Steroid hormone concentrations in plasma have been measured in blood samples taken from conscious sows with ear vein catheters. In late pregnancy, the plasma progesterone concentration ranged from 6 to 12 ng/ml and it decreased in all animals before the onset of parturition. Total unconjugated oestrogens increased to high values of up to about 3 ng/ml in late pregnancy and then declined after the onset of parturition. Oestrone was the predominant unconjugated oestrogen measured. Plasma corticosteroid (mainly cortisol) concentration was about 33 ng/ml and showed no consistent change at the time of parturition. During lactational anoestrum the plasma concentration of progesterone and total unconjugated oestrogens was very low, while that of corticosteroids was 21 ng/ml. When the piglets were weaned at 26-31 days, sows came into oestrus 4-12 days later, and this was preceded, or accompanied by, an increase in plasma oestrogens. In the luteal phase, plasma progesterone concentrations rose to 20-35 ng/ml. A sow whose piglets were removed at birth, showed signs of oestrus (vulval enlargement and a lordosis response), but a lack of receptivity to the boar associated with no detectable changes in the plasma oestrogen concentration; however, ovulation probably occurred since plasma progesterone values increased in a manner comparable to that found after the formation of normal corpora lutea in other sows. After a second non-receptive cycle, the sow was mated and became pregnant at the third post-weaning oestrus. At parturition the concentration of progesterone and total unconjugated oestrogens was greater in placental venous plasma than in maternal jugular plasma, which indicates placental synthesis of these hormones. A greater concentration of plasma corticosteroids in foetal blood than in placental venous or maternal jugular plasma suggests foetal synthesis in late pregnancy.

No abstract

The rumen, reticulum and omasum, the first three compartments of the compound stomach of ruminants, do not develop fully and assume their characteristic digestive functions until the young animal begins to ingest substantial quantities of solid food. When the young calf swallows milk nearly all of it bypasses the reticulo-rumen and flows rapidly through the omasum and into the abomasum as a result of reflex closure of the oesophageal groove.From the point of view of digestive functions the suckled calf is regarded as a monogastric animal but there does not appear to have been a systematic investigation ofthe events occurring in the abomasum following a milk feed. A few studies have been made on the secretory responses of abomasal pouches in suckled calves but there is no general agreement concerning the chief factors influencing secretion Shoptaw, Espe & Cannon, 1937; Grosskopf, 1959). A possible explanation for this is that the age of the calves used by the different workers ranged from a few weeks to several months and the type of preparation, the stimuli, and the experimental conditions also differed.The experiments reported in this paper were an attempt to define some ofthe major stimuli influencing abomasal secretion in calves and to provide an account of the sequence of events occurring in the abomasum following the ingestion of milk. METHODSAnimal preparatioms and maintenance. Ayrshire bull calves 3-7 days old were obtained from the Rowett Institute dairy herd and from other farms where there was a high standard of calf husbandry. Strong and vigorous calves were selected and they all underwent a period of acclimatization to experimental conditions before any operations were carried out. They were housed in individual pens in a heated (approximately 150 C) experimental room and the bedding material was wood shavings. The feeding times were 9.0 a.m., 12.30 p.m. and 4.30 p.m. when cows' whole milk warmed to 390 C was sucked from a bottle which was fitted with a teat. The volume of milk given at each feed was restricted to 560-1100 ml. and, with one exception, diarrhoea and digestive disturbances were not a problem.Pentobarbitone injected intravenously was used to anaesthetize the calves and glucosesaline was infused continuously throughout the operations. Three calves were fitted with

The role of the saliva in neutralizing the large quantities of fatty acid which are produced by the fermentations in the rumen of the sheep is well known. However, there is evidence that the absorptive properties of the reticulo-rumen epithelium also play a part in maintaining a relatively stable acidity of the rumen contents. Danielli, Hitchcock, Marshall & Phillipson (1945) observed that when fatty acid was absorbed from solutions introduced into the isolated reticulo-rumen, continual additions of acid were necessary in order to keep the pH below 6. It was suggested by Danielli et al. that at a low pH, un-ionized fatty acid was leaving the rumen more rapidly than the corresponding anion.Another mechanism involved in the neutralization of fatty acid was discovered by Masson & Phillipson (1951). These workers observed that when alkaline solutions of fatty acid were introduced into the isolated reticulo-rumen the pH drifted towards 7-3-7-8 and sometimes passed through a minimal value. Further, the appearance of total C02, mainly as bicarbonate, was closely related to the disappearance of fatty acid.The way in which the apparent interaction between fatty acid uptake and bicarbonate appearance occurs is difficult to investigate, since there are changes in seven known species of particles which may affect the pH. These are hydrogen and hydroxyl ions, carbon dioxide, bicarbonate and carbonate, ionized and un-ionized fatty acid; in addition there are unknown contributions of metabolites by the epithelium.The aim of the present work was to determine the forms in which fatty acid and bicarbonate enter and leave the solutions in the rumen. Observations were made by means of a comparatively simple system in which fatty acid was omitted from the solutions in the rumen so that information might be obtained concerning the movements of C02 and bicarbonate and thus the changes as a result of including fatty acid could be assessed. Subsequently the observations were extended to the plasma side of the epithelium. Throughout this paper the term C02 is used to describe dissolved C02 + undissociated carbonic acid; total C02 refers to C02 + bicarbonate.

HARRIS and Phillipson (1962) have recently shown the great potential value of gastro-intestinal re-entrant cannulae for studying digestive processes in the sheep. These workers described experiments which were designed to test the validity of the technique and concluded that the operation for the insertion of duodenal re-entrant cannulae did not cause any permanent disturbance to digestion. The successful experimental life of sheep fitted with re-entrant cannulae depends largely on the design of the cannulae and this paper describes the manufacture of those used by Harris and Phillipson. However, the cannulae have a wider usage since they have been used successfully for preparing pyloro-duodenal (Ash, 1961a and b), ileal (Goodall and Kay, 1962), and jejunal (Ash and Scott, unpublished) cannulated re-entrant fistulae in sheep.