Nutrient demand interacts with legume particle length to affect digestion responses and rumen pool sizes in dairy cows

Effects of legume particle length on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, and digestion and passage kinetics, 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 19-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 22.8 to 32.4 kg/d (mean=26.5 kg/d) and 3.5% fat-corrected milk yield ranged from 22.9 to 62.4 kg/d (mean=35.1 kg/d). Experimental treatments were diets containing alfalfa silage chopped to (1) 19 mm (long cut, LC) or (2) 10 mm (short cut, SC) theoretical length of cut as the sole forage. Alfalfa silages contained approximately 43% neutral detergent fiber (NDF); diets contained approximately 47% forage and 20% forage 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 legume particle length and their interaction with pDMI were tested by ANOVA. Alfalfa particle length and its interaction with pDMI did not affect milk yield or rumen pH. The LC diet decreased milk fat concentration more per kilogram of pDMI increase than the SC diet and increased yields of milk fat and fat-corrected milk less per kilogram of pDMI increase than the SC diet, resulting in a greater benefit for LC at low pDMI and for SC at high pDMI. The LC diet tended to decrease DMI compared with the SC diet. Ruminal digestion and passage rates of feed fractions did not differ between LC and SC and were not related to level of intake. The LC diet tended to decrease the rate of ruminal turnover for NDF but increased NDF rumen pools at a slower rate than the SC diet as pDMI increased. This indicated that the faster NDF turnover rate did not counterbalance the higher DMI for SC, resulting in larger NDF rumen pools for SC than LC. As pDMI increased, LC increased ruminal digestibility of potentially digestible NDF and total NDF, and SC decreased them, but total-tract digestibilities of potentially digestible NDF, total NDF, organic matter, and dry matter were lower for LC than for SC. Ruminal digestibilities of starch and organic matter interacted quadratically with level of intake. When legume 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.     

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.     

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.     

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.     

Nutrient demand interacts with legume maturity to affect rumen pool sizes in dairy cows

Effects of legume maturity on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, and digestion and passage kinetics, and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 16 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 17-d treatment periods. During the preliminary period, the pDMI of individual cows ranged from 22.9 to 30.0 kg/d (mean=25.9 kg/d) and the 3.5% fat-corrected milk yield ranged from 34.1 to 68.2 kg/d (mean=43.7 kg/d). Experimental treatments were diets containing alfalfa silage harvested either a) early-cut, less mature (EC) or b) late-cut, more mature (LC) as the sole forage. Early- and late-cut alfalfa contained 40.8 and 53.1% neutral detergent fiber (NDF) and 23.7 and 18.1% crude protein, respectively. Forage:concentrate ratios were 53:47 and 42:58 for EC and LC, respectively; both diets contained approximately 22% forage NDF and 27% 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 alfalfa maturity and their interaction with pDMI were tested by ANOVA. Alfalfa maturity and its interaction with pDMI did not affect milk yield but EC increased DMI compared with LC; thus, EC had lower efficiency of milk production than LC. The EC diet decreased milk fat concentration more per kilogram of pDMI increase than the LC diet, but milk fat yield was not affected. The lower concentration and faster passage rate of indigestible NDF for EC resulted in lower rumen pools of indigestible NDF, total NDF, and dry matter than did LC, which EC increased at a slower rate than did LC as pDMI increased. The EC diet decreased starch intake and increased ruminal pH compared with the LC diet. The rate of ruminal starch digestion was related to level of intake, but this did not affect ruminal or postruminal starch digestion. Total-tract digestibility of NDF, organic matter, and dry matter was higher for EC than LC. Microbial efficiency tended to be related to pDMI and the response differed by treatment. When alfalfa silage was the only source of forage in the diet, cows supplemented with additional concentrate to account for decreased protein and increased fiber concentrations associated with LC produced similar fat-corrected milk yields with greater efficiency than cows fed EC.     

