A review of the systemic acute phase reaction with major cytokines involved, and the hepatic metabolic changes, negative and positive acute phase proteins (APPs) with function and associated pathology is given. It appears that APPs represent appropriate analytes for assessment of animal health. Whereas they represent non-specific markers as biological effect reactants, they can be used for assessing nutritional deficits and reactive processes, especially when positive and negative acute phase variables are combined in an index. When such acute phase index is applied to separate healthy animals from animals with some disease, much better results are obtained than with single analytes and statistically acceptable results for culling individual animals may be reached.Unfortunately at present no cheap, comprehensive and easy to use system is available for assessing various acute phase proteins in serum or blood samples at the same time. Protein microarray or fluid phase microchip technology may satisfy this need; and permit simultaneous analysis of numerous analytes in the same small volume sample and enable integration of information derived from systemic reactivity and nutrition with disease specific variables. Applying such technology may help to solve health problems in various countries not only in animal husbandry but also in human populations.

Societal concern and government regulations increasingly press for restricting the use of antibiotics as antimicrobial growth promoters (AGP). The search for alternatives is on, hampered by a lack of knowledge about the exact mechanism of AGP. Feed additives, such as AGP and alternatives, interact with the intestine. In the intestine, feed components, microbiota, and the mucosa interact in a very complex and dynamic way. Various mechanisms for AGP have been proposed, invariably based on the direct antibiotic influence on the microbial composition of the intestines. In the literature on antibiotics, however, the direct effects of antibiotics on host cells, in particular inflammatory cells, have been described. It is curious that this has never been considered in the literature on AGP. Presently, a case is being made that AGP most likely work as growth permitters by inhibiting the production and excretion of catabolic mediators by intestinal inflammatory cells. Concomitant or subsequent changes in microflora are most likely the consequence of an altered condition of the intestinal wall. This common, basic mechanism potentially offers an excellent explanation for the highly reproducible effects of AGP, as opposed to those obtained by alternatives aimed at microflora management. Therefore, the search for alternatives could be aimed at nonantibiotic compounds with an effect on the inflammatory system similar to that of AGP.

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The influence of physical stress on the plasma concentration of the acute-phase proteins serum amyloid-A (SAA) and haptoglobin (Hp) was studied in 10 calves. Two different stress levels were created by housing two groups of five calves, each on different types of floor. The stress level was assessed by studying videotapes of the animals, and, subsequently, by quantifying the problems related with moving across the pens and the time the calves spent lying down and standing. Plasma concentrations of Hp, SAA, aldolase, and cortisol were measured in blood samples obtained by jugular venepuncture. Plasma SAA concentrations were significantly (p < 0.001) elevated in animals housed on the floor type associated with the highest level of physical stress, although the concentrations were within the normal range for healthy adult cattle. Hp concentrations were not elevated. The floor type did not alter the stress related biochemical variables aldolase and cortisol. It is concluded that plasma SAA concentrations rise upon physical stress, whereas Hp concentrations do not change. The absence of a significant difference in aldolase or cortisol concentrations indicates that the difference in the level of neuro-endocrine stress between the animals housed on the two floor types is only minimal. Consequently, SAA is suggested to be a sensitive variable to assess physical welfare in calves.

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The concentrations of the two acute phase proteins, serum amyloid A and haptoglobin, in serum and milk were compared in 10 cows with clinical mastitis, 11 cows with extramammary inflammatory conditions and 10 clinically healthy control cows. The concentrations of both acute phase proteins were higher in the serum and milk of the cows with mastitis than in the cows in the other two groups. Four of the cows with extramammary inflammatory conditions had serum amyloid A concentrations in serum above 100 pg/ml, but negligible concentrations in milk, indicating that a pathogen must be present in the mammary gland for serum amyloid A to accumulate in milk. The acute phase protein concentrations in milk increased significantly with increasing somatic cell count, suggesting that they may be indicators of the severity of an infection.

We previously demonstrated that oral application of the recombinant single-domain antibody fragment (VHH) clone K609, directed against Escherichia coli F4 fimbriae, reduced E. coli-induced diarrhoea in piglets, but only at high VHH doses. We have now shown that a large portion of the orally applied K609 VHH is proteolytically degraded in the stomach. Stringent selection for proteolytic stability identified seven VHHs with 7-to 138-fold increased stability after in vitro incubation in gastric fluid. By DNA shuffling we obtained four clones with a further 1.5-to 3-fold increased in vitro stability. These VHHs differed by at most ten amino acid residues from each other and K609 that were scattered over the VHH sequence and did not overlap with predicted protease cleavage sites. The most stable clone, K922, retained 41% activity after incubation in gastric fluid and 90% in jejunal fluid. Oral application of K922 to piglets confirmed its improved proteolytic stability. In addition, K922 bound to F4 fimbriae with higher affinity and inhibited fimbrial adhesion at lower VHH concentrations. K922 is thus a promising candidate for prevention of piglet diarrhoea. Furthermore, our findings could guide selection and improvement by genetic engineering of other recombinant antibody fragments for oral use.