The dairy cow's teat is the first line of defence against mastitis pathogens. The milking process may affect the teat's condition, increasing the risk of mastitis. It is well-proven that teat-ends with severe erosions or broken skin will have an increased risk of mastitis. However, more common changes in teat condition because of milking have not been related to udder health problems.
The focus of this thesis was on the relationship between teat-end condition, machine milking and occurrence of mastitis. In this thesis, two types of changes of teat-end condition were distinguished: callosity rings around the orifice and machine-induced teat swelling.
First a classification system of the callosity rings around the orifice was defined: the teat-end callosity (TEC) classification system. In this system, a distinction is made between roughness of the callosity ring (TECR) and thickness of the callosity ring (TECT). Teats can be scored in 8 categories. In an experiment, it was demonstrated that TECT and TECR increased rapidly during the first 8 weeks after calving. Cow factors such as days in milk, parity, machine-on time, and teatend shape were associated with TEC.
In order to measure machine-induced teat swelling, a methodology, using ultrasound, has been developed. Using this method, the changes of teat tissue in relation to machine milking and the recovery time of teat tissue after milking were evaluated. Machine milking had a large effect on the length of the teat-canal, the width of the teat-cistern, the width of the teat-end, and the thickness of the teat-wall. 8 h after milking, the teat-end width and the teat-canal length still differed from before milking. The teat-wall thickness and the teat-cistern width were recovered after 6 and 8 h.
The developed TEC classification system was used in a 1½ year longitudinal field study on 15 farms to examine the relationship between TEC and the incidence of clinical mastitis. From that study, it was clear that clinical mastitis does have a relationship with TEC. The relationship between TEC and mastitis was different for different mastitis pathogens. E. coli mastitis occurred more in quarters where teats had less TEC. Specific pathogens differ in their opportunistic use of orifice dysfunction to multiply, or enter the teat canal. Pointed teat-ends had higher TECT and TECR than flat or inverted teat-ends and TECT increased with a higher milk yield at peak production.
The same longitudinal dataset was used to focus on TEC as a risk condition for mastitis. Teats with a thin and smooth TEC ring showed the lowest incidence risk of clinical mastitis. They can be regarded as physiologically normal teats. An increase in the risk of clinical mastitis was observed when thickness and/or roughness of TEC increased. This is caused by less tightly closed teat canals after milking, a too high turnover of keratin, or the harbouring of pathogens in TEC. An increase in TECT and TECR can be used as an early warning signal for enhanced risk of clinical mastitis. Quarters without any callosity ring also showed an increased incidence risk of clinical mastitis during the next month. The higher risk of IMI in teats without a callosity ring may be caused by a decreased rate of keratin regeneration in the teat canal.
To evaluate TEC in the field, a simplified 4-category scoring system is suggested and used in an observational study on 200 dairy farms. Cows that have an increased risk of clinical mastitis due to more TEC build up because of milking, were the unit of interest in this study. Therefore, categories of TEC that gave an increased risk on mastitis were combined into one group: %ROUGH. Variation in %ROUGH between farms is explained by cow factors such as teat-end shape and machine-on time and milking machine factors such as the liner and the vacuum.
The overall conclusion of this thesis is that a healthy teat of a dairy cow has a good balance between the physiological reaction to machine milking and maintaining its first line of defence mechanism against invading mastitis pathogens. Increasing rates of IMI were related to one or more of the following: a high degree of machine-induced swelling, a high level of TECT, a high level of TECR and the absence of TEC. Pathways through which these machine-induced changes lowered the resistance of the teat to bacterial invasion are the openness of the teat canal, harbouring of pathogens in TEC, and significantly increased or decreased level of keratin regeneration rate. Part of the impaired reaction of the teat to machine milking may lay in the peak milkflow rate. Suggestions are made to adjust the characteristics of machine milking to the milk flow profile of an individual cow. This can minimise machine-induced teat condition problems.
Teat condition changes can be used as an early warning signal for enhanced risk of clinical mastitis. Classification of teat condition is an essential tool in milking machine research and a useful monitoring tool of the quality of milking in the field. Protocols for systematic evaluation of teat condition are available.
To read the whole thesis from Francesca Neijenhuis at Utrecht University, Faculty of Veterinary Medicine click here