Evaluation of fully oxidized β-carotene as a feed ingredient to reduce bacterial infection and somatic cell counts in cows with subclinical mastitis

Aims To assess the effect of oral supplementation with fully oxidised β-carotene (OxBC) on bacteriological cure, incidence of clinical mastitis, and somatic cell counts (SCC) in cows with subclinical intramammary infection. Methods Cows from four dairy herds were enrolled in early lactation if they had quarter-level SCC >200,000 cells/mL and they had a recognised bacterial intramammary pathogen in one or more quarters. They were randomly assigned to be individually fed from Day 0, for an average of 40 days, with 0.5 kg of a cereal-based supplementary feed that either contained 300 mg of OxBC (treatment; n=129 quarters) or did not (control; n=135 quarters). Quarter-milk samples were collected on Days 21 and 42 for microbiology and SCC assessment. Bacteriological cure was defined as having occurred when the bacteria present on Day 0 were not isolated from samples collected on Days 21 or 42. Clinical mastitis was diagnosed and recorded by herdowners up to Day 42. Results The bacteriological cure rate was greater for quarters from cows in the treatment group (13.9 (95% CI=4.1–23.7)%) than for quarters from cows in the control group (6.9 (95% CI=4.8–9.1)%; p=0.02). The prevalence of quarters that were infected on Day 42 was less in cows in the treatment group (79.9 (95% CI=62.3-97.6)%) than the control group (88.2 (95% CI=78.4-97.9)%; p=0.009). The incidence of quarters diagnosed with clinical mastitis by Day 42 was lower in cows from the treatment group (1/129 (0.78 (95% CI=0.02-4.24)%) than in cows from the control group (6/135 (4.44 (95% CI=1.65-9.42)%; p=0.03). Mean quarter-level SCC did not differ between treatment groups (p=0.34). Conclusions and Clinical Relevance Feeding 300 mg/cow/day of fully oxidised β-carotene resulted in a higher bacteriological cure rate, a lower prevalence of intramammary infection following 6 weeks of feeding, and a lower incidence of clinical mastitis compared to untreated controls. This offers a non-antimicrobial approach to reducing prevalence of intramammary infection in dairy cows.