Shrink, weighing accuracy, and weighing precision of mineral supplement in five commercial dairies in the Western United States.

Shrink, accuracy, and precision of ingredient weighing are critical factors of efficiency in TMR-fed dairy systems. Those factors have been evaluated for major feeds; however, we are not aware of any reports for mineral supplement. Farms commonly mix mineral supplement with other low-inclusion ingredients into a premix which is used later as a single ingredient for TMR formulation. Our objectives were to evaluate shrink, weighing accuracy, and weighing precision of mineral supplement during premix formulation, and variation in concentration of minerals in mineral supplement and TMR, in five large dairies in the Western United States. We used the automated weight-tracking system at each farm to account for all the mineral supplement loaded into the mixing-wagon and collected samples of mineral supplement and TMR from time of mineral supplement delivery at the farm until 100% of it was consumed. Mean, standard deviation and coefficient of variation (CV) for each variable were calculated with SAS 9.4. Average shrink was estimated at 2.0% for mineral supplement during storage and loading, ranging from 0.37% to 3.25%. Mineral supplement weighing deviation from the targeted amount was 1.54% on average for the five dairies with a 95% CV. Mineral composition of mineral supplements averaged 11.3%, 0.27%, and 3.16% for Ca, P, and Mg, and 215, 881, and 1533 ppm for Cu, Mn, and Zn, respectively. Mineral compositions in TMR averaged 0.84%, 0.41%, and 0.37% for Ca, P, and Mg, respectively; and 15.1, 71, and 94.5 ppm for Cu, Mn, and Zn, respectively. The CV of all minerals except Ca, were larger for mineral supplement than TMR, and with the exception of P in mineral supplement, CV of trace minerals were larger than CV values for macro minerals. Our shrink estimates for mineral supplement represent an initial approximation to this issue. Results of our weighing deviation analysis suggest some room for improvement on the precision of weighing mineral supplement at the time when premix is prepared at the farm, which could improve consistency in chemical composition of the premix and consequently reduce the variation (CV values) of mineral concentrations in TMR.

Duration of maternal undernutrition differentially alters fetal growth and hormone concentrations.

To investigate the impact of duration of maternal undernutrition in twin sheep pregnancies, ewes were either fed 100% (C) or 50% of their nutrient requirements from 28 to 78 d gestational age (dGA) and readjusted to 100% beginning at 79 dGA (LC) or continuously restricted from 28 to 135 dGA (LL). Weights of the fetus, empty carcass, brain, and liver were greater in the LC than LL fetuses at 135 dGA (P ≤ 0.05). Although umbilical vein (UmV) glucose concentrations did not differ, the UmV:umbilical artery (UmA) glucose gradient was smaller (0.26 ± 0.03 vs 0.38 ± 0.03 and 0.39 ± 0.04 mmol L(-1); P ≤ 0.05) in LL than C and LC fetuses, respectively. Umbilical vein concentrations of IGF-1 were less (46.7 ± 5.62 vs 74.3 ± 6.71 ng/mL; P ≤ 0.05) in LL than LC fetuses. Additionally, LL fetuses tended (P ≤ 0.10) to have lower UmA concentrations of insulin (0.24 ± 0.13 vs 0.70 ± 0.15 ng/mL) and IGF-1 (66.6 ± 7.51 vs 91.4 ± 8.97 ng/mL) than LC fetuses. Although most of the observed differences occurred between LC and LL pregnancies, LC fetuses tended (P ≤ 0.10) to have greater UmV and UmA pCO2 than C fetuses. Furthermore, the UmV:UmA O2 content gradient tended to be greater (5.02 ± 0.43 vs 3.41 ± 0.47; P ≤ 0.10) in C than LL fetuses. UmA placental lactogen also tended to be greater (46.6 ± 4.40 vs 31.1 ± 4.69 ng/mL; P ≤ 0.10) in LL than C fetuses. These data suggest that in twin pregnancies, maternal undernutrition followed by realimentation induces a different fetal outcome compared with continuous nutrient restriction, and both may differ physiologically from control fed pregnancies.

Evaluation of Saccharomyces cerevisiae fermentation product as an alternative to monensin on growth performance, cost of gain, and carcass characteristics of heavy-weight yearling beef steers.

