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Protein fermentation (PF) is the degradation of protein by microbiota in the gastro-intestinal tract. It results from high intake of indigestible protein and/or increased endogenous losses, and it may be the cause of gut health issues. This is important as the use of less digestible protein sources for poultry is expected to increase as a consequence of the food-feed discussion. Here we review the relations between dietary protein, caecal PF and gut health and identify critical knowledge gaps. Finally, we suggest methods for the investigation of caecal PF. The majority of the microorganisms have never been cultured, however, through cultivation-independent molecular approaches, many new taxa have been identified. Researchers have identified taxa that are enriched in healthy/ unhealthy birds. The mechanisms underlying these associations remain unclear. PF results in the production of potentially detrimental metabolites. This generally results in a higher pH, further encouraging PF. Studies on the effects of PF (metabolites) on gut health in poultry are limiting. For the in vivo evaluation of PF an increase in protein flow into the caeca is required, which can result from an increased level of dietary indigestible protein. Heat damage reduces protein digestibility and can therefore be used to create a within ingredient contrast for in vivo studies. A remaining challenge is that the relation between indigestible protein level and subsequent PF is not straightforward, as fractional separation of digesta occurs in poultry, allowing part of the digesta to bypass the caeca. To further study the extent to which microorganisms will ferment the protein fraction flowing into the caeca, in vitro studies can be applied. However, their application depends on the ability to separate the fraction of pre-digested feed that is likely to enter the caeca. Altogether, an increase in PF will affect microbiota composition, metabolite production, and potentially gut health.

High interindividual variation in growth performance is commonly observed in veal calf production and appears to depend on milk replacer (MR) composition. Our first objective was to examine whether variation in growth performance in healthy veal calves can be predicted from early life characterization of these calves. Our second objective was to determine whether these predictions differ between calves that are fed a high- or low-lactose MR in later life. A total of 180 male Holstein-Friesian calves arrived at the facilities at 17 ± 3.4 d of age, and blood samples were collected before the first feeding. Subsequently, calves were characterized in the following 9 wk (period 1) using targeted challenges related to traits within each of 5 categories: feeding motivation, digestion, postabsorptive metabolism, behavior and stress, and immunology. In period 2 (wk 10-26), 130 calves were equally divided over 2 MR treatments: a control MR that contained lactose as the only carbohydrate source and a low-lactose MR in which 51% of the lactose was isocalorically replaced by glucose, fructose, and glycerol (2:1:2 ratio). Relations between early life characteristics and growth performance in later life were assessed in 117 clinically healthy calves. Average daily gain (ADG) in period 2 tended to be greater for control calves (1,292 ± 111 g/d) than for calves receiving the low-lactose MR (1,267 ± 103 g/d). Observations in period 1 were clustered per category using principal component analysis, and the resulting principal components were used to predict performance in period 2 using multiple regression procedures. Variation in observations in period 1 predicted 17% of variation in ADG in period 2. However, this was mainly related to variation in solid feed refusals. When ADG was adjusted to equal solid feed intake, only 7% of the variation in standardized ADG in period 2, in fact reflecting feed efficiency, could be explained by early life measurements. This indicates that >90% of the variation in feed efficiency in later life could not be explained by early life characterization of the calves. It is speculated that variation in health status explains a substantial portion of variation in feed efficiency in later life. Significant relations between fasting plasma glucose concentrations, fecal pH, drinking speed, and plasma natural antibodies in early life (i.e., not exposed to the lactose replacer) and feed efficiency in later life depended on MR composition. These measurements are therefore potential tools for screening calves in early life on their ability to cope with MR varying in lactose content.

