Factors Affecting Gestation Length Among Swine

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Stillbirth

Although relationship between gestation length and number of stillbirth were not significant, Imboonta and Kuhaaudomlarp (2012) found out that sows with an average gestation length of 117 days had the lowest stillbirth. Rydhmer et al. (2008) also connected lengthy gestation to lower number of stillbirth. Leenhouwers et al. (1999) believed that higher rate of stillbirth happens on sows with shorter gestation period since the piglets were born immature.

Season of the year

Lush (1943) pointed out that there can be instances wherein the season of the year, when the pregnancy started, affect the gestation length. This claim was contradicted by Garnett & Rahnefeld (1979). Results of their study provided no significant differences between the gestation lengths of swine which pregnancy began from May to December and from those that are pregnant from December to May. The same outcome was observed by Leigh (1981), however, a highly significant relationship between breed x season interaction and gestation length was also obtained.

Atmospheric pressure

Changes in atmospheric pressure can be stressful for pregnant cattle that may result into corticoid secretion and eventually parturition. This phenomenon was observed on the study done by Dvorak (1978) wherein the relationship between atmospheric pressure and calving incidence was put into test. Given the same principle, a similar study was conducted earlier by Lewis et al. (1968) to determine if changes in atmospheric pressure could cause variation on the gestation period among swine. Unlike cattle, their findings revealed no significant relationship between the two variables.

Hormone Injection

Farrowing performance of a swine including the number of pigs born alive, number of still born pigs, total placental weight, and birth weight can be affected by the administration of hormones during gestation. The effect can either be beneficial or harmful depending on the timing of injection. In the study conducted by Knight et al. (1983), progesterone and oestrone were administered exogenously to different gilts. The study involved three trials and was further subdivided into three treatments. Based on the results, one of the treatments in Trial 3 did not only affect the farrowing performance of the swine significantly but also the gestation length. The three treatments for Trial 3 include: daily injection of the hormones for Day 20 to Day 25 of pregnancy, daily injection of hormones from Day 25 to Day 30, and last, the control group, received corn oil for Day 20 to Day 30 of gestation. The second treatment, the one that received hormone injections for Day 25-30, resulted to a shorter gestation period of 112 days compared to the other two treatments with114.5 days and 114 days. However, Knight et al. (1983) associated this shorter gestation length as the cause of more stillborn pigs for the second treatment. On the case of Trial 1 and Trial 2, there were no significant differences in terms of gestation length.

Heritability

Based from the results of various researches, gestation length is considered a moderately to highly heritable trait. Heritability estimates from daughter dam regressions acquired by Garnett and Rahnefeld (1979) were 0.42, 0.72, and 0.69 for the Lacombe, Yorkshire, and Yorkshire dams bred to Lacombe boars, respectively. A related study by Fahmy and Bernard (1972) that involved three lines of Yorkshire pigs selected for carcass score and feed utilization acquired a heritability estimate of 0.45. On the other hand, Cox (1964b) obtained a heritability estimate of 0.60 ± .06 for Duroc and Hampshire breeds. These results imply that the trait is affected highly by the genetic component but less of the environmental factor. Contrary to the previous results, low heritability estimates for gestation length of 0.16 and 0.19 were reported by Imboonta and Kuhaaudomlarp (2012) and Rydhmer et al. (2008), respectively.

Repeatability

Repeatability is the magnitude of variation on a trait or character caused by individual differences and how it can affect the total variation of the population (Lessells & Boag, 1987; Boake, 1989). Sasaki and Koketsu (2007) studied swine in commercial farms and obtained a repeatability value of 0.50 for gestation length. According to their interpretation, the 0.50 repeatability estimate means that differences among the sows contribute largely to the total variation in the gestation length of the entire population. There is also a higher possibility for the sow’s gestation length to be consistent from first parity to the next parity.

Cox (1964b), Kennedy & Moxley (1978), and Imboonta and Kuhaaudomlarp (2012), however, arrived at lower repeatability coefficients of 0.42, 0.32, and 0.24, respectively. The inconsistencies in the values, according to Sasaki and Koketsu (2007), may be attributed to the fact that the swine under their study were crossbreds raised under commercial farms while in the case of Cox (1964b) and Kennedy & Moxley (1978), their studies focused on purebred swine under university farms. In addition to that, Imboonta and Kuhaaudomlarp (2012) believed that the induced farrowing practices together with the effect of heterosis gave way to a higher repeatability estimate for Sasaki and Koketsu (2007) compared to their result.

References

Bernard, C. S., Fahmy, M. H., & Holtman, W. B. (1971). Crossbreeding swine: Reproductive performance of seven breeds of sows bred to produce crossbred progeny. Canadian Journal of Animal Science.

Biggers, J. D., Curnow, R. N., Finn, C. A., & McLaren, A. (1963). Regulation of the gestation period in mice. Journal of Reproduction and Fertility, 125-138.

Boake, C. B. (1989). Repeatability: its role in evolutionary studies of mating behavior . Evolutionary Ecology, 173-182 .

Carmichael, W. J., & Rice, J. B. (1920). Variations in farrow: with special reference to the birth weight of pigs.

Cassady, J. P., Young, L. D., & Leymaster, K. A. (2002). Heterosis and recombination effects on pig reproductive traits. J. Anim. Sci., 2303–2315.

Cox, D. F. (1964a). Relation of the litter size and other factors to the duration of gestation in the pig. Journal of Reproduction and Fertility, 405-407.

Cox, D. F. (1964b). Genetic variation in the gestation period of swine. Journal of Animal Science, 746-751.