I. Food consumption, live weight, anatomical measurements on the gut organs and the absorptive capacity of the small intestine for L-leucine and D(+)-glucose were made on virgin (control), pregnant and lactating albino rats. 2.Food intake increased by approximately 60 yo during pregnancy and a further 250 yo during lactation.3. Pregnancy did not markedly influence the gross anatomy of the gastrointestinal tract. There was evidence for increased villus height and percentage water in the small intestine and for increased length of the colon during pregnancy.4. During lactation, the alimentary canal progressively increased in weight and size. It partially regressed following weaning.5. All anatomical measurements, except the length of the small intestine, completely regressed to control values within 20 d of weaning. The increased intestinal length had not completely regressed by day 30 post-weaning.6. No significant change was observed in absolute absorption of glucose or leucine during pregnancy.7. Absolute absorption of leucine and of glucose was increased during lactation. Greatest absorption occurred on the 10th day of lactation.8. Results for absorption of leucine and glucose per unit length indicated that the ability of the mucosal cells to absorb or the number of absorptive cellsimm had changed during lactation and the post-lactation periods.

1. The rates of passage of markers of fluid and particulate digesta through the sheep alimentary tract have been described mathematically in single-injection experiments by analysing the concentration curves of marker excretion in faecal dry matter and then predicting these concentrations by means of an equation containing two exponential terms. Three components related to this equation are a transit time for digesta in the intestines, a half-time of marker in the reticulo-rumen and a half-time tentatively associated with the passage of marker through the caecum and proximal colon. With this approach no surgical interference with an animal is required to obtain meaningful information about gut function.2. Abomasal cannulation did not affect the rate of passage of 51Cr EDTA through the gut.3. The mean half-times (T1/2) for 51Cr EDTA in the reticulo-rumen and hind-gut, respectively, were 646 and 236 min for a roughage diet and 890 and 607 min for a diet consisting mainly of wheat grain, both diets providing approximately the same amounts of digestible dry matter. These results indicated that the changes in half-times were proportionately much greater in the caecum and proximal colon than in the reticulo-rumen. The mean transit time of marker through the digestive tract also increased from 721 to 1345 min when the concentrate diet was given.4. The complex of chromium-51 with EDTA was excreted faster in faeces than cerium-144–praseodymium-144 when both were given together as a single injection into the reticulorumen. This was caused mainly by differential rates of elimination of water and particulate matter from the reticulo-rumen.

SummaryA series of acute experiments has been carried out on sheep to study some of the factors which influence the rate of absorption of lactic acid from the ligated washed·out forestomachs.The rate of absorption of lactic acid was faster from an 0 ·12M than from an O· 06M solution and faster from a solution at pH 4 than from a solution at pH 5. The absorption rate was less from a solution with a tonicity of 440 m·osmoles than from a solution with a tonicity of 300 m-osmoles. The absorption rate of lactic acid was also decreased with the concomitant absorption of a mixture of acetic, propionic, and butyric acids from acid solutions but not from alkaline solutions.The rate of absorption of lactic acid was slow relative to the volatile fatty acids from solutions which were either acid or alkaline.Anaesthetization of the sheep with sodium pentobarbitone did not decrease the rate of lactic acid or volatile fatty acid absorption from the non-ligated, washedout reticulo-rumen.The results are in conformity with the hypothesis that the diffusion barrier of the reticulo-rumen wall to nutrients in the digesta is a lipid membrane containing water-filled pores.

