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PubMed1988

Choice and foraging: the effects of accessibility on acceptability.

Pigeons responded in a successive-encounters choice procedure in which accessibility of the less profitable of two outcomes varied either in terms of probability of encounter or search time to encounter (keeping search time to the more profitable outcome constant). When the less profitable outcome was made more probable its acceptance became more likely. However, when search time to encounter the less profitable outcome was shortened, its acceptance became less likely. Both results are consistent with the delay-reduction hypothesis and with an optimality model developed for application to the successive-encounters choice procedure.

Animals↗
PubMed1996

Residence time and choice in concurrent foraging schedules.

Five pigeons were trained on a concurrent-schedule analogue of the "some patches are empty" procedure. Two concurrently available alternatives were arranged on a single response key and were signaled by red and green keylights. A subject could travel between these alternatives by responding on a second yellow "switching" key. Following a changeover to a patch, there was a probability (p) that a single reinforcer would be available on that alternative for a response after a time determined by the value of lambda, a probability of reinforcement per second. The overall scheduling of reinforcers on the two alternatives was arranged nonindependently, and the available alternative was switched after each reinforcer. In Part 1 of the experiment, the probabilities of reinforcement, rho(red) and rho(green), were equal on the two alternatives, and the arranged arrival rates of reinforcers, lambda(red) and lambda(green), were varied across conditions. In Part 2, the reinforcer arrival times were arranged to be equal, and the reinforcer probabilities were varied across conditions. In Part 3, both parameters were varied. The results replicated those seen in studies that have investigated time allocation in a single patch: Both response and time allocation to an alternative increased with decreasing values of lambda and with increasing values of rho, and residence times were consistently greater than those that would maximize obtained reinforcer rates. Furthermore, both response- and time-allocation ratios undermatched mean reinforcer-arrival time and reinforcer-frequency ratios.

Journal Article↗
PubMed2006

Phosphorus and sediment loss in a catchment with winter forage grazing of cropland by dairy cattle.

The loss of phosphorus and sediment to surface waters can impair their quality. It was hypothesized that the practice of winter grazing dairy cattle on cropland of moderate slope (5-20%) would exacerbate the loss of P and suspended sediment (SS) from land to water. In a small (4.3 ha) catchment two flumes were installed, upstream and downstream of one field (about 2 ha) that had been cropped for 2 yr and grazed in winter (June-July) by dairy cattle. Flow proportional samples were taken and measured for dissolved reactive phosphorus (DRP), particulate phosphorus (PP), total phosphorus (TP), and SS. During the 2002 hydrologic year (March-February) loads of SS increased per hectare downstream (1449 kg ha(-1)) compared to upstream (880 kg ha(-1)). The same increase from upstream (873 kg ha(-1)) to downstream (969 kg ha(-1)) happened in 2003. However, while in 2003 TP increased downstream by 1.64 kg ha(-1) compared to upstream (0.24 kg ha(-1)), in 2002 an increase of only 0.006 kg ha(-1) at the downstream flume occurred compared to upstream (0.98 kg ha(-1)). Investigation of P transport pathways suggested that overland flow contributed <0.1 kg P ha(-1) to stream flow, 10 and 5% of TP load in 2002 and 2003, with the greater load in 2002 reflecting more rainfall in that year. The contribution to stream flow by subsurface flow was estimated at 0.3 kg P ha(-1). Stream bed sediments showed an increase in total P concentration in summer when no flow occurred due to the admission by the farmer of 10 cattle upstream of the cropped paddock in summer 2001-2002 and 20 cattle between the two flumes in 2003 to graze stream banks. This action was calculated to contribute via dung at least, the remaining P lost: about 0.5 kg P in 2002 and 1.0 kg P in 2003. Clearly, not allowing animals to "clear-up" stream banks is a priority if good surface water quality is to be achieved. Furthermore, compared to stock access the impact of winter grazing cropland on P losses was minimal, but SS load was increased by an average of 75%.

Animal Husbandry↗
PubMed1991

Relationships of body weight, forage composition, and corn supplementation to feed intake and digestion by Holstein steer calves consuming bermudagrass hay ad libitum.

