Relationships between milk urea and production, nutrition, and fertility traits in Israeli dairy herds.

The objectives of this study were to identify and evaluate production and environmental factors that influence milk urea (MU) in Israeli dairy herds, to analyze the relationships between MU concentration and nutritional variables, and to examine a possible association between MU and pregnancy rate (PR). Production and environmental data were obtained from the Israeli Dairy Herd Improvement (DHI) Center (n = 1,279,600). Programmed total mixed rations (feeds and quantities) on milk-test day were collected from 42 dairy herds. Data on 36,073 cows that were inseminated close to milk-test day and pregnancy diagnosis results were obtained from the DHI data bank. Highly significant positive relationships were found between MU concentration and milk yield and fat percentage; relationships between MU and milk total protein percentage and somatic cell count were negative. Milk urea levels were higher during the summer months and were higher for adult cows. These levels increased as lactation progressed. Milk urea was positively associated with dietary levels of crude protein, ruminal digestible protein, and neutral detergent fiber contents; it was negatively associated with ration energy and nonstructural carbohydrate contents. Significant influences of specific feeds on MU were detected. A significant negative association was found between MU level and PR. Least squares means for PR for cows in the lowest and highest MU quartiles were 38.4 and 36.1%, respectively. Increasing levels of MU were negatively related to reproductive performance of dairy cows, but the risk of nonpregnancy caused by high levels of MU was lower than reported in previous studies.

Mammary infection with Staphylococcus aureus in cows: progress from inoculation to chronic infection and its detection.

The progress of Staphylococcus aureus infection from inoculation to the early chronic stage was examined in 12 Israeli-Holstein cows (four primiparous and eight multiparous) for up to 48 d after inoculation. Before inoculation, the primiparous cows were free from any infection and the multiparous cows were infected by coagulase-negative staphylococci. Two quarters in each cow were inoculated intracisternally following milking with 2000 cfu of a local prevailing Staph. aureus strain, VL-8407. Infection was established in 21 out of 24 quarters. The control quarters remained free from infection during the study, with no significant change in function. No statistically significant differences were found between primiparous and multiparous cows in the responses examined. Somatic cell count (SCC) increased within 24 h of inoculation and remained high for the duration of the study. In the infected quarters mean ln (SCC) increased within 24 h from 9.9 +/- 0.5 before inoculation to 13.0 +/- 0.2 after inoculation; most of the cells were neutrophils. N-acetyl-beta-glucosaminidase activity, expressed as ln (nnmol/min per l), was increased from 0.9 +/- 0.6 to 2.4 +/- 0.2 by inoculation, and was highly correlated with SCC. The Staph. aureus count fluctuated with no particular relationship with SCC. The phagocytic activity of neutrophils was significantly lower in the inoculated than in the control quarters and this difference increased with time after inoculation. CD8+ T lymphocytes were the main subpopulation of lymphocytes found in inoculated quarters. After inoculation, maximum but not minimum electrical conductivity (EC) recorded during milking increased significantly. The rises in maximum EC varied significantly among cows. The rises in SCC were associated with a persistent increase in EC in only one of the eight cows examined. No clinical signs were observed, and milk yield and composition were not affected during the study period. The results suggest that some strains of Staph. aureus may induce a relatively mild response in mammary glands of cows in mid lactation, and that the concomitant development of such chronic Staph. aureus infections in two quarters may not be detected by changes in the EC of composite milk and in the yield of the cow.