Eating Rate of Lactating Cows Fed Four Physical Forms of the Same Grain Ration

Eleven cows in midlactation were fed grain rations in pelleted (.4 cm diameter), coarse (premix pellet with cracked corn), Ett® (crumbled pellet), or meal forms. Eating rate was measured during morning feedings for 5 consecutive days following a 2-day adjustment. Eating rate was computed by 4-min intervals during the 28-min eating period. Fat-corrected milk production, intake of corn silage, and of alfalfa hay averaged 19.3, 15.1, and 3.4 kg per day for all cows. Differences of ration intake were greatest during the first 8 min. Rate of eating was most rapid for the pelleted ration followed by coarse, Ett®, and meal forms. Total 28-min intake paralleled intake during initial 8 to 12 min. Physical form influenced ration intake initially when eating time was limited. Subsequent intake reduction probably is related to physiological feedback which also may be affected by physical form of the ration.     

Brown Midrib Corn Silage in Dairy Cattle Rations,

Two groups of 12 Holstein cows past peak lactation were fed complete mixed diets containing either brown midrib corn silage or its normal genetic counterpart. All cows were fed a standardization ration containing another corn silage prior to and after the experimental period. Performance during the experimental period was expressed as deviation from standardization. Cows fed brown midrib silage produced .66 kg more milk per day that tested .28 percentage units less fat during the 4-wk experimental period than during standardization. Control cows produced .10 kg more milk per day in the experimental period as compared to standardization without difference in fat test. On a fat-corrected basis (4%) there was no difference in milk yield between treatments.     

Feeding Value of Dry Corn,Ensiled High Moisture Corn,and Propionic Acid Treated High Moisture Corn Fed with Hay or Haylage for Lactating Dairy Cows

Trial 1. Fifty lactating Holstein and Brown Swiss cows were assigned to six groups in a 3 × 2 factorial design and fed one of six diets for 16 wk: (1) dry corn + hay, (2) dry corn + haylage, (3) ensiled high moisture corn + hay, (4) ensiled high moisture corn + haylage, (5) propionic acid treated corn + hay, and (6) propionic acid treated corn + haylage. Quantities equal in dry matter of dry corn, ensiled corn, and acid treated corn were offered in the ratio of 1 kg concentrate (corn and supplement) for each 2.75 kg milk produced. Forage was fed free choice. Means adjusted by covariance for cows fed diets 1 to 6 averaged: dry matter intake (kg/day), 16.7, 20.0, 17.4, 20.6, 17.1, 20.0; 4% fat-corrected milk (kg/day), 21.8, 21.1, 22.6, 23.5, 22.4, 23.4; milk fat percent, 3.54, 3.45, 3.63, 3.53, 3.62, 3.80; and acetate to propionate ratio 3.53, 3.85, 3.73, 3.66, 3.13, 3.32. Cows fed ensiled corn and acid treated corn produced more 4% fat-corrected milk than did cows fed dry corn. The molar percent acetate to propionate ratio in rumen fluid of cows fed acid treated corn was lower than for cows fed dry corn or ensiled corn.Trial 2. Dry corn or propionic acid treated corn was fed to 12 cows in combination with a supplement, 4.54 kg of hay, and ad libitum haylage. Means adjusted by covariance for cows fed dry corn and acid treated corn averaged: dry matter intake (kg/day), 18.2 and 17.7; 4% fat-corrected milk (kg/day), 20.6 and 20.1; and total digestible nutrients (%) 63.7 and 58.7.Any of these methods are acceptable for storing corn, and feeding this corn in properly supplemented diets will yield acceptable lactation performance.     

