GENERATION NEXT LOVES MATHS
WITH LIVESTOCK IMPROVEMENT SEMEN YOU ARE MAKING HIGHER LEVELS OF GENETIC GAIN, FASTER. THIS ISN’T A ONE OFF IMPACT. IT ACCUMULATES (LIKE INTEREST) TO CREATE A MULTIPLIER OF GENETIC GAIN. GENERATION INTERVAL
is shortened by breeding with young animals. For example, if we only use progeny tested bulls as sires of sons, they will be at least five years old. By using genomic selection we are now using some bulls for contract mating as yearlings.
THE BREEDERS EQUATION The rate of genetic gain for any trait, in any species, is explained by the Breeders Equation:
RATE OF GENETIC GAIN
SELECTION INTENSITY is increased when
SELECTION INTENSITY X ACCURACY X GENETIC VARIATION GENERATION INTERVAL
Therefore, to increase the rate of genetic gain, the farmer should seek to influence the four variables, increasing those above the line, and decreasing the generation interval. The equation follows simple rules of arithmetic. For example;
A
B
C
2 12 6
4 12 3
3 18 6
Therefore, if the generation interval is reducedB or if the selection intensity, accuracy or genetic variationC increased, the rate of genetic gain will increase.
the animals used for breeding are selected from larger populations. If we looked for bull mothers just in a single region, selection intensity would be relatively low compared to a nationwide search using the LIC database which includes millions of herd tested cows across the entire country.
ACCURACY
refers to the extent to which the measure we use represents the trait in question. For example, a bull’s Calving Difficulty BV is based on the % of assisted births in his daughters when they are first-calving heifers. This is considered more accurate as a measure of Calving Difficulty than, say, average birth weight of his calves.
GENETIC VARIATION is essential if genetic progress is to be made. For example, all cows have four legs so we cannot breed a fivelegged cow. There is no genetic variation in the number of legs. By comparison, the genetic variation for protein production is large, so we can select high-ranking sires and dams and achieve genetic progress for this trait.
GENETIC GAIN The Genetic Gain graph below shows the proportion that genetics contribute to the trend in milk solids production. Plus highlights the fact the average New Zealand cow is not increasing in size/weight.
GENETIC GAIN 80 70 60 50
Kg
40 30 20 10 0 90 991 992 993 994 995 996 997 998 999 000 001 002 003 004 005 006 007 008 009 1 1 2 2 2 2 1 2 2 1 2 2 1 2 1 2 1 1 1
19
MILKSOLIDS PERFORMANCE TREND
MILKSOLIDS GENETIC TREND
LIVEWEIGHT GENETIC TREND
Over the past 19 years, average New Zealand Milk solids production has increased by 70 kg per cow. Of this 42kg is attributed to Genetic Improvement while the average live weight has remained constant.
THE STAIRCASE EFFECT The Cumulative Genetic Gain Graph shows that yearly there are small gains but cumulatively over 10 years the improvement is great.
THE STAIRCASE EFFECT
CUMULATIVE GAIN
INCREASING GENETIC MERIT
1ST YEAR
2ND YEAR
3RD YEAR
10TH YEAR
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