Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion in calves. 5. The effect of giving milk once and twice daily, and of weaning.

1. The effects of giving milk once or twice daily (Expt 1) and of weaning (Expt 2) on the flow rate of digesta through the duodenum and on pancreatic secretion were studied in four and two Ayrshire calves respectively. The calves were prepared with duodenal re-entrant and pancreatic sac cannulas. 2. In Expt 1, when whole milk was offered ad lib. once daily, the calves ingested 141 g/kg live weight (46 g dry matter (DM)/kg live weight 0.75) at a single meal. The subsequent pattern of flow and total recovery of polyethylene glycol from the duodenum suggested that none of the ingested milk passed into the rumeno-reticulum. As the total daily quantity of milk ingested when the calves were fed once and twice daily was similar, it was concluded that abomasal distension is unlikely to be the sole factor limiting milk intake in the preruminant calf. 3. With twice-daily feeding, there were no differences in the pattern or total flow of fluid, electrolytes, nitrogen or fat through the duodenum of the calves following the 09.00 and 21.00 hours meals. The pattern of flow of duodenal and pancreatic fluids and the concentration of electrolytes, N and fat were markedly different when the calves were fed once or twice daily. The patterns of flow of fluid and the concentration of electrolytes in the duodenal digesta reflected the frequency of feeding and the size of the meal and the consequent balance between feed and endogenous components of the digesta. The quantity of the apparent endogenous secretion and pancreatic secretion was markedly less when the calves were fed once daily. 4. In Expt 2, the two Ayshire calves were given whole milk twice daily (diet MM), whole milk once daily with concentrates (diet MC), concentrates alone (diet CC) or dried grass alone (diet DG). The calves consumed 46, 49, 45 and 51 g DM/kg live weight 0.75 when given diets MM, MC, CC and DG respectively. 5. The twice-daily fluctuations in the flow and concentration of fluid, electrolytes, N and fat in the duodenal digesta and the pancreatic fluid observed when diet MM was given were replaced by relatively constant flow rates and composition when diet CC or DG was given. 6. Over the 24 h experimental period 97, 70, 50 and 58% of the DM and 112, 98, 99 and 84% of the N in the feed passed through the duodenum of calves when given diets MM, MC, CC and DG respectively. 7. When dry food was given, the rate of pancreatic fluid secretion was markedly lower (11.3 and 13.5 ml/kg live weight for diets CC and DG respectively) than when diet MM (19.7 ml/kg live weight) was given.

Milk-substitute diet composition and abomasal secretion in the calf.

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 after giving the diet containing MHM than when any of the other three diets was given. 3. Acid secretion from the pouches for the different diets was in the order: FPC greater than MHM greater than SHM greater than or equal to SF. 5. Protease secretion from the pouches, assayed at pH 2-1, was in the order: MHM greater than SHM = FPC greater than 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.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 3. Further studies on the addition of fat to skim milk and the use of non-milk proteins in milk-substitute diets.

1. The flow of digesta through the duodenum and the concurrent secretion of the pancreas were studied in four Friesian calves given four milk-substitute diets. The diets were: reconstituted, "mildly" pre-heated, spray-dried skim-milk powder with (SKF) or without (SK) margarine fat or with 5o percent of the skim-milk powder in diet SKF replaced by soya-bean flour (ASKF) or fish-protein concentrate (BSKF), together with dried whey. The diets were given ad lib. twice daily from 13 to 37 d of age, each diet being given for 6 consecutive days. Collections of duodenal digesta and pancreatic secretions, from cannulas, were made for 12 h after feeding the 6th and 12th meals ("experimental" meals) for each diet. 2. The diets fed as "experimental" meals contained polyethylene glycol (PEG) as a fluid (whey) marker and goat's milk containing (3H)lysine as a marker for total protein; beta-carotene was added as a lipid marker to the three diets containing margarine fat. 3. Over the 12 h postprandial period, the patterns of duodenal digesta flow and secretion of pancreatic fluid did not differ markedly between the four diets. The abomasal outflow of both nitrogen and lipid in a 12 h postprandial period was related to their intakes from the "penultimate" (5th and 11th) meals for diets SKF and SK BUT TO THEIR INTAKES AT THE "EXPERIMENTAL MEALS" FOR DIETS ASKF and BSKF. Secretion of pancreatic enzyme activity was highest during the 1st hour after feeding but the main outflow from the abomasum of total N and lipid occurred 5-10 h after feeding. 4. The time required for all the whey marker (PEG) to pass through the duodenum was similar for diets SKF and SK, but only 53 and 42 percent respectively of the ingested protein marker passed through the duodenum in the 12 h after feeding. More acid appeared to be secreted by the abomasum when diet SK was given; also less undigested protein passed out of the abomasum after giving this diet. It is concluded that the physical absence of fat globules in the abomasal clot increases the degree of proteolysis. 5. The secretions of pancreatic fluid and pancreatic enzyme activity were all markedly lower for diet SK than for diet SKF. 6. With diets containing non-milk proteins (ASKF and BSKF), abomasal proteolysis was less efficient and the ingested protein passed out of the abomasum more rapidly than for diet SKF. There was no difference in the rate of abomasal outflow of the whey fluids between diets SKF, ASKF and BSKF. 7. In comparison with diet SKF, diets ASKF and BSKF tended to induce less pancreatic enzyme secretion over a 12 h postprandial period, with the exception of lipase. 8. There appeared to be no direct relationship between the quantities of any of the pancreatic enzymes secreted during a postprandial period and either the concurrent flow of duodenal digesta or the total quantities of dietary constituents passing through the duodenum.