Nutrient demand interacts with forage family to affect intake and digestion responses in dairy cows

The effect of feed intake in the preliminary period on responses to diets containing alfalfa silage or orchardgrass silage was evaluated using 8 ruminally and duodenally cannulated Holstein cows in a crossover design experiment with a 14-d preliminary period and two 15-d treatment periods. Responses measured were DMI, rates of fiber digestion and passage, and milk production. Cows were 139 ± 83 (mean ± SD) d in milk at the beginning of the preliminary period. During the preliminary period, 3.5% fat-corrected milk yield ranged from 23.9 to 47.6 kg/d (mean = 36.9 kg/d) and preliminary voluntary DMI (pVDMI) ranged from 14.2 to 21.3 kg/d (mean = 18.6 kg/d). The 2 treatments were a diet containing alfalfa silage as the sole forage (AL) and a diet containing orchardgrass silage as the sole forage (OG). Alfalfa silage contained 43% neutral detergent fiber (NDF; dry-matter basis) and orchardgrass silage contained 48% NDF; diets contained ∼23% forage NDF and 27% total NDF, so forage-to-concentrate ratio was 53:47 for AL and 48:52 for OG. Digestibility of NDF was lower for AL in the rumen and whole tract compared with OG, and milk fat concentration tended to be greater for OG than for AL. Mean 3.5% fat-corrected milk yield and DMI were not different between AL and OG. Response of DMI to forage family depended on pVDMI, as indicated by a significant interaction between treatment and pVDMI in predicting DMI. As pVDMI increased, DMI increased when cows were fed AL but not when they were fed OG. That is, as appetite increased, intake was more restricted for the more physically filling OG than for the less physically filling AL. This more positive DMI response to AL over OG among high-pVDMI cows is corroborated by interactions between treatments and pVDMI for both ruminal NDF turnover rate and indigestible NDF passage rate response. Therefore, the effects of alfalfa and orchardgrass forages on intake and fiber digestion depended on the extent to which fill limited feed intake of an individual cow.     

Nutrient demand interacts with forage family to affect nitrogen digestion and utilization responses in dairy cows

The effect of preliminary feed intake on responses to diets containing alfalfa silage or orchardgrass silage was evaluated using 8 ruminally and duodenally cannulated Holstein cows in a crossover design experiment with a 14-d preliminary period and two 15-d treatment periods. Responses measured were intake, digestion, and utilization of N. Cows were 139 ± 83 (mean ± standard deviation) days in milk at the beginning of the preliminary period. During the 14-d preliminary period, 3.5% fat-corrected milk yield ranged from 23.9 to 47.6 kg/d (mean = 36.9 kg/d) and preliminary voluntary dry matter intake (pVDMI) ranged from 14.2 to 21.3 kg/d (mean = 18.6 kg/d). Treatments were a diet with alfalfa silage as the sole forage (AL) and a diet with orchardgrass silage as the sole forage (OG). Alfalfa silage contained 20.5% crude protein (CP; dry matter basis) and orchardgrass silage contained 20.4% CP; AL contained 18.3% CP and 5.6% estimated rumen-undegraded CP, and OG contained 18.8% CP and 6.3% estimated rumen-undegraded CP. Mean N intake was similar between treatments, ruminal N digestibility was greater for AL (30.4%) than for OG (17.7%), and whole-tract N digestibility did not differ between treatments. Intake and duodenal flow of N depended on a treatment × pVDMI interaction; both N intake and duodenal flow increased more for AL than for OG as pVDMI increased. Duodenal flow of microbial N and the efficiency of microbial N production from OM also depended on a treatment × pVDMI interaction in a manner similar to N intake and duodenal flow. However, treatment × pVDMI interactions also indicate that as pVDMI increased and N intake increased for AL compared with OG, a decreasing proportion of the additional N consumed from AL was digested and used for increased milk protein production or body tissue gain. Therefore, when feeding less-filling diets, such as those containing large proportions of legume forage, to high-producing cows, reducing dietary N concentration could increase the efficiency of N utilization and reduce the extent to which greater DMI leads to greater N excretion.     

