The Fertility BV (re-calving within 42 days of the start of calving) is currently calculated by eight predictor traits, but new measures of cow fertility could improve its accuracy.
To identify new traits, we generated a unique herd of 550 heifers with high (+5%) and low (-5%) Fertility BV. We studied their fertility and other traits during rearing (2015-17) and their first (2017-18) and second (2018-19) lactations.
What are the key findings?
- High Fertility BV heifers reached puberty 21 days earlier and 25 kg lighter than the low Fertility BV heifers, despite growing at the same rate.
- High Fertility BV heifers also had a 9% higher 6-week In-Calf rate during their first mating period, compared with low Fertility BV heifers.
- 6-week in-calf rates were over 30% greater during lactation 1 and 2 in high Fertility BV cows.
- The superior reproductive performance in high Fertility BV cows was driven by their greater ability to resume cycling post-calving. This led to 38% and 25% greater 3-week submission rates during lactations 1 and 2, respectively.
- Without hormonal interventions, almost half of the low Fertility BV cows had still not cycled after 6 weeks of breeding during lactation 1.
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What does this mean?
- Genetic selection for cow fertility results in tangible differences to herd reproductive performance.
- A cow’s genetic merit for fertility affects her ability to start cycling post-calving and therefore calve in the first six weeks next season.
- Using high Fertility BV bulls will improve your herd’s fertility.
- There are biological differences controlling reproduction that can be used to identify new traits to improve the Fertility BV.
- Both 'puberty' and 'heifer reproductive measures' are potential early predictors of subsequent cow fertility.
What next?
We are conducting a study to measure puberty onset and its genetic relationship to subsequent cow fertility in 5000 animals across over 50 commercial herds.
This scale-up study began in Autumn 2019 working with farmers with good quality herd records. We are using large numbers of animals with diverse Fertility BV to obtain robust estimates of genetic relationships across a range of farming operations.
The purpose is to assess the value of including puberty as a predictor trait to improve the Fertility BV.
