Background

Beef suckler cows comprise approximately half (1.1m) of the cow population in Ireland. Late-maturing continental breeds now account for over 75% of suckler cows, of which, 85% are bred to continental sire breeds (McGee, 2012). They are operated within systems where grazed grass is the major dietary input. These cows are predominantly spring-calving with their progeny taken to finish at about 20 (heifers) and 24 (steers) months of age or greater (O’Donovan et al., 2010). Thus, where progeny are taken through to slaughter, there are usually two grazing seasons and one or two indoor winter periods (e.g. Drennan and McGee, 2009). Frequently, the production system may involve selling the progeny as live animals, including shortly after weaning, at the beginning (as yearlings) or end (at 1.5 years old) of the second grazing season. Of the predominant feedstuffs readily available in Ireland, efficiently managed grazed grass is the cheapest, followed by grass silage which, in turn, is cheaper than concentrates (Finneran et al., 2012). Therefore, the rationale for these grass-based production systems is the considerably lower comparative cost of grazed grass as a feedstuff together with its potentially high nutritive value and thus, high animal performance compared to forage-based diets offered indoors. The objective is to maximise financial returns by enabling the genetic capacity of beef cattle to be met within grass-based systems.

Central to the biological and economical sustainability of suckled beef production is an efficient cow. In calf-to-weaning and calf-to-beef systems the cow consumes over 80% and 50%, respectively, of the feed required annually. Consequently, feeding the suckler cow is the major expense incurred in suckled calf production and optimising cow productivity within the context of the production system operated is essential. The lifetime productivity of the beef bred female commences from the onset of puberty and will be dictated by subsequent critical events including age at first calving, duration of the postpartum interval for each successive calving, conception and pregnancy rate and ultimately manifested as length of inter-calving intervals and number of calves weaned over her lifetime (Diskin and Kenny, 2014). Good reproductive performance i.e. producing close to one healthy calf per cow exposed for breeding is critical and ideally cows need to first calve at 2 years old as it is biologically and economically more efficient (Crosson and McGee, 2012).

Likewise, high lifetime live weight gain of progeny i.e. attaining high weight for age during pre-weaning (combining cow milk yield and the animal’s own genetic capacity for growth) and post-weaning (genetic merit, feeding management and exploiting compensatory growth) coupled with good carcass traits (high kill-out proportion, good carcass conformation and adequate carcass fat score and meat quality traits), is essential.

This paper will address aspects of suckler cow efficiency (at the animal and system level), including breed types, genetic merit, feed efficiency and cow management in the context grass-based systems of production.

Cow breed types and genetic merit

Within the beef herd in Ireland an increasing proportion of the genotype of both the dams and sires has come from late-maturing breeds such as Charolais and Limousin. The cow breed structure is very mixed, comprising of many breed types and countless combinations of these. The advantages of heterosis or hybrid vigour for reproduction and maternal traits in beef suckler cows have been widely demonstrated (ca. +13% – calf weight weaned per cow exposed for breeding) and there are further advantages in progeny performance from using a sire from a third breed (ca. +8%) (Buckley et al., 2005). The benefits of hybrid vigour from cross-breeding are due to a combination of: enhanced reproductive performance, lower calf mortality and higher calf growth to weaning.

In Ireland the main replacement breeding strategies available to farmers are sourcing replacement heifers from the dairy herd or from the suckler herd. From all the cow breed comparisons carried out at Teagasc, Grange to date, the Limousin X Holstein-Friesian remains the benchmark cow breed type (McGee, 2012). This ‘cow type’ has a relatively moderate feed intake, good reproductive performance and produces progeny with (i) a high passive immunity (ability to fight-off disease) due to higher colostrum production of the dam, (ii) a high weaning weight due to higher milk production of the dam, (iii) high carcass weight per day of age, mainly due to higher pre-weaning growth and (iv) relatively good carcass classification traits (conformation and fat score) and carcass composition characteristics. However, crossbred beef breed cows with good maternal traits can achieve almost comparable performance (McGee, 2012).

Although there is a breed ranking for different traits, there is variation within genotype and consequently, a relatively large overlap between genotypes for many traits. Efforts to improve the genetics associated with beef suckler cow production traits need to be based on selection according to individual animal performance (within the breed type chosen). The challenge is, reliably identifying these high performing animals and proliferating their genetics through structured animal breeding programmes.

In Ireland, two new beef breeding economic indexes for use in the suckler herd were launched in autumn 2012 by the Irish Cattle Breeding Federation (ICBF), namely, the ‘Terminal Index’ and the ‘Maternal Index’ (now called ‘Replacement Index’) (Evans and Cromie, 2012). Sires should be selected on the basis of the Terminal Index (and sub-indices) where progeny are produced for slaughter, and on the basis of the Replacement Index (and sub-indices) where replacement heifers – home-bred or purchased – are selected for breeding. The accuracy of the Irish maternal genetic evaluations in beef cattle was assessed using national field data (McHugh et al., 2014) with results indicating that selection of breeding animals for favourable maternal genetic attributes resulted in favourable improvements in phenotypic performance. A research herd comprising two diverse genotypes, high and low ‘Replacement Index’, was established at Teagasc Grange to validate the Replacement Index (Prendiville and McHugh, 2014). This evaluation study is on-going.

