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Two levels of chromium (Cr) yeast, 0.2 ppm and 0.4 ppm, were fed in a typical feedlot ration to supply approximately 1.8 and 3.1 mg Cr per head per day to feedlot steers in a university research feedlot on the southern High Plains of Texas for 196 days.

Average daily gain, dry matter intake and feed efficiency were not affected by the 0.2 ppm treatment; however, the 0.4 ppm treatment reduced average daily gain and dry matter intake while increasing the feed:gain ratio. Cattle supplemented with 0.4 ppm chromium had larger longissimus muscle areas and decreased final yield grades, hot carcass weights and marbling scores.

Organic chromium improved carcass traits while not adversely affecting performance when fed at 0.2 ppm of feedlot diets. No effects of treatment on cortisol levels were seen, except on day 196 when steers receiving 0.2 ppm Cr had elevated serum cortisol compared to the other treatments.


Introduction

Rate of growth and feed conversion by feedlot cattle are highly influenced by feed intake and energetic efficiency (NRC, 1996). Chromium is an important trace element in the regulation of blood glucose and immune response in humans and laboratory species (NRC, 1997). Chromium is known to be a structural component of a glucose tolerance factor, which potentiates the action of insulin and is an essential trace mineral for normal metabolism of carbohydrates and lipids (NRC, 1989; Mertz, 1993).

Recently, chromium has been shown to improve reproduction, growth and carcass characteristics of pigs fed organic sources of chromium (Boleman et al., 1995; Lindemann et al., 1995; Kornegay et al., 1997; Mooney and Cromwell, 1997).

Research regarding the use of chromium on immune response in cattle has shown that benefits from supplemental chromium include enhanced cell-mediated immunity, reduced blood cortisol levels and increased antibody titers (Chang and Mowat, 1992; Kegley et al., 1996; Mallard and Borgs, 1997). Moonsie-Shageer and Mowat (1993) demonstrated the effectiveness of supplemental chromium on reducing morbidity in stressed feeder calves. However, research pertaining to chromium in the diets of beef cattle has been less consistent in its effect on performance and growth parameters.

The effect of chromium as a potential carcass modifier has been well documented in research with swine (Page et al., 1993; Gebert andWenk, 1994; Boleman et al., 1995). Recent research by Kornegay et al. (1997) found that chromium increased longissimus muscle area, and when pigs were fed chromium at lighter weights for a longer period of time the increase in longissimusmuscle area was greater compared to shorter feeding periods.

Similar results were found by Mooney and Cromwell (1997) who, in addition to increased longissimus muscle area, found that chromium improved carcass protein deposition rate and decreased fat percentage. Hasten et al. (1997a; 1997b) found similar results in work with rats in regard to reduced fat accretion when supplemental chromium was fed. The present experiment examined the effects of Bio-Chrome (Alltech Inc.), organic chromium derived from yeast, on performance and carcass characteristics of feedlot steers.


Materials and methods

The objectives of this research were to determine the effects of organic chromium on dry matter intake, average daily gain, feed: gain ratio, blood cortisol levels and carcass characteristics of feedlot steers.


ANIMALS AND DIETS

The 196 day trial was conducted at the Texas Tech University Burnett Center research feedlot on the southern High Plains of Texas during the winter of 1997 and spring of 1998. One-hundred and five crossbred steers (283 kg) composed of primarily Angus, Hereford, Charolais and Simmental breeding were kept outdoors in pens of seven animals over a partially slotted concrete floor and equipped with an automated feed delivery system.

Feed for each pen was individually batched and delivered at approximately 09:00 each morning. Prior to feeding, feed remaining in bunks was visually estimated and used to adjust intake. Treatments consisted of basal diet (control), basal diet plus 0.2 ppm chromium from Bio-Chrome (0.2 ppm Cr), and basal diet plus 0.4 ppm chromium from Bio-Chrome (0.4 ppm Cr).

Diets fed daily to the steers were typical feedlot diets consisting of a steam-flaked grain sorghum and cottonseed hull base (Table 1). Upon arrival steers were immediately processed, which included anti-clostridial vaccination (Ultrabac/Somubac™, SmithKline Beecham), deworming (Ivomec™, Meriel) and antibiotic (Micotil™, Elanco Animal Health).

Steers were implanted with Synovex-S™ (Fort Dodge Animal Health), individually ear tagged, tail bobbed, weighed and placed on a step-up receiving diet containing chlortetracycline and sulfamethiazine (AS 700, Roche Animal Health). The following day animals were sorted by weight and randomly assigned by weight to five pens of seven steers per pen for a total of 35 steers per treatment. The Bio-Chrome treatments were started immediately after sorting and fed while steers were moved up to the high concentrate diet (28 days), and were fed for the remainder of the study.


Table 1. Composition of experimental diets.