Alfalfa Silage or Hay Versus Corn Silage as the Sole Forage for Lactating Dairy Cows

In Trial 1, three rations were fed to 21 cows in a 3 × 3 Latin square: 60% alfalfa silage, 60% corn silage, and 79% corn silage (dry matter basis) with the balance from corn and soybean meal. Acid detergent fiber measures indicated alfalfa and corn silage were of excellent quality. Milk production was similar on 60% forage rations but lower on 79% corn silage. Milk fat was reduced on 60% corn silage. In Trial 2, four rations were fed to 16 cows in a 4 × 4 Latin square: 63% alfalfa silage, 60% alfalfa hay, 60% corn silage, and 76% corn silage. Alfalfa forages were higher in acid detergent fiber but corn silage was similar to Trial 1. Dry matter digestibility was highest on 60% corn silage, intermediate on 63% alfalfa silage and 76% corn silage, and lowest on 60% alfalfa hay. Milk production was similar on the diets containing 60 and 63% forage and lower on 76% corn silage. Milk protein concentration was reduced on the alfalfa diets. Highest protein secretion and feed conversion was supported by 60% corn silage. In both trials, potentially digestible neutral detergent fiber from alfalfa was more digestible than that from corn silage, and concentrations of urea in milk and blood were highly correlated. Results indicate high quality alfalfa silage is comparable to corn silage for milk production.     

Breeding Practices on Selected North Carolina Dairy Farms

In 1978, 147 North Carolina dairy farms were surveyed concerning their breeding practices. Average herd size was 121 cows (range 24 to 440). Of 17,773 cows 78.5% and of 4,300 heifers 25.5% were bred by artificial insemination. Approximately 25% of dairymen indicated they had increased artificial insemination in the past 3 yr, whereas 12% reported less. A bull was used on 88% of farms. Herds having the same number of cows but using 100% artificial insemination on the milking herd averaged more days open (13.3), longer calving intervals (.44 mo), and more cows leaving the herd because of reproductive problems (8.3% vs. 5.8%) compared to herds using 80 to 99% artificial insemination. Herds using 0 to 75% artificial insemination were intermediate between the two. Herds using 100% artificial insemination and those using 80 to 99% averaged 7050 kg milk and 1.8 services per conception. Herds using 0 to 75% artificial insemination had lower milk production (480 kg). Larger herds had lower reproductive performance. Herds with higher average milk production had more services per conception. Average estimated transmitting abilities of 88 natural service sires were 371 kg milk, ?.05% fat and 10 kg fat.     

Zinc-65 metabolism, secretion into milk, and biological half-life in lactating cows

Following oral dosing, zinc-65 metabolism was studied in 10 first-lactation Holstein cows during the 5th and 6th wk of an experiment in which a high beet pulp, low-zinc diet (16.6 ppm) was fed without and with (39.5 ppm total zinc) supplemental zinc. For the 14 days after dosing, cows fed low zinc had a much higher net zinc-65 absorption (53.4 versus 34.8%) and consistently secreted far more zinc-65 into milk (14.4 versus 6.3%). The zinc secreted into milk of cows fed low zinc during the 14 days had been in the body a shorter time than in controls, indicating greater dependences on recently consumed zinc for secretion into milk. The biological halflife (in lactating ruminants defined as the time required for one-half of the zinc-65 dose to leave the body via feces and milk) was shorter for the cows fed low zinc. Lactating cows are able to absorb a high percentage of dietary zinc, and lactation is a major factor in zinc metabolism and homeostasis. Major changes in zinc metabolism occur before performance is affected.     

Exogenous β-mannanase improves feed conversion efficiency and reduces somatic cell count in dairy cattle