Effects of pretrial milk yield on responses of feed intake,digestion, and production to dietary forage concentration

The relationships between pretrial milk yield and effects of dietary forage-to-concentrate ratio on dry matter intake (DMI), digestion, and milk yield were evaluated using 32 Holstein cows in a crossover design with two 16-d periods. Cows were 197 +/- 55 (mean +/- SD) days in milk at the beginning of the experiment. Milk yield averaged 33.9 kg/d and ranged from 16.5 to 55.0 kg/d for the 4 d before initiation of treatments. Treatments were diets with forage-to-concentrate ratios of 67:33 and 44:56. Forages were alfalfa silage and corn silage, each at 50% of forage dry matter (DM). Neutral detergent fiber (NDF) concentrations of high-forage and low-forage diets were 30.7 and 24.3% of DM, respectively. Dry matter intake was 1.7 kg/d higher for cows fed the low-forage diet. Milk yield was 2.3 kg/d greater on low forage than on high forage, but 3.5% fat-corrected milk yield and yield of milk fat were not different between treatments. Individual DMI response to the low-forage diet relative to the high-forage diet (low-high) was positively and linearly related to pretrial fat-corrected milk yield, but fat-corrected milk yield response demonstrated a quadratic relationship with pretrial fat-corrected milk yield. Milk yield responded more positively to low forage among low- and high-producing cows than among moderate-producing cows. Energy partitioned to body reserves and to milk, and passage rate of indigestible NDF, also responded to dietary forage level in quadratic relationships with pretrial milk energy output. Individual responses of intake, production, and fiber digestion to a change in forage-to-concentrate ratio were dependent on production level.     

Dietary forage concentration affects the feed sorting behavior of lactating dairy cows

The objective of this study was to determine whether the amount of forage in a total mixed ration influences feed sorting by cows and whether the extent of this sorting changes as they adapt to a new diet. Six lactating Holstein cows, individually fed once per day, were provided each of 2 diets in a crossover design (dry matter basis): 1) a higher forage diet (HF; 62.3% forage), and 2) a lower forage diet (LF; 50.7% forage). Dry matter intake, feeding behavior, and sorting activity were monitored for each cow on each diet for 7 d. Fresh feed and orts were sampled daily for each cow and subjected to neutral detergent fiber (NDF) and particle size analysis. The particle size separator contained 2 screens (18 and 9 mm) and a bottom pan, resulting in 3 fractions (long, medium, and short). Sorting activity [for each fraction, NDF and physically effective NDF (peNDF)] was calculated as the actual intake expressed as a percentage of the predicted intake. Overall, sorting activity was greatest on the LF diet, with cows sorting for short particles but against long particles, medium particles, NDF, and peNDF. On the HF diet, cows sorted against long particles, NDF, and peNDF and sorted for short particles. Treatment × day interactions occurred for sorting for short particles and against peNDF, indicating that it took cows 1 d to adjust their sorting behavior to the LF diet. Cows on the LF diet consumed more dry matter but spent less time feeding, which resulted in a greater intake rate compared with cows on the HF diet. These results indicate that cows rapidly adjust their sorting behavior when subjected to a dietary change, and they exhibit more sorting for short particles and against long particles, NDF, and peNDF when fed an LF diet.     

Nutrient demand interacts with forage family to affect digestion responses in dairy cows

Effects of forage family on dry matter intake (DMI), milk production, ruminal pool sizes, digestion and passage kinetics, and chewing activity and the relationship of these effects with preliminary DMI (pDMI), an index of nutrient demand, 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) and 3.5% fat-corrected milk yield ranged from 24.3 to 60.3 kg/d (mean=42.1 kg/d). Experimental treatments were diets containing either a) alfalfa silage (AL) or b) orchardgrass silage (OG) as the sole forage. Alfalfa and orchardgrass contained 42.3 and 58.2% neutral detergent fiber (NDF) and 22.5 and 11.4% crude protein, respectively. Forage:concentrate ratios were 60:40 and 43:57 for AL and OG, respectively; both diets contained approximately 25% forage NDF and 30% total NDF. Preliminary DMI 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. Forage family and its interaction with pDMI did not affect feed intake, milk yield, or milk composition. The AL diet increased indigestible NDF (iNDF) intake and decreased potentially digestible NDF (pdNDF) intake compared with OG. The AL diet increased ruminal pH, digestion rates of pdNDF and starch, and passage rates of pdNDF and iNDF compared with OG, which affected ruminal digestibility. Passage rate of iNDF was related to pDMI; AL increased iNDF passage rate and OG decreased it as pDMI increased. The AL diet decreased ruminal pool sizes of pdNDF, starch, organic matter, dry matter, and rumen digesta wet weight and volume compared with OG. The AL diet decreased ruminating time per unit of forage NDF consumed compared with OG, indicating that alfalfa provided less physically effective fiber than orchardgrass. The AL diet, but not OG, increased ammonia N, nonammonia nonmicrobial N, and nonammonia N fluxes as pDMI increased. Efficiency of microbial protein synthesis was positively related to pdNDF passage rate for OG, but not AL. The faster rates of digestion and passage for AL compared with OG decreased rumen pool size but did not increase feed intake for cows consuming AL. Digestion responses to forage family were affected by nutrient demand of cows.     

