1. The formation in vivo of retinoic acid from microgram quantities of intrajugularly administered [15-(14)C]retinol was demonstrated in the rat. 2. Endogenously formed retinoic acid (about 0.1mug./rat) was found in liver, and to a much smaller extent in intestine, 12hr. after retinol administration. 3. Excretion of some of the endogenously formed retinoic acid occurred in the bile of bile-duct-cannulated rats. 4. Excretion of unaltered retinoic acid in the urine of intact rats did not occur even after the intrajugular administration of preformed retinoic acid.

Two digestion trials, using 20 ram lambs (Experiment 1) and 8 cows (Experiment 2) provided ad libitum access to mature prairie grass hay, were conducted to evaluate controlled release intraruminal chromic oxide boluses and alkaline hydrogen peroxide lignin as markers for estimating forage intake by the fecal output/indigestibility ratio. A soybean meal and 3 urea based supplements were fed to lambs in Experiment 1. For both experiments, daily fecal output was weighed and sampled for 6 days (Experiment 1) and 5 days (Experiment 2) beginning 7 days after oral administration of CrzOJ controlled release boluses. Rectal fecal grab samples were also collected at 1000 daily and at 4-hour intervals on day 4 of collections for Experiment 2. For both experiments CrzO, excretion rates based on total collections were used to evaluate CrzO, controlled release boluses and alkaline hydrogen peroxide lignin predictive value in place of manufacturer's stated release rate. In experiment 1, fecal CrzOJ output was 224 mglday + 3.9 compared to the manufacturer's stated release rate of 201 mg CqOJlday. Fecal alkaline hydrogen peroxide lignin recovery was 97.8% + 1.9. Samples composited over the 6-day collection period predicted fecal output, apparent dry matter digestibility, and dry matter intake similar (p = 44, .15 and 55; respectively) to actual values. Supplemental treatment and dry matter intake had no effect (P 1 .38) on daily fecal Crz03 output or alkaline hydrogen peroxide lignin recovery. In Experiment 2, fecal Crz03 was 1,662 mg/day + 63 compared to the manufacturer's stated release rate of 1,505 mg CrzOl/day. Fecal alkaline hydrogen peroxide lignin recovery was 95.9 % + 7. Using 5-day composited samples, predicted fecal output, dry matter digestibility, and dry matter intake were similar (p = .49, .21 and .49; respectively) to actual values. Increasing the number of daily grab samples increased R2 values between actual and predicted fecal output and dry matter digestibility. Fecal grab samples and total fecal collection samples provided a similar relationship (R'=.71) between actual and predicted dry matter intake when each were composited over 5 days. Time of day did not affect fecal Cr203 or alkaline hydrogen peroxide lignin concentrations. These results suggest that grab samples collected Published with the approval of the Director of the South Dakota Agr. Exp. Sta. as Publ. No. 2631 of the Journal Series. Manuscript received 1 Sept. 93. 418 once daily on 5 consecutive days can be used to predict fecal output when Cr,O, controlled release boluses are used. Although recoveries of fecal alkaline hydrogen peroxide lignhr were near 100% in these experiments, digestibility estimates using this internal marker were variable and adversely influenced predictions of dry matter intake.

An in vitro wheat fermentation study (Exp. 1) was conducted to investigate the effect of pH (pH 7, 6, 5 and 4) on rumen lactate and VFA production. In another study (Exp. 2), lambs were fed high concentrate diets containing either no additions (control), 2% sodium bentonite, 2% limestone, 2% NaHCO3 or 10% alfalfa hay. The effect of these diets was determined on ruminal and systemic measurements before and after dietary adaptation. Effect of the control, bentonite, limestone and NaHCO3 treatments on nutrient digestibilities and mineral retentions after adaptation were also determined. Lactate production in the rumen fluid incubated at pH 7 or 6 was negligible. Reducing incubation pH from 6 to 5 resulted in accumulation of both total and L(+)-lactate, but further reduction to pH 4 did not result in an additional increase in lactate production. Variations in incubation pH or time did not affect the ratio of D to L isomers. Lowering the incubation pH to below 6 reduced total VFA production and increased the acetate to propionate ratio. In Exp. 2, the feeding of buffers or alfalfa hay was effective in maintaining a more normal feed intake and ruminal pH, and reduced ruminal lactate. Blood measurements were not affected by dietary treatment. When animals were adapted to the experimental diets, the dietary buffers did not influence rumen and blood measurements. Lambs fed 2% NaHCO3 digested more (P less than .05) organic matter, crude protein, N-free extract and starch, and 2% limestone increased (P less than .05) fiber digestibility. Dietary buffers tended to increase fecal pH and reduce fecal starch Magnesium retention with 2% bentonite, Ca retention with 2% limestone and Na and Mg retention with NaHCO3 were all increased (P less than .05).

No abstract

Flow-cytometric procedures were used to determine effects of dietary Zn and Si variations on rat testicular cell development, including integrity of caudal epididymal sperm chromatin structure defined as the susceptibility of DNA to denaturation in situ. Concentrations of 4 (deficient), 12 (adequate), and 500 (excessive) mg of Zn/kg of diet were used with Si concentrations of 0 (low), 540 (medium), and 2,700 (high) mg/kg of diet in a 3 x 3 factorial arrangement. Three-week-old Sprague-Dawley male rats were fed the experimental diets for 8 wk. Rats fed the Zn-deficient/Si-low diet demonstrated significant deviations in the ratio of testicular cell types present, including a reduction of S phase and total haploid cells. Furthermore, approximately 50% of epididymal sperm had a significant decrease in resistance to DNA denaturation in situ. In the Zn-deficient/Si-medium treatment, the effects of Si on animal and testicular growth, distribution of testicular cell types, and sperm chromatin structure integrity were quite similar to the effects of the Zn-adequate diets. A toxic effect of Zn on sperm chromatin structure integrity observed in the Zn-excess/Si-medium treatment seemed to be counteracted by Si in the Zn-excess/Si-high treatment. Silicon at medium and high levels seems to affect Zn metabolism through potentiation and antagonistic reactions, respectively. Zinc deficiency likely disrupts the normal sperm chromatin quaternary structure in which Zn plays a role by providing stability and resistance to DNA denaturation in situ.