Variability of Resting Mammary Blood Flow in Nonlactating Holstein Cows

Variability of rates of mammary arterial blood flow was studied in four dry unbred Holstein cows fitted with electromagnetic blood flow transducers around the right mammary artery. Cows were assigned to a 4 × 4 Latin square design balanced for residual effects. Treatments were estradiol 17β (.1 mg/kg body weight), progesterone (.25 mg/kg body weight), estradiol and progesterone combination, or alcohol. Rates of blood flow for cows resting appeared to be related to previous milk production or age. Rates of blood flow differed among cows, days, and treatments. However, time of day measurement was taken had no detectable influence on mammary blood flow. Residual variances attributed to cow, day, hour, and treatment were heterogeneous. Heterogeneity was greatest for cows and days; range was about threefold (high/low). Scale effects were not evident. Coefficients of variation were low with a range of 17 estimates from .63 to 1.51%. These coefficients are about 10% of those for goats. Variance of a single measurement taken during a 15-min recording was 36.48 when mean flow was 674.3 ml/min and systematic effects from time were removed. Residual variance during a 15-min period not adjusted for systematic time trends was 41.40. Heterogeneity of variance suggests caution in testing treatment effects on mammary blood flow because of possible excessive significant F tests.