Changes in feeding level during early pregnancy affect fertility in gilts.

Modified feeding combining the benefits of restricted feeding after ovulation and abundant feeding during implantation in autumn was tested. Three groups of eight gilts were housed with individual feeding stalls and fed 40 MJ per day of a commercial ration. Following insemination gilts were fed 27 MJ per day (LLL) or 54 MJ per day (HHH) for 34 days or 27 MJ per day for 10 days, 54 MJ per day for 7 days followed by 27 MJ per day until day 34 (LHL). Blood for progesterone analysis was collected daily during the week of ovulation and then twice a week until the end of the study. For LH assay, blood was collected from five gilts from each group at 15 min interval for 10 h on the day 15 of pregnancy. Gilts were weighed three times at intervals of 4 weeks. The effect of dietary treatment was significant (P<0.05) on body weight gain from days 0 to 30 of pregnancy, 1201, 287 and 438 g per day for groups HHH, LLL and LHL respectively. The pregnancy rate at day 34 was significantly higher (P<0.005) in HHH-group (100%) compared with LLL (25%) and LHL (38%) although HHH group had significantly lower (P<0.05) progesterone concentration on days 9 and 12. The basal LH level was significantly higher (P<0.01) in HHH group compared to LHL group (mean +/- S.D.) (0.98 +/- 0.22 and 0.60 +/- 0.08, respectively). Gilts in HHH group had a significantly higher mean LH concentration (1.18 +/- 0.24) than those in group LHL (0.7 +/- 0.07) (P<0.05), but not in group LLL (0.93 +/- 0.15) (P=0.09). There was a tendency (P=0.058) for amplitude to be higher for gilts in HHH group. The LHL feeding strategy did not provide the benefits anticipated. Instead, it was the HHH feeding strategy that provided a distinct advantage in pregnancy rate. The mechanism mediating supportive effect of high feeding level on the maintenance of early pregnancy is yet to be determined.

Effect of a gonadotrophin-releasing hormone antagonist on luteinising hormone secretion and early pregnancy in gilts.

The aims of the present study were: (1) to determine the duration of suppression of luteinising hormone (LH) following a single treatment with a gonadotrophin-releasing hormone (GnRH) antagonist (BIM-21009; Biomeasure) at a dose of 100 microg kg(-1); (2) to block LH pulses only for certain days of pregnancy; and (3) to determine the period of early pregnancy most susceptible to suppression of LH. Three groups of gilts were injected with 100 microg kg(-1) on Day 16 (n = 5), 14 (n = 6) or 19 (n = 4) of pregnancy. Blood for LH analysis was collected at 20-min intervals for 12 h on the day before treatment and during varying stages of early pregnancy. Blood for progesterone analysis was collected daily and development of pregnancy was followed using real-time ultrasound. Prior to treatment, gilts had 2.6 +/- 0.7 LH pulses per 12 h. The GnRH antagonist abolished LH pulses for a period of 2.7 +/- 1.8 days and, thereafter, suppressed the resumed LH pulses (P < 0.05). Pregnancy was disrupted in three pigs (20%) with a mean treatment-to-abortion period of 4.7 days concurrent with a mean treatment-to-progesterone decline interval of 4.3 days. In a proportion of pigs, short-term LH suppression may cause early disruption of pregnancy.

Early disruption of pregnancy as a manifestation of seasonal infertility in pigs.

All gilts and sows in production from which the detailed production information was available in a 160-sow unit were included to the study. In winter-spring, there were complete data available from 47 animals and in summer-autumn from 64 animals. The farm had a consistent history of the seasonally reduced farrowing rate in summer-autumn. Success of inseminations was monitored during a 4-month breeding period in winter-spring and in summer-autumn. Each animal was bled twice a week for 6 weeks starting a day before insemination and the blood samples were assayed to determine serum progesterone concentration. The blood samples were also assayed for cortisol to detect any acute infectious response. Starting on day 18, animals were pregnancy tested by transcutaneous real time ultrasound twice a week. In winter-spring, the farrowing rate was 72% (58 inseminations, 1.2 inseminations/sow) and in summer-autumn 63% (81 inseminations, 1.3 inseminations/sow). In winter-spring, there was only one detected case of early disruption of pregnancy (EDP), whereas nine such cases were recognised in summer-autumn. Five out of those nine animals returned to oestrus with a mean insemination to oestrus interval of 25.8+/-1.6 days. One sow returned to oestrus 35 days after insemination and three sows did not return to oestrus within 45 days. However, two of these sows had progesterone profiles that indicated an undetected oestrus around day 25. In those nine animals, no acute phase infectious response as indicated by a rise in serum cortisol was evident. Serum progesterone concentrations in the animals eventually loosing the pregnancy tended to be lower on day 13 (no significant difference) and were significantly lower on day 20 when compared with animals remaining pregnant. There was no difference in serum progesterone levels of pregnant animals between winter-spring and summer-autumn. Litter size was not affected by the season. The weaning to oestrus interval tended to be longer in summer-autumn. This study showed that the seasonally decreased farrowing rate is partly caused by EDP. The lowered progesterone concentrations in summer-autumn were demonstrable only in "problem animals".

