A key aim of pig farmers is to maintain a high productivity year-round as this is essential in sustaining a profitable farming business. It has been recognised since the 1970s that an increasing problem on pig breeding farms is the variation in seasonal fertility that occurs in the domestic sow throughout annual production (LOVE TEXTBOOK, STORK 1979). This is due to sensitivity to certain environmental factors in which the sows are kept which have a subsequent impact on sow fertility and reproductive performance (Peltoniemi _and _Virolainen _2006 _Seasonality _of _ reproduction.
pdf). A major concern is the reduced farrowing rate due to reductions in fertility, which has undesirable effects on conception rate and subsequent litter size (Bertoldo et al., 2009) (Xue et al 1994, Peltoniemi et al 1999, Tast et al 2002). This has a detrimental economic effect on farm profits and production efficiency due to a reduction in fast growing, healthy piglets produced per sow (PDF) Seasonal variation in the ovarian function of sows, n.
d.). Many papers have shown that the periods of impaired fertility occur at the end of summer and beginning of autumn season and arise due to a multitude of sow and environmental factors including photoperiod and temperature (Bassett et al 2001) (LOVE ET AL).
A reduction in fertility during this time can be seen as an extended weaning to oestrus interval, shorter oestrous, an increase in number of still borns and delayed puberty in gilts to name a few. (PAGE 91). NICK EXAMPLE REPORT REFERENCE (Peters 1998 Intro paragraph 1)
Farrowing rate, weaning to oestrous interval as well as age of puberty in gilts have been reported to be influenced by season (De Rensis et al.
, 2017; Peltoniemi et al., 1999) (REnSIS see conclusion)
The domestic sow is a non-seasonal breeder therefore able to produce litters throughout the year maintaining high productivity (auvingne et al 2010). The domestic pig has descended from the European Wild Boar, a short-day seasonal breeder and has retained some seasonality through reained genetics despite domestication, as seen by the ability to produce litters throughout all seasons despite some fertility reductions in late summer and early autumn(LOVE TEXTBOOK) Peltonieme et al 1999) (PDF) Seasonal variation in the ovarian function of sows, n.d.) (Mauget 1982). Day length shortening occurs from mid-summer into autumn and if a sow is served during this period, she may successfully conceive but not produce a litter due to short day length inhibiting progesterone levels (BLUE NOTTINGHAM TEXTBOOK). This ensures parturition will not occur in unfavourable winter weather, so food availability, shelter and warmth will be available for the subsequent litter, to increase chances of piglet’s survival after parturition during the 3 month lactation in the summer months (GLOSSOP 1998) (Mauget 1982).This phenomenon is known as the feral factor which is thought to originate in the primeval sow and shortening day length seems to be an essential factor in implementing it (blue nottingham textbook p 105)
Photoperiod is considered to be one of the main environmental factors that has a significant impact on seasonal fertility (LOVE ET AL 1993)(Mauget 1985). Photoperiod is defined as the period of time in a 24 hour day where a domestic species, notably the wild boar, is exposed to daylight or artificial light (BLUE Nottingham textbook). Photoperiod is thought to be a more significant contributor in stimulating oestrous and mating behaviours (Senger 2005). In many mammals particularly the sow, the hormone melatonin is secreted from the pineal gland which is sensitive to natural light and acts as neuromediator on the hypothalamo-pituitary-ovarian axis to regulate circadian rhythms and how SHORT DAY BREEDERS respond to variations in light intensity on reproductive ability (Ramrez et al., 2009) (LOVE ET AL 1993). A high light intensity has been shown to be a requiment for sows to generate a distinct diurnal melatonin rhythm.
However this high level in sows in late summer and early autumn has been suggested to have an impact on fertility (LOVE TEXTBOOK). There is an inverse relationship between day light hours and melatonin production but it should be noted that the intensity of light also has an effect on reproductive ability as it inhibits release of gonadotrophins from the pituitary gland thereby effecting follicular development and ovulation. (1-s2.0-0301622696000073-main.pdf, n.d.)(BLUE NOTTINGHAM TEXBOOK). Photoperiod can be controlled better in indoor farms as the number of hours of light in the service area can be controlled (LahrMann 1989 – NICK REPORT, paragraph 2).
Temperature is another significant environmental factor that has an effect on infertility with heat stress thought to be a critical factor. (Wettermann and Bazer 1985). Despite lower temperatures in the UK, heat stress can occur during peak days in the summer months and has a negative impact on sow fertility (STORK 1979, PETERS AND PITT 2003). Higher temperatures above 22 degrees have an undesirable effect on feed intake which can cause the sow to go into negative energy balance which has a detrimental effect on lactation and result in abortions. If appetite is supressed, insulin levels are reduced and soon hormonal progesterone production is compromised and she may lose the litter due to impaired embryo development (Wettermann and Bazer 1985).