Silage chop length and hay supplementation on milk yield, chewing activity, and ruminal digestion by dairy cows

The effects of whole-plant corn silage (CS) particle size and long unprocessed grass hay (LH) supplementation on milk yield, chewing activity, and ruminal digestion in dairy cows were evaluated in 2 experiments. In Experiment 1, corn silage harvested at fine (6 mm; FCS) or coarse (23 mm; CCS) theoretical cut length were fed to 22 lactating Holstein cows. Treatments were 2 total mixed rations containing 58% of dry matter (DM) as FCS or CCS. Diet DM intake tended to be higher in cows fed FCS than those fed CCS (23.4 vs. 22.1 kg/d). However, milk yield and composition, body condition score, and plasma metabolite concentrations were not affected by the dietary treatments. In the second experiment, 5 cannulated Holstein cows were used in a 5 × 5 Latin square design to evaluate the effects of the addition of LH to the diets evaluated in Experiment 1 on chewing activity and ruminal digestion. Treatments were 5 total mixed rations: FCS-based diet plus the addition of 0, 5, or 10% LH (DM basis) and CCS-based diet plus 0 or 5% LH. Long hay addition linearly decreased DM intake in cows fed FCS-based diets (25.0 to 21.7 kg/d), but increased DM intake in those fed CCS-based diets (22.7 to 27.1 kg/d). The intake of neutral detergent fiber (NDF) increased with LH addition in CCS-based diets (7.6 vs. 9.4 kg/d). Rumination time increased (16.8 to 21.0 min/kg of DM intake) when LH was added to FCS-based diets, but it decreased when included in CCS-based diets (18.8 vs. 12.9 min/kg of DM intake). Ruminal pH was higher (5.9 vs. 5.7) and lag-time for in situ NDF disappearance was shorter (3.5 vs. 8.7 h) for cows fed CCS compared with cows fed FCS. The rate of NDF disappearance tended to be higher for the CCS-based diet with 5% LH than for the diet with 0% LH (2.0 vs. 4.4%/h), but solids passage rate was not affected by the treatments. These results suggest that addition of LH to FCS-based diets does not affect ruminal environment or digestion, but depressed DM intake. In contrast, addition of LH to CCS-based diets may improve ruminal NDF digestion, increasing DM intake by reducing filling effect and time needed for rumination.     

Effect of particle size of forage and rumen cannulation upon chewing activity and laterality in dairy cows

Three ruminally cannulated Holstein dairy cows housed in free stalls (with .7% slope) were fed three total mixed rations, differing in silage particle size, in a 3 x 3 Latin square design. Observations on cow behavior were made every 5 min during 24 h for each of three periods. Additional observations of six cows (three intact, three cannulated) housed under identical conditions yielded information concerning recumbent rumination activity and laterality. Results indicated that decreasing particle size of forage reduced time spent ruminating, whether standing or recumbent, and had no effect upon rumination rate or number of rumination bouts per 24-h period. Eating time was unaffected by treatment. Effect of forage particle size upon baseline rumination activity appeared to be most pronounced from 0800 to 2000 h, although maximum rumination activity occurred during nighttime hours. Ruminally cannulated cows demonstrated increased right-side laterality (70%) compared with intact cows (47%), but the cows tend to ruminate while lying on their left side. The percentage of time spent ruminating while recumbent on the left side was similar (55%) for intact and cannulated cows.     

Nutrient demand affects ruminal digestion responses to a change in dietary forage concentration

Previous research in our laboratory has indicated that the physical filling effects of high-forage diets become increasingly dominant in determining feed intake and milk production as nutrient demand increases. This effect was tested further by using 14 ruminally and duodenally cannulated Holstein cows in a crossover design experiment with a 14-d preliminary period and two 15-d experimental periods. During the preliminary period, 3.5% fat-corrected milk yield was 15 to 60 kg/d (mean = 40 kg/d), and preliminary voluntary dry matter intake (pVDMI) was 20.6 to 30.5 kg/d (mean = 25.0 kg/ d). Treatments were a low-forage diet (LF), containing 20% (dry matter basis) forage neutral detergent fiber (NDF), and a high-forage diet (HF), containing 27% forage NDF. The ability of linear and quadratic factors of pVDMI to predict the difference in responses of individual cows to treatments (Y_LF - Y_HF) was tested by ANOVA, with treatment sequence as a covariate. In contrast to results of previous research, differences in dry matter intake and fat-corrected milk yield responses to LF and HF did not depend on pVDMI. This might be because of the combined physical fill and metabolic satiety effects of LF, especially in cows with the greatest pVDMI. Digestion or passage of NDF might have been inhibited on LF among high-pVDMI cows. As pVDMI increased, NDF turnover time increased more on LF than on HF. Among high-pVDMI cows, the NDF turnover time was unexpectedly greater on LF than on HF. With increasing pVDMI, the digestion rate of potentially digestible NDF decreased at a similar rate on both diets. Passage rates of potentially digestible NDF and indigestible NDF were not related to pVDMI, regardless of treatment. Greater starch fermentation (resulting from greater starch intake) for LF as pVDMI increased likely inhibited NDF digestion through pH-dependent and pH-independent effects. Inhibition of NDF digestion might cause LF and HF to have similar effects on dry matter intake, depending on the nutrient demand of individual cows.     

