Effect of a chromium yeast supplement in growing-finishing pig diets on performance, carcass traits and fatty acid composition of adipose tissue

Ninety-six Pulavian x Pietrain crossbreed pigs (48 gilts and 48 barrows) were allotted to three treatments: 1. control w i th the basal diets for growing (25-65 kg body weight) and finishing period (65-105 kg B W ) ; 2. 1 kg o f basal diets supplemented w i th 0.2 mg kg" Cr f rom chromium yeast, and 3. 1 kg o f basal diets supplemented w i t h 0.5 mg kg"' Cr f rom chromium yeast. The pigs were housed i n pens (4 gilts or 4 barrows per pen). Feed and water were available ad libitum and individual live weights and pen feed consumption were recorded on days 30, 60,90 and 110 (at slaughter) o f the t r ia l . Average daily gains and feed ut i l izat ion were not significantly affected by Cr supplementation. Backfat thickness over the shoulder as well as subcutaneous fat o f ham were reduced significantly in pigs supplemented w i t h Cr. Lean o f ham increased significantly i n both experimental groups. A significant reduction in saturated fatty acid (SFA) content and an increase in the polyunsaturated fatty acid ( P U F A ) level o f backfat and o f leaf fat was noticed in the experimental groups. These results indicate that dietary supplementation o f organic chromium may increase muscle and decrease fat deposition w i th lower content o f SFA and higher content o f P U F A in adipose tissues o f backfat and leaf fat. K E Y W O R D S : growing-finishing pigs, organic Cr, carcass quali ty, fatty acids 88 GRELA E.R. ET A L . INTRODUCTION Chromium (Cr) is well known as an essential trace element for normal metabolism of carbohydrates, proteins and lipids in human and animal nutrition (Offenbacher and Pi-Suner, 1988; Mertz, 1993). I t is physiologically active and non-toxic only in the trivalent form at concentrations of approximately 0.1 mg kg" diet. Chromium is known to take part in several biological functions; it is an active constituent of glucose tolerance factors (GTF), stimulates RNA synthesis and is a natural antioxidant (Evock-Clover et al., 1993; Mirsky,1993; Mowat,1993; Stearns et al.,1995 ). Mertz (1993) and Amoiken et al. (1995) demonstrated the positive effect of Cr on insulin and, therefore, on carbohydrate and protein metabolism. Seerley (1993) found that protein deposition could be increased and fat deposition reduced when Cr is supplemented. This author demonstrated that growth parameters of stressed animals supplemented with organic Cr were beneficially affected. Page et al. (1993) informed that chromium supplemented in the form of chromium picolinate to the diet at a rate of 0.2 mg kg" decreased backfat thickness and serum cholesterol levels in finishing pigs and increased loin eye area and percentage of lean. The amount of fat in carcass tissue is an important concern in human nutrition, as people prefer lean meat because of the global trend towards reducing animal fat in diets. Thus, genetic or nutritional and pharmacological manipulation of fatty acid synthesis should lead to production of leaner animals. It was recently established that dietary polyunsaturated fatty acids inhibit lipogenesis and the activities of the lipogenic enzymes (Otten et al., 1993; Hillgartner et al., 1995). And so, the higher content of polyunsaturated fatty acids in fat tissue and diminished fat deposition caused by dietary organic chromium supplementation may have a positive effect on carcass characteristics. In recent studies, supplements of 0.2 and 0.5 mg kg"' of organic chromium have been found effective in improving carcass characteristics in pigs (Evock-Clover et al., 1993; Page et al., 1993; Seerley, 1993; Lindemann et al.,1995; Wenk, 1995). The aim of the present study was to assess the effect of organic chromium in the trivalent form supplemented to the diet in two different concentrations of 0.2 mg kg" and 0.5 mg kg" as chromium yeast (bioplex Cr ) on growth performance, carcass traits and fatty acid composition of backfat, leaf fat and intramuscular fat of growing-finishing pigs. M A T E R I A L AND METHODS Animals Ninety-six Pulavian x Pietrain crossbreed pigs of both sexes (48 gilts and 48 barrows) from twelve litters of an experimental herd were randomly allotted to C H R O M I U M YEAST FOR PIGS 89 three treatments: 1. control with the basal diets for the growing (25-65 kg body weight) and finishing periods (65-105 kg BW); 2. basal diet + 0.2 mg C r + 3 from chromium bioplex in 1 kg of diet; 3. basal diet + 0.5 mg C r + 3 from chromium bioplex. The initial weight was 25 kg and slaughter weight was about 105 kg BW. The pigs were housed in pens with concrete slate floors (4 gilts or 4 barrows per pen). Feed and water were available ad libitum. Individual live weights and pen feed consumption were recorded on days 30, 60, 90 and 110 (at slaughter) of the trial. The temperature of the room was controlled and maintained at 22+ 1°C with air speed < 0.05 cm s". Diets Mixed basal diets were prepared from commercial feeds. The composition of the grower (up to 65 kg BW) and finisher diets is presented in Table 1. Al l nutrients including vitamins and trace elements were consistent with the level recommended by the Nutrients Requirements of Pigs (1993). Chromium in organic form as Cr bioplex' was added to the basal diet (Table 1) at 0.2 and 0.5 mg kg". Chemical composition, including D M , crude ash, crude fibre, ether extract, crude protein, minerals (Ca and P) and amino acid composition, was determined according to routine laboratory procedures ( A O AC, 1980). Chromium in diets was analyzed as described by Anderson and Kozlovsky (1985). Carcass measurements Pigs were stunned by electric shock and then killed by exsanguination. After slaughter, the 12 right carcasses ( 6 gilts and 6 barrows ) of each treatment were chilled overnight and the following data were recorded using the Polish Pig Progeny Station method: carcass weight, length of carcass, backfat thickness over the shoulder, between the third and fourth lumbar vertebra, on the midback between the third and fourth last rib and on the rump at three locations over the cranial, medial and caudal part of the gluteus muscle, loin and ham weight before the ham was further dissected into lean, subcutaneous fat and bone, loin eye area and weight of right side leaf fat. Samples and analysis About 20 g backfat from two layers and muscle tissue were removed from the middle part of M. longissimus dorsi. Samples of 20 g were excised from the leaf fat. A l l samples were stored at -20°C until analysis. Total lipids were extracted quantitatively from tissue samples with chloroform-methanol (2:1 v/v) according