Two hundred fifty-two cross-bred yearling steers (406 ± 24 kg BW) were used in a completely randomized block design with a 2 × 2 factorial arrangement of treatments (7 pens/treatment) to evaluate the effects of dietary Saccharomyces cerevisiae fermentation product (SFP) and monensin (MON) on growth performance and carcass characteristics. Dietary treatments arranged as a 2 × 2 factorial were 1) with or without SFP and 2) with or without MON. Finishing diets contained 19.7% of DM as dried distiller's grains with solubles. Both SFP and MON were added in the total mixed ration in place of an equal amount of cornmeal (DM basis; target intake = 2.8 g of SFP and 33 mg of MON/kg of dietary DM). Each treatment group was offered ad libitum access to a transition ration from d 1 to 8 and then to the finishing ration from d 9 to 125. Body weights were collected on d 0, 28, 56, 84, 110, and 125. Initial and final BW was an average of 2-d weights (d -1 and 0 and d 124 and 125, respectively). Steers were shipped for harvest on d 125. Overall ADG was decreased (P = 0.03) in steers supplemented with SFP, but final BW was similar among treatments. Feeding SFP was associated with lighter (P < 0.01) HCW and a greater (P = 0.01) number of carcasses grading USDA Choice. Twelfth rib fat thickness was not affected by SFP (P = 0.82) or MON (P = 0.35), but numerical decreases in 12th rib fat thickness among cattle receiving SFP or MON alone contributed to a tendency (P = 0.07) for greater 12 rib fat thickness when SFP and MON were provided. There was no effect of treatment on cost of gain (P ≥ 0.21). The effects of SFP in the current study may have been limited in heavy yearling steers due to consumption of a finishing diet containing 19.7% dried distiller's grains with solubles.

Naturally colonized beef cattle populations fed combinations of yeast culture and an ionophore in finishing diets containing dried distiller's grains with solubles had similar fecal shedding of Escherichia coli O157:H7.

Beef steers (n = 252) were used to evaluate the effects of dietary supplement on fecal shedding of Escherichia coli O157:H7. Seven pens of 9 steers (63 steers per treatment) were fed diets supplemented with or without yeast culture (YC) or monensin (MON) and their combination (YC × MON). YC and MON were offered at 2.8 g/kg and 33 mg/kg of dry matter intake, respectively. Environmental sponge samples (from each pen floor, feed bunk, and water trough) were collected on day 0. Rectal fecal grab samples were collected on days 0, 28, 56, 84, 110, and 125. Samples were collected and pooled by pen and analyzed for presumptive E. coli O157:H7 colonies, which were confirmed by a multiplex PCR assay and characterized by pulsed-field gel electrophoresis (PFGE) typing. On day 0, E. coli O157:H7 was detected in 7.0% of feed bunk samples and 14.3% of pen floor samples but in none of the water trough samples. The 71.4% prevalence of E. coli O157:H7 in fecal samples on day 0 decreased significantly (P < 0.05) over time. E. coli O157:H7 fecal shedding was not associated with dietary treatment (P > 0.05); however, in cattle fed YC and YC × MON fecal shedding was 0% by day 28. Eight Xba I PFGE subtypes were identified, and a predominant subtype and three closely related subtypes (differing by three or fewer bands) accounted for 78.7% of environmental and fecal isolates characterized. Results from this study indicate that feeding YC to cattle may numerically decrease but not eliminate fecal shedding of E. coli O157:H7 at the onset of treatment and that certain E. coli O157 subtypes found in the feedlot environment may persist in feedlot cattle.

Effects of sex and short-term magnesium supplementation on stress responses and longissimus muscle quality characteristics of crossbred cattle.

Calf-fed heifers (n = 72) and steers (n = 72) were supplemented with 4 levels (0, 0.25, 0.50, and 0.75%) of dietary Mg as MgO during the final 14 d of finishing and were commingled 1 d before slaughter (inducing stress by mixing unfamiliar cattle) to examine the effects of sex class and Mg supplementation on stress responses and LM quality characteristics. Heifers and steers exhibited markedly different stress responses. Heifers were more excitable than steers during preslaughter handling events and exhibited a short-term physiological stress response that involved acute sympatho-adrenal activation and resulted in increased meat toughness, without a concomitant increase in muscle pH. Steers, on the other hand, exhibited greater physical activity, associated with agonistic behavior, during the mixing period and therefore produced carcasses with lesser (P = 0.008) LM glycogen concentrations and greater (P = 0.042) 48-h LM pH values, compared with heifers. Steers also produced tougher (P = 0.008) LM steaks than did heifers. Within the range of pH values observed in this study (5.3 to 6.1), positive, linear relationships between 48-h LM pH and mean LM shear force (P < 0.05) were observed in both heifers (r = 0.25) and steers (r = 0.37). Effects of pH on LM shear force (P < 0.05), which were most pronounced at 3 and 7 d postmortem, diminished during postmortem aging and were no longer evident (P > 0.05) once LM samples had been aged for 21 d. Results suggested that toughness of LM steaks from beef carcasses with final LM pH values greater than 5.65 could be problematic unless LM cuts are aged for approximately 18 d or longer. Supplementation with dietary Mg increased (P = 0.011) serum Mg concentration, but had no effect (P > 0.05) on any of the physiological stress indicators or LM quality characteristics measured in this study. There was no evidence to support the premise that Mg supplementation of cattle lessens the effects of preslaughter stress on beef quality characteristics.

