Agriculture Reference
In-Depth Information
low intake of feed for other reasons. Similarly, a low feed level may, in synergy with other
risk factors such as in seasonal infertility, increase the risk of pregnancy failure. Kongsted
et al.
(2004) found that in group-housing conditions that allowed competition for feed,
sows with the lowest back-fat gain (or even loss) during the first 25 days of gestation had
a higher risk of pregnancy failure. Even in systems with electronic sow feeding, where
competition for feed is minimised, sows with a lower feed intake compared with their
allowance from days 10 to 30 of gestation, had a lower pregnancy rate (Athorn
et al.
,
2013; Sawyer
et al.
, 2013). It can therefore be suggested that at least part of the increased
pregnancy failures in group-housed sows that are sometimes ascribed to social stress may
be a consequence of malnutrition. Langendijk (unpublished data) found that fasting gilts
on days 10 and 11 after ovulation reduced litter size from 10.9 to 8.8, however, Razdan
et al.
(2004) found no such effect in gilts fasted on days 13 and 14. There are only a few
studies to date that point at a nutritional risk component of pregnancy losses in group-
housing and it is therefore still not clear to what extent these losses are stress related,
nutritionally driven, or both. To reduce social stress due to lack of nutritional satisfaction,
fibrous diets are being introduced more and more in group-housing systems. Inclusion of
10% crude fibre in an isocaloric diet resulted in the same farrowing rate and litter size in
first-litter sows (Athorn
et al.
, 2011b) and in gilts (Langendijk
et al.
, 2011) on a control
diet, and did not affect embryo survival or pregnancy rate in gilts (Athorn
et al.
, 2012a).
To achieve satiety levels comparable to that of
ad libitum
fed sows, however, fibre content
may have to be increased to allow close to ad lib feeding (Jensen
et al.
, 2012; Knudsen
et
al.
, 2000).
As is the case with competition in group-housing, seasonal influences on LH secretion and
pregnancy failure may be aggravated by undernutrition, an idea pioneered by Love
et al.
(1995). Even though variation in feed intake may only mildly affect LH and progesterone,
there are some indications that during periods of seasonal infertility, these effects may be
involved in pregnancy failure. Some reported data suggest that there are seasonal effects
on progesterone supply towards the uterus (Virolainen
et al.
, 2005a). Furthermore, it has
been proposed that LH secretion may be weak under long days combined with restricted
feeding during implantation. This would result in decreased progesterone secretion
by the ovaries, thereby affecting oestradiol signalling by the embryos around day 17
of pregnancy, and causing interruption of pregnancy and return to oestrus between
days 25-35, which is typical for seasonal infertility (Tast
et al.
, 2002). In contrast, short
days in combination with a high plane of nutrition stimulated pineal gland secretion of
melatonin and LH secretion from the pituitary; and maintained pregnancy (Peltoniemi
and Virolainen, 2006). These observations are supported by the beneficial effects of
abundant feeding on pregnancy rates in gilts (Virolainen
et al.
, 2004).
2.4.6
Specific nutrients that influence embryo development and survival
In the 80s and 90s of the last century, vitamins were some of the first functional
nutrients to be researched in relation to sow reproductive performance. Folic acid has
received considerable attention in that era. A review by Lindemann (1993) concluded
that supplementation of sow gestation diets with folic acid improves litter size, but the
mechanism remains unclear. Most commercial diets now add folic acid at a rate of 0.2
