Effect of dietary neutral detergent fiber concentration and forage source on performance of lactating cows

'Mott' dwarf elephantgrass, forage sorghum, 'Tifton 81' bermudagrass, and whole corn plant were stored as silage and fed as the only forage source in diets formulated to 31, 35, and 39% NDF. The 12 diets were fed for ad libitum intake as a TMR to midlactation Holstein cows, primarily to determine the effect of NDF concentration and forage source on DMI and milk production. Increased dietary NDF concentration linearly decreased DMI (3.69 to 3.35%) and OM intake (3.39 to 3.06%) as a percentage of BW and linearly increased NDF intake as a percentage of BW (1.15 to 1.32%). Production of milk (23.0 to 21.7 kg/d) and 4% FCM (20.7 to 19.6 kg/d) and percentage of milk protein (3.16 to 3.07%) decreased linearly as dietary NDF concentration increased. Cows fed dwarf elephantgrass silage or corn silage, which were higher quality forage sources based on greater rates and extents of fiber digestion, consumed more DM and produced more milk than cows fed sorghum silage or bermudagrass silage. Cows fed diets containing sorghum silage had the lowest DMI and milk production. Apparent digestibility of NDF and ADF from corn silage and dwarf elephantgrass silage was greater than that of sorghum silage and bermudagrass silage. In addition to dietary NDF concentration, digestibility of dietary fiber influences DMI and milk production.     

Effects of fiber from tropical corn and forage sorghum silages on intake, digestion, and performance of lactating dairy cows

Tropical corn silage was compared with sorghum silage as a basal forage in the diets of high producing dairy cows. Sorghum and tropical corn silages were each included in place of ground corn at incremental concentrations in the experimental diets. Eight separate diets were fed, four diets containing each silage ranging in forage neutral detergent fiber (NDF) from approximately 25 to 31% and ranging in total NDF from approximately 41 to 45%. Diets were arranged in a 2 x 4 factorial design and were fed to lactating cows (n = 24; pretrial mean milk production = 39 kg/d; body weight = 656 kg; and days in milk = 81). As concentrations of dietary NDF increased, intake and milk production decreased linearly. The impact of dietary NDF on intake was greater for diets based on tropical corn silage than for diets based on sorghum silage. Energy intake and milk production were reduced, but cows consumed more fiber when challenged with higher dietary concentrations of fiber. The in vitro rate and extent of digestion of dietary samples were correlated with intake response. The rate of in vitro fiber digestion was slower for samples that contained tropical corn silage than for samples that contained sorghum silage. In vivo digestibility measurements were influenced by intake and dietary composition. Results of this trial indicated that sorghum silage can have equal or slightly greater nutritional value than tropical corn silage when these forages are fed at equal concentrations of dietary fiber.     

Timothy grass or alfalfa silage for cows in midlactation: effect of supplementary barley

Twenty-four multiparous Holstein cows averaging 104 d of lactation were used in a trial with a split-plot design to evaluate the nutritive value of two silages, timothy grass or alfalfa, both treated with formic acid and stored in plastic bag silos. Silages were offered for ad libitum intake either alone or with 17 or 34% (dry matter basis) dry-rolled barley. Both silages contained similar amounts of acid detergent fiber (ADF) (27.5 and 26.7% for timothy grass and alfalfa, respectively). After 110 d of storage, alfalfa silage contained higher amounts of organic acids and NH3 N but had lower soluble N. Total dry matter intake (DMI) and silage DMI were similar between cows fed both silages. Increased barley proportion decreased silage DMI (19.2 to 14.2 kg/d). Apparent total tract digestibility of dry matter was unaffected by treatment. The digestibility of neutral detergent fiber and ADF was higher for the timothy grass silage than for alfalfa silage and was unaffected by the barley percentage added to either silage. Milk yield was lower (23.9 to 22.6 kg/d) for cows fed the highest proportion of barley. The 4% fat-corrected milk yield was unaffected by treatment. Percentages of fat, protein, and total solids in milk were higher for cows fed diets with the higher barley content. Milk fat and protein yields were similar among treatments. Urea in blood was lower for cows fed timothy grass silage than for cows fed alfalfa silage (4.68 vs. 6.23 mg/100 ml). These results suggest that timothy grass silage and alfalfa silage, when stored at a similar ADF content, have comparable nutritive value for midlactation cows.     

