Apparent digestibility, fecal particle size, and mean retention time of reduced lignin alfalfa hay fed to horses

Reduced lignin alfalfa (Medicago sativa L.) has the potential to provide a higher quality forage source for livestock by improving forage digestibility. This study was conducted to evaluate apparent digestibility when feeding reduced lignin and non-reduced lignin alfalfa hay to adult horses, and to examine mean fecal particle size (MFPS) and mean retention time (MRT) between alfalfa forage types. In 2017, reduced lignin (‘54HVX41’) and non-reduced lignin (‘WL355.RR’) alfalfa hay was harvested in Minnesota at the late-bud stage. Alfalfa hays were similar in crude protein (CP; 199 g kg -1), neutral detergent fiber (NDF; 433 g kg -1), and digestible energy (DE; 2.4 Mcal kg -1). Acid detergent lignin (ADL) concentrations were lower for reduced lignin alfalfa hay (74 g kg -1) compared to non-reduced lignin alfalfa hay (81 g kg -1). Dietary treatments were fed to six adult, stock-type horses in a crossover study. Experimental periods consisted of a 9-d dietary adaptation phase followed by a 5-d total fecal collection phase, during which horses were housed in individual boxstalls and manure was removed on a continuous 24-h basis. At 12-h intervals, feces were thoroughly mixed, subsampled in duplicate, and used for apparent digestibility and MFPS analysis. On day 2 of the fecal collection phase, horses were fed two indigestible markers, cobalt (Co) and ytterbium (Yb), which were fed as Co-EDTA and Yb-labelled NDF residue, respectively. Additional fecal samples were taken at 2-h intervals following marker dosing until 96-h post-dosing to evaluate digesta MRT. Data was analyzed using the MIXED procedure of SAS, with statistical significance set at P ≤ 0.05. Dietary treatment (i.e., alfalfa hay type) was included as a fixed effect, while experimental period and horse were considered random effects. Dietary treatments were similar in dry matter intake (DMI; 1.6% BW) and time to consumption (TTC; 7.6 h). Apparent dry matter digestibility (DMD) was greater for reduced lignin alfalfa (64.4%) compared to non-reduced lignin alfalfa (61.7%). Apparent CP and NDF digestibility did not differ between dietary treatments, averaging 78% and 45%, respectively. Dietary treatments were similar in MFPS (0.89 mm) and MRT for both liquid (23.7 h) and solid (27.4 h) phase material. These results indicate an improvement in DMD for reduced lignin alfalfa hay when fed to adult horses, with no change in forage consumption, fecal particle size, or digesta retention time.

Effects of the Turbulent Schmidt Number on the Mass Exchange of a Vegetated Lateral Cavity