Model for estimating enteric methane emissions from United States dairy and feedlot cattle.

Methane production from enteric fermentation in cattle is one of the major sources of anthropogenic greenhouse gas emission in the United States and worldwide. National estimates of methane emissions rely on mathematical models such as the one recommended by the Intergovernmental Panel for Climate Change (IPCC). Models used for prediction of methane emissions from cattle range from empirical to mechanistic with varying input requirements. Two empirical and 2 mechanistic models (COWPOLL and MOLLY) were evaluated for their prediction ability using individual cattle measurements. Model selection was based on mean square prediction error (MSPE), concordance correlation coefficient, and residuals vs. predicted values analyses. In dairy cattle, COWPOLL had the lowest root MSPE and greatest accuracy and precision of predicting methane emissions (correlation coefficient estimate = 0.75). The model simulated differences in diet more accurately than the other models, and the residuals vs. predicted value analysis showed no mean bias (P = 0.71). In feedlot cattle, MOLLY had the lowest root MSPE with almost all errors from random sources (correlation coefficient estimate = 0.69). The IPCC model also had good agreement with observed values, and no significant mean (P = 0.74) or linear bias (P = 0.11) was detected when residuals were plotted against predicted values. A fixed methane conversion factor (Ym) might be an easier alternative to diet-dependent variable Ym. Based on the results, the 2 mechanistic models were used to simulate methane emissions from representative US diets and were compared with the IPCC model. The average Ym in dairy cows was 5.63% of GE (range 3.78 to 7.43%) compared with 6.5% +/- 1% recommended by IPCC. In feedlot cattle, the average Ym was 3.88% (range 3.36 to 4.56%) compared with 3% +/- 1% recommended by IPCC. Based on our simulations, using IPCC values can result in an overestimate of about 12.5% and underestimate of emissions by about 9.8% for dairy and feedlot cattle, respectively. In addition to providing improved estimates of emissions based on diets, mechanistic models can be used to assess mitigation options such as changing source of carbohydrate or addition of fat to decrease methane, which is not possible with empirical models. We recommend national inventories use diet-specific Ym values predicted by mechanistic models to estimate methane emissions from cattle.

Feeding distillers grains supplements to improve amino acid nutriture of lambs consuming moderate-quality forages.

We hypothesized that providing dried distillers grains with solubles (DDGS) would improve the N retention and use of nutrients by wethers fed a moderate-quality bromegrass hay. Additionally, we hypothesized that treatment effects on nutrient fluxes would be similar after 3, 6, or 9 wk on treatment. Chronic indwelling catheters were surgically implanted in a mesenteric artery, mesenteric vein, hepatic vein, and portal vein of 9 Suffolk x Dorset wethers (initial BW +/- SD = 57.4 +/- 6.1 kg). Wethers had ad libitum access to moderate-quality bromegrass hay (8.44% CP, DM basis) and received 100 g/d of either a corn-based (Corn, n = 4) or a DDGS-based (n = 5) supplement. There was no difference in DMI (P = 0.85) or DM digestibility (P = 0.46) between the 2 groups. There was a numerically greater N intake (21.5 vs. 18.4 g/d; P = 0.14) and N retention (4.4 vs. 2.5 g/d; P = 0.15) when wethers were supplemented with DDGS instead of Corn. Wethers fed DDGS had a greater (P = 0.008) release of alpha-amino N from the portal-drained viscera (PDV, 37.9 mmol/h) than those fed Corn (14.1 mmol/h). Similarly, there was a shift (P = 0.004) from a net splanchnic uptake to a net release of alpha-amino N in wethers fed DDGS (9.1 mmol/h) compared with those fed Corn (-9.6 mmol/h). However, there was no difference in ammonia release from the PDV (P = 0.49) or hepatic release of urea-N (P = 0.19) between the 2 treatments. There were very limited interactions between nutrient fluxes and the length of time after the initiation of treatments. However, there was a tendency (interaction, P = 0.07) for the PDV release of alpha-amino N to be greater at 6 and 9 wk after the initiation of the treatments than after 3 wk on treatment for wethers fed DDGS, although there was no difference over time for wethers fed the Corn supplement. Additionally, there were changes in numerous nutrient fluxes between 3 and 6 wk after the initiation of treatments regardless of treatment. These data indicate that DDGS is a viable supplement to enhance the nutriture of ruminants consuming moderate-quality forages. Additionally, these data indicate that the effects are discernible after 3 wk on treatment, with modest alterations in nutrient flux after additional time on treatment.

