Postpartum Mating Performance of Ewes Involved in a Twice-Yearly Lambing Program

Whiteman, J. V.; Zollinger, William A.; Thrift, F. A.; Gould, M. B.

doi:10.2527/jas1972.354836x

Cited by 32 publications

(16 citation statements)

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“…The conception of about 40% is not satisfactory, since mating occurred under natural conditions (Figure 1). Although the average period of 39 days from lambing to removal of rams in the present study was somewhat shorter than the 44 days given by Whiteman et al (1972), there were about 40 % of dry ewes in the previous production cycle and a great proportion of ewes that lambed in the previous production cycle had a much longer period between lambing and removal of rams than the 44 days. The autumn mating of 1971 overlapped with lambing by 11 days and the mating period lasted 70 days; the mating period in autumn 1973 overlapped with lambing by 28 days and lasted only 51 days.…”

Section: Resultscontrasting

confidence: 66%

Application of light control to shorten the production cycle in two breeds of sheep

Vesely¹

1978

Anim. Sci.

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An average of 60 Rambouillet and 60 Suffolk ewes was maintained under an intensive management system to lamb about every 7 months. Decreased daylength was used for oestrus induction in normally anoestrous periods. The experiment lasted 3-7 years, during which time six lamb crops were produced, three of them as a result of outof-season mating. Ewes of each breed were subdivided into three experimental groups and each breed-group was maintained under one of three different light treatments before and during out-ofseason mating. Imposed Treatment 1 consisted of a pre-mating period under natural daylight followed by a mating period of short daylength (8 h/day). Ewes under imposed Treatments 2 and 3 were exposed to 16 h of light during the pre-mating period and to 8 h of daylight during the mating period. This did not affect conception significantly in the Rambouillet but it did in the Suffolk. Different intensities and wavelengths of light during the long daylight period (16 h/day) were used in Treatments 2 and 3 but did not cause different responses. In Rambouillet ewes the first mating (out-of-season) gave 73 % conception. It was followed by two in-season matings with 72 and 85 % conceptions. The last three matings (out-of-season, in-season, outof-season) resulted in 57, 42, and 58 % conceptions. In the Suffolk ewes, the conceptions were 30, 88, 77, 3, 77, and 10% in the same order as those for Rambouillet. The average production of Rambouillets on the three treatments was 166 lambs per 100 ewes per year (165, 177, 157) whereas Suffolks produced 132 lambs (120, 143, 135). Control Rambouillet and Suffolk ewes maintained under natural daylight year-round produced 139 and 117 lambs.

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Section: Resultscontrasting

confidence: 66%

Application of light control to shorten the production cycle in two breeds of sheep

Vesely¹

1978

Anim. Sci.

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“…In these data, approximately 20% of ewes exposed in spring conceived. Such reduced conception rates during spring have consistently been reported in Dorsets and other breed types (Whiteman et al, 1972;Notter and Copenhaver, 1980;Fogarty et al, 1984;Iniguez et al, 1986). Although Dorsets are considered a desirable breed for accelerated lambing because they tend to have an extended breeding season (Dufour, 1974), clearly they exhibit enough seasonality to restrict performance in such programs.…”

Section: Discussionmentioning

confidence: 65%

Ewe fertility in the STAR accelerated lambing system.

Lewis

Notter

Hogue

et al. 1996

Journal of Animal Science

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Effects of environmental factors such as ewe age, season of exposure, and time from lambing to exposure on fertility were evaluated using records on 1,084 Dorset ewes in the STAR accelerated lambing system. The STAR program consisted of five 30-d concurrent breeding and lambing periods per year beginning on January 1, March 15, May 27, August 8, and October 20. Fertility in the flock changed in a cyclic and predictable fashion during the year. Changes in prolificacy were less consistent but also tended to show cyclic variation. Matings that occurred within the typical breeding season (August, October, and January) were more fertile than those occurring in March and June. However, fertility also varied with the age of the ewe and the time since the ewe's last lambing. Except in June, fertility at the first postpartum mating increased as ewes aged. In March and June matings, adult ewes that had just weaned lambs were less fertile than ewes that had failed to conceive in the previous season and therefore had longer postpartum intervals. However, in October and January, ewes that had just weaned lambs were more fertile. A matrix of expected pregnancy rates, or probabilities of fertility, was constructed using a mixed GLM to describe the combined effect of season, ewe age, and time since lambing on ewe fertility in accelerated lambing.

