Feedlot Cattle Growth Research Articles

Use of feed additives to improve feed efficiency and growth of feedlot cattle

The producers must observe feed efficiency (FE) and profitability in feedlot cattle under scenarios of high production costs associated with feeding. The most efficient and persistant way to change FE is using genetic tools. However, genetic selection in cattle is slow compared to the use of feed addititves, which work to stabilize ruminal pH, induce beneficial changes in the rumen microbial population, and increase efficiency in energy and protein metabolism. The literature is extensive about antibiotics, ionophores, and non-ionophores increasing FE. Nowadays, the use of "naturals" products as growth promoters has gained great relevance, and promising results has been reported. ). Therefore, this study aimed to review the use of feed additives in beef cattle feeding.

232 State of the Art: Zinc and Copper Nutrition for Feedlot Cattle

Abstract Beef cattle require several trace minerals for optimal function, but of these, zinc (Zn) and copper (Cu) are arguably the most widely studied. Zinc and Cu both have essential roles in feedlot cattle growth, health, and carcass merit, yet they could not be more different. Ruminants are tolerant of quite high dietary Zn concentrations but will readily absorb and store Cu to the point of eventual toxicity. Zinc is ubiquitous in the body, needed for countless bodily processes, while Cu is more specialized, essential for a handful of biochemical processes. Because Zn is involved in so many proteins, a Zn biomarker in cattle (or any species) has remained elusive. In contrast, liver Cu is a well-accepted status index in ruminants, though reference ranges for adequacy are wide and non-specific. In addition, because of a shared affinity for the storage protein metallothionein, Zn and Cu may prove antagonistic to one another. Differences in bioavailability of Zn and Cu sources add further complexity to designing an optimal trace mineral supplementation program. This presentation will cover a review of the Zn and Cu feedlot literature from the past several years, in addition to pooled analysis of in-house data from our laboratory, with the goal of offering recommendations for best practices for Zn and Cu nutrition of feedlot cattle.

Effects of rubber matting on feedlot cattle growth performance, locomotion, and carcass characteristics in slatted floor facilities.

The objective was to determine effects of old and new rubber matting in a slatted, indoor cattle feeding facility on cattle growth performance, locomotion, and carcass characteristics. In experiment 1, fall-born Angus × Simmental steers (N = 207; body weight = 222±38kg) were blocked by weight and assigned to 32 pens. Pens were randomly assigned to 1 of 4 treatments: no matting/concrete (CONC1), 12-yr-old Animat Pebble matting (OLD1), new Animat Maxgrip matting (MG), and new Animat Pebble matting (PEB1). Steers were fed a common diet for 209 d with a minimum stocking density of 3.40 m2 per animal. Final body weight (BW) and average daily gain (ADG) were affected (P = 0.02 and P < 0.01, respectively) by treatment with steers on PEB1 finishing heaviest with the greatest growth, MG and CONC1 intermediate, and OLD1 finishing at the lightest final BW with the least growth. Flooring treatment did not affect overall dry matter intake (DMI; P = 0.16) or gain to feed ratio (G:F; P = 0.94). Flooring treatment did not affect (P ≥ 0.19) any carcass traits. Locomotion scores (LS) were affected (P < 0.01) by flooring treatment with CONC1 having the worst mobility while OLD1, MG, and PEB1 were similar (P ≥ 0.24). Locomotion score had a day effect (P < 0.01) where cattle gait and mobility worsened as days on feed increased. In experiment 2, fall-born Angus × Simmental steers (N = 189; BW = 352±43kg) were blocked by weight and assigned to 21 pens. Pens were randomly assigned to 1 of 3 treatments: no matting/concrete (CONC2), 15-yr-old Animat Pebble matting (OLD2), and new Animat Pebble matting (PEB2). Steers were fed a common diet for 152 d with a stocking density of 2.65 m2 per steer. After 152 d on feed, flooring treatment did not affect (P ≥ 0.30) BW, ADG, or DMI nor did treatment affect (P ≥ 0.17) carcass traits. However, steers housed on OLD2 or PEB2 had improved locomotion scores (P = 0.02) compared with steers housed on CONC2. Locomotion score had a day effect (P < 0.01) as cattle gait and mobility worsened with greater number of days on feed, regardless of treatment. Overall, results suggest that new rubber matting increased ADG and HCW during a 209-d trial when cattle were stocked at 3.4 m2 in small pens and that rubber matting regardless of age improved cattle locomotion scores in slatted indoor feeding facilities.