1. The effect of different protein sources in milk-substitute diets on abomasal acidity and proteolytic activity was studied in Friesian calves, aged 20–58 d (Expt 1). The diets contained ‘mildly’ preheated, spray-dried skim-milk powder (MHM), ‘severely’ preheated, spray-dried skim-milk powder (SHM), fish-protein concentrate (FPC) or solvent-extracted soya-bean flour (SF) as the main protein source.2. Gastric juice was collected from abomasal pouches before feeding and at 15 min intervals for 8 h after the morning feed. Samples of digesta were obtained from the abomasum at 1 h intervals during the same period.3. Digesta pH was lower and titratable acidity higher 0-3 h after giving the diet containing MHM than when any of the other three diets was given.4. Acid secretion from the pouches for the different diets was in the order: FPC > MHM > SHM ≥ SF.5. Protease secretion from the pouches, assayed at pH 2.1, was in the order: MHM > SHM = FPC > SF.6. The effect of dry matter (dm) intake and concentration on abomasal acidity was also studied in calves given diets which contained MHM (Expt 2). This diet was reconstituted at either 100 or 149 g dm/kg liquid diet and fed at either 32.5 or 49.0 g DM/kg live weight 0.75 per d. Samples of abomasal digesta were collected as in Expt 1.7. A high intake of dm at a low dm concentration resulted in low acidity of the digesta in the first 3 h after feeding, which suggested a dilution effect. Comparison of two diets of different dm concentration, which were fed in the same volume of liquid, indicated that the greater the dm intake, the greater was the amount of acid secreted.8. It is concluded that the protein sources varied in their ability to stimulate abomasal acid and protease secretion and it is suggested that this may relate to calf performance.

1.Five sheep were given 400,625, 850, 1075 and 1300 g lucerne chaffid according to a 5 x 5 Latin square design to perturbate a mathematical model describing the rate of passage of digesta in terms of rate constants for the reticulo-rumen (k,) and caecum and proximal colon (ka), and a transit time (n) for the intestines. These values were obtained from the concentration curves of W r EDTA and 1r4Ce-14rPr (lO4Pr) excretion in faeces for comparison with similar measurements obtained directly.2. The retention times of markers in the reticulo-rumen, caecum and proximal colon and intestines all decreased by approximately 50 % as intakes were increased from 400 to 1300 g/d. For both markers, the direct and indirect measures of half-time in the reticula-rumen were essentially identical. The predicted (indirect) values for half times in the caecum and proximal colon were smaller than the direct values (P < 0405) but the correlations between them were significant (P < 0.01) for "Cr EDTA (r 066) and l4Vr (r 0.78). The direct measures of transit time were smaller (P < 0.025) by 5-10 a/. than the predicted values but correlations between them were significant (P < 0.01) for W r EDTA (r 0.91) and for lrrPr (r 0.93). Thus the model predicted the changes produced in the rate of passage of digesta and its usefulness and limitations are discussed. 3. With lr4Pr ,k, for the reticulo-rumen and TAka for the caecum and proximal colon were both positively correlated (P < 0-025) with the organic matter digestibilities. Ttk, decreased at half the rate of Ttkl with increasing intakes. This wcluld have favoured compensatory digestion in the large intestine.This experiment in pertubatian analysis was designed to evaluate further a mathematical model of digesta passage thiough the alimentary tract of the sheep. Grovum & Williams (1973~) showed that the rate of passage of digesta in sheep given either 800 g lucerne chaff or diets consisting of wheat and lucerne chaff could be described with an equation having as independent variables: the transit time of marker through the intestinal tract (TT), the half-time of marker in the reticulo-rumen (Tjk,) and the half-time of marker pertaining mainly to the caecum and proximal colon (Tik,).In the experiment now reported, the rate of passage of digesta through the gut was increased by increasing the level of food intake and values of TT, Tik,, and Tik, were compared with corresponding measurements made more directly. The biological relevance of these values for rate of passage was studied by relating them to the apparent digestibility of the food, the concentrations of volatile fatty acids (VFA) in the reticulo-rumen and the water content of the faeces. E X P E R I M E N T A L SheepThree Merino wethers (castrated males) (sheep nos. 1, 2 and 3) and two ewes (sheep nos. 4 and 5 ) with permanent rumen (Hecker, 1969) and abomasal (Jarrett, 1948) fistulas were 15 N U T 38