Blood perfusion of teat tissue in dairy cows: Changes associated with pre-milking stimulation and machine milking.

Mechanical forces during machine milking of dairy cows evoke circulatory impairment of the teat tissue that may affect the teats' defense mechanisms against mastitis pathogens. Ample research describes dimensional changes of different teat traits after machine milking, whereas reports that describe changes in blood circulation of dairy cows' teats are limited. Therefore, the objectives of this study were to (1) describe changes in teat blood circulation that occur after pre-milking teat stimulation and machine milking and (2) study the effect of 2 different milking liners on machine milking-induced changes in teat blood flow. In a randomized trial, Holstein dairy cows were stratified by parity, stage of lactation, and average daily milk yield during the previous week, and allocated to 1 of 2 treatment groups. Treatment consisted of 1 milking observation with either a round or multisided concave milking liner. Teat scans were taken of the left front and the right hind teats using power Doppler ultrasonography. Imaging occurred before pre-milking udder preparation (T1), after completion of pre-milking udder preparation but before milking-unit attachment (T2), and immediately after unit detachment (T3). Perfusion intensity measurements from teat scans were performed with a commercially available software program. Data from 109 cows were analyzed. A general linear mixed model showed differences in perfusion intensity between time points. Least squares means (95% confidence intervals) for T1, T2, and T3, respectively, were 0.035% (0.026-0.047), 0.124% (0.093-0.164), and 0.095% (0.073-0.124). Conversely, no statistically significant differences between treatment groups were observed. We conclude that teat blood circulation is subjected to several influences, including inherent circulatory regulation mechanisms, as well as extrinsic factors such as machine milking. Future research is warranted to decipher the magnitude of their influence and to further our understanding of how these changes relate to the susceptibility to intramammary infection and milking performance.

An observational study investigating the association of ultrasonographically assessed machine milking-induced changes in teat condition and teat-end shape in dairy cows.

Mechanical forces during machine milking induce changes in teat condition which can be differentiated into short-term and long-term changes. Machine milking-induced short-term changes in teat condition (STC) are defined as tissue responses to a single milking and have been associated with the risk of new intramammary infection. Albeit, their association with teat characteristics, such as teat-end shape, has not been investigated by rigorous methods. The primary objective was to determine the association of STC, as measured by ultrasonography, with teat-end shape. The second objective was to describe possible differences in the recovery time of teat tissue after machine milking among teats with different teat-end shapes. Holstein cows (n=128) were enrolled in an observational study, housed in free-stall pens with sand bedding and milked three times a day. Ultrasonography of the left front and right hind teat was performed after teat preparation before milking (t-1), immediately after milking (t 0) and 1, 3, 5 and 7 h after milking (t 1, t 3, t 5, t 7). The teat tissue parameters measured from ultrasound scans were teat canal length, teat-end diameter, teat-end diameter at the midpoint between the distal and proximal end of the teat canal, teat wall thickness, and teat cistern width. Teat-end shape was assessed visually and classified into three categories: pointed, flat and round. Multivariable linear regression analyses showed differences in the relative change of teat tissue parameters (compared with t-1) at t 0 among teats with different teat-end shapes, with most parameters showing the largest change for round teats. The premilking values were reached (recovery time) after 7 h in teats with a pointed teat-end shape, whereas recovery time was greater than 7 h in teats with flat and round teat-end shapes. Under the same liner and milking machine conditions, teats with a round teat-end shape had the most severe short-term changes. The results of this observational study indicated that teat-end shape may be one of the factors that contribute to the severity of STC.

Short communication: Teat-end shape and udder-level milking characteristics and their associations with machine milking-induced changes in teat tissue condition.

Machine milking-induced changes in teat tissue condition, such as congestion and edema, have been associated with teat canal openness, penetrability, and thus susceptibility to new intramammary infections and diminished animal well-being. The primary objective of this study was to investigate the association of teat-end shape and machine milking-induced short-term changes in teat tissue condition. Our secondary objective was to study the association of udder-level milking characteristics and short-term changes. Data from 125 Holstein cows were analyzed in a longitudinal prospective cohort study. Cows were housed in freestall pens with sand bedding, fed a total mixed ration, and milked 3 times per day. Teat-end shape was classified into 3 categories: pointed, flat, and round. Udder-level milking characteristics were obtained from electronic on-farm milk meters. Short-term changes in teat tissue condition after machine milking were assessed visually. Multivariable generalized mixed model analysis showed an association between teat-end shape and short-term changes. Compared with teats with round teat-end shape, the odds ratio (95% confidence interval) for short-term changes was 1.68 (0.53-5.31) and 0.03 (0.004-0.19) in teats with pointed and flat teat-end shape, respectively. There was an association between milking characteristics and short-term changes such that higher milk flow rate during the first 15 s of milking decreased the likelihood of short-term changes. The adjusted probability of short-term changes for a milking observation of a mid-lactation cow and an average first 15-s milk flow rate of 0.5 and 1.5 kg/min was 53.0% (42.8-63.8) and 32.9% (15.2-57.3), respectively. Our results suggest that teat-end shape may be one of the risk factors that contribute to machine milking-induced short-term changes. Milking characteristics (e.g., first 15-s milk flow rate) may have the potential as a measure to indirectly monitor teat tissue changes associated with machine milking on a daily basis, though further research is needed to validate this hypothesis and to establish thresholds that could serve as on-farm guidelines.