A NOTE ON THE SUITABILITY OF THE IN VITRO DIGESTIBILITY TECHNIQUE FOR VERY SMALL PLANT SAMPLES

The two-stage in vitro digestibility technique was scaled down to use 0.1 g samples. The accuracy of predicting in vivo DM digestibility by the use of micro-samples was studied, using 35 samples of four grass species of known in vivo digestibility. When the sample size was reduced from the normal 0.5 g to 0.1 g, the residual standard deviation of the regression relating in vitro to in vivo DM digestibility was increased from ±2.5 to ±3.4 digestibility units. Grinding the samples more finely than through a 1.0 mm screen did not improve the accuracy of predicting in vivo digestibility. It was concluded that the in vitro method may be used with micro-samples where necessary, but with less accuracy than the macro-technique. For maximum accuracy, the use of standards of known in vivo digestibility is necessary.     

THE ERROR IN PREDICTING PASTURE DRY–MATTER DIGESTIBILITY FROM FOUR DIFFERENT METHODS OF ANALYSIS FOR LIGNIN

The lignin content of 50 samples of five grasses of known in vivo digestibility were determined by the methods of Armitage, van Soest and two modifications of the van Soest technique. The error in predicting DM digestibility varied from ±3.1 for tbe Armitage metbod to ±5.0 for the van Soest method. This error compares nnfavourably witb ±2.1 previonsly obtained on tbe same samples with the in vitro technique of Tilley and Terry.     

Effects of ruminal and postruminal infusion of starch hydrolysate or glucose on the microbial ecology of the gastrointestinal tract in growing steers

Forty crossbred steers were used to determine the effects of carbohydrate supply site on the indigenous bacteria of the gastrointestinal tract. Steers were fitted with ruminal and abomasal infusion catheters and assigned randomly to one of eight groups in a complete randomized block design. The experimental period was 36 d. Treatments included: 1) a pelleted basal diet fed at 0.163 Mcal ME x (kg BW(0.75)) x 1 x d(-1) (LE); 2) the basal diet fed at 0.215 Mcal ME x (kg BW(0.75)) (-1) x d(-1) (HE); 3) the basal diet fed at 0.163 Mcal ME x (kg BW(0.75))(-1) x d(-1) with ruminal infusion of starch hydrolysate (SH) (RSH); 4) the basal diet fed at 0.163 Mcal ME x (kg BW(0.75))(-1) x d(-1) with abomasal infusion of SH (ASH); and 5) the basal diet fed at 0.163 Mcal ME x (kg BW(0.75))(-1) x d(-1) with abomasal infusion of glucose (AG). The total volume ofinfusate (5 kg x site(-1) x d(-1)) was equalized across treatments and infusion sites by infusion of water. Glucose and SH were infused at rates of 14.35 and 12.64 g x (kg BW(0.75)) x d(-1), respectively. Ruminal, cecal, and fecal samples were obtained on d 36. Ruminal pH was low (5.79) in LE steers and unaffected (P > 0.10) by increased energy intake or carbohydrate infusion. Cecal and fecal pH were 6.93 and 7.00, respectively, for LE steers. Increasing energy intake (P < 0.10) and the rate of carbohydrate infusion (P < 0.01) significantly decreased cecal and fecal pH compared with LE. Ruminal counts of anaerobic bacteria in LE steers were 8.99 log10 cells/g and abomasal carbohydrate infusion had no affect (P > 0.10) on these numbers. However, ASH and AG steers had approximately 1.5 log10 cells/g more (P < 0.01) cecal and fecal anaerobic populations. Ruminal, cecal, and fecal aerobic bacterial counts were 40, 22, and 23%, respectively, lower than anaerobic counts. Generally, aerobic counts responded similarly to the anaerobic counts. Less than 1% of the anaerobic bacteria enumerated in the rumen, cecum, and feces were coliforms, and 97% of the coliforms were Escherichia coli. Carbohydrate infusions resulted in only numerical increases in fecal coliform and E. coli concentrations (P > 0.10). Fecal E. coli were highly acid sensitive in all steers, with less than 1% surviving a 1-h exposure to low pH (2.0). This suggests that cecal or fecal pH is not a good indicator of acid resistance, and it supports the concept that there are other factors that may induce acid resistance.     