The effect of replacing dietary beet pulp with wheat treated with sodium hydroxide, ground wheat, or ground corn in lactating cows

This experiment examined the effect of complete diets composed of 60% grass silage and 40% concentrate based mainly on beet pulp, ground wheat, wheat treated with NaOH, or ground corn on milk production and ruminal fermentation of dairy cows. Milk production and fat yield were 19.8, 20.7, 20.1, and 21.2 kg/d and 0.71, 0.76, 0.72, and 0.78 kg/d, respectively (18 cows per treatment). Cows fed the diet based on ground corn had higher milk production and fat yield, but lower milk protein concentration, than did cows fed the diet based on beet pulp. Cows fed the diet based on ground corn also had higher fat yields than did cows fed the diet based on wheat treated with NaOH. Cows fed the diet based on ground wheat had lower ruminal pH than did cows fed the diet based on beet pulp (6.34 vs. 6.59) and higher ruminal NH3 concentrations (6.2 vs. 5.2 mmol/L) than did cows fed the diet based on ground corn. These results showed little difference in milk production based on wheat processing method and little advantage to replacing beet pulp with either wheat type in a high forage diet. However, milk production and fat yield were increased by replacing beet pulp with ground corn.     

Synchronization of ruminal degradation of supplemental carbohydrate with pasture nitrogen in lactating dairy cows

Twelve Holstein cows in early to midlactation (8 fitted with ruminal cannulas) were used to test the hypothesis that the synchronization of the rate of ruminal degradation of supplemental carbohydrate and N from fresh pasture would increase the amount of N retained for growth and milk production. A concentrate based on ground shelled corn was fed either at the time that pasture was fed at 0900 and 1700 h (synchronous) or 4 h after pasture was fed at 1300 and 2100 h (asynchronous). The crossover design included a 6-d adjustment period and a 10-d milk sampling period. Nitrogen balance was determined during the last 5 d of each period. Cows fed the synchronous diet had a lower mean ruminal pH. Peak ammonia concentration at 3 and 5 h after pasture feeding in the morning was reduced by approximately 33% of values obtained from cows fed the asynchronous diet. The diurnal pattern of blood urea N concentration was similar to that of ruminal ammonia, but mean daily concentrations of blood urea N did not differ between diets. Nitrogen retained for milk production and growth was not influenced by diet, and no differences in milk production, composition, or efficiency were observed. Based on changes in ruminal concentrations of ammonia, synchronous ruminal release of supplemental carbohydrate with pasture N appeared to improve the capture of ruminal N; however, these changes were transient and did not change the N status or performance of dairy cows.     

Performance, ruminal fermentation, and site of starch digestion in early lactation cows fed corn grain harvested and processed differently

Two experiments were conducted to assess the effects of corn grain processing on performance, ruminal fermentation, and starch digestion in early lactation dairy cows. Diets were based on wilted alfalfa silage and high moisture or dry corn grain that was either ground or rolled. Thirty-four cows (17 multi-parous) were used to measure effects on intake and lactational performance in a free-stall environment during wk 2 to 15 postpartum. Grinding increased dry matter intake, particularly for cows fed diets containing dry corn, and tended to increase yields of milk, protein lactose, and SNF. Cow performance was not affected by the moisture content of the corn grain. In the digestion experiment, six cows (43 d of lactation) with ruminal, duodenal, and ileal cannulas were used to measure ruminal and intestinal digestion. Search digestion in the rumen and small intestine was greater for high moisture corn, but disappearance of starch in the large intestine was greater for dry corn. Both the grinding process and the high moisture content of the corn increased starch digestibility in the total tract. Flow of microbial N in the duodenum was not affected by treatment. High moisture corn increased starch digestion in the rumen and total tract and enhanced ruminal fermentation as indicated by increased volatile fatty acids and decreased NH3 concentrations in the rumen. In the production experiment, however, only grinding improved the value of corn; ensiling at high moisture content had little effect.     