Effect of linseed oil supplementation on ruminal digestion in dairy cows fed diets with different forage:concentrate ratios

The effect of linseed oil (LSO) supplementation on total-tract and ruminal nutrient digestibility, N metabolism, and ruminal fluid characteristics was investigated in dairy cows fed diets containing different forage to concentrate ratios (F:C). The experimental design was a 4 x 4 Latin square with 2 x 2 factorial arrangement of treatments. Four lactating Holstein cows were fed a forage-rich diet without LSO (F; F:C = 65:35, dry matter basis), a forage-rich diet with LSO (FO; F:C = 65:32, 3% LSO), a concentrate-rich diet without LSO (C; F:C = 35:65), or a concentrate-rich diet with LSO (CO; F:C = 35:62, 3% LSO). Total-tract digestibility of DM and OM was greater with supplemental LSO. A tendency for greater total-tract digestibility of NDF and ADF also was observed in cows fed LSO. Ruminal digestibility of NDF or ADF decreased when CO was fed compared with C. In contrast, feeding FO increased NDF or ADF digestibility compared with F. Although ruminal starch digestion was nearly complete with all diets, digestibility was greater when cows were fed C or CO compared with F or FO. Bacterial N flow to the duodenum decreased when FO was fed compared with F. In contrast, feeding CO increased bacterial-N flow compared with C. Neither F:C nor LSO supplementation affected ruminal pH or total VFA concentration in ruminal fluid. However, molar proportion of propionate was greater with C or CO compared with F or FO and increased with LSO supplementation regardless of F:C. Molar proportion of n-butyrate decreased with LSO supplementation. Total protozoal numbers in ruminal fluid decreased markedly only when CO was fed. Overall, data show that feeding LSO had no negative effects on total-tract digestion in dairy cows but may decrease ruminal fiber digestibility when fed with high-concentrate diets. The widely spread idea that LSO decreases digestibility, arising from studies with sheep, did not seem to apply to lactating cows fed 3% LSO.     

Effects of corn grain conservation method on ruminal digestion kinetics for lactating dairy cows at two dietary starch concentrations

Effects of conservation method of corn grain and dietary starch concentration on ruminal digestion kinetics were evaluated. Eight ruminally and duodenally cannulated Holstein cows (55 +/- 15.9 days in milk; mean +/- SD) were used in a duplicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. Experimental diets contained either ground high moisture corn (HM) or dry ground corn (DG) at two dietary starch concentrations (32 vs. 21%). Mean particle size and dry-matter concentration of corn grain were 1,863 microm and 63.2%, and 885 microm and 89.7%, for HM and DG, respectively. Starch digestibility in the rumen was greater for HM treatments compared with DG treatments, but starch digestibility in the total tract was not affected by conservation method of corn grain because of compensatory digestion in the intestines. The difference in ruminal starch digestibility between HM and DG treatment was greater for high-starch diets (71.1 vs. 46.9%) compared with low-starch diets (58.5 vs. 45.9%). This interaction is attributed to a greater difference in first-order digestion rate of starch between HM and DG treatment in high-starch diets (28.2 vs. 14.6%/h) compared with low-starch diets (16.8 vs. 12.2%/h). This suggests that ruminal starch digestion is a second-order reaction limited by enzyme activities as well as substrate availability; ruminal contents of cows fed low-starch diets may have insufficient amylolytic activity for maximal starch digestion when readily fermentable starch is available. Rate of neutral detergent fiber digestion in the rumen was slower for high-starch diets and HM treatments compared with low-starch diets and DG treatments, respectively. Effects of corn grain conservation method on ruminal digestion kinetics are greatly altered by starch concentration of diets.     

