Seasonal Trend of Fertility in Pigs Essay (Literature Review)

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Introduction

Intensive management has led to great improvements in pig production. Although this management has led to all-year-round breeding in pigs, there is evidence of the effects of season on pig fertility. Seasonality in fertility in pigs is a major concern for pig farmers. Despite of much development in pig farming, fertility in pigs shows high seasonal trend. The main concern for pig farming is to maintain consistent supply of pigs in all seasons. Seasonality in pig fertility makes consistent supply of pigs almost impossible. Many researchers and scholars have addressed the phenomena as they come up explanations and solutions.

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Seasonal trend in Pig fertility

Seasonal trend of fertility in pigs have attracted attention from various scholar. Fertility in pigs is observed to have a strong seasonal trend. Almond and Bilkei observed that there was decrease in pig production during summers and early autumn (Almond, & Bilkei, 2008, p. 347). Other researchers note that despite domestication, fertility in female pigs show high seasonality. The capacity of female pigs to return to oestrus after weaning, ability to conceive, ability to maintain pregnancy and onset of puberty are highly affected by seasons. In spite of various explanations to this trend, the actual causes of seasonal fertility are not precisely known (Almond, & Bilkei, 2008, p. 347). Various scholars hold different explanation to the observable seasonal trend in fertility. Seasonal fertility trend in pigs is very important to pig farmers. Pig farmers must take note the seasonal fertility trend in order to have a long-term plan on pig production. Whine producers must be aware of the effects that seasonal fertility can have on their business.

The aim of pig production unit is to maximize pig production in an year. The intention is to maximize the number of porkers, baconers or weaners per year. Ability to maximize the number of pigs in an year translates to high profit to a pig production. Seasonal fertility in pigs has been an area of concerns for researcher and producers. Summer Infertility Syndrome (SIS) in sows has been a major challenge in pig production. The phenomenon has attracted increase attention as many researchers try to explain the phenomenon or come up with solution. The seasonal fertility trend affects the yearly production of pigs by causing less that optimal production during summers.

Various aspects of fertility in pigs have been observed to be affected by seasons. Although domestic sows show consistent pattern in oestrus activities in all season, other aspect of fertility have been observed to change with season. Delayed puberty in gilts, prolonged weaning to oestrus period, reduced fallowing rate, and reduction in litter size have been observed in some seasons (Hurtgen & Leman, 1982, p. 673). Domesticated pigs are intended to breed in all reasons. The seasonal trend in fertility, thus, affects production and profitability of pig farming. According to Mauget, the seasonal fertility trend in domesticated pigs can be an effect of biological rhythms in their ancestors. Mauget observed that the European wild boar, the ancestor to modern domesticated pigs, had seasonal breeding (Delcroix, Mauget & Signoret, 1990, p. 656). He argues that the wild boar has biological rhythms that enabled it to refrain from mating during certain time of the year. The biological rhythm enabled the boar to furrow during winter months. Prunier et al says that the effect of season on fertility is observed more in primiparous than in miltiparious sows (Prunier, Quesnel, Messias de Braganca & Kermabon, 1996, p. 217)

Seasonal fertility trend in European Boar

There have been various explanations to Seasonal infertility in pigs. One of the prominent explanations in the recent past is the influence of European wild boar. The European wild boar is observed to have a seasonal breeding trend. The wild boars are observed to have mating period starting in late autumn until early winter. This allows them to give birth in late periods of winter or early weeks of spring. Nutrition is one of important factors that are observed to influence fertility in pigs (Auvigne, Leneveu & Salle, 2010, p. 7). It is observed that births can be reported earlier than in other years when there was high-quality food in early autumn. This could allow for a second litter in summer. However, Mauget argues that all females are in anoestrus in early autumn and summer. He also argues observes that male wild boars have high seasonal variation in testosterone and testis weight. According to Mauget and Boissin, the testis weight and testosterone reach their peak in mid-winter. The seasonal infertility trend shows similarity with the breeding trend in European wild boar. The coincidence makes it possible that the seasonal infertility in modern pigs is remnant of seasonal breeding in European wild boar.

Manifestation of Seasonal Infertility Trend

Seasonal infertility is manifested in various forms in modern pig. According to Love et al, seasonal infertility is manifested by reduction in furrowing rates, prolonged weaning-to-oestrus interval, delayed female puberty and reduction in litter size (Love, 1981, p.406). Claus et al also note low libido and reduction in sperm quality as other factor that affect seasonal infertility. Various scholars cite environmental factors as responsible for the variations. Increased temperatures during summers are said to cause heat stress and lead to negative effect on fertility. The stress associated with heat is also used to explain the difference variations in fertility between gilts and sows. According to Wan et al, high stress sensitivity in gilts explains why they have higher variation in fertility than in sows (Wan, Hennessy & Cranwell, 1980, p. 562). Love et al explain that the seasonal variations in fertility can masked by better nutrition and management systems (Love, Evans & Klupiec, 1993, p. 319). They noted that individual housing of sows increased level of feeding has positive effects in reducing the effects of seasonal infertility.