66 Overview of Different Cattle Finishing Facilities: Economic Summary and Future Innovations

Abstract Environment and weather may have a significant impact on feedlot cattle growth. Most U.S. feedlot cattle are finished/fed in open-mound, dirt lots. Historic closeout data conclude that cattle performance has been optimal when finishing cattle in well groomed, dry, dirt mound lots. However, weather challenges including excessive heat, cold, or moisture conditions negatively impact cattle performance. Past attempts to provide shelter for finishing feedlot cattle with buildings/sheds have often yielded subpar finishing cattle growth expectations when compared to well-groomed dirt mounds. Improved cattle housing designs including building ventilation and flooring types are being utilized in many Northern Plains and Midwest cattle operations during the last decade. This symposium will address current designs, management issues, economic considerations and future improvement challenges for finishing cattle housing systems. Performance and economics comparing various cattle breeds and varied in-weights throughout finishing period in differing cattle facilities will be evaluated. Comparison of expected and realized performance of finishing cattle when housed in bedded barns, conventional scrape yards with sheds and cattle comfort finishing shelters will be reviewed.

PSII-19 Effect of zinc and chromium supplementation on performance and carcass characteristics in feedlot steers

Abstract One hundred and sixty-five crossbred steers were used in this experiment to investigate the influence of supplemental zinc (Zn) and chromium (Cr) on performance and carcass characteristics of feedlot steers fed steam-flaked corn-based finishing diet. Steers were blocked by initial BW (518.9 ± 8.4 kg) within cattle source (2 sources) and housed in pens containing 6–7 steers per pen. Pens within blocks were randomly assigned to treatments in a 2 x 2 factorial arrangement, with factors being: 30 or 90 mg of Zn/kg DM and 0.0 or 0.25 mg Cr/kg DM. Treatments consisted of: 1) 30 mg Zn/kg DM; 2) 90 mg Zn/kg DM; 3) 30 mg Zn + 0.25 mg Cr/kg DM; and 4) 90 mg Zn/kg + 0.25 mg Cr/kg DM. Zinc was supplemented as ZnSO4 and Cr supplemented as Cr propionate. Steers were individually weighted on 2 consecutive days prior to initiating dietary treatment and on 2 consecutive days at the end of the experiment. Dietary treatment were initiated 64 days prior to slaughter (total days on feed = 240). All cattle were transported to a commercial abattoir on the same day and slaughtered. Steers receiving supplemental Cr had greater final BW (P &amp;lt; 0.02) and ADG (P &amp;lt; 0.03) when compared to non-Cr supplemented steers. Additionally, hot carcass weight (P &amp;lt; 0.005) and marbling score (P &amp;lt; 0.03) were greater (P &amp;lt; 0.005) for steers receiving 30 mg Zn/kg DM + 0.25 mg Cr/kg DM when compared with all other treatments. Dry matter intake, morbidity and mortality, and all the other carcass measurements were similar across treatments. These data indicate that under the conditions of this experiment, Zn and Cr supplementation may influence feedlot cattle growth and carcass characteristics.

Effects of clay on toxin binding capacity, ruminal fermentation, diet digestibility, and growth of steers fed high-concentrate diets.

