Effects of Juniperus species and stage of maturity on nutritional, in vitro digestibility, and plant secondary compound characteristics.

Rising feed costs and recurring feed shortages necessitate the investigation into alternative and underutilized feed resources. Nutritional characteristics of species are either unknown or limited to leaves and ground material from small stems. Therefore, the objective was to quantify nutritional characteristics, 48-h true IVDMD (tIVDMD), microbial gas production, and secondary compound characteristics of entire woody plant material of 4 species-, , , and -at immature and mature stages of growth. Immature plants had greater CP concentrations and lower NDF concentrations ( < 0.001) than mature plants regardless of species. Mature plants also had greater ( < 0.001) concentrations of ADF compared with immature plants with the exception of . In general, immature , , and had greater ( < 0.02) tIVDMD and total 48-h and asymptotic gas production than mature plants. Immature and plants were more digested (tIVDMD; < 0.001) than immature and , but tIVDMD did not differ in mature plant material across species. Condensed tannins (CT) were greater ( < 0.001) in immature and than mature plants; differences in CT concentrations among immature species were also detected ( < 0.04). Volatile oil yields were similar across maturity and species with 1 exception: immature yielded more ( < 0.02) volatile oil than mature material. Volatile oil composition across species varied and contained a range of 65 to 70 terpene compounds. The dominant terpenes across species were generally greater ( < 0.05) in immature vs. mature plant material with the exception of . Labdane acids were negligible in , , and and greater in ( < 0.001). Ground material from mature juniper species, although inferior in nutritional quality compared with immature plants, is comparable to traditional low-quality roughage ingredients. Given that has been successfully fed in lamb feedlot diets, the similarities of , and suggest that all three species have potential to be effective roughage ingredients.

Is differential use of Juniperus monosperma by small ruminants driven by terpenoid concentration?

Differential plant use by herbivores has been observed for several woody plant species and has frequently been attributed to plant secondary metabolites. We examined the relationship between terpenoid concentration and Juniperus monosperma herbivory by small ruminants. Two groups of animals (10 goats or 5 goats plus 4 sheep) browsed 16 paddocks (20 × 30 m) containing one-seed juniper for six days during two seasons. Juniper leaves were sampled from 311 saplings immediately after browsing. Saplings were categorized by size (short [<0.5 m], medium [0.5-1.0 m], or tall [>1.0 m]), and by browsing intensity (light [<33 %], moderate [33-66 %], or heavy [>66 %]). Juniper bark was collected from 12 saplings during spring. Total estimated terpenoid concentrations in leaves and bark were 18.3 ± 0.3 and 8.9 ± 0.8 mg/g, respectively, and the dominant terpene in both tissues was α-pinene (11.1 ± 0.2 and 7.6 ± 0.7 mg/g, respectively). Total terpenoid concentration of juniper leaves was greater in spring than summer (20.6 ± 0.5 vs. 16.7 ± 0.3 mg/g, respectively) and was lower in short saplings than medium or tall saplings (16.5 ± 0.6 vs. 19.8 ± 0.4 and 19.5 ± 0.4 mg/g, respectively). Total terpenoid concentration of leaves also differed among the three defoliation categories (21.2 ± 0.6, 18.7 ± 0.5, and 16.1 ± 0.4 mg/g for light, moderate, and heavy, respectively). The smallest subset of terpenoids able to discriminate between light and heavy browsing intensity categories included eight compounds ([E]-ß-farnesene, bornyl acetate, γ-eudesmol, endo-fenchyl acetate, γ-cadinene, α-pinene, cis-piperitol, and cis-p-menth-2-en-1-ol). Our results suggest terpenoid concentrations in one-seed juniper are related to season, sapling size, and browsing by small ruminants.

Managing livestock using animal behavior: mixed-species stocking and flerds.