Implication of forage particle length on chewing activities and milk production in dairy goats

Twenty-four primiparous Alpine does fed a high concentrate ration were utilized to study the effect of forage particle length on chewing activity, ruminal components, and milk composition. Treatments were Bermudagrass hay with mean particle length of 2.38 and 3.87 mm. Forage particle length was determined with an oscillating screen particle separator. Feeding forage with 3.87-mm mean particle length to lactating dairy goats resulted in higher total chewing and rumination times, slightly higher milk fat content, and fat-corrected milk production. Results from this experiment support the hypothesis that forage particle length affects chewing activities and production of milk fat precursors in the rumen and alters milk fat content and output of fat-corrected milk. Forage particle length appeared to be an important index for forage quality and a quantitative approach could be feasible to establish a system relating forage particle length to milk production in dairy goats.     

Effects of alfalfa particle size and specific gravity on chewing activity, digestibility, and performance of Holstein dairy cows

Two experiments were carried out to test the effects of alfalfa particle size and functional specific gravity (FSG) on chewing activity, digestibility, rumen kinetics, and production of lactating dairy cows fed corn silage based rations. In experiment 1, water-holding capacity (WHC), insoluble dry matter, hydration rate, and FSG changes were determined in alfalfa hay (varying in particle size) and corn silage. Reduction of particle size increased bulk density, FSG, and the rate of hydration, and decreased WHC of alfalfa. In experiment 2, 9 midlactation Holstein dairy cows fed total mixed rations containing 3 sizes of alfalfa hay (with geometric mean 7.83, 4.04, and 1.14 mm) were used in a replicated 3 x 3 Latin square design. The diets contained 20, 20, 35, 7, 7.5, 10, 0.3, 0.1, and 0.1% of DM alfalfa, corn silage, barley, soybean meal, beet pulp, wheat bran, dicalcium phosphate, vitamin premix, and salt, respectively. The geometric means (GM) of rations were 3.34, 2.47, and 1.66 mm in long, medium, and fine alfalfa treatments, respectively. Reduction of particle size increased daily NDF intake (kg), but decreased the proportion of physically effective factor (pef) and physically effective NDF (peNDF) in the ingested rations. Reduction of particle size increased the FSG of rations and intake of DM but reduced digestibility of NDF and ash. Reduction of particle size decreased ruminal mean retention time (RMRT), but increased the ruminal particulate passage rate. Milk and FCM yield were not affected by treatments. The rumen pH, total chewing activity, rumination, eating time, and milk fat were reduced as particle size decreased, but milk protein increased. This study showed that reduction of forage particle size increased bulk density, FSG, and hydration rate of alfalfa and was the most influential factor affecting DMI, milk composition, and chewing behavior. Reduction of forage particle size had minimal impact on digestibility and milk production.     

The effect of harvesting strategy of grass silage on digestion and nutrient supply in dairy cows

