This study examined the effect of dietary rumen-protected histidine (HIS) supplementation in cattle on growth and carcass traits/product quality. Three levels of daily HIS (Balchem Corp.) were tested (control, low dose [DL], and high dose [DH]) over a 55-d finishing period in 48 crossbred steers implanted with Revalor-XS. Cattle were randomly allocated into 8 pens of 6 steers each and fed twice daily using Calan gates. Morning feed was top-dressed with the HIS as follows: control (no HIS), 50 g/steer per day (DL), or 100 g/steer per day (DH). Individual intakes were recorded, and feed and orts were analyzed every 5 d during the feeding period. Steers were harvested, carcass data was recorded, and carcasses were fabricated at a USDA-inspected facility. One longissimus lumborum (LL) and 1 gluteus medius (GM) was acquired from each animal, aged under vacuum (21 and 14 d respectively), and cut into 2.54-cm steaks. One steak was used for retail display for which subjective (to evaluate visual color components) and objective (L*, a*, and b*) color scores were recorded. Lipid oxidation on d 0 and 9 of retail display were assessed using thiobarbituric acid reactive substances. Another steak was used to evaluate cooking loss and tenderness using Warner–Bratzler shear force. Sensory taste panels were conducted (1 panel for each muscle) to determine consumer perception of the product. Muscles were analyzed using HPLC for HIS metabolite (anserine and carnosine) and HIS content. Histidine supplementation increased ADG during d 1 to 21 (DH, P = 0.07), d 42 to 60 (DL and DH, P = 0.07), and the final 50 d (DH, P = 0.07) of feeding. Supplementation with HIS also increased the lightness (DL GM, P = 0.05), degree of yellow hue (DL and DH LL, P = 0.01), oxygenated lean color (DL GM, P = 0.004), uniformity (DH GM, P = 0.03, and DH LL, P = 0.06), and overall color stability of the product from d 3 through 9 of retail display. The percent surface discoloration (DL and DH GM, P = 0.04, and DL and DH LL, P < 0.0001), degree of browning (DL and DH GM, P = 0.002, and DL and DH LL, P < 0.0001), and discoloration (DL and DH GM, P = 0.01, and DH LL, P = 0.05) of the product was decreased. The DL GM steaks were juicier (P = 0.07), more acceptable (P = 0.05), and more satisfying (P = 0.01) than the control steaks. Seventy-seven percent of panelists would purchase the DL GM product (control, 61%, and DH, 60%). In conclusion, 55 d of rumen-protected HIS treatment positively impacts consumer perception and may optimize product quality and marketability in beef cattle.

We hypothesized that variable composition in finishing rations, more specifically; the proportion of potato-by-product (PBP) and rumen protected histidine (His) supplementation may influence growth and meat quality attributes. Two different diets were fed (1) finishing ration with corn and barley as grains (CB, n = 20) and (2) substitution of 10% corn, DM basis, with PBP (PBP, n = 20). Additionally, half of each dietary treatment received 50 g/hd/d rumen protected His (HS, n = 20) while the other half received no supplement (NS, n = 20). Inclusion of 10% PBP or HS did not affect growth or carcass traits. Color stability was analyzed using Hunter color values as well as AMSA visual appraisal in both longissimus thoracis (LT) and gluteus medius (GM) muscles. The LT, but not the GM, of CB steers was more color stable over a 9 d simulated retail display compared to those fed a PB diet. Steers receiving HS produced significantly (P < 0.05) more color stable LT and GM steaks.