Mixed-species stocking can foster sound landscape management while offering economic and ecological advantages compared with mono-species stocking. Producers contemplating a mixed-species enterprise should reflect on several considerations before implementing this animal management strategy. Factors applicable to a particular producer's landscape must be considered together with goals and economic constraints before implementing mixed-species stocking. A major consideration when using mixed-species stocking is how to deal with predation losses, especially among small ruminants. An approach being adopted in some commercial operations capitalizes on using innate animal behaviors to form cohesive groups of two or more livestock species that consistently remain together under free-ranging conditions. These groups are referred to as flerds. The mixing of a flock of sheep and/or goats with a herd of cattle into a flerd has been shown to protect sheep and goats from coyote predation, as well as offering other husbandry advantages. Some of the added advantages include more efficient conversion of forage into animal protein. Creation of flerds, their maintenance and advantages are discussed.

Fractional nonablative 1,540-nm laser resurfacing of atrophic acne scars. A randomized controlled trial with blinded response evaluation.

The efficacy of nonablative fractional laser resurfacing of acne scars has been described in case reports and uncontrolled trials. The present study is the first randomized controlled trial in this field. The aim of this study was to examine the efficacy and adverse effects of 1,540-nm nonablative fractional laser treatment of acne scars. Ten patients with acne scars were included. Two intraindividual areas of similar size and appearance within contralateral anatomical regions were randomized to (1) 3-monthly laser treatments with a StarLux 1,540-nm fractional handpiece, and (2) no treatment. Blinded on-site clinical evaluations were performed before treatment, and at 4 and 12 weeks after the final treatment. End-points were overall change in scar texture (from score 0, even texture, to 10, worst possible scarring), adverse effects, change in skin colour (from score 0, absent, to 10, worst possible), and patient satisfaction (from score 0, no satisfaction, to 10, best imaginable satisfaction). Before treatment, scars were moderately atrophic and uneven in texture on both treated and untreated sides (median score 6.5, interquartile range 4.5-8; P=1). After treatment, laser-treated scars appeared more even and smooth than untreated control areas (4.5, 2-6.5, versus 6.5, 4.5-8, P=0.0156, at 4 weeks; 4.5, 2.5-6.5, versus 6.5, 4.5-8, at 12 weeks; P=0.0313). Patients were satisfied with the treatment (5.5, 1-7, after 12 weeks) and five of the ten patients evaluated their acne scars as moderately or significantly improved. No differences were found in skin redness or pigmentation between before and after treatment. Patients experienced moderate pain, erythema, oedema, bullae, and crusts. No adverse effects were seen in untreated control areas. The nonablative 1,540-nm fractional laser improves acne scars with a minimum of adverse effects.

Effects of cis-beta-ocimene, cis-sabinene hydrate, and monoterpene and sesquiterpene mixtures on alfalfa pellet intake by lambs.

The transition of grasslands to shrub-dominated scrubland reduces livestock productivity and contributes to impoverished conditions for humans in arid and semiarid regions worldwide. Many shrubs that are increasing in dominance contain secondary compounds that deter browsing by herbivores. Knowledge concerning the effects of specific compounds in herbivore diets is limited but may provide useful insights into desertification. Flourensia cernua is a dominant shrub in the northern Chihuahuan Desert that contains an abundance of terpenes. Four experiments were conducted to determine the effects of terpenes on intake of alfalfa pellets by lambs. Two individual monoterpenes (cis-beta-ocimene and cis-sabinene hydrate) were examined in Exp. 1 and 2, and mixtures of monoterpenes (borneol, camphene, camphor, 1,8-cineole, limonene, myrcene, and alpha-pinene) and sesquiterpenes (beta-caryophyllene, caryophyllene oxide, alpha-copaene, and alpha-humulene) were examined in Exp. 3 and 4, respectively. Forty-five lambs (9 lambs/treatment) were individually fed treated alfalfa pellets for 20 min each morning for 5 d. Five treatments (0x, 0.5x, 1x, 2x, and 10x; multiples of the concentrations of the same terpenes in F. cernua) were applied to alfalfa pellets (637 g, DM basis) in an ethanol carrier. The experiments were preceded by a 10-d adaptation period of the lambs to untreated pellets. Except during the 20-min test, the lambs were maintained outdoors and fed untreated alfalfa pellets (total mean intake = 4.7% of BW, DM basis). Day x treatment interactions were detected (P < 0.04) in Exp. 1 and 4 because of a greater intake for 0x than for the other treatments on d 1 (Exp. 1) and a lower intake for the 10x treatment on d 1 and 2 (Exp. 4). A trend for decreased intake (g/kg of BW) as the concentration of the sesquiterpene mixture increased was observed in Exp. 3 (P = 0.093 for the linear contrast). Although there was a tendency for the sesquiterpene mixture to decrease intake, cis-beta-ocimene, cis-sabinene hydrate, and the monoterpene mixture did not appear to affect intake by lambs. Thus, sesquiterpenes may exert antiherbivory properties under certain conditions that may contribute to shrub dominance with extended periods of livestock foraging.

