When does the hind become a priority over the calf in autumn? When should our focus switch from weaning weight (this years production) to hind conception and mating date (next years production)? We can attempt to answer these questions now that we know some of the science linking condition score with reproduction.
Drs David Stevens and Geoff Asher, AgResearch Invermay.
Originally published as an After the Feild-Day Fact Sheet
The number of live calves produced each season is a major driver for profitability. It is normally expressed as the number (or weight) of surviving calves produced annually per breeding hind – or the ‘weaning rate’ of the herd. The number of calves born will both directly and indirectly impact on farm production and profitability.
Direct effects are due to having less calves for sale.
- Current calf losses range from 2-15% in mixed age hinds, and 5 -25% (or greater) in first calvers.
- This affects potential income by approximately $225/100 hinds mated, for every 1% shift in survival (valued at weaning as a 50kg weaner @ $4.50/kg LW).
Indirect effects are related to later calving, higher culling, and the changing age structure of the herd.
Understanding the trade-offs that we make that influence this dynamic of the herd
Later calving means lower weaning weight. Less calves means more dries so a higher number of replacements need to be kept. As a result younger hinds will tend to rear lighter calves (calves born to first calvers are born on average 17 days later and potentially 5.5kg lighter at weaning). The number of calves sold also declines as weaning percentage declines.
Understanding the trade-offs that we make and how they influence this dynamic of the herd.
Leaving the calf on the hind in autumn will help improve calf liveweight gain. On-farm studies show that calves may grow on average 50g per day faster between March and June if left unweaned. Variation between farms is high, and can be higher than 50g per day, showing that farmer management is very important to results.
Post-rut weaning may delay conception date by an average of 10 days, equivalent to 4kg weaning weight.
Again farm to farm variation is high, and is influenced by management of the farmer. The extra growth rate of the calf may add 4kg to June weight (80 days at 50g per day), but 10 days later conception may lower June weight by 4kg (10 days at 400g per day). The two practices tend to cancel one another out over time and often hind condition is the buffer. Poor hind condition can lead to further reproductive losses.
Hind condition score ratings
|Mating BCS 3||Mating BCS 2.5||Mating BCS 2|
|Calf Survival (Per calf scanned)||95%||95%||95%|
|Hind Death rate||3%||3%||3%|
|Calves Weaned/100 hinds mated||90||86||78|
|Est. start of calving||14 Nov||21 Nov||28 Nov|
Condition score and changes in condition score are relatively sensitive indicators of potential performance.
Condition score 3 or reduced down to 3
- Very few conception failures and high pregnancy rate.
- Slight delay in conception only if condition score loss was rapid.
Down to 2.5
- 7-10 days delay in conception.
- 5-10% barren hinds.
Down to 2.0
- 10-14 day delay in conception.
- 15-20% barren hinds.
Down to 1.5
- General reproductive collapse.
Loss of condition score in hinds is most likely in late summer and early autumn when the amount of feed available declines below approximately 1800kg DM/ha. The table above shows how a lower BCS at mating reduces the number of calves weaned, and delays the start of calving.
This loss of BC directly impacts the return per hind and increases the necessary cost of feed. It is cheaper to buy feed to keep condition score on the hind, rather than trying to gain it back later.
|Dry MA Hinds/100||2||7||15|
|Expected weaning weight next year||56.1||53.1||49.9|
|KG calf weaned/kg MA hind mated||0.5||0.5||0.4|
|Cost of BCS loss/hind mated||-$19||-$39|
|Cost to maintina BCS||$5||$9.50|
|Cost to replace BCS||$12.5||$22.50|
Both direct and indirect impacts can be calculated at the whole herd level. On the table below they are calculated as if we are running a herd at a constant BCS of 3, 2.5 or 2.
Because the hinds are lighter, we can run more, so each example is calculated using the same amount of feed as the original herd of 1000 hinds in condition score 3, weaning in early March, culling wet dries and hinds over 10 years old.
|BCS 3||BCS 2.5||BCS 2|
|Days to Weaning*||118||111||104|
|Calves for sale||691||666||598|
Even by being able to run more hinds if they are in lower condition we still find that the economic optimum is when hinds have a condition score of 3, so we can use hind condition score as an indicator when making weaning decisions.*Days to weaning are higher for better feed hinds because the calves are born earlier.
Targets to consider
- 98% conception rate in Mixed-Age hinds.
- 85% in the first cycle.
- 7 November start of calving.
Triggers for making decisions
- Are my hinds in condition score 3 in mid-January?
- Am I ready to wean? (see Weaning Management)
- Can I get my stag in early?
- How much feed do I have and what is the quality?
- How fast are my calves growing?