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.