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.     

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.     

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.     

Fatty acid digestibility and lactation performance by dairy cows fed fats varying in degree of saturation

Holstein cows fed fats varying in degree of saturation were used to evaluate lactation performance (35 multiparous and 15 primiparous cows) and fatty acid digestibility (5 cows). Data from wk 2 and 3 of lactation were used for covariable adjustment of data from wk 4 through 19. Diets were a basal diet (control) with no added fat and four diets with 5% added fat from tallow, tallow plus partially hydrogenated tallow in proportions of 2:1 or 1:2, or partially hydrogenated tallow; iodine values were 45, 35, 26, and 16 for the diets with added fat, respectively. Digestibilities of OM, NDF, and N were not affected by fat supplementation (mean of four fat treatments vs. control) or by degree of fat saturation. Fatty acid digestibility was lower for cows fed fat than for those fed the control diet and decreased linearly with increased fat saturation. In both trials, DMI increased linearly as fat saturation increased. In the digestion trial, cows fed fat tended to have lower DMI than those fed the control diet, primarily because of the unsaturated fat. In the production trial, DMI was similar for cows fed the control diet (22.3 kg/d) or the diet with added fat from tallow (22.1 kg/d) and tended to be higher for cows fed the diet containing partially hydrogenated tallow (23.9 kg/d). Milk production was higher for cows fed fat than for cows fed the control diet, but 4% FCM was unaffected. Milk fat and protein percentages were not affected by fat supplementation but increased linearly with increased fat saturation. Mean body condition score of cows increased as fat saturation increased. The lower digestibility of the diet with added fat from partially hydrogenated tallow was offset by higher DMI and percentages of milk fat and protein as fat became more saturated.     

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.     

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.     

Brown midrib sorghum silage for midlactation dairy cows

Brown midrib sorghum silage was compared with alfalfa, corn, and normal sorghum silages for its effect on performance, ruminal metabolism, and digestive kinetics of Holstein dairy cows in midlactation. Twelve cows averaging 90 +/- 5 DIM were assigned to one of four diets in replicated 4 x 4 Latin squares with 4-wk periods. Additionally, 3 ruminally fistulated cows (95 +/- 20 DIM) were assigned to the same diets in a 3 x 4 Youden square for measurement of ruminal characteristics. Diets were fed as isonitrogenous TMR that contained 65% silage (DM basis). The DMI was greater for the corn and brown midrib sorghum (4% of BW/d) than for the alfalfa and normal sorghum diets (3.4% of BW/d). The brown midrib sorghum supported FCM production that was similar to that of cows on corn and alfalfa diets (25.8 kg/d), but cows fed normal sorghum produced less milk and fewer milk components. Source of silage had no effect on eating time, but rumination was least for the alfalfa diet. Ruminal pH and ammonia concentrations were similar for all diets. Total VFA concentrations were greatest for the corn and brown midrib sorghum diets. The brown midrib sorghum had greater in situ extent of ruminal NDF digestion than did the normal sorghum, which agreed with in vitro data. The brown midrib sorghum used in this experiment supported FCM production similar to the corn and alfalfa silages commonly fed to dairy cows in midlactation.     

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.     

Production responses by early lactation cows to whole sunflower seed or tallow supplementation of a diet based on barley

