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PubMed1995

Effects of experience and juvenile hormone on the organization of the mushroom bodies of honey bees.

There is an age-related division of labor in the honey bee colony that is regulated by juvenile hormone. After completing metamorphosis, young workers have low titers of juvenile hormone and spend the first several weeks of their adult lives performing tasks within the hive. Older workers, approximately 3 weeks of age, have high titers of juvenile hormone and forage outside the hive for nectar and pollen. We have previously reported that changes in the volume of the mushroom bodies of the honey bee brain are temporally associated with the performance of foraging. The neuropil of the mushroom bodies is increased in volume, whereas the volume occupied by the somata of the Kenyon cells is significantly decreased in foragers relative to younger workers. To study the effect of flight experience and juvenile hormone on these changes within the mushroom bodies, young worker bees were treated with the juvenile hormone analog methoprene but a subset was prevented from foraging (big back bees). Stereological volume estimates revealed that, regardless of foraging experience, bees treated with methoprene had a significantly larger volume of neuropil in the mushroom bodies and a significantly smaller Kenyon cell somal region volume than did 1-day-old bees. The bees treated with methoprene did not differ on these volume estimates from untreated foragers (presumed to have high endogenous levels of juvenile hormone) of the same age sampled from the same colony. Bees prevented from flying and foraging nonetheless received visual stimulation as they gathered at the hive entrance. These results, coupled with a subregional analysis of the neuropil, suggest a potentially important role of visual stimulation, possibly interacting with juvenile hormone, as an organizer of the mushroom bodies. In an independent study, the brains of worker bees in which the transition to foraging was delayed (overaged nurse bees) were also studied. The mushroom bodies of overaged nurse bees had a Kenyon cell somal region volume typical of normal aged nurse bees. However, they displayed a significantly expanded neuropil relative to normal aged nurse bees. Analysis of the big back bees demonstrates that certain aspects of adult brain plasticity associated with foraging can be displayed by worker bees treated with methoprene independent of foraging experience. Analysis of the overaged nurse bees suggests that the post-metamorphic expansion of the neuropil of the mushroom bodies of worker honey bees is not a result of foraging experience.

Aging↗
PubMed2003

Partial nectar loads as a cause of multiple nectar transfer in the honey bee (Apis mellifera): a simulation model.

Honey bee foragers transfer their nectar loads to receiver bees within the nest. Surprisingly, they often transfer to more than one receiver (published values range from 1.9 to 2.7). Several adaptive hypotheses have been proposed to explain why multiple transfer occurs. One hypothesis, information improvement, states that multiple transfer arises as an adaptive forager-driven process. Foragers use the delay in finding a receiver to assess the relative work capacities of foragers and receivers, performing recruitment dances when appropriate. Multiple transferring improves their delay information. We used a stochastic simulation model to investigate the non-adaptive partial loads hypothesis. We determined the extent to which partial crop loads and receiver filling and emptying rules (i.e. how much nectar to accept before leaving the transfer area) can cause multiple transfer. As many as 1.9 nectar transfers per returning forager were generated within biologically realistic parameter space. We suggest that much multiple transfer arises as a non-adaptive consequence of partitioning nectar foraging between foragers and receivers, but that this will also result in foragers having better information about the relative work capacities of foragers and receivers as a useful consequence. We suggest that the number of transfers caused by partial loads could also be increased by an adaptive forager-driven effort to improve their information concerning the balance of foragers and receivers and we outline a framework wherein the information improvement hypothesis can be directly tested.

Adaptation, Psychological↗
PubMed1995

Urea ammoniation effects on the feeding value of guineagrass (Panicum maximum) hay.

