Alterations in hemograms and serum biochemical analytes of steers after prolonged consumption of endophyte-infected tall fescue.

The objective of the current study was to delineate changes that occur in serum analytes and blood cellular elements in cattle that graze endophyte-infested (Neotyphodium coenophialum) tall fescue. Tall fescue is grown on more than 35 million acres (14.2 million ha) of pasture in the United States, and three-fourths of the pastures are infected with the endophyte at a 60% or greater level. Tall fescue toxicosis caused by endophyte-produced ergot alkaloids continues to be the most important grass-related disease in the United States, in terms of economic loss to animal producers. However, the agronomic attributes of tall fescue make it an attractive forage species because of its ability to withstand cool temperatures, drought, poor soil conditions, and intensive defoliation from herbivore species, including insects. Tall fescue toxicosis is a complex disease and the need exists to understand the mechanisms of the toxic effects in order to institute effective, prophylactic control measures. Our group previously reported changes that occur in serum biochemical analytes of cattle that graze endophyte-infected tall fescue. An additional year's worth of data have been added, strengthening and corroborating these data. Consistent and significant changes associated with tall fescue toxicosis during the 3-yr study included decreased serum concentrations of cholesterol, globulin (increased albumin/globulin ratio), prolactin, total protein, and copper. The activity of alanine aminotransferase was decreased in serum, whereas an increase in serum concentrations of creatinine and total bilirubin occurred. The present report also documents comparative hemograms of cattle that grazed endophyte-infected or endophyte-free tall fescue over a prolonged period. The mean erythrocyte counts were increased in cattle that grazed endophyte-infected tall fescue, whereas mean corpuscular hemoglobin and mean corpuscular volume were decreased, as were mean eosinophil counts. Thus, repeatable changes have been identified that occur in serum biochemical and blood cellular values of cattle grazing endophyte-infected tall fescue that will aid in understanding the pathogenesis of the disease. In addition, these consistently altered parameters can be used to assess the effectiveness of potential prophylactic treatments.

Evaluation of Chlorhexidine as a Premilking Teat Disinfectant for the Prevention of Intramammary Infections During Lactation.

A study was conducted for 15 months to evaluate efficacy of a 0.35% chlorhexidine teat dip as a premilking teat disinfectant based on reduction of naturally occurring new intramammary infections. Predipping was compared with a negative control using a split-udder experimental design. All teats were dipped after milking with the same 0.35% chlorhexidine teat dip. Most new major pathogen intramammary infections were caused by Streptococcus species, primarily Streptococcus uberis and Streptococcus equinus and gram-negative bacteria, primarily Escherichia coli . Percentage of quarters newly infected by major mastitis pathogens was 30.6% lower in mammary glands with teats predipped and postdipped in chlorhexidine than in mammary glands with teats postdipped only, and differences between treatment groups approached significance. New infections by coagulase-negative Staphylococcus species were significantly lower in mammary glands with teats predipped and postdipped than in mammary glands with teats postdipped only. When all mastitis pathogens were combined, percentage of quarters newly infected by major and minor mastitis pathogens was significantly lower in the predipped and postdipped group than in the postdipped only group. No statistical differences in incidence of clinical mastitis between treatment groups were observed. No chapping or irritation of teats was observed and no adverse effects were detected using chlorhexidine as a premilking and postmilking teat disinfectant. Results of this study suggest that premilking teat disinfection with chlorhexidine in association with good udder preparation and postmilking teat disinfection can further reduce the occurrence of new intramammary infections during lactation.

Influence of recombinant bovine somatotropin (sometribove) on mononuclear cells during the nonlactating period.