Influence of chlortetracycline and dietary protein level on visceral organ mass of growing beef steers

Thirty-two beef steers (285 +/- 3 kg BW) were used to determine the effects of chlortetracycline and dietary protein level on visceral tissue mass, chemical composition, intestinal morphology, and proliferation rate indices. Steers were allotted randomly by weight to a factorial arrangement of dietary treatments consisting of either 10 or 13% CP diets top-dressed with a corn meal carrier (500 g/d) containing either 0 or 350 mg of chlortetracycline. After 84 d, steers were slaughtered and visceral organs removed and separated. Rinsed wet tissue mass was recorded; total RNA, total DNA, tissue DM, and tissue N content were determined; and tissue sections were prepared for immunohistochemical analysis. Thin tissue sections were evaluated to determine crypt depth and villus height as well as proliferation rate by immunohistochemical detection of the nuclear antigen Ki67. Rumen and abomasum weights and small intestinal length were greater (P < 0.04) in steers fed the 13% CP diet than in those fed the 10% CP diet on both an absolute weight basis and a percentage of empty BW. Chemical composition of the small intestinal and ruminal segments were largely unaffected by increased dietary protein. Increasing the dietary CP also increased the villus height in duodenal (P = 0.02) and the crypt depth of jejunal (P = 0.03) sections. Dietary administration of chlortetracycline decreased (P < 0.01) small intestinal weight both on absolute and empty BW bases. Nitrogen and RNA concentrations of the small intestinal segments were unaffected (P > 0.1) by dietary administration of subtherapeutic levels of chlortetracycline; however, because of increases (P < 0.05), or tendencies for an increase (P < 0.1), in the tissue content of DNA, the ratio of N to DNA was decreased (P < 0.05) or tended to be decreased (P < 0.1) in the small intestinal segments of the chlortetracycline-treated animals. The observed decrease in small intestinal epithelial mass does not appear to be due to alterations in cell proliferation rate but rather cell size. Consistent with this finding, cell proliferation, as determined by Ki67 antigen staining, was not affected by dietary treatment. Chlortetracycline administration decreased small intestinal mass that may be a result of decreased cell size.     

Potential Inoculum Sources of Phaeomoniella chlamydospora in South African Grapevine Nurseries

Petri disease of grapevine is primarily caused by Phaeomoniella chlamydospora. This pathogen affects mostly young grapevines, but is also implicated in esca disease of older grapevines. Little is known about the disease cycle of this fungus. Infected propagation material was identified as a major means of dissemination of the pathogen. Recently, the pathogen was also detected from soil in South Africa and airborne conidia have been found in vineyards. The aim of this study was to use a molecular detection technique to test different samples collected from nurseries in South Africa at different nursery stages for the presence of P. chlamydospora. A one-tube nested-PCR technique was optimised for detecting P. chlamydospora in DNA extracted from soil, water, callusing medium and grapevine wood. The one-tube nested-PCR was sensitive enough to detect as little as 1 fg of P. chlamydospora genomic DNA from water and 10 fg from wood, callusing medium and soil. PCR analyses of the different nursery samples revealed the presence of several putative 360 bp P. chlamydospora specific bands. Subsequent sequence analyses and/or restriction enzyme digestions of all 360 bp PCR bands confirmed that all bands were P. chlamydospora specific, except for five bands obtained from callusing media and one from water. Phaeomoniella chlamydospora was positively detected in 25% of rootstock cane sections collected from mother blocks, 42% of rootstock cuttings and 16% of scion cuttings collected during grafting, 40% of water samples collected after pre-storage hydration, 67% of water samples collected during grafting, 8% of callusing medium samples and 17% of soil samples collected from mother blocks. These media can therefore be considered as possible inoculum sources of the pathogen during the nursery stages.     

