Felicity Hamlyn-Hill, formerly Queensland Government
Geoffry Fordyce, Queensland Alliance for Agriculture and Food Innovation
A good heifer management program is an essential component in overall reproductive management and ensuring performance of the breeding herd. Good heifer management achieves early puberty, higher weaning rates, low mortalities and early identification of females for turnoff. The objective is for only efficient breeders entering the main cow herd at 3.5 years of age.
The need for a good heifer management system is required because:
- Heifers suffer greater nutritional demands than cows as they are attempting to reproduce and grow simultaneously.
- Unless mating is well controlled, a high proportion of heifers can have their initial lactation during a dry season, because puberty can be reached at any time. Usually only well-managed heifers will conceive during their initial lactation.
The above factors result in low calf output and high mortalities. As well, inappropriate timing of initial lactation, coupled with poor nutrition, may permanently stunt heifers, thus reducing their turnoff value.
A good heifer management program should have the following components:
- Heifer control (heifer paddocks)
- Desired critical mating weight (CMW)
- Mating management
- Nutritional management
- Management of weaning
- Selection and culling
- Disease control
- Genetic improvement
Most properties require a third of the area allocated for females in which to graze heifers. At a minimum, a sound heifer management system requires 2 secure paddocks, one being twice the size of the other. The smaller paddock is for weaners. At 18 months these should be transferred to the larger paddock.
At 3.5 years of age selected heifers are transferred to a mature breeder paddock. If further paddocks are available, there are options to segregate heifers on age or management needs: pregnant versus non pregnant; turnoff versus breeding.
Desired critical mating weight (CMW)
Having some idea of CMW well in advance helps producers manage nutrition and growth to achieve high pregnancy rates. Critical mating weight (CMW) is the minimum weight at which heifers should be mated to achieve a high pregnancy rate when first joined. Weight is one of the most significant influences over the time at which heifers reach puberty and begin to cycle.
In the past there has been a tendency for producers to rely upon standard rules of thumb such as a widely used figure in the north of 280 kg as the weight at which to first join heifers. However producers should take the time to properly consider the specific CMW for their individual circumstances, rather than rely on industry benchmarks.
CMW will differ between breeds, and the average weight of mature cows. CMW takes account of:
- expected average and variation in weight at puberty; average weight at puberty is typically two-thirds of mature cow weight and variation is high
- time of heifer selection
- period of mating
- the time taken for healthy cycling heifers to conceive
- the target pregnancy rate
- sire effects.
A simple benchmark for producers of modern tropical cattle is to aim to have the maiden heifer herd at an average weight of 400kg when the mob is pregnancy tested after joining.
CMW should not be confused with average weight at puberty and average group weight at mating, both of which are much higher. It is important to remember an average weight for puberty means that only half the heifers in the mob will have reached puberty at this weight, so a heavier average will be required to ensure most heifers will have reached puberty well before the end of first joining so they can conceive. Heifers reach puberty at an average of two-thirds of the average weight of an operation’s mature cows (i.e. five year old cows in score three condition).
In selecting the best time of year to join, it is recommended to synchronise lactation with the wet season to improve the chance of heifers successfully rearing calves and of re-conceiving during the first or second lactation. A heifer that calves synchronised with the wet season is much easier and cheaper to manage than one that calves out of season.
As a general rule, once females began to cycle, a joining period spanning three cycles or nine weeks is required to achieve a 95% pregnancy rate. About 90% will get pregnant within a couple of cycles and 95% within three cycles.
A bull ratio of 2–2.5% is recommended. Bulls should pass a Bull Breeding and Soundness Examination or BBSE. See Bull Breeding Soundness Examination (BBSE). This is of even greater importance if single sire mating is used.
Nutritional management is important so that heifers:
- reach desired critical mating weight (CMW)
- are in body condition score 3 or better at calving
- maintain adequate body condition and growth during their first lactation.
Weaner nutrition is critical as poor growth in this period can increase weight at puberty, thus reducing early lifetime fertility. A good simple approach is to manage nutrition to keep heifers well above maintenance so the skeleton keeps growing. For more information see Weaning and Weaner supplements.
Heifers must have access to adequate pasture, water and supplementation to keep them in the best possible condition. When heifers (and older breeders) lose condition prior to calving, their reproductive systems tend to shut down, which significantly reduces their chances of re-conceiving during lactation.