<p>Computational Fluid Dynamics (CFD) has been established as a relevant technique to investigate the qualitative and quantitative characteristics of complex environmental flows, such as transient storage zones. In numerical studies involving mass transport of solutes and sediment (e.g., mean retention time and mass exchange rate), one fundamental variable is the turbulent Schmidt number (Sct) which defines the ratio of momentum diffusivity to mass diffusivity in turbulent flows, and thus affects the concentration of solute within the solution impacting on the estimation of mass related variables. This is particularly important for transient storage zones, such as lateral cavities and groyne fields, as they are known for their role in nutrient retention and release, and sediment entrapment. This numerical study aims to examine the influence of the turbulent Schmidt number in the mean retention time and mass exchange rate between a channel and a vegetated/non-vegetated lateral cavity.</p><p> </p><p>The cavity was <em>L</em> = 0.25m long (x-axis), <em>W</em> = 0.15m wide (y-axis) and had a depth of <em>H</em> = 0.10m (z-axis). The aspect ratio between the width and the length resulted in 0.6 which corresponded to a single circulation system (Sukhodolov et al., 2002). The flow had a bulk velocity of <em>U</em> = 0.101 m/s that corresponds to a Reynolds number of 9000. The vegetation drag was represented by an anisotropic porous media calculated with the Darcy-Forchheimer model (Yamasaki et al., 2019), the vegetation density was constant at <em>a</em> = 0.1332%. Large Eddy Simulation (LES) was applied to define the flow field in that domain, using the Wall Adapting Local Eddy-viscosity (WALE) to account subgrid effects. A passive scalar was injected inside the lateral cavity to investigate its transport and diffusion in a range of Sct from 0.1 to 2.0. The numerical results of the flow field were validated using literature experimental data considering 3 different meshes to achieve mesh independence (Xiang et al., 2019).</p><p> </p><p>The effect of Sct variation was, then, analysed in both vegetated and non-vegetated scenarios, for a total of 40 different simulations. The volumetric average scalar concentration in the cavity was fitted into a first-order decay model <em>(C</em> = <em>C<sub>0</sub>.e<sup>-t/T<sub>D</sub></sup></em>), where <em>C<sub>0</sub> = 1</em> is the initial concentration, <em>t</em>  (s) is time and <em>T<sub>D</sub></em>  is the mean residence time. The mass exchange rate was defined as <em>k</em> = <em>W/(T<sub>D</sub>.U)</em> . Preliminary results showed in the vegetated scenarios a limited effect of Sct on the mass exchange rate, which varied from 1% if the Sct value was doubled.</p><p><strong>References</strong></p><p>Sukhodolov, A., Uijttewaal, W. S. J. and Engelhardt, C.: On the correspondence between morphological and hydrodynamical patterns of groyne fields, Earth Surf. Process. Landforms, 27(3), 289–305, doi:10.1002/esp.319, 2002.</p><p>Xiang, K., Yang, Z., Huai, W. and Ding, R.: Large eddy simulation of turbulent flow structure in a rectangular embayment zone with different population densities of vegetation, Environ. Sci. Pollut. Res., 26(14), 14583–14597, doi:10.1007/s11356-019-04709-x, 2019.</p><p>Yamasaki, T. N., de Lima, P. H. S., Silva, D. F., Preza, C. G. de A., Janzen, J. G. and Nepf, H. M.: From patch to channel scale: The evolution of emergent vegetation in a channel, Adv. Water Resour., doi:10.1016/j.advwatres.2019.05.009, 2019.</p>

Filling gaps in the seed dispersal effectiveness model for Prosopis flexuosa: quality of seed treatment in the digestive tract of native animals

For endozoochorous species, the quality component of seed dispersal effectiveness depends in part on the treatment seeds receive in the animal's gut. Covering a variety of taxa, diet, digestion system and body size of Prosopis flexuosa seed dispersers, we analysed differences among species in (1) mean retention time of ingested seeds, (2) recovery of viable seeds, (3) seed germination in comparison with seeds collected from trees and (4) germination of seeds after two different periods of retention in the gut. Feeding experiments were conducted with captive individuals of Dolichotis patagonum, Lycalopex gymnocercus, Rhea americana, Chelonoidis chilensis and Lama guanicoe. On the first day, we provided them with fruits containing controlled amounts of seed, and on the subsequent days, we collected faeces in order to recover seeds. We performed germination and viability tests on seeds coming from faeces and collected from trees. The results showed differences among species in the mean retention time of seeds. Chelonoidis chilensis had the longest mean retention time, but its effect on seed recovery and germination was similar to that of the other species, except for L. guanicoe, which showed the lowest seed recovery. When scarification and promotion of seed germination were considered, herbivorous mammals and tortoises (L. guanicoe, D. patagonum and C. chilensis) were the ones increasing germinability, whereas R. americana and L. gymnocercus did not significantly increase final seed germination percentage, which was similar to that for seeds collected from trees. P. flexuosa seeds receive a variety of treatments from endozoochorous dispersers, which might result in an overall fitness benefit for a plant living in unpredictable environments.

Body weight and sex effects on digesta mean retention time in growing Saanen goats

