The responsiveness of bovine neutrophil L-selectin and CD18 to in vivo glucocorticoid administration was characterized by flow cytometric analysis. Blood was sampled intensively from dairy cows treated for 3 days with placebo, cortisol, or dexamethasone. Immunostaining was performed on whole blood (100 microliters) that was left unstimulated or was stimulated with platelet-activating factor (PAF; 1 microgram/ml blood) prior to incubation with fluorescein isothiocyanate-conjugated monoclonal antibodies against L-selectin and CD18. Results were expressed as the percentage of positive-staining cells and as mean fluorescence intensity (MFI) of those cells. Total leukocyte count and leukocyte differentials were also performed on all blood samples. Dexamethasone caused nearly complete down-regulation of L-selectin (P < .01) on the surface of gated cells and reduced to half the MFI of CD18 (P < .01). Compared with values for the placebo group, dexamethasone began to cause L-selectin down-regulation within 8 h after the first injection and these effects persisted until 48 h after the third injection. This was correlated in time with an acute reduction in the proportion of cells that stained positive for L-selectin (from 98% before dexamethasone injections to a low of 17% by 40 h after the first injection). Dexamethasone also caused leukocytosis and neutrophilia during this time interval. In contrast, CD18 down-regulation was delayed until 16 h after the second dexamethasone injection and persisted for roughly 8 days. However, at no time during the experiment did dexamethasone influence the proportion of gated cells staining positive for CD18 (always 100%). Effects of cortisol were generally similar in pattern to those of dexamethasone but were more subtle and more readily detected when PAF was added to blood prior to immunostaining. These results strongly suggest that one mechanism of the anti-inflammatory action of glucocorticoids is to induce dramatic down-regulation of L-selectin and CD18 adhesion molecules on blood neutrophils.

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Transportation causes stress in cattle that may alter numerous physiological variables with a negative impact on production and health. The objectives of the current study were to investigate the physiological effects of truck transportation and to characterize a pattern of phenotypes in the circulation that may aid in the early identification of stress-susceptible animals that often succumb to severe respiratory disease. Thirty-six young beef bulls (Aberdeen Angus, n = 12; Friesian, n = 12; and Belgian Blue x Friesian, n = 12) were subjected to a 9-h truck transportation by road. Blood (10 mL) was collected at -24, 0, 4.5, 9.75, 14.25, 24, and 48 h relative to the initiation of transportation (0 h). Plasma was collected for the assay of various metabolic, inflammatory, and steroid variables, and total leukocyte counts were determined in whole blood at each time point. Body weight and rectal temperature were recorded at -24, 9.75, and 48 h. Transportation decreased measures of protein metabolism in the plasma, including albumin (P = 0.002), globulin (P < 0.001), urea (P = 0.006), and total protein (P < 0.001), and increased creatine kinase (P < 0.001). The energy substrate beta-hydroxybutyrate was not changed (P = 0.27). Acute phase proteins haptoglobin and fibrinogen were both decreased (P < 0.001), whereas total leukocyte counts were elevated (P = 0.002). Circulating steroid concentrations were altered, because a classical acute increase in plasma cortisol was observed with the onset of transit (P < 0.001), in association with a decrease in dehydroepiandrosterone (P = 0.07), resulting in a profound increase in cortisol:dehydroepiandrosterone ratio (P < 0.001). Plasma testosterone was decreased, whereas plasma progesterone was increased (P < 0.001) in association with the increase in cortisol (P < 0.001). There was also an effect of breed for all variables except plasma urea, creatine kinase, and testosterone, perhaps indicating that a genetic component contributed to the physiological response to transportation stress, although without any clear trend. Taken together, this profile of physiological variables in the circulation of transportation-stressed bulls may aid in the future detection of disease-susceptible cattle after transportation. Further research to validate these potential biomarkers is necessary.

. 74: 16'7-201. Unprecedented numbers of technical papers, abstracts, and short communications have been published in the past decade regarding the effects of exogenous bovine growth hormone on milk production, health, and reproductive efficiency of treated dairy cows. In well-managed dairy herds, exogenous growth hormone increases milk production without altering normal variability in milk composition. This has held true regardless of dairy breed tested, geographical location studied, or feeding management system used. Also consistent across studies is the rapidity of the galactopoietic effect of administered bovine growth hormone, which arises from altered partitioning and use of post-absorptive nutrients and increased synthetic capacity of the mammary gland. Growth hormone and its associated peptide, insulin-like growth factor-I, are now known to provide chronic lipolytic, diabetogenic, and gluconeogenic signals to target tissues culminating in increased mammary gland availability of glucose and nonesterified fatty acids. Together with yet ill-defined effects on mammary secretory tissue, this homeorhetic control of metabolism elicited by exogenous growth hormone is so efficient that treated cows are not more susceptible to metabolic disorders than untreated cows. However, some studies have reported an increased frequency of mastitis in groups of treated cows. This has been attributed mainly to increased milk volume in the mammary glands of treated cows and no convincing data are available that show decreased mammary gland immunity as a result of growth hormone treatments. On the contrary, an expanding body of evidence implicates growth hormone as a key neuroendocrine factor that is required for immunological competence. Trends of decreased reproductive efficiency in cows treated with growth hormone have also been reported, but available data imply that this is probably an indirect effect via prolonged negative energy balance in cows treated in early lactation rather than a direct negative effect on estrous cycling via altered reproductive hormone profiles. The objectives of the present review are to bring into focus and summarize pertinent biological discoveries regarding the treatment of dairy cows with recombinant bovine growth hormone, and to explore areas where additional growth hormone research is needed or warranted.Key words: Growth hormone, somatotropin, dairy cows, insulin-like growth factor-I Burton, J. L., McBride, B. W., Block, E., Glimm, D. et Kennelly,E. 1994. L'horrnone de croissance bovinemais au point bibliographique. Can. J. Anim. Sci. 74: . D'innombrables m6moires techniques, r6sum6s analytiques et communications brdves ont 6t6 publi6s dans la dernidre d6cennie au sujet des effets de I'hormone de croissance bovine exogdne sur la production laitidre, sur la sant6 et sur les fonctions de reproduction des vaches laitidres trait6es. Dans les 6levages laitiers bien conduits, la GH exogbne accroit la production de lait sans modifier la variabilit6 normale de sa composition, et cela inddpendamme...

The objective of the present study was to determine the effects of supplemental dietary chromium on immune responses of dairy cows subjected to physical and metabolic stresses associated with late pregnancy, calving, early lactation, and peak milk yield. Nine periparturient dairy cows were supplemented with chelated Cr (.5 ppm/d) from 6 wk prepartum (wk -6) through 16 wk postpartum (wk 16), and 10 cows were unsupplemented controls. To assess humoral immune responses, all cows were immunized with ovalbumin (OVA; s.c.) and human erythrocytes (HRBC; i.v.) on wk -2 and 2, and sera from weekly blood samples were assayed for content of antigen-specific antibody. Cell-mediated immunity was assessed in vitro using antigen (OVA)- and mitogen-stimulated peripheral blood mononuclear cell (PBMC) blastogenesis of cells collected biweekly from wk -2 and 6. Supplemental Cr caused anti-OVA antibody responses (P < .01) and mitogen-stimulated blastogenic responses of PBMC (P = .05) to be elevated, was associated with lowered OVA-stimulated blastogenic responses of PBMC (P < .01), and had no overall effect on antibody responses to HRBC (P > .10) relative to responses of control cows. These results confirmed and extended our previous observations that supplemental Cr can alter specific immune responses of stressed cattle.

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