When steers (n = 4) were fed increasing amounts of concentrate (0, 45, or 90% of DM) and decreasing amounts of forage, the VFA concentration increased (P < .001) and ruminal pH, acetate:propionate ratio, and dissociated ammonia declined (P < .001). Acetate:propionate ratio and dissociated ammonia were highly correlated (r2 = .82 and .65, respectively) with ruminal pH. In vivo acetate:propionate ratio was highly correlated (r2 = .78) with the capacity of the bacteria to produce methane from H2 and CO2 in vitro, and in vivo pH-dissociated ammonia was correlated (r2 = .59) with the capacity of the bacteria to produce ammonia from protein hydrolysate. The role of pH in regulating methane and ammonia production was supported by the effect of pH in vitro. When bacteria from cattle fed concentrate or forage were incubated at pH values from 6.5 to 5.7, methane production decreased (P < .001) from 48 to 7 nmol x mg protein(-1) x min(-1) and from 14 to 2 nmol x mg protein(-1) x min(-1), respectively. The reduction in in vitro pH (6.5 to 5.7) also decreased (P < .001) the rates of ammonia production, but only if the bacteria were obtained from cattle fed forage (28 to 15 nmol x mg protein(-1) x min(-1)). Bacteria from cattle fed 90% concentrate had similar (P > .05) rates of ammonia production at pH 6.5 to 5.7 (approximately 12 nmol x mg protein(-1) x min(-1)). These results indicated that ruminal pH affected ruminal methane production, acetate:propionate ratio, deamination, and ammonia concentration.

We used chemical composition and in vitro digestibility data from temperate and tropical forages to develop relationships between indices of lignification and forage indigestible NDF. Neutral detergent fiber indigestibility increased nonlinearly as the lignin concentration of the NDF increased. Differences in estimated indigestible NDF using equations developed for a specific forage class (C3 and C4 grasses and legumes) were small and are probably not biologically significant when compared to those estimated from a common equation. Selected equations were compared with the Cornell Net Carbohydrate and Protein System (CNCPS) for the prediction of ADG. The linear equation (2.4 times NDF lignin content) used by the CNCPS and the Beef NRC had some of the largest errors due to mean bias. A log-log model [4.37 x (lignin/NDF)(.84)] provided the best combination of low total prediction error, low mean bias, and minimal error due to regression bias when permanganate lignin was used. A similar equation based on sulfuric acid lignin [6.17 x (lignin/NDF)(.77)] also met the above criteria. These equations then were evaluated with the CNCPS model against animal growth data from diets ranging in forage quality. Regardless of the equation used for predicting unavailable fiber, the CNCPS underpredicted daily gain, with mean biases ranging from -.10 to -.22 kg/d. Regression bias ranged from .13 to .14 kg/d and the coefficients differed from unity (P = .0001). The new equations gave numerically lower energy allowable ADG by steers compared to the linear equation currently used by the CNCPS model. The estimates were lower due to a higher predicted indigestible NDF, which resulted in a lower estimated forage energy value.

This study evaluates the effect of dry-season concentrate supplementation on growing cattle performance grazing tropical pasture and the impact of nitrogen fertilization on the growth rate of tropical pasture (tons of dry herbage mass/ha/110 days) and on the subsequent stocking rate and cattle performance during the rainy season (kg body weight gain/ha/110 days). The animal and plant responses were curvilinear to the increasing amount of nutrient supply and followed the typical saturation kinetics of enzyme systems, a Michaelis-Menten relationship. The Lineweaver-Burk data transformation explained efficiently the animal and plant responses to the nutrient supply. This methodology consists in evaluating the linear regressions of the reciprocal of animal and plant responses as a function of the reciprocal of nutrient supply. The half maximum growth rates for plant and animal to nutrient supply were verified with the proportions from .048 to .056 of the amount needed to cause .95 of theoretical maximum responses. From the curvilinear response, it can be verified that the marginal increase in animal and plant growth rate reduces as the amount of nutrient supply increases. D

Fear is a very strong stressor, and the highly variable results of handling and transportation studies are likely to be due to different levels of psychological stress. Psychological stress is fear stress. Some examples are restraint, contact wi th people, or exposure to novelty. In many different animals, stimulation of the amygdala with an implanted electrode triggers a complex pattern of behavior and autonomic responses that resemble fear in humans. Both previous experience and genetic factors affecting temperament will interact in complex ways to determine how fearful an animal may become when it is handled or transported. Cattle trained and habituated to a squeeze chute may have baseline cortisol levels and be behaviorally calm, whereas extensively reared animals may have elevated cortisol levels in the same squeeze chute. The squeeze chute is perce ived as neutral and nonthreatening to one animal; to another animal, the novelty of it may trigger intense fear. Novelty is a strong stressor when an animal is suddenly confronted with it. To accurately assess an animal's reaction, a combination of behavioral and physiological measurements will provide the best overall measurement of animal discomfort.

