Increased teat wall thickness in response to machine milking.

Area of Science:

• Veterinary Medicine
• Animal Science
• Dairy Husbandry

Background:

• Machine milking can cause transient increases in teat wall thickness.
• The underlying cause of this phenomenon, particularly the role of ultrasonographic findings and histological correlations, remains unclear.
• Previous studies have documented teat wall thickening but lacked direct histological evidence to pinpoint the origin.

Purpose of the Study:

• To evaluate and compare milking-related changes in teat tissue using B-mode ultrasonography in Simmental and Holstein dairy cows.
• To correlate ultrasonographic observations with histological findings of teat tissue.
• To investigate the hypothesis that mechanical forces during machine milking lead to transient congestion of blood vessels in the teat wall.

Main Methods:

• B-mode ultrasonography was used to scan teats of dairy cows before and immediately after machine milking.
• Teat tissue samples from Simmental cows were collected shortly after milking for histological analysis by light microscopy.
• Histological sections were compared with those from a lactating, non-milked Angus cow and ultrasonographic findings in a periparturient Holstein cow.

Main Results:

• Ultrasonography revealed anechoic tubular structures in the inner teat wall post-milking, identified histologically as thick-walled veins.
• The diameter of these veins significantly increased after milking compared to pre-milking measurements, with the effect being more pronounced in Holstein cows.
• No evidence of edematous extravasation was found in either ultrasonography or histology, in both milked and non-milked cows.

Conclusions:

• The transient increase in teat wall thickness following machine milking is primarily caused by the engorgement of thick-walled veins within the teat tissue.
• Mechanical forces from vacuum and compression during milking likely induce this venous congestion.
• These findings provide histological and ultrasonographic evidence supporting the vascular congestion hypothesis for milking-induced teat wall thickening.