BULL SELECTION – MAKING THE DECISION EASY!

The choice of bull used on your dairy cows today determines the production, type and health of your herd for many years in the future.  Sifting though all the promotional data and factual information available on sires is a significant task at a busy time of year.  However setting an objective by indicating basic and simple breeding criteria can pay dividends for both the herd and the farm business.  Choosing a bull should be based on some or all of the following considerations:

a) Production traits: milk, fat and protein;

b) Type traits: udder, feet and legs;

c) Health and longevity traits: productive life, somatic cell count (SCC), and calving ease.

It is essential to prioritize or rank the various traits important to your own farm situation.  The weight placed on each of these traits should be a direct reflection of future market demands.  At lower milk prices, the milk compositional quality payments will contribute a larger proportion of the milk price and therefore make high milk component sires more desirable for dairy herd profitability.  General advice in the past has been to consider health and welfare traits such as SCC as secondary and to be taken into account only after initial screening on production and conformation.  However, the continuing emphasis towards improving cow longevity means these traits for SCC and fertility need to be given higher priority.

The purpose of Predicted Transmitting Ability (PTA) is to rank bulls against set selection criteria.  If a bull has a PTA of +1,000  KG of milk, it does not mean that his daughters will produce 1,000  KG more milk than their herd mates.  It means, that the daughters of this bull have an average milk production 1,000  KG higher than the daughters of the bulls used in the genetic base.  All PTA’s are expressed in terms of deviations from a fixed genetic base which is currently the PTA2005.  The base year heifer equivalent production for PTA2005 is 7538  KG milk, 3.79 percent  fat and 3.22 percent protein.  An example PTA for a bull could be expressed as follows:

The daughters of this bull are expected to give on average 384 KG more milk, 24.1 KG more fat and 17.6 KG more protein than cows whose sire has a PTA of 0 KG milk, 0 KG fat and 0  KG protein.

PTAs are also available for somatic cell count (SCC) and lifespan expressed as a percentage, i.e.  percent PTA.  The overall range of  percent PTAs found is +/- 30 percent.  In practice however, 95 percent of the bulls lie in the range +/- 10 percent. As with production PTAs, the interpretation is the same.  For example, taking two bulls, one with a  percent PTA of –10 percent and the other with a  percent PTA of +10 percent.  The first bull is expected to pass on to its daughters a 10 percent reduction in SCC levels, whereas the second bull is expected to pass on a 10 percent increase.  The difference between the daughters of the bulls is therefore 20 percent. It is important to note that a negative  percent PTA SCC indicates a reduction and is therefore desirable as this should lead to a reduced incidence f mastitis.

The fertility index offers producers the potential to make considerable improvements in herd fertility throughout the breeding season.  With a range of values from – 10 to +10, higher index bulls will result in improved fertility.  Every point increase in a bull’s fertility index is assumed to decrease calving interval by approximately half a day, and improve non return rates by around 0.5 percent in his daughters.  Caution must be exercised when interpreting the fertility index as it’s heritability is not high in comparison to the production traits.  Producers should not use it as a primary selection criterion as there is a danger of breeding cows with good fertility at the expense of milk production.

Profit Index or £PIN is an economic index calculated from milk, fat and protein PTAs. Each of the PTAs for milk, fat and protein are weighted according to:

PIN is expressed as a financial value and reflects the expected increase in revenue per lactation for each daughter.  Profitable Life Index or £PLI is another economic index (similar to PIN) but it recognizes that milk production is not the only factor to influence profitability and it includes weightings for production and longevity.

Sire selection should focus on where the anticipated market is likely to be in four to five years.  The aim should be to improve the current cow genetics.  Sire selection has a long-term impact, as the daughters produced from the mating will remain for a considerable number of years.  The purchase of semen should therefore be viewed not as a short-term expense, but as a long-term investment into the efficiency and profitability of the herd.