Production PTAs (predicted transmitting abilities) show the potential for traits such as milk, fat, protein and persistency to be passed on to the next generation.
These PTAs allow selections that produce cows to suit your milking contract.
Genetic indexes for production were the first to be introduced and have played an essential part in the increases in milk production that farmers have achieved in recent decades.
Milk, fat and protein
The production traits for which all male and female dairy cattle are assigned a genetic index are as follows:
- Milk (kg)
- Fat (kg)
- Fat (%)
- Protein (kg)
- Protein (%)
The range of values for a PTA will vary from trait to trait. For example, a milk (kg) PTA may exceed 1,000 kg, whereas a fat (kg) PTA is unlikely to be more than 50 kg.
Bulls’ persistency PTAs give you an indication of their daughters’ ability to maintain production throughout lactation.
Persistency PTAs are expressed as a percentage of yield at 280 days compared with yield at 60 days. These vary depending on breed, but for Holstein bulls, they commonly fall within the range of 57% (low persistency) to 67% (high persistency).
A higher persistency PTA generally reflects a flatter lactation curve, which is believed to result in fewer metabolic problems. This may result in better health and fertility. However, there’s not yet any UK research to confirm the genetic link between lactation shape and health traits.
We recommend only using persistency PTAs for a secondary screening of bulls.