Insights from Animal Reproduction

Abstract

The litter size is an important trait in prolific species such as rabbits and pigs. However, selection on litter size has had limited success in these species because of its low heritabil-ity and sex-limited expression. The litter size is a complex physiological trait in prolific species, affected by several components that are expressed sequentially, for example, ov-ulation, fertilization, embryo development, and fetal survival. The selection for ovulation rate or/and prenatal survival has been proposed to improve litter size indirectly. However , these alternative methods have not reached the expected response rate. Implantation is also a critical point in successful gestation, one-third to one-half of prenatal mortality occurring during peri-implantation. The uterus must provide an adequate microenviro-ment for the growth and development of embryo and for receptivity to implantation. There are multitudes of cellular events involved in crosstalk between embryo and maternal uterus during peri-implantation. A better understanding of molecular mechanisms affecting the implantation process could help to propose new strategies for litter size improvement in prolific species.

Estimating proportions of identical twins and twin survival rates in cetaceans using fetal data

“…For instance, a report published in 2011 found Hawaiian monk seal (Monachus schauinslandi) twin fetuses were less likely to survive than singleton fetuses born in the same year (Schultz et al, 2011). Though species differ, it is generally believed that in those which produce multiple young per gestation, an embryo needs a minimum amount of space within the uterus to attach and survive, so a decrease in uterine capacity means a smaller number of embryos may develop (Carreira, 2016). Previous studies examining the likelihood of fetuses surviving to term have found the body condition of the mother to be predictive of fetal survival: fetal length and weight are lower for mothers with poorer body condition (Christiansen et al, 2014;Lockyer, 2007), suggesting that mothers reduced their energetic investment in their fetus proportionately to their body condition to maintain parental survival (Christiansen et al, 2014).…”