Effects of winter stocker growth rate and finishing system on: II. Ninth-tenth-eleventh-rib composition, muscle color, and palatability.

Angus-cross steers (n = 198; 270 kg; 8 mo) were used in a 3-yr study to assess the effects of winter stocker growth rate and finishing system on 9-10-11th-rib composition, color, and palatability. During the winter months (December to April), steers were randomly allotted to 3 stocker growth rates: low (0.23 kg/d), medium (0.45 kg/d), or high (0.68 kg/d). At the completion of the stocking phase, steers were allotted randomly within each stocker growth rate to a high concentrate (CONC) or to a pasture (PAST) finishing system. All steers were finished to an equal time endpoint to minimize confounding due to animal age. At the end of the finishing phase, steers were transported to a commercial packing plant for slaughter and a primal rib (NAMP 107) was removed from 1 side of each carcass. The 9-10-11th-rib section was dissected into lean, fat, and bone, and LM samples were analyzed for palatability and collagen content. Hot carcass weight and 9-10-11th-rib section weight were greater (P = 0.01) for high than low or medium. Winter stocker growth rate did not alter 9-10-11th rib composition. The percentage of fat-free lean, including the LM and other lean trim, was greater (P = 0.001) for PAST than CONC. Total fat percentage of the 9-10-11th-rib section was 42% lower (P = 0.001) for PAST than CONC due to lower percentages of s.c., intermuscular, and i.m. fat. The percentage of total bone in the 9-10-11th-rib section was greater (P = 0.001) for PAST than CONC. Finishing beef cattle on PAST increased (P = 0.001) the percentage of lean and bone and reduced (P = 0.001) the percentage of fat in the carcass based on published prediction equations from 9-10-11th rib dissection. Stocker growth rate did not influence the objective color scores of LM or s.c. fat. Longissimus muscle color of PAST was darker (lower L*; P = 0.0001) and less red (lower a*; P = 0.002) than CONC. Juiciness scores were greater (P = 0.02) for CONC than PAST. Initial and overall tenderness scores as well as Warner-Bratzler shear force values did not differ (P > or = 0.28) among finishing systems. Beef flavor intensity was lower (P = 0.0001) and off-flavor intensity greater (P = 0.0001) for PAST than CONC. Total collagen content was greater (P = 0.0005) for PAST than CONC; however, there were no differences in percentage soluble or insoluble collagen. Growth rate during the winter stocker period did not influence rib composition, color, or beef palatability. Finishing steers on forage reduced fat percentages in the rib and LM without altering tenderness of beef steaks.

The effect of anabolic implants on intramuscular lipid deposition in finished beef cattle.

Two experiments were conducted to determine the effects of anabolic implants on performance, changes in ultrasound measurements, carcass quality, cellularity of i.m. and s.c. adipose depots, and mRNA expression of acetyl CoA carboxylase (ACC), stearoyl CoA desaturase (SCD), and lipoprotein lipase (LPL) in i.m. adipose tissue of finished beef cattle. Angus heifers (experiment 1: n = 10; 411 kg of BW) and steers (experiment 2: n = 18; 279 kg of BW) were randomly allotted as control (C) or implanted with Synovex-Plus (SP) at d 0 and midway through the finishing period. The cattle were fed a high-concentrate diet and were weighed at approximately 28-d intervals. Heifers and steers were finished for 108 and 133 d, respectively. At slaughter, a section of the LM (sixth to ninth rib) was removed, and i.m. adipose tissue was dissected for mRNA analysis. Subcutaneous and i.m. adipose tissues also were collected for determination of cellularity. At 48 h postmortem, carcass data were collected, and a steak (12th rib) was removed for analysis of lipid and fatty acid composition. Body weight did not differ (P > 0.10) between treatments until after reimplanting of the heifers (d 55) or steers (d 73). Average daily gain was 36 and 16% faster (P < or = 0.01) for implanted heifers and steers, respectively, compared with their control counterparts. Implanting resulted in larger (P < or = 0.10) HCW and LM area for heifers and steers. However, implanting did not affect (P > 0.10) dressing percent, fat thickness, percentage of KPH, yield grade, or marbling score. Intramuscular lipid content and concentrations of major fatty acids did not differ (P > 0.10) between treatments. Percentage of SC adipocytes was greater at larger diameters ( > 150 microm), whereas the majority of i.m. adipocytes were at small to middle diameters (50 to 150 microm). The number of i.m. adipocytes per gram of tissue was greater (P < 0.05) for SP than C and also were greater (P < 0.05) than the number of s.c. adipocytes in SP heifers. In experiment 2, adipocytes per gram of tissue tended to be greater (P = 0.07) for SP than C and were greater (P < 0.01) for i.m. than s.c. In experiment 1, average cell diameter and volume did not differ (P > 0.10) between treatments and tissues, but in experiment 2 both cellularity traits were greater (P < 0.01) for s.c. than for i.m.. Implanting did not alter mRNA expression of ACC, SCD, or LPL in i.m. adipose tissue. This study shows that anabolic implants do not appear to have direct effects on i.m. lipid deposition.