Chromium levels need to be appropriate as it is a precursor of insulin production. P107. A study carried out by Peltoniemi et al investigates seasonal infertility in a herd in Finland where environmental temperatures remained around 25 degrees and conclusions seemed to say photoperiod had a bigger impact that temperature (De Rensis et al., 2017) The relationship between photoperiod, environmental temperature and sow fertility if difficult to clearly define due to the fact that seasonal fertility issues are multi-factorial and this is something that current research is attempting to clarify (Auvigne et al 2010)
Very low secretion of LH during lactation (Armstrong et al., 1986b; King and Martin, 1989; Tokach et al., 1992) or insufficient increase in LH immediately after weaning (King and Martin, 1989; Tokach et al., 1992) seem to play an important role in nutritional-induced anoestrus.
It has been postulated that early disruption in pregnancy during the period of seasonal infertility is due to insufficient LH to support to corpora lutea development which leads to early embryonic mortality and result in a termination of pregnancy . This early disruption to pregnancy is thought to be a more significant factor in causing reduced farrowing rates than conception failure or embryonic mortality before the initial maternal recognition of pregnancy signal because with in an inadequate LH signal, progesterone will not be able to support the developing embryo.
Reductions in follicular progesterone has been associated with reduced oocute developmental competence. Progesterone is the hormone that maintains pregnancy, so a reduction in progesterone levels results in a return to oestrous thereby negatively impacting the farrowing rate and production output from the farm.
A study carried out by Bertoldo et al (2011a) in sows from different farms, showed that in the absence of an increase in ovulation rate the total number of antral follicles was greater in summer than in winter however, differences in farm conditions were noted. The study suggested that the follicular response to LH surge was deficient. It was alternatively hypothesised by Peltoniemi et al 1997 that the reduced LH pulse amplitude observed in summer may not have stimulated development of additional ovulatory follicles. Therefore there was a lower number of pregnancy supporting CL on their ovaries leading to lower chances on conception during the seasonal infertility period.
Reductions in follicular progesterone have also been associated with reduced oocute developmental competence and poorer oocyte quality (Bertoldo et al 2010). Bertoldo et al 2009 (NICK PAPER FIND REFERENCE) – decreased levels of progesterone in follicular fluid during final oocyte maturation
While the distribution of antral follicles appears to be minimally incfluenced by season, follicular fluid progesterone content in substantially reduced during summer months. Futhermore this reduction in follicular fluid progesterone content is closely associated with the reduction in oocyte quality. We propose that during the seasonal infertility period a suppressed endocrinological environment brings about a decline in ovarian progesterone production and a concomitant reduction in oocyte development competence. Inferior conceptus development resulting from poor oocyte quality may lead to a failure of the conceptus to initiate implantation and/or maintain pregnancy. Thus, reduced oocyte developmental competence during the summer months may contribute to the increased incidence of irregular returns-to-oestrus seen in summer-mated sows.
Reduction in fertility has significant impacts on productivity due to variable and fixed costs of running a profitable farming business. Farm profits are affected by the costs of raising the pigs regardless of the eventual output of productivity from the herd. Management strategies, rather than genetic selection of sows, have made it possible for the domesticated sow to give birth to more than two litters each year Love et al 1993 . The current goal of modern breeding sow is a farrowing index of 2.5 (litters/year). Seasonal infertility has an negative impact on anoestrous and the weaning to oestrous interval which can make it difficult for farms to reach this goal (Claus et al 1985 NICK PAPER IMPACTS OF FERTILTIY). The biggest economic setback affecting farrowing targets is due to pregnancy loss after implantation and the consequential reduction in farrowing rate (Bertoldo et al 2012). Therefore it is essential for producers to identify sows that have poor reproductive performance (Bertoldo et al., 2009)
There is a lack of UK investigations and therefore limited understanding of seasonal variation in fertility in UK pig farms in general. The present study was conducted to investigate seasonal infertility on a UK pig farm.
With global temperatures on this rise, seasonal infertility is expected to become more of an issue due to temperature stress and increased exposure to daylight. Due to a multitude of reasons eg welfare, capital costs etc outdoor breeding is increasing hence the effect of seasonal infertility will be greater. Reports on the easonal effects on littersize have been equivocal (LOVE et al 1993, Xue etl al 1994)(found in (Peltoniemi et al., 1999). Soutdoor outdoor systems account for 40% of UK sows (Basset el al 1996 NICK REPORT)
Having considered previous work, several factors warrant further investigation. In addition to this, research into the effect of season on litter size has yielded contradictory results. Therefore, litter size was chosen for investigation.
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