Less than one quarter of suckler replacements calve down at 24 months of age on Irish farms. On average, suckler replacements are approximately 31 months old by the time they calve down for the first time.

Calving at 24 months always generates plenty of debate among farmers. While it may not be applicable – or preferred – on every farm, it is the most profitable option for farmers rearing their own replacements.

An example of the basic input costs associated with rearing homebred heifers to calve at 24 and 36 months of age are outlined in Table 1.

The example is based on a spring-calving herd, with heifers having an average date of birth of 1 March.

Inputs

The starting point assumes good-quality continental heifers weaned in autumn, with a potential sale value of €900.

The example then assumes animals are wintered until April on silage (€25/t) and 2kg/day of concentrate (€250/t).

From April to mid-October, heifers are grazed and served using AI at 15 months of age in early June.

Costs are also included for the animal’s second winter, plus pre-calving minerals and straw use at calving time, with similar costings for a 36-month calving system.

Cost comparison

From the example outlined, there is a cost saving of approximately €250/head by calving heifers at 24 months of age. For a herd calving 10 heifers annually, this amounts to €2,500/year.

There is also the added bonus of having a calf to sell one year earlier with 24-month-old calving, potentially worth €700 to €800 when weaned.

Targets

Calving at 24 months requires early-born calves reared under good management and there are a couple of target weights to keep in mind.

Breeding weight at 15 months of age should be at least 60% of mature cow weight, with heifers weighing 90% of mature cow weight at calving.

This means a minimum breeding weight of 420kg to 450kg for mature cows weighing 700kg to 750kg.

At a target of 450kg liveweight at 15 months of age, heifers require a lifetime gain of 0.9kg/day from birth, allowing for a birth weight of 40kg.

Taking a liveweight of 280kg on 1 November, after weaning and housing during mid-October, heifers need to gain 170kg before breeding on 1 June. This is a daily gain of 0.8kg/day.

Increasing liveweight to 300kg by 1 November reduces weight gain to 0.7kg/day to hit the target breeding weight on 1 June.

Downsides

Although it is more cost effective to calve homebred replacements at 24 months, there are downsides to consider. Herds that calve from April to June or herds operating on heavier ground often struggle to get heifers hitting target breeding weights due to lighter calves housed during the first winter.

Failing to hit weight targets will stunt animals. This increases calving difficulty and makes it much harder to get cows back in-calf again.

This puts farmers off calving at 24 months, as culling rates are subsequently higher. Calving down at 30 to 36 months usually avoids this problem.

Five steps to calving at 24 months of age

When it comes to calving heifers at 24 months of age in spring herds, management of the animals during their first winter is critical to get adequate weight gain from a silage diet.

For farmers considering calving at 24 months of age, outlined are five steps to managing replacement heifers over winter.

1 Select replacements now

Given the outlined target weight gains and the limited nutritional value from grazed grass in late autumn, replacement heifers destined to calve at 24 months are better off being housed now. Once housed, they can start to be weaned. Having both tasks completed by November gives more time to get adequate weight gain on animals over winter. Delaying housing and weaning until the end of October will make it harder to meet target breeding weights.

2 Front-loading concentrates

Once heifers are housed and settled, offer good-quality silage and front-load concentrates during the first half of the housing period. When front-loading concentrates, the animal still eats the same quantity over winter. For example, over a 150-day winter at a flat rate of 2kg/day, heifers consume 300kg. By feeding 3kg/day over the first 75 days, then reducing concentrate levels to 1kg/day for the second 75-day period, the animal still eats 300kg of meal. But animals should be heavier midway through winter and more likely to be on track to meet target weights. Continue feeding concentrate at the lower rate up until turnout for replacement heifers.

3 Early turnout

Replacement heifers should get first preference for early turnout to drive weight gain in spring.

By front-loading meal and feeding the lower concentrate rate during the second half of winter, heifers will be in a leaner condition and ready to go to grass.

4 Parasite treatment

Once heifers are housed, treat for fluke, worms and lice as early as possible. This means choosing a flukicide that targets early immature and mature fluke burdens.

5 Regular weighing

Regular weighing every month is recommended and will identify if animals are on track to meet targets. If not, management needs to be altered immediately.

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