Measuring milk fat
The introduction in the 1890s of the Babcock test for measuring the fat content of milk prevented unscrupulous farmers from watering down their milk to get paid for more volume. The test was applied to herds, so that cows producing the fattiest milk could be used in selective breeding. In 1896 a farming magazine was enthusiastic about the test:
It is most desirable that this fair, just and equitable system be adopted, as it puts a premium on good breeding, careful handling, good feeding and the delivery of the milk at the factory in good condition.
Testing showed that some cows gave four times more butterfat over a season than the poorest cows. Early tests showed the fat content of milk was 3–4%; in the 2000s it was 4.5%–5.1%. Agricultural and Pastoral associations quickly realised that production records were more important than a cow’s appearance or pedigree.
Herd testers were often women. They travelled from one dairy farm to the next – in the early days by horse and trap, and later by van or small truck – to test milk samples. The tester usually arrived in time for the afternoon milking, stayed the night on the farm, and was up for the morning milking at 5.30–6.00 a.m. For the Babcock test, milk samples were collected from each cow at each milking.
Organised herd testing began at the Dalefield Dairy Company, Wairarapa, in 1909, and by 1922 the first cooperative herd-testing scheme was under way in Waikato. Four years later there were 30 such schemes in the country. Between 1922 and 1930, production per cow grew by 29% – from 175 pounds (79 kilograms) of milk fat per season to 225 pounds (102 kilograms). Herd-testing schemes were amalgamated into six associations, and test procedures were regulated by the government to ensure uniformity.
The herd-testing service reached a peak in the proportion of cows tested in 1996–97, when 2.5 million cows (90% of all cows) were tested. Ten years later, about 2.8 million (70%) were tested. The farmer-owned company Livestock Improvement Corporation and competing genetics company Ambreed provided testing services.
Milk solids are calculated from the fat and protein content in milk. These are measured by the amount of infrared light that is absorbed when shone through a milk sample. Somatic cells (which indicate the presence of an infection) are also counted at this time to check if the milk has been contaminated.
Testers visit a farm an average of four times a year and sample milk from each cow in the herd. The samples are sent for laboratory analysis (a total of 10 million analyses are made per year) and the results sent back to farmers and breed societies. The average results per cow tested in the 2005/6 season were 3,951 litres of milk, 186 kilograms of milk fat (4.71% by weight) and 146 kilograms of milk protein (3.69% by weight), totalling 332 kilograms of milk solids (8.4% by weight) from 266 days of milking. Farmers are paid for total milk solids.
Keeping records of the production from offspring of a cow (progeny testing), and relating this to the bull parent (sire surveying), began in 1934, with the aim of breeding the best stock, and researching methods of artificial insemination. Herd testing showed which bulls sired the most productive daughters. Semen collected from a top bull could be used to fertilise many more cows than would be possible by natural insemination.
The first list of proven sires was published by the Dairy Board in 1941. In 1949 a commercial artificial insemination service began in Waikato and Taranaki – a world first. The 1950s brought improved techniques for freezing semen. It was stored at very low temperatures and then thawed for use, which meant semen from the best bulls could be used long after they were dead.
The Livestock Improvement Corporation (LIC) performs more than 3 million inseminations each year (about 80% of all dairy cows and heifers). Bulls and cows are ranked against the breeding worth index, which is an estimate of the animal’s genetic merit, and takes into account milk fat, protein and volume, and live weight, fertility and longevity. Since the 1950s the LIC sire-proving scheme has contributed more than $15 billion to the New Zealand economy by genetically improving the national herd.