Intraepithelial leucocytes in the bovine uterine tube.

The epithelium of the uterine tube consists of ciliated cells and secretory cells. Basal cells are a third cell type observed in tubal epithelium and they are located principally in the basal part of the epithelium. The objectives of this study were to characterize these basal cells in normal and superovulated heifers and to determine whether they participate in the replacement of the ciliated and secretory cell populations. All heifers received cloprostenol (PG) to induce oestrus (day 0). Superovulated heifers received 24 mg pFSH at doses of 4.5, 3.5, 2.5 and 1.5 mg given twice daily. Control and superovulated heifers were slaughtered on days 1, 3, 5 and 7 of the oestrous cycle. Another group of normal cycling heifers was slaughtered on days 2-3 and 11-13 of the oestrous cycle and used for immunocytochemistry. Samples from ampulla, pre-isthmus and isthmus of the uterine tube were collected and processed for light and transmission electron microscopy. Quantitative examination by light microscopy showed that there was a significant difference in the number of basal cells between the regions of the heifers' uterine tube. On the basis of ultrastructure two populations of basal cells were observed. One (type I) had a nucleus with much condensed heterochromatin and very sparse cytoplasmic organelles. The second cell (type II) had a nucleus with heterochromatin typically clumped around the nuclear envelope. Its cytoplasm contained many organelles including a number of lysosomes. The ultrastructural features of these cells were similar in all regions and at all days of the oestrous cycle examined. Immunocytochemistry revealed that type I basal cells were lymphocytes and type II basal cells were macrophages.

The extent and timing of prenatal loss in gilts.

The potential litter size of gilts that is based on the ovulation rate is much higher than the actual litter size, which depends on the fertilization rate and subsequent prenatal mortality. Prenatal mortality is divided into embryonic mortality (before Day 30) and fetal mortality (after Day 30). Prenatal loss includes both fertilization failure and prenatal mortality. Crossbred gilts (n = 149) were bred at the first observed estrus after being exposed to the boar at 200 days of age. Time of the first insemination after estrus detection was determined by measurement of vaginal conductivity using a Walsmeta meter. A second insemination was administered either 8 or 16 hours later. Artificial insemination with fresh semen (0 to 3 days old) was used throughout the experiment. Gilts were slaughtered on Day 3 (n = 26), Day 10 (n = 42), Day 30 of gestation (n = 45) or they were allowed to farrow (n = 36). Gilts slaughtered on Day 3 were used to estimate the fertilization rate. Gilts slaughtered on Day 10 and Day 30 were used to calculate embryonic mortality, while fetal mortality was calculated from the gilts that farrowed. The mean (+/-SEM) number of corpora lutea (CL) was 13.15+/-0.46, 13.36+/-0.37 and 12.97+/-0.39 for gilts slaughtered at Days 3, 10 and 30, respectively (P>0.05), and the mean (+/-SEM) number of normal embryos recovered was 11.12+/-0.69, 9.46+/-0.55 and 9.33+/-0.58, respectively. Litter size at parturition was 9.10+/-0.54. There was a significant difference between the number of normal embryos on Day 3 and Day 30 (P=0.05) and also between the number of normal embryos at Day 3 and the number of piglets at term. Ninety percent of the ova were recovered at Day 3. The fertilization rate was calculated either 1) assuming that unrecovered ova had a similar fertilization rate as the recovered ova (FRER=94.5+/-2.0%) or 2) assuming that unrecovered ova were unfertilized (FROR=84.5+/-2.5%). It was concluded that FRER was a more accurate estimation of the fertilization rate. Based on this fertilization rate, embryonic mortality between Day 3 and Day 10 was 20.8+/-8.3%, with an additional 12.5+/-7.1% loss between Day 10 and Day 30, when all gilts were included (P = 0.308). Thus the total prenatal loss, including fertilization failure, up to Day 10 was 26.3% and to Day 30 it was 38.8%. Fetal mortality was 2.2%, giving a total prenatal mortality (excluding fertilization failure) of 35.5% and a prenatal loss of 41%. Most of the prenatal loss was due to embryonic mortality. In those gilts that remained pregnant most of the embryonic loss occurred before Day 10 (19.0+/-6.3%; P=0.003). There was no further loss between Day 10 and 30 of pregnancy. There was a significant difference between the loss from Day 3 to Day 10 compared with the loss from Day 10 to Day 30 (P=0.05); therefore, most of the embryonic loss in pregnant gilts occurred before Day 10. Since fetal mortality was 3.2+/-6.3%, most of the prenatal loss was due to embryonic mortality.

The effects of administration of gonadotrophins and estrogens on prenatal survival in gilts.