Interactions of tallow and hay particle size on yield and composition of milk from lactating Holstein cows

An 18-wk lactation study was conducted to determine whether the effects of tallow on the lactation performance of dairy cows were influenced by particle size of hay in the ration. A total mixed ration containing 50% concentrate, 25% corn silage, and 25% alfalfa hay (dry matter basis) was fed to Holstein cows. Four total mixed rations were developed based on differences in the percentage of tallow in the concentrate and particle size of alfalfa hay: 1) 0% tallow, long-cut hay; 2) 0% tallow, short-cut hay; 3) 5% tallow, long-cut hay; and 4) 5% tallow, short-cut hay. Ration had no effect on dry matter intake, body weight gain or change in body condition score. Tallow increased milk and milk protein yields but reduced milk protein concentration. However, the effects of tallow on milk and milk protein yields were the same, regardless of hay length in the ration. A tendency for an interaction of tallow and hay particle size was detected for fat-corrected milk (FCM) because tallow increased FCM more when hay was short. Ration had no effect on volatile fatty acids in ruminal samples collected via a stomach tube. In this study, the effects of tallow on milk yield and composition from Holstein cows were the same, regardless of hay particle size in the ration. The tendency for tallow to increase FCM more when hay was short suggests at least a limited role of forage particle size in the determination of how fat supplements in dairy rations affect lactation performance.     

Milk yield, intake, and blood traits of lactating cows fed grass silage conserved under different harvesting methods

Thirty-two Holstein cows (8 primiparous) were assigned to negative control or to one of three treatments to assess three forage harvesting and conservation techniques. Forage was harvested as low moisture silage by either a cylinder-type forage harvester, a self-loading forage harvester, or a round baler. Treatment diets were fed from wk 4 to 15 of lactation and consisted of silages harvested by the respective methods supplemented with concentrate at 1.1% of BW. Unsupplemented silage harvested by a cylinder-type forage harvester was used as a control. Daily DMI was higher for cows fed supplemented heap silage cut with either a cylinder-type forage harvester (23.7 kg) or a self-loading forage harvester (22.6 kg) than for cows fed the control (20.0 kg) or supplemented round bale silage (20.1 kg). Milk yield was highest for cows fed supplemented heap silage cut with a cylinder-type forage harvester (26.6 kg/d) and lower for those fed supplemented heap silage cut with a self-loading forage harvester (22.7 kg/d) or the control (20.8 kg/d). Milk composition and digestibilities of DM, N, ADF, and energy were similar among treatments. Postfeeding NEFA concentration decreased more for control cows than for those fed supplemented silage, which was related to greater BW loss. The high milk yield for cows fed supplemented heap silage cut with a cylinder-type forage harvester could be related to a high DMI and low BW gain.     

Substitution of neutral detergent fiber from forage with neutral detergent fiber from by-products in the diets of lactating cows

Four lactating dairy cows that were ruminally and duodenally cannulated were used in an experiment with a 4 x 4 Latin square design to determine the effects of the substitution of neutral detergent fiber (NDF) from forage with NDF from wheat middlings, corn gluten feed, or a blend of distillers dried grains and hominy. Dietary crude protein and NDF averaged 18 and 31%, respectively, for the diet with 71.2% of the NDF from forage (control diet) and for diets with 55% of the NDF from forage (by-product diets). The substitution of NDF from these by-products for forage NDF did not affect dry matter intake (20.1 kg/d) or digestibility of organic matter. Total tract digestibility of acid detergent fiber was lower for cows fed the diet containing a blend of distillers dried grains and hominy than for cows fed the diet containing corn gluten feed. Microbial crude protein synthesis, milk production (23.9 kg/d), and milk fat percentage were similar for all cows, regardless of diet. Cows fed the diets containing wheat middlings or a blend of distillers dried grains and hominy had reduced ruminal pH compared with that of cows fed the diet containing corn gluten feed or the control diet. Diets containing 55% of total NDF from forage with 31% of total NDF from corn gluten feed, wheat middlings, or a blend of distillers dried grains and hominy can supply sufficient effective fiber to maintain normal ruminal function.     

