Bacteriological cure rate and changes in milk composition in mastitis vaccinated ewes affected with subclinical mastitis

Aim: The aim of this study was to investigate the effects of using a commercially-available polyvalent mastitis vaccine on the bacteriological cure rate of existing subclinical mastitis in Awassi sheep. Materials and Methods: A total of 164 lactating ewes were divided into two main groups according to udder health and milk somatic cell count (SCC): Group 1=normal (N; n=80) and Group 2=subclinical mastitis (SC; n=84). Each group was then subdivided randomly into two treatment groups: N vaccinated (Nvax; n=38), N non-vaccinated (Nnvax; n=42), SC vaccinated (SCvax; n=42), and SC non- vaccinated (SCnvax; n=42). The vaccine was administered as per manufacturer's recommendations. Milk samples were collected aseptically from all ewes before vaccine administration (T0)and again on days 28 (T2) and 42 (T3) of the experiment. Results: In the SC group, the bacteriological cure rates in vaccinated and non-vaccinated ewes were 76% and 69%, respectively. In N group, the new intramammary infection rates in vaccinated and non-vaccinated ewes were 48% and 50%, respectively. Vaccination of normal ewes resulted in a significant (p<0.05) reduction in bacterial growth rate both at day 28 and day 42 of the study. The prevalence of new intramammary infection rate in Nvax ewes on days 28 and 42 was 19% and 20%, respectively. The prevalence of new intramammary infection rate in Nnvax group on days 28 and 42 was 33% and 30%, respectively. In SCvax group, the bacterial growth rate on days 28 and 42 was 44% and 35%, respectively. In SCnvax group, the bacterial growth rate on days 28 and 42 was 27% and 32%, respectively. There was no statistically significant effect of vaccination on any of the studied milk composition parameters. Conclusions: This is a preliminary study that indicated a possible protective effect of vaccination against mastitis in sheep. Further, case-controlled studies are indicated to estimate the level of immunity this vaccine provides to vaccinated sheep.