Urea metabolism in beef steers grazing Bermudagrass, Caucasian bluestem, or gamagrass pastures varying in plant morphology, protein content, and protein composition.

Pastures of Bermudagrass (Cynodon dactylon, BG), Caucasian bluestem (Bothriochloa caucasica, CBS), and gamagrass (Tripsacum dactyloides, GG) were evaluated from the perspectives of forage composition, selection during grazing, and N metabolism in beef steers. All pastures were fertilized with 78 kg/ha of N approximately 60 and 30 d before sample collection. In 2000 and 2001, 12 steers (250 kg of BW) were blocked based on BW and then assigned randomly to a replicated, randomized complete block design, with 2 pastures of each forage and 2 steers per pasture. Three other steers with esophageal fistulas were used to collect masticate samples to represent intake preferences. Herbage mass was >1,900 kg/ha. After at least 14 d of adaptation, urine and blood samples were collected for determination of serum urea N and percentage of urinary N in the form of urea. One steer per pasture (6 steers per year) was infused i.v. with (15,15)N urea for 50 h before collecting urine for 6 h to measure urea N enrichment, urea entry rate, urinary urea excretion, gut urea recycling, and return of urea N to the ornithine cycle. The canopy leaf:stem DM ratio differed (P = 0.01) among BG (0.50), CBS (1.01), and GG (4.00). Caucasian bluestem had less CP (% of DM) than GG or BG in the canopy (9.6 vs. 12.0 or 12.3, P = 0.07) and in the masticate (9.8 vs. 14.7 or 13.9, P = 0.04). Bermudagrass had less true protein (% of CP) than CBS or GG in the canopy (72.9 vs. 83.3 or 83.0, P = 0.07) and in the masticate (73.7 vs. 85.8 or 88.0, P = 0.04). Compared with GG and BG, CBS had less serum urea N (10.1 or 12.2 vs. 2.5 mM, P = 0.01), urea entry rate (353 or 391 vs. 209 mmol of N/h, P = 0.07), and urinary urea excretion (105 or 95 vs. 18 mmol of N/h, P = 0.04), and a greater return of urea N to the ornithine cycle as a proportion of gut urea recycling (0.109 or 0.118 vs. 0.231, P = 0.02). Urea production and recycling in these steers responded more to the N concentration in the grasses than to differences in plant protein fractions. There was no evidence of improved N capture by the steers due to changes in the leaf:stem ratio among the grasses at the herbage mass evaluated.

The influence of oscillating dietary protein concentrations on finishing cattle. I. Feedlot performance and odorous compound production.

We hypothesized that oscillation of the dietary CP concentration, which may improve N retention of finishing beef steers, would reduce production of manure odor compounds and total N inputs while yielding comparable performance. Charolais-sired steers (n = 144; 303 +/- 5 kg of initial BW) were used in a completely randomized block design (6 pens/treatment). The steers were fed to 567 kg of BW on the following finishing diets, which were based on dry-rolled corn: 1) low (9.1% CP), 2) medium (11.8% CP), 3) high (14.9% CP), or 4) low and high oscillated on a 48-h interval for each feed (oscillating). Steers fed low tended (P = 0.08) to have less DMI (7.80 kg/d) than steers fed medium (8.60 kg/d) or oscillating (8.67 kg/d), but not less than steers fed high (8.12 kg/d). Daily N intake was greatest (P < 0.01) for steers fed high (189 g), intermediate for medium (160 g) and oscillating (164 g), and least for low (113 g). The ADG was lower (P < 0.01) for steers fed low (1.03 kg) than for those fed medium (1.45 kg), high (1.45 kg), or oscillating (1.43 kg). Similarly, steers fed low had a lower adjusted fat thickness (P < 0.01) and yield grade (P = 0.05) and tended (P = 0.10) to have less marbling than steers fed the other 3 diets. In slurries with feces, urine, soil, and water, incubated for 35 d, nonsoluble CP was similar among slurries from steers fed medium, high, or oscillating, but was less (P < 0.01) in slurries from steers fed low. However, throughout the incubation period, slurries from steers fed high or oscillating had greater (P < 0.01) concentrations of total aromatics and ammonia than those from steers fed low or medium. Also, the slurries from steers fed oscillating had greater (P < 0.01) concentrations of branched-chain VFA than manure slurries from steers fed any of the other diets. These data indicate that although there is no apparent alteration in the performance of finishing steers fed diets with oscillation of the dietary protein, there may be undesirable increases in the production of compounds associated with malodor.

