Milk Extraction

Te Ao Hou, June 1963, Page 59

Milk Extraction Only a small proportion of the milk secreted within the cow's udder is held in the milk cisterns. It is mostly contained within the alveoli, the tiny secretory units of the udder. The secretory tissue is provided with a muscle mechanism which forces the milk down tiny ductiles into the milk cistern. From here it is extracted by either hand or machine milking. The muscle mechanism is controlled from the pitutiary gland which produces several hormones. Oxytocin is a chemical substance produced by the pitutiary gland and carried by the blood stream to the udder where it causes immediate and strong contractions of the muscles surrounding the alveoli. The release of oxytocin is initiated by stimulation of the teats and udder, and hence the need for proper stimulation of the cow to ‘let-down’ her milk at milking time. All the normally available milk contained by the udder can be removed by an efficient milking machine provided the milking process is completed while the let-down effect is still operative. This may last only two minutes in some cows, and ten to twelve minutes in others. This is why individual cows vary so much in their milking behaviour and why poor milking technique can result in the drying-off of some cows. Ruakura experiments, using identical twins, have shown how necessary and valuable stimulation is. One set of cows were stimulated for 30 seconds, the stimulation involving hosing with cold running water and rubbing by hand, followed by massage of the teats and lower udder and squirting of each teat. The second set of cows were not given any stimulus. The 30 second stimulation resulted in an average increase of 71 lbs of butterfat or 32 per cent per cow. The average production figures for the stimulated cows were 294 lbs of fat in 250 days, and the non-stimulated, 223 lbs of fat in 203 days. Milking time was 20 seconds shorter per cow in the stimulated group and on the basis of milk produced, a reduction of 1 ¼ minutes per cow. So the Ruakura experiment shows that the use of pre-milking 30 second hand stimulation can result in a substantial increase in production over the system where the machine is relied upon for stimulus. The udder must be massaged vigorously for proper stimulation and dirt removed from the teats with running water. There is no advantage in using warm water. A squirt of milk should then be taken from each quarter as a check for the presence of abnormal milk. There must be no delay in applying the teat cups. Delay is dangerous because of the short let-down time of many cows. When the milk flow indicator of the machine shows a rate of about ½lb per minute the cups should be taken off. For cows which need machine-stripping because of teat cup crawl the cups should be pulled down when the indicator shows a flow rate of about 1 lb per minute. However, it should be remembered that a large amount of machine-stripping is an indication of poor stimulation.