The Milking Herd - A Depreciable Item

When it comes to repair and maintenance it is easy to compare a herd of dairy cows with an item of farm machinery such as a tractor. Just as a tractor will be reliable if well maintained and driven with care so will a herd of cows continue to perform if the right management strategies are regularly implemented.

 

How Can We Compare Herds?
Age:
There is a wide variation in the percentage of cows in each age bracket across herds. There are some herds with no cows older than seven years whilst others may have at least 30% of their herd in this age bracket. This has implications for BMCC, metabolic disease, fertility and clinical mastitis.
Type:
Breed, size, condition score, genetics and temperament vary between herds. All have a potential impact on performance.
Fertility:
The simple measure of the percentage of the herd that maintain a pregnancy in the first six weeks of mating, combines most fertility parameters. It varies from 80% to well below 40%.
Production:
Average litres, fat and protein production per cow is often used to compare herds. Herd test recording provides the opportunity to describe individual cow performance.
Milk Quality:
The BMCC is a reliable indicator of the level of mastitis in the herd. It gives indirect clues to many aspects of herd management such as clinical mastitis, milking harvesting equipment and milking management.
Death Rate:
It is surprising how much variation occurs in death rates between herds. Some farms lose up to 10% of the herd annually, many from metabolic disease at calving. Other farms consistently have less than 2% per year.
Disease Status:
Johnes Disease and Enzootic Bovine Leucosis have statutory control in Victorian dairy herds. For diseases like salmonellosis, there will be different immune status between herds. The Major Stresses on the Herd
Calving:
This has the potential to shorten the life of the cow or reduce her ability to lactate because of complications, such as mastitis or uterine infections. Heifers and older cows will be most prone to these losses.
Production:
The physiological process of lactating at the high level bred into our dairy herds has a significant impact on their health. Apart from susceptibility to conditions specific to lactation such as acetonaemia, it also increases susceptibility to other diseases.
Bulling:
Injury and lameness are potential complications.
Lameness:
Tracks and dairy yards, rough or hasty movement of cows and use of dogs contribute.
Illnesses:
Metabolic disease, mastitis and salmonella are the three more significant diseases causing stress on herds.
Undernutrition:
Most cows in the district are not fed to their potential. Undernutrition causing stress and subsequent losses occurs frequently in winter and summer.
Maintenance vs. Repair
The tractor analogy explains the difference between herds performing well with few losses compared with herds where deaths, reproductive losses and mastitis are constant problems.

Like a tractor, the herd undergoes a major service at the start of each season when new heifers are brought into the herd. If they are well grown, calving early and in plentiful supply they will adequately replace the worn parts of the herd. The older cows, the chronic high cell counts, the repeat clinical mastitis cases and the late calvers or non pregnant cows are culled. A tractor that has had a busy year and needs four new tyres will not perform as well next year if only two retreads are put on. This often happens in herds when there is a shortage of high quality replacement heifers. The maintenance requirement of the herd will be greater when wear and tear has been high. For example, if the herd is underfed we could expect many late calvers next year. Similarly when poor milking machine function or milking management occurs, a higher level of clinical and subclinical mastitis results. Both situations lead to high maintenance requirements.

To maintain a static size, a herd will need 20-30% replacements annually to avoid a gradual decline in herd quality. It is important that the replacements are not small, late calving heifers (retreads).

The well maintained herd, just like the tractor, will require fewer repairs through the year between major services. Fertility performance will be high, few cows will be culled for mastitis, less deaths will occur so the replacement rate will be lower. Many of these herds still introduce at least 25% of heifers to the herd each year and in doing so can apply pressure to the lower performing cows in the herd.



Click here to view the rest of the 1999 February newsletter.