EFFECTS OF A CORE ANTIGEN VACCINE AGAINST GRAM-NEGATIVE BACTERIA ON PHYSIOLOGICAL AND YIELD PARAMETERS OF DAIRY-COWS DURING LATE LACTATION AND THE DRY PERIOD

The objective of the study was to assess the effects of a core antigen vaccine against Gram-negative bacteria on feed consumption, milk yiel d, somatic cell count, hematologic parameters, and milk progesterone c oncentrations for dairy cows in late lactation and the dry period. Six ty-eight multiparous Holstein cows from two farms were paired by days in milk and were randomly selected to receive either the vaccine or pl acebo. Cows received a secondary immunization with the same product (v accine or placebo) 3 wk following the primary immunization. The physio logic and yield outcomes were measured prior to each immunization, at the time of each immunization, and for one or more periods following e ach immunization. No significant differences between vaccinated and pl acebo groups were detected for daily milk weight, daily feed intake, s omatic cell score, rectal body temperature, or milk progesterone conce ntration (pregnant cows). Cows in the vaccinated group had significant elevations in total blood leukocyte counts following the secondary im munization, which was due to an increase in the neutrophil fraction 24 h postimmunization.