Age at first calving in the Irish suckler herd has moved in the wrong direction over the years, with the bulk of sucklers calving for the first time after 30 months. Breed selection and, in particular, a move away from selecting replacements on material traits to selecting replacements bred from terminal sires, has been a significant contributor to an increased age at first calving.

Boost in productivity

Calving at 24 months of age provides the potential to increase herd output and also the lifetime performance of the animal. It can also make for a more straightforward replacement policy (less groups of stock on the farm) and reduce replacement costs. However, it must be stressed at the outset that it is a more complex system to operate and there is no room for poor performance. Its success is dependent on selecting the correct type of animal and hitting key performance targets. Failure to hit these targets can lead to significant problems and can actually lead to reduced herd output or lower lifetime performance. Where the chance of achieving these targets is low, it is advisable to stay away or delay progressing down the route of 24-month calving.

Correct heifer selection

Correct heifer selection is central to successfully calving heifers at two year of age. Heifers should be selected from proven dams with a strong source of milk.

Where milk was lacking in the cow that bred the heifer, it will be very hard to lift the milk yield significantly in one generation, even if the heifer has been bred from a sire with strong milk yield characteristics.

The best situation is where the dam had a good milk yield and the sire also had good milk yield characteristics.

Selecting replacements from the earlier calving cows and those with proven good fertility records will help maintain good fertility levels in the herd and also give the maximum time period for replacements to reach target mating weights.

The replacement heifer should also have good maternal traits and a good temperament. HerdPlus, the breeding information service operated by ICBF, is an essential tool to identify heifers with good maternal traits.

Replacements should also be not too “beefy” or excessive in terms of muscle or growth rate. A good deep-bodied O+ grade (dairy cross or traditional breed heifer) or R grading heifer (continental bred) will suffice.

Selecting extreme muscled heifers to calf at 24 months of age will bring numerous added complications and require a very high level of herd management.

Achieve weight targets

Achieving recommended weight targets is essential to minimise calving related problems and also to ensure an animal’s mature weight and size or lifetime performance is not compromised.

There are two key weight targets. The first is that animals should reach 60% of their mature weight at mating (13 to 14 months of age) and the second is that animals should reach 90% of their mature weight at calving.

It is advisable to weigh heifers now and take action where necessary to boost where performance and increase animal liveweight. The most preferential option where animals fall below the weight target is to prioritise animals for early turn-out to grass or, where this is not yet possible, introduce concentrate supplementation.

A diet of early grass has the potential to boost growth rates to over 1kg liveweight gain per day, while supplementing animals on ad-lib good quality silage (68-70DMD) with 2kg concentrates will deliver in the region of 0.6kg to 0.7kg liveweight gain per day.

Do not over-feed young heifers in satisfactory body condition (BCS 3 to 3.5) as it will only serve to make animals over-fat.

Supplementation rates can be increased where silage quality is poor (increase by 1kg for every 5DMD) or where animals are in poor body condition (BCS 2 to 2.5) and increasing the supplementation rate will help to improve condition and animal weight pre-mating.

Figure 1 shows an example of the required performance to successfully calf heifers at 24 months of age.

Correct management

First calf heifers will generally take 20-30 days longer to resume oestrus activity than mature cows.

For this reason, it is important to mate heifers to calf before the main suckler herd.

The breeding season should also be limited to six to nine weeks. This should be sufficient to get in excess of 90% of the heifers in-calf.

Prolonging the breeding season will increase the risk of poor fertility animals being mated. It will also limit the chances of bringing heifers into the main suckler herd and maintain a tight calving interval and calving spread in subsequent years.

Heifers should be managed as a separate group both pre- and post-calving. They should also be prioritised for early turnout to grass post-calving.

Sire selection

Easy calving is a must. The goal is to get a live calf on the ground without subjecting the heifer to a difficult calving. This will help ensure mortality levels are kept to a minimum plus a difficult calving can have a knock-on effect on subsequent conception rates. Do not take a chance on unproven bulls and select a sire with high reliability figures for calving ease.