Exogenous fibrolytic enzymes have been shown to be a promising way to improve feed conversion efficiency (FCE). β-Mannanase is an important enzyme digesting the polysaccharide β-mannan in hemicellulose. Supplementation of diets with β-mannanase to improve FCE has been more extensively studied in nonruminants than in ruminants. The objective of this study was to investigate the effects of β-mannanase supplementation on nutrient digestibility, FCE, and nitrogen utilization in lactating Holstein dairy cows. Twelve post-peak-lactation multiparous Holstein cows producing 45.5 ± 6.6 kg/d of milk at 116 ± 19.0 d in milk were randomly allotted to 1 of 3 treatments in a 3 × 3 Latin square design with 3 periods of 18 d (15 d for adaptation plus 3 d for sample collection). All cows were fed the same basal diet and the 3 treatments differed only by the β-mannanase dose: 0% dry matter (DM; control), 0.1% of DM (low supplement, LS), and 0.2% of DM (high supplement, HS) supplemented to the basal diet. Supplementation of β-mannanase enzyme at the LS dose reduced dry matter intake (DMI) but did not affect milk yield or milk composition. Cows receiving LS produced 90 g more milk per kg of DMI compared with control cows. Somatic cell count (SCC) in milk was lower for cows fed the LS diet compared with cows fed control diets. Cows fed LS diet had lower DM, organic matter and crude protein digestibility compared with cows fed control diets. Starch, neutral detergent fiber, and acid detergent fiber digestibility were not affected by LS. Milk yield, DMI, SCC, and nutrient digestibility did not change for HS. Despite the reduced crude protein digestibility, reduced N intake led to similar fecal N excretions in LS cows and control cows (234 vs. 235 g/cow per day). Urinary N excretions remained similar between enzyme-fed and control cows (~190 g/cow per day), although the percentage of N intake partitioned to urinary N tended to be greater in LS than in control cows (31 vs. 27%). Cows fed LS significantly improved the percentage of apparently absorbed N partitioned to milk protein N (42 vs. 38%). When supplemented at 0.1% of dietary DM, β-mannanase can improve FCE and lower the SCC of dairy cows without affecting milk yield, milk composition, or total manure N excretions of dairy cows.     

Effect of forage to concentrate ratio with sorghum silage as a source of forage on rumen fermentation,N balance,and purine derivative excretion in limit-fed dairy heifers

Sorghum silage has been shown to be a good alternative to corn silage for dairy cows; however, studies regarding heifers are insufficiently explored. Therefore, the objective of this study was to evaluate effects of changing forage to concentrate ratio (FOR:CON) in diets based on sorghum silage on N digestibility, rumen fermentation, N balance, C excretion, and microbial N yield in limit-fed dairy heifers. A split-plot 4 × 4 Latin square design with 19-d periods (15 d of adaptation and 4 d of sampling) was conducted with 8 rumen cannulated dairy heifers (age 13.7 ± 0.6 mo and weight 364.8 ± 17.6 kg). Heifers were fed sorghum silage–based diets with 4 FOR:CON (85:15, 75:25, 65:35, and 55:45) balanced for similar metabolizable energy intake per unit of body weight and crude protein concentration. Diets were fed to allow 900 to 1,000 g/d body weight gain and were fed once daily. Total collection of feces and urine was completed on d 15 to 19 to determine N, C, urea N, allantoin, uric acid, and creatinine excretion. Rumen contents were sampled on d 19 at 0, 1.5, 3, 4.5, 6, 9, 13, 17, 21, and 23 h after feeding to measure pH, volatile fatty acid (VFA), ammonia-N, and free AA concentrations. The pH decreased linearly while ammonia-N and free AA levels increased linearly with decreasing FOR:CON of diets. Although mean total VFA did not differ among treatment diets, molar proportions of VFA did. Acetate proportion decreased while propionate and butyrate increased with decreasing FOR:CON. Intake of N and urea N excretion decreased with decreasing forage proportion in diets while total N excretion, apparent N digestibility, and N retention were not different. Intake of C and excretion in feces (g/d) decreased linearly with decreasing FOR:CON in diets. Creatinine, allantoin, and uric acid excretion were not affected by FOR:CON; however, microbial N yield tended to increase linearly with greater concentrate in diets. Heifers limit fed diets based on sorghum silage demonstrated the effect of available ammonia-N and readily fermentable carbohydrates with subsequent effects on nutrient utilization when different FOR:CON were applied. Based on the presented results, FOR:CON 65:35 had the most suitable balance of available ammonia-N and readily fermentable carbohydrates for the most optimal results.     

