CHAPTER 1
Dairy Farming Systems
There have been major changes in dairying in the last thirty years, with both average herd size and milk yield increasing significantly: there are now many herds of 500-plus cows producing 12,000–14,000 litres per lactation. These increases in milk production have occurred as a result of changes in the world markets and have been made possible by improved genetic merit as well as better understanding of dairy cow nutrition and computerized ration formulation.
However, increased yield and larger herd size have been accompanied by a variety of problems that cause economic losses, and in some herds the losses are so high that they outweigh improved performance. For example, despite intensive research there has been no progress in reducing the incidence of mastitis or lameness in dairy herds, with average incidence for each disease running at over 20 per cent (and in some herds at more than 50 per cent). Despite technological advances that should improve fertility management, fertility results are deteriorating, and the number of forced culls is increasing, with many cows culled in their first or second lactation. This represents a great waste of potential and investment.
The challenge to every dairy producer is therefore to achieve the most cost-effective milk production for his or her own unit. This is not necessarily accomplished by producing the highest possible yield, but by making best use of the resources available: farm location, land quality and acreage, housing, skill and availability of labour, genetic potential of the herd, management and capital.
This chapter explores the principles of dairy production and the factors affecting its costs.
DAIRY SYSTEMS
A number of factors influence herd milk yields, and farmers may choose anything from a low-input–low-output system to a high-input–high-output system. Low-input–low-output herds are almost invariably based on spring-calving grazing systems: they rely on a low purchased-feed rate and try to produce the bulk of their milk from grazed grass. Average yields are around 4,500–6,000 litres per cow per year, so metabolic stress on cows tends to be low, with low incidence of disease and fertility problems, and a low culling rate. At the other extreme, high-input–high-output systems are based on housed cows that are fed high levels of concentrate. They require careful ration formulation and tight fertility management. Yields will be high, ranging from 8,000–12,000 litres per cow per year in the UK, and higher in the United States. Metabolic stress on the cows tends to be high. Either system can work to generate a profitable dairy enterprise, provided that management is good and targets are met. The key difference is that grazing-based systems are weather dependent, whereas high-yield systems can provide total control over feed supply, which reduces risk and variability.
MILK PRODUCTION
For the first days after calving the cow produces colostrum to provide her calf with antibodies that protect it from disease (see also Chapter 3). The colostrum changes to normal milk by the fourth day after calving. The calf is generally removed from the cow about twenty-four hours after birth (the calf should not be removed earlier because it will not have received as much colostral protection as it needs); in some herds calves remain with cows for longer.
Provided that everything is normal, the cow is ready to join the milking herd within one to four days after calving. Yield increases rapidly, with peak lactation of more than 60 litres daily for high-yielding cows. The transition from dry to peak yield therefore represents a very high metabolic challenge and, not surprisingly, is associated with the highest incidence of disease and weight loss.
Most milk is produced in early lactation, so it is essential that the cow calves regularly (see the graph on page 9). It is generally most cost efficient if s...