Laboratory, digestion, and growth studies evaluated urea as a source of ammoniation for quality improvement in guineagrass (Panicum maximum) hay. In a laboratory trial, 5.0-kg portions of hay were reconstituted with water to yield final forage moisture concentrations or 25 of 40% and treated with urea at 0, 4, 6, or 8% of the forage DM, with or without urease addition. Main effects of forage moisture or urease addition did not influence (P > .10) CP or NDF concentration or in vitro OM disappearance (IVOMD) of the guineagrass hay. Hay CP concentration and IVOMD increased linearly (P < .01), whereas concentrations of hemicellulose and ADL decreased linearly (P < .05) with increasing urea level. In other experiments, round bales of hay (320 kg) were reconstituted with water to yield final forage moisture concentrations of 25 or 40% and treated with urea at 0, 4, or 6% of the forage DM. The urea solution was applied as a spray onto the cut edges of the bales, or by low pressure (10 psi) injection. Two- and three-way interactions (P < .05) existed among forage moisture concentration, urea application method, and urea level for CP and NDF concentration and IVOMD of the guineagrass hay. Greatest enhancements in these forage quality characteristics were obtained when the urea solution was sprayed onto the hay at the 25% forage moisture concentration. In two digestion and two growth trials, round bales of hay were treated with 0, 4, and 6% urea sprayed onto the hay at the 25% forage moisture level. In each growth trial, 30 St. Croix white hair castrated male sheep (Trial 1:34 +/- 5.5 kg, Trial 2: 17 +/- 3.5 kg) were allotted to six pens of five head each, resulting in two pens per treatment. In the digestion trials, six similar sheep were used in a replicated 3 x 3 Latin square design. In the digestion and growth trials, hay intake increased in a quadratic (P < .05) manner with increasing urea level. Apparent NDF and ADF digestibilities increased linearly (P < .05) with increasing urea level. Linear improvements in ADG (P < .05) and gain/feed (P < .07) were observed with increasing urea level. Urea ammoniation offers potential for improving the feeding value of tropical forages and provides an option for quality forage during the dry season.

Ammonia↗
PubMed2005

Characteristics of lambs fed concentrates or grazed on ryegrass to traditional or heavy slaughter weights. II. Wholesale cuts and tissue accretion.

Targhee x Hampshire lambs (average BW 24 +/- 1 kg) were used to determine the effect of finishing on concentrate or by grazing ryegrass forage on slaughter weights of 52 kg (N) or 77 kg (H) on tissue accretion and lamb wholesale cutout. When fed to similar slaughter weights, the wholesale cuts of concentrate-fed lambs were heavier (P < 0.05) than the same cuts from forage-fed lambs; however, when expressed as a percentage of side weight, carcasses of forage-fed lambs had a higher (P < 0.001) percentage of leg than concentrate-fed lambs. Increasing slaughter weight from 52 to 77 kg resulted in a 1-kg increase in loin weight for lambs finished on concentrate and a 0.60-kg increase for lambs finished on forage (diet x slaughter weight, P < 0.03); however, the increased loin weight for lambs finished on concentrate was due largely to increased fat deposition. For lambs slaughtered at 77 kg, those finished on forage had more lean mass in the leg, loin, rack, and shoulder than those finished on concentrate, but lean mass in these cuts did not differ between diets for lambs slaughtered at 52 kg (diet x slaughter weight, P < 0.01). At the normal slaughter weight (52 kg), concentrate-fed lambs had 50% more dissectible fat than forage-fed lambs, whereas at the heavy slaughter weight, a 79% greater amount of dissectible fat was observed for concentrate- vs. forage-fed lambs (diet x slaughter weight, P < 0.001). Lean and fat accretion rates were higher (P < 0.001) for concentrate-fed lambs than for forage-fed lambs. The lean-to-fat ratio of forage-fed lambs was higher (P < 0.001) than that of concentrate-fed lambs; however, forage finishing decreased accretion rates of all tissues compared with concentrate feeding, and these differences between forage and concentrate feeding were magnified at heavier slaughter weights.

Adipose Tissue↗
PubMed2000

Determination of when during the lactation cycle to start feeding a cellulase and xylanase enzyme mixture to dairy cows.