The influence of oscillating dietary protein concentrations on finishing cattle. II. Nutrient retention and ammonia emissions.

We hypothesized that oscillation of the dietary CP concentrations would improve efficiency of N use and reduce N loss to the environment. Charolais-cross steers (n = 8; 315 +/- 21 kg of BW) were used in a replicated 4 x 4 Latin square design. The steers were allowed ad libitum access to the following diets: 1) 9.1% CP (low), 2) 11.8% CP (medium), 3) 13.9% CP (high), or 4) low and high oscillated on a 48-h interval on each diet (oscillating). Dry matter intake did not differ among treatments (P = 0.46), but N intake differed (P < 0.01) from 94 (low) to 131 (medium), 142 (high), and 133 g/d (oscillating), as designed. Dry matter digestibility increased (P < 0.01) from 71.8% (low) to 75.8% (medium), 77.7% (high), and 77.5% (oscillating). Nitrogen digestibility increased (P < 0.01) from 62.2% (low) to 67.2% (medium) to 70.1% (high) and 70.9% (oscillating). Nitrogen retention was greater (P < 0.01) in steers fed oscillating (55.0 g/d) than in the steers fed low (34.8 g/ d) or high (40.2 g/d), but N retention of steers fed medium (49.8 g/d) differed (P = 0.02) only from that of steers fed low. Urinary urea N did not differ between steers fed medium (19.5 g/d) or oscillating (21.3 g/d) but was lowest (P < 0.01) for those fed low (8.2 g/d) and greatest for those fed high (39.2 g/d). Daily heat production (kcal/BW(0.75)) tended (P = 0.09) to be less for the steers fed low (177) than those fed medium (189), high (188), or oscillating (182). Cumulative in vitro ammonia volatilization from the manure of steers fed oscillating was lower (P < 0.01) for the initial 5 d of incubation than from manure of those fed medium, but there was no difference after 11 d of incubation. Additionally, there was a decrease (P < 0.01) in in vitro ammonia volatilization as protein concentration in the diet decreased from high to medium to low. These data indicate that oscillation of the dietary protein improved N retention of finishing steers compared with those in high and low N diets and that these changes were great enough to correspondingly alter ammonia volatilization from manure.

Net portal and hepatic flux of nutrients in growing wethers fed high-concentrate diets with oscillating protein concentrations.

We hypothesized that oscillating dietary CP would improve N retention by increasing the uptake of endogenous urea N by portal drained viscera (PDV), compared with static dietary CP regimens. Chronic indwelling catheters were surgically implanted in the abdominal aorta, a mesenteric vein, a hepatic vein, and the portal vein of 18 growing Dorset x Suffolk wethers (44.6 +/- 3.6 kg of BW). Wethers had ad libitum access to the following diets in a completely randomized block design: 1) Low (9.9% CP), 2) Medium (12.5% CP), or 3) Low and High (14.2% CP) diets oscillated on a 48-h interval (Osc). Dry matter intake was greater (P = 0.04) for the Osc diet (1,313 g/d) than the Low diet (987 g/d) and was intermediate for the Medium diet (1,112 g/d). Nitrogen intake was not different between the wethers fed the Osc (25.4 g/d) and Medium diets (22.2 g/d), but was lower (P < 0.01) in wethers fed the Low diet (16.0 g/d). Wethers fed the Osc diet (6.7 g/d) retained more (P < 0.04) N than did those fed the Medium diet (4.0 g/d). Hepatic arterial blood flow was not different (P = 0.81) between wethers fed the Osc (31 L/h) or Medium diet (39 L/h) but was greater (P = 0.05) in wethers fed the Low diet (66 L/h). Net release of alpha-amino N by the PDV did not differ (P = 0.90) between the Low (37.8 mmol/h) and Medium diets (41.5 mmol/h) or between the Osc (53.0 mmol/h) and Medium diets (P = 0.29). Net PDV release of ammonia N was less (P = 0.05) for the Low diet than for the Medium diet, and this was accompanied by a similar decrease (P = 0.04) in hepatic ammonia N uptake. Urea N concentrations tended to be (P = 0.06) less in arterial, portal, and hepatic blood in wethers fed the Low diet compared with those fed the Medium diet. Wethers fed the Osc diet tended (P = 0.06) to have a greater PDV uptake of urea N than did those fed the Medium diet, but there was no difference between the Osc and Medium diets (P = 0.72) in hepatic urea N release. Net PDV uptake of glutamine tended to be greater (P < 0.07) in wethers fed the Low diet (6.7 mmol/h) than those fed the Medium diet (2.7 mmol/h). These data indicate that oscillating dietary protein may improve N retention by increasing endogenous urea N uptake by the gastrointestinal tract.