INTRODUCTION
Chromium (Cr) is well known as an essential trace element for normal metabolism of carbohydrates, proteins and lipids in human and animal nutrition (Offenbacher and Pi-Suner, 1988;Mertz, 1993). It is physiologically active and non-toxic only in the trivalent form at concentrations of approximately 0.1 mg kg" 1 diet. Chromium is known to take part in several biological functions; it is an active constituent of glucose tolerance factors (GTF), stimulates RNA synthesis and is a natural antioxidant (Evock-Clover et al., 1993;Mirsky,1993;Mowat,1993;Stearns et al.,1995 ). Mertz (1993) and Amoiken et al. (1995) demonstrated the positive effect of Cr on insulin and, therefore, on carbohydrate and protein metabolism. Seerley (1993) found that protein deposition could be increased and fat deposition reduced when Cr is supplemented. This author demonstrated that growth parameters of stressed animals supplemented with organic Cr were beneficially affected. Page et al. (1993) informed that chromium supplemented in the form of chromium picolinate to the diet at a rate of 0.2 mg kg" 1 decreased backfat thickness and serum cholesterol levels in finishing pigs and increased loin eye area and percentage of lean.
The amount of fat in carcass tissue is an important concern in human nutrition, as people prefer lean meat because of the global trend towards reducing animal fat in diets. Thus, genetic or nutritional and pharmacological manipulation of fatty acid synthesis should lead to production of leaner animals. It was recently established that dietary polyunsaturated fatty acids inhibit lipogenesis and the activities of the lipogenic enzymes (Otten et al., 1993;Hillgartner et al., 1995). And so, the higher content of polyunsaturated fatty acids in fat tissue and diminished fat deposition caused by dietary organic chromium supplementation may have a positive effect on carcass characteristics. In recent studies, supplements of 0.2 and 0.5 mg kg"' of organic chromium have been found effective in improving carcass characteristics in pigs (Evock-Clover et al., 1993;Page et al., 1993;Seerley, 1993;Lindemann et al.,1995;Wenk, 1995).
The aim of the present study was to assess the effect of organic chromium in the trivalent form supplemented to the diet in two different concentrations of 0.2 mg kg" 1 and 0.5 mg kg" 1 as chromium yeast (bioplex Cr 1 ) on growth performance, carcass traits and fatty acid composition of backfat, leaf fat and intramuscular fat of growing-finishing pigs.