Roasted soybeans, blood meal, and tallow as sources of fat and ruminally undegradable protein in the diets of lactating cows

The effect of roasted soybeans, blood meal, and tallow as sources of fat and RUP for lactating dairy cows was studied. Forty-five cows, blocked by age, calving date, and milk yield during the previous lactation, were assigned randomly to the following treatments (ingredient in the DM, RUP as a percentage of CP, and fat in the DM, respectively): 1) soybean meal (16, 35, and 3.2%), 2) whole roasted soybeans (18, 40, and 6.2%), 3) ground roasted soybeans (18, 40, and 6.2%), 4) blood meal (2.7, 40, and 3.2%), and 5) blood meal plus tallow (2.7 and 3, 40, and 6.2%). Diets were fed from wk 3 to 18 of lactation and consisted of 20% alfalfa silage, 30% corn silage, and 50% concentrate. The DMI of blood meal and whole roasted soybean diets was about 11% lower than DMI of the soybean meal diet. Milk yield (38.4 kg/d) and milk fat percentage (3.37%) were similar among diets. The roasted soybean diets resulted in the lowest milk protein percentage. Less than 2.7% blood meal might be advisable for diets fed to high yielding dairy cows to avoid reduced DMI.     

Juice-extracted grass pellets and sodium bicarbonate for cows fed timothy silage of two chop lengths

Eighteen multiparous Holstein cows in midlactation were used in a switchback design trial to evaluate the effect of chop length (3 or 30 mm) of timothy grass silage, containing less than 30% ADF and treated with formic acid, on DMI and cow performance. Within chop length, addition of NaHCO3 (2% of DMI) or the replacement of 30% of silage DM with juice-extracted grass pellets was also evaluated. Cows were fed a TMR composed of 90% silage and 10% concentrate. Silage preservation characteristics were not different between chop lengths. The DMI and apparent digestibility were similar among treatments. Yields of 4% FCM (24.9 vs. 22.7 kg/d), fat (1.03 vs. .93 kg/d), and protein (.83 vs .77 kg/d) were higher with the short chopped silage. Milk protein, milk NPN content, and serum urea were higher for cows fed long chopped silage. Yields of milk and milk constituents were not affected by the addition of juice-extracted grass pellets or NaHCO3. Fat percentage and fatty acid composition of milk remained unchanged by treatments. Reduction of particle size, from 30 to 3 mm, of timothy grass, treated with formic acid at harvest and using compaction at ensiling in bag silos, did not affect silage conservation characteristics but did improve milk, fat, and protein yields when cows were fed high silage diets.     

Digestion and energy balance in lactating dairy cows fed varying ratios of alfalfa silage and grain

Forty-four multiparous and 43 primiparous Holstein cows were used to study the effect of dietary alfalfa silage: grain ratio on digestion, passage of digesta, and energy balance in a complete lactation experiment. Cows were placed on one of five treatments with forage contents from 38.2 to 98.2% (DM basis) during the first 12 wk of lactation. Forage content was increased during wk 13 to 26 of lactation to give diets containing 48.2 to 98.2% forage and again during wk 27 to 44 to give diets containing 68.2 to 98.2% forage. Both DMI and DM digestibilities decreased as proportion of dietary forage increased. The DM digestibilities for multiparous and primiparous cows ranged between 69.3 and 57.3% during early lactation and 64.9 and 55.5% during late lactation. Increased percentage of forage in the diet decreased and then increased (quadratic relationship) the ruminal retention time of La, a marker applied to the alfalfa silage in early and late lactation. Time cows spent eating and ruminating per kilogram of DMI increased as proportion of forage in the diet increased. Cows fed diets with a high proportion of alfalfa silage remained in negative energy balance longer than cows fed high grain diets. Intake of NEL (calculated by either of two methods) minus NEL output (milk, maintenance, and BW change) resulted in net balances of NEL after 36 wk of lactation within 5% of NEL intake and indicated that estimates of the NEL value of feedstuffs used in this experiment were reasonably accurate.     

