30 August 2010

13 minute read

Feeding Beef-Type Cows

Aggressively feeding high-energy, high-concentrate diets to culled market cows prior to harvest is an effective means of increasing carcase fat content, increasing red-meat yield, increasing marbling, altering carcase fat composition and appearance (whiter fat), improving lean colour and improving cooked meat palatability (matulis et al., 1987; boleman et al., 1996; cranwell et al., 1996b; schnell et al., 1997; apple, 1999; woerner, 2009). Sawyer et al. (2004) showed that feeding beef cows more conservatively (30 per cent roughage diet for 54 days) resulted in 30 per cent increases in cost of gain versus more aggressive feeding strategies (stepping cows up from a 30 per cent to a 10 per cent roughage diet in 10 days or a 20 per cent roughage diet in 20 days and feeding them for a total of 54 days).

Likewise, the most common industry practices for finishing cows towards white-fat premiums include aggressively feeding cows an 80 to 90 per cent concentrate diet for 50 to 100 days prior to harvest. Studies have shown that the sharpest increases in feed efficiency (fe) and average daily gain (adg) are noticed from 15 to 42 days on feed (sawyer et al., 2004) and 29 to 56 days on feed (matulis et al., 1987), while the lowest fe and adg are encountered in the earliest and latest finishing periods. These differences in fe and adg are explained by cows acclimating to a drastic change in diet in the early stages of feeding and the effects of compensatory gain dissipating in the later stages of feeding. At the same time, most studies agree that hot carcase weights (hcw), carcase muscling, lean colour scores (brighter) and fat colour scores (whiter) can all be significantly improved in the first 56 days of feeding (matulis et al., 1987; boleman et al., 1996; cranwell et al., 1996b; schnell et al.,

Maximised the solubility of collagen in the lm in as little as 14 (schnell et al., 1997) and 28 days (cranwell et al., 1996b) on feed, and another study (boleman et al., 1996) showed that collagen solubility tended to continually increase with time on feed up to 84 days. Consequently, cranwell et al. (1996b) was able to link lower warner-bratzler shear force (wbsf) values and increased subjective tenderness ratings and sensory panel scores with increased collagen solubility. Without making a link to collagen solubility, matulis et al. (1987) was also able to identify drastic improvements in lm tenderness for cows that had been fed a high-concentrate diet for 56 days. It may seem that feeding cows for 50 to 60 days is the answer to achieve significant carcase quality improvements and improvements in tenderness ratings while experiencing optimal fe and adg. However, commercial cow packers commonly receive and process cows that have been fed high-concentrate diets for considerably longer periods of time.

Multiple studies (cranwell et al., 1996b; sawyer et al., 2004; schnell et al., 1997) were not able to identify differences in marbling in cows that were not fed high- concentrate diets and cows that had been fed a high-concentrate diet for up to 56 days. Additionally, schnell et al. (1997) was not able to identify differences in flavourattributes, including off-flavours, of the lm from cows fed high-concentrate diets from 0 to 56 days. However, studies that have evaluated carcase and palatability characteristics of cows fed more than 80 days have noted improvements in marbling levels as well as decreased sf values (matulis et al., 1987; boleman et al., 1996; woerner, 2009) and increased sensory panel tenderness ratings (boleman et al., 1996 and woerner, 2009). To this point, commercial packers commonly finish cows using high-concentrate diets for a period of time that exceeds 80 days in order to achieve additional attributes including increased carcase Fatness, increased marbling and decreased prevalence of off-flavours. In addition, feeding cows for an extended period provides an increased amount of white exterior fat, which is utilised by cow processing companies to meet customer specifications for ground beef that require higher fat percentages. Additionally, increased marbling levels and a decreased incidence of off-flavours found in cows fed for extended periods may contribute to a more satisfactory eating experience for consumers and higher demand in foodservice.