Three experiments were conducted to determine the effect of increasing concentrations of a smectite clay on toxin binding capacity, ruminal fermentation, diet digestibility, and growth of feedlot cattle. In Exp. 1, 72 Angus × Simmental steers were blocked by BW (395 ± 9.9 kg) and randomly allotted to 3 treatments (4 pens/treatment and 6 steers/pen) to determine the effects of increasing amounts of clay (0, 1, or 2%) on performance. The clay was top-dressed on an 80% concentrate diet at a rate of 0, 113, or 226 g/steer daily to achieve the 0, 1, and 2% treatments, respectively. Steers were slaughtered at a target BW of 606 kg. In Exp. 2, 6 steers (596 ± 22.2 kg initial BW) were randomly allotted to the same 3 treatments in a replicated 3 × 3 Latin square design (21-d periods) to determine the effects of increasing amounts of clay on ruminal pH, VFA, and nutrient digestibility. In Exp. 3, 150 mg of clay was incubated in 10 mL of rumen fluid with 3 incremental concentrations (6 replicates per concentration) of aflatoxin B (AFB) or ergotamine tartate (ET) to determine binding capacity. During the first 33-d period, there was a quadratic effect of clay on ADG ( < 0.01) and G:F ( < 0.01), increasing from 0 to 1% clay and then decreasing from 1 to 2% clay. However, during the second 30-d period, clay linearly decreased ADG and G:F ( ≤ 0.03) and overall ADG, DMI, and G:F were not impacted ( ≥ 0.46). Clay linearly decreased marbling score ( = 0.05). Hepatic enzyme activity did not differ among treatments on d 0 or at slaughter ( ≥ 0.15). Clay linearly decreased ruminal lactate and propionate, linearly increased formate and the acetate:propionate ratio ( ≤ 0.04), and tended ( = 0.07) to linearly increase butyrate. Clay tended to linearly increase ( = 0.06) OM and CP apparent digestibility. Ruminal pH, urine pH, and other digestibility measures did not differ among treatments ( ≥ 0.15). Clay was able to effectively bind AFB and ET at concentrations above the normal physiological range (52 and 520 μg/mL), but proportional adsorption was decreased to 35.5 and 91.1% at 5,200 μg/mL ( < 0.01) for AFB and ET, respectively. In conclusion, clay effectively binds ruminal toxins, decreases ruminal lactate, and improves performance only during adaptation to a high-concentrate feedlot diet.

A3 Early Career Award Speaker: Interactions between trace minerals and growth promoting practices in beef cattle

Trace minerals (TM) are necessary to support optimum animal growth. While TM requirements to prevent deficiency were recently updated, the requirements of beef cattle to support optimal performance remain ill defined. Advancements in animal genetics and utilization of technologies to promote growth of feedlot cattle have dramatically advanced production efficiencies in the beef industry. Trace minerals (Co, Cu, Fe, I, Mn, Se and Zn) are integral in a variety of growth processes in the body, including supporting metalloproteins involved in DNA synthesis, collagen production, energy utilization and critical antioxidant enzymes. Over 80% of feedlot cattle are estimated to receive hormone implants to enhance growth and efficiency. Recently, we examined the effect of feeding no supplemental TM, TM supplemented at NRC recommendations, or TM supplemented at industry recommended concentrations (all inorganic sources), fed to Angus cross steers receiving no implant or implanted with Component TE-IS, followed by Component TE-200 on d 56. Harvested on d 124, HCW was, as expected, improved (P = 0.0001) by implant, but HCW was also improved by 15 kg (P = 0.01) in steers supplemented at industry TM concentrations vs. those receiving no supplemental TM. Additional work is needed to clarify the potentially greater need for TM in cattle receiving hormone implants. Introduction of beta adrenergic agonists revolutionized late stage finishing cattle performance, increasing feed efficiency, ADG, and often HCW of cattle. In a series of studies we have found that increasing supplementation of Zn (from a combination of inorganic and organic sources) to steers fed ractopamine hydrochloride increases cattle performance (ADG, feed efficiency, and HCW in some studies) during the ractopamine feeding period. Zinc is thought to inhibit breakdown of the intracellular signalling molecule, cAMP, perhaps potentiating the growth response. Alternately, demand for Zn and other TM may simply be greater due to increased growth rates. We recently found the retention of Zn and N to be positively correlated and that both ractopamine hydrochloride and Zn increase N retention in steers. It seems likely that growth enhancing technologies influence TM requirements of cattle, and further work is needed to determine TM requirements that optimize cattle performance and maximize producer profitability.

