Effects of service sire on prenatal mortality and prolificacy in ewes1

Abstract

Ability to select service sires that minimize partial or complete losses of pregnancy could have major economic impacts in sheep production systems. This study tested the null hypothesis that survival of potential progeny did not vary with breed type of service sire or among individual rams. Data included 980 ewes on 10 farms; each ewe was pregnant to 1 of 67 rams of 12 breeds. Number of conceptuses was estimated once during pregnancy by ultrasonography, either transrectal (embryos) or transabdominal (fetuses), and was compared with number of lambs born to estimate losses. Data were examined first for number of lambs born and second for documented losses. Individual service sires affected number born (P < 0.001), which varied from 0.70 to 2.45 lambs per pregnant ewe. The main effects of breed type on lambs born were not significant, but breed types of both service sires (P < 0.0002) and ewes (P < 0.001) interacted with diagnosed number of conceptuses. Lambs born varied with ewe age (P < 0.0001) and among farms (P < 0.0001), and statistically, farms interacted with number of diagnosed conceptuses (P < 0.0001); season had no effect. In documented losses, there were both main effects of individual service sire and a service sire × number of diagnosed embryos interaction (P < 0.005). Thus, ewes bred to some rams were more apt to lose single pregnancies, whereas ewes bred to other rams were more apt to lose 1 or more embryos or fetuses from multiple pregnancies. Breed type of service sire affected (P < 0.05) prenatal death. Complete losses of single conceptuses tended to be greater in ewes bred to black-faced or hair-type rams (service sire breed type × number of diagnosed conceptuses; P < 0.09). Breed type of ewes also varied in incidence of complete losses (P < 0.05); hair-type ewes (46%) lost more (P < 0.02) documented conceptuses from examination to birth than black-faced (27%), white-faced (20%), or dairy-type (25%) ewes. Greater losses of singles than of multiples occurred in black-faced (37% vs. 18%) and hair-type (64% vs. 27%) ewes than in other breeds (ewe breed type × number of conceptuses; P < 0.03) per ewe. Surprisingly, purebred conceptuses were lost less often (24%) than crossbreds (36.4%; P < 0.002). Selection of rams based on records of prenatal losses in ewes they serviced may be a method to decrease embryonic and fetal wastage. However, further study to determine repeatability of differences among service sires from year to year will be required.

Using transrectal ultrasound to examine the effect of exogenous progesterone on early embryonic loss in sheep

“…In the current study, TRUS detected no further loss after day 19 (peri-implantation), indicating that the critical period for embryonic loss was from fertilisation to shortly after implantation. Indeed, low levels of prenatal loss have been reported to occur throughout ovine gestation [ 11 , 32 ], yet they were not detected in this study. Nevertheless, these results agree with previous studies in sheep, who report that the majority of embryonic loss occurs prior to day 30 [ 1 , 6 , 18 , 38 ], with most loss concentrated to the period immediately preceding day 19 [ 39 ].…”

“…Ewes were inseminated by intrauterine laparoscopy, 55 hours post sponge removal with 50×10 6 motile spermatozoa/ewe (insemination volume of 0.1 mL) using standard industry techniques [ 31 ]. Ewes were inseminated with semen from the same ram (and combined ejaculate) to avoid variation in the effect of sire on prenatal embryo loss and prolificacy in ewes, as discussed by Holler et al [ 32 ] and Carr et al [ 33 ]. Ewes were sedated and given pre-operative analgesia via an intramuscular injection of Xylazil (5 mg; Ilium Troy; Glendenning, Australia).…”

QTLs and Candidate Genes Associated with Semen Traits in Merino Sheep

“…Therefore, it is important to assess the breeding soundness of rams prior to natural breeding, or alternatively, assess semen quality prior to artificial breeding programs. Likewise, the sire has a significant influence on the number of lambs born, with the breed of ram also influencing prenatal mortality [9]. Poor conception outcomes, in turn, may result in fewer lambs being born and may also potentially extend the joining and lambing periods, which could have subsequent negative impacts on the productivity and profitability of sheep farming enterprises.…”

Reproductive Performance of Garut Ewes Fed Sorghum-Indigofera after Stimulation with Pregnant Mare Serum Gonadotropin

“…Fertility and fecundity rates have often been considered as characteristics carried from ewes (Murphy et al, 2020). However, male genetic and non-genetic factors can also influence the litter size and reproductive performance (Holler et al, 2014). Furthermore, the libido and sperm quality conditions of bucks can affect the lambing rate of ewes (David et al, 2015).…”