The effects of feeding rations that differ in fiber and fermentable starch within a day on milk production and the daily rhythm of feed intake and plasma hormones and metabolites in dairy cows

A daily pattern of feed intake, milk synthesis, and plasma metabolites and hormones occurs in dairy cows fed a total mixed ration once or twice a day. The objective of this study was to determine if feeding multiple rations within a day, complementing these rhythms, would improve milk production. Twelve Holstein cows were used in a replicated 3 × 3 Latin square design with 21-d periods. Cows were housed in tie stalls with feed tubs, and feed weight was recorded every 10 s for observation of feeding behavior. Rations were a low fiber and high fermentable starch ration [LFHS; 27.4% neutral detergent fiber (NDF) and 31.7% starch based on 55.7% corn silage and 14.1% steam-flaked corn], a high fiber and low fermentable starch ration (HFLS; 31.7% NDF and 22.3% starch based on 44% corn silage, 26.3% alfalfa haylage, and no steam-flaked corn), and a total mixed ration that was a 1:3 ratio of LFHS and HFLS (30.7% NDF, 24.5% starch). The control treatment (CON) cows were fed the total mixed ration at 0700 h, the high/low treatment (HL) fed HFLS ration at 0700 h and LFHS ration at 2200 h, and the low/high (LH) treatment fed LFHS ration at 0700 h and HFLS ration at 1100 h (LFHS and HFLS rations fed at a 1:3 ratio). No effect was found of treatment on daily milk, but LH decreased milk fat concentration and yield compared with HL (0.2 percentage units and 0.24 kg, respectively). Daily dry matter and NDF intake and total-tract digestibility did not differ between treatments. The HL treatment reduced intake at the morning-conditioned meal after feeding and reduced intake before the evening feeding. A treatment by time of day interaction was found for fecal NDF and indigestible NDF concentration, blood urea nitrogen (BUN), plasma insulin, and fatty acid concentration, and body temperature. The CON and LH treatments increased the daily amplitude of fecal NDF by 1.0 and 1.1 percentage units compared with HL. Plasma insulin was higher in HL than CON at 0100 and 0400 h, but lower at 1300 and 1900 h. Plasma fatty acids were higher for CON than HL at 0700 h and HL was lower than LH at 0400 and 1900 h. Plasma BUN was higher for HL than control at 0100 h, but lower at 1000 h. Body temperature in CON and HL treatments followed a similar diurnal pattern, whereas body temperature for LH was lower than that of HL treatment at 1300 and 2300 h. No daily rhythm was found of fecal indigestible NDF concentration, plasma glucose, or fatty acids detected in the HL treatment, and the amplitude of plasma insulin and BUN was lower for HL compared with CON (70 and 60% decrease, respectively). In conclusion, feeding 2 rations that differ in fiber and fermentable starch modifies diurnal rhythms in dairy cows. Furthermore, feeding a high fiber and low fermentable starch ration during the high intake period of the day may stabilize nutrient absorption across the day.     

By-Product Feeds for Lactating Dairy Cows: Effects of Cottonseed Hulls,Sunflower Hulls,Corrugated Paper,Peanut Hulls,Sugarcane Bagasse,and Whole Cottonseed with Additives of Fat,Sodium Bicarbonate,and Aspergillus oryzae Product on Milk Production

In Experiment 1, Holstein cows (32) fed diets in three 28-day periods were used to evaluate a 3 × 2 × 2 factorial arrangement of fiber sources (sunflower hulls, pelleted cottonseed hulls, and pelleted undelinted cottonseed hulls at 35% of dry matter), fat (0 or 2.5%). and sodium bicarbonate (0 or 1.0%). Sixteen cows also received Aspergillus oryzae product (56.7 g/day) continuously. Sunflower hulls decreased daily intake (19.4 versus 25.1 kg), milk (23.3 versus 26.5 kg), milk protein (2.85 versus 2.95%), and body weight change (?.08 versus .90 kg), but milk fat percent was higher (3.54 versus 3.32%). Sunflower hulls depressed digestibility of dry matter, organic matter, and acid detergent fiber. Added fat reduced milk fat and protein percents. Experiment 2 evaluated fiber sources (20% ground corrugated cardboard boxes, combination of 10% cardboard and 10% peanut hulls, or 30% cottonseed hulls), animal fat (0 or 2.5%), sodium bicarbonate (0 or .75%), and condensed molasses solubles by-product from rum distilling (0 or 10%). Corrugated boxes effected lowest intake (18.0 kg/day), cottonseed hulls highest intake (23.5 kg/day), and combination intermediate (20.2 kg/day). Added fat depressed fat percent. Condensed molasses solubles lowered milk yield but increased milk fat percent (3.76 versus 3.30), molar percent of acetic acid, and ratio of acetic to propionic. In two other experiments whole cottonseed (12.5 or 15% of dry matter) with corn silage, pelleted steam pressure treated sugarcane bagasse, or cottonseed hulls increased milk yield but decreased milk fat percent, especially with pelleted bagasse.     

