Long-term effects of acetate and propionate on voluntary feed intake by midlactation cows.

Our objective was to separate the effects of physical fill and acetate production in the regulation of voluntary feed intake. Eight ruminally fistulated Holstein cows in midlactation were fed a low forage diet or a high forage diet with or without continuous ruminal infusion of buffered acetate or propionate in a duplicated 4 x 4 Latin square with 21-d periods. Cows consumed about 3.5% of body weight as dry matter, and voluntary dry matter intake (DMI) was approximately 6% greater when cows were fed the low forage diet than when cows were fed the high forage diet. Infusion of 7.1 Mcal of net energy for lactation as acetate or propionate resulted in a reduction in DMI relative to the DMI when the high forage diet was fed alone; propionate infusion reduced intake more than did acetate infusion. Consumption of neutral detergent fiber was approximately 1.19 and 1.25% of body weight when cows were fed the low and high forage diets, respectively. Milk production was approximately 35 kg/d regardless of the diet fed, but an increase in milk fat production by cows receiving the acetate or propionate infusion resulted in an increase in fat-corrected milk. Neither neutral detergent fiber fill nor a threshold for acetate utilization appeared to limit DMI.

The effect of preservatives based on propionic acid on the fermentation and aerobic stability of corn silage and a total mixed ration.

For 3 successive yr, whole-plant corn was ensiled in laboratory silos with low percentages of silage preservatives, the primary active ingredient of which was propionic acid. Preservatives were added to forage just prior to ensiling at rates of 0.1 to 0.2% of the fresh forage weight. In all 3 yr, treatments had minor effects on fermentation end products, except that the concentration of propionic acid was greater because of its addition. The mean low and high percentages of preservatives increased aerobic stability of the treated silages by 19 and 57 h, respectively, in Experiment 1 and by 17 and 38 h, respectively, in Experiment 2. In Experiment 3, aerobic stability was improved by > 90 h by preservatives (0.2% addition). In a lactation study, a total mixed ration (46% dry matter) was mixed without or with (0.2 or 0.3%) a stabilizer that was designed to prevent spoilage in the feed bunk. The high dose resulted in orts with a lower pH and temperature after 24 h in the feed bunk. However, dry matter intake and milk production were unaffected by treatments. Chemical preservatives based on propionic acid added at low rates did not affect fermentation but were effective in the reduction of heating in corn silage and in a total mixed ration.

Effects of a live yeast culture and enzymes on in vitro ruminal fermentation and milk production of dairy cows.

Live yeast culture (Saccharomyces cerevisiae) grew best on malt extract agar and required incubation under aerobic conditions to maximize the number of viable cells. In sterile, anaerobic ruminal fluid that had been supplemented with malt extract, yeast cells remained viable and metabolically active for up to 48 h, as indicated by the production of ethanol. A supplement containing live yeast and enzymes was fed twice daily with a diet of 50:50 (wt/wt) forage to concentrate (dry matter basis) to continuous fermentors inoculated with mixed ruminal microorganisms. The supplement had no effect on major fermentation acids or pH. After the last supplement with yeast was fed, numbers of yeast immediately decreased in the fermentors and were not detectable after 24 h. In the first of two lactation experiments, Holstein cows in midlactation were offered a diet with corn silage as the primary forage source. Half of the cows received a top-dressing based on corn that contained 10 g/d of the yeast and enzyme supplement. The supplement had no effect on milk production, milk composition, or dry matter intake. In a second lactation experiment, high producing cows in early lactation were fed 0, 10, and 20 g/d of the supplement. Cows fed the control diet produced 36.4 kg of milk/d, and milk production was 39.3 and 38.0 kg/d from cows fed 10 and 20 g of yeast/d, respectively.

An enzyme additive for corn silage: effects on silage composition and animal performance.

Whole-plant corn was harvested at the soft dough stage of maturity, was left untreated or was treated with an enzyme additive containing cellulase and hemicellulase, and was ensiled in bag or mini silos. Silage fermentation was not markedly altered by treatment, regardless of silo type; however, enzyme treatment reduced NDF and ADF contents of silage and reduced in vitro NDF digestibility after 196 d of storage in mini silos. For corn silage stored in bag silos, enzyme treatment had no effect on fibrous components; however, for ruminal continuous cultures, a diet containing treated silage decreased the acetate to propionate ratio. Nutrient digestion was not different in lambs fed untreated or treated corn silage, but N retention was greater in lambs fed the latter. Treatment of corn silage with the enzyme additive had no effect on DMI, milk production, milk composition, or feed efficiency when silage was fed at 43% (DM basis) of the total mixed diet of the dairy cows. Enzyme treatment had minimal effects on silage fermentation, inconsistent effects on fibrous components of silage, and improved N retention in lambs but had no effect on production of dairy cows.

Effects of an enzyme additive on composition of corn silage ensiled at various stages of maturity.

Corn forage at the milk, soft dough, and black layer stages of maturity (22, 28, and 44% DM, respectively) was treated with an enzyme additive at 1, 10, or 100 times the recommended dose and ensiled in laboratory silos at 26 degrees C. By in vitro assay, the additive contained a full complement of cellulase and hemicellulase activities. The pH and temperature optima for cellulase and hemicellulase activities were 4.8 and 50 degrees C, respectively. Regardless of dose, the additive had no effect on fermentation acids or nitrogenous compounds in silage at any maturity; however, high doses increased the glucose content of silage at the milk stage of maturity and increased ethanol content at the soft dough stage. Across maturities, addition of the enzyme additive resulted in a linear decrease in ADF, NDF, and hemicellulose content of corn silage but decreased the acid detergent lignin content of silage only at the milk and black layer stages of maturity. The enzyme additive had no consistent effect on in vitro NDF digestion.

Additives containing bacteria and enzymes for alfalfa silage.

First-cutting alfalfa was wilted, harvested from alternate rows, left untreated or treated with additives containing lactic acid bacteria and enzymes (cellulase, amylase, and pectinase), and ensiled in bag silos. Inoculation increased lactic acid bacteria from 5 x 10(4) to 1 x 10(6) cfu/g of forage. Because treatments were bagged consecutively, the DM of treated silages was higher than that of untreated silage. However, after 4 d of ensiling, the pH of treated silage, about 4.3, was lower than that of untreated silage, 4.7, and remained lower throughout the ensiling period. After 177 d of ensiling, total lactate was about 25% higher, and ammonia N was about 40% lower, in treated silage. In addition, NDF and ADF contents were lower in treated than in untreated silage. Between 51 and 177 d of storage, glucose content increased in treated silage, but not in untreated silage, suggesting that some plant cell-wall hydrolysis occurred during prolonged storage. In vitro digestion of NDF did not differ among treatments during early incubation, but the extent of digestion after 36 and 48 h was lower in treated than in untreated silage. The microbial and enzyme silage additives used in this study improved fermentation characteristics and reduced fiber content of silage but decreased the in vitro digestibility of fiber.