Despite benefits to crop rotations and recent increases in value, the United States produces only a third of the canola ( Brassica napus L.) it consumes. To encourage production expansion, an experiment in Moscow, ID, evaluated dual‐purpose winter canola in a biennial system for forage and seed production. Two winter canola cultivars were sown at three planting densities (4.5, 6.7, and 9.0 kg ha −1 ) over four planting dates (May through September) in 2008, 2009, 2010, and 2011. Vegetative biomass during the first year was harvested and ensiled to determine silage quality. Cultivars performed similarly over all treatments for forage yield and quality. The two highest planting densities yielded more forage, but no seed yield differences were detected. Total dry matter forage yield (DMFY) was greatest for May plantings (5.2 t DM ha −1 ), while August seeded canola yielded 2.4 t DM ha −1 . Baldur produced higher seed yield than Athena by 352 kg ha −1 , while planting dates had significant, but inconsistent effects on seed yield compared to the fall‐planted, uncut control, which averaged 2389 kg ha −1 . Fiber content of canola silage (canolage) was extremely low while crude protein (CP) remained consistently high. Canolage quality was exceedingly high, however, high silage pH indicated poor ensiling, which likely led to excessive loss of organic material in the silage that increased ash content. Early‐planted winter canola withstood multiple forage harvests without having a large impact on seed yield most years and economics indicate this may be a feasible management practice.

The relationship between residual feed intake (RFI) and end product quality was evaluated in 133 steers from 5 Angus sires with low, moderate, or high percent intramuscular fat EPD. Steers (320.1 ± 35.76 kg) were evaluated for RFI during a 70- to 84-d growing period and classified into 3 groups based on RFI: efficient (less than -0.5 SD below the mean; n = 41), marginal (±0.5 SD from the mean; n = 48), and inefficient (>0.5 SD above the mean; n = 44). There were no differences among RFI groups for ADG, BW, fat thickness, carcass weight, YG, QG, or palatability traits. Inefficient steers had greater (P < 0.01) DMI than did marginal and efficient steers, and marginal steers had greater DMI (P < 0.01) compared with efficient steers. Marbling was greater (P < 0.01) in inefficient steers than in efficient steers, and inefficient steers had greater (P < 0.05) marbling compared with marginal steers. However, of all traits evaluated, RFI was only correlated with DMI (r = 0.57; P < 0.0001), feed conversion ratio (r = 0.48; P < 0.0001), marbling (r = 0.26; P < 0.01), and QG (r = 0.27; P < 0.01). Data suggest that feed efficiency in steer progeny of Angus sires divergent for intramuscular fat EPD is not related to carcass characteristics, with the possible exception of marbling score. However, due to the absence of a relationship between RFI and sensory traits, and the potential for a sire effect, it does not appear that end product quality attributes are related to feed efficiency.

An experiment was conducted in market dairy cows to determine the effect of feeding time and ractopamine hydrochloride (RAC) on growth performance, carcass characteristics, and end product quality. In 3 replicates, 9 Holstein cows per replicate (n = 27; 659 +/- 25.3 kg initial BW) culled from 3 dairies were randomly assigned to 3 treatments: 1) slaughter immediately (control), 2) feed for 90 d (NoR), or 3) feed for 90 d with RAC (312 mg.cow(-1).d(-1)) for the final 32 d (RAC). On d 0, NoR and RAC cows were placed in individual pens and fed a high concentrate diet (86% concentrate, DM basis) for 90 d before slaughter. All cows were subjectively scored for BCS and locomotion score on d 0, and NoR and RAC cows were evaluated again after 90 d. Individual DMI was recorded daily throughout the trial, and BW was collected every 14 d. Age and age x treatment did not affect (P > 0.05) any of the traits evaluated in this study. When cows fed for 90 d (NoR and RAC combined) were compared with nonfed controls, fed cows had greater (P < 0.001) final BCS, BW and HCW, lower (P < 0.001) final locomotion score, and greater (P < 0.03) dressing percentage, external fat thickness, and marbling score. Fed cows also tended to have more desirable yield grade (P = 0.08), ribeye area (P = 0.11), fat color (P = 0.09), lean maturity (P = 0.06), and quality grade (P = 0.09) compared with control cows. Warner-Bratzler shear force was not affected (P = 0.23) by feeding. However, a 12-member trained sensory panel revealed that fed cow carcasses had more desirable (P < 0.04) tenderness, juiciness, and overall acceptability than control cow carcasses. Flavor intensity also tended (P = 0.10) to be more desirable for fed vs. control cows. No difference (P > 0.10) in off-flavor was detected among treatments. Finally, there was no effect (P > 0.10) of RAC on growth performance, carcass characteristics, or end product quality. In conclusion, feeding a high concentrate diet for 90 d improved important live animal, carcass, and end product characteristics related to the quality and palatability of beef from market dairy cows; however, no effect of RAC supplementation was observed.