Female pelvic floor: endovaginal MR imaging of normal anatomy

Five types of processed corn were compared to determine the effects of processing on lactational performance and nutrient digestibilities in dairy cows. Forty lactating Holstein cows averaging 160 +/- 60 d in milk were randomly divided into five groups on the basis of pretreatment milk yields and were fed diets containing 40% corn grain for 56 d. Treatments were 1) finely ground corn, 2) coarsely ground corn, 3) steam-flaked corn at a low density, 4) steam-flaked corn at a medium density, and 5) steam-rolled corn. Cows fed the diet containing steam-flaked corn at a medium density had a higher milk yield (37.1 kg/d) than did cows fed the diets containing coarsely ground corn, steam-flaked corn at a low density, or steam-rolled corn; cows fed the diet containing finely ground corn had an intermediate milk yield (35.5 kg/d). Efficiency of feed utilization was greater, and dry matter intake was lower, for cows fed the diet containing finely ground corn than for cows fed the other diets. The fat content of milk was higher for cows fed the diets containing coarsely ground corn and steam-rolled corn than for cows fed the diet containing steam-flaked corn at a medium density. Milk protein and SNF contents and yields of protein, lactose, and SNF did not differ among diets. Apparent starch digestibilities in the total digestive tract were lower for diets containing coarsely ground corn (87.4%) and steam-rolled corn (91.3%) than for the other diets (X = 96.3%). Milk yield was highest for cows fed the diet containing steam-flaked corn with a medium density. Fine grinding resulted in the greatest efficiency of feed utilization.     

Feed intake relative to stage of lactation for dairy cows consuming total mixed diets with a high or low ratio of concentrate to forage

This experiment examined the effect of feed quality on the relationship between intake and stage of lactation in dairy cows. Two total mixed diets composed of grass silage and concentrate were formulated. The high concentrate total mixed diet was designed to meet energy requirements, and the low concentrate total mixed diet was designed to limit intake. Twenty-four Holstein-Friesian cows were offered the total mixed diets in a full 2 x 2 change-over design with control treatments. The changeover was at 153 d in milk (DIM). For the statistical analyses, two periods of 13 wk, one period before and one period after the changeover, were used. Dry matter intake (DMI), milk yield, body weight, and body condition score were significantly greater for cows fed the high concentrate total mixed diet than for cows fed the low concentrate total mixed diet. Significant interactions between total mixed diet and period were observed for DMI and milk yield. However, no significant residual effects of changing from one total mixed diet to the other were observed. The interactions were due to substantially different slopes of DMI and milk yield relative to DIM for cows fed the two different total mixed diets. For cows fed the low concentrate total mixed diet, there was no effect of stage of lactation on DMI; the slope was 0. For cows fed the high concentrate total mixed diet, there was a significant decline in DMI as lactation progressed.     

Biogenic amines in silage, apparent postruminal passage, and the relationship between biogenic amines and digestive function and intake by steers