A 2-yr study to evaluate the effectiveness of whole sunflower seed as a source of fat was conducted with 18 primiparous and 31 multiparous Holstein cows. The three diets evaluated were a basal diet based on barley (control), a basal diet supplemented with 2.7% tallow, and a basal diet supplemented with 7.1% whole sunflower seeds. The DMI of lactating cows during the 16-wk test period was not influenced by supplementation with either sunflower seeds or tallow. Milk production was 34.4, 34.6, and 35.5 kg/d for cows fed the control diet or the diets supplemented with sunflower or tallow, respectively, and was not influenced by diet. The production and concentrations of milk protein, fat, and SNF also were not influenced by diet. The concentrations of C6:0 to C14:1 fatty acids were highest in the milk of cows fed the control diet. The concentrations of C10:0 to C16:1 were higher when cows were fed the diet with the tallow supplement than when they were fed the diet with the sunflower supplement. However, the concentrations of C18:0 to C18:2 and C20:0 were higher in the milk of cows that were fed the sunflower supplement than in the milk of cows that were fed the tallow supplement or the control diet. Concentrations of individual VFA and the ratio of acetate to propionate were not influenced by diet. Body weight, body condition score, and reproduction parameters were similar for all diets, suggesting that there were no effects on subsequent production. The performance of cows fed whole sunflower seeds as a source of energy appeared to be similar to the performance of cows fed traditional high energy diets based on barley. The fatty acid profile of the milk of cows fed diets supplemented with sunflower seeds was more favorable than that of the milk of cows fed diets supplemented with tallow.     

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.     

Effects of ruminal versus duodenal dosing of fish meal on ruminal fermentation and milk composition

Three midlactation Holstein cows with ruminal and duodenal cannulas were used in a 3 x 3 Latin square design to determine whether ruminal or postruminal alterations in metabolism were responsible for the changes in milk composition that frequently are associated with dietary fish meal. Cows were offered a diet of 60:40 forage to concentrate (aliquots at 6-h intervals) that was supplemented with isonitrogenous amounts of soybean meal (1.3 kg of DM/d) dosed into the rumen or fish meal (1.0 kg DM/d) dosed either into the rumen or into the duodenum. The DMI, ruminal NDF digestion, and flows of total N and microbial N to the duodenum decreased for cows receiving fish meal. Dietary N flow increased when fish meal was dosed into the rumen. Total concentration of ruminal VFA was greater for cows receiving the soybean meal treatment; however, treatment had no effect on the ratio of ruminal acetate plus butyrate to propionate. Milk and FCM yields were unaffected by treatment, but milk fat content decreased, and milk protein content increased when cows were supplemented with fish meal. The difference in mammary arteriovenous glucose difference decreased when cows were dosed with fish meal. Changes in plasma NEFA and triglycerides were small and inconsistent. Results from this experiment suggest that effects of fish meal on milk composition are due to postruminal alterations in metabolism.     

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.     

Effect of dietary forage concentration and buffer addition on duodenal flow of trans-C18:1 fatty acids and milk fat production in dairy cows

The objective of the study was to determine the effects of dietary fat source on duodenal flow, apparent absorption, and milk fat incorporation of trans-C18:1 fatty acids. Four ruminally and duodenally cannulated multiparous Holsteins cows in mid to late lactation were fed a basal diet containing 36% corn silage, 24% alfalfa haylage, and 40% concentrate (dry matter basis). Diets contained 0% supplemental fat (control diet), 3.7% high oleic sunflower oil, 3.7% high linoleic sunflower oil, or 3.7% partially hydrogenated vegetable shortening; treatments were administered in a 4 x 4 Latin square design with 3-wk experimental periods. The flow of trans-C18:1 to the duodenum was higher for cows fed diets supplemented with fat than for cows fed the control diet (283 vs. 64 g/d). Incomplete biohydrogenation accounted for the increased flow of trans-C18:1 to the duodenum in cows fed diets containing high oleic and high linoleic sunflower oil. Increased flow of trans-C18:1 in cows fed the diet containing partially hydrogenated vegetable shortening most likely originated from the trans-C18:1 in the diet. Milk fat percentages were 3.48, 3.07, 3.18, and 3.38% for cows fed the control diet and diets containing high oleic sunflower oil, high linoleic sunflower oil, and vegetable shortening, respectively. Milk trans-C18:1 increased from 2.9 to 11.2% of the total fatty acids for cows fed the control diet and the diets supplemented with fat, respectively. Milk trans-C18:1 were equal across all diets supplemented with fat. Ruminal and total tract digestion of organic matter, neutral detergent fiber, and N did not change with fat supplementation. Results showed that trans-C18:1 is increased in the milk of cows with reduced milk fat; however, excessive amounts of trans-C18:1 in milk do not necessarily correspond directly to milk fat depression.     

