The effect of supplementary selenium source on apparent and true absorption, retention, performance, and selenium status in lactating Holstein cows.

Selenium is an essential trace mineral for dairy cattle and can be provided in the diet in various forms that may differ in bioavailability. The objective of this study was to determine how source of Se affects animal performance, Se status, retention, and apparent and true absorption. Multiparous Holstein cows (n = 24; 597 ± 49 kg body weight) were blocked by days in milk (DIM; 161 ± 18) and randomly assigned to receive 0.3 mg Se/kg of dry matter (100% of NASEM requirements) of either organic Se (ORG; selenized yeast) or inorganic Se (INO; sodium selenite). The Se premix was top-dressed on a common total mixed ration fed daily and mixed into the top 15 cm directly before feeding. Following an 11-wk adaptation period, cows received simultaneous infusions of an intraruminal isotope dose of 77Se in the same chemical form as the premix, and an intravenous dose of 82Se in an inorganic form. Infusions were followed by a 4-d period of blood and rumen fluid sampling, and total collection of feces, urine, and milk. Daily dry matter intake (23 ± 0.6 kg), milk yield (35 ± 1.2 kg), and serum Se (0.11 ± 0.003 µg/g) were not different between treatments during the adaptation period, but milk Se concentrations were greater for ORG compared with INO. Serum 77Se maximum concentration (Cmax) and area under the curve (AUC) were not different between treatments for 72 h following infusion, but rumen fluid 77Se AUC was higher for ORG than INO. Apparent absorption (64 ± 1.4%), and retention (44 ± 1.5%) of the 77Se dose did not differ between treatments. True absorption was calculated using 82Se enrichment in serum and feces and was determined to be 69 ± 1.3% and did not differ between treatments. Fecal excretion of the 77Se dose was not different between treatments (36 ± 1.4%), but ORG had lower urinary excretion and higher milk excretion compared with INO. These results indicate that organic Se resulted in greater Se concentration of milk and lower urinary Se excretion into the environment, but absorption, Se status, and performance of the cow were not affected by Se source at this supplementation level.

Potential roles of nitrate and live yeast culture in suppressing methane emission and influencing ruminal fermentation, digestibility, and milk production in lactating Jersey cows.

Concern over the carbon footprint of the dairy industry has led to various dietary approaches to mitigate enteric CH4 production. One approach is feeding the electron acceptor NO3-, thus outcompeting methanogens for aqueous H2. We hypothesized that a live yeast culture (LYC; Saccharomyces cerevisiae from Yea-Sacc 1026, Alltech Inc., Nicholasville, KY) would stimulate the complete reduction of NO3- to NH3 by selenomonads, thus decreasing the quantity of CH4 emissions per unit of energy-corrected milk production while decreasing blood methemoglobin concentration resulting from the absorbed intermediate, NO2-. Twelve lactating Jersey cows (8 multiparous and noncannulated; 4 primiparous and ruminally cannulated) were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Cattle were fed diets containing 1.5% NO3- (from calcium ammonium nitrate) or an isonitrogenous control diet (containing additional urea) and given a top-dress of ground corn without or with LYC, with the fourth week used for data collection. Noncannulated cows were spot measured for CH4 emission by mouth using GreenFeed (C-Lock Inc., Rapid City, SD). The main effect of NO3- decreased CH4 by 17% but decreased dry matter intake by 10% (from 19.8 to 17.8 kg/d) such that CH4:dry matter intake numerically decreased by 8% and CH4:milk net energy for lactation production was unaffected by treatment. Milk and milk fat production were not affected, but NO3- decreased milk protein from 758 to 689 g/d. Ruminal pH decreased more sharply after feeding for cows fed diets without NO3-. Acetate:propionate was greater for cows fed NO3-, particularly when combined with LYC (interaction effect). Blood methemoglobin was higher for cattle fed NO3- than for those fed the control diet but was low for both treatments (1.5 vs. 0.5%, respectively; only one measurement exceeded 5%), indicating minimal risk for NO2- accumulation at our feeding level of NO3-. Although neither apparent organic matter nor neutral detergent fiber digestibilities were affected, apparent N digestibility had an interaction for NO3- × LYC such that apparent N digestibility was numerically lowest for diets containing both NO3- and LYC compared with the other 3 diets. Under the conditions of this study, NO3- mitigated ruminal methanogenesis but also depressed dry matter intake and milk protein yield. Based on the fact that few interactions were detected, LYC had a minimal role in attenuating negative cow responses to NO3- supplementation.

Effects of once- versus twice-a-day feeding of pasteurized milk supplemented with yeast-derived feed additives on growth and health in female dairy calves.