Animals
Ninety-six Pulavian x Pietrain crossbreed pigs of both sexes (48 gilts and 48 barrows) from twelve litters of an experimental herd were randomly allotted to three treatments: 1. control with the basal diets for the growing (25-65 kg body weight) and finishing periods (65-105 kg BW); 2. basal diet + 0.2 mg Cr +3 from chromium bioplex 1 in 1 kg of diet; 3. basal diet + 0.5 mg Cr +3 from chromium bioplex 1 . The initial weight was 25 kg and slaughter weight was about 105 kg BW. The pigs were housed in pens with concrete slate floors (4 gilts or 4 barrows per pen). Feed and water were available ad libitum. Individual live weights and pen feed consumption were recorded on days 30, 60, 90 and 110 (at slaughter) of the trial. The temperature of the room was controlled and maintained at 22+ 1°C with air speed < 0.05 cm s" 1 .

Diets
Mixed basal diets were prepared from commercial feeds. The composition of the grower (up to 65 kg BW) and finisher diets is presented in Table 1. All nutrients including vitamins and trace elements were consistent with the level recommended by the Nutrients Requirements of Pigs (1993). Chromium in organic form as Cr bioplex' was added to the basal diet (Table 1) at 0.2 and 0.5 mg kg" 1 .
Chemical composition, including DM, crude ash, crude fibre, ether extract, crude protein, minerals (Ca and P) and amino acid composition, was determined according to routine laboratory procedures (AO AC, 1980). Chromium in diets was analyzed as described by Anderson and Kozlovsky (1985).

Carcass measurements
Pigs were stunned by electric shock and then killed by exsanguination. After slaughter, the 12 right carcasses ( 6 gilts and 6 barrows ) of each treatment were chilled overnight and the following data were recorded using the Polish Pig Progeny Station method: carcass weight, length of carcass, backfat thickness over the shoulder, between the third and fourth lumbar vertebra, on the midback between the third and fourth last rib and on the rump at three locations over the cranial, medial and caudal part of the gluteus muscle, loin and ham weight before the ham was further dissected into lean, subcutaneous fat and bone, loin eye area and weight of right side leaf fat.

Samples and analysis
About 20 g backfat from two layers and muscle tissue were removed from the middle part of M. longissimus dorsi. Samples of 20 g were excised from the leaf fat. All samples were stored at -20°C until analysis. Total lipids were extracted quantitatively from tissue samples with chloroform-methanol (2:1 v/v) according   Folch et al. (1957). About 10 mg of total lipids was used for preparation of fatty acid methyl esters as outlined by Rotenberg and Andersen (1980). The composition of fatty acid methyl esters was determined by gas-liquid chromatography (GLC). Heptadecanoic acid was added as the internal standard. About 1 mg of the esters was injected into a Perkin-Elmer gas chromatograph Model 900 equipped with an automatic Model AS 41 injection system and a flame ionization detector (FID). The methyl esters were analyzed using a 1.83 mx6.35 mm glass column packed with 1S% ethylene glycol succinate (EGS) on 80/100 mesh Chromosorb W, AW DMCS. Temperature: 140°C isothermal for 24 min, then programming an increase of 1.5°C min" 1 to 190°C. Carrier gas : nitrogen, 20 ml/min. Authentic standards of typical fatty acids (Chrompack, The Netherlands) were used to identify peaks.
All chemical analyses were performed in duplicate.

Statistical analysis
Statistical significance of the difference between means of fatty acid contents and carcass quality data of treatments (P<0.05) was assessed by the t-Student test. The results are given as the arithmetic means and standard error of means (SEM).

Performance
Average daily gains were not affected significantly by Cr supplementation, but there was a trend, more markedly expressed in gilts than in barrows, for higher gain in the growing and finishing period (Table 2).