Influence of genotype and diet on steer performance, manure odor, and carriage of pathogenic and other fecal bacteria. II. Pathogenic and other fecal bacteria.

This study assessed the influence of cattle genotype and diet on the carriage and shedding of zoonotic bacterial pathogens and levels of generic Escherichia coli in feces and ruminal contents of beef cattle during the growing and finishing periods. Fifty-one steers of varying proportions of Brahman and MARC III [0 (15), 1/4 (20), 1/2 (7), and 3/4 Brahman (9)] genotypes were divided among 8 pens, such that each breed type was represented in each pen. Four pens each were assigned to 1 of 2 diets [100% chopped bromegrass hay or a diet composed primarily of corn silage (87%)] that were individually fed for a 119-d growing period, at which time the steers were switched to the same high-concentrate, corn-based finishing diet and fed to a target weight of 560 kg. Feces or ruminal fluid were collected and analyzed at alternating intervals of 14 d or less. Generic E. coli concentrations in feces or ruminal fluid did not differ (P > 0.10) by genotype or by growing diet in the growing or finishing periods. However, the concentrations in both feces and ruminal fluid increased in all cattle when switched to the same high-corn diet in the finishing period. There was no effect (P > 0.25) of diet or genotype during either period on E. coli O157 shedding in feces. Forty-one percent of the steers were positive for Campylobacter spp. at least once during the study, and repeated isolations of Campylobacter spp. from the same steer were common. These repeated isolations from the same animals may be responsible for the apparent diet (P = 0.05) and genotype effects (P = 0.02) on Campylobacter in feces in the finishing period. Cells bearing stx genes were detected frequently in both feces (22.5%) and ruminal fluid (19.6%). The number of stx-positive fecal samples was greater (P < 0.05) for 1/2 Brahman steers (42.9%) than for 1/4 Brahman (25.0%) or 3/4 Brahman steers (22.2%), but were not different compared with MARC III steers (38.3%). The greater feed consumption of 1/2 Brahman and MARC III steers may have resulted in greater starch passage into the colon, accompanied by an increase in fecal bacterial populations, which may have further improved the ability to detect stx genes in these cattle. There was no correlation between either ADG or daily DMI and the number of positive samples of E. coli O157, Campylobacter spp., or stx genes, which agrees with our current understanding that these microorganisms occur commonly in, and with no measurable detriment to, healthy cattle.

Influence of genotype and diet on steer performance, manure odor, and carriage of pathogenic and other fecal bacteria. III. Odorous compound production.

Three beef cattle diets were assessed for their potential to produce odorous compounds from cattle feces excreted during the growing and finishing periods. Eight pens containing 51 steers of varying proportions of Brahman and MARC III genotypes were fed either a chopped bromegrass hay diet or a corn silage diet for a 119-d growing period. After the growing period, all steers were switched to the same high-corn finishing diet (high corn) and fed to a target weight of 560 kg (finishing period). Fecal slurries were prepared from a composite of fresh fecal pats collected in each pen during both periods and incubated anaerobically. In additional flasks, starch, protein, or cellulose was added to the composite fecal subsamples to determine the preferred substrates for fermentation and odorous compound production. The content and composition of the fermentation products varied both initially and during the incubation, depending on the diet fed to the steers. The corn silage and high corn feces had the greater initial content of VFA (381.0 and 524.4 micromol/g of DM, respectively) compared with the bromegrass feces (139.3 micromol/g of DM) and accumulated more VFA than the bromegrass feces during the incubation. l-Lactic acid and VFA accumulation in the high corn and corn silage feces was at the expense of starch, based on starch loss and the production of straight-chain VFA. In the bromegrass feces, accumulation of branched-chain VFA and aromatic compounds and the low starch availability indicated that the protein in the feces was the primary source for odorous compound production. Substrate additions confirmed these conclusions. We conclude that starch availability was the primary factor determining accumulation and composition of malodorous fermentation products, and when starch was unavailable, fecal microorganisms utilized protein.

Feeding high-moisture corn instead of dry-rolled corn reduces odorous compound production in manure of finishing beef cattle without decreasing performance.

