Variance components of teat dimensions in dairy cows and associated factors.

Traditionally, all cows within a herd are milked with the same teat cup liner, although it is hypothesized that considerable variation in teat dimensions exists between cows and quarters within cows. To study at which level (herd, cow, or quarter) most variation in teat dimensions resides, and to identify factors explaining (part of) this variation, both a cross-sectional (n=2,715) and a longitudinal study (n=8,678) were conducted. Using an objective and easy-to-use measuring device, teat length and teat diameters were determined. In both studies, most variation in teat dimensions was present at the cow or within-cow level, and not at the herd level, indicating that choosing a teat cup liner that is identical for all cows in a herd is far from optimal. Quarter position (front versus hind), parity and lactation stage were identified as factors associated with teat length and teat diameters. Generally, front teats were longer and broader than hind teats. Teat length and diameters increased with parity, although the increase in teat length was not significant from second parity onwards in front teats, based on observations from the longitudinal study. After the first 30 d in milk, teat length substantially and significantly increased, whereas teat diameters decreased. We conclude that better results in teat condition, and eventually in udder health, might be yielded when different teat cup liners are chosen for front versus hind teats or for cows of different parity or lactation stage, with special attention to the first 30 d in milk. However, the biological relevance of these differences should be examined first.