....is like putting money in the bank - the more you put in during the whole rearing period, the more you will get paid out.
Replacement heifers are the most valuable asset on the farm, representing the best genetic material and carrying the future production potential of your herd; they are also often the most neglected, despite the $1000+ cost of bringing them into the herd as a two year-old.
NZ survey data estimate that 30% of replacement heifers are below target-mating weights in October, which leads to:
Increased wastage: only 67% of calves identified as replacements for the herd may calve as three-year olds, meaning there is a 33% loss rate between rearing and completion of the first lactation. The lighter the heifer, the greater the chance she will be lost from the herd.
Production losses: a heifer that is 10% below target live-weight can be expected to produce 9kgMS less in her first lactation. The closer a heifer is to her calving weight target, the more milk she will produce in her first lactation - every extra kg of live-weight is worth an extra seven litres of milk.
Reproductive failure: the major influence on the onset of puberty for yearlings is live-weight, so the lower the average live-weight, the greater the proportion of late or empty heifers. Light-weight heifers are five times more likely to be empty than the heaviest heifers in the group.
Once in the herd, failure to cycle becomes the major problem as these new entrants struggle to settle into the herd hierarchy and successfully compete for the available feed. The problem is worse when they are below target weight to start with and actually have an increased feed demand just to support the extra growth required. By comparison, well-grown heifers will have a reproductive performance equal to that of mature cows.
|
Mature live-weight (kg) |
400 (Jersey) |
450 (J x F) |
500 (Friesian) |
|
|
6 months |
30% |
120 |
135 |
150 |
|
Mating |
60% |
240 |
270 |
300 |
|
Calving |
90% |
360 |
405 |
450 |
These are minimum target weights and require an average growth rate of 0.6kg EVERY day for the total rearing period or 20kg per month. To achieve these growth rates, management needs to focus on:
- Efficient calf-rearing through to weaning
- Generous dry matter intakes after weaning allowing for maintenance, live-weight gain and then pregnancy, especially the last 4 months
- High-quality feed - energy (ME), protein % and digestibility
- An efficient worm control programme
- Trace element sufficiency (copper, cobalt and selenium levels)
- Appropriate disease control and vaccination status
