Submitted to: Ruminant Physiology International Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 8, 2004
Publication Date: January 3, 2006
Citation: Elsasser, T.H., Ingvartsen, K.L., Kahl, S., Capuco, A.V. 2006. In: Ruminant Physiology, Sejrsen, K., Hvelplund, T. Neilsen, M.O., eds. Wagemingem Academic Publishers, Netherlands. pp. 415-447. Interpretive Summary: Cows, dairy cows in particular, experience a relatively intense period of depressed immune function in the six weeks surrounding calving and the transition to full milk production. The exact reasons for this depressed immune function is not clearly understood, but it is very apparent that during this time these cows are very susceptible to bacterial infections as well as many metabolic diseases. We have in this paper summarized important data and theories on this problem and its causes. Significant new information is available to indicate that a large part of the problem is simply a part of the process of pregnancy where hormones like progesterone subdue an over aggressive immune system to assist in maintaining the development of the fetus. In addition, there are some problems stemming from a nutritional imbalance that occurs when the cow's metabolism uses far more nutrients than the animal can eat and consequently metabolites its own tissues to supply the needed calories and proteins. Finally, new evidence indicates that there may exist during this time an under production of natural defense compounds like the antimicrobial peptide adrenomedullin. Together, management systems that can better balance the nutrition and stresses in these animals will prove beneficial in maintaining healthy productive cows.
Technical Abstract: Birth and parturition, lactation, weaning, castration, and seasonal diet change constitute defined, and, for the most part, naturally occurring periods in animals' lives where a needed priority for a specific biological function temporarily challenges the stability of other physiological processes. While a tremendous quantity of data has been amassed in attempts to categorize nutritional, hormonal, and immunological perturbations associated with these stresses, clear cause and effect relationships remain elusive and thus biochemically-defined, pathway-based decision structures towards preventive intervention lack in favor of the more traditional treatment of symptoms. Many of the physiological conflicts of this sort can be appreciated in the delicate, but critically balanced state of the periparturient dairy cow and the need to recognize the importance of individual animal variability in the management scheme. We present here some newer findings and implications regarding endocrine-immune interactions and effects suggesting targets towards which intervention strategies could be developed for physiological critical periods. As examples of principle, the ability for growth hormone to critically regulate at multiple points the activity of nitric oxide synthases in the immune response to inflammation and the metabolic fate of nitric oxide are discussed.Similarly, the differential regulation of multifunctional peptides like adrenomedullin are presented.