We used 48 multiparous Holstein cows to compare the response of dairy cows to a direct-fed mixture of cellulase and xylanase enzymes (1.25 L of enzyme concentrate/tonne of forage dry matter) applied to the forage portion (60% corn silage and 40% alfalfa hay) of a total mixed diet starting either in the close-up dry period, at calving, or at peak milk production. Cows were blocked by calving date and, within blocks, randomly assigned to one of four treatment diets. Treatments were: 1) an untreated control diet, 2) enzyme addition to the forage from wk 6 to 18 postpartum, 3) enzyme addition to the forage from calving to wk 18 postpartum, and 4) enzyme addition to the forage from wk 4 prepartum to wk 18 postpartum. Total mixed diets were 65% forage and 35% concentrate prepartum, and 50:50 forage:concentrate postpartum. The production of milk, solids-corrected milk, fat-corrected milk, and energy-corrected milk was higher for cows fed enzyme-treated diets than for cows fed control diet. Production was similar for cows in all enzyme-treated groups, although numerically highest for cows that started receiving enzyme-treated forages right after parturition and numerically lowest when started prepartum. Concentrations of fat, protein, and lactose in milk were similar for all treatments; yields of protein and fat were higher for cows fed enzyme-treated forages. Dry matter intake and body condition scores, both prepartum and postpartum, were similar for all diets. Eating rates, as determined in two 24-h studies, were similar for control and enzyme-treated diets. The feeding of enzyme-treated forages increased milk production. While the effect of when the feeding of enzyme-treated forages started was not statistically significant, we recommend starting soon after parturition because of the greatest total milk production when starting at that time.

Animal Feed↗
PubMed2005

Effects of a proteolytic feed enzyme on intake, digestion, ruminal fermentation, and milk production.

The effects of exogenous proteolytic enzyme (EPE) on intake, digestibility, ruminal fermentation, and lactational performance were determined using 8 lactating Holstein cows in a double 4 x4 Latin square experiment with a 2 x2 factorial arrangement of treatments. Diets based on barley silage and alfalfa hay as the forage sources were formulated to maintain different forage to concentrate ratios [60:40 vs. 34:66, dry matter (DM) basis]. Four dietary treatments were tested: high forage (HF) without EPE (HF-EPE), HF with EPE (HF+EPE), low forage (LF) without EPE (LF-EPE), and LF with EPE (LF+EPE). The EPE, which contained proteolytic activity but negligible fibrolytic activity, was added to the concentrate portion of the diets after pelleting at a rate of 1.25 mL/kg of DM. Adding EPE to the diet increased total tract digestibilities of DM, organic matter, N, acid detergent fiber, and neutral detergent fiber, with larger increases in digestibility observed for cows fed LF+EPE. Effects of added EPE on in vivo digestibility were consistent with improvements in gas production and degradability of the individual components of the TMR observed in vitro. Ruminal enzymic activities of xylanase and endoglucanase increased with addition of EPE to the diet, which may have accounted for improvements in fiber digestion. However, feeding EPE unexpectedly decreased feed intake of cows, which offset the benefits of improved feed digestibility. Consequently, milk yield of cows fed high or low forage diets decreased with adding EPE. Nevertheless, dairy efficiency, expressed as milk/DM intake, was highest for the LF+EPE diet. Addition of EPE to the diet increased milk fat and milk lactose percentages, but decreased milk protein percentage of cows fed a low forage diet. For cows fed high forage diets, EPE only increased milk lactose percentage. Efficiency of N use for milk production was decreased for both the high and low forage diets when EPE was added to the diet. Mean ruminal pH was lowered when EPE was added a low forage diet, likely due to the increased degradation of forage and concentrate, but there was no effect of EPE on rumen pH when cows were fed high forage diets. Profiles of VFA and microbial yield were not affected by adding EPE to the diets. Adding EPE to a total mixed ration containing alfalfa hay, barley silage, and concentrate improved nutrient digestibility in the total tract, and the response was maximized with a high concentrate diet. However, improvements in digestibility were offset by decreased feed intake, likely due to increased ruminal acidosis.

Animal Feed↗
PubMed1989

Effect of particle size of alfalfa hay on intake, digestibility, milk yield, and ruminal cell wall of dairy cattle.

