Diagram 1, the production cycle of a dairy cow.
As you can see the dairy cow should be in milk for around 305 days a year and have a drying off period of around 60 days. After calving the cow should be back in calf after 85 days, this is to keep the ratio of 1 calf/ cow/ year. This ratio will get the highest yield out of the cow and keep a good profit margin for the farmer.
The cow will produce differing yields of milk throughout the year; the yield will follow what is called a lactation curve as seen below in diagram 2. This diagram shows that the peak yield comes around four to five weeks. After the peak yield the yield will drop by about 2% per week.
Diagram 2 showing the lactation curve of a dairy cow, source www.delaval.co.uk
This is the period of time where the cow is producing its highest milk yield. The milk yield climbs for a period of 35 – 45 days until a peak is reached then the yield will begin to fall. Due to the high amounts of milk that the cow is producing at this stage of lactation there may be a loss in body condition as a result of the cow being in negative energy balance (N.E.B). N.E.B is where the cow is not receiving enough energy to produce milk without losing weight as it is using its own body reserves to meet the demand. The cow will reach peak dry matter intake (D.M.I.) after approximately 70 days, this creates a time lag between the peak yield of the cow and the peak D.M.I of the cow, this will cause a N.E.B and therefore there will be a negative liveweight change. Therefore the loss of body condition in early lactation is necessary to allow the peak milk production to be produced.
The body condition of a cow is measured on a scale of 1 – 5 with 1 being very thin and 5 being very...