Despite the important role of digesta mean retention time (MRT) on digestive efficiency of ruminants, it is poorly investigated in total gastrointestinal tract (GIT) of growing ruminants, especially in goats. The objective of this study was to evaluate the effect of body weight (BW) and sex on GIT MRT of particles and solutes in growing Saanen goats. A dataset from two studies, comprising 103 individual records of castrated males (n = 36), females (n = 34), and intact males (n = 33) Saanen goats slaughtered at 15, 22, 30, 37, and 45 kg BW, was used. Goats were fed basically with total mixed ration composed by dehydrated corn plant (Zea mays) milled to pass a 10-mm screen, cracked corn grain, and soybean (Glycine max) meal. Variables evaluated were BW, feed intake, feed intake level, composition of ingested diet, wet weight of GIT tissues, wet digesta pool size, digesta composition (dry matter and neutral detergent fiber [NDF]), indigestible NDF:NDF ratio of ingested diet and GIT digesta, MRT of particles (MRTiNDF) and solutes (MRTCr), and reticulorumen selectivity factors (large particles/solutes). Reticulorumen, omasum, abomasum, small intestine, cecum, and colon–rectum segments were evaluated. The dataset was analyzed as mixed models considering sex, BW, and sex × BW interaction as fixed effects, and study and residual error as random effects. Sex did not affect MRTiNDF in any GIT segments. Females and intact males presented similar reticulorumen MRTCr (5.6 h; P = 0.92) and they presented lower reticulorumen MRTCr than castrated males (7.0; P ≤ 0.04). Total GIT MRTCr was similar between castrated males and females (15.7 h; P = 0.11) and between females and intact males (14.2 h; P = 0.76). Body weight (BW) did not affect MRTiNDF in reticulorumen and colon–rectum and total GIT MRTCr (P ≥ 0.11). Reticulorumen and omasum MRTCr increased as BW increased (P < 0.01), and abomasum MRTCr decreased as BW increased (P = 0.02). Feed intake, and wet tissues and wet pool size of all GIT segments increased as BW increased, except abomasum wet pool size (P ≤ 0.01). The mechanism related to sex effect on MRT has to be elucidated. Reticulorumen MRTiNDF and total GIT MRTCr were modulated by intake and capacity of reticulorumen and GIT, respectively. On the other hand, reticulorumen MRTCr seemed to be regulated by reticulo-omasal orifice opening and saliva secretion.

Rumen parameters and passage rate in cattle fed diets based on sugarcane hydrolyzed with calcium oxide

Nine non-lactating Holstein x Gyr cattle were fed with rations based on chopped sugarcane supplied in natura (control) or hydrolyzed (fresh matter basis) for 24 h with 1% or 2% calcium oxide (CaO), which corresponds to 3.1% or 6.2% CaO on a dry matter (DM) basis, respectively. Ruminal parameters (pH and ammonia N, acetate, propionate and butyrate concentrations) as well as the kinetics of fluid and particulate passage in the gastrointestinal tract from cattle were evaluated. A design using three 3 x 3 contemporaneous Latin Squares (LS) was adopted. The studies of kinetics of fluid and particulate passage were performed using the external markers cobalt-EDTA and chromium-mordanted-NDF, respectively. The ruminal parameters were analyzed according to a 3 x 3 LS replicated three times with repeated measures in time using mixed models that included the fixed effects of treatment (level of CaO), time of sampling and their interaction and the following random effects: LS, animal(LS), period of LS and period*animal (LS). The kinetic parameters of fluid and particulate passage were analyzed using mixed models with treatment as a fixed effect and period of LS, animal(LS) and LS as random effects. The linear and quadratic effects of the treatments were analyzed using orthogonal contrasts. Significant differences were declared at P ? 0.05. No treatment*time interaction was observed (P > 0.05) for any ruminal parameter. A linear effect (P = 0.0279) of CaO inclusion on ruminal pH was observed, but there were no effects (P > 0.05) of the treatments on the ammonia N, acetate, butyrate and total volatile fatty acid ruminal concentrations. There was a quadratic effect (P = 0.05) of the addition of CaO on the ruminal propionate concentration. There was no effect (P > 0.05) of the treatments on the particulate rate of passage in the rumen as well as on the mean retention time in this compartment and in the total gastrointestinal tract. On the other hand, the addition of CaO to sugarcane promoted a linear increase (P = 0.0258) in the particulate post-ruminal passage rate and, consequently, a linear reduction (P = 0.0363) of the mean retention time in the cecum-proximal colon. There was no effect (P > 0.05) of the sugarcane hydrolysis with CaO on the ruminal parameters of the kinetics of fluid passage (dilution rate, retention time and turnover rate). The addition of 3.1% or 6.2% CaO on a DM basis (1% or 2% CaO on a fresh matter basis, respectively) of sugarcane does not improve ruminal fermentation, nor does it increase the fluid or particulate passage in the rumen of non-lactating Holstein x Gyr cattle.