Heavy veal calves (4–6 mo old) often develop problems with insulin sensitivity. This could lead to metabolic disorders and impaired animal growth performance. Studies in various animal species have shown that the supplementation of short-chain fructo-oligosaccharides (scFOS) can improve insulin sensitivity. We therefore studied the effects of scFOS supplementation on insulin sensitivity in heavy veal calves. Forty male Holstein-Friesian calves (BW = 190 ± 2.9 kg; age = 162 ± 1.4 d at the start of the trial) were fed either a control milk replacer (MR) diet or a diet in which one-third of the lactose was replaced by glucose, fructose, or glycerol for 10 wk prior to the start of the trial. At the start of the trial, calves were subjected to a frequently sampled intravenous glucose tolerance test to assess whole-body insulin sensitivity (muscle and hepatic insulin sensitivity). Calves within each dietary treatment group were ranked based on their insulin sensitivity value. Half of the calves received scFOS (12 mg/kg of BW) with the MR for 6 wk (supplementation was equally distributed over the insulin sensitivity range). Subsequently, a second frequently sampled intravenous glucose tolerance test was conducted to assess the effect of scFOS. In addition, fasting plasma levels of glucose, insulin, triglycerides, and cholesterol were determined to calculate the quantitative insulin sensitivity check index and triglyceride:high-density lipoprotein cholesterol ratio (fasting indicators of insulin sensitivity). Whole-body insulin sensitivity was low at the start of the trial and remained low in all groups [1.0 ± 0.1 and 0.8 ± 0.1 (mU/L)−1 · min−1 on average, respectively]. Supplementation of scFOS did not improve insulin sensitivity in any of the treatment groups. The quantitative insulin sensitivity check index and the triglyceride:high-density lipoprotein cholesterol ratio also did not differ between scFOS and non-scFOS calves and averaged 0.326 ± 0.003 and 0.088 ± 0.004, respectively, at the end of the trial. We conclude that scFOS supplementation does not improve insulin sensitivity in heavy veal calves regardless of the carbohydrate composition of the MR. This is in contrast to other animals (e.g., dogs and horses), where scFOS supplementation did improve insulin sensitivity. The absence of an effect of scFOS might be related to the dosage or to metabolic differences between ruminants and nonruminants. Increasing evidence indicates that dietary interventions in veal calves have little or no effect on insulin sensitivity, possibly because of low levels of insulin sensitivity.

Veal calves at the age of 4 to 6 mo often experience problems with glucose homeostasis, as indicated by postprandial hyperglycemia, hyperinsulinemia, and insulin resistance. It is not clear to what extent the ontogenetic development of calves or the feeding strategy [e.g., prolonged milk replacer (MR) feeding] contribute to this pathology. The objective of this study was therefore to analyze effects of MR feeding, weaning, and supplementation of short-chain fructo-oligosaccharides (FOS) on the development of glucose homeostasis and insulin sensitivity in calves during the first 3 mo of life. Thirty male Holstein-Friesian calves (18 +/- 0.7 d of age) were assigned to 1 of 3 dietary treatments: the control (CON) group received MR only, the FOS group received MR with the addition of short-chain FOS, and the solid feed (SF) group was progressively weaned to SF. The CON and FOS calves received an amount of MR, which gradually increased (from 400 to 1,400 g/d) during the 71-d trial period. For the SF calves, the amount of MR increased from 400 to 850 g/d at d 30, and then gradually decreased, until completely weaned to only SF at d 63. The change in whole body insulin sensitivity was assessed by intravenous glucose tolerance tests. Milk tolerance tests were performed twice to assess changes in postprandial blood glucose, insulin, and nonesterified fatty acid responses. Whole-body insulin sensitivity was high at the start (16.7 +/- 1.6 x 10-4 [mu U/mL](-1)), but decreased with age to 4.2 +/- 0.6 x 10-4 [mu U/mL](-1) at the end of the trial. The decrease in insulin sensitivity was most pronounced (-70%) between d 8 and 29 of the trial. Dietary treatments did not affect the decrease in insulin sensitivity. For CON and FOS calves, the postprandial insulin response was 3-fold higher at the end of the trial than at the start, whereas the glucose response remained similar. The SF calves, however, showed pronounced hyperglycemia and hyperinsulinemia at the end of the trial, although weaning did not affect insulin sensitivity. We conclude that whole body insulin sensitivity decreases by 75% in calves during the first 3 mo of life. Weaning or supplementation of short-chain FOS does not affect this age-related decline in insulin sensitivity. Glucose homeostasis is not affected by supplementation of short-chain FOS in young calves, whereas postprandial responses of glucose and insulin to a MR meal strongly increase after weaning.