Volatile compounds on the leaf surface of intact and regrowth tarbush (Flourensia cernua DC) canopies.

Shrub expansion into desert grasslands is a serious problem resulting in loss of forage and rangeland productivity. Flourensia cernua DC (tarbush) is one such shrub contributing to the decline of Chihuahuan Desert grasslands. Our previous research has shown tarbush consumption by sheep and goats to be negatively related to leaf surface concentration of individual terpenes and epicuticular wax. Concentrations of compounds such as terpenes often change with plant age and phenology. Our objective was to examine the effect of altering the vegetative state of tarbush on volatile chemicals. Ninety tarbush plants were randomly selected, and all biomass within 10 cm of the soil surface was removed from 45 plants during winter dormancy. Leaves were collected the following summer during active growth from the canopy of intact controls and resprouts. Leaf surface volatiles were analyzed by gas chromatography-mass spectroscopy and subjected to univariate analysis of variance and stepwise discriminate analysis. Of the 87 compounds present on tarbush leaves, 35 were greater in canopy samples and 16 were greater in regrowth samples based on univariate analysis (P<0.05). Mean concentration of total volatiles on canopy leaves tended to be less (P=0.062) than that of regrowth (3,642 vs. 4,684 microg/g DM). Nine compounds in the discriminant analysis (alpha-muurolene, iso-borneol, unknown#6, p-cymen-8-ol, unknown#7, sabinene, beta-caryophyllene, delta-cadinene, and alpha-copaene) explained 95% of the variation between canopy and regrowth samples. Lower cumulative concentration of volatile compounds in canopy than regrowth samples suggests repsrouts may be less vulnerable to herbivory than intact tarbush.

Effects of gamma-terpinene, terpinolene, alpha-copaene, and alpha-terpinene on consumption of alfalfa pellets by sheep.

Although plant secondary chemistry influences shrub consumption by free-ranging ruminants, the effects of many specific compounds on herbivores have not been examined. We conducted four experiments to examine effects of individual terpenes on alfalfa pellet intake by lambs. Forty-five lambs were individually fed alfalfa pellets sprayed with gamma-terpinene, terpinolene, alpha-copaene, or alpha-terpinene at one of five concentrations in an ethanol carrier. Treatments (0, 0.5, 1, 2, and 10x) were multiples of the concentration (x) of a specific terpene on the leaf surface of Flourensia cernua (a low-preference shrub for domestic ruminants). Terpenes were applied to alfalfa pellets (0.64 kg.lamb(-1).d(-1), DM basis), and consumption was measured during a 20-min interval for 5 d. A day effect was detected for gamma-terpinene on intake (P < 0.001 for both linear and quadratic contrasts). No effect of terpinolene, alpha-copaene, or alpha-terpinene on intake was detected in this study. None of the terpenes tested was strongly related to intake of alfalfa pellets by lambs under the conditions of this study.

Transport of phenolic compounds from leaf surface of creosotebush and tarbush to soil surface by precipitation.

