Accounting for over 75% of the total variable costs, feed is the single largest variable cost on Irish beef farms.
Between concentrates and conserved forage, grazed grass is the cheapest feed source in a grass-based system and beef finishers should aim to maximise animal output from grass.
However, the main feed costs on beef farms occur during the winter period, when animals are kept indoors and – especially – where farmers are trying to finish cattle.
According to Teagasc’s Dr. Mark McGee, who spoke at this week’s National Beef Conference, grazed grass accounts for 66% of animals’ diets on most research farms in Ireland. Grass silage and concentrates account for just 27% and 7% respectively. These figures are based on dry matter intakes.
For weanling animals, heading into their first winter indoors, the optimum winter growth rate is 0.5-0.7kg/day. At this rates, weanlings will avail of compensatory growth on grazed grass next spring.
Concentrate supplementation required for weanlings to grow 0.5kg/day over the winter will vary depending on silage quality. Weanling heifers and steers being fed grass silage, with a dry matter digestibility (DMD) of 60%, should be supplemented with 2-3kg of concentrates per day.
Weanlings receiving silage with a DMD of 65% should be fed 1.5-2kg of supplements per day; heifer and steer weanlings receiving silage with a DMD of 70% or 75% should be supplemented with 1.0-1.5kg or 0-1kg/day respectively.
McGee said: “Feed utilisation efficiency for finishing cattle primarily depends on the weight of the animal, the potential for carcass growth and the duration of the finishing period.
High-quality grass silage alone will not supply sufficient nutrients to sustain adequate growth rates to exploit the growth potential of most cattle; so concentrate supplementation is required.
For farmers aiming to finish steers over the winter, feeding grass silage with a DMD of 65%, and aiming for an average daily gain (ADG) of 1kg/day – these steers need to be fed 7-8kg/day.
Steers being fed silage with a DMD of 70% and 75% require supplementation at a rate of 5.5-6.5kg/day and 4-5kg/day respectively.
In addition, for finishing heifers, daily supplementation should be reduced by 1.5-2.0kg/day. The rate of concentrates required to finish bulls should be increased by 1.5-2kg/day on the steer rates.
It must be noted, where grass silage DMD is poor (60%) and animal growth potential is high, feeding concentrates ad-libitum should be considered. However, when feeding high levels of concentrates ad- libitum, particularly cereals, there is a risk of acidosis.