The objectives of this experiment were to evaluate the effects of pre-harvest feeding, feeding duration, and use of a beta agonist (zilpaterol hydrochloride) on market dairy cow feedlot performance and carcass characteristics. The experiment was set up in a randomized block design, with pen as the experimental unit. A total of 160 lactating market dairy cows (already culled from herds) were used for the project. Cattle were assigned to one of the following five treatments: harvest immediately on day 0 (Con), feed for 70 days without zilpaterol (70no), feed for 70 days with zilpaterol from day 4 7 to day 67 (70zil), feed for 105 days without zilpaterol (105no), and feed for 105 days with zilpaterol from day 82 to day 102 (105zil). Cattle were fed in a commercial feedlot in southern Idaho and received a high concentrate potato by-product- based ration. There was a feeding duration length x zilpaterol interaction (P < 0.005) for final body weight (BW). The 70no, 70zil, and 105no cows had greater (P < 0.05) final BW compared to control cows, while 105zil cows had greater (P < 0.05) final BW compared to control and all other fed treatments. The effect of zilpaterol supplementation on average daily gain (ADG) was inconsistent, since 105zil cows had a greater (P < 0.05) ADG vs. 105no cows, yetADG was not different (P > 0.10) among 70no and 70zil cows. No differences were observed (P > 0.10) for the feed-to-gain ratio from the main effects of feeding length or zilpaterol supplementation. Final hot carcass weight (HCW) was greater (P < 0.0001) among fed compared to control cows, and cows receiving zilpaterol had greater (P < 0.03) HCW than cows not receiving a B-agonist. Measured ribeye area (REA) was greater among fed (P < 0.001) compared to control cows and also greater (P < 0.01) among cows receiving zilpaterol compared to no zilpaterol. The effects of feeding duration and zilpaterol supplementation on feedlot performance and carcass characteristics were inconsistent.

Two hundred forty-nine samples of barley grain representing varieties from 13 growing locations were obtained to evaluate variability in nutritive value and to characterize the relationship between chemical composition and digestibility. Ranges for barley NDF, ADF, starch, bulk density (BD), and in vitro total digestibility (IVTD) were 11.8 to 25.6%, 2.2 to 8.8%, 48.2 to 72.5%, 569 to 784 g/L (44 to 61 lb/bu), and 66.7 to 85.1%, respectively. In vitro total digestibility was most closely related to NDF (r = −0.69, P < 0.001); this relationship improved when correlation was determined by variety (r = −0.81; P < 0.001) and location (r = −0.93, P < 0.001). Thirty-two steers were then adapted to a diet consisting of 80% dry-rolled barley (DM basis) from 1 of 8 divergent sources. Steers were assigned randomly to the 8 dietary treatments and in vivo digestibility was measured during 3 experiments replicated over time. Digestibility of DM, OM, and starch were not different between barley sources. Using least squares means for laboratory measures of the 8 sources of barley, NDF was negatively correlated with starch (r = −0.83, P < 0.05) and IVTD (r = −0.87; P < 0.05). Starch was positively correlated with BD and IVTD (r = 0.71 and 0.83, respectively; P < 0.05), and BD was positively correlated with IVTD (r = 0.83; P < 0.05). None of the laboratory variables measured in this study was an adequate predictor of barley digestibility from the digestive tract of feedlot steers.