With the advent of the new beef ‘Replacement’ Index, coupled with higher reliability beef bull genetic evaluations, increased rates of genetic gain and production efficiency within the national beef suckler herd should be possible.

Feed efficiency in suckler cows

Feed provision is the largest variable cost (70%+) in beef production systems. As outlined earlier, the cow herd consumes a high proportion of the annual feed inputs. Since about 70% of the total energy consumed by beef cattle goes towards maintenance requirements, this means that cow maintenance costs are a considerable proportion of the total feed costs of beef production systems. Consequently, feed efficiency (FE) is central to economical and environmentally sustainable production systems. Traditionally, FE of livestock has been expressed as the level of bodyweight or carcass growth attained for a given quantity of feed. It is generally agreed that use of this type of ratio trait, commonly referred to as ‘feed conversion efficiency’ or its inverse ‘feed conversion ratio’ (kg feed per unit of gain) in breeding programmes generally leads to selection of faster growing cattle with larger mature size. Consequently, if the gains in progeny growth efficiency are partially or fully offset by an increase in feed requirements of the (heavier) breeding cow herd, there will be little or no change in production system FE. Thus, there has been much interest, worldwide, in examining alternative FE traits. The concept of residual feed intake (RFI), rather than feed conversion ratio, is becoming the preferred measure of FE; this trait is genetically independent of growth and body size. It is calculated as the difference between actual feed intake and predicted feed intake, with negative or smaller values more desirable than positive or larger values; animals with low RFI (efficient) eat less than expected based on their weight and growth (production).

Beef cattle differing in FE consume substantially diverse amounts of feed to achieve the same production. For example, Teagasc research on RFI has shown that in any group of growing cattle there can be up to 20% difference in the feed consumed by the most efficient cohort compared to the least efficient cohort of animals for the same level of growth and performance (e.g. Crowley et al., 2010; Fitzsimons et al., 2013; 2014a; Kelly et al., 2010a, b; Lawrence et al., 2012). Likewise, we have shown that differences of this magnitude are evident within populations of (pregnant) beef suckler cows (McGee, 2009; Lawrence et al., 2011, 2013; Fitzsimons et al., 2014b). Additionally we, and others, have demonstrated significant genetic variance in RFI (Crowley et al., 2010) and that, genetically, it is not antagonistically associated with desirable growth or carcass traits in growing beef cattle (Crowley et al., 2011a) or performance traits in beef suckler cows, with the exception of possibly delaying the onset of puberty (Crowley et al., 2011b). However, the latter can be negated by including measures of body fatness in the base model used to calculate RFI (Basarab et al., 2013). Furthermore, our research has shown that low RFI animals produce less methane daily than their high RFI counterparts (Fitzsimons et al., 2013). Again, the challenge is to reliably and cost-effectively identify these feed efficient animals.

Worldwide, breeding values of bulls for feed intake or FE are typically derived from progeny performance based on ad libitum access to energy dense rations whereas, in many countries including Ireland, the lifetime gain of most commercial beef cattle is achieved from diets consisting, to a significant extent, of lower energy density feeds such as grazed grass and/or ensiled forages.

There is evidence from our own work, and that of others, that although somewhat repeatable, ranking of beef cattle for FE offered the same diet is not necessarily consistent over different phases of their lifetime, and this may be further exacerbated when diets differing in energy density are fed successively (i.e. forage versus concentrate based diets), as per commercial practice. This strongly indicates the presence of what is termed a ‘genotype X environment’ interaction for the trait, in other words that the relative feed efficiency of a particular animal depends on the type of feed it is offered or management system within which it is reared. For example, our data have shown that growing beef heifers ranked as divergent for RFI on a grass silage plus concentrate diet indoors did not differ in herbage intake (during early pregnancy) when subsequently grazing pasture (Lawrence et al., 2012). However, the existence of such a phenomenon has not been adequately tested to-date.

Recently, a large research programme, funded by the Irish Department of Agriculture, Food and the Marine, has commenced at Teagasc, Grange with the objectives of (i) quantifying the repeatability of performance and FE across different diets and (ii) identifying the key genes controlling the trait so that such information can ultimately be incorporated into the planned genomic selection based breeding programme for beef cattle in Ireland. This should, in time, aid the identification of animals that are most profitable to produce under our grass-based production systems.

Grass-based Production Systems

Grazed grass and grass silage

Due to the considerably lower comparative cost of grazed grass as a feedstuff, maximising the proportion of high digestibility, grazed grass in the annual feed budget is critical. Grassland management revolves around a flexible rotational grazing system, with the objective of providing high yields, of high digestibility leafy grass over a long grazing season. However, due to the seasonality of grass growth in Ireland, an indoor winter period is inevitable. The duration of this indoor period is dictated by factors such as prevailing climatic and weather environments, soil and sward type, and grazing conditions. Providing sufficient grass silage of appropriate digestibility for the indoor winter period is also central to the production system. For the spring-calving suckler cow, grass silage is the primary and usually sole (depending on silage nutritive value and cow body condition score (BCS)), feedstuff offered during this time.