Effects of fatty acid supplements on ruminal and total tract nutrient digestion in lactating dairy cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on ruminal digestion kinetics, and ruminal and postruminal nutrient digestion. Eight early lactation ruminally and duodenally cannulated cows (77 ± 12 days in milk, mean ± SD) were used in a replicated 4 × 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Saturated FS linearly decreased ruminal digestibility of dry matter and organic matter and linearly decreased ruminal neutral detergent fiber (NDF) digestibility. The reduction in ruminal NDF digestibility was because of a linear decrease in digestion rate and a linear increase in passage rate of potentially digestible NDF with increasing saturated FS. Total tract digestibility of NDF was not different between treatments because of compensatory postruminal digestion. Ruminal fatty acid and C18 fatty acid digestibility tended to increase linearly with increasing unsaturated FS, and postruminal C18 fatty acid digestibility decreased with increasing saturated FS. Saturated FS linearly decreased ruminal organic matter digestibility and decreased intestinal long-chain fatty acid digestibility, although differences in fatty acid digestibility may be partially explained by fatty acid intake.     

Nutrient demand interacts with grass maturity to affect milk fat concentration and digestion responses in dairy cows

Effects of grass maturity on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, digestion and passage kinetics, and chewing activity and the relationship of these effects with preliminary DMI (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 23.5 to 28.2kg/d (mean=26.1kg/d) and 3.5% fat-corrected milk (FCM) yield ranged from 30.8 to 57.2kg/d (mean=43.7kg/d). Experimental treatments were diets containing orchardgrass silage harvested either (1) early-cut, less mature (EC) or (2) late-cut, more mature (LC) as the sole forage. Early- and late-cut orchardgrass contained 44.9 and 54.4% neutral detergent fiber (NDF) and 20.1 and 15.3% crude protein, respectively. Forage:concentrate ratio was 58:42 and 46:54 for EC and LC, respectively; both diets contained approximately 25% forage NDF and 30% total NDF. Preliminary DMI, an index of nutrient demand, was determined during the last 4d of the preliminary period when cows were fed a common diet and used as a covariate. Main effects of grass maturity and their interaction with pDMI were tested by ANOVA. The EC diet decreased milk yield and increased milk fat concentration compared with the LC diet. Grass maturity and its interaction with pDMI did not affect FCM yield, DMI, rumen pH, or microbial efficiency. The EC diet increased rates of ruminal digestion of potentially digestible NDF and passage of indigestible NDF (iNDF) compared with the LC diet. The lower concentration and faster passage rate of iNDF for EC resulted in lower rumen pools of iNDF, total NDF, organic matter, and dry matter for EC than LC. Ruminal passage rates of potentially digestible NDF and starch were related to level of intake (quadratic and linear interactions, respectively) and subsequently affected ruminal digestibility of these nutrients. The EC diet decreased eating, ruminating, and total chewing time per unit of forage NDF intake compared with the LC diet. When grass silage was the only source of forage in the diet, cows supplemented with additional concentrate to account for decreasing protein and increasing fiber concentrations associated with more mature grass had similar feed intake and produced similar FCM yields as cows fed less mature grass.     

Effects of fumarate on ruminal ammonia accumulation and fiber digestion in vitro and nutrient utilization in dairy does