Reduced Farrowing rates

Love defined farrowing rate as the percentage of mated sows that succeed to farrow. Farrowing rate is calculated getting the number of sows that furrow over the number of sow that was involved in mating. According to Love at al, there is typical reduction in farrowing rates in late summer and early autumn. In an individual study, Love observed that there was delay in returning to oestrus after mating during summer-autumn and compared to winter-spring (Love, 1978, p. 298). Love et al carried a study that showed similar observations and those observed by Love. In the study, twenty five to thirty percent of sows observed to be pregnant in autumn were not able to farrow. The percentage was high as compared to only four-percentage failure observed during winters. The studies showed the importance of early intervention on pregnancy issues increasing pig production.

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Reduced farrowing rates have been observed in many studies. Despite of general reduction in farrowing rates, the severity of the reduction differ from one study to the other. In a study, Stork observed a three to five percentage season based reduction in farrowing rates in Britain. In a study on pigs in North America, Lucia et al found a three-percentage reduction in furrowing rates because of seasonal variations. In Finland, the farrowing rates were observed to be reduced by a rate ranging from five percentages to ten percentages in the months of August to October. Higher rates of reduction of farrowing rate have been observed in other place. Love et al report a reduction of as high as fifty percentages in severe cases in Australia. In most cases, the percentage of reduction in furrowing rates ranged from ten to fifteen percentages. In a study in Italy Enne et al observed a forty percent furrowing rate in sows that mated during summer (Enne, Beccaro & Tarocco, 1979, p.119). In general, the various studied showed seasonal reduction in farrowing rates.

The variations in severity of seasonal infertility have various explanations. Paterson et al relate the variation with different environmental and managerial factors. Love et al observed the variation to vary with different weeks, years, different groups of pigs in a pig farm and from one piggery to the other (Love, Klupiec, Thornton & Evans, 1996, p. 217). According to Love, the great variation in seasonal infertility makes it difficult to control the situation. Traditional methods for detecting failed pregnancy cannot be effective requiring the use of more advanced methods.

Delayed Puberty

Various scholars identify delayed puberty as one of the manifestation of seasonal infertility. Hughes (1982) and Paterson et al observed that gilts reached puberty late in infertility period than in other periods of the year. In a study to investigate the effect of season on puberty, Paterson et al made observations that justified the season affected the number of days required for puberty (Paterson & Pearce, 1990, p. 197). In a study on gilts in Australia, it was observed that 53 percent of gilt took 225 days to reach puberty when exposed to short day lighting. On the other hand, only 13 percent of gilt reached puberty in the same duration when exposed to long day lighting. Other environmental factors such as boar contact also affect puberty (Paterson, Pearce & Antuono, 1991, p.344). However, according to Peterson et al, seasonal delays remain even with favourable environmental conditions. Mauget (1987) had observed similar trend in European boar in natural settings. Mauget explained that occurrence of puberty in European boar depends on season after the threshold age and weight is reached. He argues that if the threshold is reached in late spring, puberty is delayed until the following winter.

Prolonged weaning to oestrus interval

Various authors have noted effect of season on interval between weaning and oestrus (Prunier et al., 1996, p. 107). According to Hutgen and Leman, interval between weaning and Oestrus in primiparous sows prolong in infertility period. According to Prunier et al., primiparous sows went through total anoestrus after weaning. Prolonged weaning to oestrus interval is not a major problem in Finland. Peltoniemi et al. explain the observation by saying that case is because of low average number of sows in farms in the country (Peltoniemi, Easton, Love, Klupiec & Evans, 1995, p. 372).

Environmental Factors

Photoperiod

Photoperiod is defined as the dark and light periods. Many scholars on pig farming have been interested with the effect of photoperiod on pig fertility. Bassett, Brat and Sharpe observed that variation in the length of the day had effect of reducing fertility (Diekman, Clapper, Green & Stouffer, 1991, p. 673). They claim that long day length in summer was responsible for reduction in fertility in summers. They also claim that high ambient temperatures in summers also could affect pig productivity. According to Prunier et al, the interaction between photoperiods and temperatures also had negative affected on fertility. Effect of photoperiod on reproduction in pigs is not well documented as in other animals such as sheep. In addition, there has been controversial literature on whether pigs have photoperiod effect. According to Mauget, photoperiod is the major environmental factor that affects reproduction in European wild pigs. He argues that photoperiod effect help to control the start of breeding period in European wild pigs. Variation in the length of the day was observed to the stimuli that help to control the reproduction pattern of the wild pigs. However, despite of the documented effects on photoperiod on breeding pattern in European wild pigs, little attention has been givens to the effect of manipulating light in modern pig facilities. Photoperiod can affect various aspects of fertility in pigs. According to Foxcroft, effective lighting programs in pigs’ facilities can help to correct reduction in fertility because of change in day length (Foxcroft, 1997, p. 49). Effects of light on fertility have also been reported by other scholars. Paterson et al suggest that pig facilities require high light in order to differentiate between day and night. Griffith and Minton suggest a light intensity of more than 113 required in pigs’ facilities in order to overcome the effect of seasonal infertility (Griffith &Minton, 1992, p. 107).