This study examined the effects of primary growth (PG) and regrowth (RG) timothy-meadow fescue silages harvested at 2 stages of growth on feed intake, cell wall digestion and ruminal passage kinetics in lactating dairy cows. Four dairy cows equipped with rumen cannulas were used in a study designed as a 4 × 4 Latin square with 21-d periods. The experimental silages were offered ad libitum with 8 kg/d of concentrate. Ruminal digestion and passage kinetics were assessed by the rumen evacuation technique. Silages of PG were on average more digestible than RG silages. The concentration of neutral detergent fiber (NDF) and indigestible NDF (iNDF) increased and the concentration of digestible organic matter in dry matter (DM) of silages decreased with advancing maturity in PG and RG. Cows consumed more feed DM, energy, and protein and produced more milk when fed PG diets rather than RG diets. Delaying the harvest decreased DM intake and milk production in PG and RG. There were no differences between PG and RG in rumen pH, ammonia N, or total volatile fatty acid concentrations. The intake of N, omasal canal flow of total nonammonia N and microbial N, excretion of N in feces, and ruminal true digestibility of N were higher for PG than for RG diets. The efficiency of microbial N synthesis was not different between PG and RG. Intake and omasal canal flow of organic matter, NDF, and potentially digestible NDF (pdNDF) were higher in PG than in RG. Whole-diet digestibility of organic matter, NDF, or pdNDF in the rumen or in the total tract was not different between PG and RG despite the higher digestibility of PG silages measured in sheep. Rumen pool sizes of crude protein and iNDF were lower for PG diets, whereas the pool size of pdNDF was higher for PG diets than for RG diets. The rate of passage of iNDF was higher for PG diets than for RG diets, with no difference between them in rate of digestion or passage of pdNDF. The lower milk production in cows fed regrowth grass silages compared with primary growth silages could be attributed to the lower silage DM intake potential. Chemical composition of the silages, rumen fill, digestion and passage kinetics of NDF, or the ratio of protein to energy in absorbed nutrients could not explain the differences in DM intake between silages made from primary and regrowth grass.     

Exchanging physically effective neutral detergent fiber does not affect chewing activity and performance of late-lactation dairy cows fed corn and sugarcane silages

The objective of this study was to determine whether replacing the physically effective neutral detergent fiber (peNDF) of corn silage with sugarcane silage peNDF would affect performance in dairy cows. Twenty-four late-lactation Holstein cows were assigned to eight 3 × 3 Latin squares with 21-d periods. The dietary treatments were (1) 25% peNDF of corn silage, (2) 25% peNDF of sugarcane silage, and (3) 12.5% peNDF of corn silage + 12.5% peNDF of sugarcane silage. The physical effectiveness factors (pef) were assumed to be 1 for corn silage and 1.2 for sugarcane silage, as measured previously by bioassay. Thus, peNDF was calculated as neutral detergent fiber (NDF) × pef. The concentrate ingredients were finely ground corn, soybean meal, pelleted citrus pulp, and mineral-vitamin premix. Dry matter intake (22.5 ± 0.63 kg/d), 3.5% fat-corrected milk yield (28.8 ± 1.13 kg/d), milk composition (fat, protein, lactose, urea, casein, free fatty acids, and somatic cell count), and blood metabolites (glucose, insulin, and nonesterified fatty acids) were unaffected by the treatments. The time spent eating, ruminating, or chewing was also similar among the diets, as was particle-sorting behavior. By contrast, chewing per kilogram of forage NDF intake was higher for the sugarcane silage (137 min/kg) than the corn silage diet (116 min/kg), indicating the greater physical effectiveness of sugarcane fiber. Based on chewing behavior (min/d), the estimated pef of sugarcane silage NDF were 1.28 in the corn silage plus sugarcane silage diet and 1.29 in the sugarcane silage diet. Formulating dairy rations of equal peNDF content allows similar performance if corn and sugarcane silages are exchanged.     

Effect of dietary strong ions on chewing activity and milk production in lactating dairy cows

The objective of this experiment was to determine effects of strong ions on chewing activity and short-term lactational performance of dairy cows. Forty multiparous Holstein cows were used in a replicated 5 × 5 Latin square design with a 2 × 2 factorial arrangement of equimolar treatments for cations (sodium and potassium), anions (chloride and bicarbonate), plus a control diet. Periods were 14 d in length with the last 4 d for data and sample collection. Diets were formulated to 29% neutral detergent figer and 17.5% crude protein. Sodium bicarbonate was included at 1% of dry matter in one treatment diet, and other treatments (sodium chloride, potassium chloride, and potassium bicarbonate) were added to be equimolar to sodium bicarbonate in their respective diets. Chewing activity was recorded every 5 min for the last 24 h of each period. Dry matter intake was not affected by treatment (mean = 27.9 kg/d). Bicarbonate treatments increased yields of milk, milk fat, and fat- and solids-corrected milk compared with chloride treatments, but cation treatments did not affect any measured variable. The 4 ion treatments reduced ruminating time per day when compared with control by decreasing the length of rumination bouts. This effect was not specific to cations or anions suggesting a mechanism related to increased ruminal osmolality.     