During the last 100 years, many desert grasslands have been replaced by shrublands. One possible mechanism by which shrubs outcompete grasses is through the release of compounds that interfere with neighboring plants. Our objective was to examine the movement of secondary compounds from the leaf surface of creosotebush and tarbush to surrounding soil surfaces via precipitation. Units consisting of a funnel and bottle were used to collect stemflow, throughfall, and interspace precipitation samples from 20 creosotebush (two morphotypes) and 10 tarbush plants during three summer rainfall events in 1998. Precipitation samples were analyzed for total phenolics (both species) and nordihydroguaiaretic acid (creosotebush only). Phenolics were detected in throughfall and stemflow of both species with stemflow containing greater concentrations than throughfall (0.088 and 0.086 mg/ml for stemflow and 0.022 and 0.014 mg/ml for throughfall in creosotebush morphotypes U and V, respectively: 0.044 and 0.006 mg/ml for tarbush stemflow and throughfall, respectively). Nordihydroguaiaretic acid was not found in any precipitation collections. The results show that phenolic compounds produced by creosotebush and tarbush can be transported to the soil surface by precipitation, but whether concentrations are ecologically significant is uncertain. Nordihydroguaiaretic acid was not present in the runoff from creosotebush.

Effects of four mono- and sesquiterpenes on the consumption of alfalfa pellets by sheep.

Effects of individual terpenes on alfalfa pellet intake by lambs were examined in four experiments. Forty-five lambs (nine lambs/treatment) were individually fed alfalfa pellets sprayed with either camphene, myrcene, caryophyllene oxide, or beta-pinene at one of five concentrations (one terpene per experiment). Treatments (0, 0.5, 1, 2, and 10x) were multiples of the concentration (x) of a specific terpene in tarbush. Terpenes were applied to alfalfa pellets (0.64 kg x lamb(-1) x d(-1), DM basis), and consumption was measured during a 20-min interval for 5 d. Lambs were maintained and fed alfalfa pellets in one group (except during 20-min tests) at a mean total daily intake of 4.7% of BW (DM basis). Camphene and caryophyllene oxide tended to decrease intake (linear contrasts were P = .0651 and P = .0504, respectively), whereas myrcene and beta-pinene exerted no effect on the consumption of alfalfa pellets by lambs. Camphene and caryophyllene oxide may be involved in the differential herbivory of individual tarbush plants by livestock.

Pen confinement of yearling ewes with cows or heifers for 14 days to produce bonded sheep.

Mixed species stocking is commonly a more ecologically sound and efficient use of forage resources than single species stocking, especially in pastures having complex assemblages of forage species. However, in many environments livestock predation on especially smaller ruminants adds an extra challenge to mixed species stocking. When mixed sheep and cattle remain consistently as a cohesive group (flerd), predation risks are lessened, while fencing and herding costs are reduced. To establish a cohesive group (bond), a 30-day bonding period in which young sheep and cattle pairs are penned together is currently recommended. The purpose of this research was to test if a bond could be produced in <30 days (14 days) using pen confinement; thus reducing feed, labor, and overhead costs. Additionally, we tested whether cow age affects cohesiveness of bonded pairs immediately following 14 days of pen confinement. Sixteen mature cows (7-8 years of age) and sixteen 9-month-old heifers were randomly paired with one of 32 yearling ewe lambs. Eight cow/ewe (PC) and eight heifer/ewe (PH) pairs were maintained individually in 2mx6m pens for 14 days. The other eight-cow/ewe (NC) and heifer/ewe (NH) pairs were separated by species with each species maintained on separate pastures for the 14-day period. After 14 days, pairs were released in observation paddocks and separation distance between treatment pairs was measured during a 30-min open field test. Other behaviors were also noted and recorded during the field test. Separation distance did not differ (P=0.973) between the PC and PH treatments; however, separation distance for NC versus NH (P<0.004), NC versus PC (P<0.001), and NH versus PH (P<0.002) all differed. Mean separation distance (meters) and standard errors were 40+/-3.9, 3+/-0.3, 76+/-5.3, and 4+/-1.4 for NH, PH, NC, and PC treatments, respectively. Overall, the animals that were penned spent more time grazing and less time walking than animals not previously penned for 14 days. Penned animals also vocalized less than non-penned animals during the open field test. The bond sheep formed to the bovines was not affected by cow age. These data suggest that inter-specific bond formation using pen confinement can be accomplished within 14 days, representing a 53% savings in time and associated costs when compared to pen confinement lasting 30 days.

