Influence of yeast culture supplementation and advancing season on steers grazing mixed-grass prairie in the northern Great Plains: I. Dietary composition, intake, and in situ nutrient disappearance.

Twelve beef steers (368 +/- 25.3 kg) and four beef heifers (559 +/- 79.5 kg) fitted with ruminal cannulas were used to evaluate effects of yeast culture (YC) and advancing season on dietary chemical composition, intake, and in situ CP and NDF degradation. Treatments were control and YC supplementation (28.4 g.steer-1.d-1 dosed ruminally). Steers grazed from late June to early November 1991 on mixed-grass prairie. Experimental periods consisted of 10 d for adaptation and a 13-d collection phase. Forage samples collected from YC-supplemented steers had greater (P < .10) soluble N and in vitro OM disappearance than forage from controls throughout the grazing season. Organic matter intake was greater (P < .10) by YC-supplemented steers during June. Fecal output and OM intake increased (P < .10) from June to September. Increases (P < .10) in in situ NDF disappearance were noted at 8, 16, and 24 h in June, at 8, 48, and 72 h in July, and at 8 h in August for the YC treatment group. Supplemental YC did not affect (P > .10) rate or lag time of NDF disappearance. In situ CP disappearance (ISCPD) was greater (P < .10) at all times except 48 h in June, at 48 and 72 h in July, and at 0, 4, 8, and 12 h in August for YC-supplemented steers. Steers supplemented with YC had an increased extent (P < .10) of ISCPD in July and an increase in CP degradation rate in June; however, total CP degradation was greater (P < .10) during June for control than for YC steers.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of yeast culture supplementation and advancing season on steers grazing mixed-grass prairie in the northern Great Plains: II. Ruminal fermentation, site of digestion, and microbial efficiency.

Twelve ruminally and duodenally cannulated beef steers (initial BW 368 +/- 25.3 kg) and four ruminally cannulated beef heifers (initial BW 559 +/- 79.5 kg) were used to evaluate the effects of yeast culture (YC) and advancing season on ruminal fermentation, microbial protein synthesis, ruminal fluid kinetics, and site of digestion. Treatments were control and YC supplementation (28.4 g.steer-1.d-1 dosed ruminally). Steers grazed from late June to early November 1991 on mixed-grass prairie. Ruminal pH decreased (P < .10) from late July to early October. Fluid dilution rate decreased (P < .10) as the grazing season advanced, whereas ruminal fluid volume and flow rate increased (P < .10) from late July to early October. Ruminal ammonia concentration (milligrams/deciliter) was lower (P < .10) during late July and late August than during late June and early October at 4, 8, 12, and 16 h after sunrise in YC-supplemented steers. Molar proportions of propionate and butyrate were greater (P < .10) in control than in YC-supplemented steers at 0, 4, 12, and 24 h and 0, 4, and 12 h after sunrise, respectively, during late July. Acetate (mol/100 mol) was greater (P < .10) during late July and late August than in late June and early October for YC-supplemented steers at 0, 4, and 8 h after sunrise. True ruminal OM digestion was greatest (P < .10) in late June, intermediate in late July and late August, and least in early October. Supplementation with YC increased (P < .04) true ruminal OM digestion in late June and late July. Steers receiving YC had greater (P < .07) duodenal bacterial N flow in late July. These data indicate that yeast culture supplementation can increase true OM digestibility early in the grazing season. Advancing season seems to result in increased ruminal fluid volume, lower true ruminal OM digestion, and greater microbial efficiency.

Influence of season on dietary composition, intake, and digestion by beef steers grazing mixed-grass prairie in the northern Great Plains.

We used six beef steers (377 +/- 12.7 kg) to evaluate the effect of advancing season on dietary composition, forage intake, and digestion. Six 10-d sample collections were conducted from mid-June to mid-December 1995. Diet quality data demonstrated a linear (P < .01) decline in CP and in vitro OM digestibility (IVOMD), whereas NDF, ADF, acid detergent-insoluble CP (ADICP; percentage of CP), and undegradable intake protein (UIP; percentage of CP) increased linearly (P < .01) with advancing season. Fecal output and ruminal OM fill (percentage of BW) demonstrated linear and cubic responses (P < .10) across the grazing season. Intake of OM (percentage of BW) followed quadratic and cubic (P < .10) patterns across season. Rate (percentage per hour) of in situ NDF disappearance (ISNDFD) decreased and lag time increased linearly (P < .01) with advancing season. Likewise, quadratic (P < .07) and cubic (P < .06) responses were observed for rate and lag time of ISNDFD. The rapidly degraded CP fraction increased (P < .10) linearly, and the rate of in situ CP disappearance (ISCPD) followed a linear and quadratic decrease (P < .10) with advancing season. In summary, these data indicate decreases (P < .10) in dietary CP, IVOMD, ISNDFD, and ISCPD with advancing season. In addition, seasonal increases (P < .10) in forage NDF, ADF, ADICP, UIP (percentage of DM) and fecal output were observed and correspond to the grazing of increasingly mature forage. These data suggest that mixed-grass range forage consumed by cattle in western North Dakota during November and December is deficient in degradable intake protein (DIP). Investigation of protein supplementation (particularly DIP) during these times is warranted.

The effect of uterine anestomosis on the action of the IUCD in rats.

PIP: Experiments with the presence of an intrauterine contraceptive suture in 1 horn of a rat uterus established that the antidecidualizing effect of the IUD was transmitted from 1 horn to the other through a patent uterine anastomosis. Similar experiments without such luminal continuity showed that mere tissue-to-tissue contact was insufficient for transmissions of the antidecidualizing effect.^ieng