Boost for NZ, Nordic Jerseys genetic link
A new collaboration is underway to improve the genetic links between the New Zealand and Nordic Jersey cattle populations.
I spend a lot of time out onfarm in my job, talking to farmers about their cows, breeding plans and how the economic indices assist in decisionmaking.
I often get asked about production worth, in particular: how can a cow producing 500kgMS have a low PW? The simple answer is there is more to PW than milk solids.
LIC in 1996 added PW to breeding worth (BW) and lactation worth (LW) -- our three pillars of animal evaluation.
The PW economic index provides an estimate of the lifetime producing ability of a cow and the efficiency at which she can convert feed into profit.
A number of factors can influence how much a cow will produce -- how well she has been reared, her age, what she is being fed, and environmental conditions, to name a few.
PW is designed to provide an accurate, objective calculation, to aid farmers’ decisions relating to the culling and purchasing of dairy cows. It includes components associated with genetic merit and permanent environmental factors which will affect a cow’s performance throughout her life, e.g. hybrid vigour (heterosis).
It considers the age of a cow and how she ranks against her peers of the same age. It also weighs up the balance between milk volume, protein and fat data from herd tests. Liveweight, from an efficiency point of view, is also incorporated.
Herdmate comparisons
PW takes an animal’s recorded herd test results for milkfat, protein and volume and compares these to how the rest of her herdmates of the same age and season performed.
This practice of comparing ‘like’ animals within a herd means that only your animals on your farm are compared against each other, within their identified contemporary groups.
This is what makes PW about the production of your cows on your farm.
The differences between records for animals in the same contemporary group provide a better indication of an animal’s relative genetic merit than the actual records themselves, and thus removes the effects associated with temporary environmental factors and management.
Milk volume vs protein vs milkfat
Just because an animal appears to be producing well doesn’t necessarily mean she is doing so efficiently or profitably.
PW does more than review production data; it also considers how much volume is produced and the ratio of milkfat to protein. The animal evaluation system balances the income and costs associated with these three factors.
Two cows could be producing the same amount of milksolids, but under the current economic weightings the animal that is producing more protein will be the more profitable animal and have a higher PW (everything else being equal).
If one of those cows was to produce less volume but the same milk solids she would also have a higher PW as she is more efficient. The cow that produced more volume but the same milk solids will incur more costs to the farmer -- in feed to generate the extra volume and cost at the factory to remove the liquid component.
Currently, the industry’s economic value for protein breeding value is $6.63 and milk fat breeding value is $1.90.
Emphasis on first three lactations
Finally, in calculating the potential performance of an individual animal, more emphasis is placed on the animal’s first three lactations, which is how age comes into the equation.
This is because we are trying to predict the lifetime performance of an animal as early on in her life as possible, so that farmers can make decisions on whether they should retain that animal in their herd or not.
Once an animal reaches eight years of age, herd test information stops feeding into the PW calculation.
Realistically, if she’s still in the herd at this stage then generally she must still be producing well and have proven her right to be in the herd.
