How Effective Is the Offensive Line in Your Herd?

Dairy Pipeline: January 1998

by Jerry Jones
Extension Dairy Scientist, Milk Quality and Milking Management
Virginia Tech

They always say that a strong defense is a good offense. The teat end is the first line of defense in fending off mastitis infections in a dairy herd. The teat end provides a block or barrier against entry of mastitis-causing bacteria into the teat cistern, I have referred to it as an offensive rather than a defensive line. Somatic cells are the second line of defense. The teat end's sphincter muscle, a ring of smooth muscle surrounding the teat canal, functions to keep the teat canal closed, prevent milk from escaping, and prevents bacteria from entering the teat. The cells lining the teat canal produce keratin, a fibrous protein with lipid components (long chain fatty acids) that have bacteriostatic properties. This keratin forms a barrier against bacteria. If the milk secreting cells (the alveoli) are the quarterback, how do attacking bacteria get by the offensive line? The ball is snapped as the first teatcup is applied. During milking, bacteria may be present near the opening of the teat canal. Bacteria are propelled into the teat canal and teat cistern when there is admission of undesired air into the milking unit. Also after milking the sphincter muscle in the teat canal remains dilated for 1-2 hours and bacteria present during this time can enter the teat canal. Liner slips, created by vacuum fluctuations, can propel bacteria through healthy teat ends. Trauma to the teat renders it more susceptible to bacterial invasion, colonization, and infection because of damage to keratin or mucous membranes lining the teat sinus. The canal of a damaged teat may remain partially open. Invasion is easy because the offensive line has left a gap. Conditions which contribute to trauma include: incorrect use of udder washes or cleaning compounds, wet teats, improper mixing or freezing of teat dips, frostbite, failure to prep cows or pre-milking stimulation for milk ejection, overmilking, and insertion of mastitis tubes or teat cannulae. Try to minimize conditions that are associated with high impact force against the teat end, including liner slips, excessive temporary vacuum losses, low vacuum reserve or level, inefficient vacuum regulation, blocked air vents, restrictions in the short milk tube, poor cluster alignment, abrupt milking unit removal without shutting off vacuum, or poor liner condition. Before you put this offense on the field, your game plan should include environmental conditions (pasture, free stalls) that keep teats clean. Then look at cow prep for milking (foremilk stripping, pre-dipping, drying with cloth or paper towels, and effective use of post-milking teat dipping). If the offensive line is doing its job, it becomes easier for somatic cells to clean up.

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