Two experiments were conducted to evaluate digestion kinetics of alfalfa (Medicago sativa L.) substitution for grass hay in beef cattle. In Exp. 1, forage combinations evaluated in situ consisted of 0% alfalfa-100% big bluestem (Andropogon gerardi Vitman), 25% alfalfa-75% big bluestem, 50% alfalfa-50% big bluestem, and 100% alfalfa-0% big bluestem. Nonlinear regression was used to determine the immediately soluble fraction A, the potentially degradable fraction B, the undegraded fraction C, and the disappearance rate of DM and NDF. Dry matter fraction A increased linearly (P = 0.03), and DM and NDF fraction B decreased linearly (P = 0.01) with increasing alfalfa substitution. Rate of DM and NDF disappearance increased linearly (P = 0.02) with increasing alfalfa substitution. In Exp. 2, treatments were arranged as a 2 x 2 factorial testing alfalfa substitution [none or 25% (as-fed basis)] to orchardgrass hay (Dactylis glomerata L.) and intake level [restricted to 1% of BW daily (DM basis) or ad libitum]. Nutrient intakes were lowest (P = 0.05) by steers fed restricted diets, intermediate by steers fed orchardgrass ad libitum, and greatest by steers fed orchardgrass plus alfalfa ad libitum. Intake level and forage source had no effect (P >/= 0.23) on total tract apparent digestibility of all nutrients except CP. Steers fed orchardgrass plus alfalfa had 33% greater (P = 0.01) total tract apparent digestibility for CP than those fed orchardgrass alone. Lag time of DM and NDF disappearance was not affected (P >/= 0.20) by alfalfa supplementation or intake level. Rate of DM and NDF disappearance of orchardgrass was faster (P = 0.01) in steers fed orchardgrass plus alfalfa, at both restricted and ad libitum levels of feeding, than in animals fed orchardgrass alone. Mean retention times of large and small particles of orchardgrass tended to be shorter (P = 0.06) when steers consumed ad libitum vs. restricted diets. Small orchardgrass particles tended to have a faster (P = 0.09) rate of passage under ad libitum feeding conditions and with alfalfa addition. Ad libitum intake was associated with a shorter mean retention time of orchardgrass and faster rate of passage of small orchardgrass particles, whereas alfalfa addition increased the rate of passage of small orchardgrass particles and the rate of DM and NDF disappearance.

Six ruminally and duodenally cannulated Angus-Jersey crossbred steers (450 kg of BW) were used in a 6 x 6 Latin square to evaluate the effect of kernel vitreousness and moisture on intake and digestibility of high-moisture corn. Arranged in a 2 x 3 factorial, diets included a floury (FLO) or a vitreous (VIT) endosperm corn hybrid harvested at 28.1% (DRY), 31.2% (MID), or 35.7% (WET) kernel moisture content. Diet DM consisted of 88.25% high-moisture corn, 6% chopped alfalfa hay, 2% corn gluten meal, 0.75% urea, and 3% supplement. Supplement was included to ensure that the diets contained a minimum (DM basis) of 0.6% Ca, 0.6% K, 0.2% S, 33 mg/kg of monensin, and 11 mg/kg of tylosin. Geometric mean diameter of lyophilized high-moisture corn tended to be less (P = 0.06) for VIT than for FLO, and the calculated particle surface area was 15.8% greater (P = 0.03). An interaction of vitreousness with the quadratic effect of moisture was noted (P < 0.001), such that fraction a and effective degradation for starch tended to be greater for the vitreous hybrid at the least and greatest moisture content but lower for the vitreous hybrid at the intermediate moisture content. Intake and ruminal disappearance of DM, OM, and starch were not influenced by vitreousness or moisture, with ruminal starch disappearance averaging 90.9%. Intestinal starch digestion measured as a percentage of starch entering the intestines averaged 91% and was greater (P < 0.05) for VIT than FLO corn. Averaged across moisture levels, total tract starch digestibility was greater (P < 0.003) for VIT than FLO. Compared with FLO kernels, VIT kernels appeared to be more brittle and therefore shattered more readily when rolled, particularly at the driest kernel moisture level. Furthermore, increased surface area of smaller particles may have been responsible for the greater starch utilization from VIT corn. In contrast with the results from other in situ and in vivo trials with dry-rolled corn grain, in which the starch from vitreous hybrids was less rapidly or completely digested, hybrids with more vitreous starch, when fed as high-moisture corn, had greater total tract starch digestibility, primarily due to greater postruminal starch digestion.