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“…Effects of calf removal were most favorable when associated with timed inseminations (Kiser et al, 1980;Geary et al, 2001b) and if cows were in sub-optimal body condition (Kiser et al, 1980), but were less reliably observed in cows mated at estrus (Geary et al, 2001a). In sheep, reducing suckling intensity by separating spring-lambing ewes from their lambs during the daylight hours had no obvious positive effect on spring fertility (Whiteman et al, 1972), but that study did not include a control group. Further study is thus required to determine if lamb separation and progesterone injections are beneficial in less-fertile ewes.…”

Section: Discussionmentioning

confidence: 95%

“…Whiteman et al (1972) reported that only 23% of lactating Dorset, Rambouillet and Dorset × Rambouillet crossbred ewes managed in a twice-yearly lambing system in Oklahoma lambed again following spring lambing and 60 days of ram exposure beginning on April 20 (i.e. ∼16 days after the mean lambing date).…”

Section: Discussionmentioning

confidence: 99%

“…These systems all recommend early weaning of lambs in order to improve fertility in spring matings, but early weaning is often not consistent with forage-based lamb production. Attempts to breed lactating ewes in spring have consistently been disappointing (Bourke, 1964;Whiteman et al, 1972;Cognie et al, 1975;Pope et al, 1989), and use of hormone or light manipulation to improve spring fertility has generally not been successful in lactating ewes (Restall et al, 1978;de Nicolo et al, 2006;Martemucci and D'Alessandro, 2010). Selection to improve ewe fertility in a crossbred (50% Dorset, 25% Rambouillet, 25% Finnish Landrace) sheep population mated in May and June at Virginia Tech (37°N latitude) resulted in significant selection response (Notter and Cockett, 2005) and correlated increase in duration of the breeding season (Vincent et al, 2000;Notter et al, 2011;Goff et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Strategies for rapid rebreeding of lactating ewes in the spring

Goff

Notter

Vanimisetti

et al. 2014

Animal

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Rapid rebreeding of winter-and spring-lambing ewes is essential if ewes are to lamb more than once per year, but fertility of lactating ewes is often low and early weaning of lambs may be undesirable in forage-based production systems. Selection to improve fertility in spring matings has been successful and led to development of ewes with a reduced seasonal anestrus. Potential for rapid rebreeding of lactating out-of-season breeding (OOS) ewes was tested in three studies. In Experiment 1, effects of short-term lamb removal on rebreeding was evaluated over 2 years using 71 January-lambing OOS ewes. At an average of 63 days postpartum, 36 ewes had lambs removed for 72 h, and all ewes were joined with rams. Circulating progesterone levels indicated that 74% of ewes ovulated before lamb separation; 91% of ewes mated within 5 weeks of ram exposure, 85% were diagnosed as pregnant and 75% lambed. The average interval between lambings was 225 days. In contrast to results observed in cattle, none of the measured variables was affected by lamb separation ( P > 0.20). Experiment 2 compared rebreeding performance of 24 OOS and 23 St. Croix ewes that lambed in January and averaged 60 days postpartum at ram introduction. More OOS ewes ovulated, mated and became pregnant during the first 21 days of ram exposure (83.3%, 58.3%, and 41.7%, respectively; P < 0.001) compared with St. Croix ewes (26.1%, 0%, and 0%, respectively). After 39 days of ram exposure, pregnancy rates still favored OOS ewes (66.7% v. 39.1%; P = 0.06), but the percentage of ewes that lambed did not differ ( P > 0.20) between OOS (47.8%) and St. Croix ewes (34.8%). In the third study, 34 March-lambing OOS ewes were exposed to rams on May 3 at an average of 40 days postpartum to characterize their reproductive performance. After 39 days of ram exposure, 52.9 ± 8.7% of the ewes had mated, and 38.2 ± 8.5% were diagnosed as pregnant. However, only 20.6 ± 7.0% of the ewes produced viable lambs, suggesting a high level of uterine insufficiency. Spring fertility of lactating OOS ewes in these studies was one of the highest reported in the literature and indicated that selection for fertility in spring mating would improve reproductive performance in accelerated lambing programs. However, exposure of lactating OOS ewes to rams at 30 to 50 days postpartum was associated with high prenatal lamb mortality.

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Postpartum Mating Performance of Ewes Involved in a Twice-Yearly Lambing Program

Cited by 32 publications

References 0 publications

Application of light control to shorten the production cycle in two breeds of sheep

Application of light control to shorten the production cycle in two breeds of sheep

Ewe fertility in the STAR accelerated lambing system.

Strategies for rapid rebreeding of lactating ewes in the spring

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