Physiological adaptation to the environment

The ability of an animal to cope with new environments arises from its capacity to respond to environmental variables and maintain body equilibrium (homeostasis). Each compensating mechanism depends on, and is a part of, a physiological feedback process. The severity (intensity and duration) of an environmental change relative to the animal's capacity to respond determines the potential disruption to the animal's equilibrium and the resources that must be invested to regain homeostasis. However, an environmental change sufficient to seriously challenge one individual may be insufficient to produce a measurable response in another. The principles behind the responses occurring in animals as a consequence of a change in their physical environment are illustrated in this review by examples drawn from responses of animals to cold stress. Behavioral opportunities sometimes are constrained in farm animals, and internal metabolic responses tend to become more prominent in such situations. Furthermore, as a disturbing factor persists, the immediate defensive responses are replaced by longer-term and adaptive mechanisms that reduce the burden on the animal. As we gain greater understanding of the environment-animal interface and the sensitivity and response of animals to disruption, we will be better able to establish and maintain suitable environments for our farm animals.     

Alpha-naphthyl acetate esterase activity is not a specific marker for ovine T lymphocytes

Alpha-naphthyl acetate esterase (ANAE) activity was demonstrated in ovine lymphocytes harvested from blood on Ficoll-metrizoate gradients. The enzyme's specificity for T lymphocytes, identified by immunofluorescent staining of T cell-specific antigens, was assessed. Correlation analysis of the results obtained using unfractionated lymphocytes from 12 sheep showed no correlation between ANAE activity and the expression of T cell antigens (r = 0.22). When lymphocytes from 4 sheep were fractionated on nylon wool columns a mean of only 43.2% of the cells in the non-adherent population were ANAE-positive whereas 94.7% of these cells were identified as T lymphocytes. Blood lymphocytes from 5 animals were separated into 3 fractions using Percoll discontinuous density gradients. No significant relationship was seen between ANAE activity and T cells in Fractions 1 and 3 (r = 0.41 and 0.21). Fraction 2 cells, however, did show a significant positive relationship (r = 0.91) between these two features but the biological significance of this relationship is unknown. It was concluded that ANAE activity is not a specific marker for ovine T lymphocytes.     

Ex-post estimation for agricultural pest systems

A smoothing method for ex-post estimation of agricultural systems with state variables that are observed imperfectly is introduced and an application is made to the case of a soybean defoliator pest. The estimation problem is to utilize all the information available to the decision maker and obtain the best estimate. The technique utilizes the information contained in an insect simulation model of how the system evolves over time given a set of inputs, and samples collected throughout the growing season. The results obtained show that, for the model used, a considerable reduction in the variances of the estimates generated by the smoothing process was achieved.     

Respiratory mucociliary clearance in the horse in health and disease, and its pharmaceutical modification.

The structure and possible functions of respiratory secretions are reviewed. In the equine, goblet (mucus producing) cells are the main source but little information is available on the volume or composition of equine respiratory secretions. Airway mucus has complex and incompletely understood physical characteristics which can be partially assessed by a wide range of in vitro and biological techniques. The complex relationship between mucus structure and its propulsion by the airway cilia are discussed, both in health and with pulmonary disease. Mucokinesis in the horse has been assessed visually, by bronchoscopically observing intratracheal markers and also by the use of radiographic and radioactive markers. All techniques indicate a tracheal mucus velocity of approximately 20 mm/min. A large number of mucokinetic agents have been claimed therapeutically to increase mucokinesis, using a range of mechanisms. These include mucus diluents, surface acting agents, mucolytics, bronchomucotropic agents, ciliary augmentors and broncho-dilators. A critical review of the literature shows that the bronchodilator clenbuterol is the most effective mucokinetic agent assessed to date in the equine.     

Comparisons of nonspecific and specific immunomodulation by oxolinic acid, oxytetracycline and levamisole in salmonids

Oxolinic acid, a promising drug for the treatment of bacterial fish disease agents, was tested for possible immunomodulatory effects on fish. Another antibiotic oxytetracycline, known to be immunosuppressive at higher treatment doses, and levamisole, a known immunostimulator for higher vertebrates, were also compared for causing changes in the nonspecific defense compartment and the specific immune system in rainbow trout. Groups of fish were immunized with Yersinia ruckeri O-antigen bacterin in combination with selected doses of the drugs. The nonspecific defense activity was measured by demonstrating neutrophil metabolic activity by the nitroblue tetrazolium assay, by counting engulfed bacterial cells for a phagocytic index and by counting leukocytes with adherent bacterial cells for the adherence index. The specific immune response was monitored by the passive hemolytic plaque assay demonstrating the numbers of antibody-producing cells. The results showed that oxolinic acid, used at recommended doses for the treatment of bacterial diseases, did not cause immunosuppression in either the nonspecific defense or specific immune system compartments, whereas tetracycline at 10 mg/kg caused reduced activity in both. Fish given levamisole injections before the antigen injection showed a stimulated nonspecific defense but a much reduced specific immune response.