In gilts ovulation occurs over a 4 to 8-hour period, with 70% of the ova being shed over a relatively short span of time. These oocytes supposedly give rise to more developed embryos at Days 10 to 12 which advance the uterine environment and reduce survival rates of less developed embryos because of an asynchronous environment. The aim of this experiment was to reduce embryo mortality by influencing the duration and pattern of ovulation. Crossbred gilts (n=98) were bred at their first observed estrus after being exposed to boars at 200 days of age. Estrus detection was carried out daily at 0000, 0800 and 1600 hours. All gilts were artificially inseminated with fresh semen, with a minimum of 2.7 billion spermatozoa, at both 16 and 32 hours after detection of estrus. Gilts were randomly assigned to one of the following treatments at detection of estrus: 1) 500 IU (2 ml) chorionic gonadotrophin (hCG) injected intravenously at the onset of estrus (n=22); 2) 16 microg (4 ml) gonadotrophin releasing hormone (GnRH) injected intravenously at the onset of estrus (n=25); 3) 11.5 microg estrogen added to the semen at the time of AI (n=25); 4) control, untreated gilts (n=26). All gilts were slaughtered at Day 30 of gestation (Day 0=day of detected estrus). The mean (+/-SEM) number of ovulations in pregnant gilts per treatment was 13.0+/-0.52, 12.6+/-0.51, 13.6+/-0.54 and 13.3+/-0.52, while the mean (+/-SEM) number of normal embryos per treatment was 10.3+/-0.67, 10.5+/-0.66, 10.3+/-0.69 and 10.5+/-0.67 for hCG, GnRH, estrogen and control groups, respectively, for an embryonic survival rate of 80+/-4.2%, 83+/-4.1%, 74+/-4.3% and 79+/-4.2% in pregnant gilts. If nonpregnant gilts are included, the embryonic survival rate for treatments 1 to 4 was 76+/-7.0%, 73+/-6.5%, 60+/-6.5%, and 64+/-6.4%, respectively. There was no significant difference between treatments for any of these variables. There was no evidence that administration of hCG, or GnRH at the onset of estrus, or the addition of estrogen to semen improved embryonic survival in gilts by Day 30 in this experiment.

Concentrations of luteinising hormone and progesterone in pregnant and non-pregnant heifers.

An experiment was conducted to determine if concentrations of luteinising hormone or progesterone were different in pregnant or non-pregnant heifers for seven days before and 20 days after a successful or non-successful insemination. Heifers with an oestrous cycle length of 18 to 24 days only were used and they were bled at 08.00, 16.00 and 24.00 each day for seven days before and for 20 days after insemination with thawed semen (treatment 1) or semen diluent (treatment 2). Animals allocated to treatment 3 had the embryo nonsurgically flushed from the uterus at days 10 to 12 while animals allocated to treatment 4 were inseminated with semen diluent and then had a viable embryo transferred to the uterus between days 10 and 12. All animals were slaughtered between 19 and 21 days after insemination and pregnancy rate determined. There were no differences in basal luteinising hormone levels between treatments. Blood concentrations of progesterone were not different before insemination and for 16 days after insemination for pregnant (11 out of 15) and non-pregnant heifers (14) allocated to treatments 1 and 2. Between days 17 and 20, progesterone concentrations declined in non-pregnant heifers. Transfer of an embryo to non-pregnant heifers on day 10 to 12, did not affect progesterone concentrations, but non-surgical flushing of the embryo caused a decline in blood concentrations of progesterone. It was concluded that basal blood concentrations of luteinising hormone and progesterone, in samples taken three times daily were not different in pregnant or non-pregnant heifers before and for 16 days after insemination.

Reproductive wastage following artificial insemination of heifers.

Hereford cross beef heifers at pasture were inseminated at a detected oestrus with thawed semen and were slaughtered at the following intervals after insemination: day 3 (60 heifers); day 8 (71); day 14 (65); day 18 (78) and day 28 (29). The recovery rates of ova at days 3 and 8 were 87 and 77 per cent respectively. The percentage of heifers that were pregnant at the respective time intervals after slaughter were 81, 84, 75, 60 and 62. There was no difference in the proportion of normally developing ova or embryos between days 3 and 8, 8 and 14, 14 and 18 or 18 and 28. There were significant differences in the number of animals with variable embryos between days 3 and days 18 + 28 (P less than 0.025); 8 and 18 + 28 (P less than 0.01); and 14 and 18 + 28 (P less than 0.05). Based on the results and other data in the literature, fertilisation failure can account for up to 20 per cent of reproductive wastage. Embryonic mortality accounts for most of the remaining wastage and occurs gradually between days 8 and 18. Pregnancy rates at days 18 and 28 approximate to calving data.