Carcass composition
Backfat thickness over the shoulder as well as subcutaneous fat of ham were reduced significantly in pigs supplemented with Cr (Table 3). Lean of ham increased significantly in both experimental groups receiving 0.2 mg and 0.5 mg Cr per kilogram of diet. The longissimus dorsi muscle area was 5.3-6.9% greater in pigs fed supplemented diets than in those given the control diet, but this effect was not significant (Table 3). Loin weight was higher in both experimental groups supplemented with Cr, but this effect was not significant. The weight of ham was significantly higher in gilts than in barrows in all experimental groups. Weight of leaf fat tended to be reduced in pigs fed supplemented diets compared  with those receiving the control diet, but the effect was not significant. Intramuscular fat content in loin and ham was not affected by Cr supplementation (Table 3).

Fatty acid composition
Fatty acid composition of backfat in pigs was influenced by supplementing with Cr, causing a significant reduction in saturated fatty acid (SFA) content and also a significant increase in the polyunsaturated fatty acid (PUFA) level (Table 4). This effect was more pronounced in gilts than in barrows (Table 4). A similar effect was noticed in fatty acid composition of leaf fat in pigs supplemented with Cr in comparison to values obtained in control pigs ( Table 5). The tendency for higher PUFA and lower SFA contents was also observed in the intramuscular fat of the longissimus dor si muscle of pigs fed the Cr supplement (Table 6).

DISCUSSION
The results of these experiments do not support those of some other authors (Lindemann et al., 1993(Lindemann et al., , 1995 demonstrating improved productivity (daily gains, feed utilization) when pigs were fed on diets supplemented with organic Cr. Our results show only a trend of better feed utilization and average daily gains, more markedly expressed in gilts than in barrows. The results of our observations indicate that organic chromium supplementation decreased some of the adipose parameters (backfat thickness over the shoulder, backfat thickness in the midback and rump taken from five measurements, subcutaneous fat of ham) and increased carcass lean (lean of ham). Additionally, the composition of fatty acids showed a trend for higher content of polyunsaturated fatty acids and lower for saturated fatty acids. These data may also have potential benefits through diminishing the activities of lipogenic enzymes when used for human consumption. The molecular basis for the inhibitory effects of PUFA on lipogenesis, insulin and thyroid hormones are positive factors while glucagon is a negative one (Hillgartner et al.,1995). Growth hormone, glucocorticoids, and insulin-like growth factors (IGF) also regulate the activities of lipogenic enzymes, but the roles of these agents in the dietary regulation of lipogenic enzymes are unknown in animals and humans. The amount of fat deposition and the simultaneous accretion of muscle in pigs fed Cr are similar to the effects of exogenous growth hormone and /^-adrenergic agonists (Pringle et al., 1993;Amoiken et al., 1995). The best known effects of Cr on insulin receptor sensitivity and increased protein synthesis in muscle, together with higher growth hormone secretion, may to some extent explain the mechanism of the observed results in Fatty acid composition of backfat of fattening pigs, % of identified FA   ' standard error of the mean a, b -P^0.05 reduced lipogenesis and increased muscle accretion in pigs. Many of the effects attributed to chromium cannot be explained by the action of these hormones only.
In our study, a supplement of 0.2 mg kg" 1 of organic chromium was effective, and carcass leanness did not improve when the concentration was raised to 0.5 mg kg" 1 . Thus the recommended and safe supplement dosage under experimental conditions could be the lower amount of 0.2 mg kg" 1 of organic chromium.
The favourable responses to dietary Cr supplementation seem to be related and dependent on some other dietary constituent and to different degrees of stress connected with individual or group feeding (Boleman et al., 1995). Other metabolic, hormonal and enzymatic factors such as endogenous muscle proteinase (calpain-calpastatin) may be involved and need further investigation ( Pringle et al., 1993 ).

CONCLUSIONS
Supplementation of diets with chromium (0.2 or 0.5 mg kg" 1 ) in organic form as a chromium yeast (bioplex Cr) did not significantly affect the performance of growing-finishing pigs, but decreased the amount of fat in the carcass (backfat thickness over the shoulder, backfat thickness in the midback and rump taken from five measurements, subcutaneous fat of ham) and increased carcass lean (lean of ham). There was a trend for reduction in saturated fatty acid content and increase in PUFA of adipose tissue in supplemented pigs. Dietary chromium supplementation accelerates development of lean body weight in growingfinishing pigs and may improve the efficiency of productivity when applied in conventional diets that do not supply adequate levels of this trace element.