Pre-joining management in southern beef cattle production is integral to optimal breeding performance of the herd. Heifers are often the focus of much attention because of their significant potential contribution to future earnings of the herd. They have key susceptibilities over older cows – their immune system is still maturing and they are continuing to grow themselves whilst also being reproductive.
Here are some suggestions on how producers might aim to maximise their heifers’ health and reproductive potential:
1. Focus on Critical Mating Weight (CMW)
Critical Mating Weight (CMW) by definition is a target weight for maiden heifers when they’re first joined to bulls to receive 84% pregnancy rate in a 6 week joining period (2 cycles). In British beef breeds this is usually around 280-300 kg but in larger framed, Bos indicus or European breeds, the CMW is around 300-320 kg. The earlier a heifer reaches her CMW, the earlier she will start cycling and be able to conceive (puberty).
An easy simplified idea of CMW is the weight of a heifer when she has grown to 60-65% of her mature cow weight. If her mature weight is 500kg, then her critical mating weight is 300 kg. This weight is considered minimum so producers should be aiming to have heifers heavier than this at the time of joining.
Faster growing animals will therefore reach their CMW earlier. It may be helpful to weigh heifers at puberty to identify those faster-growing individuals. Regular weighing can also be useful three months prior to joining, so adequate time is available to increase nutrition and growth prior to joining. Follow up weighing can assess progress.
2. Vaccinations & Animal Health
Internal parasites (worms) in cattle can reduce growth rates in heifers, which can then delay onset of puberty, optimal breeding timeframes and potentially pregnancy rates in heifers. Regular faecal egg counts (FECs) are an important tool in monitoring parasite burdens and guiding drench decisions. They can also be used to assess the efficacy of a chosen drench when repeated 10 days after drenching application.
Pestivirus (bovine viral diarrhoea virus, BVDV) is estimated to cost Australia’s southern beef industry over $63 million annually. Heifers have a greater chance of being unexposed to the virus (up to 40-60% naïve) and therefore represent significant potential reproductive losses if they become infected during pregnancy. Losses range from early embryonic losses, abortions, stillborn or persistently-infected (PI) calves (carriers). Blood tests can determine levels of exposure. A vaccine is available and given prior to joining. Biosecurity measures also play an important role in keeping the disease out of a herd.
Vibriosis / Campylobacteriosis causes infertility in herds with conception rates as low as 40% during an outbreak. It is a very common and highly infectious venereal disease. A vaccination is available to both bulls and heifers/cows to prevent reproductive losses.
Leptospirosis is caused by infection with a “water-loving” bacteria causing early embryonic losses, abortions, stillbirths or the birth of weak calves. It is also a zoonotic disease meaning that people can become ill from infection. Vaccination is available as a 7-in-1 in combination with clostridial disease vaccination.
Trace mineral deficiencies, while uncommon in our region, can affect growth rates and reproductive performance in heifers. Supplementation with trace elements such as copper, cobalt and selenium can potentially improve growth rates in heifers and young cattle where a deficiency exists.
3. The Joining Period
A tighter joining period for heifers (6 weeks) has a number of benefits:
- Allow greater selection pressure on fertility
- Shorten the calving period the following year
- Allow for an even batch of calves in terms of weights and ages
- Increase the recovery time for heifers before the following joining
Joining heifers 3-4 weeks before the rest of the herd gives them more time to recover from calving and begin cycling before the following joining. It also allows producers time to supervise calving before the rest of the herd begins.
4. Selecting for Fertility
Pregnancy testing is an important tool producers can utilise to select breeding heifers on fertility and reproductive effectiveness. Pregnancy testing can be performed from 5-8 weeks after the bull has been removed. Foetal aging can also be used to retain those heifers who became pregnant earliest.
5. Bull Selection
In selecting bulls for heifers, consider:
- Birthweights – as very large calves can cause increased birthing problems and intervention (dystocia)
- Ease of calving
- Gestation length
- Bulls with higher scrotal circumference are linked to having heifers reaching puberty at an earlier age
For more information:
Selecting and Managing Beef Heifers (DPI)
Tips to Manage Heifers Pre-joining (MLA)
