Effects of nutrient intake and sexual age of the dam at mating on fetal development in swine

Fifty-four Duroc gilts (mean wt = 88 kg, mean age = 164 d) were fed a 15% protein diet either ad libitum (F) or at a rate of aproximately 50% of ad libitum daily (1.8 kg: L) prior to mating at either second (Exp. 1) or first (Exp. 2) observed estrus. Gilts were checked for estrus twice daily with a mature, active boar, mated at the appropriate estrus, and fed 1.8 kg of the prebreeding diet per gilt daily until slaughter between 42 and 49 days of gestation, mated gilts were slaughtered and measurements taken on fetuses and reproductive organs. In Exp. 1, fetal weight per day of gestational age (FetWDA), placental weight (PLW), crown-to-rump length (CRL) and uterine space per fetus (SP) were greater for fetuses from L gilts than F gilts (all P < .05) with no difference in number of fetuses (P > .05). In Exp. 2, FetWDA was greater for fetuses from F gilts than L gilts (P < .05), however there was no difference due to level of feeding for PLW, CRL and SP (all P > .10). Fetal weight (FW) was highly correlated with CRL indicated that a cubic relationship existed (both r = .97). In both studies, male fetuses grew more rapidly than female fetuses (P < .05). These studies indicate that pre-breeding nutritional status and sexual age of the dam at conception have differential effects on fetal growth rate, but relationships among FW and CRL are not readily altered by pre-breeding level of feeding or sexual age of the dam at conception. Furthermore, male fetuses grow more rapidly than female fetuses throughout the initial six to seven weeks of gestation. The reason for the difference in growth rate of male and female fetuses at this stage of gestation remains obscure and requires further investigation.