Agriculture Reference
In-Depth Information
2.4
Post-mating nutrition, embryo loss and maintenance of
pregnancy
2.4.1
The feed level paradigm
Providing greater amounts of feed reduces systemic concentrations of progesterone in
gilts due to increased hepatic clearance (Prime and Symonds, 1993). Therefore, feeding
a high amount of energy is generally believed to reduce embryo survival (Jindal
et al.
,
1996). Indeed, the study by Jindal
et al.
(1996) showed that a high feed level in the early 3
day-window after ovulation had a negative impact on embryo survival. However, results
of other studies on nutritional state during early pregnancy are equivocal (Quesnel
et
al.
, 2010).
Embryo survival data obtained during early gestation (up to day 15) have to be interpreted
with caution (Table 2.1). Efficiency of flushing methods, in the case of morulas and
blastocysts (Jindal
et al.
, 1997; Soede
et al.
, 1999), can affect accuracy with which embryo
survival is determined, and recovery of very early stage embryos is currently thought to
only be a result of fertilisation efficiency and recovery procedure. The fragility of embryos
and morphological aspects once embryos start to elongate, can complicate the assessment
of the number of embryos (Ashworth
et al.
, 1999; Athorn
et al.
, 2012a; Jindal
et al.
, 1997).
It also has to be noted that in older studies plane of nutrition is applied during the
premating as well as the post-mating periods. This affects ovulation rate and, therefore,
complicates the separation of post-mating effects from effects established earlier on
(Foxcrot, 1997).
2.4.2
Feed level during established luteal function, embryo mortality
and pregnancy
In their study, Jindal
et al.
(1996) looked at the effects of varying feed levels on embryo
survival only in the period shortly after ovulation. In later studies and in industry
recommendations, this feed level effect was subsequently extrapolated, maybe wrongly
so, to the entire embryonic period. In more recent studies, feed levels were maintained
throughout the first three to four weeks of pregnancy and results indicated that the
effect of feed level differs at that time compared with the first three days after ovulation
(Table 2.1). There is a wide variation in the feed levels that have been tested. The lower feed
level generally ranges between 1.2 and 2.5 kg per day, most of which, interestingly, are still
higher than some field recommendations that go as low as maintenance. Nevertheless,
most studies that compared a high feed level with a control level throughout the first
three weeks of gestation reported no effect or an increase in embryo survival on the
high feed level. Two studies that reported a negative effect of a high plane of nutrition
during the entire embryonic phase on embryo survival, also reported a positive effect of
the same high plane on pregnancy rate (Dyck and Strain, 1983; Virolainen
et al.
, 2004).
Therefore, it may be hypothesised that on a high feed level a number of pregnancies with
small litters that would not have persisted on a low feed level, were actually salvaged by
the high feed level.