We hypothesized that feeding steers ground high-moisture ensiled corn (HMC) in lieu of dry-rolled corn (DRC) would reduce the amount of starch being excreted in the manure and the associated odorous compound production. One hundred forty-eight crossbred steers (363 +/- 33 kg of BW) were fed a DRC-or HMC-based diet in a feeding trial, and 8 Charolais-sired steers (447 +/- 22 kg of BW) were used in a nutrient balance study. Steers fed HMC tended to have a slightly lower DMI (P = 0.09), ADG (P = 0.06), and yield grade, but G:F, final HCW, and quality grade did not differ (P > or = 0.23) between treatments. Compared with feeding DRC, feeding HMC decreased (P = 0.02) starch intake from 5,407 to 4,846 g/d, decreased (P < 0.01) fecal excretion of starch from 448 to 292 g/d, and increased (P = 0.03) starch digestibility from 91.7 to 94.1%. Nitrogen intake was greater (P < 0.01) for steers fed DRC than HMC in both studies, but N retention did not differ (P = 0.55). Heat production and energy retention did not differ between the 2 treatments (P > or = 0.55). In manure slurries incubated for 35 d with soil and water, total VFA concentration was lower (P < 0.01) in manure from steers fed HMC (1,625 micromol/g of DM) compared with steers fed DRC (3,041 micromol/g of DM). Lower initial (d 0) starch concentrations and greater initial pH was also observed in the slurries from the HMC manure. By d 3 of slurry incubation, there was an increase (P < 0.01) in free glucose and l-lactic acid in the DRC slurries but not in the HMC slurries. During manure incubation, alcohol and VFA content increased (P < 0.01) and pH declined, but to a lesser extent (P < 0.01) in the HMC slurries. However, branched-chain VFA increased more (P < 0.01) in the HMC slurries than in the DRC slurries. These data suggest that feeding HMC instead of DRC decreased fecal starch and production of some potentially odorous compounds in a finishing cattle system but had little impact on animal productivity.

Fatty acid indices of stearoyl-CoA desaturase do not reflect actual stearoyl-CoA desaturase enzyme activities in adipose tissues of beef steers finished with corn-, flaxseed-, or sorghum-based diets.

We hypothesized that stearoyl-CoA desaturase (SCD) enzyme activity would not correlate with fatty acid indices of SCD activity in steers fed different grains. Forty-five Angus steers (358 +/- 26 kg BW) were individually fed for 107 d diets differing in whole cottonseed (WCS) supplementation (0, 5, or 15% of DM) and grain source (rolled corn, flaxseed plus rolled corn, or ground sorghum grain) in a 3 x 3 factorial arrangement. Flaxseed- and corn-fed steers had greater (P < 0.01) G:F (0.119 and 0.108, respectively) than sorghum-fed steers (0.093). Marbling score was decreased by WCS (P = 0.04), and LM area was decreased (P < 0.01) by sorghum. Plasma 14:0, 16:0, 16:1n-7, and 18:2n-6 were greatest in corn-fed steers, whereas plasma 18:3n-3 and 20:5n-3 were greatest in the flax-seed-fed steers (P < 0.01). Plasma 18:1trans-11 was least in sorghum-fed steers, and plasma cis-9,trans-11 CLA was barely detectable, in spite of high intestinal mucosal SCD enzyme activity (118 to 141 nmol*g tissue(-1).7 min(-1)). Interfascicular (i.f.) and s.c. cis-9,trans-11 CLA remained unchanged (P > or = 0.25) by treatment, although 18:1trans-11 was increased (P < or = 0.02) in steers fed corn or flaxseed. Steers fed flaxseed also had greater (P < 0.01) i.f. and s.c. concentrations of 18:3n-3 than steers fed the other grain sources. Oleic acid (18:1n-9) was least and total SFA were greatest (P < 0.01) in i.f. adipose tissue of steers fed 15% WCS. Lipogenesis from acetate in s.c. adipose tissue was greater (P < 0.01) in flaxseed-fed steers than in the corn- or sorghum-fed steers. Steers fed flaxseed or corn had larger i.f. mean adipocyte volumes (P < 0.01) than those fed sorghum and tended (P = 0.07) to have larger s.c. adipocyte volumes. Several fatty acid indices of SCD enzyme activity were decreased (P < or = 0.03) by WCS in i.f. adipose tissue, including the 18:2cis-9,trans-11/ 18:1trans-11 ratio. The 18:2cis-9,trans-11/18:1trans-11 ratio also tended to be decreased (P = 0.09) in s.c. adipose tissue by flaxseed; however, SCD enzyme activities in i.f. and s.c. adipose tissue were not affected by dietary WCS (P > or = 0.47) or grain source (P > or = 0.37). Differences in SFA seemed to be independent of SCD enzyme activity in both adipose tissues, suggesting that duodenal concentrations of fatty acids were more important in determining tissue fatty acid concentrations than endogenous desaturation by SCD.

Nitrogen metabolism of beef steers fed endophyte-free tall fescue hay: effects of ruminally protected methionine supplementation.