Alfalfa hay was chopped in a tubgrinder containing screens with apertures of 31, 63, or 100 mm. The hays were fed with concentrate to lactating cows (Experiment 1) and without concentrate to nonlactating, fistulated cows (Experiment 2). The objective was to find effects of forage particle size upon intake, digestibility, milk yield, and ruminal cell wall. In Experiment 1, there were no significant effects of forage particle size upon forage or total DM intake, digestibility of NDF, cellulose, nitrogen retained, milk yield, or milk fat percent. Digestibility of DM, ADF, and protein increased as particle size decreased. In Experiment 2, forage DM intake was greater for the 63 than the 100-mm forage but digestibility of cell wall and DM were not different among treatments. Ruminal volume for the 31 and 63-mm forages was greater than the 100-mm forage. Ruminal DM and ruminal cell wall were greater for the 63-mm forage than the 100-mm forage, with the 31-mm forage in between. Increased volume, DM, and cell wall probably account for increased intake of the 63-mm forage. Chopping alfalfa to these three sizes had no particularly positive or negative effects on animal productivity.

Animal Feed↗
PubMed2001

The diving behavior of blue and fin whales: is dive duration shorter than expected based on oxygen stores?

Many diving seabirds and marine mammals have been found to regularly exceed their theoretical aerobic dive limit (TADL). No animals have been found to dive for durations that are consistently shorter than their TADL. We attached time-depth recorders to 7 blue whales and 15 fin whales (family Balaenopteridae). The diving behavior of both species was similar, and we distinguished between foraging and traveling dives. Foraging dives in both species were deeper, longer in duration and distinguished by a series of vertical excursions where lunge feeding presumably occurred. Foraging blue whales lunged 2.4 (+/-1.13) times per dive, with a maximum of six times and average vertical excursion of 30.2 (+/-10.04) m. Foraging fin whales lunged 1.7 (+/-0.88) times per dive, with a maximum of eight times and average vertical excursion of 21.2 (+/-4.35) m. The maximum rate of ascent of lunges was higher than the maximum rate of descent in both species, indicating that feeding lunges occurred on ascent. Foraging dives were deeper and longer than non-feeding dives in both species. On average, blue whales dived to 140.0 (+/-46.01) m and 7.8 (+/-1.89) min when foraging, and 67.6 (+/-51.46) m and 4.9 (+/-2.53) min when not foraging. Fin whales dived to 97.9 (+/-32.59) m and 6.3 (+/-1.53) min when foraging and to 59.3 (+/-29.67) m and 4.2 (+/-1.67) min when not foraging. The longest dives recorded for both species, 14.7 min for blue whales and 16.9 min for fin whales, were considerably shorter than the TADL of 31.2 and 28.6 min, respectively. An allometric comparison of seven families diving to an average depth of 80-150 m showed a significant relationship between body mass and dive duration once Balaenopteridae whales, with a mean dive duration of 6.8 min, were excluded from the analysis. Thus, the short dive durations of blue whales and fin whales cannot be explained by the shallow distribution of their prey. We propose instead that short duration diving in large whales results from either: (1) dispersal behavior of prey; or (2) a high energetic cost of foraging.

Animals↗
PubMed2001

Tunnel orientation and search pattern sequence of the formosan subterranean termite (Isoptera: Rhinotermitidae).

Foraging behavior of the Formosan subterranean termite, Coptotermes formosanus Shiraki, was studied in the laboratory by using two-dimensional foraging arenas containing multiple foraging sites. Within each arena, 16 foraging sites were arranged in a uniform grid pattern and foragers were introduced into the arena through a central initiation site. Chi-square analysis determined the frequency of tunnels was uniformly distributed around the perimeter of the initiation site but became significantly skewed toward the foraging sites at a distance where the foraging sites could be encountered. Tunnel distribution was similar whether wood was present or absent at the foraging sites, suggesting that foragers respond to structural anomalies in the substrate rather than simply to the presence of food. Also described is the generalized sequence of events as foragers tunnel throughout the arenas.

Animals↗
PubMed1995

Comparison of performance of Boer and Spanish goats in two U.S. locations.

