Factors Affecting Gestation Length Among Swine

A Literature Review about the

Factors Affecting the

Length of Gestation Period among Swine

In general, gestation length of sows varies from 112 to 114 days (Carmichael & Rice, 1920). Measuring the days involved in the gestation period varies depending on the researcher. Some started counting from the first day of breeding but others begin from the second service. Gestation ends on the day the swine farrows. The following are several factors that affect length of gestation among swine based on various literatures presently available.

Litter size

One of the factors that can affect length of gestation is litter size. Based on a previous study by Garnett & Rahnefeld (1979) which involves Lacombe, Yorkshire, and Lacombe-Yorkshire crossbreed, there was a negative or inverse relationship between litter size and length of gestation for all the breeds under study. The same relationship was obtained by Martin et al. (1977). According to the results gathered, the gestation period decreases by about 0.32 days for every additional piglet in utero of the sow. In the case of Perry (1956), it was observed that the Large White pigs on their study with small litter size underwent longer pregnancy period of 117-126 days.

This inverse relationship between litter size and gestation period was also present in other multiparous species, however, Biggers et al. (1963) stated that sows were one of those who do not follow this relationship. Cox (1964a) supported the claims of Biggers et al. (1063) as their data showed that there is indeed no significant relationship between gestation length and litter size.

Litter Weight

Like litter size, there was also a negative relationship between litter weight and length of gestation based on the study of Garnett & Rahnefeld (1977). The same association was observed on an earlier study by Carmichael & Rice (1920). Based on the study, the litter that includes one of the heaviest pig (9.8 pounds) only underwent a gestation period of 98 days. On the other hand, the lightest pig with the weight of 0.2 pounds came from the litter that was farrowed for 115 days. Another study by Garnett and Rahnfeld (1979) showed consistent relationship between the two variables. However, it only applied to the purebreds of Lacombe and Yorkshire. Results for the crossbred between the Yorkshire dam and Lacombe boar revealed no significant relationship.

Omtvedt et al. (1965) also identified a negative correlation between the two variables but later found out that longer gestation period also lead to an increase in average pig weight at birth.

A more recent study by Rydhmer et al. (2008) contradicted the outcome of the previous studies as they found out a positive correlation. They concluded that piglets born from longer gestation period had heavier birth weights and had the tendency to grow faster.

Litter sex ratio

There were no significant relationship found between litter sex ratio and length of gestation from the studies of Omtvedt et al. (1965), Kennedy and Moxley (1978), and Garnett and Rahnfeld (1979).

Breed

Differences among the breeds of swine exhibited genetic influence on the length of gestation (Leigh, 1981). This was further supported by various previous researches. One these researches include that of Carmichael & Rice (1920) which showed that among several breeds of swine Chester White breed has the shortest average gestation period. It was followed by Duroc-Jerseys, Large Yorkshires, Tamworths, Poland Chinas and Berkshires. From the average of 114.5 days, the gestation length of Berkshires was more than 0.75 days longer.  The initial study of Garnett & Rahnefeld (1977) presented differences on the gestation length between Lacombe and Yorkshire lines wherein the former had 114.1 days while the latter had 115.2 days. Although it has slight variations in the values, results of the succeeding study of Garnett & Rahnefeld (1979) were consistent with the initial. Lacombe lines had a gestation length of 114.42 days while Yorkshire had 115.77 days. Another study was by Cox (1964b) which revealed that gestation length of Durocs was 0.5 days longer than the Hampshires.

The sire and breed of the sire also have influence on the gestation length and could lead up to 6% of the variation (Cox, 1964b). Serenius et al. (2004) also found a high sire effect of 5-9%. From the study of Bernard et al. (1971), which involves crossbreeding of different breeds, a significant difference was observed on the effect of the sire. Litters of Hampshire-sired boars had shorter gestation length in comparison to the litters sired by Berkshire or Large Black boars. Aside from this, results of the study by Kennedy & Moxley (1978) stated that the litters of Landrace boars had a 0.33 day shorter gestation period compared to Yorkshire-sired litters. Leigh (1981) proved the claims of Cox (1964b) after obtaining a result of up to 16.46% in terms of the contribution of sire effect to the variations of the gestation length. However, Garnett & Rahnefeld (1979) found no significance on the effect of sire based on their research.

Purebreed or Crossbreed

Kennedy & Moxley (1978) earlier concluded that there is no significant difference between the gestation length of purebreds and crossbreds, however, new research discovered that gestation period may vary among the two. Imboonta and Kuhaaudomlarp (2012) studied Landrace, Large Whites, and their crosses in several commercial farms in Thailand. Results revealed that gestation of crossbreds were 0.20 to 0.51 days shorter compared to a purebred Landrace. Cassady et. al (2002) also had the same conclusions since the crossbred of Large White and Landrace in their study gestated 0.56 days shorter.

Parity

In terms of parity, contradicting results from the different literatures can be derived. According to Lush (1943), it can be observed that first parity gestation is a few hours shorter compared to the succeeding parities. This is in line with the results obtained by Garnett & Rahnefeld (1979) which estimated that gilt’s gestation period is 0.70 hours less than that of sows. In contrast with this, Cox (1964a) concluded that the first pregnancy for pigs is longer by 0.36 days. Kennedy & Moxley (1978), on the other hand, discovered that compared to second, third, and succeeding parities, the first parity was actually half a day longer. A more unusual result was presented by Rydhmer et al. (2008) as they found out that the second parity was longer compared to other parities under the study. Findings from the study of Krizenecky (1935), Joubert and Bonsma (1952), as well as  Sasaki and Koketsu (2007), however, showed that the order of parity has no significant relationship with gestation length.