Effect of corn particle size on site and extent of starch digestion in lactating dairy cows

Two experiments were conducted to determine the effects of corn particle size (CPS) on site and extent of starch digestion in lactating dairy cows. Animals were fitted with ruminal, duodenal, and ileal cannulas. Dry corn grain accounted for 36% of dry matter intake. In experiment 1, 6 cows were used in a duplicate 3 x 3 Latin square design. Semiflint corn was used. Corn processing methods were grinding, medium rolling, and coarse rolling. The mean particle size of the processed corn was 730, 1807, and 3668 microm, respectively. Rumen digestibility of starch linearly decreased from 59% with ground corn to 36% with coarsely rolled corn. Similarly, small intestine digestibility linearly decreased with increased CPS, and consequently, the amount of starch digested in the small intestine was not affected by corn processing. In experiment 2, 4 cows were used in a 2 x 2 crossover design. Dent corn was used. Corn processing methods were grinding and coarse rolling. The mean particle size of the processed corn was 568 and 3458 microm, respectively. Rumen digestibility of starch decreased from 70% with ground corn to 54% with coarsely rolled corn. Small intestine digestibility of starch was not significantly affected by CPS, and the amount of starch digested in the small intestine tended to be greater for rolled than for ground corn. In both experiments, starch total tract digestibility decreased with increased CPS. In conclusion, CPS is an efficient tool to manipulate rumen degradability of cornstarch. In midlactation cows, the decrease in the amount of starch digested in the rumen between grinding and coarse rolling is partly compensated for by an increase in the amount of starch digested in the small intestine with dent genotype, but with semiflint genotype postruminal digestion is not increased and rumen escape starch is not utilized by the animal.     

Forage proportion and particle length affects the supply of amino acids in lactating dairy cows

This study was conducted to evaluate the effects of dietary factors that alter ruminal fermentability on intake, duodenal flows and intestinal digestibility of individual amino acids (AA) in lactating dairy cows. The experiment was designed as a 4×4 Latin square using 4 ruminally and duodenally cannulated lactating dairy cows. Treatments were arranged in a 2×2 factorial design; 2 forage particle lengths (FPL) of alfalfa silage (short and long) were combined with low (35:65) and high (60:40) forage-to-concentrate ratio (F:C; dry matter basis). Four diets were formulated using 2 cuts of alfalfa silage [short (7.9 mm) and long (19.1mm)], combined with 2 ratios of forage to barley grain concentrate (35:65 and 60:40). Overall, the interactions between dietary F:C and FPL on intake, duodenal flows, and intestinal digestibility of AA were marginal. Intakes of total AA and nonessential AA were not different between low- and high-F:C diets, whereas that of essential AA tended to be less with high-F:C diet as a result of lower intakes of Met, Phe, Arg, and His. The flows of total AA and microbial AA were reduced by 22 and 19%, respectively, with increasing F:C ratio in the diets due to consistently reduced flows of individual AA, whereas AA profiles (% of AA-N) of the duodenal protein were not different. Altering F:C from 35:65 to 60:40 decreased the intestinal digestibility of Ile, Leu, Thr, Val, Ala, Cys, and Ser, and consequently, tended to decrease the digestibility of total AA, essential AA, and nonessential AA. Intakes of total AA, essential AA, and nonessential AA were overall not affected by dietary FPL so FPL did not affect the flows or intestinal digestibility of AA. These results indicate that increasing dietary F:C ratio decreased overall AA supply because flow to the duodenum and intestinal digestibility of AA were decreased. However, increasing FPL had no effect on AA supply. The measured duodenal flows of AA were consistent with the predictions of the Cornell Net Carbohydrate and Protein System model for the low-forage diet, and were consistent with the National Research Council model for the high-forage diet. Furthermore, the digestibility of individual AA in the intestine varied considerably, regardless of dietary treatment. The results revealed the necessity to consider the both flows and digestibility of individual AA when optimizing ration formulation to meet AA requirements of dairy cows.     

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.     

