UBAC mastitis vaccine performance in a South African pasture-based dairy herd

Abstract

Streptococcus uberis (Str. uberis) is a major gram-positive mastitis pathogen. It has various strains that differ in virulence. This organism is difficult to treat effectively. In 2021, 47.4% of major gram-positive bacteria isolated from milk in South African were Str. uberis. Vaccination is an essential tool for proactive udder health management. The UBAC Streptococcus mastitis vaccine (UBAC) is designed on the principle of inhibition of biofilm formation by this bacterium. A recent South African study observed that all Str uberis strains produce biofilms, the formation of which the UBAC vaccine is designed to inhibit. This field study evaluated the effect of the UBAC mastitis vaccine on several critical factors related to clinical mastitis caused by Str. uberis. These factors include lowering the prevalence and severity of clinical mastitis, improving clinical and bacterial cure rates, reducing new intramammary infections, lowering SCCs, and increasing milk yield or preventing milk loss associated with Str. uberis intramammary infection (IMI). Unexpectedly, there were no significant differences (P<0.05) established between the vaccinated and control groups for incidence and severity of clinical

mastitis; clinical and bacterial cure of clinical mastitis; cows culled owing to mastitis; seven- day average milk yields; new IMI and prevalence of Str. uberis mastitis and level of somatic

cell counts. Contrary to expectation, significantly (P<0.001) more Str. uberis IMIs were cured in the control group compared to the vaccinated group. The only statistically significant benefits observed in the vaccinated group were a significantly lower prevalence of chronic mastitis cases (P < 0.001) and a higher sensitivity to tetracyclines among Str. uberis isolates from clinical mastitis cases (P < 0.001).Fewer cows had an udder severity score of 2 in the vaccinated group (Group 1). The gluteal muscles were used as the injection site owing to the layout of facilities on the study farm, contrary to the recommended use of the neck muscles according to the directions. Incidentally, severe swellings were observed at the injection site in up to 42% of cows eight hours post-vaccination. These signs persisted for up to three days, causing discomfort to the animals and causing a milk loss of one to two litres per animal for the producer. In this herd, Str. uberis caused over 30% of infections of the clinical mastitis cases. It is recommended that the UBAC vaccine is tested as a management tool in herds with a higher prevalence of IMI Str. uberis and the discomfort of animals, when injected in the neck muscles as indicated in the directions for use, should be investigated. Based on these finding only, the vaccine cannot be recommended.