Metabolic responses of lactating dairy cows to single and multiple subcutaneous injections of glucagon.

Continuous, intravenous infusions of glucagon improve carbohydrate status in lactating dairy cows without increasing concentrations of plasma NEFA. The objective was to test whether single subcutaneous injections and multiple subcutaneous injections of glucagon delivered at 8-h intervals over 14 d improve the carbohydrate status in lactating dairy cows without increasing concentrations of plasma BHBA and NEFA. In a single-injection experiment, four midlactation cows each were injected with 2.5 and 5 mg of glucagon 1 wk apart. In a multiple-injection experiment, nine cows, assigned randomly to three treatments, were injected subcutaneously with 0, 2.5, or 5 mg of glucagon every 8 h for 14 d, beginning at d 8 postpartum. Single subcutaneous injections of glucagon increased concentrations of plasma glucagon and single and multiple subcutaneous injections of glucagon increased concentrations of plasma glucose, with larger increases at the 5-mg dosage. Injections of 5 mg of glucagon increased concentrations of plasma insulin in both experiments, whereas the 2.5-mg dosage increased plasma insulin only in the multiple-injection experiment. The response of glucose and insulin to injections of 5 mg of glucagon persisted throughout the 14-d injection period. Concentrations of plasma NEFA decreased in the single-injection experiment, and concentrations of BHBA decreased after 5 mg of glucagon was injected in the multiple-injection experiment. These results document that both single and multiple injections of 5 mg of glucagon over 14 d consistently improve the carbohydrate status of dairy cows and decrease concentrations of plasma NEFA and BHBA.

Wheat middlings in high-concentrate diets: feedlot performance, carcass characteristics, nutrient digestibilities, passage rates, and ruminal metabolism in finishing steers.

We conducted two experiments to determine the feeding value and effects on diet digestibilities, passage rates, and ruminal metabolism of wheat middlings (WM) fed as a replacement for either the concentrate or roughage components of finishing diets of steers. In Exp. 1, 120 medium-framed steers were blocked by weight and randomly allocated to one of six treatments of high-concentrate diets: control (0%); 5, 10, or 15% pelleted WM replacing dry-rolled corn (DRC); and 5 or 10% pelleted WM replacing chopped alfalfa hay (ALF) components of the diet. Increasing WM replacement of DRC increased DMI (P < .01) and feed:gain ratio (FG; P < .05) linearly. A 9.2% increase in daily DMI and 10.1% increase in FG were observed at 15% of WM. Daily gain and final weight of the steers were not influenced by WM replacement of DRC. The WM replacement of ALF decreased (P < .01) daily DMI linearly, but it had no effect on ADG, final weight, or FG. In Exp. 2, six medium-framed steers, fitted with ruminal cannulas, were used in a 6 x 6 Latin square design with the same treatments as described in Exp. 1. Dry matter, OM, and starch digestibilities decreased (P < .01) by increasing replacement of DRC with WM, and replacing ALF increased DM and OM digestibilities linearly (P < .01). Wheat middlings could replace only up to 5% of DRC without reducing feed conversion efficiency and diet digestibilities, but complete (100%) or partial (50%) replacement of ALF increased digestibilities of DRC finishing diets.