Agriculture Reference
In-Depth Information
2002). In some climatic zones, embryonic losses, and as a consequence pregnancy losses,
may be aggravated in specific periods of the year. This is termed seasonal infertility.
The mechanisms for seasonal infertility are poorly understood but there are indications
that nutrition is involved; this will be discussed later. Similarly, specific management
conditions such as competition for feed in group-housing conditions may give rise to
embryo losses potentially resulting in pregnancy failure.
Following ovulation, development of the corpora lutea and secretion of progesterone occur
independently of LH input from the pituitary, at least until 10-12 days post-ovulation
(Peltoniemi
et al.
, 1995). Therefore, levels of feeding that potentially affect LH secretion
should not affect luteal tissue formation in this period. Beyond days 10-12, support of
the corpora lutea by LH does become important, although in some studies reduction in
gonadotrophic support had to be severe and chronic to result in luteal regression and
pregnancy failure. Only complete suppression of LH for 3 to 5 days will result in luteal
failure and, as a consequence, either pregnancy will not be established or abortion will
take place, depending on the stage of pregnancy (Langendijk and Peltoniemi, 2013).
2.3
Effects of premating nutrition on luteal function during
early pregnancy
The effects of pre-mating nutrition on luteal function have not been studied as such.
However, there is an abundance of studies on follicle development and ovulation rate,
some of which report carry-over effects on post-mating luteal function. Feed restriction
(1× vs. 2.5-3.5× maintenance requirements) during the second week of the luteal phase
in gilts resulted in a slower rise in progesterone after the subsequent ovulation (Almeida
et al.
, 2001; Chen
et al.
, 2012a). Administration of insulin counteracted this effect
in vivo
(Almeida
et al.
, 2001) and resulted in increased progesterone secretion
in vitro
(Mao
et
al.
, 2001). Ashworth
et al.
(1999) also reported increased progesterone in gilts fed a high
level of feed (3.5 vs. 1.15 kg per day) pre-mating, accompanied by an increase in the
weight of corpora lutea. In primiparous sow models, feed restriction during late lactation
had similar carry-over effects on post-ovulatory luteal function with progesterone
concentrations being lower in feed restricted sows (Mao
et al.
, 1999). Chen
et al.
(2012b)
fed a starch/sugar rich supplement during late lactation and reported greater progesterone
on day 4 after ovulation compared with control sows and sows fed a fat-rich supplement.
An increase in litter size was also observed. In weaned multiparous sows, post-prandial
insulin characteristics (peak and average concentrations) were positively related to post-
ovulatory progesterone concentrations (Wientjes
et al.
, 2011). It seems that pre-mating
nutritional interventions, such as feed level and insulin stimulating formulations, that
improve follicle function and development in general, have positive carry-over effects
on post-ovulatory secretion of progesterone. This may be a remnant effect on number
or quality of follicle cells that may influence their secretory capacity after luteinisation,
and the effect may be mediated by factors related to metabolic condition, such as IGF-1
and insulin.
