Influence of Both Endophyte Infestation in Fescue Pastures and Calf Genotype on Subsequent Feedlot Performance of Steers

Three experiments were conducted to determine the influence of both the concentration of endophytic fungus infestation in tall fescue pastures and calf genotype on the subsequent health and performance of steers in the feedlot. In Exp. 1 and 2, Angus steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte infestations for 182 d (Exp. 1) or 78 d (Exp. 2) with 12 steers per treatment. Steers were transported 1,600 km to Texas in October (Exp. 1) and July (Exp. 2), were fed a 93% concentrate diet during the finishing period, and were harvested at an estimated backfat thickness of 12 mm. In both trials, DMI over the entire feeding period and carcass characteristics were not affected (P>0.05) by endophyte infestation. In both trials, pasture ADG decreased, and feedlot ADG and gain to feed ratio increased as the previous pasture endophyte infestation increased (P<0.05). Serum cholesterol concentrations tended (P<0.10) to decrease with increasing endophyte infestation during the first 14 d in the feedlot. In Exp. 3, Angus and Brahman × British crossbred steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte in each of 2 yr. Six steers of each breed group were on each treatment each year. Steers were transported to Texas in late August of each year, were fed a 93% concentrate finishing diet, and were harvested at an estimated individual backfat thickness of 12 mm. As endophyte infestation increased, serum urea N concentrations and gain to feed ratios increased (P<0.05), whereas pasture ADG, initial BW, transit shrink, serum cholesterol concentrations, final BW, and carcass weights decreased (P<0.05) in Angus steers, but not in Brahman-cross steers. In these studies, the adverse effects of high endophyte infestations in fescue pastures appeared to carry over to the feedlot for ca. 14 d. However, steers from highly infested pastures can compensate for poor pasture performance with improved performance in the feedlot when no adverse health effects occur. Any impact of the endophyte seems to be similar in Brahman-cross and Angus steers.     

Intramuscular Fat Deposition in Steers Is Accelerated at a Set Body Weight

Seventy-two Angus crossbred steers (average initial BW, 351 ± 5.5 kg) were used to ascertain the breakpoint in BW above which intramuscular fat deposition was accelerated. Steers were randomly assigned to one of three treatments in an unbalanced study; treatment groups represented a BW at which steers would enter the feedlot (363, 408, or 454 kg). Until entering the feedlot, steers were grazed on pasture and supplemented to achieve 0.8 kg gain/d. Intramuscular fat deposition, measured ultrasonically, and live BW were acquired on d 0 and at 28-d intervals thereafter on each animal until harvest. In the feedlot, steers were fed a 13.4% CP concentrate diet until they reached a final BW of approximately 567 kg. After slaughter, carcass data were collected. No differences (P < 0.05) in ADG on pasture (0.85 ± 0.14 kg) or in the feedlot (1.70 ± 0.07 kg) occurred among treatments. There was good agreement between predicted and measured carcass quality grade (QG) (5.5 and 5.2, respectively). Based on broken-line analysis, deposition of intramuscular fat began to increase at approximately 378 kg regardless of BW at entry into the feedlot. The breakpoint BW for increased intramuscular fat accretion rate was calculated as 64% of mature BW of these steers.     

Growth Performance and Serum Mineral Concentrations of Stocker Calves Grazing Wheat Pastures and Fed Different Sources of Magnesium,

Magnesium supplementation has been shown to benefit feedlot cattle and is typically added at high concentrations to mineral supplements for calves grazing wheat pasture. Two experiments were conducted to determine the effects of Mg-mica supplementation on performance and serum mineral concentrations of stocker calves grazing wheat pasture. Supplemental Mg was provided at 6.1 g/d of supplemental Mg/ animal, Monday through Friday. In Exp. 1, 36 mixed-breed stocker calves (243 ± 3.9 kg BW) were stratified by BW and gender and allocated randomly to one of nine groups of four animals for a 112-d grazing study. Weight gain, shrink percentage, and serum Mg, Ca, K, Cu, and Zn concentrations did not differ (P>0.10) among calves fed either weathered Mg-mica (WMM), unweathered Mg-mica (UMM), or MgO. All serum mineral concentrations were within normal physiological ranges. In Exp. 2, 64 mixed-breed stocker steers (275 ± 1.7 kg BW) were stratified by BW and allocated randomly to one of 16 groups of four animals. Weight gain during a 50-d grazing study and subsequent feedlot period did not differ (P>0.10) among calves fed either no added Mg source or WMM, UMM, or MgO. Serum Cu was higher (P<0.05), and serum Mg was lower (P<0.05), from steers fed MgO, but all serum mineral concentrations were within normal physiological ranges. Although Mg-mica is relatively high in Fe (4%), using it as a supplemental Mg source appeared to have no negative impact on growth performance or serum mineral concentrations of calves grazing wheat pasture.     