Good management of heifer nutrition starts with good pasture management and grazing management. Seasonal conditions, pasture condition, country type, stocking rates, land condition, and grazing management all greatly influence affect pasture quality and quantity. Both pasture quantity and quality are important because both affect consumption of pasture (intake) and hence the nutritional status of the animal.
In most dry seasons in northern Australia there is a dietary shortfall or deficiency in protein, and sometimes energy, for breeding animals. This shortfall is the difference between what cattle need for production and what the pasture diet is supplying. Once the shortfall in the diet is determined this gap can be filled by feeding dry season supplements (e.g. urea based supplements) in a cost effective manner. For more information see Assessing pasture diet quality (NIRS) and Protein and urea.
Additional nutrients may be required to enable pregnant heifers to cycle again following calving. Spike feeding stimulates recovery of healthy egg development before lactation commences, allowing heifers to cycle much sooner after calving. Spike feeding is the feeding of a high quality supplement (e.g. M8U) to late pregnant heifers for a short period in the late dry season. Spike feeding increases conception rates following calving by an average of 15%. Feeding should be for a minimum 50 days, starting 6-8 weeks before calving is due to commence. For more information see Spike feeding.
Wet season supplements may be necessary to correct major mineral deficiencies, which can impact significantly on feed intake, growth rates and fertility. The key mineral deficiency in Northern Australia is Phosphorus. For more information see Phosphorus supplementation. For heifers grazing grossly deficient country supplements including phosphorus should be used all year round.
Management of weaning
Weaning removes the stress of lactation and may reduce further loss of body weight for lactating first calf heifers as it significantly alters the nutritional requirements of a heifer (or breeder). The extra energy and protein requirements needed for lactation are removed. The major benefits of good weaning management are better cow condition next season, more conceptions during the next lactation, more calves the year after, and higher steer sales in the future. It makes sense then that weaning is a critical component of a heifer (and breeder) management program.
Calves from heifers should be weaned first and all calves should be weaned at the first round. Weaning calves earlier than normal should increase the chances of heifers cycling and conceiving following calving. However, in certain situations heifers may require supplementation to commence cycling again as discussed above.
Selection and culling
Many producers over-mate heifers and then remove/cull surplus heifers based on a pregnancy test. Empty heifers that have had ample opportunity to conceive are sub-fertile or infertile and should be removed as they are not profitable themselves, and their genetics are removed from the herd. Depending on the overall results and replacement numbers required those heifers that will calve late (as a result of late puberty) can be culled as well (or identified or segregated for future reference). Other traits which should be considered when culling include temperament, growth rate, ability to hold condition, and physical defects.
Where over-mating is not conducted it is recommended that only heifers from dams with proven fertility be selected, as some important fertility traits are heritable. It is also important to use sires with above breed average EBVs for scrotal size, and days to calving.
The primary recommendation for vibriosis control is to use vaccinated bulls. Where the disease is rampant consider vaccinating heifers prior to mating, but be careful to weigh up the cost-benefit given the cost of vibriosis vaccinations.
With pestivirus, existing levels of herd immunity can substantially influence control strategies. It is suggested that producers take advice from their cattle vet when considering whether vaccinations should be used prior to mating.
Vaccination against botulism should be standard practice because of the disease’s endemic status throughout Australia.
Both age of puberty and weight at puberty are highly heritable. This means genetic progress can be made in these traits. Sire-effects alone can account for variations of at least 100 kg in weight of puberty of female puberty. Additionally heifers which conceive early in the joining period can be identified and recorded for future reference.
There is a genetic correlation between scrotal size in bulls and age of puberty in their daughters. Objective selection of bulls with above breed average scrotal size EBVs will assist in making genetic progress. For more information see Improving fertility traits.
- Critical mating weight (CMW) is the minimum weight at which heifers should be mated to ensure they have the greatest chance of cycling when they are first joined.
- Under normal, healthy conditions, 95% of cycling heifers will conceive within three cycles or nine weeks.
- Good mating management and weaning management will ensure reduced losses and improved second calf conception rates.
- Heifers which are slow to conceive at their first joining are likely to become slow breeders, and should be culled.
- Bulls should be vaccinated against vibrio.
- Age and weight at puberty are heritable. Use objective selection methods.