Influence of substituting steam-flaked corn for dry rolled corn on feedlot cattle growth performance when cattle are allowed either ad libitum or restricted access to the finishing diet.

ObjectiveThe influence of substituting steam-flaked corn (SFC) for dry rolled corn (DRC) on feedlot cattle growth performance and dietary net energy when cattle are allowed either ad libitum or 2-h restricted access to the finishing diet was evaluated.MethodsTreatment effects were tested using 96 crossbred steers (251±2 kg) during the initial 56 d of the finishing phase. Cattle were blocked by weight and randomly assigned within blocks to 16 pens (4 pens/treatment). Bunk space was sufficient (41 cm/head) to allow all steers access to the feed bunk at the same time. Treatments consisted of two finishing diets containing (dry matter basis) 77.1% corn grain processed by dry rolling (density = 0.50 kg/L) or steam flaking (density = 0.36 kg/L). Cattle were fed twice daily at 06:00 and 14:00 h, allowing for approximately 5% residual. In the case of restricted feeding, steers were allowed access to feeders for 1 h following each feeding, after which residual feed was withdrawn.ResultsThere were no treatment interactions on dry matter intake (DMI), average daily gain (ADG), gain efficiency (G:F), or dietary net energy (NE). Restricting feed access time reduced (p <0.01) feed intake, and hence, ADG. Substitution of SFC for DRC increased (p<0.01) ADG, feed efficiency (G:F), and estimated dietary NE, without affecting DMI. Based on tabular net energy of maintenance (NEm) value (2.18 Mcal/kg) for DRC, the estimated NEm value for SFC using the replacement technique, averaged 2.44 Mcal/kg; an improvement of 10.7%. The ratio of observed-to-expected dietary NE was not affected by feed access time.ConclusionSubstitution of SFC for DRC in finishing diets for feedlot cattle enhanced ADG, gain efficiency, and the NE value of the diet. Although restriction of feed access time depressed DMI and ADG, it did not affect the comparative benefit of steam flaking toward enhancement of ADG, G:F, and dietary NE.

Biofuel feedstock and blended coproducts compared with deoiled corn distillers grains in feedlot diets: Effects on cattle growth performance, apparent total tract nutrient digestibility, and carcass characteristics.