Holstein steer calves (101 to 350 kg BW) consumed bermudagrass hay ad libitum without or with supplemental ground corn up to 1.0% of BW. As BW increased, total DMI increased quadratically (-2.459 + .05448 [BW]-.000073 [BW2] + .540 [corn DMI]; R2 = .83, sy.x = .655). Each kilogram of corn DM decreased bermudagrass DMI by .46 kg. Total digestible OM intake (kg) increased with BW and corn supplementation (.314 + .0127 [BW] + .441 [corn OM intake]; R2 = .79, sy.x = .444). Feed intake level accounted for approximately 2.5 times more variability in total digestible OM intake than digestion did. Corn supplementation decreased digestion of bermudagrass NDF (62.50 - 8.468 [corn DMI, % BW]; R2 = .13, sy.x = 8.121), with a similar decrease across BW. Increasing bermudagrass DMI (% of BW) decreased bermudagrass NDF digestion slightly, but variation accounted for was only 33% of that attributable to corn DMI (% of BW). Concentrations of common fiber fractions (NDF, ADF, cellulose, hemicellulose, and ADL) in bermudagrass explained very little variation in feed intake and digestion, indicating considerable influence of other factors. Bermudagrass intake and digestion were not related, and no substantial interactions were observed among steer BW, corn level, and bermudagrass composition.

Animal Feed↗
PubMed1991

Image analysis and nonlinear modeling to determine dimensions of wet-sieved, masticated forage particles.

A procedure to estimate dimensions of digesta particles was developed and evaluated. After wet sieving, particles of masticated switchgrass and bermudagrass hays retained on sieves with apertures of 1.0 mm2 or larger were placed on moist white filter paper, separated manually, and photographed. Photographs were scanned with a flat-bed scanner, scaled to size, and digitized. Projected area, perimeter, length, and width of particles were determined by a microcomputer system. Variables derived for each particle included the form factor, which was defined as (4 x pi x area)/perimeter2, and each particle's length: width ratio. Ninety-three percent of data from two trials with steers had significant lack of fit (P less than .05 to P less than .0001) to normal, lognormal, Weibull, or gamma distributions. As an alternative, individual particle measurements were summed on a cumulative percentage basis for each variable and were fit to an inverted Gompertz function to estimate median, mode, and mean dimensions of scanned particles. Estimates from the equation fit the distribution well; asymptotic SE averaged 3.5 and 1.4% of parameter means for dimensions of masticated switchgrass and bermudagrass hay particles, respectively. No analytic solution exists for the mean, which must be estimated numerically, but analytic solutions are available for the median and mode. Use of this equation will prevent bias caused by lack of fit to a particular distribution and yield more accurate estimates of mean particle dimensions than arithmetic means.

Animal Feed↗
PubMed1993

Influence of forage species and diet particle size on the passage of digesta and nylon particles from the reticulorumen of steers.

To assess factors that influence the passage of digesta from the reticulorumen, ruminally fistulated steers (387 kg) were fed to appetite in a 4 x 4 Latin square design either orchardgrass (OG) (Dactylis glomerata L.) or switchgrass (SG) (Panicum virgatum L.) hays. The two hays were fed in either the long form or ground to pass a 2-cm screen. Steers fed OG diets had greater DMI (P < .05) than steers fed SG diets (11.7 vs 10.4 kg/d respectively). Particle size of ruminal digesta and feces determined by wet sieving was greater (P < .05) for the OG and long hay diets than for the SG and ground diets. Particle size of digesta collected from the anterior dorsal sac and anterior ventral sac of the rumen and from the reticulum did not vary (P > .25) with site. Conversely, ruminal concentrations of 1-mm nylon particles tended (P = .11) to be greater in the lower strata of the reticulorumen at 12 and 24 h after dosing. Neither a site effect nor a site x time-after-dosing interaction (P > .75) was observed for the 3- or 5-mm nylon particles, suggesting that a sorting process independent of specific gravity occurs in the rumen for smaller particles (before the reticulomasal orifice). Passage rate of the 1-mm nylon particles from the reticulorumen was greater (P < .01) for animals fed the SG than for those fed the OG diets, whereas for the 5-mm particles, passage rate was greater for the OG diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1993

Carcass and meat sensory traits of steers finished on fescue and clover, summer forage, or for different periods in drylot.

