Like all genetic indexes, the benefits of PLI accumulate over the generations. Breeding is an extremely efficient means of improving the long term profitability of a herd.
- PLI should be used as the initial screening tool in bull selection. Focus on the top 50% of bulls, ideally with a PLI of over 70. Try to avoid using bulls with PLI of less than 50.
- Look within this group for the traits which most need improving in your herd. This will vary with individual herds but should include lifespan, SCC and fertility.
- Type traits should be considered after the health and fitness traits.
- Choose a group of four or five bulls with different strenghts and weaknesses and pick at least one of these with a positive direct calving ease score to use on a maiden heifer.
- Buy more semen from each of your high reliability bulls and less from each of the lower reliability bulls.
- Avoid inbreeding which can be checked in breeding programs offered by most AI companies and breed societies.
Reliability figures give an indication of how confident you can be in a bull's indexes. The figues can range from around 30 - 99%. Risk should be spread by using some bulls with more then 95% reliability which can be used alongside other interesting, less reliable bulls on the rest of the herd.
Genetic indexes for a variety of type traits predict the sort of conformation a bull will transmit to his daughters. Some type traits influence a cows ability to produce profitable milk over a long lifetime. Others have little or no bearing on her profitability at all. The two 'functional' type traits most strongly associated with profitability are udder composite and locomotion (or feet and legs where locomotion is unavailable). Both are included in PLI. Dairy farmers may wish to place a heavier emphasis on type than included in PLI, but should be aware that selection for these traits will not necessarily improve profitability.
Range of values for type and fitness indexed currently included in PLI
|Somatic Cell Count (%)||+30||-30|
|Conformation (locomotion & udder composite)||-3||+3|