In order to produce milk, the cows have to calve and the lactation period is between one and the next calving.
The cycle is divided into four stages: early, mid and late (120 or d) and the dry time (which will last up to 65 d). The cycle is broken up into four stages. Cows calve every 12 months in an ideal environment.
Different changes take place in cows through different lactation stages.
There are also improvements in the consumption of feed, body and stage of pregnancy as well as in the development of milk. Figure 1 shows the interrelationships between the intake of feed, milk yield and live weight for Friesian cow with an period of 14 months, thus, a lactation of 360 d.
After calvation, a cow may start producing 10 kg per day of milk and then slowly fall down to 5 kg / day by the end of lactation at a maximum of 20 kg / day by about 7 weeks.
Although its maintenance needs do not differ, the production of milk do require more dietary energy and protein than the production would increase if demand falls. However, she will need extra energy to regain her body condition in late lactation.
In addition to the energy expended, cows typically use their body condition for approximately 12 weeks after calving. The energy released is used to generate milk that helps them to reach a higher peak than their diet alone could reach.
Milk yield at the peak of lactation provides for the potential milk production during the year, with an additional 200 kg per day at the peak.
During early lactation, the herd has a range of obstacles to feeding well to optimize the production. Voluntary consumption of food is the important issue.
At calving, the appetite at peak intake is just around 50-70%. The consequence is that the rising calf takes place during the driest time, reducing the volume of rumen and reducing the density and size of rumen papillae.
After peak lactation, cows are slowly increased in appetite until they can consume all the nutrients they need when the diet is very high.
While energy used in milk production during this period is less demanding as milk production decreases, energy is still necessary due to pregnancy and the fact that the body needs to become a source of energy for the next lactation. In late lactation it is usually more successful than in the dry period to improve the health of the herd.