The objective was to determine the effects of three exogenous polysaccharide-degrading enzyme preparations (EPDE) on ruminal fermentation and forestomach and total tract digestion of dietary nutrients in dairy cows. Four late-lactation, ruminally and duodenally cannulated, Holstein cows were allocated to dietary treatments in a 4×4 Latin square design experiment. The basal diet fed to the cows contained (DM basis): 400g/kg alfalfa and grass hays, 44g/kg corn and barley grains, 80g/kg whole cottonseed, and 80g/kg protein and mineral/vitamin supplements. The EPDE preparations, a blank, a predominantly amylase, a predominantly xylanase and an amylase/xylanase combination were dosed to the rumen through the cannula daily, during the morning feeding (06:00h) at 10g/cow/day. Treatments did not affect ruminal pH, ammonia concentration, protozoal counts, total and individual VFA concentration, acetate:propionate ratio, and solid and fluid ruminal digesta passage rates. Xylanase, carboxymethylcellulase and amylase activities of whole ruminal contents at 2, 4, and 6h following EPDE application were also not affected by treatments. Intake of nutrients and forestomach true and total tract apparent digestibility of neutral detergent fiber and starch also did not differ among treatments. Digestibility of DM, organic matter and N were reduced (P=0.045–0.050) by the amylase/xylanase combination versus the amylase or xylanase EPDE. The EPDE dosed intraruminally at 10g/cow/day did not affect ruminal fermentation, polysaccharide-degrading activities of ruminal contents or total tract apparent digestion of nutrients.

The objective of this study was to investigate the variability of in vitro ruminal protein degradability among barley varieties grown in Idaho. Two hundred forty seven barley samples from 12 locations (2004 cropping season) were analyzed for chemical composition and ruminal protein degradability utilizing an in vitro procedure, in which inhibitors were used to prevent microbial uptake of ammonia and amino acids released during breakdown of sample proteins. Barley samples included malting, feed, and two-, and six-row varieties. Samples were ground through a 1-mm sieve and analyzed for crude protein and in vitro protein degradability. Data were analyzed using the MEANS and GLM procedures of SAS. Concentration of crude protein in the samples averaged 10.4 ± 0.06% (minimum = 6.9% and maximum = 15.7%). Rate of ruminal protein degradability varied from 3.4 - 4.6%/h (Millennium, Idagold, Nebula, B5057) to 7.6 - 8.4%/h (Excel, Burton, CEB0149, WA1070149 and WA850197) and was not significantly different among barley varieties (P = 0.501). Estimated ruminal escape of barley protein varied from 43 - 46% (Excel, Burton, CEB0149, WA1070149 and WA850197) to 58 - 60% (Millennium, Idagold, Nebula, B5057) and was also not different among varieties (P = 0.101). The interaction between location and variety was investigated for a sub-group of samples including 12 barley varieties grown at 6 locations. Location and variety had no effect on rate of ruminal degradability (P = 0.450 and 0.574, respectively), or ruminal escape of barley protein (P = 0.701 and 0.118, respectively), but there was a significant interaction between the main effects (P = 0.003 and 0.009, respectively). Results from this study suggest that, depending on environmental factors, some barley varieties may have decreased protein degradability in the rumen.