Influence of Betaine on Pasture,Finishing, and Carcass Performance in Steers

Two experiments were conducted to investigate the effects of supplemental betaine on steer performance, fat deposition, and carcass characteristics. In Exp. 1 (grazing phase), 80 steers (317 kg) were fed either 1.0 kg of a control supplement (30% CP) or 1.0 kg of the control supplement plus 20 g of betaine per head per day. Betaine supplementation had no effect on overall gain or fat deposition (P>0.10) but increased ADG (P<0.10) during d 46 to 90 (0.64 vs 0.72 kg; control vs betaine, respectively). The pasture groups remained intact and were moved to the feedlot for 141 d and fed a control diet or the control diet plus 20 g of betaine per head per day. Betaine had no overall effect on finishing gain (P>0.10); however, this response was variable by period. Betaine increased final fat thickness and fat thickness change (P<0.10), but did not affect marbling or longissimus area (P>0.10). Supplemental betaine on pasture increased feed intake, final BW, and hot carcass weight (P<0.05) and increased final fat thickness and fat thickness change (P<0.10) during the finishing phase. In Exp. 2, supplemental betaine (40 g/d) was fed to steers (averaging 584 kg) in 11 replications during the last week before harvest. The overall weighted average increase in dressing percentage when betaine was fed was +0.34% (P<0.05). There was no effect (P>0.10) on fat thickness or marbling. Season of year did not affect response.     

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 × 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

Stocking Rate Effects on Steer Performance for Two Methods of Alleviating Fescue Toxicosis

Generally, grazing endophyte-infested tall fescue (Festuca arundinace Schreb.) in the late spring and summer is not recommended because of the effects of fescue toxicosis on cattle weight gains, which can be extreme. For steers conditioned to graze tall fescue in the early spring, stocking rate (3, 4, 5, and 6 steers/ha) effects were evaluated for two methods designed to avoid poor cattle performance during the late spring and summer (compensation period). The evaluation was conducted in 1997 and 1998. During the compensation phase, one replicate of each stocking rate was randomly assigned to 1-ha pastures of eastern gamagrass (Tripsacum dactyloides L.), and the other replicate of each stocking rate remained on tall fescue; the steers were fed a 1:1 mixture of broiler litter and corn at 2.27 kg as fed/steer per d. Average daily gain for steers fed eastern gamagrass during the compensation phase declined linearly (P<0.05) as stocking rate increased, but ADG for steers fed tall fescue plus the broiler litter-corn mixture tended to increase (P<0.10) as stocking rate increased. As a result, ADG and live weight gain (kilograms per hectare) with heavier stocking rates were higher for steers fed tall fescue plus the broiler litter-corn mixture, whereas the responses at a lighter stocking rate were higher for steers fed eastern gamagrass. At the conclusion of the compensation phase in 1998, steers fed tall fescue plus the broiler litter-corn mixture had lower (P<0.05) serum prolactin levels, and a higher (P<0.05) proportion of steers fed tall fescue had rough hair coats compared with those fed eastern gamagrass. Results of this study show that, for steers grazing tall fescue pastures, either eastern gamagrass or supplementation with a broiler litter-corn mixture can provide acceptable performance, but responses are affected by grazing pressure. Symptoms of fescue toxicosis can still occur, however.     

