The ABC of replacement suckler heifers

There are a number of simple but important factors which apply when sourcing replacements for the sucker herd.

Ai

Replacement heifers should be mated to specially selected AI sires.  Most people cannot justify having a bull to mate a small number of heifers so AI widens the choice.  In addition, young bulls typically have a calving ease EBV accuracy of 40-50 percent.  This is NOT the amount of the trait that is passed on but rather the likelihood of the EBV changing with more data.  In contrast, a widely used AI sire could have a calving ease EBV accuracy of 90 percent or more.  This means the value is unlikely to change over time.  Therefore, a widely used AI sire with a high calving ease EBV is more likely to result in trouble free calving.  One of the barriers to use of AI is the time required to heat detect so synchronisation is an alternative which reduces labour.

Breeding

Farmers often have a preferred breed and continually select stock of that breed.  As animals become increasingly purebred hybrid vigour is lost.  This results in poorer fertility, calf survivability and weaned calf output.  Replacement heifers should be crossbred to maintain hybrid vigour.  This doesn’t mean mongrels but rather the result of a planned crossbreeding programme.  Two or three breed criss cross rotations are the easiest systems to manage in practice and will increase calf output by 20-23 percent over pure breeding systems.

Calving age

Many replacement heifers are still calved at three years of age.  This is wasteful of resources.  Calving heifers at two years of age increases the rate of genetic progress, allows 13 percent more cows to be carried on the same resources, allows poor performers to be culled by 30 months of age and gives a faster return on investment.  Meeting weight for age targets is important if heifers are to be mated at 15 months of age.  Heifers need to achieve 65 percent of their mature weight at bulling (typically 420kg for continental heifers).  

Table 1:  Weight and age targets for two year old calving heifers

Disease free

There are a range of diseases that can affect the fertility and productivity of a suckler herd.  Some of these can be controlled very cheaply and easily by vaccination while other diseases are more complex and hard to control.  Consult with your vet to determine the most appropriate testing and vaccination regime for your herd. There is an AFBI herd health scheme which allows herds to attain accredited status for a range of diseases.  Individual health certificates can be obtained which indicate an animal’s health status and vaccination history.  Particular care should be taken when purchasing breeding stock, especially heifers, that they have a known health status which is similar to, or higher than, your herd’s.

EBVs

Often heifers are selected on the basis of their visual appearance including non-functional traits such as length and curliness of hair, colour of belly and/or udder, presence of eye patches, size and conformation.  None of these is of any value in predicting if they will be able to calve unassisted, produce sufficient milk or progeny with good growth rates.  There are a range of EBVs which do apply to commercial cattle production and breeding stock should be selected using the traits that are of economic importance to each specific situation.

The College of Agriculture, Food and Rural Enterprise (CAFRE), in conjunction with a number of farmers and the NI Simmental Club, has initiated a group to plan the development of a replacement heifer supply chain.  This supply chain will be supported by key technology transfer work undertaken by CAFRE technologists and advisers into strategies for breeding and rearing replacement heifers.  When buying heifers be sure to ask about genetics and health status before purchasing.