Temperature and heat stress

Effect of heat stress on fertility has been associated with temperatures that are higher than 32 degree centigrade. The effect of heat stress has been associated with seasonal infertility under different climatic conditions across all continents (Pusateri, Smith, Smith, Thomford, & Diekman, 2000, p. 143). However, the variation in seasonal infertility does not seem to correlate with differences across the continents. The relationship between temperatures and infertility calls for need to have effective thermal management in pigs’ facilities (Hennessy, & Williamson, 2008, p.218). In a study to investigate the effect of temperature on reproduction, temperatures were elevated. From the experiment it was observed that increase in temperature led to increase in conception rate but led to decrease in embryo survival rate.

Conclusion

Seasonal infertility is a major area of concern for pig production. The main objective of modern pig management facilities is to maximize pig production in all seasons. Despite of advanced systems, seasonal infertility continues to be observed. Low fertility rates in summers and early autumns have attracted attention from various authors. The attention offered on the issue show it importance in pig farming. More research on the phenomenon can help in coming up with appropriate interventions.

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Reference

Almond, P. & Bilkei, G. (2008). Seasonal infertility in large pig production units in an Eastern-European climate. Australian Veterinary Journal.83(6). Pp344-346.

Auvigne, V. Leneveu, P. & Salle, E. 2010. Seasonal infertility in sows: A five year study analyze the role of heat stress and photoperiod. Theriogenology.

Delcroix, I., Mauget, R. and Signoret, J.P. (1990). Existence of synchronization of reproduction at the level of the social group of the European wild boar (Sus scrofa). Journal of Reproduction and Fertility. 89. pp 613-617.

Diekman, M.A., Clapper, J.A., Green, M.L. and Stouffer, D.K. (1991).Reduction in age of puberty in gilts consuming melatonin during decreasing or increasing day length. Journal of Animal Science.69, pp 2524-2531.

Enne, G., Beccaro, P.V. and Tarocco, C. (1979).A note on the effect of climate on fertility in pigs in the Padana Valley of Italy. Animal Production. 28, pp115-117.

Foxcroft, G.R. (1997). Mechanisms mediating nutritional effects on embryonic survival in pigs. Journal of Reproduction and Fertility. 52, pp.47-61.

Griffith, M.K. and Minton, J.E. (1992). Effect of light intensity on circadian profiles of melatonin, ACTH, and cortisol in pigs. Journal of Animal Science. 70, 1992: 492-498.

Hennessy, D. & Williamson, P. (2008), Stress and Summer infertility in pigs. Australian Veterinary Journal. 61(7). Pp 212-215.

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Hughes, P.E. (1982). Control of Pig Reproduction: Factors affecting the natural attainment of puberty in the gilt. London: Butterworths.

Hurtgen, J.P. and Leman, A.D. (1982). Seasonal influence on the fertility of sows and gilts. Journal of Veterinary Medicine. 177, pp 631-635.

Love, R.J. (1978). Definition of a seasonal infertility problem in pigs. Veterinary Record, 104. pp 238-240.

Love, R.J. (1981). Seasonal infertility in pigs. Veterinary Record. 109. pp 407-409.

Love, R.J., Evans, G. and Klupiec, C. (1993). Seasonal effects on fertility in gilts and sows. Journal of Reproduction, Fertility and Supplies. 48. pp191-206.

Love, R.J., Klupiec, C., Thornton, E.J. and Evans, G. (1996).An interaction between feeding rate and season affects fertility of sows. Animal Reproduction Science.39. pp 275-284

Paterson, A.M. and Pearce, G.P. (1990). Attainment of puberty in domestic gilts reared under long day or short-day artificial light regimens. Animal Reproduction Science. 23 pp 35-144.

Paterson, M., Pearce, G.P. and Antuono, F.D. (1991). Seasonal variation in attainment of puberty in isolated and boar-exposed domestic gilts. Animal Reproductive Science. 24. pp323-333.

Peltoniemi, O.A.T., Easton, B.G., Love, R.J., Klupiec, C. and Evans, G. (1995). Effect of chronic treatment with a GnRH agonist (Goserelin) on LH secretion and early pregnancy in gilts. Animal Reproductive Science.40. pp121-133.

Prunier, A., Quesnel, H., Messias de Braganca, M., Kermabon, A.Y. (1996). Environmental and seasonal influences on the return-to-estrus after weaning in primiparous sows. A review of Livestock Production Science. 45. pp103-110.

Pusateri, A.E., Smith, J.M., Smith, J.W., Thomford, P.J. and Diekman, M.A. (2000). Maternal recognition of pregnancy in swine. I. Minimal requirement for exogenous estradiol 17 to induce either short or long pseudopregnancy in cycling gilts. Biological Reproduction. 55. 576-589.

Wan, S. Hennessy, D. & Cranwell, P. (1980). Seasonal infertility, stress and adrenocortical responsiveness in pigs. Animal Reproduction Science. 34(3). pp 265-279.

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