Effects of AGRADO® on Growth Performance and Health of Newly Received Feedlot Calves

Two experiments were conducted to determine the effect of an antioxidant (AGRADO®; Solutia Inc., St. Louis, MO) on the growth, gain to feed ratio, and health of receiving calves. In Experiment 1, 96 mixed breed heifer calves (206 ± 1.4 kg initial BW) were purchased at sale barns and delivered as a single group to the research facility near Fayetteville. All heifers were fed a total mixed diet containing 30% cottonseed hulls, 53% cracked corn, and 11% soybean meal for 42 d with either 0 or 150 mg AGRADO®/kg diet. Fewer (P<0.05) of the heifers fed supplemental AGRADO® were treated for respiratory disease (73% vs 83%), and medication cost was lower (P<0.05) for heifers fed supplemental AGRADO ($6.33 vs $9.49 per pen). Supplemental AGRADO® did not affect (P>0.10) ADG, daily feed intake, and gain to feed ratio. In Experiment 2, 86 bull and steer calves (237 ± 2.2 kg initial BW) were managed and fed as in Experiment 1 for a 41-d study. In this trial, supplemental AGRADO® had no significant effect on the number of sick calves or medication costs, but gain to feed ratio was improved (P<0.05) during the first 28 d of the trial. These results indicate that supplemental AGRADO® may improve the health or growth performance of newly received feedlot cattle.     

Growth Performance by Stocker Steers Fed Magnesium-Mica During a Grazing and Feedlot Period

Two experiments were conducted to determine the effects of Mg-mica supplementation on grazing and feedlot performance of stocker steers. In Exp. 1, eight groups of six steers were fed a basal diet of 80% ground grain sorghum, 15% corn silage, and 5% control protein supplement (DM basis) or a supplement containing Mg-mica (9% of supplement; 4.5 mg/kg diet DM) for 141 d. Marbling scores tended (P<0.10) to be greater, and the percentage of carcasses grading USDA Choice or higher was greater (P<0.05), from steers fed Mg-mica than from those fed the control supplement. In Exp. 2, eight groups of nine head each were offered either a control grain sorghum-based supplement or one containing 34 g/d of Mg-mica (2.7 g Mg) while grazing smooth bromegrass pastures for 112 d. Pasture groups were then placed in feedlot pens for 120 d and fed a basal diet similar to that described above. Two groups fed each pasture supplement received a control supplement, and two received a supplement containing Mg-mica (10% of supplement; 5 mg/kg diet DM). Steers fed Mg-mica during the pasture phase tended to have heavier (P=0.11) hot carcass weights, higher (P<0.05) dressing percentages, numerically (P>0.10) higher marbling scores, and a higher percentage of carcasses grading USDA Choice than steers fed the control supplement during the pasture phase. Therefore, adding Mg-mica to pasture supplements or feedlot diets appears to have no impact on grazing or feedlot performance, but may improve carcass quality.     

Effects of High Dietary Calcium Propionate and Dietary Cation-Anion Balance on Calcium Metabolism and Longissimus Muscle Tenderness in Finishing Steers,

Forty-eight Angus and Angus-cross steers (initial BW = 657 ± 5.7 kg) were used in a 2 × 2 factorial design to determine whether feeding an anionic diet or high dietary concentrations of a soluble calcium (Ca propionate) source or both would alter Ca metabolism and subsequently longissimus tenderness. Treatments consisted of 1) control, 2) 4% Ca propionate (CaProp), 3) 2% NH ₄Cl (anionic diet), and 4) CaProp plus 2% NH₄Cl. Experimental diets were fed for 7 d prior to slaughter. Steers were individually fed using electronic Calan gate feeders. Blood samples were obtained on d 3 and 7 at 2 h post feeding for plasma Ca determination. A striploin steak was obtained from each carcass at 48 h post harvest for muscle Ca analysis and Warner-Bratzler shear force (WBSF) determination. Addition of CaProp or NH₄Cl to the high concentrate finishing diet reduced (P < 0.01) ADG and DMI during the 7-d feeding period. The anionic diet reduced ADG to a greater extent than did CaProp. Average daily gain and DMI were lowest for steers fed both NH₄Cl and CaProp, indicating that their effects were additive. Carcass characteristics were not affected by CaProp, but the anionic diet tended to reduce hot carcass weights (P=0.13) and longissimus areas (P=0.09). Plasma Ca concentrations were slightly greater in steers fed CaProp on d 3 (P < 0.10) and 7 (P < 0.01) of the study. The anionic diet did not affect plasma Ca. Muscle Ca concentrations and WBSF values were not affected by either CaProp or the anionic diet. Results indicate that beef tenderness was not enhanced in steers fed a diet high in CaProp or those fed an anionic diet.     