During a 3-yr period 184 steers were allotted to five treatment groups. Group 1 steers were pastured on fescue-clover and slaughtered in the spring at approximately 540 d of age. Group 2 steers were pastured on fescue-clover then placed on summer pasture regimens and slaughtered at approximately 620 d of age. Group 3 steers were treated the same as Group 2 then placed in the drylot for 45 d. Group 4 steers were treated the same as Group 2 steers then placed in the drylot for 75 d. Group 5 steers were placed in drylot after weaning and conditioning and were slaughtered at endpoints that corresponded with those for Group 3. Steers selected for slaughter at each endpoint were those evaluated to have reached the most optimum slaughter weight and finish by project personnel. Carcasses of steers from fescue-clover and summer pasture had lower yield grades and a lower quality grade than carcasses of steers from drylot (P < .05). Carcasses of steers from fescue-clover and summer pasture had a more yellow fat covering than carcasses of steers that received a concentrate (Treatments 3, 4, and 5, P < .0001). Fescue-clover- and summer pasture-fed steers had a higher percentage of lean and a lower percentage of fat in the 9-10-11th rib section than did steers that received concentrate (P < .005). Chemical analysis of the lean tissue of the 9-10-11th rib section indicated that summer pasture-fed steers had a lower percentage of ether extract and higher percentage of moisture than the lean tissue from steers that received concentrate (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1994

Effect of the addition of live yeast (Saccharomyces cerevisiae) on growth and carcass quality of steers fed high-forage or high-grain diets and on feed digestibility and in situ degradability.

The effects of adding yeast culture (Saccharomyces cerevisiae, 5 x 10(9) live organisms/g of growth medium) at 10 g/steer daily to three diets consisting of 75% alfalfa silage and 25% barley, 96% corn silage and 4.0% soybean meal, or 75% dry-rolled barley and 25% alfalfa hay on performance of growing and finishing steers and carcass characteristics, feed digestibility, and degradability in the rumen were determined. In separate trials over 2 yr, the performance of steers fed the three diets with no supplementary live yeast (control; C) or with live yeast (Y) was determined using 72 Hereford steer calves in eight pens each year in a randomized complete block design. The diets were fed sequentially and the steers were randomized before diets were switched. Each year at the end of the high-grain feeding segment of the trial, the steers were slaughtered when ultrasound backfat was such that the carcass would grade A1 or A2 (Canadian grades). The digestibility of feed DM, CP, and NDF of the three diets was determined sequentially using six and eight mature, ruminally cannulated steers in 2 yr, respectively. The degradation characteristics of the three diets in the rumen were determined using the nylon bag technique in two steers for each additive treatment. In the 1st yr, the feed efficiency of the corn silage diet was lower (P < .05) for C than for Y steers (5.9 vs 6.8). Differences (P < .05) were not observed between C and Y steers for any of the performance or carcass characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1994

Effect of intraruminal propionic acid infusion on metabolism of mesenteric- and portal-drained viscera in growing steers fed a forage diet: I. Volatile fatty acids, glucose, and lactate.

This experiment investigated the effect of intraruminal infusion of propionic acid on ruminal VFA metabolism and the absorption of nutrients by the mesenteric- and portal-drained viscera of seven Friesian steers, average BW 127 kg, fed a dried grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d for 7 d. Ruminal acetate and propionate irreversible loss rates and carbon exchange between VFA and CO2 were measured during continuous intraruminal infusions of 2-14C-acetic acid and 2-14C-propionic acid. Ruminal acetate irreversible loss rate was not affected by propionic acid infusion (overall mean 8.09, error mean square [EMS] 2.68 mol/d), whereas propionate irreversible loss increased incrementally with PA supply (3.22 vs 4.16, EMS .61 mol/d, for control and 1.0 mol of propionic acid/d, respectively, P = .09). Glucose irreversible loss rate was increased at the highest level of PA infusion (2.84, 2.83, and 3.22, EMS .06 mol/d, for control, .5, and 1.0 mol of propionic acid/d, respectively; P = .02 for control vs .5 + 1.0), although the proportion of glucose irreversible loss derived from propionate remained constant (.6). Net absorption into venous blood showed that propionate was extensively metabolized in the rumen wall and that the tissues of the small intestine utilized acetate. Utilization of glucose was reduced in portal tissues as a result of intraruminal infusion, and the data were used to derive a model of glucose and lactate interrelationships in gut tissues.

Absorption↗
PubMed1995

A collaborative study of in situ forage protein degradation.

