Results from the recent CAFRE/AFBI Heifer Rearing Survey showed that the average heifer in Northern Ireland calves at 28 month of age. However from both a financial perspective and ease of management, heifers calving at 23 to 25 months are more profitable than those that are older at calving.  Farmers cited several reasons why they found it difficult to calve at 24 months including: heifers are too small for serving and can’t compete in the herd, particularly during winter feeding. On a number of farms 24 month calving is practiced successfully. At Greenmount heifers have consistently calved at an average of 24 months over the last five years. First lactation production last year averaged 7,400 litres in 305 days with an average calving interval of 385 days. However, the question is still raised by many farmers is, what are the pro’s and con’s of 24 month calving?

The benefits farmers see from calving older, heavier and more mature heifers is that they generally produce more milk in their first lactation. However the financial benefit from the extra production from older heifers is outweighed by higher heifer rearing costs and poorer fertility performance in first lactation. In addition to this, heifers that calve at 24 months have a longer productive life, producing milk for around one lactation more than heifers calving at 30 months – thereby substantially increasing both lifetime yield and daily lifetime yield.

When to serve heifers for 24-month calving

To calve heifers at an average age of 24 months, the heifer needs to be in-calf at 15 month of age – and this means starting to breed heifers at 13½ months if they are of suitable size and weight at this age. In the Future Herd, heifers become eligible for breeding at 13½ months and weigh over 370 kg. Smaller heifers are allowed to grow out until they reach this weight. All heifers are served with semen from an easy-calving bull for the first two services. Where possible, sexed semen is used for first service to maximise the number of heifer calves and conventional semen is used for the second service. Last year heifers were served with semen from Kelstein Dynasty, while Sandy-Valley Onyx and Emil II were used on heifers the previous year. Conception rates to sexed semen at first service last year were 51% while the conception rate to conventional semen at second service was 65%. Heifers that return to heat after the second service are served naturally with an Aberdeen Angus bull.

Rearing management of heifers

At Greenmount, calves have been reared on a twice daily bucket-fed system to allow students gain calf rearing experience. Weaning is at 6 weeks of age when calves are eating 0.7 kg concentrate per day or more. This winter a number of calves will be reared using an automatic calf feeding system. Technology projects will be linked to reducing the cost of calf rearing through restricting the level of milk supplied as concentrate intake levels increase to help minimise the post-weaning growth check.

At grass, calves in the Future Herd are essentially split into two groups – an older group of pre-Christmas born calves that graze in a leader-follower system with the in-calf heifers, and a younger group of post-Christmas born calves that graze in a leader-follower system with the sheep. In both systems, the calves graze paddocks first in the grazing cycle. Throughout the grazing season, the older calves are supplemented with 1 kg SuperGrower concentrate while the younger calves are supplemented with 2 kg concentrate.

On housing again, the 6-12 month old calves are fed second or third cut silage supplemented with 2 kg concentrate. When the heifers are confirmed in-calf, the heifers continue to be fed the same silage but concentrates are no longer fed, even at grass the following year.

Parasite control

It is important that calves remain health throughout the grazing season. If the calves carry a worm burden growth rates will be decreased and 24 month calving will not be achieved. Therefore parasite control is critical. The routine for Future Herd replacements is as follows.

At turnout, 3-6 month old calves are given a pulse-release bolus while the younger calves a treated with a pour-on product at 5 and 12 weeks after turnout. The in-calf heifers are given a single dose of pour-on in mid to late June, at least eight weeks prior to calving to comply with milk withhold recommendations. On housing again in the autumn, the heifer calves are treated for worms, fluke and lice at or shortly after housing.

Summary

Moving towards 24 month calving increases farm profit through savings in heifer rearing costs, improved fertility performance in first lactation and higher lifetime yields. Monitoring heifer growth through use of the CAFRE/Thompsons weighband is key to making informed management decisions, with a target liveweight gain of 0.7–0.8 kg/day from 12 weeks through to calving. On this basis, heifers should be 340-370 kg at 13-15 months when they are being served and 550-580 kg at first calving around two years of age.

By: David Mackey, Greenmount Campus, CAFRE and Richard Moore, John Thompson and Sons Ltd