Varying degradation rates of total nonstructural carbohydrates: effects on ruminal fermentation, blood metabolites, and milk production and composition in high producing Holstein cows.

Twelve multiparous Holstein cows (6 ruminally cannulated and 6 intact) at 56 to 77 d of lactation were used in an experiment with a 3 x 6 Latin square design. Cows were fed three total mixed rations that varied in degradation rates of total nonstructural carbohydrates (6.04, 6.98, and 7.94%/h). No interactions between treatment and square were detected. Higher ruminal degradation rates of dietary total nonstructural carbohydrates increased the nonammonia N (NAN) pool of the liquid fraction but did not alter the dry matter or volume of fractional pools, microbial NAN pools, or microbial composition. Treatment did not affect dry matter intake, total concentrations of volatile fatty acids, or fiber digestibility. As ruminal degradation rates of total nonstructural carbohydrates increased, the following effects were observed: 1) the turnover rates of solids increased linearly; 2) ruminal NH3 N concentrations and degradabilities of organic matter and N decreased, but propionate concentrations, bacterial efficiency, and total NAN flows tended to increase; 3) blood glucose and insulin concentrations were not affected, but blood urea N and nonesterified fatty acids were decreased; 4) intestinal and total tract digestibilities of organic matter and total nonstructural carbohydrates increased; and 5) milk production and milk true protein content and yield increased, but energetic efficiency of milk production did not change. The highest dietary ruminal degradation rate of total nonstructural carbohydrates increased the amount of nutrients digested in the intestine and increased milk production.

Varying degradation rates of total nonstructural carbohydrates: effects on nutrient uptake and utilization by the mammary gland in high producing Holstein cows.

Six ruminally cannulated Holstein cows at 56 to 77 d of lactation were fed three total mixed rations that varied in ruminal degradation rates of total nonstructural carbohydrates (6.04, 6.98, and 7.94%/h). The design was a 3 x 6 Latin square with 21-d experimental periods. Cows were catheterized in the jugular vein and in one of the caudal superficial epigastric veins. Increases in the ruminal degradation rate of total nonstructural carbohydrates 1) elevated mammary blood flow and blood concentrations of nonessential amino acids; 2) decreased arteriovenous differences and extraction rates of essential and most nonessential amino acids, but not of Gln and Glu (analyzed together) and glucose; 3) increased mammary uptake of Gln, Glu, and glucose; milk protein concentrations of Glu, Pro, and Asp; and total nonessential amino acids; and 4) did not alter uptake to output ratios of amino acids in the mammary gland, however, of the nonessential amino acids, only the uptake to output ratios for Glu and Gln increased (19%). Glucose and amino acid arteriovenous differences were not strongly correlated with their arterial concentrations. Increases in the ruminal degradation rate of total nonstructural carbohydrates increased intestinal digestibilities of total nonstructural carbohydrates and protein and increased uptake of energy substrates by the mammary gland, resulting in a 13% improvement in the utilization of nonessential amino acids for milk protein synthesis and in higher milk production and milk protein yields.

Effects of processing method on degradation characteristics of protein and carbohydrate sources in situ.

Two ruminally cannulated Holstein cows in early lactation were used to determine the effects of heat treatment and particle size on fractional degradation rates and ruminal degradabilities of DM, CP and total nonstructural carbohydrate of dry shelled corn and soybeans. A randomized complete block design with cows as blocks was used. Carbohydrate sources were cracked corn, chick cracked corn, finely ground corn, and steam-flaked corn. Protein sources were soybeans that were roasted at 144 degrees C, cracked, or ground through a 4-mm screen and raw soybeans that were cracked or ground through a 4-mm screen. Reduction in particle size increased both degradability of total nonstructural carbohydrate in the rumen. Heat treatment decreased degradability of CP and increase degradability of total nonstructural carbohydrate in the rumen for both protein and carbohydrate sources. Roasting of soybeans decreased degradability of all AA except Lys. However,reduction in particle size had a stronger effect than heat treatment on ruminal degradability of CP and AA of soybeans, but had the opposite effect on total nonstructural carbohydrate degradability from corn. Methionine, Leu, and Thr had the lowest ruminal degradability across all soybean sources, and Lys and Val were the most degradable. The AA profile of the RUP fraction of soybeans differed from that of the original feed-stuff and was affected by processing method.