Effects of Organic Chromium on Protein Synthesis and Glucose Uptake in Ruminants

In vitro glucose uptake and protein synthesis were measured using serum from feedlot steers fed diets supplemented with organic Cr (OCr); glucose clearance was studied using sheep as a model. Treatments investigated for glucose uptake and protein synthesis were 1) control (0 ppm supplemental Cr), 2) 0.2 ppm supplemental OCr from high Cr yeast, and 3) 0.4 ppm supplemental OCr from high Cr yeast that contained 2,000 ppm Cr (2 mg Cr/g Saccharomyces cerevisiae yeast) added to a 90% concentrate feedlot diet. The form of OCr supplied by high Cr yeast is presumably a glucose tolerance factor (GTF), which potentiates the action of insulin, and consists of Cr³⁺ centrally bound to or associated with cysteine, glutamate, glycine, and nicotinic acid residues. Serum harvested from steers fed 0.2- and 0.4-ppm OCr diets increased (P<0.05) protein synthesis in primary bovine muscle cultures. Glucose uptake rate by muscle cell cultures was increased (P<0.09) by serum from OCr-supplemented steers. Treatments investigated for glucose clearance by lambs were 1) control (0 ppm supplemental Cr), 2) 0.2 ppm, 3) 0.4 ppm, and 4) 0.8 ppm supplemental OCr from high Cr yeast added to a 85% concentrate finishing diet. Glucose clearance in lambs was improved (P<0.05) by addition of 0.2 and 0.8 ppm OCr to the diet. These results are interpreted to suggest that increased carcass muscling in ruminants fed OCr-supplemented diets is a result of improvements in amino acid uptake and glucose metabolism within muscle cells.     

Feedlot and Carcass Performance of Angus-, Brangus-, Gelbvieh-, and Gelbray-Sired Crossbred Steers

Feedlot and carcass traits were evaluated for steers (n = 231) sired by Angus (A), Brangus (BA), Gelbvieh (G), and Gelbray (GB) bulls (n = 29) out of first cross (F₁) Brahman-Hereford cows. Steers were produced over 4 y and were born during spring and fall calving seasons. Brahman inheritance was 25% in A- and G-sired steers, and 44% in BA- and GB-sired steers. After weaning, steers were stockered before entering the feedlot. Steers produced in 1993 and 1994 were fed in Louisiana and individually harvested at a targeted backfat thickness of 10 mm. Steers born in 1995 and 1996 were fed in Oklahoma and group harvested at an average backfat thickness of 10 mm. Data were analyzed separately by feedlot location because of significant location and sire breed x location effects. Angus-sired steers had smaller (P<0.05) longissimus areas (LMA) and higher (P<0.01) marbling scores(MS) and quality grades than G-sired steers across both locations. Tenderness was more desirable (P<0.05) for A-sired steers compared with G-sired steers when fed in Louisiana. Angus- and G-sired steers had larger (P<0.01) LMA than BA- and GB-sired steers across both locations. Tenderness was similar (P>0.10) between steers with 25% and 44% Brahman inheritance. These data suggest that more desirable carcass quality and tenderness can be achieved with the use of A sires, relative to the other sire breeds, when mated to F₁ Brahman-Hereford dams. Improved carcass cutability resulted with the use of G sires, and in steers with 25% Brahman inheritance.     

Influence of Feed Intake Fluctuation,Feeding Frequency,Time of Feeding,and Rate of Gain on Performance by Limit-Fed Steers

Four experiments were conducted to determine the effects of feed intake fluctuation, feeding frequency, time of feeding, and rate of gain on performance by limit-fed steers. Mean initial BW for steers in Experiments 1, 2, 3, and 4 were 378 ± 43, 225 ± 19, 227 ± 20, and 249 ± 17 kg, respectively. All experiments were complete random designs, and pen was the experimental unit. In Experiment 1, 10% daily variation in feed intake resulted in decreased (P<0.10) ADG and ratio of gain to feed (G/F) compared with steers fed either a constant amount or a 10% weekly variation in feed intake. In Experiment 2, steers fed once daily at 0800 h; once daily at 1700 h; twice daily at 0800 and 1700 h; or thrice daily at 0800, 1230, and 1700 h did not affect (P>0.10) ADG or G/F. Average daily gain and G/F by steers programed to gain 1.25 kg/d were not affected (P>0.10) by 10% fluctuation in feed intake or twice daily feeding in Experiment 3. Treatments used in Experiment 4 consisted of 1) steers fed to gain 0.9 kg/d, 2) steers fed to gain 0.9 kg/d with 10% daily feed intake fluctuation, 3) steers fed to gain 1.25 kg/d, and 4) steers fed to gain 1.25 kg/d with 10% daily feed intake fluctuation. Fluctuation in feed intake did not affect (P>0.10) ADG at either rate of gain. Results suggest that feed intake fluctuation in limit-fed cattle might decrease performance early in the feeding period; however, cattle seem to adapt to fluctuating feed intake as the feeding period progresses. Time and frequency of feeding did not affect performance by limit-fed steers.     

