Early and late-maturing bulls: What’s the difference in growth and feed efficiency?

Recent research undertaken at Teagasc, Grange – by Eddie O’Riordan, Mark McGee and Aidan Moloney – examined the carcass growth and feed efficiency of early and late-maturing suckler bulls.

The study compared spring-born, early and late-maturing suckler bulls – on two different production systems –  slaughtered at three different carcass weights.

All bulls involved in the study were purchased as weanlings at commercial marts in autumn. The early-maturing breeds consisted of Aberdeen Angus and Hereford-sired animals, with an average liveweight of 338kg.

On the other hand, the late-maturing breeds were Charolais and Limousin-sired animals, with an average liveweight of 369kg at the start of the study.

The two production systems were:
  • A high-concentrate (ad-lib) diet, until they reached a target carcass weight of 340kg, 380kg or 420kg;
  • Ad-lib grass silage plus 2kg concentrates/head/day for the winter. Grazed grass for 100 days and – following rehousing – an ad-lib concentrate diet until slaughter at the same target carcass weights – 340kg, 380kg and 420kg.

When averaged across the two production systems and three carcass weights, the late-maturing bulls had a one unit better carcass conformation and a one unit lower carcass fat score (on the 15-point scale) than the early-maturing bulls.

Due to their lower kill-out proportion, the early-maturing bulls needed to be – on average – 21kg (liveweight) heavier at slaughter to achieve the same carcass weight as their late-maturing counterparts.

Additionally, late-maturing bulls were approximately 40 days younger at slaughter than early-maturing bulls at the same carcass weight.

System one

For the first system, (ad-lib concentrates) average daily gain (ADG) decreased from 1.61kg/day to 1.60kg/day and to 1.46kg/day as the late-maturing bulls grew to the carcass weights of 340kg, 380kg and 420kg respectively.

In addition, late-maturing bulls had an estimated carcass gain of 0.83kg/day and 0.82kg/day when the carcass weight increased from 340kg to 380kg, and from 380kg to 420kg respectively.

beef

The corresponding ADG for the early-maturing bulls was 1.59kg/day, 1.42kg/day and 1.32kg/day and carcass gains of 0.63kg/day and 0.61kg/day were recorded.

Furthermore, the early-maturing bulls consumed 32% more feed than late-maturing bulls to achieve the same carcass gain.

System two

Looking at the second production system – when the bulls were finally housed and placed on the ad-lib concentrate diet – late-maturing bulls had an ADG of 1.61kg/day over the short-housing period needed to reach the 340kg carcass target.

In addition, they had an ADG of 2.01kg/day and 1.63kg/day when taken to carcass weights of 380kg and 420kg respectively.

For these Charolais and Limousin-sired bulls, carcass gain was 1.7kg/day between 340kg and 380kg and 1.0kg/day between 380kg and 420kg carcass.

Corresponding liveweight values for the Angus and Hereford-sired bulls were 2.19kg/day, 2.10/kg/day and 1.15kg/day and carcass growth rates of 1.1kg/day and 0.65kg/day were recorded.

As would be expected, the food conversion ratio (FCR) decreased as carcass weight increased, but the late-maturing bulls had a better FCR than the early-maturing bulls; the early-maturing bulls consumed 41% more feed than the late-maturing bulls for the same carcass growth.

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