Replacing dairy components from milk replacer (MR) with vegetable products has been previously associated with decreased protein and fat digestibility in milk-fed calves resulting in lower live weight gain. In this experiment, the major carbohydrate source in MR, lactose, was partly replaced with gelatinized corn starch (GCS) to determine the effect on protein and fat digestibility in milk-fed calves. In total, 16 male Holstein-Friesian calves received either MR with lactose as the carbohydrate source (control) or 18% GCS at the expense of lactose. In the adaptation period, calves were exposed to an increasing dose of GCS for 14 weeks. The indigestible marker cobalt ethylenediaminetetraacetic acid was incorporated into the MR for calculating apparent nutrient digestibility, whereas a pulse dose of chromium (Cr) chloride was fed with the last MR meal 4 h before slaughter as an indicator of passage rates. The calves were anesthetized and exsanguinated at 30 weeks of age. The small intestine was divided in three; small intestine 1 and 2 (SI1 and SI2, respectively) and the terminal ileum (last ~100 cm of small intestine) and samples of digesta were collected. Small intestinal digesta was analysed for α-amylase, lipase and trypsin activity. Digestibility of protein was determined for SI1, SI2, ileum and total tract, whereas digestibility of fat was determined for SI1, SI2 and total tract. Apparent protein digestibility in the small intestine did not differ between treatments but was higher in control calves at total tract level. Apparent crude fat digestibility tended to be increased in SI1 and SI2 for GCS calves, but no difference was found at total tract level. Activity of α-amylase in SI2 and lipase in both SI1 and SI2 was higher in GCS calves. Activity of trypsin tended to be higher in control calves and was higher in SI1 compared with SI2. A lower recovery of Cr in SI2 and a higher recovery of Cr in the large intestine suggest an increased rate of passage for GCS calves. Including 18% of GCS in a milk replacer at the expense of lactose increased passage rate and decreased apparent total tract protein digestibility. In the small intestine, protein digestion did not decrease when feeding GCS and fat digestion even tended to increase. Overall, effects on digestion might be levelled when partially replacing lactose with GCS, because starch digestion is lower than that of lactose but fat digestion may be slightly increased when feeding GCS.

In pigs, high protein diets have been related to post-weaning diarrhoea, which may be due to the production of protein fermentation metabolites that were shown to have harmful effects on the intestinal epithelium in vitro. In this review, we discussed in vivo effects of protein fermentation on the microbial composition and their protein catabolic activity as well as gut and overall health. The reviewed studies applied different dietary protein levels, which was assumed to result in contrasting fermentable protein levels. A general shift to N-utilisation microbial community including potential pathogens was observed, although microbial richness and diversity were not altered in the majority of the studies. Increasing dietary protein levels resulted in higher protein catabolic activity as evidenced by increased concentration of several protein fermentation metabolites like biogenic amines in the digesta of pigs. Moreover, changes in intestinal morphology, permeability and pro-inflammatory cytokine concentrations were observed and diarrhoea incidence was increased. Nevertheless, higher body weight and average daily gain were observed upon increasing dietary protein level. In conclusion, increasing dietary protein resulted in higher proteolytic fermentation, altered microbial community and intestinal physiology. Supplementing diets with fermentable carbohydrates could be a promising strategy to counteract these effects and should be further investigated.