The objective of this study was to evaluate effects of fumarate on ruminal ammonia accumulation and fiber digestion in vitro and on feed intake and nutrient utilization in dairy does. Batch cultures of mixed rumen microorganisms were used to study effects of different concentrations of fumarate on fermentation with various N sources (ammonia as ammonium bicarbonate, casein amino acids, casein peptides, gelatin peptides) and feeds (bermudagrass hay, mixed diet of 60% bermudagrass hay plus 40% concentrate) for 6 and 24 h, respectively. Substrates were grouped into pairs for separate incubations. Monosodium fumarate was added to incubation tubes to achieve final concentrations of 0, 5, and 10 mM fumarate. More ammonia accumulated at the end of incubation with added ammonium bicarbonate. Ammonia concentration was higher for peptide compared with amino acid incubation, and for casein peptide compared with gelatin peptide. Addition of fumarate linearly decreased ammonia for all N sources and for feed substrates. For all substrate types, fumarate treatment increased acetate, propionate, and total volatile fatty acids (VFA), decreased acetate to propionate ratio, and tended to reduce branched-chain VFA. Digestion of feed neutral detergent fiber (NDF) by rumen microorganisms was improved by fumarate along with elevated endoglucanase and xylanase activities. In an animal metabolism experiment, 8 dairy does (4 per treatment) were used in a completely randomized design for 21 d. Does were fed a hay plus concentrate diet without (control) or with fumarate (6 g/head per day) supplementation to determine feed intake, whole-tract nutrient digestibility, and N utilization. Fumarate treatment did not affect weight change or feed intake but increased whole-tract digestion of gross energy, crude protein, and cellulose. Digested N was increased by fumarate supplementation; however, N retention was unaffected. Plasma glucose concentration was elevated with fumarate but urea N concentration remained unchanged. Fumarate addition had significant effects on rumen microbial fermentation by decreasing ammonia and branched-chain VFA, and by increasing acetate and propionate, and NDF digestion. These effects were reflected in the improvement in whole-tract gross energy, crude protein, and cellulose digestion and elevated plasma glucose concentration when dairy does were supplemented with fumarate.     

Effects of short-term variation in forage quality and forage to concentrate ratio on lactating dairy cows

Within-farm variation in forage composition can be substantial and potentially costly, and it presents challenges for sampling the forage accurately. We hypothesized that day-to-day variation in forage neutral detergent fiber (FNDF) concentrations and diet variation caused by sampling error would have negative effects on production measures in lactating dairy cows. Twenty-four Holstein cows (73 d in milk) were used in 8 replicated 3 × 3 Latin squares with 21-d periods. Treatments were (1) control (CON), (2) variable (VAR), and (3) overreacting (ORR). On average, over the 21-d period, all 3 treatments were the same [24.7% FNDF and 48.2% forage dry matter (DM) composed of 67% alfalfa silage and 33% grass silage]. The CON treatment was essentially consistent day-to-day in total forage and FNDF concentrations and proportion of alfalfa and grass silages. The VAR treatment changed daily (in a random pattern) in proportion of alfalfa and grass silages fed, which resulted in day-to-day changes in FNDF (range was 21.5 to 28%). The ORR treatment varied in a 5-d cyclic pattern in total forage and FNDF concentrations (26, 24, 28, and 21.5% FNDF). Over the 21 d, ORR (25.1 kg/d) had higher DM intake compared with CON (24.5 kg/d) and VAR (24.3 kg/d). Milk production (42.8 kg/d), milk fat (3.5%), and milk protein (2.8%) were not affected by treatment; however, a treatment × day interaction was observed for milk production. Lower daily milk yields for VAR and ORR compared with CON were rare; they only followed sustained 4- and 5-d periods of feeding higher FNDF diets compared with CON. In contrast, increased daily milk yields for VAR and ORR versus CON were more frequent and followed sustained diet changes of only 2 or 3 d. Lipolytic and lipogenic-related enzyme mRNA abundances in subcutaneous adipose tissue were not affected by treatment. Treatment × day interactions were observed for milk fatty acid markers of cellulolytic bacteria (iso-14:0, iso-15:0, iso-16:0) and lipolysis (18:0) and generally followed the expected response to changes in daily rations. Overall, extreme daily fluctuations in FNDF had no cumulative negative effect on production measures over a 21-d period, and daily responses to transient increases in FNDF were less than expected.     

Effects of replacement of late-harvested grass silage and barley with early-harvested silage on ruminal digestion efficiency in lactating dairy cows

