EVALUATION OF BOVINE TEAT CONDITION IN COMMERCIAL DAIRY HERDS: 3. GETTING THE NUMBERS RIGHT

Classification of bovine teat condition can be used to assess the effects of milking machines, milking management or environment on teat tissue and the risk of new intra-mammary infections. Veterinarians and others require a simple and reliable method for evaluating teat health in dairy herds. Teat condition can be classified using continuous measures (e.g., teat thickness measured in mm) or categorical scores (e.g., smooth or rough). Categorical data are often presented using a numerical scale (e.g., teat end condition = 1, 2, 3, or 4). This may lead to false statistical conclusions if the relative risk factors are not distributed according to their numerical value. Other common statistical problems of evaluating teat condition in the field are insufficient sample size, using improper statistical tests for skewed data, and samples not representing the population in question. For more information on sample size, statistical inference, and guidelines for the collection of statistically defensible data, see LeMire et al. (1998, 1999). This paper provides simple guidelines for statistical evaluation of the teat conditions (Table 1) proposed in the companion paper by Mein et al. (2001). Sampling all cows: In small herds (up to 100 cows) it may be practical to score the entire herd. In this case the entire population of cows has been measured and the sample mean is equal to th