The amount of dietary protein is associated with intestinal disease in different vertebrate species. In humans, this is exemplified by the association between high-protein intake and fermentation metabolite concentrations in patients with inflammatory bowel disease. In production animals, dietary protein intake is associated with postweaning diarrhea in piglets and with the occurrence of wet litter in poultry. The underlying mechanisms by which dietary protein contributes to intestinal problems remain largely unknown. Fermentation of undigested protein in the hindgut results in formation of fermentation products including short-chain fatty acids, branched-chain fatty acids, ammonia, phenolic and indolic compounds, biogenic amines, hydrogen sulfide, and nitric oxide. Here, we review the mechanisms by which these metabolites may cause intestinal disease. Studies addressing how different metabolites induce epithelial damage rely mainly on cell culture studies and occasionally on mice or rat models. Often, contrasting results were reported. The direct relevance of such studies for human, pig, and poultry gut health is therefore questionable and does not suffice for the development of interventions to improve gut health. We discuss a roadmap to improve our understanding of gut metabolites and microbial species associated with intestinal health in humans and production animals and to determine whether these metabolite/bacterial networks cause epithelial damage. The outcomes of these studies will dictate proof-of-principle studies to eliminate specific metabolites and or bacterial strains and will provide the basis for interventions aiming to improve gut health.

Effects of solid feed (SF) level and roughage-to-concentrate (R:C) ratio on ruminal drinking and passage kinetics of milk replacer, concentrate, and roughage were studied in veal calves. In total, 80 male Holstein-Friesian calves (45 ± 0.2 kg of body weight) were divided over 16 pens (5 calves per pen). Pens were randomly assigned to either a low (LSF) or a high (HSF) SF level and to 1 of 2 R:C ratios: 20:80 or 50:50 on a dry matter (DM) basis. Roughage was composed of 50% corn silage and 50% chopped wheat straw on a DM basis. At 27 wk of age, measurements were conducted in 32 calves. During the measurement period, SF intake was 1.2 kg of DM/d for LSF and 3.0 kg of DM/d for HSF, and milk replacer intake averaged 2.3 kg of DM/d for LSF and 1.3 kg of DM/d for HSF. To estimate passage kinetics of milk replacer, concentrate, and straw, indigestible markers (CoEDTA, hexatriacontane C36, Cr-neutral detergent fiber) were supplied with the feed as a single dose 4, 24, and 48 h before assessment of their quantitative recovery in the rumen, abomasum, small intestine, and large intestine. Rumen Co recovery averaged 20% of the last milk replacer meal. Recoveries of Co remained largely unaffected by SF level and R:C ratio. The R:C ratio did not affect rumen recovery of C36 or Cr. Rumen fractional passage rate of concentrate was estimated from recovery of C36 in the rumen and increased from 3.3%/h for LSF to 4.9%/h for HSF. Rumen fractional passage rate of straw was estimated from Cr recovery in the rumen and increased from 1.3%/h for LSF to 1.7%/h for HSF. An increase in SF level was accompanied by an increase in fresh and dry rumen contents. In HSF calves, pH decreased and VFA concentrations increased with increasing concentrate proportion, indicating increased fermentation. The ratio between Cr and C36 was similar in the small and large intestine, indicating that passage of concentrate and straw is mainly determined by rumen and abomasum emptying. In conclusion, increasing SF level introduces large variation in passage kinetics of dietary components, predominantly in the rumen compartment. The SF level, rather than the R:C ratio, influences rumen recovery of concentrate and roughage. Our data provide insight in passage kinetics of milk (Co representing the milk replacer) and SF (Cr and C36 representing roughage and concentrate, respectively) and may contribute to the development of feed evaluation models for calves fed milk and SF.

