Resilient grass-based systems for beef cattle
In beef production systems, feed provision is the single largest direct cost incurred, accounting for approximately 75% of total costs of production. Beef specialist Catherine Egan and researcher Mark McGee have advice and information.
Due to the considerably lower comparative cost of grazed grass as a feedstuff, beef production systems should aim to increase animal output from grazed pasture. However, an indoor ‘winter’ period of varying duration is inevitable on all Irish farms. The main feed costs on grass-based beef systems relate to feeding grass silage and concentrates, and especially when feeding finishing cattle. The key principles for ‘first’ winter, ‘second’ grazing season and ‘finishing’ period management are similar for both suckler- and dairy-bred cattle.
Feeding ‘weanlings’ during the winter
To minimise feed costs and exploit subsequent compensatory (“catch-up”) growth at pasture during the following grazing season, live weight gains of 0.5-0.6 kg/day through the first winter is acceptable for steers, heifers (and suckler bulls) destined to return to pasture in spring. Research at Teagasc Grange has shown that there is little point in over-feeding weanlings in winter as, during the subsequent grazing season, cattle that gained less over the winter had the highest live weight gain at pasture, resulting in most of the winter weight advantage ‘disappearing’ by the end of the grazing season. However, cattle growing too slowly during winter (<0.5 kg/day) will not be able to compensate sufficiently at pasture, and consequently, will not reach target weights later in life.
Dry matter digestibility (DMD) is the primary factor influencing the nutritive value of grass silage and consequently, the performance of cattle. Low DMD silage means higher levels of concentrate supplementation have to be used to achieve the same growth rates; this highlights the importance of having good silage quality for growing cattle.
Second grazing season management
As every tonne of additional grass dry matter (DM) consumed by a grazing animal will add €105/ha extra profit to a beef farm, it is important that investment in grazing is prioritised to give the maximum return. The foundation underpinning good grass production and utilisation is having adequate soil fertility, unimpeded drainage, targeted application of fertiliser and good grazing infrastructure, coupled with appropriate grazing management practices. A target live weight gain of 1 kg/day throughout the second grazing season should be attainable without meal supplementation; however, this is often not the case. Improving grassland management is an area where high weight gain can be achieved at low cost. Turning cattle out to grass as early as possible in spring and ensuring an adequate supply of good quality leafy grass is an important start. Grazing tightly and finishing the first rotation ‘on time’ is critical for good utilisation and ensuring high quality grass during subsequent grazing rotations. High animal performance can be accomplished by targeting grazing covers of 8-10 cm (~1,200-1600 kg/DM/Ha), grazing out tight (~4 cm), while allowing 18 to 21 days for grass regrowth ‘recovery’. This is broadly captured in the phrase “Grown in 3 weeks, graze in 3 days” and forms the basis for a rotational grazing paddock system. If grass supply exceeds demand, surplus grass can be removed as round bale silage. Building up grass covers is required if cattle are to remain at pasture in late autumn. A key focus of autumn grazing management is to finish the grazing season with the desired farm cover, ensuring there will be sufficient grass for early-turnout the following spring. Prevailing soil type and weather conditions have a large impact on the duration of the grazing season.
As grazed grass is considerably cheaper than grass silage (or concentrates), early finishing of cattle at pasture in autumn, before housing becomes necessary, is less costly. Carcass growth response to concentrate supplementation while grazing will primarily depend on the availability and quality of pasture and level of supplemented concentrate; response is higher where grass supply is low and where grass quality is poorer, and declines as concentrate supplementation level increases. In autumn the diet of grazing cattle is generally unbalanced, in terms of energy and protein, because there is usually excess degradable protein in autumn grass. Research at Grange has shown dietary energy rather than protein is the limiting factor and, where supplementation occurs, concentrate energy sources are required.
Even high-quality grass silage is incapable of sustaining adequate growth rates to exploit the growth potential of most cattle so concentrate supplementation is required. Each 1 unit decline in DMD of grass silage requires an additional 0.3-0.4 kg concentrate daily to sustain performance in finishing cattle. Efficiency of feed utilisation by finishing cattle primarily depends on weight of animal (decreases as live weight increases), potential for carcass growth (e.g. breed type, gender, compensatory growth potential) and duration (decreases as length increases) of finishing period. The optimum level of concentrate supplementation primarily depends on animal production response (kg gain/kg concentrate), forage substitution rate (the decrease in silage DM intake per unit of concentrate intake) and the relative prices of animal product and feedstuffs. It is important to ensure that an adequate level of an appropriate mineral/vitamin mix is included in the ration.
Concentrate feed ingredients
Comparisons of feedstuffs should always be based on their ‘net’ energy (and protein) values on a DM basis. Interactions or ‘associative effects’ between grass silage and concentrate feed ingredients have consequences for feed utilisation, and thus, the nutritive value assigned to feed ingredients. This means that relative feeding (and economic value) of by-product feed ingredients is contingent on concentrate feeding practices, such as inclusion level in the concentrate ration and the amount of concentrates fed, e.g. soya hulls may have an equivalent or inferior feeding value to rolled barley depending on feeding circumstances.
Energy is the most important nutrient required by growing-finishing cattle. Weanling and finishing, steers and heifers generally do not require protein supplementation when fed barley-based concentrates and high DMD grass silage, but for suckler bull weanlings, recent research at Grange showed a significant, but small, response to protein supplementation. However, all cattle are likely to respond to supplementary protein in barley-based concentrates when grass silage has moderate to low DMD and/or low protein content, especially weanlings.