Level of nitrogen (N) intake and ruminally protected methionine supplementation were evaluated in eight Angus growing steers (initial BW 253+/-21 kg, final BW 296+/-21 kg) in a replicated 4+/-4 Latin square design. The steers were fed two endophyte-free tall fescue (Festuca arundinacea) hays that contained 2.2 (LO) or 2.8% (HI) of DM as N and were either supplemented or not with ruminally protected methionine (10 g metabolizable methionine/d). Diets were fed to provide adequate energy for 0.5 kg ADG and sufficient protein for maintenance (LO), or protein to support 0.5 kg ADG (HI). Following at least 14 d of adjustment, N balance was measured for 6 d. Isotopic urea was infused (15N15N-urea, 0.164 mmol urea N/h) via a jugular catheter for 56 h and urine was collected from 48 to 56 h to measure urea kinetics. Jugular blood was collected during the balance trial, and serum was analyzed for serum urea N (SUN). By design, daily N intake was greater (P < 0.05) for HI (112 g) than for LO (89 g). Compared with LO, steers when fed HI had greater (P < 0.05) daily DMI (4,217 vs 4,151 g), fecal N (34.4 vs 31.2 g), N digested (77.1 vs 57.7 g), urine N (48.3 vs 37.5 g), urine urea N excretion (34.6 vs 24.8 g), and N retained (29.8 vs 21.1 g). When fed HI steers also had higher (P < 0.05) urine urea N concentration (276 vs 219 mM), SUN (8.7 vs 6.7 mM), N digestibility (69.1 vs 64.9%), percentage of urinary N present as urea (71.5 vs 66.7%, P < 0.053), and rate of urea N production (59.6 vs 49.2 g/d) but lower (P < 0.05) percentage of urea N produced that was returned to the ornithine cycle (15.03 vs 19.2 1%) than when fed LO. Methionine supplementation decreased daily urine N (41.2 vs 44.6 g, P = 0.10) and increased both the amount of N retained daily (27.9 vs 23.7 g, P < 0.089) and the percentage of N digested that was retained (40.4 vs 34.6%, P < 0.094). In summary, supplemental methionine met a specific dietary limitation by increasing the amount of digested N that was retained by the steers.

Urea flux in beef steers: effects of forage species and nitrogen fertilization.

The effects of two forage species and N levels on urea kinetics and whole-body N metabolism were evaluated in eight Angus steers (initial BW 217+/-15 kg). In a replicated, 4 x 4 Latin square design, steers were fed gamagrass (Tripsacum dactyloides L.) or switchgrass (Panicum virgatum L.), each of which had 56.2 (LO) or 168.5 (HI) kg of N fertilization per hectare. Diets provided adequate energy for 0.5 kg ADG. Nitrogen balance and urea kinetics were measured from d 22 to 27 of each period. Urine samples collected during intravenous infusion of bis 15N urea were used to calculate production and recycling of urea N from relative abundance of urea isotopomers. Jugular blood serum was analyzed for serum urea N (SUN). Gamagrass differed from switchgrass (P < 0.05) in daily DMI (4,273 vs 4,185 g), N intake (72 vs 67 g), DM digestibility (61.0 vs 63.6%), fecal N (30.6 vs 28.3 g/d), urine urea N (10.5 vs 8.0 g/d), and percentage of urinary N present as urea N (53.5 vs 40.0%). After adjustment for differences in N intake, fecal N still tended to be greater (P < 0.09) for gamagrass than for switchgrass. The LO differed from the HI (P < 0.01) in daily N intake (63 vs 76 g), DM digestibility (61.3 vs 63.3%), urine N (13.6 vs 25.9 g/d), and N retained as a percentage of N digested (57.3 vs 43.5%). Compared to switchgrass, gamagrass had greater SUN, N digestibility, and N digested as N level increased (forage x N level interactions, P < 0.05). As N level increased, N retention increased from 19.5 to 23.5 g/d in gamagrass and decreased from 20.5 to 18.1 g/d in switchgrass (interaction, P < 0.07). The HI group was greater than the LO intake group (P < 0.03) in endogenous production of urea N (44.4 vs 34.0 g/d), gut entry rate of urea N (31.6 vs 28.2 g/d), and the amount of urea N that re-entered the ornithine cycle (9.4 vs 7.9 g/d). However, the percentage of urea N entering the gastrointestinal tract that was recycled was constant among treatments (29.1%), indicating that almost 70% of the urea N that entered the gastrointestinal tract was potentially available for anabolic purposes of the steers as a component of microbial products that were absorbed or excreted in the feces. In summary, N levels affected N metabolism of steers more when they were fed gamagrass than when they were fed switchgrass. Although the absolute amounts of N moving through the system changed with variations in intake, the proportions remained similar, with a greater efficiency of N use at low N intakes.