Udder blood flow in unanesthetized, lactating goats measured with nitrous oxide

The N2O diffusion method, which was previously successfully adapted to the measurement of udder blood flow in anesthetized goats, was adapted to the same measurement in unanesthetized goats. For the N2O inhalation, masks were made for each goat, and each animal was trained to stand quietly while breathing through it. Sampling, analyses, and calculations were made as before. Seventeen determinations were made on seven goats in midlactation whose rates of milk secretion ranged from 29 to 147 ml/hr. The method appeared to be valid for the conscious animal. Udder blood flow ranged from 16 to 34 ml/min per 100 g udder tissue, and varied directly and linearly with the rate of milk secretion. These values agreed closely with those found by Linzell and by Rasmussen, each of whom used different in vivo methods on lactating goats. It is concluded that the N2O method can be used satisfactorily for the measurement of an average udder blood flow over a period of time of approximately 30 min in conscious, standing goats.