^aTrace mineral premix contains (ppm) I, 559; Mn, 3815; Zn, 3815; Cu, 375; Co, 23; Fe, 1840.
^bVitamin A premix provides 300,000 IU of Vitamin A acetate per kg.
^cVitamin E premix provides 1765 IU of a-tocopherol per kg.
^dRumensin/Tylan premix provides 360 mg/hd/d of Monensin and 66.64 mg/hd/d of Tylosin
^eChromium premix contains 80 ppm Cr.



The 0.2 ppm Cr treatment group received a premix (0.25% of the diet) consisting of ground grain sorghum and Bio-Chrome (80 ppm Cr). The 0.4 ppm Cr treatment group received the same premix at 0.50% of the diet. The chromium premix in each treatment group replaced steamflaked grain sorghum in the basal diet to ensure that diets were isonitrogenous and isocaloric for each treatment group.


MEASUREMENTS

Individual steer weights were recorded at 28-day intervals during the experiment. Average daily gain, feed:gain ratio and dry matter intake were calculated for each period. Blood samples were collected from each steer in the morning on days 0, 14, 28, 56 and 196 via jugular venipuncture for cortisol determination.

Immediately upon collection blood samples were placed on ice for transport back to the laboratory where serum was separated and stored at -20°C until cortisol analysis was conducted usin a cortisol specific radioimmunoassay kit (Coat-A-Count, Diagnostic Products Corporation).

At the conclusion of the study steers were transported by truck to a commercial packing plant where liver abscess scores, final yield grade, marbling scores, dressing percentage, longissimus muscle area, and quality grade were measured by trained personnel.

This completely randomized experiment was analyzed using GLM procedure of SAS (1995). Pen was the experimental unit and means were separated using Fischer’s Protected Least Significant Difference Test.


Results and Discussion

PERFORMANCE EFFECTS

Effects on average daily gain, dry matter intake and feed efficiency No differences were detected for average daily gain, feed:gain ratio or dry matter intake during the first 56 days of the study (Table 2). These data are consistent with previous studies conducted by Chang et al. (1992) and Kegley et al. (1996) who also found these parameters unaffected by chromium supplementation.

However, steers receiving the 0.4 ppm Cr treatment tended (P = 0.17) to eat less feed during the first two periods. During these two periods a seasonal effect may have been present which suppressed performance because of temperature fluctuations in excess of 17wC per day for the majority of the 56 day interval.


Table 2. Effect of Bio-Chrome on average daily gain, dry matter intake and feed efficiency of steers days 0-56.





During the final 140 days of the study (Table 3) no differences in dry matter intake among treatments were detected (Tables 3 and 4). However, steers receiving 0.4 ppm Cr had lower average daily gain (P <0.05) and increased feed:gain (P< 0.05) which is consistent with results obtained by Chang and Mowat (1992) who found that supplemental chromium at 0.2 ppm did not improve performance compared to control cattle.

In contrast, Moonsie-Shageer and Mowat (1993) found that chromium improved intake and daily gain when fed at 0.2 ppm. Average daily gain and dry matter intake increased for all treatments during the final 140 days when compared to performance during the initial 56 days of the study, which further suggests an environmental effect on performance during the first 56 days of the study.

Overall, cattle receiving 0.2 ppm Cr were not different (P <0.05) from control steers in the performance variables measured (Table 4). However, 0.4 ppm Cr (treated cattle) weighed less (P<0.05) at the completion of the study, had lower average daily gain (P<0.05) and higher feed:gain (P<0.05) than both the control and 0.2 ppm Cr treatments.


Table 3. Effect of Bio-Chrome on average daily gain, dry matter intake and feed efficiency of steers days 57-196.


^a,bMeans in the same row with different superscripts differ (P<0.05).



Table 4. Effect of Bio-Chrome on overall average daily gain, dry matter intake and feed efficiency of steers days 0-196.


^a,bMeans in the same row with different superscripts differ (P<0.05).



EFFECTS OF BIO-CHROME ON CARCASS CHARACTERISTICS AND SERUM CORTISOL

The 0.2 ppm Cr treatment increased (P <0.05) hot carcass weight over 0.4 ppm Cr treatment with control steers being intermediate (Table 5). Dressing percent, marbling score and final yield grade were reduced (P <0.05) compared to control and 0.2 ppm Cr treatments when the 0.4 ppm Cr treatment was fed.

Longissimus muscle area was increased (P <0.08) with increasing level of Cr supplementation. Kornegay et al. (1997) and Mooney and Cromwell (1997) both reported a similar effect in pigs supplemented with 0.2 ppm Cr. No effects of treatment on serum cortisol were seen on days 0, 14, 28 and 56; however on day 196 steers on the 0.2 ppm Cr treatment had an increased (P<0.05) serum cortisol.


Table 5. Effects of Bio-Chrome level on carcass characteristics.


¹Marbling scores: 300=traces, 400=slight, 500=small.
^a,b,cMeans in the same row with different superscripts differ (P£0.05).
^x,y,zMeans in the same row with different superscripts differ (P=0.08).

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Authors: GREGORY V. POLLARD and C. REED RICHARDSON
Texas Tech University, Lubbock, Texas, USA 

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