New Traits To Improve Genetic Merit For Fertility
2 min read
The Fertility Breeding Value (BV) enhances genetic merit in cow fertility. Under 'Pillars of New Dairy System', there's a goal to refine Fertility BV for quicker genetic improvements. The current Fertility BV is based on eight predictor traits, but introducing new measures might boost its precision. A study on 550 heifers revealed that high Fertility BV heifers matured faster and showed better reproductive performance. The findings imply that selecting for cow fertility brings real changes in reproductive outcomes. Moreover, focusing on early puberty might enhance fertility. Now, extensive studies are underway to explore new traits and their impact on fertility, including wearable devices and pregnancy test records to better gauge a sire’s fertility ranking.
The Fertility Breeding Value (BV) has led to gradual improvements in genetic merit for fertility. Under 'Pillars of New Dairy System', we aim to increase the accuracy of the Fertility BV to accelerate genetic improvement in fertility.
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.
We are now testing practical ways to measure new traits at a larger scale. We are following a 2018-born cohort of 5000 cows in 54 herds across 3 regions (Waikato, Taranaki, Otago) to estimate the genetic relationships between novel traits and subsequent cow fertility.
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.
To date, we have estimated an age at puberty trait by blood sampling heifers monthly to detect elevated progesterone. Puberty rate was highly variable, so we surveyed farmers to investigate animal and herd management factors influencing puberty onset. This will help design future routine data collection.
We also determined that age at puberty is moderately heritable (between 20% and 30%) indicating it will respond to selective breeding. We will now analyse first and second lactation data to determine if genetic selection for earlier age at puberty improves reproductive performance.
Other measures under investigation include using wearable activity monitoring devices to estimate age at first heat (as an alternative to age at puberty) and the timing and strength of pre-mating heats in first lactation.
The scale-up study will also provide insights into using pregnancy testing records to measure timing of conception. These are now widely recorded by farmers and could provide earlier, more accurate information on a sire’s ranking for fertility.
How can we lift the national average six-week in-calf rate from its current position of 67%? To find out what we’ve learned and what those findings mean for farmers, join DairyNZ senior scientist Chris Burke, DairyNZ PhD student Melissa Stephen, and Taranaki farmer Tracey Berquist.