Twelve Holstein cows (63 DIM; 6 primiparous) were offered a common diet and monitored for 21 d (11 d of adaptation, 10 d of collection) with a data acquisition system to measure continuously feed and water intakes and chewing behavior. Objectives were to examine relationships among feeding behavior variables for noncompeting cows producing various quantities of milk and to determine experimental designs with adequate power to detect reasonable treatment differences in future experiments. Coefficients of variation across cows ranged from 5 to 41% for the variables studied. Milk production was correlated positively with DMI and water intake within and across parities. For multiparous cows, production was related positively to meal size (r = .78) and length of eating bouts (r = .75) and unrelated to meal number and eating rate. For primiparous cows, production tended to be related positively to meal number (r = .55) and eating rate (r = .87) and unrelated to meal size. Rumination and total time spent chewing per unit of DMI were correlated negatively (r = -.58) with milk production within and across parities. These correlations suggest that differences exist among cows for chewing efficiency. Reasons why high producing cows consume and chew more effectively deserve further study. Contrast differences of 10% of means for variables examined had an 80% probability of detection with a Latin square design utilizing 12 cows monitored for 5 d.

Twelve multiparous, rumen-cannulated cows (17 DIM) were fed 25 or 35% NDF diets without or with added rumen-inert bulk as water-filled plastic containers (500 ml each) within three 4 x 4 Latin squares (21-d periods). Added bulk equaled 25% of pretrial rumen volume for each cow. Objectives were to challenge cows with rumen fill in the form of dietary NDF and inert bulk to determine whether bulk affects intake similarly for diets of different NDF content or whether changes in behavior or rumen function allow cows to adapt to higher fill. Inert bulk had no effect on DMI for cows fed 25% NDF but decreased DMI for cows fed 35% NDF (18.7 vs. 16.6 kg/d). Volume of rumen digesta plus inert bulk, 102 L, was similar for 35% NDF treatments regardless of presence or absence inert bulk. Additional NDF or inert bulk increased the number of ruminating bouts per day, chewing time per unit of DMI or NDF intake, frequency of reticular contractions during rumination, and fractional passage rate of NDF from the rumen. Although these changes may help to alleviate fill, they were insufficient to maintain intake under conditions of high fill. Intake by cows receiving high fiber diets can be limited by reticulorumen capacity. Future study is required to determine the effect of rumen fiber digestion, fiber particle size, and animal characteristics on fill-limited intake.

Rising global carbon dioxide levels may lead to profound changes in plant composition, regardless of the degree of global warming that may result from the accumulation of this greenhouse gas. We studied the interaction of a CO2 doubling and two levels of nitrogen fertilizer on the growth and chemical composition of tall fescue (Festuca arundinacea Schreber cv. KY‐31) when infected and uninfected with the mutualistic fungal endophyte Neotyphodium coenophialum Morgan‐Jones and Gams. Two‐year‐old plants were harvested to 5 cm every 4 weeks, and after 12 weeks of growth plants grown in twice ambient CO2 concentrations: photosynthesized 15% more; produced tillers at a faster rate; produced 53% more dry matter (DM) yield under low N conditions and 61% more DM under high N conditions; the % organic matter (OM) was little changed except under elevated CO2 and high N when %OM increased by 3%; lignin decreased by 14%; crude protein (CP) concentrations (as %DM) declined by 21%; the soluble CP fraction (as %CP) increased by 13%; the acid detergent insoluble CP fraction (as %CP) increased by 12%, and in vitro neutral detergent fiber digestibility declined by 5% under high N conditions but not under low N. Plants infected with the endophytic fungus: photosynthesized 16% faster in high N compared with under low N; flowered earlier than uninfected plants; had 28% less lignin in high N compared with under low N; and had much smaller reductions in CP concentration (as %DM) and smaller increases in the soluble CP fraction (as %CP) and the acid detergent insoluble CP fraction (as %CP) under elevated CO2. Such large and varied changes in plant quality are likely to have large and significant effects on the herbivore populations that feed from these plants.

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The objective of this study was to determine the effect of forage fiber digestibility as part of a total mixed diet on intake and production of cows with intakes that were likely limited by rumen fill, using treatments that were not confounded by fiber source, concentrate, or ratio of forage to concentrate. Two alfalfa silages with similar NDF concentrations (40%) but different NDF digestibilities (40 vs. 45% after 24 h of in vitro fermentation) were harvested, mixed with concentrate to achieve diets containing 35% NDF, and offered to 12 multiparous cows (13 DIM) in a two-period balanced crossover design. Samples taken during silage feeding revealed that diets differed in both NDF digestibility (3 percentage units) and NDF content (1.8 percentage units), making interpretation of results difficult. Nonetheless, milk production (36.3 vs. 38.2 kg/d) and DMI (19.4 vs. 20.4 kg/d) were significantly higher with the higher NDF digestibility diet. Apparent in vivo DM and NDF digestibilities, total rumen VFA after feeding, and molar percentage of propionate were also higher with this diet. Equal NDF intake between diets suggested that higher DMI was due to the lower NDF content in the more digestible NDF diet. Higher NDF digestibility might also increase DMI; further experimentation is necessary with larger unconfounded differences in fiber digestibility at the time of feeding.