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 fat. During early lactation the cow should have a body condition of 2.5. If the cow is too thin then there may be problems with conception rates to first service which affect the calving ratio of the cow which in turn will have a bad effect on the profits of the farmer. Thin cows will have inadequate energy reserves to sustain them through the lactation which means the farmer will loose money.
To minimize the N.E.B the cow should be in the correct body condition before calving down, a score of 3.0 is appropriate. If the cow is too fat the she will not have the appetite to eat in early lactation which will affect the peak milk yield. It is key that the food intake is maximized post calving therefore the cow should have ad libitum access to forage at all time, the forage should also be of a high quality in early lactation, this is not as important when you move down the cycle. To overcome any limitations of forage concentrates like Molasses and Maize should also be used. A good concentrate mix for a dairy cow should contain starch sources of varying degradabilites, Molasses is rapidly degradable source while maize is a slowly degradable source of starch. There are two methods for feeding concentrates, in parlour and out of parlour. In parlour feeding systems the parlours are fitted with concentrate dispensing hoppers which dispense into the feed manger. A cow will receive 5kg per milking while a heifer will receive 4kg per milking. Out of parlour feeding is where feed is given out by transponders, in small amounts very often. Picture 1 shows an in parlour feeder system. Each cow will require adequate space to feed otherwise there will be overcrowding.
Photograph 1 showing an in-parlour feeder. Source www.dairymaster.com
Late lactation and dry cow management
In the last 2/3rds of the lactation cycle the cow should be gaining weight. The condition score of the cow should be moving towards 3.0. If the cow is not responding to the feeding and stays skinny...