The Impact of Hormonal Growth Promotants on Carcass Composition and Meat Quality

Index (click on the links below)

1. Introduction
2. Discussion

2.1 The effect of HGPs on Carcass Composition

2.2 The effect of HGPs on Beef Quality

2.2.1 The effect of HGPs on Marbling
2.2.2 The effect of HGPs on Meat Color
2.2.3 The effect of HGPs on Tenderness
2.2.4 The effect of HGPs on Palatability
2.2.5 HGPs and Human Health Issues

3. Conclusion
4. References

Naturally produced hormones in animals play an important role in the physiological, biochemical, and behavioral changes associated with growth and development. Because of economic incentives, the beef industry has attempted to improve the efficiency of growth and carcass composition of cattle through the use of naturally occurring and synthetic hormones. In the USA Hormonal Growth Promotants (HGPs) have been used since 1947 to improve growth rates and reduce the cost of gain (Montgomery et al. 2001). Currently approximately 90% of U.S. lot fed cattle are implanted with HGPs (Anon. 2003). Since 1979 HGPs have been widely adopted by both the pasture and particularly the grain fed sectors of the Australian beef industry to improve feed efficiency. Following the development of the MSA model, there has been increased focus on meat quality in Australia. This has resulted in increased interest in the effect of HGPs on meat quality in addition to their effect on carcass composition. There has been considerable discussion about incorporation of HGPs into the MSA model. This paper discusses i) the impact of HGPs on carcass fat and muscle ii) the impact of HGPs on consumer palatability scores as well as traits that affect meat quality such as marbling, meat color, and tenderness and iii) HGP residual levels and meat quality.

2. Discussion.....................................................................................................go to Top

2.1 The effect of HGPs on Carcass Composition.... ..go to Top

Beermann (1994) stated that implanting cattle increases their mature size. Consequently, implanting increases the quantity of muscle growth and tends to delay fat deposition. Therefore, at the same liveweight, implanted cattle would be expected to have a higher percentage of muscle and a lower percentage of fat than non-implanted cattle (Figure 1).

Figure 1 a) Liveweight growth curves for large and small mature size animals and b) comparison of body composition at the same live weight (Thompson et al. 2001a).

However, an experiment by Hunter et al. (2001a) showed that when comparisons were made at the same carcass weight, oestradiol treatment had no significant effect on the yield of retail beef or on the degree of fatness. Hunter et al. stated that the additional yield of beef from steers treated with oestradiol was principally due to the increased growth rate and the heavier carcasses of those steers.

According to Beermann’s statement that implanting cattle increases their mature size, at the same age or time on feed implanted cattle would be expected to have a greater weight of muscle and an equal or lower weight of fat (Figure 2). In Australia, dressing percentage would therefore be expected to be increased slightly at a constant time end point due to less internal fat. Retail beef yield would also be expected to be slightly higher for implanted cattle.

Figure 2 a) Liveweight growth curves for large and small mature size breeds and b) comparison of body composition at the same age (Thompson et al. 2001a)

HGPs are classified as oestrogenic, androgenic, or a combination of both. In live animals oestrogens are principally produced by the female ovaries and androgens are principally produced by the male testes.

Oestrogenic implants increase protein deposition by increasing the concentration of somatotropin or growth hormone (GH) and insulin secreted (Thompson et al. 2001b). GH directly or indirectly stimulates anabolic processes such as cell division, skeletal growth and protein synthesis (growth promoting activity) whilst increasing the oxidation of fat (lipolytic activity) and inhibiting the transport of glucose into body tissues. The primary physiological role of GH is thought to be preserving body protein, stimulating the incorporation of amino acids into the muscle whilst diverting glucose and fatty acids away from tissue deposition, thus making them available as alternative sources of energy (Thompson et al. 2001a).

Androgenic implants result in a net increase in muscle protein deposition (Thompson et al. 2001). The mechanism involves a direct interaction of androgen with muscle cell receptors, thereby increasing protein synthesis via the release of GH and IGF-1.

Thompson et al. (2001a) state that GH increased by oestrogenic implants inhibits proteolysis and androgens also reduce cortisol activity in muscle cells thereby reducing the rate of protein catabolism. However, ratios of urinary N-methylhistidine (NMH):creatine calculated to provide an index of skeletal muscle protein degradation relative to unit of muscle mass indicate that muscle protein degradation closely parallels total body protein mass and is not altered by anabolic agent treatment (estradiol-17ß, trenbolone acetate (TBA) or estradiol-17 ß plus TBA) (Hayden et al. 1992). Gopinath and Kitts (1982) also demonstrated that NMH:creatinine ratios were not affected by diethylstilbestrol, Synovex-S or Zeranol treatment.

