Udder and teat conformational risk factors for elevated somatic cell count and clinical mastitis in New York Holsteins

Abstract

Our primary objective was to identify udder and teat conformational risk factors associated with the occurrence of elevated somatic cell count (SCC) and clinical mastitis using a prospective cohort study design with careful assessment of exposure and disease outcomes. Mastitis prevalence was evaluated by parity across 6 sampling periods representing key physiological transitions during lactation: 0-1 day in milk (DIM), 3-5 DIM, 10-14 DIM, 50-60 DIM, 90-110 DIM, and 210-230 DIM. Cows were scored for front and rear teat length, width, end shape, and placement, fore udder attachment, udder cleft, udder depth, rear udder height, and rear udder width. Two independent multivariable logistic regression models were used to generate odds ratios (OR) for elevated SCC (≥ 200,000 cells/ml) and farm-diagnosed clinical mastitis. We identified that loose fore udder attachment (reference level: strong fore udder attachment, OR = 2.1, 95% confidence interval (CI) = 1.2-3.8) and flat teat end shape (reference level: round teat end shape, OR = 1.4, 95% CI = 1.1-1.9) increased the odds of an elevated SCC event, whereas a negative California Mastitis Test score at 0-1 DIM decreased the odds of an elevated SCC event (OR = 0.6, 95% CI = 0.4 to 0.8). Loose fore udder attachment (reference level: strong fore udder attachment, OR = 3.7, 95% CI = 1.3-10.7), flat teat end shape (reference level: round teat end shape, OR = 1.5, 95% CI = 1.0-2.4), low rear udder height (reference level: intermediate rear udder height, OR = 2.8, 95% CI = 0.3-6.2), and increasing rear teat width (OR = 2.2, 95% CI = 1.2-4.4) heightened the odds of developing clinical mastitis. We identified that within our study cohort, loose fore udder attachment and flat teat ends had an important association with increased odds of both an elevated SCC event and clinical mastitis diagnosis. The identification of these udder and teat conformational risk factors for mastitis can provide farmers an effective and inexpensive tool to manage mastitis.

Keywords: Logistic regression; Mastitis; Teat conformation; Udder conformation.