Crossbred steers (British × Continental; = 192; initial BW 391 ± 28 kg) were used to evaluate the effects of feeding ethanol coproducts on feedlot cattle growth performance, apparent nutrient digestibility, and carcass characteristics. Steers were blocked by initial BW and assigned randomly to 1 of 6 dietary treatments within block. Treatments (replicated in 8 pens with 4 steers/pen) included 1) control, steam-flaked corn-based diet (CTL), 2) corn dried distillers grains with solubles (DGS; DRY-C), 3) deoiled corn dried DGS (DRY-CLF), 4) blended 50/50 corn/sorghum dried DGS (DRY-C/S), 5) sorghum dried DGS (DRY-S), and 6) sorghum wet DGS (WET-S). Inclusion of DGS was 25% (DM basis). The DGS diets were isonitrogenous, CTL was formulated for 13.5% CP, and all diets were balanced for ether extract. Final shrunk BW, ADG, and DMI did not differ among CTL and DGS treatments ( ≥ 0.19). Overall G:F did not differ from CTL for DRY-C, DRY-CLF, or WET-S ( ≥ 0.12); however, G:F was 9.6% less for DRY-S compared with CTL ( < 0.01) and tended ( = 0.09) to be less for DRY-C/S than CTL. For grain source, ADG and G:F were less for DRY-S vs. DRY-C ( < 0.05), but blending DRY-C/S tended ( = 0.07) to increase ADG and increased ( = 0.05) carcass-adjusted G:F vs. DRY-S. For WET-S, final BW and ADG were greater ( < 0.05), and G:F tended ( = 0.06) to be greater than for DRY-S. There was no difference in ADG, DMI, or G:F of steers fed DRY-C vs. DRY-CLF ( ≥ 0.35). Apparent DM and OM digestibility did not differ for CTL, DRY-C, DRY-CLF, and WET-S ( ≥ 0.30) but were lower for DRY-C/S and DRY-S ( < 0.05). Nutrient digestibility was lower for DRY-S vs. DRY-C ( < 0.01), but apparent digestibility of OM, DM, NDF, ADF, CP, ether extract, and starch were increased ( < 0.01) for DRY-C/S vs. DRY-S. Although starch digestibility did not differ between DRY-S and WET-S ( 0.18), digestibility of other measured nutrients was greater for WET-S vs. DRY-S ( < 0.01). Ether extract digestibility was greater for DRY-CLF vs. DRY-C ( < 0.05). Carcass weight, dressing percent, and marbling score did not differ between CTL and DGS diets ( ≥ 0.23). For DRY-S, HCW was lower than for DRY-C ( = 0.02); however, compared with DRY-S, HCW tended to be greater for DRY-C/S ( = 0.10) and WET-S ( = 0.07). At a moderately high (25% DM) inclusion, blending C/S or feeding WET-S resulted in cattle growth performance and carcass characteristics similar to those of CTL and corn-based coproducts.

Influence of flake fragmentation on the feeding value of steam-flaked corn in finishing diets for feedlot cattle

Two trials were conducted to evaluate the influence of fines on the feeding value of steam-flaked corn (SFC) in finishing diets for feedlot cattle. Three levels (0, 333 and 667g/kg) of re-rolled SFC replaced standard SFC (0.31kg/L) in a corn-based finishing diet (DM basis). Diets were offered as total mixed rations. Re-rolled SFC consisted of standard air-dry SFC that was passed through the rollers a second time to simulate loss of flake integrity which can occur during feed-handling. In experiment one, the influence of fines in SFC on growth performance was evaluated in eighteen crossbred steers (294±5kg) in a replicated 3×3 Latin square design. Daily weight gain was similar (P>0.10) among treatments, averaging 1.31kg/d. Dry matter intake tended to be greater (quadratic effect, P=0.06) for diets containing re-rolled steam-flaked corn. Gain efficiency and dietary NE were not influenced by dietary treatments (P>0.10). In experiment two, six Holstein steers (308±17kg) with cannulas in the rumen and proximal duodenum were used in a replicated 3×3 Latin square design to evaluate treatment effects on characteristics of digestion. Reductions in particle size of SFC due to rerolling did not influence ruminal or total tract digestion of OM, NDF, N, or starch (P>0.10). Likewise, there were no treatment effects (P>0.10) on ruminal microbial efficiency, ruminal pH, or ruminal VFA molar proportions. It is concluded that the impact of flake disintegration during conveyance and handling on feedlot cattle growth performance and characteristics of digestion will be marginal, if appreciable.