Information quantifying performance of Boer goats in the United States is lacking. To overcome this knowledge void a simulation study was performed to determine how Boer goats would compare to Spanish goats in two locations, Texas and Oklahoma. Within each of these locations forage conditions were altered from high forage (HF), medium forage (MF), and low forage (LF). Forage conditions were altered within location to emulate the variation in forage conditions that could occur in each location. Management varied from fall breeding (FB) to year-round breeding (YRB). Across breed and forage conditions, YRB resulted in higher levels of performance than FB for births per doe, number of kids sold per doe, sale weight per doe, and biological efficiency (weight sold[kg]/dry matter consumed [kg]). Boers did produce more sale weight per doe than Spanish on HF. However, the Boer's advantage was decreased or negated when exposed to MF or LF conditions. Both breeds had similar levels of performance for number of kids sold per doe under HF conditions. Under MF or LF the Spanish goats had greater levels of kids sold per doe. Neither breed simulated had a consistent advantage in both locations and varying forage conditions, but, in general, as forage conditions worsened Boer performance ranked below that of the Spanish goats. These results indicate that a complete endorsement of the Boer cannot be made. Effective use of the Boer goat will depend on the forage resource base and producers' ability to provide inputs, such as supplementation, to the goat production system.

Animal Feed↗
PubMed2001

Effects of nitrogen fertilization and harvest date on yield, digestibility, fiber, and protein fractions of tropical grasses.

To evaluate the response of three tropical forage species to varying rates of nitrogen (N) fertilization [0, 39, 78, 118, 157 kg of N/(ha x cutting)] and five summer harvests, forage DM mass and nutritive value were evaluated in a randomized complete block design with a split-split plot arrangement of treatments. Plots (n = 60) were established in 1996, and five harvests were conducted every 28 d from June through September in 1997 and 1998, with fertilizer applications occuring after each harvest. Fertilization with 78 kg of N/(ha x cutting) increased forage mass in these grasses by 129% (P < 0.01) compared with no N fertilization. Additional N did not result in further increases of forage mass. Bermudagrass (Cynodon dactylon) produced more forage DM [P < 0.01; 1,536 +/- 43 kg/(ha x cutting)] than stargrass [Cynodon nlemfuensis; 1,403 +/- 43 kg/(ha x cutting)] or bahiagrass [Paspalum notatum; 1,297 +/- 43 kg/(ha x cutting)]. Peak forage mass for all species occurred in late June and July. In vitro organic matter digestibility (IVOMD) of stargrass increased (P < 0.01) linearly with fertilization. A quadratic response to N fertilization (P < 0.01) was noted in IVOMD of bermudagrass, whereas bahiagrass was not affected. Bermudagrass was more (P < 0.01) digestible (57.5 +/- 0.4) than stargrass (54.6 +/- 0.4) and bahiagrass (51.9 +/- 0.4%). As fertilization level increased, NDF decreased linearly (P < 0.01) in all three forages. Total N concentration increased (P < 0.01) linearly as N fertilization increased in all forages. Total N concentration was highest (P < 0.01) in stargrass (2.4%, DM basis) compared with bermudagrass (2.2%) and bahiagrass (2.0%). Total N concentration was depressed in all forages for late June and July harvests (P < 0.01). Fertilization increased (P < 0.05) the concentration (% of DM) of all protein fractions. In July and August, nonprotein N was reduced 11.8% (P < 0.01), whereas ADIN increased in July (P < 0.01). Bahiagrass had less N in cell contents than did bermudagrass and stargrass but had a greater concentration of N associated with the cell wall. Managerial factors, including rates of N fertilization and harvest dates, can have profound effects on the nutritional value of forage. An increased understanding of these effects is imperative to improve supplementation programs for ruminants.

Animal Feed↗
PubMed2003

Effectiveness of short-term feeding strategies for altering conjugated linoleic acid content of beef.