An in situ procedure was used in four collaborative trials to evaluate the variation in estimates of ruminal escape protein among eight laboratories. A standard smooth bromegrass hay was established and evaluated in all four trials, and Trials 3 and 4 also included the standard hay material that was retained on a 75-microns sieve. Polyester bags (10 cm x 20 cm) containing 5 g of sample were soaked in water (39 degrees C) for 20 min and incubated ruminally for 16 h in a bag made of mesh material. Bag rinsing after in situ incubation consisted of a primary phase in which the mesh bags containing sample bags were washed with water (39 degrees C) in 19-L white plastic buckets. Repeated cycles of filling, agitating, and dumping were performed until the rinse water was clear. Secondary rinsing was performed on individual bags by rinsing the exterior with water (39 degrees C) followed by rinsing through the unsealed opening the interior residue to the bottom of the bag for 1 min (Trials 1 and 2). Secondary rinsing for Trials 3 and 4 was the same as for Trial 1, but with only enough water (39 degrees C) and time to rinse the residue to the bag bottom. Mean estimates of escape protein (EP/CP) were: Trial 1, 27.4 +/- 3.08; Trial 2, 30.8 +/- 3.21; Trial 3, 31.1 +/- 3.04 (non-sieved); and Trial 4, 27.7 +/- 3.06 (non-sieved). Reasonable control of error was accomplished by technician training, including the use of a videotape to clarify the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1995

Influence of altering ruminal degradation of soybean meal protein on in situ ruminal fiber disappearance of forages and fibrous byproducts.

The objective was to determine the effects of altering ruminal CP degradation of soybean meal (SBM) by roasting (Exp. 1) on ruminal characteristics and extents of in situ disappearance of DM, OM, and fiber components (Exp. 2). A control diet (8.2% CP) containing oat hulls, corn silage, starch grits, ammoniated corn cobs, and molasses was supplemented to 17.1% CP with unroasted SBM (SBM-0) or SBM roasted at 165 degrees C for 75, 150, or 210 min (SBM-75, SBM-150, and SBM-210, respectively). In Exp. 1, SBM was incubated for 0, 2, 4, 8, 12, 16, and 24 h in the rumen of two steers that were fed the SBM-0 diet. Extents of ruminal CP degradation and rates of N disappearance decreased (P < .05) linearly with increasing roasting time of SBM. In Exp. 2, five ruminally cannulated steers were used in a 5 x 5 Latin square design and were fed the five diets listed above during five 11-d periods. On d 11, five substrates (alfalfa hay, orchardgrass hay, corn silage, soy hulls, and wheat straw) were incubated in the rumen for 24 h. Extents of in situ disappearance of DM, OM, and fiber (NDF, ADF, cellulose, hemicellulose, and total dietary fiber) were analyzed as a split-plot design. No substrate x diet interaction (P > .05) was observed for any of the measurements evaluated. Extents of in situ disappearance (24 h) of DM, OM, and fiber were highest (P < .05) when the control diet was fed and were lowest (P < .05) when the SBM-0 diet was fed. Decreasing the availability of SBM protein in the diet by roasting increased (P < or = .10) extents of in situ disappearance of DM, OM, and fiber linearly. These extents were similar for steers fed the control diet or the diet containing SBM-210. Ruminal concentrations of NH3 N, branched-chain VFA, and valerate were highest (P < .05) and ruminal pH lowest (P < .05) when the SBM-0 diet was fed. Results indicated a rapid ruminal fermentation of both protein and readily available carbohydrates of SBM (resulting in pH below 6.0) during the first 4.5 h after feeding the SBM-0 diet. Making both protein and readily available carbohydrates of SBM more slowly fermentable by roasting slowed early fermentation processes, maintained higher ruminal pH, and encouraged earlier and faster ruminal fiber digestion.

Animal Feed↗
PubMed1996

Effect of intraruminal propionic acid infusion on metabolism of mesenteric- and portal-drained viscera in growing steers fed a forage diet: II. Ammonia, urea, amino acids, and peptides.

