EARLY PREGNANCY IN THE PIG

Abstract

Summary. Observations have been made on fifty-eight sows and gilts killed between 2 and 40 days after mating to study various aspects of early pregnancy, and to determine the incidence of embryonic loss, and the time and stage of development when this loss occurs. The corpus luteum count was found to provide an accurate estimate of the number of ova ovulated. No difficulty was encountered in recovering all the eggs from the Fallopian tubes, but only 89% of the expected number were recovered from the uterus. In forty mated animals killed before the 10th day after the onset of oestrus, 95·5% of all eggs recovered were fertilized. The stages in cleavage of the eggs and the elongation of the blastocysts are described. Development was normal in all tubal eggs, but 22% of those recovered from the uterus between the 6th and 9th days were degenerating. Embryonic loss in thirteen pigs killed between the 13th and 18th days was 28·4%; the greater part of this loss occurred in two of the animals. The loss in a third group of five gilts killed between the 25th and 40th days was 34·8%, about one-half of which was contributed by one of the animals. The uterus was found to elongate throughout the first 18 days of pregnancy and the elongation was most rapid between the 2nd and 6th days when a 50% increase in length occurred. Linear growth is correlated with increase in uterine weight. These facts are contrasted with those obtained for other species. Many of the corpora lutea in animals killed before the 10th day become distended to form cysts. This condition was considered to be transient as few were found between the 10th and 18th days and none at later stages. A sudden increase in the size of the 'normal' corpus luteum takes place soon after the 6th day, at the time of blastocyst formation.