Managing heifers for lifetime productivity
The heifers you select for breeding from the current year’s weaned calves will influence future herd productivity.
For this reason, it is important that they are genetically superior for commercially important traits than the dams in the current breeding herd.
A balance between fertility and carcass traits is the goal and this will differ for each production system and target market.
In general, there is an economic benefit in calving heifers at two years of age, as they are likely to have a higher lifetime production than heifers caving at three years of age.
In southern Australian beef production systems heifers are therefore expected to calve for the first time between 22 and 24 months of age and in about 12-month intervals subsequently.
Age of puberty is a heritable trait which has been shown to determine: the ability of a heifer to become pregnant in her first joining season; rebreed and remain in the herd in subsequent years, as well as affect her lifetime production.
It is not surprising then that selection for early age of puberty has been suggested as the simplest method for improving breeding cow longevity and profitability.
For heifers to express their genetic potential, getting in-calf early and rearing a good quality calf every year, one must not forget that adequate nutritional management is essential, as some body condition targets need to be met at crucial times (joining and calving).
In addition, growth must not be hindered by parasite burdens, trace element deficiencies or other diseases, emphasising the importance of best practice health husbandry. Further information on condition scoring methods and targets can be found on: Condition Scoring of Beef Cattle.
Appropriate growth pre and post-joining is also beneficial in preventing birthing difficulties in heifers (steady growth patterns ensuring heifers are not too fat or thin).
Bull choice is also important to avoid difficult births. Estimated Breeding Values (EBVs) can be of great assistance in selecting bulls.
Use of bulls with high Calving Ease Direct and low Birth Weight EBVs are recommended for the heifer breeding herd.
Scrotal size EBVs in bulls is also related to their own fertility and the fertility of his progeny (both male and female), higher EBVs for this trait are favourable.
Comprehensive material on the definition and uses of EBVs can be found on: A basic guide to Breeplan EBVs.
Visual inspection of bull conformation should also be used in the selection process not only to avoid characteristics that may increase birth difficulty events (big head, angular shoulders) but also to ensure long term productivity.
Detailed information on bull visual inspection is provided on: Bull Soundness -Structural.
None of these bull selection procedures will be of much use if the bull has fertility problems or is physically unable to breed.
An annual Veterinary Bull Breeding Soundness Exam will ensure they are fit for the job and avoid unpleasant surprises when it is time to check if the heifers are in-calf. Further information on this type of examination can be found on the Australian Cattle Veterinarians website.
A good understanding of heifer visual conformation and its effect on calving difficulty and longevity is important when selecting replacement heifers. Further information on this subject can be found on: Beef conformation basics.
Combining carcass EBV information and visual inspection are also important to maximise carcass traits, ensuring the herd is well muscled (which will increase profit) but also has adequate fat cover.
What is the target joining weight for your heifers?
Fertility of the first oestrus is low, thus it is desirable that heifers have already cycled a couple of times before they are joined.
Target joining weight, also referred to as critical joining weight, is the weight in which a large enough percentage of heifers are expected to be already cycling to ensure acceptable pregnancy rates (>85%) by the end of the joining season.
It is also important to highlight that the target weight is not to be used as an average for the heifer herd, but must be reached by every heifer destined for breeding by the onset of the joining season.
They are usually between 60-65% of the mature cow weight of the herd (weight of five year old cows at weaning). It will differ from breed to breed and even within a breed depending on cow type. Compared to early mature types, late maturing type cows have higher mature cow weights and are leaner.
Mature cow weights have increased for most breeds over the last 10-20 years, meaning that old 'rules of thumb' for target joining weights for British and European breeds may no longer be applicable.
Results from the Beef CRC Maternal Productivity Project showed that although joining weight was the most important factor influencing heifer fertility, fat was also influential.
Fat cover may be influenced by nutrition and genetics, with later maturing types tending to lay down fat at a heavier weight.
Maternal productivity project
The project examined 579 Angus heifers selected for either divergent rib fat EBV or divergent Net Feed Intake (NFI) EBV. They were moved soon after weaning to either DAFWA’s Vasse Research Centre or the Southern Australia Research and Development Institute’s Struan Research Station.
Heifers were 11–18 months of age when they were joined for nine weeks.
Heifers were weighed and fat scanned regularly. Calving dates were used to calculate when heifers conceived and to extrapolate pregnancy rates expected for a six week joining period.
While there was no significant difference in pregnancy rates between the high and low NFI heifers (results not presented), the high fat EBV heifers had higher pregnancy rates than the low fat EBV heifers (Table 1). High fat heifers had eight and twelve percent higher pregnancy rates than the low fat heifers under nine and six week joining periods respectively.
| Genotype | Weight (kg) | Rib fat (mm) | Pregnancy rate under 9 weeks joining (%) | Pregnancy rate under 6 weeks joining (%) |
|---|---|---|---|---|
| High Rib Fat EBV | 360 | 4.4 | 91 | 77 |
| Low Rib Fat EBV | 364 | 3.5 | 83 | 65 |
| Difference between genotypes | 4 | 0.9 | 8 | 12 |
Statistical analysis looked into the effect of age, weight and fat on whether or not heifers conceived.