The effect of supplemental concentrate fed during the dry period on morphological and functional aspects of rumen adaptation in dairy cattle during the dry period and early lactation

Ten rumen-cannulated Holstein-Friesian cows were used to examine the effect of feeding supplemental concentrate during the dry period on rumen papillae morphology and fractional absorption rate (k_a) of volatile fatty acids (VFA) during the dry period and subsequent lactation. Treatment consisted of supplemental concentrate [3.0 kg of dry matter (DM)/d] from 28 d antepartum (ap) until the day of calving, whereas control did not receive supplemental concentrate. Cows were fed for ad libitum intake and had free access to the dry period ration (27% grass silage, 28% corn silage, 35% wheat straw, and 11% soybean meal on a DM basis) and, from calving onward, to a basal lactation ration (42% grass silage, 42% corn silage, and 16% soybean meal on a DM basis). From 1 to 3 d postpartum (pp), all cows were fed 0.9 kg DM/d of concentrate, which increased linearly thereafter to 8.9 kg of DM/d on d 11 pp. At 28, 18, and 8 d ap, and 3, 17, 31, and 45 d pp, rumen papillae were collected and k_aVFA was measured in all cows. On average, 13.8 (standard deviation: 3.8) papillae were collected each from the ventral, caudodorsal, and caudoventral rumen sacs per cow per day. The k_aVFA was measured by incubating a standardized buffer fluid (45 L), containing 120 mM VFA (60% acetic, 25% propionic, and 15% butyric acid) and Co-EDTA as fluid passage marker, in the evacuated and washed rumen. Treatment did not affect ap or pp DM and energy intakes or milk yield and composition. Treatment increased papillae surface area, which was 19 and 29% larger at 18 and 8 d ap compared with 28 d ap, respectively. Surface area increased, mainly due to an increase in papillae width. However, treatment did not increase k_aVFA at 18 and 8 d ap compared with 28 d ap. In the control group, no changes in papillae surface area or k_aVFA were observed during the dry period. In the treatment group, papillae surface area decreased between 8 d ap and 3 d pp, whereas no decrease was observed for control. From 3 to 45 d pp, papillae surface area and k_aVFA increased for all cows by approximately 50%, but the ap concentrate treatment did not affect k_aVFA pp. In conclusion, the efficacy of supplemental concentrate during the dry period to increase papillae surface area and k_aVFA in preparation for subsequent lactation is not supported by the present study. Current observations underline the importance of functional measurements in lieu of morphological measurements to assess changes in the adapting rumen wall.     

Automatic Individual Feeding of Concentrates to Dairy Cattle

Two methods of feeding concentrates according to milk production were compared in a switchback experimental design. Twenty-four cows were assigned to two groups and the groups balanced according to age, milk production, fat-corrected milk production, and body weight. The cows were fed individually their daily allowance of concentrate while in the milking parlor or with an electronic feeder which dispersed concentrates at any hour of the day. All cows received corn silage in a feed bunk. Daily milk production increased .71 kg when cows were fed concentrates electronically. However, there were no significant differences in daily concentrate intake, production of fat-corrected milk, butter-fat percentage, or solids-not-fat percentage for the two treatments.     