Effects of varying dietary forage particle size in two concentrate levels on chewing activity, ruminal mat characteristics, and passage in dairy cows

The objective of this study was to investigate the effects of varying dietary forage particle size on chewing activity, ruminal mat characteristics, passage, and in situ ruminal and total tract digestion in dairy cows at a low- and high-concentrate inclusion. The experiment was designed as a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments. Four ruminally cannulated late-lactating dairy cows were restrictively fed (17 kg of dry matter/d), in four 23-d periods, 1 of 4 different diets varying in the theoretical particle size (6 and 30 mm) of hay (56.6% NDF of dry matter) and in the levels (approximately 20 and 60%, dry matter basis) of a cereal-based concentrate. Ingredients of the ration were offered separately to the cows; dietary hay and low-level concentrate were offered twice daily at 0800 and 1600 h, whereas concentrate of the high-level treatment was offered in 4 meals a day at 0800, 1200, 1600, and 1900 h. This study showed that altering the forage particle size from 6 to 30 mm in a low-concentrate diet significantly increased the rumination time and ruminal mat consistency without affecting ruminal fermentation and passage. Further, particle breakdown and proportion of mat in the rumen increased, and in situ hay dry matter degradability improved, which in turn indicated a higher capacity of ruminal digesta to degrade fiber. On the other hand, increasing the forage particle size in a diet containing a high amount of concentrate increased the proportion of dry matter retained on a 1.18-mm screen from 37.5 to 42.0% and extended the rumination time by 100 min/d, as well as increasing the ruminal mat consistency. However, ruminal particle breakdown, short-term ruminal pH, fibrolytic capacity of the digesta, and proportion of mat in the rumen decreased. This was also reflected in a higher bailable liquid pool, increased fractional passage rate of solid digesta from the reticulorumen, and increased retention time in the hindgut, which in turn indicated a shift of fiber digestion from the rumen to the lower digestive tract. This study showed that the response of chewing or ruminating activity alone seemed to be insufficient to assess the dietary physical effectiveness or fiber adequacy in limit-fed dairy cows when high-concentrate diets were fed separately. Based on the results of this study, we concluded that inclusion of coarsely chopped hay in the high-concentrate diet did not appear to further improve rumen conditions and digestion when the rations were formulated to exceed the fiber requirements in limit-fed dairy cows.     

Nutrient digestion and lactation performance of dairy cows fed combinations of prilled fat and canola oil.

Four combinations of prilled fat and canola oil were fed to 10 lactating Holstein cows in a replicated 5 x 5 Latin square to determine whether mixing plant oil with a rumen inert fat had additive effects on digestive and lactation responses. Five diets of concentrate and corn silage (1:1, DM basis) contained either no added fat (control) or 5% fat comprising 100, 67, 33, or 0% prilled fat and the remainder canola oil. The fat supplement containing 100% prilled fat appeared to be rumen-inert because it caused no changes in ruminal VFA concentration, acetate to propionate ratio, or total tract fiber digestion. Prilled fat increased milk production, FCM, and milk fat percentage but decreased milk protein percentage, including casein content. Increasing canola oil in the fat supplement caused linear declines in ruminal VFA, acetate to propionate ratio, and milk production. Milk production efficiency (weight FCM/weight DMI) exceeded the control diet when fat supplements contained 100 or 67% prilled fat but dropped below control for 33 and 0% prilled fat. This study demonstrates additive effects of combining canola oil with hydrogenated, prilled fat on ruminal fermentation but nonadditive effects on milk production efficiency and milk composition. At low levels of supplementation, plant oils, such as the canola oil used in this study, can inhibit ruminal fermentation but still maintain milk production efficiency.     

Starch and stage of maturity of grass silage: site of digestion and intestinal nutrient supply in dairy cows

The interaction between the quality of grass silage and starch supplementation on ruminal digestion was studied in an experiment with a 2 x 2 factorial design using four dairy cows. Treatment factors were grass silage harvested after either 21 or 37 d of regrowth and two concentrations of steam-flaked corn starch (0 or 4 kg/d). Ruminal volume and flow of duodenal digesta were estimated. When forage was harvested at a more mature stage, only minor effects were noted for silage composition and, consequently, ruminal and intestinal digestion. The addition of starch to the diet tended to reduce ruminal digestion of neutral detergent fiber. The reduction in ruminal digestion was not compensated by increased digestion in the large intestine. Starch increased duodenal nonammonia N flow because of an increase in bacterial N flow. The increase in bacterial N was accompanied by a reduction in the escape of feed N from the rumen. Results from this study indicate that the addition of ruminally available starch to diets based on grass silage reduced ruminally degradable neutral detergent fiber and increased the duodenal supply of protein. These effects have to be taken into account to predict production responses to extra starch.