P. A. Clough

703. Cineradiographic observations on machine milking

Machine milking has been studied in three cows by cineradiography at 50 frames/sec. The findings of Pier et al.(5) have been confirmed. The effects of variation in the pulsation rate, ratio and liner tension were investigated and the results compared with those obtained by other methods. The proportion of each milking cycle during which milk flows has been determined.

Mechanics of machine milking: II. The flow-rate pattern within single pulsation cycles

The milk flowing during a single pulsation cycle was collected in a circle of contiguous cups which rotated in a chamber at 1 rev/pulsation cycle just below the end of the teatcup liner. The mean flow rate during the time taken for each collecting cup to pass under the milk stream was calculated and the flow-rate curve for the milkflow period of the pulsation cycle plotted. Flow rates were measured at 130, 97, 65, 32 and 16 c/min, and also after the pulsator had been stopped with the liner open for 0·5 min (0 pulsation). It was concluded from the series of flow-rate curves at the different pulsation rates that flow rate from the teat increased in about 0·05 sec to a steady value which continued for 0·5 sec or so, and then declined over a period of about 1·5 sec to a new constant value approximately equal to that shown after milk had flowed continuously from the teat for 0·5 min. These results suggest that once the pressure difference across the streak canal during milking forces the teat sphincter open a considerable time elapses before the muscle control system responds, and that a further much longer period elapses before the full closing force of the sphincter is exerted. Thus, it would appear that at pulsation rates of about 50 c/min and above, the streak canal is closed by pressure exerted on the teat by the closing liner, the sphincter muscle playing no active part because its response rate is slow compared with the pulsation rate. At lower pulsation rates the flow rate declines during each cycle because the sphincter muscle has time to exert a closing force to a greater or lesser extent depending on the duration of the milkflow period.

A comparison of the milking characteristics of transparent and conventional teatcup liners

The milking characteristics of 4 transparent and 8 conventional rubber teatcup liners in new condition were compared for peak flow rate, machine time and strip yield, using 30 cows in two 15×15 Latin squares. The milking characteristics of transparent liners were similar to those of normal liners at the same cluster weight. The 4 transparent liners were then compared with 4 of the conventional liners using 16 cows in two 8×8 Latin squares, to observe the movement of teats within the liners throughout milking. The various analyses indicated significant differences between liners but the ranked liner mean values showed the transparent liners widely distributed in the range. It was concluded that findings from studies of teatcup action using transparent liners could be expected to apply also to conventional liners. The conventional liners were selected to form groups differing mainly in one physical characteristic only (stiffness of the mouthpiece, wall thickness, bore and rubber hardness). Within groups, there were no significant differences in milking properties of practical importance, but between groups there were small differences in machine time and strip yield. Two properties of the liners which appeared important in controlling movement of the teat into the liner were bore of the barrel and friction, bore having the greater influence at the beginning and friction being the dominant influence at the end of milking. With the transparent liners it could be seen that the end of the teat was frequently bathed in milk. Both with transparent and with conventional liners it was surprising how often the teat penetrated so deeply that complete collapse of the liner in each pulsation cycle was prevented.

663. The relationship between milk secretion and the rate of milking by machine

Lactation has two phases: the continuous process of secretion and the mechanism of ejection which occurs only during milking. Because ejection is a transitory phase it is to be expected that within certain limits milk yield will be inversely related to the duration of milking, which was, in fact, demonstrated many years ago with hand-milked cows(1). With machine milking the situation is different because the forces which the machine applies to the udders of all cows within a herd are the same, and thus the differences in milking rate that occur are due to differences between the cows. Under these conditions, if milking rate can be shown to affect milk yield it is a demonstration of how the physiological factors controlling milking rate can modify the expression of the inheritance of milk secretion.

582. Immersion cleaning of milking equipment

A method of cleaning milking equipment is described which involves the immersion of all items coming into contact with milk in a caustic soda solution for the whole period between milkings. It is expected that this method of maintaining the equipment in satisfactory bacteriological condition would need less attention to detail than existing techniques. The procedure outlined may only be applied to apparatus which can be packed into a basket no larger than can be readily handled. It therefore applies only to direct-to-can milking equipment, and suitable milking and immersion cleaning apparatus are described. The process has been tried for a year on 8 commercial farms. The results are promising in that milk of good quality has been consistently produced, but the bacteriological state of the milking clusters was often below present standards. Deposition of calcium soap and inorganic calcium salts was marked on farms where the total hardness of the water was of the order of 200 p.p.m. Work is continuing.

Mechanics of machine milking: I. Pressures in the teatcup assembly and liner wall movement

A method is described of measuring pressures in a teatcup assembly using strain gauge transducers and simultaneously following movement of the liner wall by means of a cine camera. In preliminary experiments with a narrow bore type liner it was found that pressures below the teat could vary during a single pulsation cycle from a few inches of mercury below atmospheric pressure (inHg vacuum) to as high as 25 inHg vacuum in the absence of an airbleed. Bleeding air into the barrel of the liner or into the clawpiece considerably reduced fluctuation in pressure, and the vacuum barely rose above the nominal milking vacuum of 15 inHg. Reducing the rate of change of pressure in the pulsation chamber did not greatly affect the maximum vacuum obtained. Opening and closing of the liner by pressure change in the pulsation chamber was under some conditions considerably delayed by the pressure conditions existing inside the liner. It is suggested that inertia effects of milk in the cluster and the natural frequency of the system are largely responsible for the observed pressure changes under the teat.

Factors affecting vacuum within the teatcup liner during milking

Factors associated with the milking cluster and the long milk tube which cause a diminished or a fluctuating vacuum within the liner of the teatcup assembly during simulated milking with an artificial udder fell into 3 groups. 1. Lower milk flow rates and admission of air at the clawpiece greatly decreased vacuum fluctuation within a pulsation cycle and increased the mean level of vacuum in the liner during that part of the cycle in which milk was flowing from the teat. 2. Larger bore of the short milk tube connecting the liner to the clawpiece, pulsation of the teatcup liners in pairs instead of all 4 together, and larger volume of the clawpiece bowl in the main decreased fluctuation in vacuum within the liner. 3. Larger bore and shorter length of the long milk tube connected to the clawpiece and decreased height above the outlet of the clawpiece to which the milk was raised mainly increased the mean vacuum in the liner during that part of the cycle in which milk was flowing from the teat. In a milking experiment with 75 cows mean overall fluctuations in milking vacuum within the liner in a pulsation cycle at peak flow were 11·5 and 4·8 inHg and corresponding mean levels of vacuum during that part of the cycle when milk was flowing from the teat were 11·75 and 13·0 inHg. There were no differences in milking performance of practical consequence.