In summary, both oestrogenics and androgenics increase protein deposition. Primarily through altered nutrient partitioning, these hormones are thought to reduce fat deposition.

When oestrogenic and androgenic implants are used in combination, they act independently resulting in an additive effect.

Combination implants containing trenbolone acetate (TBA) are referred to as “aggressive” implants because they generally increase growth rate, improve feed efficiency, and delay fattening to the greatest extent (Montgomery 2003). Studies (Bartle et. al. 1992; Duckett et. al. 1996; Roeber et. al. 2000) have reported lower percentages of kidney, pelvic, and heart fat in cattle implanted with combination implants. Foutz et al. (1997) found that implants increased subprimal and total side lean yields compared to controls; the largest increases of 2.3 and 2.8% respectively, occurred in steers receiving TBA plus an oestrogen. Similarly Griffith (1982) found that a combination of the oestrogenic compound zeranol plus TBA increased lean yields from 2.7% to 3.7%. However studies have shown little or no effect of implant treatment on external fat thickness (Gerken et. al. 1995; Samber et. al. 1996; Foutz et. al. 1997; Roeber et. al. 2000).

Cattle must have adequate nutrition before implants can positively affect gain and feed efficiency. The greatest response to implantation tends to be observed in cattle near peak periods of lean tissue deposition (Blezinger 2003). Heifers and steers show the greatest response to steroid implants, whereas bulls do not show much response (Dikeman 2003). Bulls differ in that they may deposit more, rather than less, fat when implanted. In general, breeds or types of cattle that have the greatest response for muscle growth show the greatest response to implants. Greater responses are often observed during the first few weeks after implantation, suggesting a peak and then a decline in circulating concentrations of the hormones (Hayden et. al. 1992).

2.2 The Effect of HGPs on Beef Quality.............................go to Top

Unfortunately, the effect of HGPs on meat quality has received little attention until recently.

2.2.1 The effect of HGPs on Marbling............................................go to Top

Treatment of cattle with an HGP is likely to result in a small decrease in marbling (Hunter et al. 2001b). This effect is consistent with the anabolic nature of HGPs and their propensity to increase muscle deposition rather than fat deposition. In a review of 37 experiments in the USA in which steers were finished on grain-based diets, Duckett et al. (1997) detected a mean reduction of 24% in marbling associated with use of a variety of HGPs. The analysis of experimental data found that mild oestrogens depress marbling to a lesser extent than strong oestrogens or combinations of a mild oestrogen with an androgen. Reviewing the literature, Morgan (1997) found that the percentage of carcasses grading USDA Choice (approximately AUS-MEAT Marble Score 2.27) was decreased 5% with a mild oestrogen implant and 25% when cattle were implanted with a TBA containing implant.
Beermann (1995) reported that the liveweight required to attain “small” marbling necessary to grade USDA low Choice is increased 25 to 45 kg in steers administered TBA x oestradiol combination implants. This was thought to be because of the delayed fattening pattern of cattle receiving the implants.
There is evidence that some of the HGP induced decrease in marbling is associated with a dilution of intramuscular fat in a larger muscle. In studies in the USA, HGPs have increased ribeye area from 4% to 7% by implantation (Milton et al 1996, Duckett et al 1999).

2.2.2 The effect of HGPs on Meat Color..................................go to Top

Scanga et al. (1998a) found that reimplanting heifers with an oestrogenic implant, produced a greater percentage of dark cutters than heifers reimplanted with either androgens or combination HGPs. The effect of sex is believed to be due to females having a more excitable temperament due to a higher level of oestrogen secretion in combination with the implanted exogenous oestrogen (Voisinet et al. 1997). Reimplanting heifers before slaughter with products that were not primarily oestrogenic (combination implants) reduced the occurrence of dark cutters from 10.4 per thousand cattle shipped to 5.2 per thousand cattle shipped.

Steers, when treated with a combination implant at feedlot entry and as a reimplant, produced a higher percentage of dark cutters when compared to other moderate growth-promoting implant strategies. When steers were implanted with oestrogenic HGPs, either as the cattle entered the feedlot or as a final reimplant before harvest, the occurrence of dark cutters was reduced from 9.2 per thousand cattle shipped to 2.0 and 0.5 per thousand cattle shipped respectively.

