Controlling reproduction in sheep

Abstract

I ntravaginal progestagen pessaries + pregnant mare's serum gonadotrophin (PMSG) for controlling the oestrous cycle and for inducing out-of-season breeding have been commercially available for many years. However, extremely good mating management is required if acceptable results are to be achieved. More recently the role of the pineal hormone, melatonin, in the regulation of seasonal breeding has been recognized, and this has led to the development of slow-release formulations for use under farm conditions. Early indications are that such preparations can advance the breeding season by about 4 to 6 weeks, with lambing percentages in early (January) lambing flocks comparable with those of traditional (March) lambing flocks.Recent developments in the use of laparoscopy as an aid to intrauterine insemination and multiple ovulation and embryo transfer (MOET) should play a major role in breed improvement. Intrauterine insemination can markedly improve conception rates following the use of frozen semen compared with the conventional cervical technique, as well as eliminating the incidence of fertilization failure in embryo transfer donors. In addition, laparoscopic collection and transfer of embryos permit repeated collections from the same donor ewes and are much more acceptable than surgical techniques from the welfare point of view.

Genetic improvement of hill ewes

“…5-68) per ewe treated) were similar to those obtained in lowland breeds (Haresign, 1990). However, in a further Scottish Blackface ewe there were 17 corpora albicantia present, suggesting that, although this animal had responded to treatment, the corpora lutea had regressed prematurely.…”

Evaluation of intrauterine insemination of sheep with frozen semen: effects of time of insemination and semen dose on conception rates

“…This suggests that the dose of PMSG employed was unable to override completely effects of body condition score on ovulation rate. As well as producing too many high multiple litters, too high a dose of PMSG also increases the incidence of complete pregnancy failure (Haresign, 1990), and this to some extent may have compromised conception rates to Al in both experiments. PMSG for Mule ewes within the breeding season was too high.…”

Factors affecting the pregnancy rate of Bangladeshi ewes following Laparoscopic Artificial Insemination (LAP-AI)

“…On the other hand, frozen-thawed semen survives in the ewe tract maintaining its capacity to fertilize ova for approximately 18-35 hours. So, the time of insemination is more important for frozen-thawed semen than fresh semen due to capacity for survival (Robinson et al, 1989) and the optimum time for LAP-AI of ewes is close to the time of ovulation when using frozen-thawed semen (Haresign, 1990). However, it is concluded that the most preferable time of insemination is at the end of estrus in ewes through laparoscopic AI (Gourley and Reise, 1990;Haresign, 1990) because when the ovulation is performed at an early age before ovulation it may increase embryo mortality (Maxwell et al, 1984).…”

“…Now it is possible to obtain a higher pregnancy rate following AI, even with poor quality frozen semen through the development of semen cryopreservation and estrus synchronization. However, ewes bred with frozen semen typically have a lower pregnancy rate, 23-48% following TC-AI (Maxwell and Hewitt, 1986;Kumar and Naqvi, 2014) than LAP-AI, 50-80% (Maxwell and Hewitt, 1986;Haresign 1990; Bari and Haresign, 1998) due to the convoluted and tortuous nature of the cervix and the presence of 4-7 cervical rings (Kershaw et al, 2005;Kaabi et al, 2006) which prevents deep AI. In LAP-AI semen is deposited directly into the lumen of the uterine horns bypassing the cervix of the ewe (Sathe, 2018).…”