Effects of stressors on early pregnancy in the sow.
Razdan Pia, Mwanza Alfred, Tummaruk Padet, Hultén Fredrik, Kindahl Hans, Rodriguez-Martinez Heriberto, Forsberg Mats, Einarsson Stig.
Dept. of Obstetrics and Gynaecology, Centre of Reproductive Biology, SLU, Uppsala
Introduction
The management procedures in modern intensive pig production include a number of events, which might act as stressors on the animals. It is, for example, common to mix unfamiliar pigs in new groups, which leads to aggressive interactions between sows and sometimes periods of food deprivation for more submissive animals. In the present project we evaluated the effect of stress in form of food deprivation and ACTH-stimulation immediately after ovulation and during day 13 and 14 of pregnancy.
Materials and Methods
All experiments have been carried out during and after the second oestrus after weaning in crossbred multiparous sows. The time of ovulation has been determined through transrectal ultrasonography. First day of standing oestrous was counted as day 1 of pregnancy. Blood sample was taken every second hour during treatment periods with permanent silastic tubing. In the first part of the project, 11 sows were deprived of food (FD1-group) from the morning after ovulation until slaughter and 10 sows (C1-group) was fed according to Swedish standards and used as controls. Twelve sows (A1-group) were injected with synthetic ACTH (Synacthen DepotŇ at a dose of 0.01 mg/kg body weight) every 6th hour from four to eight hours after ovulation until slaughter. Ten sows were used as controls (C2-group). The sows were slaughtered approximately 48 hours after ovulation and the isthmic part of the oviduct was divided into three parts and these, together with the uterine horns, were flushed separately. Oviductal transport rate was then determined by counting the ova or embryos in each segment. In the second experiment the cleavage rate of the embryos was determined as well as the frequency distribution of accessory spermatozoa in the zona pellucida. In the second part of the project the sows were treated during day 13 and 14 of pregnancy following the same schedule as above. Six sows were allocated to the A2-group and injected with synthetic ACTH and five sows were deprived of food (FD2-group) for 48. Another six sows were used as controls (C3-group). The sows were slaughtered at day 30±2 of pregnancy and the genital tract was recovered. The weight and length of the foetuses and the placenta were measured as well as the volume of the allantoic fluid, weight of allantochorion, uterus and total foetal unit. Blood plasma was analysed for cortisol, progesterone, oestrone, PGF2a -metabolite, insulin, free fatty acids and triglycerides.
Results
The FD1-group had a significantly higher frequency (P<0.05) of ova in the proximal and middle isthmus compared to the controls. The ova in the FD1-group had, on average, passed 1.4 segments at the time of slaughter while in the C1-group the ova had passed 3.0 segments on average (P<0.001). The FD1-group sows also had significantly higher levels of PGF2a - metabolite compared with the C1-group in the first experiment (P<0.001). Embryos in the A1-group showed a lower (P=0.056) cleavage rate (2.4 cells per embryo) compared to the C2-group (2.8 cells per embryo). The frequency distribution of accessory sperm number in the zona pellucida was also significantly (P<0.05) lower in the E2-group than in the C2-group. No significant difference in the transport rate of the embryos between A1- and C2-group was found. Plasma levels of PGF2a -metabolite were decreased from 18-hours after ovulation and onwards in the A1-group compared to the C2-group (P<0.01) during the same period. No differences in progesterone levels between groups were observed.
There was a significant increase in the blood plasma level of cortisol during the treatment period in the A2-group while the FD2-group had a significant increase only the first day of treatment. The FD-sows had a significant increase in plasma level of progesterone during the treatment period and a decrease in the insulin levels. Sows of the A2-group, on the other hand, had a significant increase in the insulin concentration but no change in the levels of progesterone compared with the C3-group. No significant differences between groups in survival and growth rate of the embryos could be detected during the post mortem examination but the placentas in the FD2-group was on average heavier (120 g) than those of both the A2-and C3-group (102g and 105g, respectively (p=0.3)).
Discussion and conclusion
Postovulatory stress impeded the cleavage rate of the embryos and decreased the sperm numbers in the oviductal reservoir. Postovulatory food deprivation also lowered the oviductal transport rate, which might be due to elevated levels of prostaglandin F2a -metabolite. PGF2a has been revealed to increase the in vitro motor activity of the isthmus and its circular muscle layer. The FD2-group had a significantly higher level of progesterone compared with the C3-and A2 –group and it could be speculated that this might lead to larger placentas. Both the FD2-and C3-group sows had a rise in their blood plasma levels of oestrone at day 19 of pregnancy. An increase in blood plasma oestrone among the A2-group sows did not occur until day 21 of pregnancy. This delayed peak of oestrone could be an indication of immature embryos. No significant difference between groups in terms of embryo growth and development was observed at the time of slaughter, which indicates a compensation for the possible effects of stress.