Genetics Theory
A genetic index is a measure of an animal’s ability to pass its genes on to the next generation. These could be for any trait that can be inherited and measured. Here, we introduce the basics of genetic indexes and predicted transmitting abilities (PTAs), why they are needed and how they are calculated.
High-quality cows with good genetics are at the heart of profitable dairy farming. Without this, there is a limit to your herd’s performance, no matter how good your management is.
This is not just about genetics for milk production, it is also about health, welfare, management and type traits, which all contribute to your profitability.
Poor breeding decisions can mean the difference between profit and loss, yet the time, cost and effort needed to make good breeding decisions is much the same as for bad ones.
The effects of breeding decisions build up over generations, meaning that improvements can be introduced over just a few years through the breeding choices you make.
A genetic index is a measure of an animal’s ability to pass its genes on to the next generation. These could be genes for production, health, lifespan, conformation or for any trait that can be inherited and measured.
Although we are most familiar with genetic indexes for milk, fat and protein, their application for non-production traits is becoming increasingly important, especially for animal health and welfare.
In the UK, most genetic indexes are expressed as predicted transmitting abilities (PTAs), which predict the extent to which a trait will be passed on to an animal’s offspring.
PTAs do not predict the offspring’s actual performance, which will vary widely depending on management, but instead predict the amount of a trait the offspring will, on average, receive from its parents, compared with ‘average’ parents whose PTA is zero.
This principle applies to both male and female PTAs, and both to indexes based on actual and progeny performance and those based on family and genomic information.
Genetic indexes attempt to disregard the effects of environment and to strip performance down to the bare genetics. This means that a 12,000-litre cow from a high-input system can be compared with one in an extensive herd averaging 6,000 litres. Equally, bulls whose daughters are milking in different production systems can also be fairly compared.
Using genetic indexes, you can make accurate breeding decisions based on the predicted performance of a bull’s daughters.
Our profit indexes – Profitable Lifetime Index (£PLI), Spring Calving Index (£SCI) and Autumn Calving Index (£ACI) – can save you time analysing the many individual traits that are available to dairy farmers.
The indexes allow you to easily rank animals that transmit the most profitable combination of genetic traits to suit your farming system.
They show the additional profit a bull is expected to pass on to his daughters compared with a bull with an index of zero in a year-round, spring block- and autumn block-calving system respectively.
These indexes are reviewed every year by a forum that includes farmers, breed societies, vets and other breeding industry stakeholders. The forum fine-tunes the indexes as the need arises, looking at the genetic progress dairy breeds are making and the long-term market outlook for inputs and output.