Effects of hops on ruminal fermentation, growth, carcass traits and shedding of Escherichia coli of feedlot cattle

Experiments were conducted to evaluate the effects of hops on ruminal fermentation, fecal shedding of Escherichia coli and the growth of feedlot cattle. In a feedlot experiment, 60 British × Charolais steers (393 ± 3.6 kg) were randomly assigned to individual pens and fed a barley grain and barley silage-based diet for a 55-day growing and a 105-day finishing period. Hops were added to the growing diet at levels of 0, 119, 238 and 476 mg/kg dry matter (DM) and to the finishing diet at levels of 0, 238, 476 and 952 mg/kg DM. Fecal samples were collected to determine the effects of hops on shedding of E. coli. Carcass data from all steers were collected at a commercial abattoir at the end of the finishing period. Inclusion of hops in growing or finishing diets at these rates did not affect the shedding of E. coli or the feed intake, growth, feed efficiency, carcass characteristics or fatty acid composition of diaphragm tissue of steers. However, average daily gain of steers supplemented with the highest level of hops during the growing and finishing period was 6% higher ( P = 0.11) than the controls. In an in vitro experiment, DM disappearance (IVDMD) and concentration of volatile fatty acid (VFA) linearly ( P < 0.01) increased in the growing diet incubations with increasing levels of hops. Compared to the control treatment, addition of hops to the growing diet increased ( P < 0.05) gas production, VFA concentration, percentage of propionate in the total VFA and IVDMD ( P < 0.001), but lowered ( P < 0.05) the percentage of acetate and the acetate:propionate ratio. Hops added to the finishing diet linearly increased gas production ( P < 0.05). Hops at levels up to 476 mg/kg DM in a growing diet and up to 952 mg/kg DM in a finishing diet improved ruminal fermentation in vitro, but did not improve the growth or efficiency of feedlot cattle. Inclusion of higher levels of hops in the diet may be favorable for ruminant production.

Effect of feed delivery fluctuations and feeding time on ruminal acidosis, growth performance, and feeding behavior of feedlot cattle1,2

Research was conducted to determine whether fluctuations in the amount of feed delivered and timing of feeding affect ruminal pH and growth of feedlot cattle. In Exp. 1, the effects of constant (C) vs. fluctuating (F) daily feed delivery on ruminal pH were assessed in a crossover experiment (two 28-d periods) involving six mature, ruminally cannulated steers. The diet consisted of 86.8% barley grain, 4.9% supplement, and 8.3% barley silage (DM basis) and was offered ad libitum for 2 wk to estimate DMI by individual steers. Steers in group C were offered a constant amount of feed daily equal to their predetermined DMI, whereas steers in group F were offered 10% more or less than their predetermined DMI on a rotating 3-d schedule. Ruminal pH of each steer was measured continuously via an indwelling electrode placed in the rumen during the last 6 d of each period. Mean pH tended to be lower (0.10 units) for F than C (5.63 vs. 5.73; P = 0.15), and ruminal pH of steers in group F tended to remain below 5.8 (P = 0.03) or 5.5 (P = 0.14) for greater proportions of the day than steers in group C. Inconsistent delivery of feed lowered ruminal pH, suggesting increased risk of subclinical acidosis. In Exp. 2, a 2 x 2 factorial was used to study the effects of pattern (C vs. F) and feeding time (morning [0900] vs. evening [2100]) on the feeding behavior and performance of 234 (310 +/- 23 kg) Charolais x Hereford beef steers during backgrounding and finishing phases over 209 d. One pen per treatment was equipped with a radio frequency identification (GrowSafe Systems Ltd., Airdrie, Canada) system that monitored bunk attendance by each steer throughout the trial. Pattern of feed delivery did not affect (P = 0.16) DMI (7.36 kg/d), ADG (1.23 kg/d), G:F (0.17), or time spent at the bunk (141 min/d), nor were pattern of feed delivery x time of feeding interactions observed (P = 0.18). Late feeding increased (P < 0.05) daily DMI (7.48 vs. 7.26 kg), ADG (1.28 vs. 1.00 kg/d), and G:F (0.21 vs. 0.15). These studies indicate that the risk of subclinical acidosis was increased with fluctuating delivery of feed, but the greater risk of acidosis did not impair growth performance by feedlot cattle. Consequently, daily intake fluctuations of 10% DMI or less that do not alter overall intake by feedlot cattle are unlikely to have any negative consequences on growth performance.

