Effect of fiber content and particle size of alfalfa silage on performance and chewing behavior.

A low NDF drought-stressed 1988 alfalfa silage (32.6% NDF) and a higher fiber 1988 alfalfa silage (46.4% NDF) were fed to lactating cows to evaluate effects on feed intake, fat test, and chewing behavior. Two groups of Holstein cows, 16 primiparous housed in tie stalls and 16 multiparous in free stalls, were assigned to diets based on parity and milk yield. The low NDF silage was fed for 6 wk in a TMR with 21.5% NDF and was compared with a TMR with 31.9% NDF. During an additional 4-wk period, one-half of each dietary group was fed a ration in which one-half of each silage was rechopped to reduce particle size. All rations contained a 1:1 ratio of forages to concentrates (DM basis) and were fed for ad libitum intake. Diets with 21.5% NDF and reduced particle size had no influence on milk fat percentage, 4% FCM yield, or plasma glucose. Cows fed these diets had reduced chewing time, due largely to decreased rumination time. Rumination and total chewing times per unit DMI and FCM also were lowest on these diets. Intake of DM on a BW basis was lowest for cows fed the low NDF rechopped silage diet. Cows fed in tie stalls had more eating bouts than those in free stalls, but total eating times were similar. Sufficient amounts of effective fiber appeared to be present in low NDF and rechopped silage diets to prevent the systemic events leading to milk fat depression but not to prevent a reduction in chewing time.

Determining pore size distribution in wet cellulose by measuring solute exclusion using a differential refractometer.

Solute exclusion was used to determine the pore volume and micropore size distribution of wet cellulosic materials. Glucose, cellobiose, and polyethylene glycol (PEG) (8 to 130 A in diameter) were used as molecular probes. Four replicates of cellulosic samples, with each sample being analyzed 4 to 8 times, gave the concentrations of each molecular probe before and after contact with cellulose. Sugar concentrations were determined by the DNS method and PEG concentrations by a differential refractometer. Deviations arising from sample-to-sample variability result in variations of solute uptake from which the pore size distribution was determined. The need for replicate samples and a statistical approach to data analysis is indicated. Consequently, the data were fitted to an empirical logistic model function based on the minimum of the residual sum of squares using the finite-difference, Levenberg-Marquardt algorithm. A smooth increasing function resulted. We report experimental methodology employing a differential refractometer, common in many laboratories having a liquid chromato-graph instrument, combined with statistical treatment of the data. This method may also find application in determining pore size distribution in wet, hydrophilic polymers used in some types of membranes, chromatographic supports, and gel-type resins.

Effect of pretreatments and fermentation on pore size in cellulosic materials.

Surface area has been proposed as a major factor determining the extent of enzymatic hydrolysis of cellulose. We used cornstalk residue (CR) and Solka Floc BW-300 (SF) as substrates and NaOH (a cellulose swelling agent) and iron sodium tartrate (FeTNa, intercolates between cellulose microfibrils) as pretreatments to study the effect of surface area on extent of fermentation. Micropore sizes (8-130 A) were determined by a solute exclusion technique using glucose, cellobiose, and polyethylene glycols as molecular probes. The pore size distributions follow the logistic model function: I = a/[1+exp(b - cX)] where I is pore volume; X = log D; D is the molecular probe diameter; and a, b, and c are constants. The pore volumes of CR (1.9 mL/g) and SF (1.6 mL/g) are increased to 2.1 mL/g by pretreatment with NaOH. Pretreatment of SF with NaOH and cornstalk residue with FeTNa caused an upward shift in the pore size distribution. Fermentation of untreated CR by rumen microbes resulted in a 46% loss of dry matter while increasing the internal pore size and decreasing the pore volume to 0.9 mL/g. Fermentation of NaOH pretreated CR resulted in a 73% loss of dry matter with little change in pore size, total pore volume, or fiber composition. Fiber analysis indicated that selective utilization of hemicellulose over cellulose in both fermentations was small. The data show that: (1) removal of hemicellulose and lignin increases dry matter disappearance upon fermentation of the remaining material; (2) relative to the size of bacterial cellulases (40-160 A), the pretreatments have little effect on increasing accessibility of surface internal to the cellulose particles; and (3) the micropore changes caused by NaOH or FeTNa treatment do not explain the enchanced fermentation obtained for treated cornstalk residue. These observations infer that external or macropore surface properties may be a significant factor in determining the extent of utilization of the solid substrates by cellulolytic microorganisms.

Characterization of limestones and their effects in vitro and in vivo in dairy cattle.