Effect of corn silage supplementation on intake and milk production in cows grazing grass pasture.

The objective was to determine the effects on milk production and DMI of 2.3 kg/d of corn silage DM fed to lactating cows grazing grass pasture and fed supplemental grain. Thirty Holstein cows, averaging 32 kg of milk at the start of the trial, intensively grazed grass pasture for 8 wk. One-half of the cows received 2.3 kg/d of corn silage DM in two equal feedings, and one-half of the cows were used as controls (no corn silage). All cows were fed grain at 1 kg of grain DM/4 kg of milk. Corn silage had no effect on milk production or milk composition. Cows fed corn silage did not have improved BW gain or body condition score. Each unit of corn silage consumed replaced 1.2 units of pasture, but total DMI was not different because of supplementation with corn silage. Blood urea N concentrations were lower for cows fed corn silage. Supplementation of high producing Holsteins grazing grass pastures with 2.3 kg/d of corn silage DM had no effect on milk production, milk composition, or total DMI.

Supplemental dietary fat and ruminally protected amino acids for lactating Jersey cows.

Eight Jersey cows receiving a 50:50 ratio of forage to concentrate on a DM basis were used in a replicated 4 x 4 Latin square design to determine the effects of added fat (3.4% of dietary DM) and ruminally protected AA (8 g of Met and 24 g of Lys daily) on yield and composition of milk. Treatments were 1) basal control, 2) added fat, 3) added AA, and 4) fat plus AA. Compared with no added fat, fat supplementation increased 4% FCM yield (24.7 vs. 23.0 kg/d) and milk fat yield (1.05 vs. .97 kg), depressed milk protein content (3.58 vs. 3.74%), and altered fatty acid composition of milk. Blood triglyceride and NEFA were elevated (34.4 vs. 29.5 mg/dl and 175.1 vs. 143.7 microeq/L, respectively) by added fat. Supplementation with AA elevated blood Lys, Met, and urea N without increasing milk protein yield. Increase in blood NEFA was further augmented by fat plus AA supplementation, but no changes in concentrations of Lys or Met in blood were found. Addition of AA did not alleviate the depression of milk protein content when supplemental fat was added to the diet for Jersey cows.

Improved techniques for dissociating particle-associated mixed ruminal microorganisms from ruminal digesta solids.

Combinations of physical and chemical methods were evaluated for their ability to remove particle-associated microorganisms (PAM) from saline-washed ruminal digesta solids (SWRDS). Physical methods included chilling and storage, homogenization, multiple extraction, and agitation with marbles. Chemical methods included use of low pH, Tween 80, formaldehyde, methanol, tertiary butanol, and methylcellulose. Microbial removal from SWRDS was determined directly by using epifluorescence microscopy and indirectly by measuring removal of diaminopimelic acid and total purines. Different combinations of methods resulted in removals of 46 to 82% for particle-associated bacteria (PAB), 52 to 98% for particle-associated protozoa (PAP), and 60 to 83% for PAB plus PAP. Two methods were considered most effective, based on microscopy; both removed similar amounts of PAB (79 to 82%) and PAB plus PAP (80 to 83%). In one method, SWRDS were stored for 24 h at 4 degrees C in a solution of pH 2 saline, .1% Tween 80, 1.0% methanol, and 1.0% tertiary butanol. In the other method, SWRDS were incubated for 30 min in .1% methylcellulose before storage for 24 h at 4 degrees C in pH 2 saline, .1% Tween 80, and 1.0% methanol. Common to both treatments was subsequent homogenization of the suspensions for 15 s followed by washing the digesta solids seven times with the treatment solutions. Both methods resulted in values that exceeded those reported previously for removal of PAM from ruminal digesta solids.