The objective of this study was to compare the effects of feeding preweaning dairy calves pasteurized milk once or twice a day with or without a combination of yeast-derived products. Holstein heifer calves (n = 48) from The Pennsylvania State University dairy herd were fed 3.8 L of colostrum in 1 feeding and randomly assigned to 1 of 4 treatments (once-a-day milk feeding with or without live yeast culture and mannan-rich fraction and twice-a-day milk feeding with or without live yeast culture and mannan-rich fraction). All calves were fed 6 L of milk daily. Weekly growth measurements and blood samples were taken 3 h after the morning milk feeding for all animals. Growth measurement included body weight, hip width, and withers height. Calf starter refusal was recorded weekly, and a sample was taken to determine dry matter intake. Daily health scores were recorded for each calf using a standard scoring system. Intake, growth measurements, haptoglobin, and health scores data were analyzed using repeated measures analysis with calf included as a random variable. Preweaning average daily gain was 553.4 and 512.1 g/d for calves fed milk once and twice a day, respectively, and we found no difference between treatments. Preweaning calf starter intake was 242.3 and 198.7 g/d for calves fed milk once and twice a day, respectively, and we found no treatment differences. Preweaning calf starter intake was 224.3 and 216.6 g/d for calves fed yeast and without yeast, respectively. Withers height and hip width were similar in calves fed milk either once or twice a day; however, calves fed yeast tended to have greater withers height and hip width than control calves. Haptoglobin concentration as a measure of stress had least squares means of 4.0 and 9.5 ± 3.5 µg/mL for calves fed milk once or twice a day, respectively, and we found no difference among treatments. Scours score and total daily score were similar for calves fed milk once or twice a day. These results suggest that feeding milk once a day can be successfully applied to a calf feeding system and that yeast products may improve structural growth.

Rumen microbial responses to supplemental nitrate. I. Yeast growth and protozoal chemotaxis in vitro as affected by nitrate and nitrite concentrations.

Nitrates have been fed to ruminants, including dairy cows, as an electron sink to mitigate CH4 emissions. In the NO3- reduction process, NO2- can accumulate, which could directly inhibit methanogens and some bacteria. However, little information is available on eukaryotic microbes in the rumen. Protozoa were hypothesized to enhance nitrate reductase but also have more circling swimming behavior, and the yeast Saccharomyces cerevisiae was hypothesized to lessen NO2- accumulation. In the first experiment, a culture of S. cerevisiae strain 1026 was evaluated under 3 growth phases: aerobic, anoxic, or transition to anoxic culture. Each phase was evaluated with a control or 1 of 3 isonitrogenous doses, including NO3-, NO2-, or NH4+ replacing peptone in the medium. Gas head phase, NO3-, or NH4+ did not influence culture growth, but increasing NO2- concentration increasingly inhibited yeast growth. In experiment 2, rumen fluid was harvested and incubated for 3 h in 2 concentrations of NO3-, NO2-, or sodium nitroprusside before assessing chemotaxis of protozoa toward glucose or peptides. Increasing NO2- concentration decreased chemotaxis by isotrichids toward glucose or peptides and decreased chemotaxis by entodiniomorphids but only toward peptides. Live yeast culture was inhibited dose-responsively by NO2- and does not seem to be a viable mechanism to prevent NO2- accumulation in the rumen, whereas a role for protozoal nitrate reductase and NO2- influencing signal transduction requires further research.

Rumen microbial responses to supplemental nitrate. II. Potential interactions with live yeast culture on the prokaryotic community and methanogenesis in continuous culture.

Nitrates have been fed to ruminants, including dairy cows, as an electron sink to mitigate CH4 emissions. In the NO3- reduction process, NO2- can accumulate, which could directly inhibit methanogens and possibly other microbes in the rumen. Saccharomyces cerevisiae yeast was hypothesized to decrease NO2- through direct reduction or indirectly by stimulating the bacterium Selenomonas ruminantium, which is among the ruminal bacteria most well characterized to reduce both NO3- and NO2-. Ruminal fluid was incubated in continuous cultures fed diets without or with NaNO3 (1.5% of diet dry matter; i.e., 1.09% NO3-) and without or with live yeast culture (LYC) fed at a recommended 0.010 g/d (scaled from cattle to fermentor intakes) in a 2 × 2 factorial arrangement of treatments. Treatments with LYC had increased NDF digestibility and acetate:propionate by increasing acetate molar proportion but tended to decrease total VFA production. The main effect of NO3- increased acetate:propionate by increasing acetate molar proportion; NO3- also decreased molar proportions of isobutyrate and butyrate. Both NO3- and LYC shifted bacterial community composition (based on relative sequence abundance of 16S rRNA genes). An interaction occurred such that NO3- decreased valerate molar proportion only when no LYC was added. Nitrate decreased daily CH4 emissions by 29%. However, treatment × time interactions were present for both CH4 and H2 emission from the headspace; CH4 was decreased by the main effect of NO3- until 6 h postfeeding, but NO3- and LYC decreased H2 emission up to 4 h postfeeding. As expected, NO3- decreased methane emissions in continuous cultures; however, contrary to expectations, LYC did not attenuate NO2- accumulation.