Background: The proportion of starch disappearing from the small intestinal lumen is generally lower in ruminants than in monogastric animals, and there are indications that the starch digestion capacity in ruminants is limited.Objectives: Milk-fed calves were used to study the rate-limiting enzyme in starch hydrolysis and to quantify starch fermentation in ruminants.Methods: Forty male Holstein-Friesian calves were fed milk replacer containing either lactose (control) or 1 of 4 corn starch products. The following starch products differed in the enzyme ratios required for their complete hydrolysis to glucose: gelatinized starch [alpha-amylase and (iso)maltase], maltodextrin [(iso)maltase and alpha-amylase], maltodextrin with alpha-1,6-branching (isomaltase, maltase, and alpha-amylase), and maltose (maltase). In the adaptation period, calves were stepwise exposed to an increasing dose of the starch product for 14 wk to allow maximal adaptation of all enzyme systems involved. In the experimental period, apparent total tract and ileal starch product disappearance, total tract starch product fermentation, and alpha-amylase, maltase, and isomaltase activities were determined at 18% inclusion of the starch product.Results: Maltase and isomaltase activities in the brush border did not increase for any of the starch product treatments. Luminal alpha-amylase activity was lower in the proximal (3 9 +/- 3.2 and 2.7 +/- 1.7 U/mg Co for control and starch product calves, respectively) but greater in the distal small intestine of starch-fed calves than in control calves (0.0 +/- 0.0 and 6.4 +/- 1.5 U/mg Co for control and starch product calves, respectively; means +/- SEs for control and means +/- pooled SEMs for starch product treatments). Apparent deal (61.6% +/- 6.3%) and total tract (99.1% +/- 0.4%) starch product disappearance did not differ between starch product treatments, suggesting that maltase activity limits starch digestion in ruminants. Total tract starch product fermentation averaged 414 +/- 43 g/d, corresponding to 89% of intake, of which Half was fermented before the terminal ileum, regardless of starch product treatment.Conclusion: Fermentation, rather than enzymatic digestion, is the main reason for small intestinal starch disappearance in milk-fed calves.

Calf milk replacer (MR) contains 40 to 50% lactose. Lactose strongly fluctuates in price and alternatives are desired. Also, problems with glucose homeostasis and insulin sensitivity (i.e., high incidence of hyperglycemia and hyperinsulinemia) have been described for heavy veal calves (body weight >100 kg). Replacement of lactose by other dietary substrates can be economically attractive, and may also positively (or negatively) affect the risk of developing problems with glucose metabolism. An experiment was designed to study the effects of replacing one third of the dietary lactose by glucose, fructose, or glycerol on glucose homeostasis and insulin sensitivity in veal calves. Forty male Holstein-Friesian (body weight = 114 +/- 2.4 kg; age = 97 +/- 1.4 d) calves were fed an MR containing 462 g of lactose/kg (CON), or an MR in which 150 g of lactose/kg of MR was replaced by glucose (GLU), fructose (FRU), or glycerol (GLY). During the first 10 d of the trial, all calves received CON. The CON group remained on this diet and the other groups received their experimental diets for a period of 8 wk. Measurements were conducted during the first (baseline) and last week of the trial. A frequently sampled intravenous glucose tolerance test was performed to assess insulin sensitivity and 24 h of urine was collected to measure glucose excretion. During the last week of the trial, a bolus of 1.5 g of [U-C-13] substrates was added to their respective meals and plasma glucose, insulin, and C-13-glucose' responses were measured. Insulin sensitivity was low at the start of the trial and remained low [1.2 +/- 0.1 and 1.0 +/- 0.1 (mU/L)(-1) x min(-1)], and no treatment effect was noted. Glucose excretion was low at the start of the trial (3.4 +/- 1.0 g/d), but increased in CON and GLU calves (26.9 +/- 3.9 and 43.0 +/- 10.6 g/d) but not in FRU and GLY calves. Postprandial glucose was higher in GLU, lower in FRU, and similarin GLY compared with CON calves. Postprandial insulin was lower in FRU and GLY and similar in GLU compared with CON calves. Postprandial C-13-glucose increased substantially in FRU and GLY calves, indicating that calves are able to partially convert these substrates to glucose. We concluded that replacing one third of lactose in MR by glucose, fructose, or glycerol in MR differentially influences postprandial glucose homeostasis but does not affect insulin sensitivity in veal calves.

