NZ Breeding Worth
Breeding Worth (BW) ranks dairy cattle on their expected ability to breed profitable and efficient replacements. BW is calculated by combining Breeding Values (BV) with the appropriate Economic Values (EV). BW and BVs are scored relative to the Base Cow whose information has been set to zero.
Breeding Values (BV) make up BW and are an estimate of a cow or bull’s genetic merit. There are eight traits in dairy cattle which have been identified as having a direct economic impact to the farmer.
Economic Values (EV) are the estimated NZ$ amount each BV is worth to the farmer.
Cattle are expected to pass half their BV onto their offspring. For example, a bull with a Milkfat BV of 40kg indicates he will sire daughters that, on average, are genetically superior to the NZ Base Cow by 20kg of Milkfat per 5t DM consumed.
- Milkfat: $1.90/kg
Milkfat is 30% heritable. You should aim to increase the Milkfat breeding value of your herd over time. In New Zealand, genetic gain has been consistent at around 1kg per year.
- Protein: $6.63/kg
Protein is 31% heritable. You should aim to increase protein breeding value over time. Genetic gain has been around +1.1 kg/year
- Milk Volume: -$0.088/l
Milk is 36% heritable. Genetic gain has been pretty consistent at around +19 litres/year with greatest rates of genetic gain in Friesians.
- Liveweight: -$1.31/kg
Liveweight is 35% heritable. You should aim to maintain liveweight breeding value over time. Liveweight breeding values are slowly increasing over time.
- Fertility: $6.41/%
Fertility is 9% heritable. You should aim to increase fertility breeding value over time. New Zealand has been able to achieve the tightest calving interval worldwide. Highly fertile cows have been necessary to achieve this. It is generally accepted that the NZ Base Cow is far more fertile than any other country’s base.
- Somatic Cell Count: -$37.09/unit SCC
Somatic cell score 15% heritable. You should aim to lower somatic cell score breeding value over time. (Negative is best). A useful approximation for farmers to note, is a difference of 0.5 in breeding value equates to a difference in expected daughter performance of 35’000 bulk milk count.
- Residual Survival/Total Longevity: $0.123/day
Residual Survival/Total Longevity is 6% heritable and indicated how long daughters are expected to be in the herd. You should aim to increase Residual Survival/Total Longevity over time.
- Body Condition Score: $94.41/BCS points
Body Condition Score is 25% heritable. You should aim to increase Body Condition Score over time. Body condition score affects dry matter intake, milk production, reproduction, and cow health and welfare.
- Gestation Length
Gestation Length is highly heritable at around 50% heritable. Gestation Length breeding values are estimated from the difference from a progenies planned calving date and her actual date of calving. Sires with negative gestation length breeding values will ensure that gestation lengths of progeny born are shorter than 282.5 for males and 281.2 days for females.
- Calving Difficulty
Calving difficulty is 4% heritable. Its breeding value is estimated from calving assistance information collected in progeny test herds and via data recorded in herd management software. Sires with negative calving difficulty breeding values will produce progeny that cause less calving difficulties than average.