19 August 2014

7 minute read

Introduction

Marbling influences beef’s ultimate eating satisfaction, and has resulted in development of premium beef products that require a high degree of marbling, writes Dr Ahola.

Recent research at Colorado State University (CSU) indicates that beef from carcasses with modest marbling (equivalent to average Choice) provides an 82 per cent probability of a positive sensory experience (Figure 1; Emerson et al., 2013), which is greater than the probability of a positive sensory experience associated with small marbling (equivalent to low Choice; 62 per cent ). Probability is maximized at 99 per cent in steaks from carcasses with slightly abundant marbling (equivalent to low Prime).

Thus, ensuring that consumers have a positive eating experience requires creation of highly-marbled beef carcasses. Unfortunately, the U.S. beef industry continues to struggle with this, as evidenced by limited industry-wide progress in marbling deposition based on National Beef Quality Audit (NBQA) data from the 2 most recent audits. According to the 2011 NBQA, industry experts estimated the “ideal” consist of beef carcasses was 69.0 per cent Choice or higher, based on demand by retailers, food service companies, etc. (Figure 2; NCBA, 2011).

However,in the 2011 NBQA only 61.0 per cent of carcasses actually graded Choice or higher. Progress up until that point had been limited, based on the fact that the percent of carcasses grading Choice or Prime increased only 6.5 per cent percent (just 3.7 percentage points) from 57.3 to 61.0 per cent during the previous 6-year period (2005 to 2011; NCBA 2005, 2011).

Marbling deposition is moderately to highly heritable (h2 range = 0.30 to 0.57; Utrera and Van Vleck, 2004), which has enabled great strides in marbling improvement due to genetic selection alone.

Conversely, the remaining variation in marbling (about half, or more, of total variation) is due to the environment, including how cattle are managed. Recent research suggests that deposition of marbling can be influenced much earlier in a beef animal’s life than previously believed, indicating an opportunity for changes to be made via management.

Thus, the objective of this paper is to provide a synopsis of factors around the time of weaning that have been shown in the scientific literature to influence eating quality and/or marbling deposition in beef cattle.

In a recent comprehensive review, Du et al. (2013) provided an overview of fat tissue development in beef cattle. Cells that become fat (adipocyte) or muscle (myocyte) tissue originate during embryonic development as “progenitor” cells (i.e. forbearers of future body cells).

Promotion of one or the other of these early cell lines results in either enhanced muscle growth (via bolstered myogenesis and creation of muscle cells) or fat cell formation including marbling deposition (via increased adipogenesis and creation of fat cells). Influencing progenitor cells via nutrition or management early in development (vs. later) is more effective due to the declining number of these cells as an animal gets older (Du et al., 2013).

Creation of fat cells begins in an embryo during mid-gestation when visceral fat develops, which continues into the newborn stage. This is followed by the start of subcutaneous, intermuscular (seam), and intramuscular (marbling) adipogenesis, which continues through pre-weaning (for both subcutaneous and intermuscular) and as late as 250 days of age (for intramuscular) as indicated by Du et al. (2013).

The authors reported that intramuscular adipogenesis can be influenced via dietary and/or management intervention during a “marbling window”, which is the timeframe from pre-weaning through about 250 days of age in which fat deposition processes may be altered (Figure 3).

Conclusions

For more than a decade, the beef industry has been unable to supply the amount of highly marbled beef (Choice or higher) consumers are demanding. And, through genetic progress alone the industry has been unable to make adequate progress. Elevated feed costs and increased concerns over the effect of beef production on the environment will further pressure marbling deposition in cattle to be a more energy efficient process.

Thus, the industry must place increased emphasis on management efforts, particularly those prior to arrival at a feedyard, that promote intramuscular fat deposition. This paper reviewed research data associated with these processes. Unfortunately, the scientific literature in many areas is very limited since the industry’s historical focus on increasing marbling has been on the feedyard phase of cattle 21 production.

Further, many studies that evaluated weaning-time activities were unable to avoid confounding effects on marbling due to the long time period from weaning to harvest, and due to experimental design (i.e. age at weaning and plane of nutrition). And, extramural funding to support research in these areas is very limited, at least from government agencies. However, it is clear that substantial influence on marbling deposition and eating quality of beef can be achieved by changes in the management of calves around the time of weaning.

10 Key Take-Home Points

1. Diet influences the volatile fatty acid (VFA) ratio, and a grain diet increases propionate (from 15-25 to 35-45 per cent of total VFA) at the expense of acetate vs. a forage diet. Acetate provides the majority of raw materials (70 to 80 per cent of acetyl units) for subcutaneous fat synthesis, while the liver generates glucose from propionate. In turn, glucose provides the majority of raw material (50 to 60 per cent ) needed to produce intramuscular fat.
2. Weaning calves early can increase marbling deposition but doesn’t necessarily enhance eating quality, and has not been shown to affect cattle that are heat adapted, grade a low percent Choice, or harvested at a backfat thickness similar to normal weaned cattle. Since early weaned cattle have accelerated fat synthesis early in life (including increased backfat deposition), they are more physiologically advanced than normal weaned calves at harvest.
3. Although data are limited, there is no evidence of decreased marbling deposition resulting from calves weaned late (i.e. 300 days of age). However, the earlier that cattle can be placed on feed (as early or normal weaned calves vs. yearlings), the greater their marbling potential.
4. Creep feeding calves weaned at a normal age (e.g. 205 days) can increase marbling deposition, but results are not consistent. Similarly, the effect of creep feed source (i.e. fiber- vs. starch-based) on marbling is not convincing. However, it is clear that providing a high energy post-weaning diet to early weaned calves will increase marbling, but neither feed source (i.e. fiber- vs. starch-based) nor rumen degradability of protein appear to matter.
5. Among early weaned calves, a high concentrate post-weaning diet increases fat deposition (both subcutaneous and intramuscular) vs. forage- or limit-feeding. Yet, due to accelerated backfat deposition, differences will not be observed if cattle are harvested at a constant backfat thickness since calves early weaned only grain will not have an opportunity to express their marbling potential.
6. Several trace minerals clearly influence marbling deposition (e.g. Cu and Zn) in the feedyard, but their dietary effect around the time of weaning has not been thoroughly studied. Further research is needed in this area.
7. Weaning method (i.e. abrupt removal, two-stage with nose flaps, fence-line, etc.) influences a calf’s level of stress at the time of weaning, based predominantly on differences in short-term performance and behavior during the immediate post-weaning period. However, larger long-term differences in performance have not been shown, and carcass traits have not been studied – further research is needed.
8. Rate of post-weaning morbidity influences marbling deposition, particularly treatment for BRD in high risk cattle. However, cattle morbidity rate in low risk does not appear to influence marbling deposition. Parasite burden at feedyard arrival altered intramuscular fat deposition, and de-worming protocols have been shown to influence carcass quality. Regardless, limited data specific to the effects of morbidity during the immediate post-weaning period are available.
9. It is accepted that castration of male calves improves marbling deposition and end-product palatability. However, in higher marbling breeds of cattle (e.g. Angus, Holstein), early castration at lighter weights improves marbling, tenderness, and palatability. Additionally, there is a benefit to end-product quality if castration at heavy weights can be avoided.
10. Administration of growth-promoting implants at branding or weaning does not hinder marbling deposition, but administering 2 or more implants to a steer during his lifetime will. Among early weaned calves, implants don’t appear to affect marbling if given at weaning. However, implants given to heavy calves early in the growing period can negatively impact marbling vs. delaying the implant when days on feed is constant.
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