Relationships among ewe milk production and ewe and lamb forage intake in Suffolk and Targhee ewes nursing single or twin lambs

Suffolk and Targhee ewes (30 each) with single or twin lambs were used in four periods beginning in late gestation and continuing through weaning to evaluate breed differences in milk production, lamb BW, and DMI by ewes and lambs. In Periods 1 (late gestation) and 2 (early lactation), ewes (Period 1) and ewes with lambs (Period 2) were individually penned, fed .45 kg of barley x ewe(-1) x d(-1) and allowed ad libitum access to chopped alfalfa. Ewes and lambs grazed native range in Periods 3 and 4. Grazed forage DMI was estimated using chromic oxide. Estimates of milk production were obtained by handmilking. Average lamb age was 4, 45, and 73 d at the beginning of Periods 2, 3, and 4, respectively. Milk production tended (P = .20) to be greater for Suffolk than for Targhee ewes. Targhee ewes produced 85% more (P = .001) wool than Suffolk ewes. From 33 d prepartum to 89 d postpartum, Suffolk ewes consistently weighed more (P = .001) than Targhee ewes. Suffolk ewe BW loss (-.15 kg/d) was greater (P = .01) than Targhee ewe BW loss (-.02 kg/d) from 33 d prepartum to 6 d postpartum. From 6 to 89 d postpartum BW gain did not differ (P = .69; .05 kg/d) between breeds. From birth to 89 d postpartum, Suffolk lambs consistently weighed more than Targhee lambs (P = .003). From birth to 89 d postpartum, ADG was greater for Suffolk than for Targhee lambs (P = .006). Targhee ewes consumed 25% more (P = .01) feed over the course of the study than did Suffolk ewes. Grazed forage DMI by Targhee lambs was 26% greater (P = .01) than DMI by Suffolk lambs. When meat production is the primary income from sheep, one potential advantage of Suffolks compared with Targhees is more rapid gain with less feed intake.     

Effect of prepartum and postpartum dietary energy on growth and lactation of primiparous cows

Sixty-seven Holstein replacement heifers (19 mo) were fed a standard (59.7% TDN) or a high energy (69.3% TDN) diet until parturition. After parturition, primiparous cows were fed either 0 or 2.8% supplemental tallow for 150 d in a 2 x 2 factorial arrangement with prepartum treatments. High energy prepartum increased BW (693.5 vs. 663.7 kg) and body condition scores (3.72 vs. 3.55) at calving. Increased energy density of the diet prepartum did not affect milk yield or composition. Supplemental dietary fat postpartum increased milk yield approximately 1.5 kg/d, but the response was not observed until 7 wk postpartum. Heifers fed the standard diet prepartum and no supplemental fat postpartum had higher DMI than other treatments. Heifers fed high energy prepartum and supplemental fat postpartum lost the greatest BW and body condition from 1 to 5 wk postpartum. Heifers fed high energy diets prepartum had higher concentrations of blood NEFA, BHBA, and liver triglycerides. Increases in BW and body condition scores at calving above approximately 660 kg and 3.5, respectively, do not enhance lactation performance. When 2.8% supplemental fat was fed to primiparous cows, milk yield improved approximately 1.5 kg/d after wk 7 of lactation.     

Starch supplementation of grass harvested at two stages of maturity prior to ensiling: intake, digestion, and degradability by dairy cows

