Nutrient Demand Affects Ruminal Digestion Responses to a Change in Dietary Forage Concentration

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Effects of forage family on rates of particle size reduction in, and passage from, the rumen and the relationship of these effects with preliminary dry matter intake (pDMI) were evaluated using 13 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 18-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 19.6 to 29.5 kg/d (mean = 25.9 kg/d). Experimental treatments were diets containing either a) alfalfa silage (AL) or b) orchardgrass silage (OG) as the sole forage. Silages were chopped to 10-mm theoretical length of cut and contained 42.3 and 58.2% neutral detergent fiber (NDF) for alfalfa and orchardgrass, respectively. Both diets contained approximately 25% forage NDF and 30% total NDF. Feed, orts, rumen, and duodenal samples were wet sieved to fractionate particles above (large) and below (small) 2.36 mm. Indigestible NDF (iNDF) was used as a flow marker. Preliminary DMI, an index of nutrient demand, was determined during the last 4 d of the preliminary period when cows were fed a common diet and used as a covariate. Main effects of forage family and their interaction with pDMI were tested by ANOVA. Approximately 75% of the NDF consumed was large and 25% was small for both treatments, but cows fed AL consumed more iNDF and less potentially digestible NDF (pdNDF) than cows fed OG. The AL diet increased the reduction rate (large to small) compared with OG despite less rumination per unit of forage NDF for AL than OG, suggesting alfalfa NDF was more fragile than orchardgrass NDF. Over 55% of particles in the rumen were below 2.36 mm for AL and OG, indicating that particle size was not a limiting constraint to passage. Passage rates (k(p)) of large iNDF and large pdNDF were similar for AL and OG, but AL increased k(p) of large pdNDF and OG decreased it as pDMI increased. The AL diet increased k(p) of small iNDF and small pdNDF compared with OG, resulting in lower rumen fill for AL than OG. The k(p) of small iNDF and small pdNDF were similar within forage family, suggesting buoyancy was not limiting passage. The OG diet increased rumen pool size of large NDF compared with AL, which likely retained small NDF, contributing to the slower k(p) of small iNDF and small pdNDF observed for OG. Particle size reduction was a prerequisite to ruminal passage but not a constraint. Selective retention of small particles was less for alfalfa than orchardgrass, resulting in lower rumen fill and less effective fiber.

Section: Resultsmentioning

confidence: 85%

“…Reduction of particle size during eating is included in the rate of particle size reduction (k r ). Passage rates (k pi ) are calculated for indigestible NDF (iNDF) and potentially digestible NDF (pdNDF); k r is calculated for iNDF only.Figure reprintedwith permission from Voelker Linton andAllen (2007).…”

mentioning

confidence: 99%

Rates of particle size reduction and passage are faster for legume compared with cool-season grass, resulting in lower rumen fill and less effective fiber

Kammes

Allen

2012

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“…A meta-analysis reported by Ferraretto et al (2013) determined that DMI was not altered by dietary starch content, milk yield increased by 0.08 kg/d for every percentage unit increase in dietary starch; however, this did not result in altered efficiency of feed conversion. Replacement of the rapidly fermentable carbohydrates provided by corn grain with fermentable carbohydrates from NFFS has resulted in little alteration in milk or milk component production (Voelker Linton and Allen, 2007;Gencoglu et al, 2010). In summary, substitution of wheat middlings and beet pulp for corn grain resulted in similar lactational performance for cows at high DMI and milk production levels.…”