Modeling intra-crown and intra-canopy interactions in red maple: assessment of light transfer on carbon dioxide and water vapor exchange

Daily and seasonal net photosynthesis (Anet), transpiration (E), absorbed photosynthetically active radiation (Qa) and light-use efficiency (epsilonc) in a red maple container nursery were simulated with MAESTRA, a three-dimensional canopy model. Effects of canopy heterogeneity were simulated by imposing changes in crown spacing. The light transfer sub-model, a distribution model of incident, direct, diffuse and scattered radiation within MAESTRA, was validated against field measurements of light interception on an intra-crown scale. In the container nursery, we found that a fiber-optic-based method of integrating photosynthetically active radiation (Q) was more suitable for crown-layer light transfer measurements and adjustments than either orthogonal line or individual quantum sensor measurements. The model underestimated intercepted Q by 9.3, 18 and 11.1% for crown layers 1, 2 and 3, respectively; however, there were linear relationships between model estimates and observations made with each of the three measurement methods. We used the validated and parameterized light transfer model to assess intra-crown and intra-canopy light transfer on a layer, crown and canopy basis, and investigated effects of tree size ratio and tree spacing interactions on Anet, E, Qa and epsilonc in the container nursery. Heterogeneous crown and canopy photosynthesis were predicted to exceed values for a uniform canopy under space-limiting conditions. Tree size ratio had large effects on Anet, E, Qa and epsilonc when light to lower-canopy layers was limited by inadequate space between crowns. Increasing Qa at lower-crown layers had the largest impact on whole-crown and whole-canopy Anet, E, Qa and epsilonc. Increases in canopy productivity led to increased water use. Simulations of heterogeneous stands with adequate soil water indicated that light absorption is maximized under space-limiting conditions as a canopy crown moves toward heterogeneity. Nursery and plantation productivity per unit land area was optimized by tactical placement of trees of several sizes, but this was accompanied by increased canopy water use.     

The impact of dietary protein source on observed and predicted metabolizable energy of dry extruded dog foods

Fifty-five observations were used to determine the ME content of 8 foods containing different protein sources. The major protein sources tested included low-oligosaccharide whole soybeans; 2 low-oligosaccharide, low-phytate whole soybeans; 2 conventional soybean meals; low-ash poultry meal; low-oligosaccharide, low-phytate soybean meal; and conventional whole soybeans. The ME content of all foods ranged from 3,463 to 4,233 kcal/kg of DM. The first objective was to utilize the observed ME data and test the accuracy of the modified Atwater equation. In this study, the modified Atwater equation generally underpredicted ME compared with the observed ME (residual mean = 247 kcal/kg). The second objective was to use individual data to develop an equation, based on the chemical composition of the food, to predict the ME content of the foods. A multivariate regression analysis was used to predict ME content based on chemical composition. Five models were fitted to the data. Model 1 included CP, ether extract (EE), and crude fiber (CF). Because the foods varied in protein sources, and the ratio of total AA (TAA) to non-AA (NAA) CP ranged from 3.5:1 to 14.4:1, it was hypothesized that accounting for the proportion of TAA and NAA in CP would improve the fit of the model. Therefore, model 2 included TAA, NAA, EE, and CF. Defining CP in terms of TAA and NAA improved the r2 of the model from 0.46 to 0.79. Subsequently, models 3, 4, and 5 replaced the CF term with ADF, NDF, and hemicellulose (HEM). Model 3 included TAA, NAA, EE, and NDF. Model 4 included TAA, NAA, EE, ADF, and HEM. Model 5 included TAA, NAA, EE, and HEM. Defining dietary fiber in terms of HEM improved the r2 of model 2 from 0.79 to 0.81. Residual analysis suggested that replacing the CF term with HEM (model 5) improved the prediction of ME content. In contrast, defining fiber in terms of NDF (model 3) did not result in an improvement over model 2, whereas the ADF term (model 4) did not (P > 0.34) contribute to the overall model. Fractionating CP into TAA and NAA components further defined the chemical composition of the food. These data suggest that defining protein composition improves the accuracy of predicting the ME content of dog foods.