27-05-2025
Pasture quality can aid liveweight gain
Managing pasture quality offers massive potential for improving bull performance.
That was the key message from a Mid Northern North Island Beef Council Beef Production Field Days event.
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.
That means 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, ongoing. Feed conversion efficiency
A Friesian bull grows from 300kg to 600kg. It goes on to pasture cover of 2800kg of dry matter per hectare (DM/ha) and grazes it down to 1500kgDM/ha.
Assuming the highest quality of feed is available, with 11 megajoules of metabolisable energy per kilogram of dry matter (MJME/kgDM), the fastest the bull could reach its finishing weight of 600kg would be 29 weeks.
Compare this with the 113 weeks it would take to hit finishing weight if the animal was on 9MJME/kgDM quality pasture.
With the bull reaching its finishing weight so quickly — within 29 weeks, compared with 113 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. A bull would finish within 44 weeks (compared with 113 weeks on 9MJME/kgDM), 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:
Higher-quality pasture contains more green material, higher ratios of clover to grass and leaf to stem, more young (recently grown) content than older content, and cooler temperatures.
Lower-quality pasture has more dead material, lower clover to grass and leaf to stem ratios, more older material, and warmer temperatures.
Clover leaf declines most slowly, grass leaf declines more quickly, and stem declines most quickly.
Diet selection and feed quality:
The higher a pasture cover, the greater opportunity a bull has to select what it chooses to eat. It will choose the highest-quality components first. So, as overall pasture cover decreases, so does the overall pasture quality.
You then see a lower dry matter intake, because of the lower-quality pasture.
The key is to move young stock off grazed pasture sooner rather than later. The lower-quality feed left behind can be cleaned up by low-priority stock or by topping. — Beef + Lamb New Zealand