A steer finishing trial was performed to determine the effect of short-term dietary regimens on conjugated linoleic acid (CLA) content of muscle tissues. The experimental design was an incomplete 3 x 2 factorial, with three levels of soybean oil (SBO; 0, 4, and 8% of diet DM) and two levels of forage (20 vs. 40% of diet DM). Forty Angus x Hereford steers averaging 504 +/- 29.0 kg were allotted randomly to one of four treatments for the last 6 wk of the finishing period. Treatments were: 80:20 concentrate:forage control diet (C); 80:20 concentrate:forage + 4% SBO (C4); 60:40 concentrate:forage + 4% SBO (F4); and 60:40 concentrate:forage + 8% SBO (F8). After 42 d on the experimental diets, steers were sacrificed and samples were collected from the chuck, loin, and round muscle groups. Fatty acid (FA; mg/100 mg of FA) composition was determined by gas-liquid chromatography. Data were statistically analyzed with mixed models procedures. The performance and carcass quality model included the effects of SBO and forage. The model for FA composition included the effects of SBO, forage, muscle group, and interactions. Orthogonal contrasts were used to determine linear effects of SBO. There were no differences in growth performance among treatments (P > 0.05). Increasing dietary SBO linearly decreased dressing percent (P = 0.04), and tended to linearly decrease marbling score (P = 0.12) and quality grade (P = 0.08). The only CLA isomer detected in tissue samples was cis-9,trans-11. Addition of SBO to diets linearly increased linoleic acid (18:2n-6; P = 0.04) and tended to linearly increase linolenic acid (18:3n-3; P = 0.10) in muscle tissues. The CLA in lean tissues was decreased (P = 0.005) with SBO-containing diets. These findings suggest that increased PUFA may limit ruminal production of CLA and trans-vaccenic acid (VA) and/or may depress stearoyl-CoA desaturase expression or activity in lean tissues, which in turn limits CLA formation and accretion in tissues. Increasing dietary forage tended to increase 18:0, 18:2n-6, CLA, and 18:3n-3 (P < 0.15), suggesting that increased forage may mitigate toxic effects of PUFA on ruminal biohydrogenation, thereby increasing the pool of CLA and VA available for CLA formation and accretion in tissues. Short-term feeding of elevated SBO and forage levels can alter FA profiles in muscle tissues.

Animal Feed↗
PubMed1993

Milk yield, intake, and blood traits of lactating cows fed grass silage conserved under different harvesting methods.

Thirty-two Holstein cows (8 primiparous) were assigned to negative control or to one of three treatments to assess three forage harvesting and conservation techniques. Forage was harvested as low moisture silage by either a cylinder-type forage harvester, a self-loading forage harvester, or a round baler. Treatment diets were fed from wk 4 to 15 of lactation and consisted of silages harvested by the respective methods supplemented with concentrate at 1.1% of BW. Unsupplemented silage harvested by a cylinder-type forage harvester was used as a control. Daily DMI was higher for cows fed supplemented heap silage cut with either a cylinder-type forage harvester (23.7 kg) or a self-loading forage harvester (22.6 kg) than for cows fed the control (20.0 kg) or supplemented round bale silage (20.1 kg). Milk yield was highest for cows fed supplemented heap silage cut with a cylinder-type forage harvester (26.6 kg/d) and lower for those fed supplemented heap silage cut with a self-loading forage harvester (22.7 kg/d) or the control (20.8 kg/d). Milk composition and digestibilities of DM, N, ADF, and energy were similar among treatments. Postfeeding NEFA concentration decreased more for control cows than for those fed supplemented silage, which was related to greater BW loss. The high milk yield for cows fed supplemented heap silage cut with a cylinder-type forage harvester could be related to a high DMI and low BW gain.

Animal Nutritional Physiological Phenomena↗
PubMed2003

Recruitment of honeybees to non-scented food sources.

