Comparing vacuum stability in milking claws

By Dr. Lionel Brazil, Carol Collar, Ted Jones, Dr. Jim Cullor, and Dr. John Kirk 

Recently new claws with increased outlet sizes have been developed and marketed. Studies were conducted by the University of California-Davis, Milk Technology Laboratory at the Veterinary Medicine Teaching and Research Center in Tulare to measure and compare vacuum in four claws with differing outlet inner diameters (ID) under controlled conditions of flow and lift on the milking machine test bench.   Four representative claws were tested from a group of 15 at the Milk Technology Laboratory. All of the 5/8-inch claws had similar characteristics and two were chosen for further evaluation.   Of the four selected, two claws had milk outlets with ID of 5/8 inches; one measured 6/8 of an inch, and another measured 7/8 of an inch. Each claw was fitted with 70 inches of milk hose that matched the claw outlet ID to which it was attached. Hoses were connected to the milk line through inlets matching the size of the hose.   Each claw was assembled with a set of identical liners and teat cups. Claw vacuum measurements were obtained by inserting a 12-gauge needle into one short milk tube of each claw assembly. Milk-line vacuum measurements were obtained from identical needles placed into milk-line inlets.   All tests were performed using a simulated udder. Water was substituted for milk on the test bench. The simulated udder allowed for control of water flow to represent various levels of milk production.   Claw vacuum stability was observed under varying conditions of lift (zero, six and 12 inches) and flow (1 and 1.5 gallons per minute) The experiment was conducted on three consecutive days. Each day, the four claws were tested under all combinations of lift and flow for a total of 72 tests. Measuring vacuum stability   Overall, the most stable vacuum was delivered by 6/8-inch and 7/8-inch claws at zero lift (Figure 1). Increasing lift of the milk degraded the performance of all four claws, with the larger claws and particularly 7/8 inch, still maintaining some advantage (Figure 2). The milk flow rate also altered the claw vacuum levels (Figure 3 & 4).  (click images to enlarge)

Figure 1

Figure 3

Figure 5

Figure 2

Figure 4

Figure 6

Mean claw vacuum was highest in the larger ID outlet claws compared to the smaller diameter outlet claws.   Under simulated milking conditions, a cow would give milk at varying flow rates with an increase to the peak flow and thereafter decreasing until the milking machine is detached. The 7/8-inch inlet claw maintained a narrow range of vacuum at the claw as compared to the 5/8-inch inlet claw (Figure 5).   To maintain the same average claw vacuum level in the 5/8-inch inlet claw as in the 7/8-inch inlet claw, the system vacuum had to be raised almost 1.5 inches Hg. (Figure 6). At the same time vacuum range in the 5/8-inch inlet claw increased significantly over that of the 7/8-inch inlet claw.   More stable vacuum contributed to higher mean claw vacuum for larger claws in this experiment. The majority of the dairies after conversion to larger capacity claws have observed increased milking speed due in part to higher average claw vacuum.   Higher claw vacuum could also reduce liner slips and provide more persistent teat end vacuum in both the open and closed phase of pulsation which could improve milking efficiency.   It should be noted that vacuum stability range varied between claws. With zero inches lift and one gallon per minute flow, the 7/8-inch claw had a range of about 5 mm Hg; the 6/8-inch claw range was about 10 mm Hg, and the 5/8-inch claws had ranges of about 25 and 30 mm Hg. Improving vacuum stability within these ranges may have subtle benefits that enable more rapid, gentle and complete milk out.     For more detailed information, contact Lionel Brazil at the UCVMTRLT Milk Technology Laboratory (559-688-1731).   Dr. Lionel Brazil is a University of California (UC) dairy specialist; Carol Collar is the UC Extension dairy farm advisor for Kings County; Ted Jones is the UC statistician; Dr. Jim Cullor is the director of the UC Veterinary Medical Teaching and Research Center, Milking Technology Laboratory, in Tulare, Calif. and Dr. John Kirk is a UC extension veterinarian.