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 x 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

Thiamin Status and Growth Performance of Cattle New to the Feedlot Environment as Affected by Amprolium and Supplemental Dietary Thiamin

Mixed breed steers (n = 96; 211 ± 1.48 kg) were used for a 35-d trial to determine the effects of amprolium and supplemental thiamin on thiamin status and growth performance of stressed cattle. Amprolium at 0 or 5 mg/kg initial BW and thiamin at 0 or 140 mg/kg DM were fed in a 2 × 2 factorial arrangement of treatments. Amprolium was top-dressed on the daily feed for the first 21 d of the study; each steer had 50-cm bunk space available. Steers were kept in 3.7 m × 30.5 m drylots (n = 16; 6 steers per pen and 4 pens per treatment) and were fed a corn, soybean meal, cottonseed hull-based total mixed ration. A pen was used as the experimental unit. Steers fed amprolium had increased ADG from d 0 to 7 (P<0.01). Supplemental thiamin tended to increase ADG from d 0 to 21 (P<0.10). Blood thiamin monophosphate (TMP) concentrations were affected by a sampling day × supplemental thiamin interaction (P<0.001). Blood TMP concentrations were increased by supplemental thiamin on d 7, 14, 21, and 28 (P<0.001) and tended to be increased on d 35 (P=0.08). A sampling day × amprolium interaction was detected for TMP (P<0.05) and blood thiamin pyrophosphate (TPP; P<0.05) concentrations. Blood TMP and TPP concentrations were decreased on d 14, 21, and 28 (P<0.05) in the steers fed amprolium, but amprolium did not affect (P>0.10) TMP and TPP concentrations on d 7 and 35. Thiamin supplementation had no effect on the number of coccidial oocysts in feces, but steers fed amprolium had reduced numbers of coccidial oocysts (P<0.05). Supplemental thiamin and amprolium did not improve overall ADG, ADFI, or gain to feed for the 35-d trial.     

Effects of an Estradiol Implant on Locoweed Consumption,Toxicity, and Recovery in Growing Beef Steers

Two experiments were conducted to determine effects of an estradiol implant (Compudose®) on locoweed consumption and toxicity in growing steers. In Exp. 1, 16 crossbred steers (185.3 ± 6.1 kg) were randomly assigned to two replicated treatments and received either an estradiol implant or no implant. Steers were assigned to one of four pastures and were rotated through all pastures, which differed in locoweed distribution, to allow equal access. Bite counts were recorded twice daily at 0600 and 1700 h during a period when steers were likely to consume locoweed. For bite counts, steers were observed for 5 min each, starting at 0600 and at 1700 h, and the number of bites taken of cool- and warm-season grasses, forbs, and locoweed were recorded. Blood was collected on d 0, 7, 28, 35, 63, and 119, and individual BW was recorded on d 0, 35, 63, and 119. Proportion of bites of locoweed consumed by implanted vs nonimplanted steers did not differ (P>0.10). Likewise, ADG, serum alkaline phosphatase activity, and thyroxine concentrations did not differ (P>0.10) between implanted and nonimplanted steers. In Exp. 2, 20 crossbred steers (212.3 ± 6.1 kg) were divided into four groups and individually fed in a 2 × 2 factorial arrangement of treatments. Treatments included: 1) estradiol implant + locoweed, 2) implant, no locoweed, 3) no implant + locoweed, and 4) no implant, no locoweed. Steers were implanted at d 0 and fed either a ground forage diet containing 80% sudangrass hay and 20% locoweed, or a diet of 100% sudangrass hay. Implanted steers had improved ADG vs nonimplanted steers (P<0.10) through 63 d on trial, but no differences were observed in steers fed locoweed vs sudangrass hay diets (P>0.90; locoweed x implant, P>0.10). Alkaline phosphatase activity was greater (P<0.05) for steers fed locoweed vs those not receiving locoweed on d 7, 14, and 21, whereas, thyroxine concentration was lower (P<0.06) in steers fed locoweed than those not fed locoweed on d 14 and 21. Estradiol concentrations were greater in implanted steers vs those not implanted (P<0.05). These results suggest no effect of an estrogen implant on locoweed consumption or on severity of locoweed toxicity by beef steers.     