A 4 x 4 Latin square experiment was conducted to examine abomasal passage of biogenic amines in steers fed silage and their related effects on intake, digestibility, and digestive function. Thirty percent of the dry matter (DM) in the diets consisted of alfalfa forage, which was fed as either hay or silage. The DM from alfalfa silage DM was substituted at 0, 33, 67, and 100% for DM from alfalfa hay and was fed to four ruminally and abomasally cannulated steers. The roughage component of the diet constituted 50% of the DM and consisted of 60% alfalfa silage or hay and 40% tropical corn silage. The concentrate was composed mainly of ground corn. The concentrations of putrescine and cadaverine in abomasal digesta increased as alfalfa silage in the diet increased. Abomasal recovery of biogenic amines, a product of their concentration in abomasal digesta and the passage of DM through the abomasum, was negatively correlated with intake. Abomasal recovery of most amines was 5 to 20% of intake. Abomasal recovery of cadaverine was correlated with depressed intake. Total DM intake was reduced 8.3 to 25.8% as the proportion of alfalfa silage in the diet increased. Frequency of reticular contractions, intake, ruminal DM digestibility, ruminal outflow, volatile fatty acids, and total tract DM digestibility decreased in steers fed diets that contained more alfalfa silage. Ruminal fluid pH and NH3 concentration increased in steers fed more alfalfa silage; however, mass and the DM percentage of ruminal contents decreased linearly. Postprandial insulin concentrations were quadratically related to the proportion of alfalfa hay or silage in the diet. Intraruminal metabolism of biogenic amines is extensive based on the relatively low quantities recovered in abomasal digesta; however, the amounts recovered in abomasal digesta were related to intake depression and associated physiological effects.     

Alteration of milk fat by variation in the source and amount of starch in a total mixed diet fed to dairy cows

The effect on milk yield and composition of the supplementation of the diets of dairy cows with wheat or potato peelings was studied at three different starch intakes (< 5, 6, and > 7.5 kg/d) for dry matter intakes around 20 kg/d. Starch supply was varied using different dietary concentrations of corn silage. Trials were conducted using Latin square designs, and all cows were fed a total mixed diet composed of corn silage, grass silage, or both; soybean meal; a mixed meal with formaldehyde treatment; minerals; and one of the following energy concentrates: potato peelings or wheat. Dry matter and energy intakes varied significantly only at the low starch concentration; higher intakes were observed when the potato peelings were fed. Body weight, milk yield, true protein content, lactose content, and protein yield were not affected by treatment. Milk fat content was higher (+3.3 g/kg) when potato peelings were fed at the high starch concentration but was unaffected at the low and medium starch concentration. Slow degradation of starch from the potato peelings in the rumen could enhance a higher delivery of precursors of milk fat synthesis in the udder. The effect on fat yield differed among starch concentrations. Milk fat content appeared to decrease for cows fed diets containing quickly degradable starch at a starch intake > 7 kg/d.     

Fatty acid composition of milk from Holstein cows fed oleamide or canola oil

Based on previous in vitro results that showed reduced biohydrogenation of oleamide by ruminal microbes, this study was conducted to determine whether the addition of oleamide to the diets of dairy cows would enhance the C18:1 concentration in milk. Nine first lactation Holstein cows were fed three diets in a 3 x 3 Latin square replicated three times. Each period lasted 3 wk. The total mixed diets consisted of 42% corn silage and 58% concentrate (dry matter basis) with either no added fat (control), 3.5% high oleic canola oil, or 3.5% oleamide. Dry matter intake was reduced when oleamide was added to the diet but not when canola oil was added. Milk yields were the same for cows fed all three diets. Canola oil reduced fat-corrected milk yield and milk fat concentration, but these were not affected by oleamide. Milk protein concentration was lower for cows fed oleamide than for cows fed canola oil. Milk C18:1 averaged 23.16% of total fatty acids for cows fed the control diet and increased to 35.13% when canola oil was fed. Oleamide further increased C18:1 to 48.16% of total fatty acids in milk. All fatty acids with > or = 16 carbon chain length were reduced by oleamide. Oleamide was more effective than was canola oil in this study at increasing the oleic acid content of bovine milk. Oleamide reduced dietary intake when added at 3.5% of the dietary dry matter but still had no effect on milk yield or milk composition.     