Extracts of Flourensia cernua (L): volatile constituents and antifungal, antialgal, and antitermite bioactivities.

The chemical components of tarbush (Flourensia cernua) leaves were fractionated by extracting successively with hexanes, diethyl ether, and ethanol. Volatile profiles of each fraction were identified by using GC-MS. The hexanes fraction contained mostly monoterpenoids, while the ethanol fraction volatiles were primarily sesquiterpenoids. Crude fractions were tested for activity against fungi, algae, and termites. Application of as little as 1 microg of the essential oil from the hexanes fraction was sufficient to provide visible antifungal activity in bioautography assays. The diethyl ether fraction showed selective activity against the cyanobacterium responsible for the 2-methylisoborneol-induced off-flavor sometimes associated with catfish farming operations. All three fractions exhibited a high degree of antitermite activity.

Extracts of Flourensia cernua reduce consumption of alfalfa pellets by sheep.

Effects of three extracts (hexanes, ether, and ethanol) from tarbush (Flourensia cernua) on intake of alfalfa pellets by lambs were examined. Forty-five ewe lambs were fed one of five treatments for five days (randomized complete block, three lambs per block on each treatment). Treatments were alfalfa pellets (CON) or alfalfa pellets plus ethanol carrier (CAR), hexanes extract (HEX), ether extract (ETH), or ethanol extract (ETOH). Extracts were applied to alfalfa pellets at the same concentration as in an equivalent amount of tarbush (as fed basis) in experiment 1 and at 10-fold dilutions of that concentration in experiment 2. Treatments were isolated from tarbush leaves by using a sequential extraction with hexanes, diethyl ether, and 100% ethanol. Lambs received 640 g of alfalfa pellets (dry matter basis) each morning and intake was monitored during a 20-min interval. Lambs were maintained and fed alfalfa pellets (4.7% of body weight) as one group except during this interval. In experiment 1, mean intake by lambs during the 20-min interval was 361, 393, 204, 212, and 228 g for CON, CAR, HEX, ETH, and ETOH, respectively (SEM = 28.9). All three extracts decreased intake (P < 0.001) compared to CON or CAR. Intake did not differ among the three extracts (HEX, ETH, and ETOH) or between the two controls (CON and CAR). Mean intake did not differ among treatments in experiment 2 (468, 455, 389, 381, and 431 g for CON, CAR, HEX, ETH, and ETOH, respectively; SEN = 30.5; P = 0. 187). Several compounds are probably responsible for the low palatability and differential use of tarbush typically exhibited by livestock.

Effect of individual terpenes on consumption of alfalfa pellets by sheep.

We examined effects of individual terpenes on alfalfa pellet intake of lambs in five experiments. Forty-five lambs (nine lambs/treatment) were individually fed alfalfa pellets sprayed with either p-cymene, alpha-humulene, 1,8-cineole, 3-carene, or sabinene at one of five concentrations (one terpene per experiment). Treatments (0, .5, 1, 2, and 10x) were multiples of the concentration (x) of a specific terpene in tarbush that was related to differential herbivory by livestock in previous studies. Terpenes were applied to alfalfa pellets (.64 kg x lamb(-1) x d(-1), DM basis), and consumption was measured during a 20-min interval for 5 d. Lambs were adapted to handling and pen feeding for 10 d and were maintained and fed alfalfa pellets in one group (except during 20-min tests) at a mean total daily intake of 4.7% of BW (DM basis). None of the five compounds decreased alfalfa pellet consumption during the 20-min interval. These five mono- and sesquiterpenes do not seem to be responsible for differential herbivory of individual tarbush plants by livestock.

