46 P. Razdan et al. before day 10 of pregnancy (Lambert et al. 1991). Stress is associated with hormonal and metabolic changes and has a negative effect on reproductive performance (Mburu et al. 1998, Mwanza et al. 2000a, Tsuma et al. 1996b) but the exact mechanisms mediating these effects are not fully understood. A statistically signiﬁ- cant rise in blood plasma concentration of cor- tisol after 2 days of food deprivation has already been shown in the studies of Mburu et al. (1998) and Tsuma et al. (1996a). Progesterone as a potential mediator of the nu- tritional status during early pregnancy and its inﬂuence on embryo survival, oviductal and en- dometrial development has been thoroughly in- vestigated and widely discussed (Ashworth et al. 1991, Buhi et al. 1990, Jindal et al. 1996, Jindal et al. 1997, Mao et al. 1998, Mburu et al. 1998, Pharazyn et al. 1991, van der Lende et al. 1994). It is generally agreed that an abnormal change in the blood plasma progesterone levels after ovulation might induce a slight asyn- chrony between embryonic and uterine devel- opment which in turn might reduce embryo vi- ability (Pope 1988). Mburu et al. (1998) found that food deprivation immediately after ovula- tion hastened the physiological increase in blood plasma progesterone and retarded cleav- age rate of the ova as well as decreased the number of spermatozoa in the oviductal reser- voir. The objective of the present study was to inves- tigate if there is any correlation between the changes in the hormonal proﬁles and the ova transport time after stress caused by food depri- vation and if the earlier argued asynchrony between the gamete and uterine development may partly be explained by a change in the transport time of the ova. Materials and methods Animals The experiment was performed with a total of Acta vet. scand. vol. 42 no. 1, 2001 21 crossbred (Swedish Landrace × Swedish Yorkshire) sows in their second to fourth parity. The weight of the sows was between 155-240 kg when they were brought from a commercial farm on the day of weaning. They were placed in individual pens on straw at the Department of Obstetrics and Gynaecology, Swedish Univer- sity of Agricultural Sciences, Uppsala, Sweden. The sows were studied during 2 oestruses where the ﬁrst oestrus after weaning was used to predict the interval from onset of standing heat to ovulation in the second oestrus of each sow (Mburu et al. 1995). The sows were fed 2.9 kg of a commercial ration divided into 2 meals at 7:00 am and 3:00 pm, according to Swedish standards (Simonsson 1994). Water was pro- vided ad libitum. The sows were randomly di- vided into 2 groups, one control group (C, n =10), which continued to be fed as above and one experimental group (E, n =11) deprived of four meals of feed starting with the ﬁrst morn- ing meal after the second ovulation. One of the E-group sows was excluded from the experi- ment due to injury and had to be slaughtered 18 h after ovulation. Two of the remaining 20 sows, one from each group, had to be excluded from the blood sampling part of the study due to failing jugular vein catheters. Oestrous detection and ovulation Detection of oestrus was performed twice a day (morning and evening) from mid pro-oestrus and every 4 h from late pro-oestrus by testing the sows with back-pressure in front of a boar. Standing oestrus was deﬁned as when the sows were standing to back pressure in the presence of a boar. The time of ovulation was determined through transrectal ultrasonography. An annu- lar array sector scanner (type Scanner 250, Pie Medical b.v Maastricht, the Netherlands) with a 5 MHz multiple scan angle transducer was used as described by Mburu et al. (1995). Ultraso- nography was performed every fourth hour