Effect of machine milking on bovine teat sinus injury and teat canal keratin

Introduction In Ireland, cows are generally milked with milking machines with 3.2kg clusters, with wide-bore tapered liners (31.6mm – 20.6mm) and 4x0 pulsation (WB). Outside of Ireland, most milking machines have 1.65kg clusters, narrow-bore liners (25.0mm – 20.0mm) and 2x2 pulsation (NB). O’Callaghan (2001) showed that the mouthpiece cavity vacuum was higher with wide-bore tapered liners than with narrow bore A study was undertaken to establish, through morphological analysis, changes in teat cellular structure which may occur as a result of machine milking with different machine settings. Two milking machine systems were compared in two experiments. There were two treatments, namely, NB with 1.65kg clusters, 275ml claws, narrow-bore tapered liners (25.0mm – 20.0mm) with 2x2 pulsation, and WB with 3.2kg clusters, 150ml claws, wide-bore tapered liners (31.6mm – 20.6mm) and 4x0 pulsation. Cows were randomised into groups for Experiment 1 based on milk yield, cell count and teat-end condition; they were randomised in Experiment 2 based on lactation number. In Experiment 1, eight cows were assigned to either WB or NB milking systems for 118 days at the end of lactation. Clusters were removed at a milk flow-rate of 0.2 kilograms per minute or after five minutes of over-milking. In Experiment 2, eighteen cows were assigned to either WB or NB systems post-calving, and were milked for a complete lactation. Three cows from each milking system were subsequently allowed a 42-day dry period before culling. The cows in both experiments were slaughtered and their teats were recovered and fixed in a formalin solution within three hours of their last milking, or after the 42-day dry period. Sections of teat tissue were examined under a light microscope and assessed for teat sinus morphology. The teat sinus was visually scored from zero to five for epithelial damage, increased red blood cells and oedema. The total score for each teat was then expressed as total teat sinus injury (TSI). The area of the teat canal epithelium and the area of keratin were measured and the amount of teat canal keratin (TCK) was expressed as a percentage of the overall area. There was not a difference in TCK between the milking systems, when first lactation cows were compared. There were lower (p<0.05) oedema scores with the NB milking system than with the WB system in Experiments 1 and 2. Teats over-milked for five minutes had higher (p<0.001) TSI and lower (p<0.01) TCK than teats from which clusters were removed at a milk flow-rate of 0.2kg/min. The areas of TCK as a percentage of the teat canal epithelium was greater (p<0.001) in first lactation cows than in cows with four or more lactations completed. Front and hind teats had similar results for each teat parameter measured. TCK increased (p<0.05) following a 42-day dry period, but TSI was not significantly better.