Although the indoor winter period is usually of shorter duration than the grazing season, due to the relative costs of grazed grass and grass silage, on most suckler calf-to-weaningfarms, primary feed costs relate to winter. For example, within spring calving, grass-based, suckler calf-to-weaning systems on research farms (ca. 4.5 month winter), almost three-quarters of the feed consumed annually is comprised of grazed grass, with the remainder made up of grass silage (26%) and concentrates (1%). However, when this feed budget is expressed in terms of cost (excluding land charge), outcome is very different, in that grazed grass makes up only 45% of total feed cost, whereas grass silage accounts for 50% and concentrates accounts for 5% of total feed costs. Thus, while grazed grass is fundamental, feeding silage is a key (cost) component of suckler cow nutrition. Consequently, in order to maximise profitability of suckler systems, a long grazing season with a corresponding short indoor winter feeding period is required and provision of the cow’s winter diet at a low a cost as practicable, is necessary.

For economic reasons suckler cow nutrition generally involves mobilisation of cow body reserves in winter when feed is more expensive and deposition of body reserves during the subsequent grazing season when consuming lower cost grass (e.g. Drennan and McGee, 2004). The BCS of cows at the start of the winter feeding period has a major effect on the amount and quality of feed required. Where mature spring-calving suckler cows are in good BCS (~3.0+, scale 0–5) at the start of the winter their feed energy intake can be restricted such that some of the body fat reserves are utilised to reduce winter feed requirements. This feed energy restriction can result in a feed saving of up to 25%, equivalent to 1.0 to 1.5 tonnes fresh weight of grass silage (assuming silage dry matter (DM) of 20% & DM digestibility of 65%).

Spring calving date and turnout date to pasture

Turnout of livestock to pasture in spring has to be delayed until grass growth begins and sufficient herbage has accumulated to meet animal demand. Additionally, grazing conditions must be adequate. Commencement of grass growth is largely determined by ambient soil temperatures i.e. a grass growing day is classified as a day where soil temperature is >5 °C at 9.00 am (O’Donovan et al., 2010). This is very much location/site dependent. For example, applying this criteria to 4 temperature recorded Teagasc sites in Ireland namely, Moorepark (Cork – the South), Ballyhaise (Cavan – North) and Grange (Meath – East) over a 10 year period results in mean grass growth commencement dates of 15 February, 12 March and 25 March, respectively, with large variation between years (Williams and O’Kiely, unpublished). As a result, the degree to which early turnout to pasture can be easily exploited will vary substantially according to geographical location/site, but also from year to year in relation to meteorological, soil, sward and grazing conditions. This means that having a sufficient buffer of winter forage is critical and flexibility in grazing management is required.

Compact calving before turn out to pasture in spring in order to maximise herbage utilisation is an essential component of profitable grass-based suckler systems. Median calving date should coincide with the start of the grass growing/grazing season. Research at Grange has shown that, earlier calving and turnout to pasture (onto the grazing platform) generally improves farm net margins by reducing the proportion of more expensive grass silage (and concentrates) in the annual feed budget and replacing it with cheaper grazed grass (Crosson et al., 2009). Furthermore, slurry handling costs are reduced. However, earlier calving and turnout to pasture in spring will only increase farm net margin where an adequate supply of grass is available and grazing conditions are suitable to facilitate this. In other words, calving too early leads to a decline in profitability as higher costs, usually associated with autumn-calving systems, start to materialise.

The herbage mass available to grazing livestock during spring can be increased if all the grassland on a farm, including the area destined for first harvest silage, is utilised during the first grazing rotation although grazing spring swards designated for first cut silage may have adverse effects on subsequent silage yield especially when the interval between spring grazing and silage harvesting is relatively short (McGee et al., 2014). This has important ramifications for farm profitability considering the negative relationship between yield and cost of producing grass silage (Finneran et al., 2011, 2012). Where grazing conditions are difficult, restricted / ‘on-off’ grazing, whereby animals are given limited access time to pasture daily may be used. In a series of studies at Teagasc Grange, earlier turnout to pasture in spring (ca. 3– 4 weeks) of suckler cows via restricted (i.e. 6 hours daily – cow only) or fulltime access (cow & calf) to pasture resulted in feed cost savings of between €0.52 and €1.11 per cow per day with no recorded adverse effects on animal performance (Gould et al., 2010; 2011).

Stocking rate

Economic analysis of grass-based suckler calf-to-beef production system comparisons at Grange (e.g. 210 vs. 170 kg organic Nitrogen/ha) has shown that where individual animal performance remains high, stocking rate is the main driver of farm profitability (Crosson et al., 2009). Consequently operating at a relatively high stocking rate is important.

In summary, for lowland grass-based suckler beef systems key principles of profitable production include, operating at a high stocking rate, compact calving before turn out to pasture in spring to ensure maximum herbage utilisation, and high levels of animal performance.

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