Dairy bull proofs are a valuable tool for UK farmers in their long-term herd breeding plans, as they help sort the top bulls from the rest.

There are huge financial benefits, as the long-term profitability of a herd can be improved through breeding. The top PLI (profitable lifetime index) herds are gaining an additional £25,000 margin for every 100 cows compared with the average.

PLI is the financial improvement an animal is predicted to transmit to its daughters in a lifetime and is based on a combination of milk production traits as well as non-productive traits such as fertility, lifespan and somatic cell count (SCC).

However, instead of simply opting for the highest PLI, some farmers may opt for a bull with a more negative figure (ie lower) for SCC, particularly in herds with a high average. Similarly, farmers may opt for a higher butterfat bull to help improve their milk price in the longer term.

To help farmers use the proofs and identify the bulls to use, Farmers Weekly has teamed up with DairyCo in producing this guide to the key indices.

See the chart below.

See also: The latest genomic indices news and download the full Holstein sire indexes table and the full genomic young sire indexes table.

Traits What is it measuring? How is it measured? How is it expressed? Example Performance benefits
PTA (Predicted Transmitting Ability) A PTA indicates the amount of a particular trait an animal is, on average, predicted to pass on to its offspring. Varies by trait (see below) Varies by trait (see below) Choosing a bull with PTAs better than the cow it is mated to, will improve the offsprings. Improved performance of animals in the next generation.
Reliability Reliability figures give an indication of how confident you can be in a bull This figure is based on the amount of information contributing to a bull Reliability figures range from around 30% (low) to 99% (high). Bulls with lower reliability should be used in smaller quantities than those which have high reliabilities. Reliability (risk) should be offset against the animals genetic superiority based on its / (reward).
Overall Profitability
  Represents the financial improvement an animal is predicted to pass on to its daughters in its lifetime. Based on a combination of milk production traits (accounting for 32% of the index), and health, welfare and type traits (accounting for 68%). Good Daughters of a bull with a PLI of 00 more in their lifetime than daughters of a bull with a PLI of zero. Improved financial improvement of the herd based on better performance across a variety of traits, which have been proven to be most strongly linked to lifetime profitability.
Represents the financial improvement an animal is predicted to pass on to its daughters in its lifetime within a spring block calving system, targeting 4,500kg milk making extensive use of grazing Based on a combination of milk production traits (accounting for 29% of the index), and health, welfare and type traits (accounting for 71%).   Daughters of a bull with a SCI of n daughters of a bull with a SCI of zero.    
Production Traits
Milk, Fat, Protein kgs and Fat%, Protein% Predicts the additional yield a daughter is expected to produce in a standard 305-day lactation and recognises the components of milk. It is designed to maintain the quality of milk. Test day records from official milk recording (CIS, NMR, UDF) in the first five lactations are used and are adjusted to account for the non-genetic effects, such as lactation number, days in milk, age and month of calving. Milk kgs (-1000 to +1000)
Fat kg
Prot.kg
Fat%
Prot%
Daughters of a bull with a PTA of 650kg milk are on average predicted to produce 650kg more milk in a lactation than the daughters of an average bull whose PTA is zero. Higher genetic potential for production traits. Producers on a liquid or specialist contract may wish to consider changing the emphasis when selecting bulls. E.g. For liquid producers a heavier emphasis may be placed on kg of milk.
Fitness Traits
LS (Lifespan) Predicts the number of lactations a bull Calculated from actual daughter survival where that information is available.
When it is not, (eg. for young bulls), information on type (feet, legs and udder), cell count and family is used to make the best possible predictions of lifespan.
Expressed on a scale of around of -0.5 to +0.5-0.5 Bad
+0.5 Good
Daughters of a +0.5 bull are predicted to survive, on average, 0.5 lactations longer than daughters of a bull with a lifespan PTA of zero, so they will milk for around 150 more days. Extra longevity potential and a reduction in involuntary culling to improve replacement rates.
SCC (Somatic Cell Count) Predicts the somatic cell count of daughters during a standard 305 day lactation. Measured in the first five lactations. Expressed as a percentage on a scale between roughly -30 to +30, with negative figures being desirable as they indicate a lower SCC.-30 Good
+30 Bad
Daughters of a bull with a -10 SCC are expected to have cell counts 10% lower than daughters of a bull with a SCC Index of zero. Improved udder health, both in reduced SCC levels and number of mastitis cases, as lower SCCs also genetically improves resistance to mastitis.
F.I. (female Fertility Index) Predicts how fertile a daughter will be. Calculated predominantly from daughters Expressed on a scale of around -15 to +15 with each point representing, on average, a half day reduction in calving interval and half a percent improvement in conception rates.-15 Bad
+15 Good
A +10 bull Improved fertility with shorter calving intervals and higher conception rates.
Maintenance (Maint.) Predicts the cost of maintenance of an animal during its lactation; promoting those that are more efficient Based on an animal Expressed on a kg based scale +50kg to -50kg. Negative being favourable for reducing maintenance cost and improving efficiency. Daughters of a -10 bull and all other traits being equal, will be more efficient than a daughter from a +10 bull. Reduced maintenance cost and improvement in animal efficiency to meet chosen farming system.
Type Traits
Linear traits Predicts the sort of conformation a bull will transmit to his daughters Heifer conformation scores from official classification visits by the herdbook or CDI A bull It is most important to be aware that, because linear
assessment measures the degree and not the desirability of each trait, the highest score is in many cases not necessarily the most desirable.
Correct functional conformation problems, or select the size of cows needed to suit your system.
Composite traits
(Feet and legs, mammary and type merit)
Predicts the sort of conformation a bull will transmit to his daughters. Heifer conformation scores from official classification visits by the herdbook or CDI. Expressed on a standardised scale between -3 to +3. Animals with type evaluations below Unlike Linear traits, Composite traits score the desirability and bulls with indexes above zero are predicted to make an improvement.
The two
Improved feet and leg or mammary conformation.
Calving Traits
dCE (direct Calving Ease) Predicts the ease with which a calf by that sire will be born. Based on calving ease observations collected through regular milk recording or as part of a progeny test programme. Expressed on a scale of -4 to +4 around a breed average of 0. -4 very difficult calving
+4 very easy calving
Calves born from a bull with a calving ease score of +3.0 are expected to have a 3% more easy calvings. Reduced calving problems, which is particularly important when sires are mated to maiden heifers.
mCE (maternal Calving Ease) Predicts the ease with which a daughter of that sire will give birth. Based on calving ease observations collected through regular milk recording or as part of a progeny test programme. Expressed on a scale of -3 to +3 around a breed average of 0. -3 higher percent difficult
+3 higher percent easy
Daughters of a +2.0 bull will on average have a 2% higher number of easy births as mothers. Long-term improvement of calving ability of the female herd.