This experiment investigated the effect of intraruminal infusion of propionic acid on the net flux of nitrogenous compounds across the mesenteric- (MDV) and portal-(PDV) drained viscera of seven Friesian steers, average BW 127 kg (SEM 4.6), fed a grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d for 7 d. Blood flow in mesenteric and portal veins was determined by downstream dilution of p-aminohippuric acid in order to determine net appearance rates across the gastrointestinal tissues. Net urea and ammonia flux was unaffected by propionic acid supply. Circulating plasma free amino acid concentrations were increased (P < .05) by propionic acid infusion (2,235, 2,428, and 2,427, error mean square [EMS] 44,370 microM, for control, .5, and 1.0 mol of propionic acid/d, respectively). Net amino acid flux rates were increased at the highest rate of propionic acid infusion across MDV and PDV (4.66, 3.69, and 6.11, EMS 2.98 mol/d for MDV [P < .05] and 2.98, 2.45, and 3.73, EMS 1.69 mol/d for PDV [P < .10] for control, .5, and 1.0 mol of propionic acid/d respectively). Positive venous-arterio concentration differences for peptide-bound amino acids (PBAA) across the MDV and PDV indicated net appearance across the gastrointestinal tissues, but this was not affected by propionic acid infusion. The data show that amino acid flux across postruminal tissues can be influenced by ruminal propionic acid supply and that this does not affect PBAA appearance.

Amino Acids↗
PubMed1998

How readily will sheep walk for a preferred forage?

We studied how ewes chose between a poor-quality hay freely available and a good-quality one offered in limited quantities when they walked across an indoor test area. To determine what dictates a ewe's behavior, we varied the accessibility of the good hay by changing the quantity that rewarded the walk (2, 4, 8, 16, or 32 g) and the distance walked (23 or 46 m). Ewes were more reluctant to walk for the good hay as reward level decreased. For a given reward, average preference for good hay (P(GH)) also fell when ewes had to walk 46 m to be rewarded. In each comparison, for the same reward to distance (Rew/Dist) ratio, average P(GH) did not differ. We determined the correlation between P(GH) and Rew/Dist using data from three experiments with ewes offered a similar choice. The best model accounted for 85% of the corrected total sum of squares. Good hay procurement cost thus dictated a ewe's behavior. Choice was suboptimal only, either due to the test conditions, discrimination errors, or an animal's will to select a mixed diet. Our results suggest that, within its perceptive field, a ewe will equally walk to resources that have the same edible biomass relative to the distance to the patch.

Animal Feed↗
PubMed1999

Ruminally undegraded intake protein in sheep fed low-quality forage: effect on weight, growth, cell proliferation, and morphology of visceral organs.

To determine the influence of increasing levels of supplemental ruminally undegraded intake protein (UIP) on visceral organ weights, growth, cell proliferation, and morphology, 20 mature ewes of mixed breeding were fed a 6.55% CP grass hay:straw mixture (40:60) and assigned to one of four supplemental treatments. Supplements were control (no supplement) and low, medium, and high levels of UIP. After 42 to 46 d on treatment, ewes were infused i.v. with 5-bromo-2-deoxy-uridine (BrdU, a thymidine analog used to provide an index of the rate of intestinal cell proliferation) and slaughtered 1 h later. Visceral organs were weighed, and subsamples were obtained to evaluate visceral DNA, RNA, and protein contents (frozen samples) as well as intestinal morphology (fixed samples). Final BW; eviscerated BW (EBW); total visceral weight; and liver fresh, dry, and dry fat-free weights were increased (P<.10) in protein-supplemented ewes compared with controls, but were not influenced by increasing levels of UIP. Tissue weights of duodenum, jejunum, ileum, cecum, and colon were not greatly influenced by treatment. There were no differences among treatments in intestinal DNA and protein concentrations and the ratios RNA:DNA and protein:DNA. Jejunal RNA concentration and content was increased (P<.10) in low compared with medium and high treatments. Jejunal RNA content also was decreased (P<.10) in high compared with the medium UIP treatment. Liver RNA and protein contents were increased (P<.10) with protein supplementation. In contrast, contents of RNA, DNA, and protein in duodenum, ileum, cecum, and colon were not influenced by treatment. In addition, neither the rate of intestinal proliferation (BrdU labeling) nor intestinal morphology (crypt depth, villus length, or villus width) were affected by treatment. These data indicate that the influence of protein supplementation on visceral growth involves primarily the liver and not the intestines. These data also indicate that visceral growth, except in jejunum, are not altered by differing levels of UIP supplementation.

Animal Feed↗