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Eight rumen-fistulated Holstein cows, averaging 77 d postpartum, were used in a replicated 4 X 4 Latin square design with 28-d periods to investigate the effect of ammonium salts of isobutyrate, 2-methylbutyrate, isovalerate, and n-valerate on animal performance and their possible mechanism(s) and site(s) of action. Each cow was fed ad libitum a complete mixed diet of 55% corn silage and 45% concentrate on a dry basis that was supplemented with 1.8 kg of premix daily. Treatments were 1) control, 2) ammonium salts of volatile fatty acids in premix, 3) ammonium salts of volatile fatty acids ruminally infused, or 4) ammonium salts of volatile fatty acids abomasally infused. Mean ruminal fluid pH and concentrations of ammonia and volatile fatty acids for treatment comparisons were not different. Plasma concentrations of isobutyrate, 2-methylbutyrate, and valerate differed among treatments, but there was no significant effect on dry matter intake, milk production, milk composition, or efficiency of feed utilization. Apparent nutrient digestibility; disappearance of dry matter, cellulose, and nitrogen from polyester bags suspended in the rumen; and plasma concentrations of glucose, free fatty acids, and growth hormone also were not significantly affected by treatment.

Six rumen cannulated steers were in a replicated 3 X 3 Latin square arrangement to investigate degradability in the rumen of dry matter and crude protein from soybean meal that was untreated or treated with either 8% acetic acid or .3% formaldehyde. Polyester bags containing the soybean meals were suspended in the rumen of each steer and removed after 1, 2, 4, 8, 12, 16, and 24 h to calculate degradation rates. Soybean meals remaining in the polyester bags after 12 h of rumen exposure were collected and referred to as residues. Postruminal digestion was stimulated by incubating 200 mg of soybean meal residues with pepsin and pancreatin. Formaldehyde treatment of soybean meal was more effective than acetic acid treatment in preventing ruminal degradation of dry matter and crude protein under these experimental conditions. However, soybean meal treated with acetic acid and remaining in polyester bags after 12 h of ruminal exposure released a larger quantity of alpha-amino nitrogen during in vitro incubation with pepsin and pancreatin than did residue of soybean meal treated with formaldehyde. Acetic acid may prove to be an effective agent for increasing the supply of absorbable dietary amino acids.

The effectiveness of an encapsulated rumen-protected methionine compound (RPMet) for delivering methionine postruminally and its effect on plasma amino acid concentrations, milk production and milk composition were evaluated. Thirty multiparous Holstein cows in early lactation were randomly assigned to five levels of RPMet. RPMet was supplied at 0, 550, 1100, 1650 or 3300 mg/kg of concentrate resulting in an intake of 0, 6.9, 12.9, 19.6 or 40.2 g of supplemental DL-methionine/day for each cow. The basal diet was alfalfa-bromegrass hay and a 15.8% crude protein corn- and soybean meal-based concentrate mixture. The experiment was divided into pretreatment and treatment periods, each consisting of 21 days. Feed intake and milk production were measured daily, milk composition weekly and plasma amino acid concentrations twice daily on days 17 and 20 of the pretreatment period and on days 4, 10 and 21 of the treatment period. RPMet was effective in delivering methionine postruminally, which increased concentrations of methionine in plasma. Dry matter intake, milk production, milk composition and body weight were not significantly affected by RPMet.

Two rumen-cannulated wether sheep were fed a diet containing 1 kg of a liquid-molasses mixture, 80 g of soybean oil meal, and 100 g of chopped wheat straw once a day. In 6 weeks and thereafter, the microbiota adapted such that Quin's oval, a very large bacterium, was present in huge numbers (11.3 X 10(10) and 1.3 X 10(10) ml-1 after 73 days). Direct microscopic counts were also done on small bacteria, moderate-sized Selenomonas spp., and small Entodinium spp., which were the only protozoa seen. After the necessary dilution of rumen contents to make the microbial cells visible, Quin's ovals were seen to be much smaller in sheep 1 than in sheep 2. Most-probable-number estimates indicated that Methanobrevibacter spp. were present at 10(7) ml-1, Methanosarcina spp. were present at 10(3) ml-1, and Eubacterium limosum-like bacteria were present at 10(5) to 10(6) ml-1. In the adapted sheep, the dry portion of the diet was rapidly consumed, but the molasses mixture was consumed over a 9- to 10-h period. Volatile fatty acids in the rumen were present in very low amounts just prior to feeding and were much higher during the consumption of the diet, with about a 1:1 molar ratio of propionate to acetate between 1 and 9 h after feeding. Data were obtained on hourly feed consumption, levels of volatile fatty acids, and pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Four early lactation multiparous Holstein cows were used in a 4 x 4 Latin square to investigate the effects of source of protein (fish meal or soybean meal) and carbohydrate (corn or barley) on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. The treatments, arranged in a 2 x 2 (protein x carbohydrate) factorial were: 1) corn plus soybean meal; 2) corn plus fish meal; 3) barley plus soybean meal; and 4) barley plus fish meal. Dry matter and starch intakes were greater when corn was fed than when barley was fed. Barley-based diets were more extensively degraded in the rumen than corn-based diets and therefore provided more energy for microbial growth. However, passage of amino acids and starch to the duodenum was greater for corn-based diets than barley-based diets, because of the greater intake and lower ruminal degradability of the corn-based diets. Microbial protein constituted a larger portion of the total N and had a greater influence on the pattern and quantity of amino acids that passed to the duodenum than did protein from fish meal or soybean meal, which escaped ruminal degradation. Feeding corn-based diets increased production of milk and milk protein compared with feeding barley-based diets.