We conducted two growth trials to evaluate the effects of monensin on amino acid sparing. When Holstein steers were fed a 90% concentrate diet supplemented with soybean meal (13.5% CP), the DMI, ADG, and efficiencies of feed and nitrogen utilization were greater than with urea (P < .10). Monensin improved ADG with both nitrogen supplements (P < .01), but the positive effects of monensin on efficiencies of feed (P = .12) and nitrogen (P = .26) utilization were greater for soybean meal than for urea. Increasing amounts of monensin (0, 11, or 22 mg/kg of DM) caused a linear increase in DMI with urea. Diets with soybean had greater intakes than diets with urea (P < .01); the greatest intake was of a soybean diet with monensin at 11 mg/kg of DM. Holstein steers fed soybean meal at 13.5% CP had lower DMI and greater efficiencies of feed and nitrogen utilization than steers fed 16.7% CP (P < .10). Crude protein level had no effect on ADG (P > .10). Monensin always increased the efficiencies of feed and nitrogen utilization (P < .05), but these trends were greater for diets with 16.7 than for those with 13.5% CP. Overall, monensin decreased DMI (P < .01), but this effect was greater for 16.7% than for 13.5% CP. Because the positive effects of monensin on diet NEg (P = .16) and efficiency of nitrogen utilization (P = .26) were greater for soybean meal than for urea, it seemed that monensin was sparing amino acids.

When mixed ruminal bacteria from cattle fed timothy hay were suspended in a medium containing a low concentration of potassium, monensin and lasalocid catalyzed a rapid depletion of potassium from cells. The ionophore-mediated potassium depletion was concentration dependent, and it was possible to describe the relationship with saturation constants. Mixed ruminal bacteria never lost more than 50% of their potassium (K max ‫؍‬ 46%), and the concentrations of monensin and lasalocid needed to cause half-maximal potassium depletion (K d) were 178 and 141 nM, respectively. When cattle were fed 350 mg of monensin per day, the ratio of ruminal acetate to propionate decreased from 4.2 to 2.9, and the K d of monensin was eightfold greater than the value for mixed ruminal bacteria from control animals. Monensin supplementation also caused a twofold increase in the K d of lasalocid. Lasalocid supplementation (350 mg per day) had no effect on the ruminal acetate-to-propionate ratio, but it caused a twofold increase in the K d values of monensin and lasalocid. Increases in K d occurred almost immediately after ionophore was added to the ration, and the K d values returned to their prefeeding values within 14 days of withdrawal. Ionophore supplementation had no effect on the K max values, and approximately 50% of the population was always highly ionophore resistant. Because the K d values of even adapted ruminal bacteria were low (<1.5 M), it appears that a large proportion of the ruminal ionophore is bound nonselectively to feed particles or ionophore-resistant bacteria.

The objective of the present study was to assess the chemical and bromatological composition and in situ degradability of elephant grass silages inoculated with Streptococcus bovis isolated from cattle rumen. A complete randomized design was used with four treatments and six replications: elephant grass silage, elephant grass silage inoculated with 10 6 CFU/g Streptococcus bovis JB1 strains; elephant grass silage inoculated with 10 6 CFU/g Streptococcus bovis HC5 strains; elephant grass silage inoculated with 10 6 CFU/g Enterococcus faecium with six replications each. The pH and ammoniacal nitrogen values were lower (P<0.05) for the silages inoculated with Streptococcus bovis JB1 and HC5, respectively. The silage inoculated with Streptococcus bovis had a higher crude protein content (P<0.05) and there were no differences for the fiber contents in the silage. The (a)soluble fraction degradability, especially in the silages inoculated with Streptococcus bovis JB1 and HC5, had higher values, 30.77 and 29.97%, for dry matter and 31.01 and 36.66% for crude protein, respectively. Inoculation with Streptococcus bovis improved the fermentation profile, protein value and rumen degradability of the nutrients.

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