Induction of Lactation by Two Techniques: Success Rate,Milk Composition,Estrogen and Progesterone in Serum and Milk,and Ovarian Effects

Induction of lactation was attempted in 12 heifers and 12 cows with estradiol benzoate (.011 mg/kg body weight per day) subcutaneous for 10 days or that plus progesterone (.1 mg + .25 mg/kg body weight per day) for 7 days. Milking commenced on day 20 for those treated with the mixture and on day 11 for the others. Lactations were induced (minimum of 4.5 kg of milk/day) in five of six heifers and two of six cows by the mixture and in six of six heifers and three of six cows for estradiol benzoate. Milk production was 44% of herdmates in the 16 induced lactations. Cows on the single treatment had lower production than the other three groups. Ovarian status, cycling, cystic, or static, was affected adversely in 5 of 16 animals induced successfully. Two of the 16, both heifers, carried calves to term following induction. The transition to normal composition of milk was slower for single than double treatment. Lactose increased slowly to normal over the 1st wk of milking while protein decreased slowly. Estrogen and progesterone in milk of induced cows were approximately twice as concentrated as in normal post-parturient cows, probably because milk production was halved.     

Effect of incremental amounts of camelina oil on milk fatty acid composition in lactating cows fed diets based on a mixture of grass and red clover silage and concentrates containing camelina expeller

Camelina is an ancient oilseed crop that produces an oil rich in cis-9,cis-12 18:2 (linoleic acid, LA) and cis-9,cis-12,cis-15 18:3 (α-linolenic acid, ALA); however, reports on the use of camelina oil (CO) for ruminants are limited. The present study investigated the effects of incremental CO supplementation on animal performance, milk fatty acid (FA) composition, and milk sensory quality. Eight Finnish Ayrshire cows (91 d in milk) were used in replicated 4 × 4 Latin squares with 21-d periods. Treatments comprised 4 concentrates (12 kg/d on an air-dry basis) based on cereals and camelina expeller containing 0 (control), 2, 4, or 6% CO on an air-dry basis. Cows were offered a mixture of grass and red clover silage (RCS; 1:1 on a dry matter basis) ad libitum. Incremental CO supplementation linearly decreased silage and total dry matter intake, and linearly increased LA, ALA, and total FA intake. Treatments had no effect on whole-tract apparent organic matter or fiber digestibility and did not have a major influence on rumen fermentation. Supplements of CO quadratically decreased daily milk and lactose yields and linearly decreased milk protein yield and milk taste panel score from 4.2 to 3.6 [on a scale of 1 (poor) to 5 (excellent)], without altering milk fat yield. Inclusion of CO linearly decreased the proportions of saturated FA synthesized de novo (4:0 to 16:0), without altering milk fat 18:0, cis-9 18:1, LA, and ALA concentrations. Milk fat 18:0 was low (<5 g/100 g of FA) across all treatments. Increases in CO linearly decreased the proportions of total saturates from 58 to 45 g/100 g of FA and linearly enriched trans-11 18:1, cis-9,trans-11 18:2, and trans-11,cis-15 18:2 from 5.2, 2.6, and 1.7 to 11, 4.3, and 5.8 g/100 g of FA, respectively. Furthermore, CO quadratically decreased milk fat trans-10 18:1 and linearly decreased trans-10,cis-12 18:2 concentration. Overall, milk FA composition on all treatments suggested that one or more components in camelina seeds may inhibit the complete reduction of 18-carbon unsaturates in the rumen. In conclusion, CO decreased the secretion of saturated FA in milk and increased those of the trans-11 biohydrogenation pathway or their desaturation products. Despite increasing the intake of 18-carbon unsaturated FA, CO had no effect on the secretions of 18:0, cis-9 18:1, LA, or ALA in milk. Concentrates containing camelina expeller and 2% CO could be used for the commercial production of low-saturated milk from grass- and RCS-based diets without major adverse effects on animal performance.     

