In a series of experiments on female miniature pigs, the pattern of plasma LH and progesterone levels during the oestrous cycle, late pregnancy and lactation and after ovariectomy were characterized, and the effect of pentobarbitone treatment was tested. The preovulatory surge of LH occurred in seven out of eight animals between 00.00 and 12.0 h on day 0 of the oestrous cycle (day 1 of standing heat). Plasma progesterone strated to decline 8 days before oestrus and reached its lowest value 5 days before the preovulatory LH peak. Increases in progesteron concentration were already noticeable 48 h after the LH surge. During late pregnancy, parturition and lactation, plasma LH was low and showed only minor fluctuations, while plasma progesterone declined 4 to 5 days before parturition. Both hormones remained at low levels throughout lactation. Three weeks before parturition increases in LH were always followed by an increase in progesterone. This dependency was greatly diminished immediately before delivery. Four to 12 days after weaning the animals came into oestrus which was followed by an increase in LH and later an increase in progesterone concentrations. Ovariectomy during dioestrus resulted in a steady increase in plasma LH levels of 35-39 days. Ovariectomy caused abortion if performed on day 100 of pregnancy. It was followed by a rapid increase of plasma LH concentration. Normal parturition (around day 115) and lactation took place when animals were spayed on day 112 of pregnancy. In this case, plasma LH levels remained even lower than before ovariectomy as long as lactation was maintained. Immediately after weaning a rapid increase in the normal postovariectomy pattern of LH secretion was observed. Pentobarbitone anaesthesia (30-35 mg/kg body wt, initial dose), during pro-oestrusoestrus, for less than 5 h had no effect on the preovulatory LH increase. However, pentobarbitone anaesthesia for more than 6 h inhibitied the LH peak and ovulation if the animal was under deep anaesthesia before 24.00 h on the day before oestrus. Pentobarbitone treatment of ovariectomized pigs resulted in a clear decrease in LH levels 40 min after a single i.v. dose.

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In all mammals studied so far, with the possible exception of man, it has been shown that sperm cells emerging from the testis have to pass through at least part of the epididymis before they acquire the ability to fertilize (Bedford, Calvin & Cooper, 1973;Bedford, 1974).The literature regarding the fertilizing capacity of spermatozoa collected from different segments of the epididymis in laboratory animals has been summarized by Paufler & Foote (1968) and Orgebi n\x=req-\ Crist (1969). Little information is available for the large domestic species although bulls have been successfully inseminated with spermatozoa from the cauda epididymidis (Lardy & Ghosh, 1952;Barker, 1954;Igboeli & Foote, 1968).The present experiments were therefore conducted to examine the fertilizing capacity of spermatozoa from different regions of the epididymis in the domestic pig.Text- fig. 1. Diagram showing the segments into which the boar epididymis was divided.Epididymides were obtained by castrating sexually rested 7-24-month-old German Landrace boars under sodium pentobarbital anaesthesia. Each epididymis was divided into segments (Text- fig. 1). Initially, the segments were the caput, corpus, proximal and distal cauda epididymidis. In subsequent experiments the distal 1 cm of the corpus (Corpus 2), the most proximal (Cauda 1), and the terminal (Cauda 4) portion of the cauda were studied. Each segment was placed in a fine-meshed plastic sieve, submerged in physiological saline at room temperature, and minced gently but thoroughly with fine scissors to provide a suspension of largely intact spermatozoa almost free of contamination with blood or other tissue. Suspensions from similar epididymal segments of several boars were pooled to eliminate individual boar effects.Sperm density was determined by counting two representative samples taken from each suspen¬ sion. After diluting the samples 5-10 times depending on sperm density, haemocytometers were filled and placed in a moist atmosphere for 5 min before counting commenced. Insemination doses of 120 ml, each containing a minimum of 5 IO9 spermatozoa, were prepared by adding saline. Process¬ ing time in the laboratory was about 2 hr and the time between castration and insemination was 4-6 hr.For the inseminations, prepubertal Landrace gilts weighing about 75-85 kg were given a single i.m. injection of a combination of 400 i.u. PMSG and 200 i.u. HCG (PG 600: Intervet International), and inseminated without regard to oestrous symptoms on Days 4 and 5 after the injection. The animals were killed 3-4 weeks after insemination and the ovaries and uterine contents inspected.Of the 141 gilts treated, 119 (84%) responded to the gonadotrophin treatment with 5 or more ovulations, as judged by counts of CL, and were included in the experiment.

Plasma oxytocin concentrations were measured during late pregnancy, parturition and lactation in the miniature pig. Measurements were made of plasma oestradiol, oestrone and progesterone to determine whether there was any relationship between the concentrations of oxytocin and these steroids in the circulation. Plasma oxytocin concentrations were low or undetectable in late pregnancy. Rises of up to 68.8 mum./ml were seen at the time of delivery of the foetuses and at the expulsion of the placenta. The only steroid that seemed to relat to oxytocin release was progesterone. Oxytocin release was consistently seen when progesterone concentrations had fallen to below 10 ng/ml but no increase in concentration was observed while oestrone and oestradiol increased to their maximum concentrations of 3.86--11.6 and 0.43--0.70 ng/ml respectively. During lactation, when both oestrogen and progesterone concentrations were low, suckling caused the levels of oxytocin to increase to 7.4 muu./ml. These increases were greater during the first 2 weeks of lactation than later.