Calf milk replacers contain 40 to 50% lactose. Fluctuating dairy prices are a major economic incentive to replace lactose from milk replacers by alternative energy sources. Our objective was, therefore, to determine the effects of replacement of lactose with glucose, fructose, or glycerol on energy and protein metabolism in veal calves. Forty male Holstein-Friesian calves (114 +/- 2.4 kg) were fed milk replacer containing 46% lactose (CON) or 31% lactose and 15% of glucose (GLUC), fructose (FRUC), or glycerol (GLYC). Solid feed was provided at 10 g of dry matter (DM)/kg of metabolic body weight (BW0.75) per day. After an adaptation of 48 d, individual calves were harnessed, placed in metabolic cages, and housed in pairs in respiration chambers. Apparent total-tract disappearance of DM, energy, and N and complete energy and N balances were measured. The GLUC, FRUC, and GLYC calves received a single dose of 1.5 g of [U-C-13]glucose, [U-C-13]fructose, or [U-C-13]glycerol, respectively, with their milk replacer at 0630 h and exhaled (CO2)-C-13 and C-13 excretion with feces was measured. Apparent total-tract disappearance was decreased by 2.2% for DM, 3.2% for energy, and 4.2% for N in FRUC compared with CON calves. Energy and N retention did not differ between treatments, and averaged 299 16 kJ/kg of BW0.75 per day and 0.79 +/- 0.04 g/kg of BW0.75 per day, respectively, although FRUC calves retained numerically less N (13%) than other calves. Recovery of C-13 isotopes as (CO2)-C-13 did not differ between treatments and averaged 72 +/- 1.6%. The time at which the maximum rate of (CO2)-C-13 production was reached was more than 3 h delayed for FRUC calves, which may be explained by a conversion of fructose into other substrates before being oxidized. Recovery of C-13 in feces was greater for FRUC calves (7.7 +/- 0.59%) than for GLUC (1.0 +/- 0.27%) and GLYC calves (0.5 +/- 0.04%), indicating incomplete absorption of fructose from the small intestine resulting in fructose excretion or fermentation. In conclusion, energy and N retention was not affected when replacing >30% of the lactose with glucose, fructose, or glycerol. Increased fecal losses of DM, energy, and N were found in FRUC calves compared with CON, GLUC, and GLYC calves. Postabsorptive losses occurred with the urine for glucose and glycerol, which caused a lower respiratory quotient for GLUC calves during the night. Fructose was oxidized more slowly than glucose and glycerol, probably as a result of conversion into other substrates before oxidation.

Calf milk replacers (MR) commonly contain 40% to 50% lactose. For economic reasons, starch is of interest as a lactose replacer. Compared with lactose, starch digestion is generally low in calves. It is, however, unknown which enzyme limits the rate of starch digestion. The objectives were to determine which enzyme limits starch digestion and to assess the maximum capacity for starch digestion in milk-fed calves. A within-animal titration study was performed, where lactose was exchanged stepwise for one of four starch products (SP). The four corn-based SP differed in size and branching, therefore requiring different ratios of starch-degrading enzymes for their complete hydrolysis to glucose: gelatinised starch (alpha-amylase and (iso) maltase); maltodextrin ((iso)maltase and alpha-amylase); maltodextrin with alpha-1,6-branching (isomaltase, maltase and alpha-amylase) and maltose (maltase). When exceeding the animal's capacity to enzymatically hydrolyse starch, fermentation occurs, leading to a reduced faecal dry matter (DM) content and pH. Forty calves (13 weeks of age) were assigned to either a lactose control diet or one of four titration strategies (n = 8 per treatment), each testing the stepwise exchange of lactose for one SP. Dietary inclusion of each SP was increased weekly by 3% at the expense of lactose and faecal samples were collected from the rectum weekly to determine DM content and pH. The increase in SP inclusion was stopped when faecal DM content dropped below 10.6% (i.e. 75% of the average initial faecal DM content) for 3 consecutive weeks. For control calves, faecal DM content and pH did not change over time. For 87% of the SP-fed calves, faecal DM and pH decreased already at low inclusion levels, and linear regression provided a better fit of the data (faecal DM content or pH v. time) than non-linear regression. For all SP treatments, faecal DM content and pH decreased in time (P