Small groups of honeybees (five to nine individuals) were trained to forage at feeders 150 m, 300 m and 800 m from an observation hive. Their behaviour in the hive and at the feeder was recorded by observers that maintained continuous radio contact with one another. At low concentrations of sugar in the feeder (0.5 mol x l(-1)) foragers do not dance in the hives, their flights to the feeder are often undertaken alone, they land immediately after arrival at the site and no recruits from the hive landed on the feeder during 30 h of observation. Raising the concentration of sugar in the feeder to 2 mol x l(-1) leads to vigorous dancing by the foragers and the gradual (over 10-15 min) synchronisation of their flights so that they arrive in groups of up to five bees at the feeder and undertake circular "buzzing" flights before landing. Such behaviour of the foragers is associated with the appearance of recruits which were never seen to fly around the feeder and land alone or before the foragers. Recruits typically circle the feeder together with foragers and land with them or continue their circling flights to land about 10 s later. While circling the feeder recruits, but not foragers, will fly after a moving lure if the presentation of the lure is accompanied by the release of geraniol scent. We propose that recruits that have witnessed a waggle dance are unlikely to find a non-scented feeder unless the foragers continue their flights to that feeder and provide supplementary visual and/or olfactory cues, at least in the vicinity of the feeder. We propose that the synchronisation of the flights of foragers and their behaviour at the feeding site is a strategy designed to overcome a navigational gap in the recruiting process in which the dance can indicate the general area of a food source but not the precise position of a highly localised site.

Adaptation, Physiological↗
PubMed2001

Octopamine influences division of labor in honey bee colonies.

Forager honey bees have higher brain levels of octopamine than do bees tending larvae in the hive. To test the hypothesis that octopamine influences honey bee division of labor we treated bees orally with octopamine or its immediate precursor tyramine and determined whether these treatments increased the probability of initiating foraging. Octopamine treatment significantly elevated levels of octopamine in the brain and caused a significant dose-dependent increase in the number of new foragers. This effect was seen for precocious foragers in single-cohort colonies and foragers in larger colonies with more typical age demographies. Tyramine treatment did not increase the number of new foragers, suggesting that octopamine was exerting a specific effect. Octopamine treatment was effective only when given to bees old enough to forage, i.e., older than 4 days of age. Treatment when bees were 1-3 days of age did not cause a significant increase in the number of new foragers when the bees reached the minimal foraging age. These results demonstrate that octopamine influences division of labor in honey bee colonies. We speculate that octopamine is acting in this context as a neuromodulator.

Adrenergic alpha-Agonists↗
PubMed2005

Impacts of simulated livestock grazing on Utah prairie dogs (Cynomys parvidens) in a low productivity ecosystem.

Allometric foraging theory suggests that herbivores of greatly differing size should co-exist through niche segregation, but a few studies of large-small herbivore foraging relationships have reported competitive interactions. This study addresses the potential roles of habitat productivity and large herbivore grazing intensities on large-small herbivore foraging interactions. We examined effects of different intensity simulated grazing treatments on forage abundance and quality for Utah prairie dogs (Cynomys parvidens) in a low productivity ecosystem, and consequent effects on prairie dog individual growth rates, foraging preferences, and activity budgets. We hypothesized that simulated grazing would have predominantly facilitative impacts on Utah prairie dogs, as was found for black-tailed prairie dogs in higher productivity ecosystems. To test this hypothesis, we measured the effects of simulated grazing on forage nitrogen, digestibility, and biomass. Simulated grazing increased average forage nitrogen and digestibility while decreasing forage biomass. These effects were associated with reduced individual growth rates, increased juvenile foraging time, and reduced juvenile vigilance. Results suggest that the negative effects of reduced vegetation biomass greatly outweighed positive treatment effects in this study. However, prairie dogs in the moderate intensity defoliation treatment showed some preference for "grazed" plots over "ungrazed" plots, and this preference increased with time. Our study lends support to the idea that habitat productivity and herbivore densities may mediate shifts between facilitative and competitive interactions between different-sized herbivores.

Animals↗
PubMed2003

Yield and nutritive quality of sericea lespedeza (Lespedeza cuneata) and little bluestem (Schizachyrium scoparium) exposed to ground-level ozone.