The objective of this study was to evaluate the variability of barley quality and to better characterize the relationship between variability in chemical composition and digestibility of barley. In 2004, 249 barley samples were obtained representing different varieties from 13 locations in Idaho. Whole barley was analyzed for bulk density (BD). Representative subsamples were ground through a 1-mm screen and analyzed for DM, NDF, ADF, ash, and starch. The ranges of NDF, ADF, starch, BD, and in vitro total digestibility (IVTD) were 11.8 to 25.6%, 2.2 to 8.8%, 48.2 to 72.5%, 569 to 784 g/L, and 66.7 to 85.1%, respectively. In vitro total digestibility was most closely correlated with NDF (r = -0.69, P < 0.001). This relationship improved when correlation was determined by variety (r = -0.81; P < 0.001) and location (r = -0.93, P < 0.001). Eight sources of barley were then selected to represent the spectrum of BD, IVTD, and chemical composition. Thirty-two steers were adapted to a finishing diet consisting of 80% dry-rolled barley (DM basis) from 1 of the 8 sources. Steers were randomly assigned to the 8 diets and digestibility measurements were obtained during 3 repeated experiments. Digestibility of DM, OM, and starch were not different between barley sources. In vitro total digestibility decreased (P < 0.001) quadratically with CP and NDF, but increased (P < 0.001) quadratically with starch. Despite the correlations noted between measures of chemical composition and IVTD, relationships between measures of chemical composition and in vivo digestibility were insignificant (r < 0.25). Results of this study support the notion that 1) there is a wide range in the chemical components of barley sources and 2) fiber appears to be the most reliable predictor of barley digestibility.

The effect of type of grain (corn vs. barley) and amylopectin content of barley grain (normal vs. waxy) on ruminal fermentation, digestibility, and utilization of ruminal ammonia nitrogen for milk protein synthesis was studied in a replicated 3 x 3 Latin square design trial with 6 lactating dairy cows. The experimental treatments were (proportion of dietary dry matter): CORN, 40% corn grain, NBAR, 30% normal Baronesse barley:10% corn grain, and WBAR, 30% high-amylopectin (waxy) Baronesse barley:10% corn grain. All grains were steam-rolled and fed as part of a total mixed ration. The NBAR and WBAR diets resulted in increased ruminal ammonia concentrations compared with CORN (8.2, 7.4, and 5.6 mM, respectively), but other ruminal fermentation parameters were not affected. Ruminal digestibility of dietary nutrients and microbial protein synthesis in the rumen were also not affected by diet. Corn grain had greater in situ effective ruminal dry matter degradability (62.8%) than the barley grains (58.2 and 50.7%, respectively), and degradability of the normal barley starch was greater than that of the waxy barley (69.3 and 58.9%, respectively). A greater percentage of relative starch crystallinity was observed for the waxy compared with the normal barley grain. Total tract apparent digestibility of dry matter and organic matter were decreased by WBAR compared with CORN and NBAR. Total tract starch digestibility was greater and milk urea nitrogen content was lower for CORN compared with the 2 barley diets. In this study, the extent of processing of the grain component of the diet was most likely the factor that determined the diet responses. Minimal processing of barley grain (processing indexes of 79.2 to 87.9%) reduced its total tract digestibility of starch compared with steam-rolled corn (processing index of 58.8%). As a result of the increased ammonia concentration and reduced degradability of barley dry matter in the rumen, the utilization of ruminal ammonia nitrogen for microbial protein synthesis was decreased with the barley diets compared with the corn-based diet. In this study, waxy Baronesse barley was less degradable in the rumen and the total digestive tract than its normal counterpart. The most likely reasons for these effects were the differences in starch characteristics and chemical composition, and perhaps the different response to processing between the 2 barleys.

