Effects of concentration and source of trace minerals on performance, immunity, mineral and lipid metabolism, and carcass characteristics of beef steers1

Professional Animal Scientist, Apr 2003 by Rhoads, A R, Stanton, T L, Engle, T E, Kimberling, C V

Abstract

Two hundred seventy-nine steers were blocked by initial BW, stratified by estimated breed, and randomly assigned to pens and treatments within weight replication. Mineral treatments administered during the receiving phase consisted of Cu, Zn, Mn, and Co administered at the following levels: 1) two times the NRC (1996) recommendation from amino acid complex Availa-4(R) (Zinpro, Eden Prairie, MN); 2) at the NRC recommendation from Availa-4(R), 3) three times the NRC recommendation from inorganic minerals, or 4) six times the NRC recommendation from inorganic minerals. Steers were gradually switched from a moderate to high concentrate com-alfalfa diet. Finishing phase mineral treatments consisted of 1) mineral treatment from Availa-4(R) fed at NRC recommendations, 2) mineral treatment from Availa-4(R) fed at one and one-half times the NRC recommendation, 3) minerals from inorganic sulfate sources fed at one and one-half times the NRC recommendation, or 4) minerals from inorganic sulfate sources fed at three times the NRC recommendation. Eight pens from each treatment were harvested after being fed for a period of 198 or 230 d. Average daily feed intake was reduced (P0.05) between treatments. Steers on the organic mineral treatment at one and one-half times the NRC recommendation had greater (P

(Key Words: Finishing Steers, Trace Elements, Fatty Acid, Carcass.)

Introduction

Current NRC (1996) recommendations for trace mineral concentrations in the diets of beef cattle are formulated on a whole diet basis. Generally, the level recommended by the NRC is supplemented to cattle diets without accounting for the current trace mineral levels in the basal diet. Research has shown that Zn supplementation exceeding NRC recommendations does not improve performance or carcass characteristics (Malcolm-Callis et al., 2000). Excess supplementation of minerals such as P, Cu, and Zn most commonly results in excretion of the minerals by the animal, which may accumulate in the soil and groundwater (Jongbloed and Lenis, 1998). Different mineral sources have been fed to cattle in an attempt to achieve greater levels of absorption. Organic trace minerals have been shown to be more bioavailable (Nockels et al., 1993) and have the same availability as inorganic mineral forms (Henry et al., 1992; Rojas et al., 1995). Organic mineral supplementation with Cu Lys has been shown to exhibit higher Cu absorption and retention vs CuSO^sub 4^ supplementation in feedlot steers (Nockels et al., 1993). Rojas et al. (1995) did not observe differences in hepatic Zn concentrations when feeding Zn Met vs ZnSO^sub 4^ to wether lambs; however, when Zn Lys was fed, there was an increase in hepatic Zn concentrations compared with the result when ZnSO^sub 4^ was used as a supplement in lamb diets.

Bioavailability of certain minerals can be reduced when other minerals that exhibit antagonistic effects are consumed at the same time. Ward et al. (1993) reported that by d 84 of the feeding trial, plasma Cu was reduced to a deficient level when antagonistic minerals such as Mo and S were added to the diet. Copper supplementation at 10 and 20 mg of Cu/kg of DM in the diets of finishing beef steers has been shown to reduce backfat depth and to increase the percentage of unsaturated fatty acids in the longissimus (Engle and Spears, Engle et al., 2000a). The objectives of this study were to determine the effects of mineral concentration and source on growth performance, immunity, mineral status, carcass characteristics, and fatty acid profile in the longissimus of beef steers.

Materials and Methods

Receiving Phase. Two hundred seventy-nine crossbred steers (approximately 7 mo of age; mean BW = 264 or - 2 kg) were used in this experiment. The Colorado State University Animal Care and Use Committee approved care, handling, and sampling of the animals described herein. Steers were obtained from a private cow/calf operation southeast of Otis, CO. Upon initiation of the present study, steers were transported (approximately 209 km) to our feedlot facility in Fort Collins, CO. Upon arrival, calves were weighed, vaccinated with Bovi-Shield 4 /L5(R) and Cattle Master 4(R) (Pfizer Animal Health, Exton, PA), dewormed with Dectomax(R) (Pfizer Animal Health) pour-on, and placed in 10-head pens (7 m x 40 m) equipped with automatic waterers.

Steers were weighed on 2 consecutive d at the initiation of the experiment and implanted on d 2 with Ralgro(R) (Intervet, Millsboro, DE). Steers were blocked by BW, stratified by estimated breed, and randomly assigned to pens (7 m x 40 m; 32 pens; 8 to 11 steers per pen) within a weight replication. Pens were then randomly assigned to treatments (eight pens per treatment). Mineral treatments administered during the receiving phase consisted of Cu, Zn, Mn, and Co fed at 1) two times the NRC (1996) recommendation for beef steers from amino acid complexed minerals (Availa-4(R); Zinpro, Eden Prairie, MN), 2) the NRC-recommended rate for minerals from Availa-4(R), 3) three times the NRC recommendation from inorganic mineral sources, or 4) six times the NRC recommendation from inorganic mineral sources. Inorganic mineral sources were CuSO^sub 4^, ZnSO^sub 4^, MnSO^sub 4^, and CoCO^sub 3^. Steers were gradually switched from a moderate to a high concentrate corn-alfalfa-based finishing diet over a 31-d period (Table 1). The basal receiving diet contained 3.0 mg of Cu/kg of DM, 20.1 mg of Zn/kg of DM, and 9.6 mg of Mn/kg of DM. Diets were fed once daily in the morning, and orts were weighed on d 28 during the receiving phase and every 28 d thereafter in the finishing phase. Steers were bled on d 0, 7, 14, and 21 to determine antibody titer values for infectious bovine rhinotracheitis (IBR). Jugular blood samples were collected in non-heparinized tubes (Becton Dickinson, Franklin Lakes, NJ). On d 28, steers were weighed, and three randomly selected steers per pen were bled via jugular venipuncture. Jugular blood samples were collected in heparinized vaccutainer tubes (Becton Dickinson) for plasma Cu, Zn, and ceruloplasmin determination. A liver biopsy was obtained from the same five randomly selected steers per pen on d 0 and 28 as described by Engle et al. (1997) for determination of hepatic mineral concentration. Blood and liver samples were transported on ice to the laboratory. Blood samples were centrifuged at 1,300 x g for 25 min, and plasma was removed. Plasma and liver samples were frozen at 20[degrees]C until analyzed.