Intrauterine position effects in female swine: Subsequent reproductive performance, and social and sexual behavior

Abstract

Uterine position, relative to the sex of adjacent fetuses, is known to affect the subsequent behavior and reproductive performance of rodents. This experiment was designed to determine if similar effects are present in female swine. Donor sows were slaughtered at Day 112 of gestation, the uteri removed and piglets delivered manually. Uterine position was recorded for each pig as between 2 females (0M, n=16), between a male and a female (1M, n=25) or between 2 male fetuses (2M, n=17). Females were reared in heterosexual littermate groups until 120 days and thereafter in unisexual groups of six. Females were checked twice daily for estrus using a mature boar beginning on Day 175. 2M females tended ( P<0.15) to reach puberty sooner (187 days) than 0M (192 days) and 1M (194 days). The length of the estrous cycle and ovulation rates did not differ among groups over the first three estrous cycles. Duration of receptivity was similar among groups until the third estrus when the duration of standing heat was shorter for 2M females, both when measured in the presence (2.8, 2.7 and 2.1 days for 0M, 1M and 2M, respectively; P<0.10) and the absence of the male (2.1, 1.3 and 0.9 days for 0M, 1M and 2M, respectively; P<0.01). When in their home pen, 0M females received the fewest mounts from pen mates ( P<0.01), but mounted most often. There were no differences in the frequency of anogenital sniffing or rooting the sides of pen mates. The frequency of agonistic activity was similar among groups, however 0M females participated in fewer fights ( χ 2=5.2, P<0.10) and won fewer than expected by chance ( 0 5 ; χ 2=6.0, P<0.05). Twenty gilts ( n=8, 5 and 7 for 0M, 1M and 2M gilts, respectively) were ovariectomized and treated with estradiol benzoate. When tested in the boar's absence, the proportion of females showing a positive response to back pressure and the duration of this response was greater for 2M females ( P<0.005). Relative attractivity was tested by allowing the boar simultaneous fenceline access to 0M–2M gilt dyads. When matched for stage of receptivity, 0M and 2M gilts were equally attractive. The results indicate that prenatal intrauterine position has little effect on adult agonistic behavior, length of the estrous cycle and ovulation rate, but may affect the subsequent sexual behavior of female swine.