In milk-fed calves, quantification of the milk that enters the rumen (ruminal milk volume, RMV) because of malfunction of the esophageal groove reflex may explain part of the variability observed between animals in their growth performance. The RMV can directly be quantified by adding an indigestible marker to the diet and measuring its recovery in the rumen at slaughter, but this technique cannot be repeated in time in the same animal. The objective of the study was to evaluate three indirect methods for estimating RMV. The first method was based on the assumption that ruminal drinking delays and limits acetaminophen appearance in blood after ingestion of milk supplemented with acetaminophen. The second method was based on a negative linear relationship between RMV and urinary recovery of non-metabolizable monosaccharides (3-O-methylglucose, l-rhamnose and d-xylose) added to the milk, owing to rumen fermentation. In the third method, RMV was calculated as the difference between total milk intake and the increase in abomasal milk volume (AMV) at feeding, measured through ultrasonography shortly after feeding, or estimated from the mathematical extrapolation of AMV to feeding time, based on consecutive measurements. These methods were tested in three experiments where calves (n=22, 10 and 13) were bucket fed or partly tube fed (i.e. by inserting milk replacer into the rumen via a tube to mimic ruminal drinking). In addition, Co-EDTA and Cr-EDTA were used as an indigestible marker in one experiment to trace bucket-fed or tube-fed milk replacer, respectively, to measure RMV. The relationship between AMV measured by ultrasonography and AMV measured at slaughter improved when kinetics of AMV were extrapolated to the time of slaughter by mathematical modeling (error between predicted and measured AMV equaled 0.49 l). With this technique, RMV during feeding averaged 17% and 24% of intake in Experiments 2 and 3, respectively. Plasma acetaminophen kinetics and recovery of non-metabolizable monosaccharides in urine were partly associated with ruminal drinking, but these techniques are not considered quantitatively accurate without further information of rumen degradation and absorption. The recovery of indigestible marker measured at slaughter gave a quantitative estimate of RMV (2% in Experiment 3), but improper measurement of emptying rate of fluid from the rumen may lead to underestimation. In conclusion, measuring changes in AMV by ultrasonography, in response to milk feeding, was the most promising indirect method to quantify RMV in veal calves.

α-Amylase and the mucosal enzymes maltase and iso-maltase play an important role in the digestion of starch. Pancreatic α-amylase is responsible for the breakdown of polysaccharides into oligosaccharides such as maltose, maltotriose and dextrin. These oligosaccharides are subsequently converted to monosaccharides by small intestinal mucosal enzymes. Veal calves are fed with milk replacers (MR) which commonly contain 40-50% of lactose, originating from whey. The price of whey, however, is subjected to extremely large fluctuations, and producers of MR are in search of alternatives such as starch-based substrates (SBSs).

Calf milk replacers commonly contain 40-50% lactose. For economic reasons, starch is of interest as a lactose replacer. Compared with lactose, starch digestion is generally low in calves. Ileal disappearance of starch was only 60% in calves, whereas lactose disappeared for 97% (Coombe and Smith, 1974). This indicates that the activity of enzymes required for the hydrolysis of starch to glucose limits starch digestion in milk-fed calves. It is however unknown which enzyme system is limiting the rate of starch hydrolysis in the intestinal lumen of calves. In addition, a maximum may exist for the daily quantity of starch that can be hydrolyzed and absorbed. Potentially, enzyme systems may also adapt to the starch fed. Both may be subject to considerable inter-individual variation.