Consistent with these results, gender of cattle is commonly the determining factor when deciding what growth enhancement is to be used (Scanga et. al. 1998b). Stress caused by administering growth promotants can be attributed to sources such as the increased handling of the animal, increased nutritional requirements and the direct effect of the hormone on the animal’s disposition and sensitivity to surroundings. It is not the use of the HGPs alone that increase the incidence of dark cutting beef, but more the misuse, off-label use (Synovex-H used on steers for example) and overuse (double or triple dose implanting) of these compounds that greatly increase the risk of dark meat.

The effect on meat color was shown to be moderated if the time from reimplantation to slaughter was greater than 100 days, by an average of 38% for heifers and 69% for steers.

2.2.3 The effect of HGPs on Tenderness..........................go to Top

The effect of HGPs on tenderness is particularly important, because of the sensory dimensions that determine beef palatability, tenderness has the greatest effect (Thompson 2002).

Foutz et al. (1990), Samber et al. (1996), Morgan (1997), and Roeber et al. (1999) indicated that some aggressive implanting strategies have been implicated as a possible cause of reduced palatability, specifically tenderness. In general, both trained and consumer sensory panels rate steaks from non-implanted controls as more tender than those from implanted steers and heifers (Dikeman 2003). In addition, Warner-Bratzler shear force (WBSF) values are generally lower (more tender) for steaks from non-implanted controls than for those from implanted cattle (Table 1). However results have been variable, with a number of studies showing no impact on objective (Huck et al.1991) or sensory (Hunter et al. 2001a) measurements.

Roeber et. al. (1999) studied the effect of different implants and implant strategies using 448 steers (Table 1). Cattle were implanted at feedlot entry with one of five implant types, or not implanted. They were then re-implanted after 59 days with the same or different implants, or not implanted. This resulted in seven implant strategies and a non-implanted control group. The Revalor-S® (140 mg TBA/ 24 mg oestradiol 17B)/No implant treatment group had steaks with higher WBSF values than those from non-implanted controls. Indicating that the beef industry is currently strongly driven by cost considerations as opposed to quality, is that this is the implant strategy used by Certified Australian Angus Beef™ (CAAB). One of CAAB’s corporate objectives is to produce a high quality beef product guaranteed to be tasty, juicy, and tender. The percentage of steaks with a shear force > 3.86 (threshold value for consumer desirability) was less for non-implanted cattle and cattle implanted with Encore and Component T-S® than for the other HGP implant strategies. A consumer panel found that steaks from non-implanted controls were more tender than nearly all implant treatment groups; however there were no differences among implant groups except that steaks from the Encore and Component T-S® treatment group were more tender than steaks from all other implant treatment groups.

Table 1. Least Squares Means and Frequency Distribution of Warner-Bratzler Shear Force Values by Implant Strategy (Roeber et. al. 1999)

ab Means in the same column with different superscript letters differ (p<0.05)

Published data on HGP effects generally refer to the striploin and have not included evaluations of other muscles. More recently a large study has been undertaken as part of the Beef CRC/MSA research program (BM McIntyre unpublished data) to investigate the effect of a strong HGP implant (Revalor-S and –H) on palatability of samples from a variety of muscles. Yearling steers and heifers were slaughtered whilst still within the payout period for the implants and the striploin, rump, blade, and oyster blade cuts collected for both objective and sensory evaluation. Samples were aged for 5 and 21 days prior to testing, grilled or roasted, by consumer taste panels. Of 577 samples sensory tested, the striploin showed the largest HGP effect, with the HGP treated striploins having a ten point lower palatability score than the controls at 5 days of ageing. The magnitude of this HGP effect in the striploin decreased to about 5 palatability units after 21 days ageing. The HGP effect was also present in the rump muscles, although to a lesser degree than in the striploin. There was a clear interaction of the HGP treatment with muscle, with little evidence of the HGP effect in the blade and oyster blade muscles.

Thompson (pers. comm. 2003) explains the cut effect by different ageing rates of muscles. Striploin and rump, for example, have a higher ageing rate than oyster blade/blade. It is thought that HGPs decrease protein turnover by affecting calpastatin and this decreases the ageing rate of meat.