Changes In Plasma α-Tocopherol and Selenium of Gestating Cows Fed Hay or Silage

The effects of dietary hay or silage on plasma α-tocopherol and Se concentrations during late gestation and early lactation were studied using 40 crossbred pregnant cows and their calves. Cows received solely either timothy hay or grass silage forage from midgestation to early lactation and 21 d prior to estimated calving were or were not injected with Se (30 mg) and α-tocopherol (3000 IU). Five blood samples were collected for determination of concentrations of α-tocopherol and Se twice during late gestation and three times after calving. Blood samples from calves were collected at birth and at 10 and 30 d of age. Serum concentrations of α-tocopherol were low at birth for both groups of calves and ranged from .83 to 1.08 μg/ml of plasma. Hay had less α-tocopherol than silage (15 vs. 35 ppm in the DM). Cows fed silage had significantly higher plasma α-tocopherol concentrations (3.41 μg/ml) than cows fed hay (2.25 μg/ml). Cows given one subcutaneous injection of Se plus α-tocopherol preparation had significantly higher Se concentration in plasma (30 ng/ml) than did cows in the control group (17 ng/ml). The Se concentration in the placenta of cows that were injected with the Se preparation was significantly higher (64 ppm) than that in the control (47 ppm). Plasma Se concentration of calves at birth was correlated significantly with that of dams soon after parturition.     

Lipopolysaccharide derived from the digestive tract provokes oxidative stress in the liver of dairy cows fed a high-grain diet

The aims of this study were to measure oxidative stress parameters and to investigate the molecular mechanism triggered by grain-induced subacute ruminal acidosis in mid-lactation cows. Twelve Holstein-Friesian cows with an average weight of 455 ± 28 kg were divided into 2 groups and subjected to 2 diets over 18 wk: either a low-grain (forage-to-concentrate ratio = 6:4) or a high-grain (forage-to-concentrate ratio = 4:6) diet based on dry matter. Being fed a long-term high-grain diet resulted in a significant decrease in rumen pH and a significant increase in ruminal lipopolysaccharide (LPS) at 4 h postfeeding in the morning. The increase was also observed in LPS concentrations in the portal vein, hepatic vein, and jugular vein blood plasma as well as reduced milk yield in a high-grain diet. Cows fed a high-grain diet had lower levels of catalase and glutathione peroxidase (GPx) activity and total antioxidant capacity than cows fed a low-grain diet; however, super oxide dismutase (SOD) activity and malondialdehyde (MDA) levels were higher in both the liver and the plasma of high-grain than in low-grain cows. Positive correlations were observed between plasma LPS versus hepatic MDA, plasma MDA, and hepatic SOD activity, whereas hepatic GPx and plasma GPx were negatively correlated with plasma LPS. The relative mRNA abundances of GPX1 and CAT were significantly lower in the liver of cows fed a high-grain diet than those fed a low-grain diet, whereas SOD1 was significantly higher in cows fed a high-grain diet than cows fed a low-grain diet. The expression levels of Nrf2, NQO1, MT1E, UGT1A1, MGST3, and MT1A were downregulated, whereas NF-kB was upregulated, in cows fed a high-grain diet. Furthermore, nuclear factor E2-related factor 2 (Nrf2) total protein and mRNA levels were significantly lower than in low-grains. Our results demonstrate the relationship between the translocated LPS and the suppression of cellular antioxidant defense capacity, which lead to increased oxidative stress and suggests that the Nrf2-dependent antioxidant response may be affected by higher levels of LPS translocated to the bloodstream.     

Influence of Dietary Protein Concentration and Degradability on Milk Production,Composition, and Ruminal Protein Metabolism

Four groups of cows in early lactation, each group containing one mature cow and three cows in first lactation, were in a 4 × 4 Latin-square arrangement of treatments for us to study influences of altering quantity of undegraded dietary crude protein and quantity of crude protein on milk production and composition. Diets supplemented with protein sources were 1) soybean meal positive control (22.7% crude protein), 2) whole cottonseed-corn gluten meal (14.7% crude protein), 3) extruded whole soybean (14.5% crude protein), or 4) soybean meal supplemented (15.7% crude protein). Concentrate and sorghum silage were fed in a ratio of 62:38 dry matter. Dry matter intake was not influenced by dietary crude protein concentration or source. Cows consuming diet 2 produced less milk, milk protein, total solids, and solids-not-fat than cows receiving diets 1 and 4. Efficiency of conversion of dietary crude protein to milk protein was highest for cows receiving diet 3 and lowest for diet 1.Trial 2, a 4 × 4 Latin-square trial for collection of abomasal digesta, had four ruminal and abomasal cannulated steers and the four diets from the lactation trial; the trial was to determine the influence of source and concentrations of protein on quantity of protein reaching the abomasum daily. Crude protein intake by steers fed diet 1 was greater than for the other three diets. Percentages recovery of dietary crude protein were 122 and 130 for treatments 2 and 3, intermediate for treatment 4 (107%), and lowest for diet 1 (88.0%); crude protein digestibility in the total tract was highest for steers receiving diet 1.     

