be synchronised by ram introduction after a period of isolation and with progesterone sponges or prostaglandin F_2α therapy. Lambs average 2.0 ± 0.1 kg at birth but preweaning mortality (15%) and slow growth, resulting in 8.6 kg weaning weight, still limit overall productivity index to 11.0 ± 0.87 kg per ewe per year, and the annual reproductive rate to 1.4 lambs per ewe. In the traditional management system, where most animals are raised, further studies are required into better nutrition and control of diseases (endoparasitism) in young animals to increase reproductive efficiency, flock productivity and number of animals for finishing and slaughter. This could serve as a model for interventions in other ruminants in the agroecological zone.

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Reproductive responses associated with ram introduction in mature tropical Menz ewes after a period of isolation

Abstract

Br. Vet. J.

Anim. Reprod. Sci.

Livestock Prod. Sci.

Anim. Reprod. Sci.

Theriogenology

Small Rumin. Res.

Anim. Reprod. Sci.

Increased ovulation rate at the ram-induced ovulation and its commercial application

Use of teasing in an AI programme

Ram influence on ovarian and sexual activity in anoestrous ewes: effects of isolation of ewes from rams before joining and date of ram introduction

J. Anim. Sci.

Sheep germplasm in Ethiopia

UNEP/FAO Animal Genetic Resources Newsletter No. 1

Synchronisation of oestrus in sheep of low-normal mass under range conditions: the use of different progestagens and PMSG

South Afr. J. Anim. Sci.

A note on the effect of the direction of liveweight change about the time of mating on reproductive performance of Greyface ewes

Anim. Prod.