The incidence of liver abscessation in slaughtered beef bulls in the South Island of New Zealand

Abstract

There has been anecdotal evidence of increasing liver abscessation on bull-beef farms across New Zealand from meat processors for more than a decade, but to date, no quantitative data has been published in the field. This study objective was to establish the incidence of liver abscessation in pasture- based beef bulls, the seasonality and breed differences, the impact on carcass weight, and to compare this with published data from feedlot cattle internationally. The study used a database of 137675 bulls slaughtered in the South Island between 2000-2005. The database included breed, farm location, carcass weight, liver abscess presence and abscess grading score (absent, mild, moderate, severe). The annual incidence of liver abscessation calculated was a mean of 9.5%. This recorded value is greater than other observed incidences from pasture-based systems and reduced compared with those observed in non-medicated feedlot systems internationally. There were significant variations in all measured parameters across years, and a clear and significant seasonal variation was observed. Incidence of liver abscessation peaked across November- December (11.3 and 11% respectively) and then declined as the slaughter season progressed. The typical NZ beef industry approach to rearing bulls for slaughter makes it likely that age at slaughter is a key influence on the seasonal incidence rate, with most cattle born in spring and slaughtered after 18 months, suggesting the late spring and summer peak in incidence is due to bulls older than two years. The percentages of abscesses graded were: severe (66.4%), moderate (12.8%), and mild (20.7%). Friesian and dairy crossbreed bulls had an incidence approximately twofold greater than that females beef breeds (10.3% and 4.7% respectively). There was a significant difference in the mean carcass weights of bulls graded, with those moderate with abscessation having a mean heavier carcass weight than those graded severe, minor and no abscess.