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News
18 May 2001
Sire Breeding Values for Cow Fertility
Maintenance of the reproductive performance of New Zealand’s national herd is important for achievement of industry productivity targets at the farm level. Sire breeding values for cow fertility have been published, using data from over ten million records from the national database relating to mating and calving events in the 1990s. There is noticeable variation in the reproductive performance of the daughters of different sires. Publication of sire breeding values for cow fertility enables the industry to avoid the use of sires whose daughters have unacceptable reproductive performance.
The reproductive cycle on New Zealand dairy farms features a compact calving period in the late winter. An accepted target is for 97% of the herd to calve in the first 56 days of the calving period. To achieve a compact calving, the accepted target for submission rate in the first 21 days of the mating period is 94% (Chris Burke, Managing Your Herd To Meet Reproductive Targets, Dairying Research Corporation, 1999).
In this seasonal system, records most relevant to reproductive performance are
- whether the cow has a recorded mating in the first 21 days of the herd’s mating period;
- whether the cow succeeds in bearing a calf in the early portion of the herd’s calving period.
Over ten million such records (collected from 1990 to 2000) have been analysed to produce sire breeding values for cow fertility. The calving records relate to whether the cow has successfully carried an AI calf. (In New Zealand, nearly all herds have a limited AI period of around 4-5 weeks.)
Some bulls leave daughters that are more likely to calve during the first few weeks of the calving period - while cows are bearing AI calves. Some bulls leave daughters that are much less likely to calve in this early period. For some extreme bulls, 10% fewer of their daughters will calve in the early period (when AI calves are being born) compared to average herdmates. For bulls that are transmitting the highest cow fertility, around 5% more of their daughters will calve in this early period compared to average herdmates.
Breeding Values
Breeding Values (BV) for cow fertility have been developed for Animal Evaluation. A summary of BVs is shown in Table 1 for the bulls enrolled for Animal Evaluation, born since January 1980, and with at least one daughter with a fertility record.
Table 1: Sire Breeding Values for Cow Fertility
Breed # of Sires Average BV Maximum BV Minimum BV
Holstein Friesian 3417 -2.3 10.4 -22.5
Jersey 1704 0.9 7.8 -10.3
Ayrshire 521 -5.3 8.2 -24.8
Other 263 -3 8.5 -14.9
Interpreting the Breeding Values
The Breeding Value refers to the genetic merit of a bull to leave daughters with the ability to conceive and bear a calf early in the herd’s calving period. It is expressed as a percentage.
A Breeding Value of +6% indicates the bull will leave daughters that are 3% more likely to calve in the early calving period, compared to the daughters of bulls with a Breeding Value of zero (a bull passes half of its BV on average to its immediate offspring).
How are the BVs calculated?
Two types of records are used:
- Records of the cow showing heat and being mated in the first three weeks of the herd’s mating period (if she is mated in the first three weeks of the herd’s mating period she scores “1”, and if she fails to be mated in the first three weeks she scores “0”);
- Records of bearing an AI calf in the subsequent season (if she successfully bears an AI calf she scores “1”, and if she fails to bear an AI calf she scores “0”).
Records are used from matings in the first lactation, and re-calving in the second lactation; matings in the second lactation and re-calving in the third lactation; and matings in the third lactation and re-calving in the fourth lactation. Records from 1990 onwards have been used. In total, 10 million records have been included in the evaluation.
The evaluation makes use of the genetic inter-relationship between the records. The final reported breeding value relates to the likelihood of successfully bearing an AI calf in the second lactation. This likelihood is very closely related to the records of mating in the first three weeks of the mating period in the first lactation – so we have daughter fertility information before a sire’s first-crop heifers have re-calved as three year olds.
The genetic assessment for cow fertility is based on herdmate comparison (as it is for all traits). In effect, the percentage of a bull’s daughters being mated in the first three weeks in a particular herd is compared against the average for that age group in that herd. A bull’s proof is not advantaged or disadvantaged if he happens to have a large number of his daughters in herds where submission rates in the first three weeks are unusually high, for example.
Fertility enters the Breeding Worth indirectly as a component of longevity. Further research is directed toward identifying the direct cost of reduced cow fertility, with a view to possible inclusion of the trait as a sixth trait in the Breeding Worth (alongside Protein, Milkfat, Volume, Liveweight and Longevity).
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