2.2.4 The effect of HGPs on Palatability...................................go to Top

The 1995 Beef Consumer Satisfaction Report (NLSMB 1995) indicated there was a tendency for consumer ratings of overall beef desirability to be reduced for beef cattle given two successive androgen-containing implants when compared to beef from cattle given a single implant, two consecutive oestrogenic implants , or an oestrogenic implant followed by an oestrogen + androgenic implant.

Roeber et. al. (2000) compared consumer acceptability for cooked beef from unimplanted (control) cattle and from cattle implanted with one of seven different implant strategies (initial implant/implant at 59 days = Encore & Component T-S/no implant, Ralgro/Synovex Plus, Ralgro/Revalor-S, Revalor-S/Revalor-S, Revalor-S/no implant, no implant/Synovex Plus, and Synovex Plus/no implant). Steers were fed for 140 days. Comparisons of sensory panel evaluations for overall like/dislike were not significant (p = 0.09). However, the trend was that consumers tended to rate steaks from unimplanted steers as more desirable than steaks from implanted cattle. Correlation coefficients indicated that there was a strong, positive relationship between tenderness level, tenderness like/dislike, and overall like/dislike ratings.

Studying the effect of repetitive use of anabolic implants, Platter et. al. (2003) found that steaks from nonimplanted steers were rated as more desirable for overall eating quality than steaks from steers implanted two, three, four, or five times.

2.2.5 HGPs and Human Health Issues..................................go to Top

Whether residues of hormone implants in beef are a health risk remains a controversial issue. The 1999 Joint Expert Committee on Food Additives (JECFA) analysis estimated that a person consuming 500g of meat from implanted cattle would consume an extra 30-50 ng of oestradiol per day. This calculation utilised the highest residue levels reported for beef and considered ‘meat’ as a mixture of 300g muscle, 100 g liver, 50 g kidney, and 50 g fat (oestradiol levels are higher in organ meats than in muscle). This additional 50 ng oestradiol consumed is small, when considering that the acceptable daily intake for humans is 50ng/kg/day or 3000 ng/day for a 60kg person (Doyle 2000). Oestradiol, testosterone, and progesterone are naturally present in many foods of animal origin, and some plant foods also contain these hormones.

77 kg of beef from treated steers would need to be eaten to get the same amount of oestrogen as from eating one hen egg. 200kg of beef from treated steers would need to be eaten to get the same amount of oestrogen as from a serving of cabbage (Anon. 1986).

Figure 3. Levels of oestrogens in other foods (FEDESA – European Federation of Animal Health)

However in Europe beef from implanted cattle is not permitted, due to its potential toxicity. Europeans argue that even though excess exposure to hormones in beef from implanted cattle may be slight, pre adolescent boys and girls and the fetus in utero could be very sensitive to slight increases in hormone levels. Diets high in fat, calories, and animal protein and low in fibre have been associated with higher oestradiol, progesterone, or testosterone levels in several studies (Doyle 2000). Epidemiological and experimental data examined by the International Agency for Research on Cancer were judged to be sufficient evidence for the carcinogenicity of oestradiol to humans. Oestradiol stimulates cell division thereby increasing the possibility of random errors during DNA duplication. A small proportion of women taking oestrogen supplements develop breast or uterine cancer, indicating that oestradiol may be one of several factors important in the development of cancer.

3. Conclusion..................................................................................................go to Top

There are no major research reports demonstrating that HGPs improve meat quality. The majority of the research shows some reduction in marbling, tenderness and palatability for meat from HGP treated cattle when compared to non-implanted controls, although not all reductions are statistically significant. The type of implant or re-implant strategy, type of cattle, and length of time on feed can have a significant effect. The ‘aggressive’ use of HGPs compromises marbling and tenderness and increases the incidence of dark cutters. When the new MSA model, incorporating the effect of HGPs on beef palatability, is introduced the extent to which HGPs are used will increasingly be determined by the relative importance for consumers of palatability traits relative to cost advantages through increased weight gain, lean yield, and feed efficiency. This is likely to vary considerably between markets. Due to the effect of HGPs differing across cuts, the true value of meat from cattle that have been implanted will not be realised until a cuts-based trading system is widely implemented. As the magnitude of the HGP effect decreases with ageing future opportunities may include ageing meat and accelerating the ageing effect by tenderstretching HGP implanted carcases. Meat from cattle implanted with HGPs is safe and acceptable as they are lower in hormones of concern than many other commonly consumed foods.

4. References....................................................................................................go to Top

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