Top pasture quality improves bull performance

• Published date: 24 May 2023
• Publication title: Central Rural Life

The most efficient conversion of pasture to liveweight gain (LWG) is achieved when bulls experience high growth rates

For example, a bull growing at 0.5kg/day uses a mere 27% of its feed intake for liveweight gain; the other 73% is used for maintenance.

A bull growing at 1.5kg/day uses 53% — more than half — of its intake for liveweight gain and only 47% for maintenance.

The higher the growth rate, the greater the percentage of feed intake that goes into liveweight gain and therefore profit.

The positive impact of this efficient liveweight gain is compounded by the bull reaching finishing weight earlier, thereby freeing up feed otherwise required for that animal’s maintenance.

Feed conversion efficiency

In a study, a Friesian bull grew from 300kg to 600kg. He went on to pasture cover of 2800kgDM/ha and grazed it down to 1500kgDM/ha.

Assuming the highest quality of feed was available, at 11 megajoules of metabolisable energy per kilogram of dry matter (MJME/kgDM), the fastest the bull could reach his finishing weight of 600kg would be 29 weeks.

But if he was on 9MJME/kgDM pasture, it would take 113 weeks to hit finishing weight.

With the bull reaching its finishing weight at 29 weeks, enough feed is freed up to finish, for example, either 44 lambs at 40kg (from an initial weight of 25kg), or four more bulls.

The average feed quality on Waikato bull farms is 10MJME/kg DM. That would mean a bull would finish within 44 weeks, freeing up enough feed to finish either 22 lambs, or three more bulls.

Metabolisable energy

The most important nutritional limitation for bulls is insufficient metabolisable energy (ME) intake.

Bull liveweight gain increases as pasture quality increases. Why? Because the higher the pasture quality, the higher its ME content per kilogram of DM.

Feeding a bull more of a low-quality pasture does not compensate for the lower ME/kgDM.

Pasture quality

- Impact of pasture variables on quality

Pasture varies in many aspects, including the content of green material, leaf versus stem, clover component, etc.

High-quality pasture has:

• high content of green leaf;

• high content of clover;

• low content of stem and dead matter;

• young (recently grown) herbage;

• grown in cooler conditions.

- Diet selection and feed quality

The higher a pasture cover, the greater opportunity a bull has to select what he chooses to eat. He will choose the highest quality components first. So, as overall pasture cover decreases, so does the overall pasture quality.

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