Luckily, you don’t have to get out the calculator or have a stab at it yourself. DairyNZ-owned subsidiary New Zealand Animal Evaluation Ltd sets a National Breeding Objective and builds a series of indices to crunch the numbers and comes up with an overall index number to compare animals in an economic sense – dollars in the bank.
Breeding Worth
The old saying that production is 5% breeding and 95% feeding has no place in modern dairy farming. Research shows that on average 30% of the difference in milk production between animals, where all else including age, lactation stage and breed is equal, is because of differences in genetic merit.
Breeding Worth (BW) is the main index used and is a measure of the expected ability of the cow or bull to breed replacements which are efficient converters of feed into profit, expressed as farm income ($)/5000kg drymatter (kg DM).
The value of 5000kg DM was chosen as a reference value in 1996 when BW was introduced, because it was an approximation of the amount of feed a cow consumed at the time.
Farmers use BW to select bulls to use for artificial insemination, select the cows to breed from, choose heifers to purchase and decide which replacements to retain. It makes sense to choose those with the highest BW, because they should make the most money. But temper your decisions with checking out how reliable the numbers are.
While you can get a gut feeling for how well a cow is doing, and maybe how her daughters are milking as well, the only way to tell definitively is to measure them. So what measurements make up the BW?
DairyNZ calls them the seven traits of a highly efficient cow – protein, milkfat, milk volume, liveweight, fertility, somatic cell count, and residual survival. Residual survival is defined as herd life after accounting for the impacts of production, liveweight, fertility, and somatics – in other words, the animal is not culled for those reasons.
In genetic lingo they are called Breeding Values.
All Breeding Values and BW calculations compare a specific animal – for example, Cow 186 – to a genetic base cow, generating either positive or negative values relative to that base cow. The current genetic base cow is represented by the average of the 38,684 cows born in 2000, over the various relevant values.
To derive the BW, each Breeding Value is multiplied by the Economic Value (EV) and the answers added to reach the BW. That way the actual measurements are weighted by the economic attractiveness or not of the trait, eg protein has a high economic value but somatic cell count has a highly negative value.
The EVs are recalculated each February using farm economic models which take into account milk production, milk prices, income from culls and surplus stock, farm expenses and the cost of generating replacements.
For example, the formula for the February 2014 calculation was: Breeding Worth = (Protein x $9.170) + (Milkfat x $2.040) + (Milk volume x $-0.099) + (Liveweight x $-1.660) + (Fertility x $7.180) + (Residual survival x $0.135) + (Somatic cell x $-38.370).
The seven traits are based on data collected onfarm about the cows themselves and their progeny and relatives, through herd testing, weighing, calving records, and culling reasons. Obviously the more records that are collected for each animal, the more reliable the BW is likely to be.
Every BW consists of the actual score and the reliability.
The reliability of the index indicates how likely the index is to change as extra information is gathered, so it effectively indicates the level of confidence in the index value.
Typically a well-recorded heifer starts her life with a BW reliability of about 40%.
Information from her own production gathered through herd testing leads to the reliability increasing to about 55% and when her daughters’ production starts being recorded the reliability can increase to 70% and beyond.
In terms of sires, until a bull has daughters, BW is estimated solely on ancestry information, equating to a reliability value of about 27%.
Once a bull has 75% reliability – about 33 daughters – it is eligible for inclusion on to the Ranking of Active Sires (RAS) list.
At this stage ancestry accounts for about 16% of its BW with the balance based on the performance of his daughters.
For example, if a top bull has a BW of 322/83, 322 means the bull would be expected to breed daughters that are $161 more profitable than daughters of the base cow (he passes on half of his genes to his daughters) and the reliability is 83%. A bull would need about 80 recorded daughters milking to reach this level of reliability.
The RAS list ranks sires nominated by artificial breeding companies by BW. A sire is classified as “active” if he is likely to have at least 500 doses of semen available in the following mating season.
Production Worth
The Production Worth (PW) of a cow is an index that measures the ability of the cow to convert feed into profit over her lifetime. Farmers use the PW index figure for culling and purchasing decisions as they rank cows that are the most valuable over their lifetime performance. They can compare the PW of cows regardless of the breed, or rank the cows in their herd by PW.
The traits measured for PW are milkfat, protein, milk volume and liveweight and again the reliability increases the more a cow is recorded through herd testing. A well-recorded heifer starts her life with a PW reliability of about 20% and after five lactations and some liveweight recording the reliability will increase to about 85%. A cow that is not herd tested will rely on ancestry records and the reliability will
be low.
Lactation Worth
Lactation Worth (LW) is an index of the current season performance and used by farmers for culling cows on their current season.
The traits used to measure the LW index are milkfat, protein, milk volume and liveweight.
Other traits
Farmers all have slightly different traits that they deem important but the BW incorporates those that suit the breeding objective of identifying those that will be the most efficient converters of feed into profit.
The animal evaluation system currently provides genetic information on 26 different traits: milkfat, protein, milk, liveweight, fertility, somatic cell score, residual survival, longevity, calving difficulty, body condition score, adaptability to milking, shed temperament, milking speed, overall opinion, stature, capacity, rump angle, rump width, legs, udder support, fore udder, rear udder, front teats, rear teats, udder overall and dairy conformation. Farmers can use this information to suit their own objectives and weight traits for their own importance.
Base Cow:
The genetic base to which all cows can be compared is the average of a group of animals whose evaluation is set to zero to create a reference point. Base Cow is currently the average of all cows born in 2000.
More:
DairyNZ: http://www.dairynz.co.nz/animal/animal-evaluation/
LIC: www.licnz.com/breeding_worth.cfm