Calf milk replacers commonly contain 40-50% lactose. For economic reasons, starch is of interest as a lactose replacer. Small intestinal disappearance of starch (66%) was lower than that of glucose (85%) when infused in the abomasum of steers (Kreikemeier and Harmon, 1995), indicating that enzyme activity required for the hydrolysis of starch to glucose limits starch digestion. Which enzyme system is limiting starch digestion in milk-fed calves is unknown. Portal glucose appearance was only 57% of small intestinal starch disappearance (Kreikemeier and Harmon, 1995). This gap includes starch fermentation and glucose use by portal drained visceral tissues. In steers, abomasal infusion of a starch hydrolysate resulted in a linear decrease in ileal pH (Branco et al., 1999), illustrating that fermentation may be an important contributor to small intestinal starch disappearance.

The radiation of current elements in the vicinity of a layered medium is of great importance in understanding systems where electromagnetic interaction with an interface leads to significant desirable or undesirable effects. The discussion involves an expansion on previous theories, such as those presented by A. Sommerfeld (see "Partial Differential Equations in Physics", Academic Press, chap. 6,1964) and R.W.P. King and G.S. Smith (see "Antennas in Matter: Fundamentals", MIT Press, chap.11,1981) for the radiation of current elements near an interface. The formulation of this novel technique closely follows the methodology developed by King and Smith to determine the fields radiated by an infinitesimal horizontally-oriented electric dipole in a half-space. However, certain modifications are made that provide a more general approach. These alterations permit formulation of the fields radiated by an arbitrary distribution of electric and magnetic current sources (either in the media or on the interface) in a half-space. A flaw in King and Smith's boundary condition equations becomes apparent using this novel technique.

Computation of the higher-order small slope approximation (SSA) for electromagnetic scattering from a penetrable randomly rough surface is discussed, under the assumption of a Gaussian random process with an isotropic Gaussian correlation function. A simplified form for the first correction to the lowest order SSA theory is presented, and sample results illustrated to investigate the parameter space under which the first correction is appreciable. Reduction of the higher-order SSA to the physical optics approximation limit is also discussed for both perfectly-conducting and dielectric surfaces.

1. Human prolactin has been expressed in Escherichia coli. A cDNA fragment coding for the signal sequence and the full length prolactin molecule was cloned into the expression vector pUR291 which directs the synthesis of a beta-galactosidase prolactin fusion protein when expressed in E. coli. 2. Cultures of E. coli harbouring the recombinant plasmid pJMBG62 produced a fusion protein of the appropriate molecular weight which was detected by Western blot analysis using a polyclonal antibody raised against pituitary-derived human prolactin. 3. The fusion protein was isolated from inclusion bodies in a partially pure form and it was used as immunogen to raise antibodies against human prolactin. 4. When this partially purified fusion protein was injected into rabbits it generated antisera with good prolactin titres in animals which were rested for one year following a disappointing primary immunization with purified human prolactin.

Surgery in the hemophiliac requires close coordination of a team familiar with hemophilia care. Minimum requirements include a hematologist, a diagnostic laboratory capable of performing factor and inhibitor assays, complete blood banking facilities and an orthopedic surgeon and physiotherapist familiar with the orthopedic complications of hemophilia. Pre-surgical evaluation must include an inhibitor study and an infusion study to determine levels and half life. A single batch of 60-100,000 units of concentrate is set aside for the patient.Surgery is scheduled for early in the day and early in the week. Intramuscular anaesthetic pre-medications are avoided. The infusion is given just before induction of anaesthesia and a post infusion level determined. Surgery is started immediately and special care is taken to avoid contamination of the operating room team because of the risk of hepatitis. Surgical technique differs little from that used in the non-hemophiliac with close attention to hemostasis. Tourniquets, electrocoagulation and suction drains have been used without problems.Factor levels are not allowed to fall below 30% until sutures are removed and healing is complete. Physiotherapy may require maintenance of levels for longer periods.

SUMMARY A 55-yr-old male undergoing varicose vein surgery with an extradural block complained of chest pain. E.c.g. changes and subsequent examination of the heart including coronary angiography suggested the diagonsis of Prinzmetal’s variant angina. The therapeutic implicarions of this condition in patients undergoing anesthesia and surgery are discussed.