Effects of volatile compounds on consumption of alfalfa pellets by sheep.

We examined the effects of six volatile compounds on alfalfa pellet consumption by lambs. In each experiment, 45 lambs were individually fed alfalfa pellets sprayed with a selected compound (camphor, limonene, cis-jasmone, beta-caryophyllene, borneol, or alpha-pinene) at one of five concentrations. Treatment concentrations were multiples (0, .5, 1, 2, and 10) of the concentration of a specific compound (X) that was related to differential herbivory of tarbush by livestock in previous studies. Treatments were applied to alfalfa pellets (.64 kg x lamb(-1) x d(-1), DM basis), and consumption was measured during a 20-min interval each morning for 5 d. Lambs were adapted to handling procedures and the pelleted diet (without treatments) for 10 d. Lambs were maintained and fed (approximately 4.5 to 5% of BW) as one group except during 20-min tests. A negative linear effect of treatment concentration on intake was observed for camphor (P < .02) and alpha-pinene (P < .01), and a quadratic response was detected for borneol (P < .02). The other three compounds had no discernible effect on consumption. Although volatile compounds generally had only minor influences on consumption, the negative influences of alpha-pinene and camphor concentrations on pellet consumption suggest that these monoterpenes may partially explain differential herbivory of individual tarbush plants by livestock.

Effect of chronic ingestion of tarbush (Flourensia cernua) on ewe lambs.

Efforts to increase livestock utilization of tarbush are being coupled with studies to examine tarbush toxicity. Thirty-eight (19/treatment) ewe lambs were assigned at birth to receive either tarbush or alfalfa (15%, dry matter basis) in a sorghum-based growing ration. Lambs were pen-fed this diet 60 d pre-weaning and 60 d post-weaning. No differences existed between treatments in feed consumption. In the tarbush group, 1 lamb died of unknown causes at 90 d of age, while 3 lambs died between 115 and 120 d of age. There were no deaths in the alfalfa group. Shortly before death, lambs fed tarbush appeared lethargic, disoriented and anorectic. At 122 d of age, 5 lambs were randomly selected from each group. Feces and jugular blood samples were obtained from each lamb before being euthanized and necropsied the following day. All fecal samples were negative for occult blood. Serum gamma glutamyl-transpeptidase (P < 0.001) and aspartate aminotransferase (P < 0.001) activities and platelet counts (P < 0.05) were elevated in lambs fed tarbush, while serum calcium concentrations tended (P < 0.10) to be greater. Histologic examination revealed diffuse liver apoptosis in lambs fed tarbush. These data indicate tarbush leaves cause liver damage when fed for extended periods of time.

Effects of organic solvents on use of tarbush by sheep.

Tarbush (Flourensia cernua DC) is a native perennial shrub prevalent in many parts of the Chihuahuan Desert. Ruminants have exhibited limited use of tarbush leaves and new leaders as a forage during the summer growing season. Efforts to increase use of tarbush by lambs through spraying with various organic solvents were unsuccessful, probably because of the highly variable response. However, complete immersion of tarbush in organic solvents (acetone and ethanol) increased (P<0.01) tarbush use by ram lambs when compared to unaltered tarbush. Data suggest that removal of secondary compounds from the leaf surface of tarbush using organic solvents enhanced acceptability of tarbush to sheep.

Influence of cottonseed meal supplementation on voluntary intake, ruminal and cecal fermentation, digesta kinetics and serum insulin and growth hormone in mature ewes fed prairie hay.