Relationships between residual feed intake (RFI) and other performance variables were determined using 54 purebred Angus steers. Individual feed intake and BW gain were recorded during a 70-d post-weaning period to calculate RFI. After the 70-d post-weaning test, steers were fed a finishing ration to a similar fat thickness (FT), transported to a commercial facility, and slaughtered. A subsample of carcasses (n = 32) was selected to examine the relationships among RFI, meat quality, and palatability. Steers were categorized into high (> 0.5 SD above the mean; n = 16), medium (mid; +/- 0.5 SD from the mean; n = 21), and low (< 0.5 SD below the mean; n = 17) RFI groups. No differences were detected in ADG, initial BW, and d 71 BW among the high, mid, and low RFI steers. Steers from the high RFI group had a greater DMI (P = 0.004) and feed conversion ratio (FCR; DMI:ADG; P = 0.002) compared with the low RFI steers. Residual feed intake was positively correlated with DMI (r = 0.54; P = 0.003) and FCR (r = 0.42; P = 0.002), but not with initial BW, d 71 BW, d 71 ultrasound FT, initial ultrasound LM area, d 71 ultrasound LM area, or ADG. The FCR was positively correlated with initial BW (r = 0.46; P = 0.0005), d 71 BW (r = 0.34; P = 0.01), and DMI (r = 0.40; P = 0.003) and was negatively correlated with ADG (r = -0.65; P = 0.001). There were no differences among RFI groups for HCW, LM area, FT, KPH, USDA yield grade, marbling score, or quality grade. Reflectance color b* scores of steaks from high RFI steers were greater (P = 0.02) than those from low RFI steers. There was no difference between high and low RFI groups for LM calpastatin activity. Warner-Bratzler shear force and sensory panel tenderness and flavor scores of steaks were similar across RFI groups. Steaks from high RFI steers had lower (P = 0.04) off-flavor scores than those from low RFI steers. Cook loss percentages were greater (P = 0.005) for steaks from low RFI steers than for those from mid RFI steers. These data support current views that RFI is independent of ADG, but is correlated with DMI and FCR. Importantly, the data also support the hypothesis that there is no relationship between RFI and beef quality in purebred Angus steers.

J. Anim. Sci. Vol. 84, Suppl. 1/J. Dairy Sci. Vol. 89, Suppl. 1 and direct-fed microbials. These models typically address ruminal fermentation, and they yield useful results that, unfortunately, often differ from those observed for growth performance. Models have been developed to study both the adaptation of cattle to grain-based diets as well as the effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided valuable information related to ruminal acidosis, many of the models have been inadequate for detecting responses to treatment due to inadequate replication (required to overcome the variable responses being studied), low feed intakes by the experimental cattle (which can limit the expression of acidosis), and the feeding of cattle individually (which reduces experimental variation but limits extrapolation of the data to industry conditions). Treatment responses to a wide range of management and nutritional modulations are often explained on the basis of acidosis prevention (or stimulation), whether or not direct evidence of acidosis is available. Optimal model systems for assessing impacts of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feedyards. Data generated under these conditions could provide valuable insight into the true extent to which acidosis impacts cattle performance.

Two trials were conducted to determine the effect of linoleic acid- or oleic acid-rich safflower oil on ruminal fermentation, nutrient digestion, feedlot performance, carcass characteristics, and fatty acid composition of adipose and muscle tissues of beef cattle. In both trials, cattle were fed a finishing diet based on barley grain, wheat silage, and alfalfa hay. Oils were fed at 5% of dietary DM. In a metabolism trial, four ruminally and duodenally cannulated Angus crossbred steers were subjected to linoleic acid-rich oil or oleic acid-rich oil in a crossover design with covariate periods (no oil supplementation). In a finishing trial, 16 individually fed Angus crossbred steers and heifers (eight per diet) received linoleic acid- or oleic acid-rich oils during the last 86 d of a 116-d feeding period. Ruminal pH, ammonia concentration, protozoal counts, major VFA concentrations, acetate-to-propionate ratio, polysaccharide-degrading activities, microbial N flow to the duodenum, and the efficiency of microbial N synthesis in the rumen were not affected (P = 0.18 to 0.96) by type of oil. Type of oil had no effect on total-tract apparent digestion of nutrients (P = 0.46 to 0.98). Ruminal true nutrient digestibilities did not differ between oils (P = 0.15 to 0.99), except that the linoleic acid-rich oil decreased (P = 0.05) NDF digestibility. Dry matter intake, ADG, G:F, and carcass characteristics did not differ (P = 0.11 to 0.84) between the two oils. Overall, the difference in dietary fatty acids provided to the cattle produced few changes in tissue fatty acids. Weight percentages of c9t11 CLA were unaltered by the addition of linoleic acid to the diet compared with oleic acid, probably as a result of low vaccenic acid production in the rumen, as the pathway of biohydrogenation was apparently primarily through the t10 pathway.