Agriculture Reference
In-Depth Information
to 15 mg/kg (Gaudre and Quiniou, 2009), but whether folic acid plays a role in the
embryonic period has not been fully confirmed. Studies that show an effect of folic acid
on prolificacy report an increase in litter size born (Lindemann, 1993; Matte
et al.
, 1984).
Tremblay
et al.
(1989) reported increased embryo survival on day 30, mainly in sows that
had a high ovulation rate following eCG treatment, but Harper
et al.
(2003) and Guay
et
al.
(2002) did not find an effect on embryo survival, although the uterine environment is
clearly changed in this period by supplementing folic acid (Matte
et al.
, 1996).
Over the last decade, there has been an increasing interest in the role of specific amino
acids for the development of embryos in the blastocyst stages, during elongation and
around implantation. Arginine for example, has been shown to influence vascularisation
of the placentas by stimulating angiogenesis trough the arginine-NO pathway (Hazeleger
et al.
, 2007; Novak
et al.
, 2011) and as such was thought to benefit foetal survival and
improve litter size at term. Ramaekers
et al.
(2006) and Wu
et al.
(2010) reported an
increase in litter size when arginine was supplemented at 20-25 g/day from days 14 to 28
or from day 30 of gestation until farrowing. Hazeleger
et al.
(2007) reported an increase
in embryo survival on day 30 of gestation in sows fed 40 g/d of arginine from days 16 to
28, and this mainly in gilts with high ovulation rates following superovulation treatment.
Novak
et al.
(2011) reported no effect of arginine on embryo survival but did find an
increase in foetal weight at day 49.
Arginine has only been supplemented after implantation (day 15 onwards). To the best
of our knowledge, only Li
et al.
(2010) supplemented arginine from mating through day
25 and they found a reduction in the number of foetuses on day 25 with 0.8% arginine
inclusion. However, their study is hard to interpret because growth rates in the arginine
treatment were far lower than expected and plasma progesterone concentrations were
lower than those of controls. It is interesting to hypothesise that functional amino
acids influence embryo and trophoblast development prior to implantation and as such
improve embryo survival and growth. Based on increased concentrations in uterine and
trophoblast fluids approaching implantation, Bazer
et al.
(2013) suggested that leucine,
arginine, glutamine, glucose and fructose may act as functional nutrients affecting
blastocyst development and trophoblast elongation.
In vitro
, some of these functional
nutrients do stimulate proliferation and specific cell signalling pathways in porcine
trophectoderm cells (Bazer
et al.
, 2013). Expression of transporters and secretion of these
functional nutrients as part of a complex of histotrophs are regulated by progesterone
and oestradiol. In cattle, progesterone clearly stimulates secretion of histotrophs and this
has been reported to stimulate blastocyst elongation prior to implantation (Carter
et al.
,
2008; Clemente
et al.
, 2009). In pigs, pre-implantation effects of these functional amino
acids remain to be confirmed
in vivo
. It is interesting that progesterone supplementation
in pigs in early gestation may have negative effects on embryo survival and maintenance
of pregnancy (Soede
et al.
, 2012). However,
in vivo
supplementation prior to implantation
with the functional amino acids mentioned above has not been reported to our
knowledge. If these nutrients stimulate blastocyst elongation, benefits will depend on
whether variation between embryos within a litter remains unaltered, increases, or is
reduced, since variation between embryos has been indicated as a major cause of embryo
losses (Geisert and Schmitt, 2002).
