Over a decade ago, research at the Royal Veterinary College, London found that calving heifers at 23 to 25 months of age was optimum in terms of their subsequent fertility, milk yield and survivability through to the third calving (1). The recommendation to calve heifers close to 24 months of age is not new. But the message is just as valuable today – in fact, new data from recent studies have further reaffirmed this important practical advice.
More heifers are now calving closer to 24 months but the average age at first calving (AFC) on UK dairy farms is still too high at 27 months. Not only will this reduce the lifetime performance of this youngstock, but it will also increase rearing costs. The average cost of rearing a heifer increases significantly with the time taken to calve for the first time – reducing AFC to 24 months will decrease the cost of rearing by 15.7% compared to calving at 26 months (2).
The Irish Cattle Breeding Federation (ICBF) recently completed a study on the optimum AFC, based on 160,000 dairy heifers. Calving at 22 to 26 months of age was associated with increased survivability and increased lifetime milk yield. Of those heifers calving at 22 to 26 months, 30% survived to parity six, compared to only 11% of those that calved for the first time at 27 to 32 months of age.
Data from 437 dairy herds in the UK based on 18,406 dairy heifers found that the likelihood of calving for a second time was associated with AFC3. Heifers that calved between 23 and 24 months were most likely to calve for a second time and those calving at >30 months were least likely to calve again. Rearing healthy heifers that are fertile and remain in the herd for at least a second calving is fundamental for farm profitability. A heifer failing to calve for a second time leaves the farm before it has repaid the cost of rearing and started to make a profit. The mean number of lactations it takes to repay the investment in the rearing period is 1.5 lactations (2).
How can we ensure that heifers are reared to enable them to calve close to 24 months of age with adequate body size?
Step 1 - What’s your average mature cow body weight?
Take a selection of at least 20 (the more the better) third lactation animals of 100-120 days in milk and weigh or weigh band them to get an idea of the average mature body weight (BW) in your herd.
It’s worth repeating these measurements year-onyear because if breeding strategy changes, it could also impact on mature weight.
Step 2 - Establish your targets based on themature body weight of your herd
Ideally, heifers should be hitting the following milestones:
- 55-60% of mature BW at first breeding at 13 to 14 months of age
- 85-90% of mature BW at first calving at 24 months of age
Heifers must be in calf at 15 months if they are to calve at 24 months, so they need to be served for the first time at 13 to 14 months of
age as it takes on average 1.4 inseminations to get pregnant.
Heifers need adequate body size at first calving. This is important to reduce the risk of calving difficulties (dystocia), but body size can impact on their subsequent fertility. Heifers are still growing at first
calving – and those that are small will need to continue to grow to a greater extent, putting nutrients into growth at the expense of their
fertility.
Step 3 - What’s the average birthweight of heifer calves?
Weigh or weigh band a selection of calves at birth to establish the average birth weight of heifers on your farm.
Step 4 - Calculate your herd’s bodyweight targets throughout the rearing period
Calculate the weight gain required to hit the target BW at first breeding. (see calculations in table)
Weight gain targets required to calve at 24 months for different breeds
Step 5 - Step 5: Design a suitable feeding strategy
| Target | Holstein Example | Jersey Example |
| Age at 1st calving | 24 months | 2.5 - 3.0L |
| Age at 1st breeding (age at 1st calving minus 11 months) | 13 - 14 months (in calf by 15 months) | 13 - 14 months (in calf by 15 months) |
| Mature BW of cows (measure at lactation 3+) | 660kg | 450kg |
| BW at 1st breeding (multiply mature weight by 55%) | 660 x 0.55 = 363kg | 450 x 0.55 = 248kg |
| Weight gain required (BW at 1st breeding minus birth weight) |
363 - 40 - 323kg | 248 - 30 = 218kg |
| Average daily gain required up to 1st breeding (weight gain required divided by age at 1st breeding |
323kg /13 months= 0.8kg/d | 218kg/13 months = 0.55kg/d |
Critique your milk feeding and general nutrition strategy to ensure these targets will be met. The primary source of nutrition for a calf during the first 3 to 4 weeks of life is milk since starter intake will be minimal. Feeding more milk will help maximize the early growth potential of these young animals. As a guide, following good colostrum management, feed a minimum of 6 L/d (mixed at 125g/L or 150g/L) from day 7 reaching the peak milk allowance by 2 weeks of age. Calves offered high levels of milk must be weaned over a 3-week period to ensure food starter intake for rumen development. Housing calves in pairs of groups can also encourage starter intake. Calves should double their birth weight by weaning – if they do not hit this target, critique your rearing system in terms of environment, health and nutrition (Volac Growth Triangle).
Step 6: Design a suitable measuring and monitoring strategy
Heifers need to be weighed at regular intervals to ensure they are on target. As a minimum, weigh animals at birth, weaning, 6-months and at first breeding. Regular weighing throughout the rearing period will identify if heifers are on target and if not, corrective measures can be made before the time of first breeding.
Calving heifers for the first time close to 24 months of age minimises the length of the non-productive stage of life, but also results in better fertility, more milk and improved survival. With the mean AFC in the UK currently running close to 27 months – there is currently a large opportunity for improvement and thus to reap the benefits in terms of lifetime performance.
References
1Cooke et al., 2013 OJAS 3:1-12
2Boulton et al., 2017 Animal 11:1372-80
3Sherwin et al., 2016 Animal 10:1877-82
