Milking conditions and routine in New Zealand

Milkings commenced at seven am and three pm. For Trials 1 and 5, cows were milked through the tandem experimental dairy. For Trials 2 and 6, cows were milked with the Ruakura Milk Harvester.

In the tandem dairy, teats were wiped with a dry, clean disposable paper towel prior to cluster attachment; on the RMH, teats were checked visually for dirt and any soiled teats were washed with cold water. Cups were then applied, without any fore-milking or stimulation. During milking, a computerised recorder system monitored milk yield and milking time. Clusters were removed when milk flow declined below 0.2 litres/min using a standard automatic cup remover system.

In the experimental tandem dairy cows were milked using Alfa-Laval Agri (Tumba, Sweden) liners (3741) and shells (3144) via a Harmony claw, into a whole udder recorder jar system, using a milking vacuum of 50 kPa. Pulsation was supplied at a rate of 55 c/min (cycles/minute) and a 60:40 ratio. The physical characteristics of the liners and shells are recorded in Table 35. The same liners and shells were used with the Ruakura Milk Harvester.

Tab. 35: Physical characteristics of liner and shell used in Tandem and RMH Alfa-Laval AGRI 3741 liner ALFA-Laval 3144 shell

Mouthpiece diameter, mm 23 Inner diameter at lip, mm 40

Length mouth piece to base of teat cup, mm 163 Outer diameter at lip, mm 44

Bore, mm: Top of barrel 26 Length, mm 155

Middle of barrel 24 Inner diameter middle of barrel, mm 40 Base of barrel 31 Outer diameter middle of barrel, mm 44 Effective length, mm 146.2 Inner diameter short milk tube hole, mm 17

Liner stretch, % 11.1

Shore Hardness ° 52.0

Internal bore short milk tube, mm 8 Length short milk tube, mm 150 Length long milk tube, m 1.2 Claw weight (4 cups+liners+cluster), g 2670

The RMH was mounted on a 17 bail rotary platform that turned at a speed of 18 s/bail at the pm milking and 21 s/bail at the am milking. Up to 13 per cent of cows required two rotations to complete milking. The machine operated at two vacuum levels to create a vacuum differential, to transport the milk through the system without air admission.

The lower vacuum (50 kPa) represented the milking vacuum that was applied to the teats and was responsible for transporting milk into the claw. The high vacuum (70 kPa) was responsible for transporting the milk from the claw into the milk receiver can. A third pump transported milk from the receiver can into the vat and this had to operate against the 70 kPa of the high vacuum system (WOOLFORD and SHERLOCK 1989).

Each bail was equipped with an Electronic Control Module (ECM) with keypad. It offered the possibility to enter data for each bail, change machine operation and controlled the milking process for each cow individually.

In the claw, a sensor was placed at approximately two thirds of the depth of the claw.

Milk flowed from the teat through the short milk tube into the claw, and filled up the bowl.

When the level reached the sensor, the ECM started to count down a variable delay time (computed on the basis of flow rate) before opening the milk valve. The milk level continued to rise above the sensor. When the milk valve opened (control signal

= 75 kPa vacuum), milk flowed out of the bottom of the claw up through the central spindle (under 70 - 75 kPa vacuum) (Figure 9). The milk continued to flow until the liquid level dropped below the sensor, and the milk valve closed (Figure 10). Thus, the surface liquid was always kept above the bottom of the bowl to minimise air entrainment (SHERLOCK and WOOLFORD 1990).

Fig. 9: RMH bowl with open valve. Milk withdrawn from claw by vacuum differential (Personal communication, R.A. SHERLOCK 1999)

Fig. 10: RMH bowl with closed valve. Claw fills with milk (Personal communication, R.A. SHERLOCK 1999)

Various pulsation modes could be used when milking with the RMH. ‘Slow’ mode had a pulsation rate of approximately 50 cycles/min and a ratio of 43:57 open to closed (figure below).

Time

Vacuum

a b c d

4 kPa

4 kPa

Fig. 11: Pulsation chamber waveform in ‘slow’ pulsation mode (RMH)

The ‘fast’ mode was a dynamic pulsation mode, during which the open phase was controlled by the milk flow of the cow. The higher the flow rate, the more frequent [b]

phase extensions became. The software in the ECM registered the moment when the milk valve was opened and milk was drawn out of the claw. If the liner was due to close while the milk valve was still open, the software delayed the liner closure until the milk valve had closed. Although this delay was very short, it caused an extended [b] phase.

If the milk flow was zero kg/min, [b] phase extensions did not occur, at a peak flow of ca. 8 kg/min approximately 50 per cent of pulsation cycles presented extended [b]

phase. During a pulsation cycle with extended [b] phase, the pulsation ratio was increased and the rate decreased, yet the next one or two cycles could be completely normal. Due to this pulsation waveform, the average milking rate per cow could be increased by 23.8 per cent (WOOLFORD and SHERLOCK 1987).

Time

Vacuum

a b c d a b c d

4 kPa

4 kPa

Fig. 12: Pulsation chamber waveform in ‘fast’ pulsation mode, mean milk flow rate: 1.857 l/min (RMH)

Time

Fig. 13: Pulsation chamber waveform in ‘fast’ pulsation mode, mean milk flow rate: 1.03 l/min (RMH)

Tab. 36: Duration of pulsation phases (ms) of the different pulsation modes on RMH

1 The fast treatment with high flow rate was calculated as if all pulsation cycles had an extended [b]

phase.