The objective of this experiment was to quantify the effects of graded replacement of late-harvested grass silage and barley with early-harvested silage on nutrient digestion and rumen fermentation. Four experimental diets were fed to 4 multiparous rumen-cannulated Nordic Red cows in 4 × 4 Latin square design with 21-d periods. Dietary treatments consisted of late-cut grass silage (LS) and rolled barley, which was gradually replaced with early-cut grass silage [ES; 0, 33, 67, and 100% of the forage component (ES + LS) of the diet]. With increased proportion of ES in the diet, the proportion of barley decreased from 47.2 to 26.6% on a dry matter basis. Early- and late-cut silages were harvested at 2-wk intervals (predicted concentrations of metabolizable energy 11.0 and 9.7 MJ/kg of dry matter). The 4 diets were formulated to support the same milk production. Nutrient flows were quantified using omasal sampling technique applying the triple-marker method (Cr, Yb, and indigestible neutral detergent fiber) and ¹⁵N as a microbial marker. Feed intake decreased with graded replacement of LS and barley with ES, but milk production was not influenced by diet. Digestibility of nutrients improved with graded addition of ES in the diet with the greatest difference observed in digestibility of neutral detergent fiber (NDF) and potentially digestible NDF (pdNDF). The results suggested that improved cell wall digestibility with graded level of ES in the diet was partly related to higher intrinsic digestibility of ES than LS, and partly due to negative associative effects with an increased proportion of LS and barley in the diet. Efficiency of microbial N synthesis was not influenced by the diet, but ruminal protein degradability increased with ES in the diet. Rumen fermentation pattern was not affected by the diet despite large difference in the profile of dietary carbohydrates. Rumen pool size of NDF and pdNDF, and ruminal turnover time of NDF decreased with graded addition of ES in the diet, whereas digestion rate of pdNDF improved. The results of this study indicate that increased CH₄ yield in a parallel production study with graded addition of ES in the diet were more related to greater ruminal and total digestibility of organic matter than to the changes in rumen fermentation pattern.     

Effect of dietary crude protein concentration on ruminal nitrogen metabolism in lactating dairy cows

Ten lactating Holstein cows fitted with ruminal cannulas that were part of a larger feeding trial were blocked by days in milk into 2 groups and then randomly assigned to 1 of 2 incomplete 5 × 5 Latin squares. Diets contained [dry matter (DM) basis] 25% alfalfa silage, 25% corn silage, and 50% concentrate. Rolled high-moisture shelled corn was replaced with solvent-extracted soybean meal to increase crude protein (CP) from 13.5% to 15.0, 16.5, 17.9, and 19.4% of DM. Each of the 4 experimental periods lasted 28 d with data and sample collection performed during the last 8 d. Digesta samples were collected from the omasum to quantify the ruminal outflow of different N fractions. Intake of DM was not affected but showed a quadratic trend with maxima of 23.9 kg/d at 16.5% CP. Ruminal outflow of total bacterial nonammonia N (NAN) was not different among diets but a significant linear effect of dietary CP was detected for this variable. Bacterial efficiency (g of total bacterial NAN flow/kg of organic matter truly digested in the rumen) and omasal flows of dietary NAN and total NAN also showed positive linear responses to dietary CP. Total NAN flow increased from 574 g/d at 13.5% CP to 688 g/d at 16.5% CP but did not increase further with the feeding of more CP. Under the conditions of this study, 16.5% of dietary CP appeared to be sufficient for maximal ruminal outflow of total bacterial NAN and total NAN.     

Effect of reducing dietary forage in lower starch diets on performance,ruminal characteristics,and nutrient digestibility in lactating Holstein cows

This experiment evaluated the effect of feeding a lower starch diet (21% of dry matter) with different amounts of forage (52, 47, 43, and 39% of dry matter) on lactational performance, chewing activity, ruminal fermentation and turnover, microbial N yield, and total-tract nutrient digestibility. Dietary forage consisted of a mixture of corn and haycrop silages, and as dietary forage content was reduced, chopped wheat straw (0–10% of dry matter) was added in an effort to maintain chewing activity. Dietary concentrate was adjusted (corn meal, nonforage fiber sources, and protein sources) to maintain similar amounts of starch and other carbohydrate and protein fractions among the diets. Sixteen lactating Holstein cows were used in replicated 4 × 4 Latin squares with 21-d periods. Dry matter intake increased while physically effective neutral detergent fiber (peNDF_1.18) intake was reduced as forage content decreased from 52 to 39%. However, reducing dietary forage did not influence milk yield or composition, although we observed changes in dry matter intake. Time spent chewing, eating, and ruminating (expressed as minutes per day or as minutes per kilogram of NDF intake) were not affected by reducing dietary forage. However, addition of chopped wheat straw to the diets resulted in greater time spent chewing and eating per kilogram of peNDF_1.18 consumed. Reducing dietary forage from 52 to 39% did not affect ruminal pH, ruminal digesta volume and mass, ruminal pool size of NDF or starch, ruminal digesta mat consistency, or microbial N yield. Ruminal acetate-to-propionate ratio was reduced, ruminal turnover rates of NDF and starch were greater, and total-tract digestibility of fiber diminished as dietary forage content decreased. Reducing the dietary forage content from 52 to 39% of dry matter, while increasing wheat straw inclusion to maintain chewing and rumen function, resulted in similar milk yield and composition although feed intake increased. With the lower starch diets in this short-term study, the minimal forage content to maintain lactational performance was between 39 and 43%.     

