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Pruebas NZ y su interpretación
Reading New Zealand Bull Proofs
Breeding Worth
New Zealand ranks dairy bulls and cows by Breeding Worth (BW) for their expected ability to breed profitable and efficient replacements. The ranking compares across ages and breeds.
Currently the traits included in Breeding Worth and the associated economic values are:
BW = ($6.328 x Protein)+($1.251 x Fat)+($-0.070 x Milk) +($-0.987 x Liveweight) + ($1.638 x Fertility) + (-21.744 x Somatic Cell) + (0.033 x Residual Survival)
February 2006
In general the higher the BW of the bull the more profit likely to be produced by his offspring. The top bulls in New Zealand are now in the 200-250 BW range. Some care needs to be taken when using this figure, however, as the economic weights used in its calculation are specifically based on the New Zealand economic environment.
Traits other than production (TOP)
In general, bulls with TOP Breeding Values (BV) between -0.30 and +0.30 are not expected to influence much change in the trait. The general range for most traits is between -1.00 and +1.00.
The descriptors of rump width, capacity and dairy conformation are assessed in relation to the animal's size. This is different to almost all other major dairying countries and is beneficial because it enables the identification of animals that leave strength, width and desirable frame traits regardless of the animal's stature.
For ease of assessment Livestock Improvement New Zealand Genetics™ deviates stature within breed so customers can easily identify stature improvers and reducers within their breed group. Without this, all NZ Jerseys would appear small and all Holstein-Friesians would appear tall.
Farmer scored traits
The four management traits (Adaptability to milking, Shed temperament, Milking speed and Overall opinion) within the New Zealand TOP graph are scored by farmers who milk the bull's daughters.
Adaptability to milking measures how quickly the animal settles into the milking routine; Shed Temperament measures the cow's demeanour once she has settled into the milking routine; Milking Speed is a subjective measure of how long it takes an animal to complete the milking routine and Overall Opinion is the farmer's assessment of whether he/she liked the animal.
Total Longevity (days)
A sire transmits half of its Longevity Breeding Value to its daughters.
Consequently a bull with a Longevity Value of +200 days is expected to leave daughters that will last 100 days longer, in the average New Zealand herd, than a bull with a Longevity of zero. For comparison purposes the average pure Holstein sire has a Total Longevity BV of -172 days.
Fertility
This within breed index evaluates sires on their ability to produce daughters that conceive and bear a calf early in the herd's mating/calving period.
It is expressed as a percentage; for example, a Holstein-Friesian sire with a 6% Fertility figure is expected to leave daughters that are 3% more likely to calve in the early part of the herd's calving period than the average cow born in New Zealand in 1985. For comparison purposes the average pure Holstein sire has Fertility BV of -4.1%.
Comparing across breed
New Zealand's Animal Evaluation Model ranks animals across breeds. As Jerseys are generally smaller and produce less milk than Holstein-Friesians, most Jersey sires will have negative values for Stature, Liveweight and Milk Volume on an across breed base. To help evaluate individual bulls within breed Livestock Improvement New Zealand Genetics™ has presented Stature, Liveweight and Fertility proofs within breed for its website and catalogues.
Other Breed averages for traits that differ markedly between breeds are indicated below.
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Trait
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Holstein Breed Average
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Jersey Breed Average
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Milk Volume (l)
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1081
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-118
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Liveweight (kg)
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82.4
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-45.6
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Stature
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1.48
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-0.77
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Fertility (%)
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-5.4
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0.9
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Calving Difficulty %
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6.5
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-5.7
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MilkFat
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25.7
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12.6
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Protein
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32.1
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5.1
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Source: AEU - 13, August 2005
Calving difficulty
The Calving Difficulty BV evaluates the suitability of a bull for use over yearling heifers. As this trait has a low heritability, and therefore generally lower reliability, Livestock Improvement New Zealand GeneticsTM considers the BV, along with its reliability before assigning a bull to one of three groupings - easy, average or difficult.
Farmers are able to make an individual assessment of this BV by calling their local Livestock Improvement New Zealand Genetics™ representative.
New Zealand Fat and Protein %
The Fat % and Protein % are estimates of a sire's ability to transmit milk components. In a grass-based system the daughter of a bull that transmits a 5.0% fat test, and a cow with 4.0% fat could be expected to test 4.5%.
Percentage KiwiFriesian
Percentage KiwiFriesian indicates the degree of New Zealand Holstein- Friesian blood in a sire's ancestry.
To be classed as a KiwiFriesian a sire must have more than 50% KiwiFriesian blood. If it does not say KiwiFriesian, it does not come from Livestock Improvement New Zealand GeneticsTM
NB: KiwiFriesian was formerly referred to as New Zealand Friesian.
Short Gestation Length (SGL)
One objective of Livestock Improvement's breeding programme is to produce sires that will shorten the gestation length of the modern dairy cow. This programme is now graduating sires that will tighten calving patterns, particularly when used towards the end of the herd's mating period. These sires are indicated in our catalogue.
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