The results showed that weight was the main factor affecting pregnancy rate in heifers, followed by fat and then age being the least influential factor. In fact, once weight and fat were in the model, age was not significant.
Based on the results of the project the following tables were prepared showing the relationship between weight, fat and pregnancy rates on 400 day-old Angus heifers after either nine (Table 2) or six weeks (Table 3) joining.
It has been advocated that the heifer herd should be bred earlier and/or for a shorter period than the cow herd.
The rationale behind this are: 1) heifers require longer to recover and resume cycling after calving; 2) this allows extra time for their calves to grow and be more in line with the calves from the cow herd (possibly making marketing easier); 3) higher selection pressure for fertility can be applied and 4) concentrating their calving time decreases labour requirements for supervision. These are all practical reasons, however possible financial implications from this practice should also be considered.
Producers incur significant developing costs in raising heifers. It is estimated that a heifer needs to produce up to 10 calves before becoming profitable depending on costs and market prices.
As seen in the tables above, in order to achieve the same pregnancy rates under a six week joining as those under a nine week joining, heifers need to be heavier and/or fatter at the start of joining. To accomplish this, significant extra nutritional input will be required and this also comes at a cost.
To ensure profitability, market price of weaner calves, empty heifer cull value and feed costs need to be considered simultaneously with practical issues when making husbandry decisions.
If a nine week joining period has more financial viability, selection pressure for fertility can be applied by retaining only early born calves for replacements in the breeding herd.
This can be done by aging pregnancy when the breeding herd is pregnancy tested or by keeping records of joining and calving dates.
Retaining heavier/fatter heifers under the assumption that they will reach puberty earlier and be more productive will not necessarily provide improved herd fertility and productivity.
Aligning biological efficiency (kg of beef produced/unit of feed) with economic efficiency (profit/unit of feed) is not an easy task.
It requires a good market knowledge and balanced short term (nutrition) and long term (genetic selection) choices. This will differ for each production system. Add seasonality into the equation and things get even more complicated.
Having a plan will assist you in making decisions at any time, especially under pressure. It is important therefore to know your herd's mature weight, herd type (early or late maturing) and weaning weight.
Set a growth pathway from weaning to target weight at joining, monitor regularly (weigh heifer calves every six weeks or so) and act as required.
Conclusions from the maternal productivity project
- Weight followed by fat has the greatest influence on whether or not heifers conceive.
- Heifers selected for high rib fat EBVs (early maturing) have significantly better pregnancy rates (under either six or nine week joining periods).
- Fat should be considered as part of a balanced breeding program (no need to select for extreme high fat).
- By recording joining and calving dates you can ensure replacements are chosen from calves born early in the season pushing fertility selection further in your herd.
Bringing it all together
- Reassess the target joining weight of your heifers based on the mature cow weight of your own herd – 60-65% of average mature body weight of your herd is a good target. The target is lower for early maturing types and higher for late maturing types. Regular steady growth is important and should continue, ensuring heifers are around condition score three at calving.
- Calving heifers first as two year olds is usually associated with productivity benefits. Adequate nutritional management is required to achieve this and ensure they will get pregnant in subsequent years (keep them growing).
- Under extreme circumstances, when feed prices are too high, producers may have to accept lower heifer pregnancy rates (<85%) or defer joining (join as two year olds rather than as yearling). If this becomes the norm rather than the exception you must reassess your herd genetic make-up (mature cow weight, maturity type, etc) to achieve a better fit with your environment.
- Joining period decision for heifers (six versus nine weeks) should be based on both practical and financial implications for your enterprise. Calves born early should be retained as replacements to improve herd fertility.
- Calculate the weight gain necessary to achieve target joining weights. Using the old ‘rule of thumb’ as an example, target joining weights for British breed heifers were 280kg (back when mature cow weight was around 470 kg). Heifers joined at 15 months old with a birth weight of 30kg, needed to achieve a growth rate of 0.55kg/day from birth to joining. Consideration of the data from the maternal productivity project indicates that the target mating weights for today’s cattle is likely to be much higher and therefore higher growth rates may need to be achieved to meet these targets.
- Do you need to provide supplementary feed to heifers over summer to achieve their target growth rates and joining weights? Hayed off pasture has much lower energy and protein than green pasture. Monitor the weight and condition of your heifers carefully over the summer - your management could be the key to their success.
References
Charteris, P. L. Yearling heifer mating. http://www.beef.org.nz/research/breeding/breed_ylg.asp Accessed in 2 July 2014.
Day, M. L. and Nogueira, G. P. (2013). Management of age at puberty in beef heifers to optimize efficiency of beef production. Animal Frontiers, 3(4), 6-11.
Diskin, M. G. and Kenny, D. A. (2014). Optimising reproductive performance of beef cows and replacement heifers. animal, 8(s1), 27-39.
Mousel, E. M., Cushman, R. A., Perry, G. A. and Kill, L. K. (2012). Effect of heifer calving date on longevity and lifetime productivity. Proceedings Applied Reproductive Strategies in Beef Cattel. December, 2, 23.
Saxton, A. M.,. Stalder, K. J. and Simpson, R. B. Angus cow longevity estimates and relationship to production traits. http://utbfc.utk.edu/Content%20Folders/Beef%20Cattle/Genetics/Publicatio... Accessed in 2 July 2014.