Experiential learning in the animal sciences: development of a multispecies large-animal management and production practicum.

Students enrolled in an introductory animal science course (ASG 3003) at the University of Florida were surveyed (n = 788) over a 3-yr period to ascertain their current experience and career goals in animal agriculture. Sixty-one percent of the students indicated that they were from an urban background. Only 4% were raised on a farm or ranch where the majority of family income was attributed to production agriculture. Eighty-six percent of the students had minimal or no experience working with large domestic farm animals, but nearly 64% of the students wanted to pursue a career in veterinary medicine. Disciplinary and species interests of the students were highly associated with previous background experiences. Students from nonagricultural backgrounds, who were most likely to indicate a career interest involving veterinary medicine, were most interested (P < 0.05) in animal behavior, whereas the students of rural background were more interested (P < 0.05) in animal management. Thirty-three percent of students were primarily interested in small companion animals; 22% in horses; 20% in domestic farm animals, including beef, dairy, swine, or sheep; and 24% in undomesticated zoo animals or wildlife. The career goals indicated by most students necessitate practical application of animal husbandry skills that are often assumed as general knowledge. Thus, a multispecies large animal management and production practicum (ANS 3206) was developed to provide students with hands-on experience. It was an elective course, and students were encouraged to enroll for two consecutive semesters. Teams of students rotated responsibilities among four livestock species (beef, dairy, equine, and swine). Daily responsibilities at each of the units included feeding and monitoring growth of feedlot cattle and finishing swine, farrowing assistance and baby pig processing, and equine training and foaling assistance. Students were also involved with all facets of a working dairy. Additionally, students completed written assignments specific to their individual species responsibilities that included daily journals, worksheets, or calculation of performance measures. Weekly class meetings allowed for instruction and were used to manage the varied course activities. Using a 5-point scale (1 = poor, 5 = excellent), students indicated that the course further stimulated their interest (4.73) and facilitated their learning (4.63) of animal science concepts. Overall course evaluations ranged from 4.54 +/- 0.55 to 4.85 +/- 0.38 over a 4-yr period. As more students enter animal science programs with nonagricultural backgrounds, it will become necessary to reemphasize basic animal-handling skills and practical applications through experiential learning activities.

Interaction of forage level and monensin in diets for feedlot cattle on growth performance and digestive function

A feedlot growth-performance trial and a metabolism trial were conducted to evaluate the interaction of forage level (10 vs 20%) and monensin (0 vs 28 mg/kg, air-dry basis) on utilization of a steam-flaked corn-based finishing diet. There were no treatment interactions (P > .10) on feedlot cattle growth performance or site and extent of digestion of OM, ADF, N, and starch. Monensin supplementation did not influence (P > .10) ADG, DM intake, feed efficiency, estimated NE value of the diet, or ruminal and total tract digestibility of OM, ADF, and starch. Monensin decreased (14.5%, P < .10) passage of microbial N to the small intestine and ruminal digestion of feed N (10.4%, P < .05). Ruminal pH tended to be slightly lower (1.9%, P < .10) with monensin supplementation. Monensin did not affect (P > .10) ruminal molar proportions of acetate and butyrate. There was an interaction between forage level and monensin on ruminal molar proportions of propionate. With the low-forage diet, molar proportions of propionate were 9.4% higher with monensin supplementation. In contrast, with the high-forage diet ruminal molar proportions of propionate were 5.5% lower with supplemental monensin. Monensin did not affect (P > .10) estimates of methane production. Decreasing the forage in the diet from 20 to 10% increased ADG (10.8%, P < .10), feed efficiency (11.6%, P < .01), and diet NEg (11.3%, P < .05). Ruminal digestibility of ADF, OM, and starch were not affected (P > .10) by forage level.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Excessive Supplemental Fat on Feedlot Cattle Growth Performance and Digestive Function