A recent study was conducted that included a large number of beef-type cows entering a large commercial processor (facility processes over 6,000 head per week) that had been aggressively fed with a high-concentrate diet for a 95 day (± 1 day) period (woerner, 2009). This study revealed evidence that supports extended feeding periods to achieve definite differences in the composition of carcasees as well as lean and fat characteristics from fed, beef-type cows versus both non-fed beef cows and non-fed dairy cows entering the facility (Table 1). By feeding beef-type cows for an extended period, superior improvements in hcw, lm area, lean colour scores (lean maturity and subjective lean colour), lm collagen content and lm sf were observed for fed, beef-type cows when compared to both non-fed Beef- and dairy-type cows (woerner, 2009). Woerner (2009) also identified long-fed, beef-type cows as clearly having the greatest amount of external fat (adjusted fat thickness), which provides opportunities for packers to blend trimmings to ultimately increase the fat percentages of ground beef to more desirable levels. In agreement with the findings of woerner (2009), although duration of feeding prior to harvest was not specified, stelzleni et al. (2007) identified fed, beef-type cows entering a commercial packing facility as being superior to non-fed beef cows in identical and related carcase characteristics. Additionally, when compared to non-fed beef cows, woerner (2009) identified that long-fed, beef-type cows also had decreased probabilities of grassy, liver/organy and fishy off-flavours, and found that long-fed cows had the highest probabilities of not possessing any off-flavours (woerner, 2009).

Table 1

It also should be noted that companies that are investing in intensive, high-concentrate feeding programs also are carefully selecting cows on an individual basis based on genetic type and live-body composition prior to making the decision to place them in a feeding regime. Woerner (2009) found that the sample population of cows that entered the processing facility following an extensive feeding period was comprised of over 94 per cent british and continental types of cows with the balance of cows having phenotypes expressing brahman influence. On the contrary, over 25 per cent of non-fed cows had phenotypes that indicated brahman influence and the percentage of continental-type was reduced by over 15 per cent when compared to the fed-cow sample population.

This indicates that producers and packers have a tendency to feed a higher percentage of continental-type cows. This decision is likely based on continental-type cows producing heavier weight carcasees and greater muscling scores than all other breed types (woerner, 2009). Muscling, marbling scores, red-meat yield and carcase fatness were improved by feeding british-type cows. However, woerner (2009) identified that feeding brahman-type cows for an extended period results in improved marbling scores and increased external fat, but carcase muscling does not improve with hcw as a result of feeding. These data show advantages to feeding continental-type and british-type cows, but minimal advantages to feeding brahman-type cows.

Feeding Dairy Cows

Dairy cows make up about 30 per cent of all market-cow slaughter, and the majority of dairy cows arrive at processing facilities as direct culls from dairies or via livestock auctions. Even though these cows are not commonly placed in confinement and fed high-concentrate diets for the purposes of fattening or improving quality to qualify for white-fat premiums, these cows clearly receive a higher plane of nutrition during their lifetime than the average non-fed, beef-type cow. As a result, while fed, beef-type cows have clear advantages in muscling and hcw, studies have shown that non-fed dairy cows produce beef products that are comparable in palatability attributes to beef products from fed or white-fat, beef-type cows (stelzleni et al., 2007; woerner, 2009). Studies have shown that non-fed dairy cows produce carcasees with fat colour scores, flavourprofiles (woerner, 2009) and marbling scores (stelzleni et al., 2007 and woerner, 2009) that are similar to fed, beef-type cows. Additionally, stelzleni et al. (2007) showed that lm sf scores and sensory panel ratings for tenderness were similar for non-fed dairy cows and fed, beef-type cows, while woerner (2009) showed that non-fed dairy cows were slightly tougher than fed, beef-type cows. Both studies (stelzleni et al., 2007; woerner, 2009) agree that non-fed dairy cows were superior to non-fed beef cows for palatability traits. These findings indicate that culled dairy cows potentially could be marketed as premium cow beef products similarly to fed, beef-type cows without requiring additional resources and time on feed.

Two studies (stelzleni et al., 2007; allen et al., 2009) have made direct comparisons between non-fed and fed market dairy cows and both have identified advantages to feeding dairy cows prior to harvest. Improvement in hcw, marbling score and lean colour or lean maturity score were noticed for dairy cows fed for an extended period prior to harvest versus cows that had been harvested as direct culls from dairies (stelzleni et al., 2007; allen et al., 2009). Additionally, a study that specifically evaluated the effects of feeding dairy cows noted that finishing cows on a high-energy diet for an extended period actually eliminated or reduced lameness problems (allen et al., 2009). The authors of this study indicated that removing cows from the physical and physiological stresses of lactation and milking for an extended period was the primary reason for improvements in locomotion (allen et al., 2009), while the 2007 market cow and bull audit noted that lameness attributed to increased trim loss, less saleable product and an increased likelihood of a cow becoming nonambulatory (ncba, 2007). Nonetheless, stelzleni et al. (2007) noted that despite improvements in carcase and lm characteristics for fed dairy cows versus non-fed dairy cows, wbsf and sensory panel ratings did not indicate differences in overall tenderness, beef flavourintensity nor the incidence of off-flavours between the two types of cows. Therefore, feeding dairy cows high-energy rations for an extended period prior to harvest is not as beneficial as feeding beef-type cows to improve muscle eating quality or sensory characteristics.