To determine the influence of protein supplementation on intake and fermentation of low-quality hay, six ruminal- and cecal-cannulated Rambouillet ewes (avg wt 43.6 kg) in a crossover design were given ad libitum access to prairie hay with or without 80 g of cottonseed meal (CSM) X head-1 X d-1. Voluntary hay intake was measured the last 7 d of each 18-d period. Ruminal, cecal and blood samples were collected at 0, 1 (except cecal), 3, 6, 9, 12, 15, 18, 21 and 24 h post-supplementation on d 14 of each period to measure fluid dilution rate, fermentation characteristics and serum concentrations of insulin and growth hormone. An intraruminal dose of Yb-labeled hay, followed by fecal sampling on d 15 through 18, was used to measure particulate passage rate. Voluntary intake of prairie hay was increased (P less than .04) from 23.7 to 28.3 g/kg of body weight by CSM supplementation. Particulate passage rate constants did not differ (P greater than .15) between supplemented (3.76%/h) and control (3.72%/h) ewes, and total mean retention time was not altered (P greater than .15) by CSM supplementation. Ruminal retention time of particulates did not differ (P greater than .15) between treatments; however, intestinal transit time was faster (P less than .03; 18.1 vs 22.6 h) in supplemented than in control ewes. Estimated gastrointestinal dry matter fill was greater (P less than .05; 14.3 vs 12.9 g/kg body weight) in supplemented ewes. Ruminal fluid volume did not differ (P greater than .15) between treatments; however, supplemented ewes tended to have faster fluid dilution rates (P less than .14) and fluid outflow rates (P less than .11) than control ewes. Cecal fluid volume, dilution rate and outflow rate did not differ (P greater than .15) between groups. Ruminal and cecal pH and total volatile fatty acids were similar between treatments. Similarly, cottonseed meal supplementation did not affect (P greater than .15) ruminal or cecal ammonia concentrations. Molar proportions of ruminal and cecal individual fatty acids were not affected (P greater than .15) by CSM supplementation. Feeding cottonseed meal increased (P less than .05) serum insulin, decreased (P less than .07) serum growth hormone and increased (P less than .06) serum free fatty acids, but did not influence (P greater than .15) either serum urea N or glucose concentrations. Cottonseed meal supplementation in ewes fed prairie hay caused increased hay intake but had minimal effects on ruminal and cecal fermentation.

Relationship of rumen fluid dilution rate to rumen fermentation and dietary characteristics of beef steers.

Data from seven beef steer trials were compiled and regression analyses used to evaluate relationships among molar proportions of acetate (Ac), propionate (Pr) and butyrate (Bu), total concentration of volatile fatty acids (VFA), rumen ammonia (NH3), rumen pH, rumen fluid dilution rate (FDR), rumen fluid volume (FVOL), body weight (WT), dry matter intake (DMI) and dietary concentration and intake of crude protein (CP and CPI), acid detergent fiber (ADF and ADFI), ash (ASH and ASHI) and metabolizable energy (ME and MEI). Of the six fermentation variables, Pr (negative regression coefficient, beta) and pH (positive beta) were related (P less than .05) to FDR, but only 3 and 12% of the variation in these two variables, respectively, was explained by FDR. When FDR was described by dietary characteristics, ASHI was positively related to FDR (R2 = .16). The best two-variable model for FDR contained DMI (positive beta) and WT (negative beta) and increased R2 to .36. Fluid volume was best described by ME (positive beta; R2 = .20). The two-variable model for FVOL added ASH with a positive partial beta (R2 = .23). When fermentation variables were regressed on dietary characteristics, Ac was best described by ADF (positive beta; R2 = .71). The variable that best described Pr proportion was ADF (negative beta; R2 = .50), and addition of CP (negative beta) and MEI (positive beta) into the Pr model improved R2 to .70. Molar proportion of butyrate was related to CP (positive beta; R2 = .23), and addition of ME (positive beta) to the model improved the R2 to .31. Total VFA concentration was best described by ADFI (positive beta; R2 = .14). An R2 of .29 resulted when ME (positive beta) and CPI (negative beta) were included in the total VFA model. Rumen pH was related to ADF (positive beta; R2 = .45), and addition of CP (positive beta) to the rumen pH model increased R2 to .55. Crude protein concentration was related to ruminal NH3 level (positive beta; R2 = .42), and inclusion of ADFI (positive beta) into the model improved the R2 to .47.