Effects of active and passive gonadotrophin-releasing hormone immunization on recognition and establishment of pregnancy in pigs.

This study investigated the effects of a reduction in gonadotrophins, by means of differently timed active and passive gonadotrophin-releasing hormone (GnRH) immunization at various stages, on the maintenance of early pregnancy in pigs. In the first experiment crossbred sows (n = 11) were immunized against GnRH using a commercial vaccine on the day of farrowing, mated at the first oestrus, and a booster immunization was administered 10 days (n = 7) or 20 days (n = 4) after mating. Plasma samples were collected every second day and assayed for GnRH antibodies and progesterone. Pregnancy testing was carried out by real time ultrasound. None of the sows receiving the booster immunization 10 days after mating were pregnant on Day 18 after mating. All sows receiving the booster on Day 20 after mating aborted, with a mean vaccination-to-abortion interval of 10.0 +/- 1.5 days. In the second experiment, crossbred gilts (n = 6) were passively immunized by infusing (i.v.) GnRH immune pig serum on Day 12 after mating. Luteinizing hormone profiles were determined on the day before immunization and one day afterwards. Daily plasma samples were assayed for GnRH antibodies and progesterone. None of the gilts were pregnant 18 days after mating, compared with 5 of 6 non-immunized controls. Booster immunization 10 days after mating resulted in failure of embryonic development and establishment of pregnancy before the corpora lutea (CL) regressed, according to progesterone profiles, whereas immunization 20 days after mating resulted in regression of CL followed by abortion. Passive immunization 12 days after mating had a similar effect to the active immunization 10 days after mating. These results demonstrate two different outcomes of active GnRH immunization depending on the timing of immunization, and indicate that loss of pregnancy between Days 12 and 18 may occur due a reduction in progesterone rather than complete failure of the CL, as occurs at later stages. The findings may provide an explanation for the reduced fertility of pigs in the summer-autumn period.

Pathology of proliferative haemorrhagic enteropathy in pigs.

Examination of the small intestine of pigs with proliferative haemorrhagic enteropathy showed changes consistent with defects in vascular permeability. Early in the disease there were many eosinophils and distension of lacteals and intercellular spaces with proteinaceous material. Later the predominant features were red blood cells and exudate in tissue spaces. This was most severe and extensive at the tips of villi which were covered by a cast of cells and fibrinous exudate. Adenomatous intestinal mucosal cells contained organisms that were free within the apical cytoplasm and were morphologically identical with those seen in the related disease, porcine intestinal adenomatosis. Also these bacteria were seen free in the subepithelial mucosal area, in blood vessels and within membrane-bound vesicles in phagocytic cells in the mucosa and its blood vessels. Mast cells were prominent in some areas as were thrombosed vessels.

Nippostrongylus brasiliensis in young rats. Lymphocytes expel larval infections but not adult worms.

Young rats were not able to expel adult N. brasiliensis infections even when the worms were damaged by antibodies and the young rats were given all the cellular components (sensitized lymphocytes and bone marrow cells) shown to be necessary for the expulsion of antibody-damaged worms from adult rats. In contrast, most of the worms were expelled from young rats given sensitized lymph node cells on the day of a larval infection. These results show that the reduced ability of young rats to respond to infection by producing sensitized lymphocytes only partly explains their inability to expel the worms. It was not possible to explain the failure of young rats to expel adult worms by hypothesizing that they develop an active factor which prevents the cells from acting on the worms. It is also unlikely that worms persist in young rats because they differ in their susceptibility to cells compared with antibody-damaged worms from mature rats. This work suggests that the immune mechanism which affects the immature stages of this nematode may differ from that which controls the adult stages.

Studies of the responses of basophil and eosinophil leucocytes and mast cells to the nematode Trichostrongylus colubriformis. II. Changes in cell numbers following infection of thymectomised and adoptively or passively immunised guinea-pigs.

The role of the immune response in the generation of the basophilia and eosinophilia found during expulsion of the intestinal nematode parasite, Trichostrongylus colubriformis, by guinea-pigs was investigated by studying cell numbers in animals whose immune responsiveness had been modified by thymectomy and adoptive or passive immunisation. Basophilia, but not eosinophilia, was depressed in thymectomised guinea-pigs. Bone marrow basophil numbers were significantly increased in T. colubriformis-infected guinea-pigs following the infection of mesenteric lymph-node cells from both normal and T. colubriformis-immune syngeneic donors. Bone marrow basophil counts were also increased following the injection of immune lymph-node cells into uninfected recipients. Small intestine eosinophil numbers in adoptively immunised guinea-pigs showed a pronounced increase following infection with T. colubriformis. A smaller increase followed infection of passively immunised guinea-pigs. These results, and other work with this system, suggest that basophilia and eosinophilia during T. colubriformis infection, although associated with the immune response, might not be fully explained as direct consequences of the interaction of parasitic antigens and sensitised lymphocytes or antibodies.