Mass Transfer and Nutrient Absorption in a Simulated Model of Small Intestine

Abstract: There is an increasing need to understand how food formulations behave in vivo from both food and pharma industries. A number of models have been proposed for the stomach, but few are available for the other parts of the gastrointestinal tract. An experimental rig that simulates the segmentation motion occurring in the small intestine has been developed. The objective of developing such an experimental apparatus was to study mass transport phenomena occurring in the lumen and their potential effect on the concentration of species available for absorption. When segmentation motion was applied the mass transfer coefficient in the lumen side was increased up to a factor of 7. The viscosity of the lumen, as influenced by guar gum concentration, had a profound effect on the mass transfer coefficient. The experimental model was also used to demonstrate that glucose available for absorption, resulting from starch hydrolysis, can be significantly reduced by altering the lumen viscosity. Results suggest that absorption of nutrients could be controlled by mass transfer. Practical Application: To address health-related diseases such as obesity, novel foods that provide advanced functions are required. To achieve the full potential offered by the latest developments in the field of food material science, a fundamental understanding of the behavior of food structures in vivo is required. Using the developed gut model we have demonstrated that absorption of nutrients can be controlled by mass transfer limitations.     

Nutrient demand interacts with grass particle length to affect digestion responses and chewing activity in dairy cows

Effects of grass particle length on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, digestion and passage kinetics, and chewing activity and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 15 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 22.6 to 29.8 kg/d (mean=25.8 kg/d) and 3.5% fat-corrected milk yield ranged from 29.2 to 56.9 kg/d (mean=41.9 kg/d). Experimental treatments were diets containing orchardgrass silage chopped to either (a) 19-mm (long) or (b) 10-mm (short) theoretical length of cut as the sole forage. Grass silages contained approximately 46% neutral detergent fiber (NDF); diets contained 50% forage, 23% forage NDF, and 28% total NDF. 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 grass particle length and their interaction with pDMI were tested by ANOVA. Grass particle length and its interaction with pDMI did not affect milk yield, milk composition, or rumen pH. Long particle length tended to decrease DMI compared with short particle length, which might have been limited by rumen fill or chewing time, or both. Passage rates of feed fractions did not differ between long and short particle lengths and were not related to level of intake. As pDMI increased, long particles decreased ruminal digestion rate of potentially digestible NDF at a faster rate than short particles. As a result, long particles decreased or tended to decrease rates of ruminal turnover for NDF, organic matter, and dry matter and increased their rumen pools compared with short particles for cows with high pDMI. Long particles increased eating time, which affected cows with high intake to the greatest extent, and total chewing time compared with short particles. As intake increased, ruminal digestion (kg/d) and digestibility (%) of starch decreased, rumen pool size of starch increased, and postruminal digestion and digestibility of starch increased quadratically. When grass silage was the only source of forage in the diet, increasing chop length from 10 to 19 mm tended to decrease DMI but did not negatively affect productivity of cows, which were fed adequate fiber.     

Effects of alfalfa and cereal straw as a forage source on nutrient digestibility and lactation performance in lactating dairy cows