Recombinant bST was evaluated as a potential immunoenhancer of bovine peripheral blood and mammary gland mononuclear cells during the nonlactating period. Cows (n = 4 per group) were assigned to one of four treatments: 1) untreated, 2) treated with recombinant bST during lactation only, 3) treated with recombinant bST during the nonlactating period only, and 4) treated with recombinant bST during lactation and the nonlactating period. Recombinant bST treatment during the nonlactating period had no effect on proliferation of bovine blood or mammary gland mononuclear cells in response to stimulation by mitogens or allogeneic cells. Recombinant bST treatment during the nonlactating period enhanced interleukin-2 secretion by mononuclear cells isolated from cows treated also with recombinant bST during lactation. However, recombinant bST treatment during the nonlactating period had little effect on interleukin-2 secretion by mononuclear cells from cows not treated with recombinant bST during lactation. Results of this study suggest that recombinant bST alters effector functions rather than proliferation of bovine mononuclear cells.

Prevention of bovine mastitis by a premilking teat disinfectant containing chlorous acid and chlorine dioxide.

The objective of this study was to evaluate the efficacy of a premilking teat disinfectant for the prevention of mastitis in dairy cows under natural exposure conditions. Predipping was compared with a negative control using a split udder experimental design. All teats were dipped after milking with the same teat dip. Percentage of quarters newly infected by major mastitis pathogens was 34% lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. New IMI by Streptococcus uberis and Staphylococcus aureus were significantly lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Differences in incidence of clinical mastitis between treatment groups approached significance. Predipping and postdipping were no more effective against Gram-negative bacteria, coagulase-negative Staphylococcus species, and Corynebacterium bovis than postdipping only. No chapping or irritation of teats was observed, and no adverse effects were noted using the test product as a premilking and postmilking teat disinfectant. Results of this study suggest that predipping and then postdipping with the test product was a more effective procedure against major mastitis pathogens than postdipping only.

Premilking Teat Disinfection for the Prevention of Environmental Pathogen Intramammary Infections.

A natural exposure study was conducted for 14 months to evaluate efficacy of 0.25% iodine premilking teat disinfectant for the prevention of new intramammary infections. Predipping was compared with a negative control using a split-udder experimental design. All teats were dipped after milking with the same teat dip. Most new major pathogen intramammary infections resulted from Streptococcus species, primarily Streptococcus uberis and Streptococcus dysgalactiae , and from gram-negative bacteria, primarily Escherichia coli . New infections by gram-negative bacteria were significantly lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Percentage of quarters newly infected by major mastitis pathogens was 48.6% lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Statistical differences in incidence of clinical mastitis between treatment groups were not observed. Predipping and postdipping was no more effective against Staphylococcus species and Corynebacterium bovis than postdipping only. These data suggest that pre- and postdipping with the test product was more effective against major pathogens than postdipping only and provide additional evidence that premilking teat disinfection is an effective management procedure for prevention of environmental pathogen intramammary infections.

Efficacy of a Low Concentration Iodine Postmilking Teat Disinfectant Against Contagious and Environmental Mastitis Pathogens in Two Dairy Herds.

Two natural exposure herd studies were conducted at separate geographic locations to evaluate efficacy of a postmilking teat disinfectant that contained 0.25% available iodine. One study was conducted for 11 months in a commercial dairy with a high prevalence of contagious mastitis pathogens. Postdipping was compared with a negative control using a split-herd experimental design. The other study was conducted for 12 months in a research herd with a high prevalence of environmental mastitis pathogens. Postdipping was compared with a negative control using a split-udder experimental design. New intramammary infections by Staphylococcus aureus and Streptococcus agalactiae were reduced significantly in quarters with teats dipped in iodine compared to undipped teats in the herd with a high prevalence of contagious mastitis pathogens. However, the experimental teat dip was not effective against environmental pathogens in either herd. New infections by minor mastitis pathogens (coagulase-negative Staphylococcus species and Corynebacterium bovis ) were significantly lower in quarters of dipped teats compared to undipped teats in both herds. No irritation or chapping of teats was detected and no adverse effects were observed. These data suggest that the low concentration iodine teat dip is effective against contagious pathogens and minor mastitis pathogens, but ineffective against environmental mastitis pathogens.