Ninety medium-framed crossbred steers (245kg) were used in a 205-d feeding trial to evaluate the influence of 4, 8, and 12% supplemental fat (tallow soap stock) on feedlot growth performance. Increasing level of fat supplementation depressed ADG (P<.01), DM conversion (P<.01), and dietary NE (P<.05). Depressions in DM conversion and dietary NE were more marked at the 12% level of fat supplementation. There was a quadratic effect (P<.01) of level of fat supplementation on DM intake, with intake being higher for 12% supplemental fat than for 8% supplemental fat. Observed:expected diet NEm was 1.00 with 4% supplemental fat and declined (P<.01) to .86 with 12% supplemental fat. The NEm of tallow soap stock declined in a near rectilinear fashion from 5.65 Mcal/kg at the 4% level of supplementation to 2.85 Mcal/kg at the 12% level of supplementation. Six Holstein steers (296kg) with T cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on digestive function. Ruminal digestion of OM (P<.01), feed N (P<.01), and ADF (P<.05) decreased linearly with increasing level of fat supplementation. Most (55%) of the decline in ruminal OM digestion could be directly attributed to ruminal indigestibility of dietary fat. Increasing level of fat supplementation did not influence (P>.10) postruminal digestion of OM, ADF, starch, and N. Postruminal digestion of lipid decreased (P<.01) with increasing level of fat supplementation. Total lipid intake was a better predictor of postruminal lipid digestibility than percentage supplemental fat. True digestibility of supplemental tallow soap stock at the 8 and 12% levels of supplementation averaged 63 and 40%, respectively. Total tract OM digestion declined linearly (P<.01) with increasing level of supplemental fat. This decline was due to differences in lipid digestion. There were no associative effects of supplemental fat on total tract digestion of ADF, starch, and N. It is concluded that optimal growth performance response to supplemental fat will be obtained when levels of total lipid intake are less than 1.6g/kg body weight. Detrimental effects of excessive supplemental fat are primarily associated with depressed intestinal lipid digestibility.

Influence of Levels of Supplemental Urea on Characteristics of Digestion and Growth Performance of Feedlot Steers Fed a Fat-Supplemented High-Energy Finishing Diet

Four Holstein steers (382kg) with cannulas in the rumen and proximal duodenum were used in a 4×4 Latin square experiment. Treatments consisted of 90% concentrate (steam-flaked cornbased) diet supplemented with either 5.5% soybean meal (SBM) or .8, 1.2, or 1.6% urea (dry matter basis). All diets contained 4% tallow. There were no treatment effects (P>.10) on ruminal pH and ammonia concentrations. Ruminal digestion of organic matter, acid detergent fiber, and starch tended to increase with supplemental urea level. There was a quadratic component (P<.10) to urea level effects on total tract dry matter and organic matter digestibility, being maximal with 1.2% supplemental urea. Total tract acid detergent fiber and starch digestion increased (P<.05) with urea level. Passage of nonammonia nitrogen, microbial nitrogen, and feed nitrogen were similar (P>.10) across treatments. Nonammonia nitrogen entering the small intestine/nitrogen intake decreased linearly (P<.05) with increasing level of urea supplementation. Thirty-two Holstein steers were used in a 4×4 Latin square experiment to evaluate treatment effects on feedlot growth performance. Experimental periods were 35 d in duration. There were no treatment effects (P>.10) on daily weight gain, dry matter intake, and diet net energy. Observed:expected net energy increased (P<.10) with increasing urea level. Urea can be efficiently utilized as the sole source of supplemental nitrogen in fat-supplemented highenergy finishing diets for feedlot cattle. Furthermore, feedlot cattle growth performance may be enhanced by supplementing diets with urea at levels beyond that necessary for maximal microbial growth.