Ornithine and citrulline have different arginine-sparing capabilities when provided in an arginine-deficient diet. Rats were fed arginine-deficient diets containing ornithine or citrulline to see the effect on net fluxes of free arginine, ornithine and citrulline across the portal-drained viscera (PDV) and liver. The diets contained either 10 g arginine/kg diet (+Arg) or no arginine: the -Arg/+Ala diet contained additional alanine and the -Arg/+Orn and -Arg/+Cit diets contained ornithine and citrulline, respectively, in amounts isomolar to the amount of arginine in the control (+Arg) diet. Blood arginine concentrations were 50% lower than control values (P < 0.001) in rats fed the -Arg/+Ala or the -Arg/+Orn diet. However, addition of citrulline to the arginine-deficient diet restored blood arginine concentrations. The source of the circulating arginine in the rats fed the -Arg/+Cit diet was neither the PDV nor the liver; net splanchnic uptake of arginine was 0.3 mumol/min. Net citrulline release was substantial from the PDV (0.65 mumol/min) as well as from the splanchnic bed (0.67 mumol/min) of rats fed the -Arg/+Cit diet, such that blood citrulline concentrations were more than double (P < 0.001) those in rats fed the +Arg or -Arg/+Orn diet. Splanchnic release of citrulline in rats fed the -Arg/+Cit diet but not in rats fed the -Arg/+Orn diet supported the production of arginine in non-splanchnic organs such as, presumably, the kidney.

A natural exposure trial was conducted for 12 mo in a herd of 150 lactating Jersey cows to determine efficacy of a .35% chlorhexidine teat dip containing a glycerine emollient for the prevention of bovine intramammary infections. Right teats of cows were dipped in the experimental teat dip after milking machine removal and left teats were not dipped. The herd was free of Streptococcus agalactiae and had a low prevalence of Staphylococcus aureus. Most new major pathogen intramammary infections resulted from Streptococcus species, primarily Streptococcus uberis and Streptococcus dysgalactiae. New infections by Streptococcus species were significantly lower in teats dipped in chlorhexidine than in undipped teats. Overall efficacy of the chlorhexidine teat dip against major mastitis pathogens was 50%. The experimental teat dip also reduced coagulase-negative Staphylococcus species infections 49.0% and Corynebacterium bovis infections 65.2%. Overall efficacy against minor mastitis pathogens was 54.0%. No irritation or chapping of teats dipped in the experimental teat dip was observed.

Effects of bovine mammary secretions collected at different stages of the lactation cycle on blood mononuclear cell response to mitogens were evaluated. Mammary secretion skims and wheys collected 7 and 28 d following cessation of milking, at parturition, and during early lactation were used. Colostrum and mammary secretions obtained 7 d after milk cessation were associated with greatest inhibition of mononuclear cell blastogenesis. Milk collected during early lactation caused the least inhibition. Mammary secretion wheys caused greater inhibition of blastogenesis than skims. Dilution of mammary secretions reduced blastogenic inhibition. Phytohemagglutinin-stimulated mononuclear cells were less inhibited by mammary secretion than Concanavalin A-stimulated cells. Suppression of mononuclear cell activity, particularly during early involution and at parturition, may influence susceptibility of the bovine mammary gland to new intramammary infections during physiological transitions of the udder.

1992) Influence of apo-and iron-saturated lactoferrin and transferrin, immunoglobulin G and serum albumin on proliferation of bovine peripheral blood mononuclear cells, Food and Agricultural Immunology, 4:4, 253-257, Whey proteins from non-lactating bovine mammary secretions reduced peripheral blood mononuclear cell (PBMC) response to mitogens. Specific proteins responsible for hyporesponsiveness are unknown. This study evaluated the influence of apo-and ironsaturated lactoferrin (APOLF and FELF) and transferrin (APOTF and FETF), immunoglobulin G (IgG) and serum albumin (SA) at concentrations ranging from 0 02 to 2 5 mg ml -1 on PBMC response to concanavalin A. PBMC were collected from five pregnant Holstein cows during late lactation. Lactoferrin (LF), transferrin (TF) and IgG resulted in a dose-dependent reduction of PBMC proliferation, whereas SA had no effect. Decreased PBMC response was significant at all concentrations of APOLF and FELF, at APOTF concentrations 0.3 mg ml -1 , only at 2·5 mg ml -1 FETF, and at IgG concentrations 1·25 mg ml -1 . The degree of iron saturation of LF did not influence PBMC response; however, APOTF had a greater influence than FETF. Reduced PBMC response at low levels of LF indicate that hyporesponsiveness is not due solely to an increased protein content of the culture but may be the result of specific LF regulation of mononuclear cell proliferation.