The use of growth promotants

Growth-enhancement technologies are used as a management tool throughout the US. Commercial cattle-feeding industry to increase weight gain, increase efficiency, increase product availability and decrease the per-unit cost of beef resulting from steers and heifers (nahms, 2000 and lawrence and ibarburu, 2007). In addition to receiving growth-promoting implants, an increasing number of cattle also receive diets that have been supplemented with one of two fda-approved, beta-adrenergic agonists (beta-agonists; ractopamine hydrochloride or zilpaterol hydrochloride) during the final few weeks of finishing. While these technologies are clearly effective in young steers and heifers, research has indicated that the same technologies may not be as effective when used for finishing mature cows. With the lack of a clear understanding of the efficacy of all growth-promoting agents as well as the added cost of using growth promotants and the need to feed a high plane of nutrition for an extended period before the benefits can be realised, many producers are not utilising these technologies to finish market cows.

Terminal implants have been shown to be the most effective growth-promoting technology to improve live weight gain, hcw, carcase muscling, rea and red-meat yield in mature cows that have been fed a high plane of nutrition (cranwell et al., 1996a; cranwell et al., 1996b; funston et al., 2003). Beta-agonists have been shown to effectively improve feed efficiency, live weight gain, hcw, rib eye area (rea) and red-meat yield in young cattle (gruber et al., 2007 and vasconcelos et al., 2008); however, scientific finding indicate that there is minimal benefit to feeding mature cows the b-adrenergic agonist ractopamine hydrochloride (dijkhuis et al., 2008 and allen et al., 2009). Similarly, neill et al. (2009) found that feeding mature cows a high- concentrate diet supplemented with zilpaterol hydrochloride did not improve carcase characteristics including hcw and rea. However, neill et al. (2009) did find that feeding zilpaterol hydrochloride to cows that had received an implant that contained trenbolone acetate (tba) resulted in increased rea and heavier subprimal weights when compared to fed cows that did not receive growth promotants and fed cowsthat had only received an implant. Therefore, combining implants and beta-agonists may be an effective means of increasing red-meat yields in mature cows.

In steers and heifers, growth promotants have been shown to have adverse affects on beef palatability ratings and tenderness (platter et al., 2003; gruber et al., 2008; hilton et al., 2009). Interestingly, cranwell et al. (1996b) discovered that steaks from implanted cows had more soluble (heat-labile) collagen, a higher percentage of soluble collagen and improved sensory characteristics of tenderness (myofibrillar and overall) and connective tissue amount. While steroidal implants increase the size and diameter of individual muscle fibers contributing to increased muscle toughness, they also increase the growth rate and simultaneously increase the rate of protein synthesis. Increasing protein synthesis in the mature animal also increases the proportion of newly synthesised collagen resulting in fewer intermolecular cross-links and less stable collagen fibers with higher solubility (mcclain and wiley, 1971). As discussed previously, increased collagen solubility results in increased tenderness. This indicates that utilising steroidal implants may actually improve the tenderness of beef products resulting from fed, mature cows.

Summary

The cull cow market is a vital segment of the beef industry that provides a significant amount of ground beef and whole- muscle products to foodservice and retailer outlets. Non- fed market cows provide an abundance of lean beef, while fed, beef-type market cows (white-fat) and dairy cows add versatility by providing high-quality fat sources for improving ground beef as well as providing lower priced, high-quality, whole-muscle foodservice items. Feeding a high plane of nutrition to beef-type market cows is the most effective method to improve carcase red meat and fat yields as well as improving the overall quality and palatability attributes of market-cow beef. Steroidal implants have been shown to be an effective tool to improve fed-cow carcase traits, while additional, larger-scaled studies evaluating the use of beta-agonists in market cows are needed to develop a better understanding of their effectiveness in the cow industry. Postmortem aging and calcium chloride injection are effective post-harvest management tools to improve the tenderness and sensory characteristics of whole-muscle cow products. Solubility results in increased tenderness. This indicates that utilising steroidal implants may actually improve the tenderness of beef products resulting from fed, mature cows.

Further Reading

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