Sericea lespedeza (Lespedeza cuneata cv. Interstate 76) and little bluestem (Schizachyrium scoparium cv. Aldous) were raised from seed in a glasshouse, transplanted into 5.7-l pots and placed into open-top chambers (OTC) on 6 June 1999. Following a 7-day adjustment period, each of six OTCs (duplicate OTCs per treatment) was ventilated with either air that had been carbon-filtered (CF) to remove ambient ozone (O3); non-filtered (NF), representative of ambient air; or enriched to twice-ambient O3 concentration (2X). Primary-growth forage was harvested on days 7, 32, 46, 59 and 72 following the start of fumigation, and regrowth forage from the first primary-growth harvest was harvested on days 36, 54 and 72 following the start of fumigation. Dry matter (DM) yield of either forage species did not differ among treatments except in the final regrowth period when yield of sericea lespedeza was greater for the NF than 2X O3 treatment. In vitro DM digestibility (IVDMD) and concentrations of crude protein (CP), soluble phenolics (SP) and condensed tannins (CT) in primary-growth sericea lespedeza did not differ between treatments, but NF primary-growth forage had higher concentration of protein-precipitating tannins (PPT) than did 2X primary-growth forage. Concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were higher in NF and 2X than in CF primary-growth sericea lespedeza. Similarly, concentrations of NDF and ADL were higher, and IVDMD was lower for NF and 2X than for CF regrowth sericea lespedeza. Concentrations of ADF and ADL were lower, whereas IVDMD, in vitro NDF digestibility (IVNDFD) and concentrations of CP and SP were greater, in CF than in NF and 2X primary-growth little bluestem. Percentages IVDMD and IVNDFD and concentrations of CP and SP in NF primary-growth little bluestem were greater than those in forage exposed to 2X O3 treatment. No significant differences were observed among treatments in percentages IVDMD and IVNDFD, or concentrations of cell wall constituents or SP in little bluestem regrowth. Nutritive quality of little bluestem was decreased by < 2%, and that of sericea lespedeza by approximately 7% as a result of increased concentrations of cell wall constituents and decreased in vitro digestibility of NF and 2X compared with CF forages. Results indicate that existing and projected O3 levels can drive alterations in forage quality of select warm-season forages sufficient to have nutritional and economic implications for their utilization by ruminant herbivores.

Air Pollutants↗
PubMed1983

Rumen bacterial and fungal degradation of Digitaria pentzii grown with or without sulfur.

Sheep fed the forage Digitaria pentzii fertilized with sulfur were compared with those fed unfertilized forage for the rumen microbial population involved with fiber degradation. No differences were detected in the bacterial population as determined by anaerobic cultures on a habitat-simulating medium, xylan, or pectin, by 35S labeling techniques for microbial protein, or by transmission electron microscopic studies of bacterium-fiber interactions. Rumen volume and water flow from the rumen were not different for sheep fed each of the forages. Rumen fungi were prevalent in sheep fed sulfur-fertilized D. pentzii as shown by sporangia adhering to forage fiber and by colonies developing from zoospores in roll tubes with cellobiose plus streptomycin and penicillin. Fungi were absent or in extremely small numbers in sheep fed unfertilized forage. Nylon bag digestibility studies showed that the fungi preferentially colonized the lignified cells of blade sclerenchyma by 6 h and caused extensive degradation by 24 h. In the absence of bacteria in in vitro studies, extensive hyphal development occurred; other lignified tissues in blades (i.e., mestome sheath and xylem) were attacked, resulting in a residue with partially degraded and weakened cell walls. Nonlignified tissues were also degraded. Breaking force tests of leaf blades incubated in vitro with penicillin and streptomycin and rumen fluid from sheep fed sulfur-fertilized forage or within nylon bags in such sheep showed a residue at least twice as fragile as that from sheep fed unfertilized forage. In vitro tests for dry matter loss showed that rumen fungi, in the absence of actively growing bacteria, could remove about 62% of the forage material. The response of rumen fungi in sheep fed sulfur-fertilized D. pentzii afforded a useful in vivo test to study the role of these microbes in fiber degradation. Our data establish that rumen fungi can be significant degraders of fiber and further establish a unique role for them in attacking and weakening lignocellulosic tissues. The more fragile residues resulting from attack by fungi could explain the greater intake consistently observed by sheep eating sulfur-fertilized compared with unfertilized D. pentzii forage.

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