This study was conducted to investigate the nutrient digestibility and lactation performance when alfalfa was replaced with rice straw or corn stover in the diet of lactating cows. Forty-five multiparous Holstein dairy cows were blocked based on days in milk (164 ± 24.8 d; mean ± standard deviation) and milk yield (29.7 ± 4.7 kg; mean ± standard deviation) and were randomly assigned to 1 of 3 treatments. Diets were isonitrogenous, with a forage-to-concentrate ratio of 45:55 [dry matter (DM) basis] and contained identical concentrate mixtures and 15% corn silage, with different forage sources (on a DM basis): 23% alfalfa hay and 7% Chinese wild rye hay (AH), 30% corn stover (CS), and 30% rice straw (RS). The experiment was conducted over a 14-wk period, with the first 2 wk for adaptation. The DM intake of the cows was not affected by forage source. Yield of milk, milk fat, protein, lactose, and total solids was higher in cows fed diets of AH than diets of RS or CS, with no difference between RS and CS. Contents of milk protein and total solids were higher in AH than in RS, with no difference between CS and AH or RS. Feed efficiency (milk yield/DM intake) was highest for cows fed AH, followed by RS and CS. Cows fed AH excreted more urinary purine derivatives, indicating that the microbial crude protein yield may be higher for the AH diet than for RS and CS, which may be attributed to the higher content of fermentable carbohydrates in AH than in RS and CS. Total-tract apparent digestibilities of all the nutrients were higher in cows fed the AH diet than those fed CS and RS. The concentration of rumen volatile fatty acids was higher in the AH diet than in CS or RS diets, with no difference between CS and RS diets. When the cereal straw was used to replace alfalfa as a main forage source for lactating cows, the shortage of fermented energy may have reduced the rumen microbial protein synthesis, resulting in lower milk protein yield, and lower nutrient digestibility may have restricted milk production.     

Altering the ratio of dietary palmitic,stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility,energy partitioning,and production responses of dairy cows

The objective of this study was to evaluate the effects of varying the ratio of dietary palmitic (C16:0), stearic (C18:0), and oleic (cis-9 C18:1) acids in basal diets containing soyhulls or whole cottonseed on nutrient digestibility, energy partitioning, and production response of lactating dairy cows. Twenty-four mid-lactation multiparous Holstein cows were used in a split-plot Latin square design. Cows were allocated to a main plot receiving either a basal diet with soyhulls (SH, n = 12) or a basal diet with whole cottonseed (CS, n = 12) that was fed throughout the experiment. Within each plot a 4 × 4 Latin square arrangement of treatments was used in 4 consecutive 21-d periods. Treatments were (1) control (CON; no supplemental fat), (2) high C16:0 supplement [PA; fatty acid (FA) supplement blend provided ～80% C16:0], (3) C16:0 and C18:0 supplement (PA+SA; FA supplement blend provided ～40% C16:0 + ～40% C18:0), and (4) C16:0 and cis-9 C18:1 supplement (PA+OA; FA supplement blend provided ～45% C16:0 + ～35% cis-9 C18:1). Interactions between basal diets and FA treatments were observed for dry matter intake (DMI) and milk yield. Among the SH diets, PA and PA+SA increased DMI compared with CON and PA+OA treatments, whereas in the CS diets PA+OA decreased DMI compared with CON. The PA, PA+SA, and PA+OA treatments increased milk yield compared with CON in the SH diets. The CS diets increased milk fat yield compared with the SH diets due to the greater yield of de novo and preformed milk FA. The PA treatment increased milk fat yield compared with CON, PA+SA, and PA+OA due to the greater yield of mixed-source (16-carbon) milk FA. The PA treatment increased 3.5% fat-corrected milk compared with CON and tended to increase it compared with PA+SA and PA+OA. The CS diets increased body weight (BW) change compared with the SH diets. Additionally, PA+OA tended to increase BW change compared with CON and PA and increased it in comparison with PA+SA. The PA and PA+OA treatments increased dry matter and neutral detergent fiber digestibility compared with PA+SA and tended to increase them compared with CON. The PA+SA treatment reduced 16-carbon, 18-carbon, and total FA digestibility compared with the other treatments. The CS diets increased energy partitioning toward body reserves compared with the SH diets. The PA treatment increased energy partitioning toward milk compared with CON and PA+OA and tended to increase it compared with PA+SA. In contrast, PA+OA increased energy partitioned to body reserves compared with PA and PA+SA and tended to increase it compared with CON. In conclusion, milk yield responses to different combinations of FA were affected by the addition of whole cottonseed in the diet. Among the combinations of C16:0, C18:0, and cis-9 C18:1 evaluated, fat supplements with more C16:0 increased energy output in milk, whereas fat supplements with more cis-9 C18:1 increased energy storage in BW. The combination of C16:0 and C18:0 reduced nutrient digestibility, which most likely explains the lower performance observed compared with other treatments.