The Immune Response and Performance of Calves Supplemented with Zinc from an Organic and an Inorganic Source

Two experiments were conducted to determine the effects of supplemental zinc (Zn) from an organic and an inorganic source on growth performance, serum Zn concentrations, and immune response of beef calves. Treatments consisted of: i) control (no supplemental Zn), ii) Zn sulfate, or iii) Zn–amino acid complex. Zinc sources were supplemented to provide 360 mg of Zn/d. Experiment 1 was a 28-d study using 84 steers (240 ± 1.5 kg) fed bermudagrass hay (21 mg Zn/kg DM) with 1.8 kg/d of the appropriate corn-based supplement. In Exp. 2, 75 heifers (176 ± 2.5 kg) were fed bermudagrass hay (38 mg Zn/kg DM) and the supplements for 140 d. In Exp. 1, ADG was greater (P<0.05) from d 15 to 28 in calves fed supplemental Zn-amino acid compared with those fed Zn sulfate, but ADG did not differ (P>0.10) among treatments for the entire 28-d study. In Exp. 2, there was no effect (P>0.10) on ADG as a result of Zn supplementation. In Exp. 2, Zn-supplemented heifers had a greater response (P=0.06) to phytohemagglutinin 24 h after an intradermal injection. In Exp. 2, calves supplemented with Zn–amino acid complex had a greater antibody response to a second vaccination for bovine respiratory syncytial virus than did control or Zn sulfate-supplemented calves (treatment by day interaction, P=0.06). There was not a consistent benefit of supplemental Zn on growth of calves, but there was a positive impact of supplemental Zn on some immune-response measurements.     

Growth Performance and Serum Prolactin Concentrations of Stocker Steers Implanted with Trenbolone Acetate While Grazing Endophyte-Infected Fescue in the Spring

A 64-d grazing study was conducted with a 2 × 2 factorial arrangement of treatments to evaluate the impact of implant treatment on growth performance, hair score, and serum prolactin levels of steers grazing tall fescue with high (HE) or low (LE) levels of infection with the endophytic fungus Neotyphodium coenophialum. Mixed-breed steers (n = 130; 246 ± 3.5 kg initial BW) were allocated randomly to one of three HE or one of four LE pastures beginning April 13. Within each replication, one-half of the steers were implanted (IMP) with trenbolone acetate (40 mg) and estradiol (8 mg), and one-half were not implanted (NI). No implant treatment × endophyte level interactions were detected (P>0.10). Steers grazing HE had lower (P<0.01) BW gain, inferior (P<0.05) hair scores, and lower (P<0.01) serum prolactin concentrations on d 64 than those steers grazing LE. Total BW gains were greater (P=0.01) from IMP steers than from NI steers, but serum prolactin concentrations and hair scores did not differ (P>0.10) between IMP and NI steers on either d 36 or 64. When tabulated across forage and implant treatments, correlations were negative between overall BW gains and hair scores measured on d 64 (r = 0.28; P<0.01), and positive between overall BW gains and serum prolactin levels measured on d 36 and 64 (r = 0.33 and 0.43, respectively; P<0.001). Therefore, fescue toxicity symptoms were manifested in HE steers, and implanting trenbolene acetate and estradiol improved grazing BW gain, but no endophyte level × implant interactions were detected.     

Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism

A winter grazing/feedlot performance experiment repeated over 2 yr (Exp. 1) and a metabolism experiment (Exp. 2) were conducted to evaluate effects of grazing dormant native range or irrigated winter wheat pasture on subsequent intake, feedlot performance, carcass characteristics, total-tract digestion of nutrients, and ruminal digesta kinetics in beef cattle. In Exp. 1, 30 (yr 1) or 67 (yr 2) English crossbred steers that had previously grazed native range (n = 38) or winter wheat (n = 59) for approximately 180 d were allotted randomly within previous treatment to feedlot pens (yr 1 native range = three pens [seven steers/pen], winter wheat = two pens [eight steers/pen]; yr 2 native range = three pens [eight steers/pen], winter wheat = four pens [10 or 11 steers/pen]). As expected, winter wheat steers had greater (P < 0.01) ADG while grazing than did native range steers. In contrast, feedlot ADG and gain efficiency were greater (P < 0.02) for native range steers than for winter wheat steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for winter wheat steers than for native range steers. In contrast, 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ among treatments. In Exp. 2, eight ruminally cannulated steers that had previously grazed winter wheat (n = 4; initial BW = 407 +/- 12 kg) or native range (n = 4; initial BW = 293 +/- 23 kg) were used to determine intake, digesta kinetics, and total-tract digestion while being adapted to a 90% concentrate diet. The adaptation and diets used in Exp. 2 were consistent with those used in Exp. 1 and consisted of 70, 75, 80, and 85% concentrate diets, each fed for 5 d. As was similar for intact steers, restricted growth of cannulated native range steers during the winter grazing phase resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) compared with winter wheat steers. In addition, ruminal fill (P < 0.01) and total-tract OM digestibility (P < 0.02) were greater for native range than for winter wheat steers across the adaptation period. Greater digestibility by native range steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by native range steers in the feedlot, grazing winter wheat before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit.     

Effect of live weight gain of steers during winter grazing: I. Feedlot performance, carcass characteristics, and body composition of beef steers

Two experiments were conducted to examine the effect of previous BW gain during winter grazing on subsequent growth, carcass characteristics, and change in body composition during the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) supplemented with 0.91 kg/d of cottonseed meal. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of winter grazing, four steers were selected randomly from each treatment to measure initial carcass characteristics and chemical composition of carcass, offal, and empty body. All remaining steers were fed a high-concentrate diet to a common backfat end point. Six steers were selected randomly from each treatment for final chemical composition, and carcass characteristics were measured on all steers. Initial fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both experiments. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than for HGW steers. Final empty-body composition did not differ (P = 0.25) among treatments in Exp. 1. In Exp. 2, final carcass and empty-body fat proportion (g/kg) was greater (P < 0.03) for LGW and NR than for HGW steers. Accretion of carcass fat-free organic matter was greater (P < 0.004) for LGW than for HGW and NR steers in Exp. 1, but did not differ (P = 0.22) among treatments in Exp. 2. Fat accretion in carcass, offal, and empty body did not differ (P = 0.19) among treatments in Exp. 1, but was greater (P < 0.05) for LGW and NR than for HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than by HGW steers in Exp. 1 and 2. Differences in ADG during winter grazing and initial body fat content did not affect rate of live BW gain or gain efficiency during finishing. Feeding steers to a common backfat thickness end point mitigated initial differences in carcass and empty-body fat content. However, maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant native range.     

Estimation of Protein Requirements of Feedlot Steers

Feedlot performance, carcass characteristics, and diet composition data were collected from a survey of finishing steer experiments (40 experiments; 347 kg average initial weight; data excluded Holstein steers). Data were analyzed by weighted (observations/mean) analyses of variance to determine effects of protein intake and implanting strategy on feedlot performance and carcass characteristics. Implanting strategies were defined according to prevalent or last implant type used: no implant (None); medium-potency implants (Medium): zeranol 72 mg per dose, steroid-based implants (Synovex-S or Compudose) or trenbolone acetate (TBA) alone; high-potency implants (High): TBA in combination with either steroids or zeranol. Regression procedures were utilized to estimate CP and DIP, or MP requirements. Implant effects were independent (P>0.60) of dietary protein effects and included faster (P<0.05) gains at higher intakes (P<0.05) that resulted in improved (P<0.05) feed efficiencies. Steers responded to higher dietary CP (13.3 vs 11.4%) by increasing intake (P<0.05) which resulted in faster (P<0.05) and more efficient (P=0.09) gains. Compared to nonimplanted steers, implanted steers had heavier (P<0.05) carcasses with larger (P<0.05) ribeyes and lower (P<0.05) marbling scores. Nonimplanted steers fed 13.3% CP diets had heavier (P<0.05) carcasses than nonimplanted steers fed 11.4% CP diets. Maintenance MP requirements of nonimplanted steers were greater than those of implanted steers and similar to established MP requirements. Diets of steers implanted with high-potency implants must be supplemented to contain more than 7.5 g MP/kg BW^0.75/d, especially at heavy (>450 kg) initial BW, to maximize implant response. Implanted steers have a greater ability to respond to increased dietary protein because of reduced protein requirements for maintenance.