Swine Articles on Breeding & Reproduction

Some say the animal is so cute. Others say it is the funniest- looking thing they’ve ever seen. Either way, scientists in the United States were delighted to obtain some for research in the late 1980s. They are the Meishan (pronounced MAY-shawn) pigs of southern China. They were always known for their large litters (15-16 piglets compared to 10-12 for U.S. sows).

Researchers from various countries wanted to find out why this occurred. The first Meishan pigs (and a few other Chinese-bred pigs) were brought to the United States in 1989. After being quarantined in Florida, they were delivered to ARS’ Roman L. Hruska U.S. Meat Animal Research Center (MARC) in Clay Center, Nebraska; the University of Illinois; and Iowa State University.

This investigation was designed to assess the sensitivity, specificity and positive predictive values of amplitudedepth and Doppler pregnancy detectors when utilized for pregnancy diagnosis of mated sows. Mated sows (n = 38) were tested daily from 15 to 45 days after mating for pregnancy with the ultrasound instruments. The same procedure was performed with nonmated sows (n = 10) 15 to 45 days after estrus. Both instruments were unreliable for pregnancy diagnosis between 15 and 22 days after mating. Between 23 and 45 days after mating the Doppler pregnancy detector was more specific and had greater positive predictive values. In contrast the amplitudedepth pregnancy detector was more sensitive during the same time interval. Serum estrone sulphate concentrations were determined in samples collected between 27 and 30 days after mating or estrus, as an alternate method of pregnancy diagnosis. Serum estrone sulphate concentrations were always equal to or greater than 0.5 ng/mL in the pregnant sows, while in the nonmated sows estrone sulphate concentrations were never more than 0.5 ng/mL serum.

The advantages of accurate methods for early pregnancy diagnosis in swine include early detection of conception failure, forecasting production levels and early identification of nonpregnant animals which facilitates culling, treatment or rebreeding (1). The traditional method of pregnancy diagnosis has been failure to return to estrus about 21 days after mating. However, this method may be confused with conditions such as delayed return to estrus after breeding and "silent" heat (2). A more accurate method of early pregnancy diagnosis in sows consists of the determination of plasma or serum concentration of estrone sulphate, 23 to 30 days after mating (3,4,5). Serum concentrations of estrone sulphate in excess of 0.5 ng/mL are considered indicative of pregnancy (6,7). Elevated plasma concentrations of progesterone, assayed between 18 and 24 days after mating, have been used for presumptive pregnancy diagnosis in sows (4). However, these methods are not readily available to swine producers.