A comparison of ovulation rate and late embryonic mortality in ewe lambs and ewes and the rôle of late embryo loss in ewe lamb subfertility

Abstract

An investigation was conducted to compare late embryonic losses in ewe lambs and ewes and to determine the effect of inducing embryonic mortality on day 15 of pregnancy on reproductive function in ewe lambs. Ovulation rate and embryo survival were determined, at 15 and 30 days after mating, in a total of 83 ewe lambs and 67 ewes. Ovulation rate was lower, at spontaneous oestrus, in ewe lambs (1-07) than in ewes (1-25; P < 0-05). There was no difference in embryo survival at day 15, as 79% of ewe lambs and 80% of ewes contained expanded conceptuses. However, embryo survival was lower in ewe lambs (69%) than ewes (88%) at day 30 (¥ < 0-05). Embryonic mortality was induced in an additional 18 ewe lambs with an intrauterine injection of colchicine on day 15 post mating. Four of these animals had normal length oestrous cycles, six had inter-oestrus intervals ranging from 22 to 35 days and eight did not return to oestrus. Overall, the results of this study demonstrate that low ovulation rate and late embryonic losses make a significant contribution to subfertility in ewe lambs. Moreover, conceptus death is associated with luteal persistence, which may reduce reproductive performance by preventing remating.

Competition for nutrients in pregnant adolescents: consequences for maternal, conceptus and offspring endocrine systems

“…Sheep producers generally avoid breeding young females during adolescence because relative to adults, they have an inferior reproductive performance characterised by a variable onset of puberty and short first breeding season, low ovulation rate, failure to be mated, fertilisation failure and high embryo loss (Beck et al 1996, Kenyon et al 2014, Edwards et al 2016. The approach developed at the Rowett Institute bypasses many of these issues by using assisted conception procedures to synchronise breeding and establish singleton pregnancies in peripubertal adolescent ewes of equivalent age (~7.5 months), and standardised live-weight and adiposity at conception.…”

Recria de cordeiras em pastagem nativa melhorada submetida à fertilização nitrogenada: 2. Produção animal

“…A subfertilidade em cordeiras é uma das causas de redução da produtividade do rebanho. Embora a taxa de fertilidade sofra influência de vários fatores, 20 a 40% das cordeiras falham em produzir seu primeiro cordeiro (Davies & Beck, 1993;Beck & Davies, 1994;Beck et al, 1996).…”

Effects of Pre-Breeding Management on Ewe Lamb Fertility

“…Ewe lambs experience a decrease in overall fertility attributed to lower ovulation rates and higher embryonic mortality rates compared to mature ewes. Ewe lambs have a lower ovulation rate compared to mature ewes as demonstrated in Romney and Romney cross (1.14 v 1.82 and 1.44 v 1.84; Mulvaney et al, 2013) Clun forest (1.07 v 1.25; Beck et al, 1996), and Galway (1.51 v 3.07) breeds (Quirke and Hanrahan, 1977). Additionally, lowland Clun Forest ewes experience a subsequent increase in ovulation rate as they increase in age (ewe lambs= 1.15 v yearlings= 1.55 v two year olds= 1.75; Forrest and Bichard, 1974).…”

“…Prenatal mortality rates are elevated in ewe lambs compared to mature ewes due to a decrease in ova viability. Research has shown that there is no difference in embryonic survivability between ewe lambs and mature ewes (79 v 80%) on embryonic day 15, but by embryonic day 30, the amount of ewe lambs containing viable fetuses decreased significantly compared to mature ewes (69 v 88% respectively; Beck et al, 1996). This indicates that there is a higher rate of embryonic loss by 30 days of pregnancy in ewe lambs.…”

“…Ovulation, conception and fertility rates in ewe lambs are lower than mature ewes (Beck et al, 1996; Quirke and Hanrahan, 1977), and between 20-40% of ewe lambs exposed to rams do not lamb (Edey et al, 1978). This is likely the result of a short breeding period in ewe lambs.…”