Section: Lactation Performancementioning

confidence: 96%

Evaluation of lower-starch diets for lactating Holstein dairy cows

Dann

Tucker

Cotanch

et al. 2014

The objective of this experiment was to measure ruminal and lactational responses of Holstein dairy cows fed diets containing 3 different starch levels: 17.7 (low; LS), 21.0 (medium; MS), or 24.6% (high; HS). Twelve multiparous cows (118 ± 5 d in milk) were assigned randomly to dietary treatment sequence in a replicated 3 × 3 Latin square design with 3-wk periods. All diets were fed as total mixed rations and contained approximately 30.2% corn silage, 18.5% grass silage, and 5.0% chopped alfalfa hay. Dietary starch content was manipulated by increasing dry ground corn inclusion (% of dry matter) from 3.4 (LS) to 10.1 (MS) and 16.9 (HS) and decreasing inclusion of beet pulp and wheat middlings from 6.7 and 13.4 (LS) to 3.4 and 10.1 (MS) or 0 and 6.8 (HS). In vitro 6-h starch digestibility of the diet increased as nonforage sources of fiber replaced corn grain (% of dry matter; 73.6, HS; 77.3, MS; 82.5, LS) resulting in rumen-fermentable starch content by 14.6, 16.2, and 18.1% for the LS, MS, and HS diets, respectively. Diets had similar neutral detergent fiber from forage and particle size distributions. Dry matter intake, solids-corrected milk yield, and efficiency of solids-corrected milk production were unaffected by diet, averaging 26.5 ± 0.8, 40.8 ± 1.6, and 1.54 ± 0.05 kg/d, respectively. Reducing dietary starch did not affect chewing time (815 ± 23 min/d), mean ruminal pH over 24h (6.06 ± 0.12), acetate-to-propionate ratio (2.4 ± 0.3), or microbial N synthesized in the rumen (585 ± 24 g/d). Total tract organic matter digestibility was higher for HS compared with MS and LS diets (69.2, 67.3, and 67.0%, respectively), but crude protein, neutral detergent fiber, and starch digestibilities were unaffected. As dietary starch content decreased, in vitro ruminal starch fermentability increased and, consequently, the range between HS and LS in rumen-fermentable starch (3.5 percentage units) was less than the range in starch content (6.9 percentage units). Under these conditions, dietary starch content had no measurable effect on ruminal fermentation or short-term lactational performance of high-producing Holstein dairy cows.

“…Feed and duodenal digesta samples were collected during a research project conducted at Michigan State University (East Lansing, MI) following approval by the Institutional Animal Care and Use Committee (Voelker Linton and Allen, 2007). Prior to calving, 14 multiparous Holstein cows from the Dairy Cattle Teaching and Research Center were equipped with rumen and duodenal cannulas and housed in tie stalls.…”

Section: Animals and Treatmentsmentioning

confidence: 99%

“…Daily intakes of each vitamin were calculated as the concentration of each vitamin in the TMR multiplied by DMI. Calculations of DM DF were described by Voelker Linton and Allen (2007). Duodenal flow was calculated as B-vitamin concentrations in the duodenal sample multiplied by the daily DM flowing through the duodenum.…”

Section: Calculations and Statistical Analysesmentioning

confidence: 99%

Apparent ruminal synthesis of B vitamins in lactating dairy cows fed diets with different forage-to-concentrate ratios

Seck

Linton

Allen

et al. 2017

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Effects of the forage-to-concentrate ratio on apparent ruminal synthesis of thiamine, riboflavin, niacin, vitamin B, folates, and vitamin B were evaluated in an experiment using 14 ruminally and duodenally cannulated Holstein cows. The experiment was a crossover design with two 15-d treatment periods and a 14-d preliminary period in which cows were fed a diet intermediate in composition between the treatment diets. Treatments were diets containing low-forage (44.8% forage, 32.8% starch, 24.4% neutral detergent fiber) or high-forage (61.4% forage, 22.5% starch, 30.7% neutral detergent fiber) concentrations. Both diets were formulated with different proportions of the same ingredients. Concentrations of B vitamins were analyzed in feed and duodenal digesta. Apparent ruminal synthesis of each B vitamin was calculated as the duodenal flow minus the intake. The high-forage diet had the highest concentrations of riboflavin, niacin, vitamin B, and folates, whereas the low-forage diet had the highest thiamine concentration. Vitamin B in the diets was under the level of detection. Consequently, despite a reduction in dry matter intake when the cows were fed the high-forage diet, increasing dietary forage concentration increased or tended to increase intakes of riboflavin, niacin, and vitamin B but reduced thiamine and folate intakes. Increasing dietary forage concentration reduced apparent ruminal degradation of thiamine and apparent ruminal synthesis of riboflavin, niacin, and folates and increased ruminal degradation of vitamin B, but had no effect on ruminal synthesis of vitamin B. As a consequence, increasing the forage-to-concentrate ratio had no effect on the amounts of thiamine, riboflavin, and vitamin B reaching the small intestine but decreased the amounts of niacin, vitamin B, and folates available for absorption. Apparent ruminal syntheses of riboflavin, niacin, folates, and vitamin B were correlated positively with the amount of starch digested in the rumen and duodenal flow of microbial N, whereas these correlations were negative for thiamine. Apparent ruminal syntheses of thiamine and vitamin B were negatively correlated with their respective intakes, whereas folate intake was positively correlated with its synthesis in the rumen.