Response of lactating dairy cows to various densities of sorghum grain

To examine the effects of various densities of sorghum grain resulting in graded levels of ruminally degradable starch on lactational performance, 32 lactating Holstein cows (90 d in milk [DIM]) were assigned to four treatments for 58 d. Diets contained 37% alfalfa hay, 3% cottonseed hulls, 10% whole cottonseed, 6% soybean meal, 5% of a molasses-mineral-vitamin supplement, and 39% sorghum grain. Treatments were dry-rolled sorghum (DRS) at 643 g/L or stream-flaked sorghum (SF) at 437, 360, and 283 g/L. Dry matter intake was highest for DRS followed by SF360, with the linear (P < .01) and cubic (P < .05) effects significant. The linear decrease in milk (P < .05) and 3.5% fat corrected milk (FCM, P < .025) with decreased density of sorghum was because of large decreases on SF283. Steam-flaking increased total tract digestibilities of DM, OM, CP, starch, and ADF when compared with dry-rolling. Efficiency of conversion of feed DM to FCM and feed CP to milk protein were greater for sorghum flaked at 437 and 360 g/L than for DRS or the 283 g/L flake. The 283 g/L flake decreased DMI, milk yield, and milk fat percentage. Addition of buffer (1% NaHCO3) tended to ameliorate the decrease in DMI. These data show greater efficiency of feed utilization and conversion of feed CP to milk protein in cows fed sorghum grain flaked at 437 and 360 g/L compared with those fed dry-rolled sorghum or that flaked at 283 g/L.     

Effect of amount of dietary supplement and source of protein on milk production, ruminal fermentation, and nutrient flows in dairy cows

An experiment with a multiple Latin square design using 36 midlactation Friesian cows was carried out to determine the effect of fish meal or soybean meal in a supplement fed at two amounts (3.5 or 7 kg/d) with grass silage. The diets were also fed to four ruminally and duodenally cannulated cows to determine digestibility, ruminal fermentation, and nutrient flows. Dry matter intake, milk production, milk constituent yields, and concentrations of protein and lactose were significantly increased by the supplements when provided at 7 kg/d. The supplement containing fish meal increased milk production, protein and lactose yields, and milk protein concentration, but the increases were smaller than those obtained by increasing the amount of supplement fed. Neither the type nor the amount of supplement fed affected digestibility of dry matter or organic matter, and few significant effects on ruminal fermentation were observed. Supplements fed at the higher allowance significantly increased the flow of dry matter, organic matter, all nitrogenous components, and amino acids to the duodenum. The supplement containing fish meal significantly increased the duodenal flow of nonammonia nonmicrobial N and some amino acids. Results indicated that an increase in the concentration of supplement in the diet is more effective in increasing milk production, protein concentration and yield, and flow of amino acids to the duodenum than is increasing the concentration of ruminally undegradable protein in the supplement.     

Effect of added dietary fat on performance, rumen characteristics, and plasma metabolites of midlactation dairy cows

Effects of supplemental Jet-Sploded canola seed in the diets of dairy cows on milk yield and composition and blood metabolite concentrations were investigated. Twenty multiparous and 5 primiparous midlactation Holstein cows were assigned to treatments following a 3-wk covariate period; cows were then on the treatments for 70 d. Ten of the cows had previously been fitted with rumen cannulas. Five concentrate mixtures containing 0, 7.5, 15, 22, or 29% Jet-Sploded canola seed (Simons Feed Co., Quimby, IA) (equivalent to 0, 2.66, 5.33, 7.81, and 10.30% added fat, respectively) were formulated by substituting Jet-Sploded canola seed for barley and canola meal. Diets consisted of 25% alfalfa silage, 25% whole-crop oat silage, and 50% of one of the concentrate mixtures (dry matter basis). An increase in the amount of dietary fat from Jet-Sploded canola seed did not influence feed intake, milk yield or composition, or milk component yields. The inclusion of Jet-Sploded canola seed in the diet increased long-chain fatty acids and inhibited de novo synthesis of medium-chain fatty acids in milk. Mean total volatile fatty acids in the rumen and propionate concentration were reduced in a linear fashion by treatment. The inclusion of Jet-Sploded canola seed in the diets of mid-lactation cows altered rumen and blood metabolite concentrations; however, these changes had minimal effects on yield responses with the exception of milk fatty acid composition and milk protein content.