Capacities of limestones of differing particle size to neutralize acid in vitro and to modify pH and utilization of feedstuffs in vivo were compared. Acid neutralization during pH-stat titrations was faster for fine than for coarse limestone, and mixed microbial cultures were more resistant to pH change when they contained fine calcium carbonate. Diets containing 25:75 corn silage to concentrates and .95% calcium from either coarse or fine limestone were fed to rumen-fistulated heifers. Total ruminal volatile fatty acid concentrations were higher for the fine limestone treatment. Ruminal volumes, dry matter disappearance, and ruminal fluid pH and dilution rate did not differ between fine and coarse limestone treatments. Ruminal fluid volume, osmolality, ratios of acetate to propionate, and concentrations of total volatile fatty acids were unaffected in rumen-fistulated Holstein cows fed 60:40 corn silage to concentrates and either .5% calcium (control) or 1.0% calcium from either coarse or fine limestone. Ruminal pH increased .07 to .10 units with limestone supplementation. Ruminal fluid dilution and particulate turnover rates were slower for the coarse limestone than the control treatment. Differences between coarse and fine limestones in vitro were observed under some conditions in vivo, but they were not consistent.

Neutralization of acid in the rumen by magnesium oxide and magnesium carbonate.

Two reagent and two feed grade magnesium oxides and reagent grade magnesium carbonate, sodium bicarbonate, and calcium carbonate were evaluated to ascertain their ability to neutralize acid in the rumen. Rumen fluid pH was increased in vitro, compared to the control, by antacid compounds, and their increased ranked: calcium carbonate less than feed grade magnesium oxide A less than light magnesium oxide and feed grade magnesium oxide B less than heavy magnesium oxide less than magnesium carbonate less than sodium bicarbonate. Titrations at constant pH's ranging from 3.0 to 7.5 indicated that these magnesium compounds were reactive at pH's normally in the rumen although reactivity decreased with increasing pH. Intraruminal doses of feed grade magnesium oxide A and calcium carbonate did not change rumen fluid pH for other compounds ranked: feed grade magnesium oxide B less than magnesium carbonate less than heavy magnesium oxide. Feeding of heavy magnesium oxide or magnesium carbonate increased rumen fluid pH as compared to the control diet. Feeding feed grade magnesium oxide B in three quantities to cattle resulted in proportional increased in fecal pH and fluidity of feces. Two feed grade magnesium oxides differed in their ability to neutralize acid in the rumen.

Influence of dietary calcium and protein on fecal pH, consistency, and rate of passage in dairy cattle.

Sixteen Holstein heifers and 20 calves were in trials on the effect of 10 and 15% crude protein and .3 and .9% calcium in the diet on fecal pH and consistency and on rate of passage of the liquid phase of digesta. Time of first appearance of polyethylene glycol was an indicator of rate of passage of the liquid phase in the lower tract of the animal. Respective fecal pH and standard errors for heifers and calves increased from 5.79 +/- .03 and 5.78 +/- .03 on low calcium diets to 6.24 +/- .03 and 6.33 +/- .03 on high calcium diets. High protein diets increased fecal pH from 5.89 +/- .03 and 5.97 +/- .03 to 6.13 +/- .03 and 6.14 +/- .03 for heifers and calves. Effects of calcium and protein were additive. Neither dietary protein nor calcium affected consistency of feces or first appearance of polyethylene glycol in feces. Mean first appearances of PEG in feces were 683 +/- 13 min for heifers and 528 +/- 18 min for calves. Small correlations between fecal pH and fecal consistency and between fecal pH and first appearance of polyethylene glycol in feces indicate little or no relationship of fecal pH to these two variables. From variance in the heifer trial, 10 fecal samples are required to estimate fecal pH within +/-.16 pH units with 95% confidence.

Effect of forage-to-concentrate ratio in complete feeds and feed intake on digestion of starch by dairy cows.

In digestion trials, 16 Holstein cows were fed complete mixed feeds of (a) 75:25, (b) 60:40, (c) 45:55, and (d) 30:70 ratios of forage to concentrate on a dry basis. At an intake of feed for maintenance, digestibility of starch ranged from 96.2 to 96.8%. During the lactation phase when intakes of feed were 2.5 to 3.2 times maintenance, digestibility of starch ranged from 84.7 to 88.1%. Starch in feces represented 2.9, 3.7, 5.5, and 5.9% of the intake of dry matter during the lactation phase, and .6, 1.0, 1.3, and 1.6% of intake at maintenance for the respective rations. At high intakes of concentrate, substantial amounts of dietary starch escaped degradation in the rumen and small intestine and were lost in the feces.