Response of High Producing Dairy Cows in Early Lactation to the Feeding of Heat-Treated Whole Soybeans

Fifty-eight multiparous cows were assigned randomly to one of two rations. Control cows received a concentrate mixture that contained 20% soybean meal as the protein supplement, and the experimental cows were fed a concentrate that contained 25% heat-treated whole soybeans. The experimental period started 10 d after calving and continued for 15 wk.Experimental cows peaked later in milk production (5 vs. 3 wk) but at a higher level (39.8 vs. 39.4 kg/d) than control cows. Although milk production was less during the first 4 wk, experimental cows surpassed the controls in wk 5 and increased the advantage to 2.0 kg/cow/d by wk 15. For the total 15-wk period, average milk production was 37.0 kg/d for the experimental cows compared with 36.2 kg/d for the controls.Total dry matter intake, lactation efficiency, body weight, and reproductive performance were similar for both treatments. Cows fed heated soybeans consumed more metabolizable energy, 61.6 vs. 60.4 Mcal/d for controls. Cows on experimental diet also had higher free fatty acids in plasma (5.6 vs. 4.8 mg/100 ml) and triglycerides (25.0 vs. 20.9 mg/100 ml). The acetate-to-propionate ratio of rumen acids was significantly lower in the experimental group (3.36 vs. 3.61).     

No Associative Effects Between Corn and Haycrop Silages Fed to Lactating Dairy Cows

Four first-lactation Holstein cows were used 65 to 177 days postpartum in a 4 × 4 Latin square trial to evaluate possible associative feeding effects between corn and haycrop silages. Nutrient digestibility and nitrogen and energy balances were studied. Diets were concentrate mixture, urea-treated corn silage, and early-cut, wilted haycrop silage in dry matter ratios of 55:45:0, 55:30:15, 55:15:30, and 55:0:45. Rations were offered just below energy balance in each 28-day period. Ration components were fed separately, concurrently, and twice daily. Crude protein in concentrate, corn silage, and hay crop silage dry matter was 16.9, 11.1, and 12.5%. Milk yield (18 to 19 kg) and ration dry matter intake (2.61% body weight) were not significantly different among diets. Apparent digestibility of gross energy, dry matter, protein, and fiber was not different among diets, but fat was more digestible in corn silage. Partition of ingested energy and nitrogen was not affected by treatments except that urine nitrogen was higher in corn silage. No associative feeding effects were significant. The two silages were equivalent in supporting milk production when fed in equal dry matter amounts.     

alpha-Amylase activity in rumen fluid of cows producing milk of low and normal fat content

α-Amylase activity in cell-free rumen fluid from lactating cows was measured by Phadebas amylase test. Effects of handling and storage of rumen fluid on α-amylase activity were determined. Assays of 35,000 × g centrifuged rumen fluid stored at ?18 °C showed good reproducibility, while reproducibility of assays of samples uncentrifuged prior to freezing was poor. In frozen stored samples of rumen fluid centrifuged at 35,000 × g or 3,200 × g, α-amylase activity decreased, whereas in frozen uncentrifuged samples α-amylase activity increased with storage time. α-Amylase activity was high and showed wide variations in one cow with experimentally induced low milk fat syndrome. Enzymatic activity was correlated negatively with rumen pH and positively with total concentration of volatile fatty acids. α-Amylase activity was significantly higher in rumen fluid samples from cows with low milk fat in conventional herds compared to cows with normal milk fat in the same herds. Enzymatic activity showed negative correlation coefficients with milk fat percentage and positive with total viable counts of rumen bacteria and mole percent of rumen propionic acid in the low milk fat cows but not in the cows with normal milk fat. α-Amylase activity in cell-free rumen fluid may be a useful indicator of activity of starch-hydrolyzing rumen microorganisms.