Sire selection represents the key breeding decision, with long-term effects on animal performance, health, welfare and overall farm profitability.  Today’s breeding decisions will result in replacements entering the dairy herd in 2011, with a direct impact on herd performance lasting to 2015 and beyond.

Sire proofs work in practice

The breeding values of sires for an increasing range of traits are now available. These values are expressed as Predicted Transmitting Abilities (PTAs) which measure the average value of traits transmitted from a sire (or cow) to its progeny and are derived from the performance of the animal and all known relatives.

Increasingly, genetic information on fertility, health and longevity traits is becoming available for sires.  Whilst such traits are very much affected by herd health, feeding and management, genetics has also a significant effect.

In regard to reproductive performance, the genetic variation in daughter fertility produced from different sires has been found to be relatively large, meaning that significant genetic progress can be made.  Thus in sire selection it’s important that appropriate consideration is given to health and fertility traits, (published for example, at www.ukcows.com and www.DairyCo.org.uk )

Selection indexes are useful tools

An index of total economic merit is a combination of an animal’s predicted transmitting ability (PTA) for all economically important traits, with each trait weighted by its relative economic value.

In the UK, the index of total economic merit, Profitable Lifetime Index (PLI), has recently been amended, based on research carried out by Scottish Agricultural College (SAC) on behalf of DairyCo.  In general terms, the new PLI has a reduced emphasis on production traits and an increased weight on the ‘fitness’ traits in line with their future expected economic values. to farmers. Consequently, the predicted genetic response to selection on the new PLI indicates that alongside increased production, lifespan will increase, somatic cell count will decrease, feet and legs and udder traits will improve and the decline in fertility traits will have nearly been brought to a standstill.  In addition the new PLI is presented as a ‘true’ Profitable Lifetime Index and so reflects the profitability differences of the progeny over a lifetime, rather than per lactation as undertaken previously.

The relative economic values for traits within selection indices are determined from national farm economic models.  These models continually develop to take into consideration changing market outlooks, new environmental considerations and developments in production systems.  AFBI is currently carrying out work in this area, with SAC, examining the relative economic values for production and non-production traits in 7,000-8,000 litre systems.  Modelling work has shown these moderate output systems are optimum over a range of milk pricing/input price scenarios and are likely to be the “norm” for the majority of the industry in Northern Ireland.

Sire selection for use on maiden heifers

Ease of calving is an important consideration in selecting sires, particularly for use on maiden heifers. Calves are more likely to die if they have experienced calving difficulty.  Calves born from a difficult calving are also more likely to be weak or have low vigour, and these grow more slowly to weaning and are more susceptible to other diseases.  On the cow side, there is evidence that dystocia reduces milk yield, increases the risk of mastitis and increases the chances that a cow will be prematurely culled.

In terms of sire selection, it is important to note the negative genetic relationship between genetic merit for ease of calving and subsequent maternal calving ability.  Within a breed, female calves born more easily are expected to show greater difficulties when giving birth as dams, because of reduced pelvic dimensions.  Hence selection for both direct and maternal genetic components of calving ease is the best way forward.

Currently some genetic information is available on direct calving ease for sires.  Work by SAC is currently being undertaken, with input from AFBI Hillsborough, to better quantify the relative economic value of calving ease and enable the incorporation of direct and maternal calving ease traits into selection indexes. At present no UK data is available for maternal calving ease, hence type predictors such as rump width are the only available option.

Current sire selection

For the first time, we have information regarding the basis for sire selection by dairy producers in Northern Ireland based on the AFBI/CAFRE heifer survey. The key messages from this AFBI/CAFRE work undertaken over the last 12 months are summarised below.

• In Northern Ireland, whilst the use of AI is extensive, it is still lower than some of the other main dairy producing countries and there is scope for increased use of AI. 62% of producers use AI for the majority (50% plus) of their heifer matings. With mature cows, the use of AI is slightly greater, with 69% of producers using mainly AI for breeding.

• A high proportion of farmers consider ease of calving and PTAs for milk composition as very important criteria in sire selection (Table 1). In addition, milk yield and type traits are considered very important by a significant proportion of producers. There were no indications of any significant use of the fertility index in sire selection.

• Surprisingly, only a relatively small proportion of farmers consider that PLI is very important, with significantly more assessing it either as unimportant or had no opinion on it.

• • Table 1.  Sire selection criteria for use on maiden heifers

    Criteria	% of producers assessing as very important	% of producers with no opinion or consider unimportant
    Ease of calving	56	5
    Milk composition	44	12
    Type traits	26	21
    Milk yield	22	16
    Selection index (PLI)	7	43.5
    Cost of straw	6	34

    Genomic selection

    Increasingly, genomic (DNA) data will be incorporated into future dairy cattle selection programmes. This will enable more accurate selection index evaluations and direct increased genetic gains. Inclusion of genomic data in national evaluations is expected to increase genetic progress by around 50% over the next 10-15 years.

    The use of genomic information in the livestock industry is not a new phenomenon. Many farmers and AI companies routinely send hair samples for parentage identification, as well as the detection of genetic defects such as BLAD and CVM.

    AFBI have developed a resource in this area enabling parentage verification in support of animal identification (contact Dr Adrian Allen, VSD, Stormont: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ). Current research, in partnership with The Roslin Institute (University of Edinburgh), funded by the BBSRC, is investigating whether host genetics influences TB susceptibility in cattle. This potentially involves identification of DNA markers linked to TB resistance, which could be used to breed for reduced TB susceptibility.

    Main messages

    1. Sire proofs are a reliable indicator of progeny performance.

    2. Only high PLI bulls are made available by breeding companies.

    3. Genetic evaluations for fertility, health and welfare traits are becoming increasingly available.

    4. Selection indexes, such as PLI, are the best way to combine information on the large number of traits now available for sires. Currently, the PLI is only considered important by a minority of producers. It will be important to address this. AFBI work looking at selection indexes specific to Northern Ireland circumstances will play a role here.

    5. The accuracy of selection indexes will increase further with the introduction of genomic information. In addition, new possibilities for breeding for disease resistance are likely to develop.

    
    
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