The effects of the maturity of grass prior to ensiling and the supplementation of starch to grass silage on apparent digestibility, degradability, rumen content, and feed intake by dairy cows were investigated using a Latin square design. Treatments were silages from early or late cut grass with or without 4 kg of supplemental flaked corn starch. The silage from early cut grass contained more N and sugars than did the silage from late cut grass but was lower in neutral detergent fiber (NDF). Degradation characteristics were not different between the two silages. Apparent digestibilities of dry matter (DM), organic matter (OM), and N in the silage from late cut grass were lower than those in the silage from early cut grass, but NDF digestibility was not affected. Starch supplementation increased the lag phase for DM and OM in both silages, but the rate of degradation was decreased for NDF. Starch supplementation did not influence digestibilities of DM and OM in silage from early cut grass but decreased the digestibilities of DM and OM in silage from late cut grass. Crude protein and NDF digestibilities were decreased for silages from early and late cut grass. Starch supplementation increased NDF in the rumen of cows fed the silage from early cut grass, but NDF was not affected by starch supplementation for cows fed the silage from late cut grass. Rumen-degradable starch negatively influences degradability and apparent OM digestibility; the extent of the decrease is related to the maturity of the NDF.     

Intake, milk yield, and digestion by dairy cows fed diets with increasing fiber content from bermudagrass hay of silage

Lactating dairy cows were offered diets containing increasing quantities of Tifton 85 bermudagrass hay or silage and increasing dietary neutral detergent fiber (NDF) to determine effects of method of bermudagrass storage and dietary fiber content on intake, milk yield, and nutrient digestion. Bermudagrass was added as hay or silage at the rate of 8.5, 15.9, or 23.3% of dietary dry matter and was substituted for an equal quantity of corn silage. The method of bermudagrass storage did not affect intake [20.8 vs. 20.3 (+/- 0.3) kg/d for bermudagrass hay and silage diets; respectively], but an increase in the amount of bermudagrass and NDF in the diet did reduce intake. Dietary NDF concentration was well above minimum recommendations of the National Research Council. Milk yield was not altered by method of bermudagrass storage but declined as dietary NDF increased. Digestion of NDF tended to be lower for bermudagrass silage than for bermudagrass hay. An increase in the amount of bermudagrass in the diet improved digestion of dietary dry matter, acid detergent fiber, and NDF; however, milk yield declined because total intake declined. Improved NDF digestion caused by added bermudagrass hay or silage was confirmed by in vitro analyses. High quality bermudagrass hybrids could potentially be used in diets of lactating dairy cows because of the good digestion characteristics and relatively small effects on intake despite the high dietary fiber content. Tifton 85 bermudagrass may serve as a forage alternative for lactating dairy cows.     

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.     

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.     

Use of short intertrial intervals in single-trial experiments: a 3T fMRI-study

In three experiments (E1, E2, E3) maize silage of different physical structure and of different stage of maturity at harvest were fed to 24 (E1), 36 (E2) or 28 (E3) dairy cows. The cows were fed individually over an experimental period of five or six weeks. The maize silages had a mean DM content of 28% (E1), 32% (E2) or 36% (E3). At the stage of harvest, the stovers and the cobs had a mean DM content of < 22% (E1, E2) or 27% (E3), 40% (E1), 46% (E2) or 57% (E3), respectively. The maize was harvested with a chopping length of 4 and 8 mm (E1, E3) and of 6 and 8 mm (E2), without corn cracking (E1) or with and without corn cracking (E2, E3). The daily feed ration consisted of ad libitum offered maize silage, 1.7 kg DM hay, soya bean meal (E2, E3) and concentrate. The different chopping length of 4 mm, 6 mm or 8 mm had no effect on the maize silage intake in E1 and E2. In E3 the daily maize silage intake increased by about 1.2 kg DM per cow at a chopping length of 4 mm in comparison to 8 mm, whereas only the treatment with the combination of 4 mm chopping length and corn cracking showed a significant increase in DMI. The corn cracking improved the milk yield significantly (E2) or in a tendency (E3) at 2.0 kg (E2) or at 1.6 kg (E2), while the variation of chopping length had no effect on milk yield. The different physical structure did not influence the milk fat content with mean values of 4.65% (E1), 4.15% (E2) and 4.10% (E3), respectively. The milk protein content decreased in E2 feeding maize silage with a chopping length of 8 mm and corn cracking; but in E1 and E3 no effect was seen on protein content with mean values of 3.66% (E1) or 3.51% (E2).