C.L. Girard

Effects of dietary nitrogen levels and carbohydrate sources on apparent ruminal synthesis of some B vitamins in dairy cows

Effects of nitrogen level and carbohydrate source on apparent ruminal synthesis (ARS) of thiamin, riboflavin, niacin, vitamin B6, folates, and vitamin B12 were evaluated using 4 lactating Holstein cows distributed in a 4 × 4 Latin square design with treatments following a 2 × 2 factorial arrangement. Cows were fitted with cannulas in the rumen and proximal duodenum. The treatments were 2 N levels and 2 carbohydrate sources. The diet with the high N level provided 14% crude protein, calculated to meet 110% of the protein requirements and an adequate supply in rumen-degradable protein, whereas the diet with the low N level contained 11% crude protein, calculated to meet 80% of the protein requirements with a shortage in rumen-degradable protein. Carbohydrate source treatments differed by their nature (i.e., high in starch from barley, corn, and wheat, or high in fiber from soybean hulls and dehydrated beet pulp). All 4 diets were isoenergetic, based on corn silage, and had the same forage-to-concentrate ratio (60:40, dry matter basis). Duodenal flow was determined using YbCl3 as a marker. Each B-vitamin ARS was calculated as duodenal flow minus daily intake. The intake of several B vitamins varied among treatments, but because the animals consumed a similar amount of feed every day (average of 20 kg of dry matter/d) the difference was mostly due to vitamin content of each ingredient and their relative proportion in the diets. Decreasing N concentration in the diet reduced vitamin B6 duodenal flow and increased its apparent ruminal degradation. It also decreased duodenal flow and ARS of folates. The high-starch diets increased duodenal flow and ruminal balance of riboflavin, vitamin B6, and folates, whereas the high-fiber diets increased vitamin B12 ARS and duodenal flow. These effects on apparent synthesis are possibly due to changes in ruminal fermentation.

Effects of forage family on apparent ruminal synthesis of B vitamins in lactating dairy cows.

Effects of forage family (legume vs. grass) on apparent ruminal synthesis (ARS) and postruminal supply of B vitamins were evaluated in 2 experiments. Diets containing either alfalfa (AL) or orchardgrass (OG) silages as the sole forage were offered to ruminally and duodenally cannulated lactating Holstein cows in crossover design experiments. Experiment 1 compared diets containing AL and OG [~23% forage neutral detergent fiber (NDF) and ~27% total NDF] offered to 8 cows in two 15-d treatment periods. Experiment 2 compared diets containing AL and OG (~25% forage NDF and ~30% total NDF) offered to 13 cows in two 18-d treatment periods. Thiamin, riboflavin, niacin, vitamin B6, folates, and vitamin B12 were analyzed in feeds and duodenal digesta. Apparent ruminal synthesis was calculated as the duodenal flow of each vitamin minus its intake. Forage family affected B vitamin intakes, duodenal flow, and ARS. In both experiments, AL diets increased vitamin B6 and decreased folate intakes. In experiment 1, riboflavin and niacin intakes were greater with the OG diet, whereas in experiment 2 thiamin intake was greater but riboflavin intake was smaller with the OG diet. In spite of the low contribution of either silage to the dietary folate content, folate intake was greater with OG diets than AL due to the difference in soybean meal contribution between diets. Niacin and folate ARS were not affected by the forage family. Duodenal microbial nitrogen flow was positively correlated with ARS of riboflavin, niacin, vitamin B6, folates, and vitamin B12, but tended to be negatively correlated with thiamin ARS. Apparent ruminal synthesis of folates and vitamin B12 appear to be related to microbial biomass activity. Changes in nutrient composition of the diets likely affected the microbial population in the rumen and their B vitamin metabolism.

Particle length of silages affects apparent ruminal synthesis of B vitamins in lactating dairy cows

Effects of particle length of silages on apparent ruminal synthesis (ARS) and postruminal supply of B vitamins were evaluated in 2 feeding trials. Diets containing alfalfa (trial 1) or orchardgrass (trial 2) silages, chopped to either 19mm (long cut, LC) or 10mm (short cut, SC) theoretical particle length, as the sole forage were offered to ruminally and duodenally cannulated lactating Holstein cows in crossover design experiments. Forages chopped to a theoretical particle length of 19 and 10mm had mean particles sizes of 14.1 and 8.1mm, respectively, in trial 1, and 15.3 and 11.3mm, respectively, in trial 2. Trial 1 was conducted with 13 multiparous cows in two 19-d treatment periods; both diets contained approximately 20% forage neutral detergent fiber (NDF), 25% total NDF, and forage-to-concentrate ratios were approximately 47:53. Trial 2 was conducted with 15 cows in two 18-d treatment periods; both diets contained approximately 23% forage NDF, 28% total NDF, and had a forage-to-concentrate ratio of 50:50. Thiamine, riboflavin, niacin, vitamin B6, folates, and vitamin B12 were measured in feed and duodenal content. Daily ARS was calculated as the duodenal flow minus the intake. In trial 1, daily intake of individual B vitamins was increased with the LC diet, but ARS of thiamine, riboflavin, vitamin B6, and folates was reduced. In trial 2, except for folates, intakes of the other B vitamins were decreased with the LC diets, whereas ARS of riboflavin, niacin, and vitamin B6 was increased. Daily ARS of thiamine, riboflavin, niacin, and vitamin B6 were correlated negatively with their intake, suggesting that ruminal bacteria reduced their synthesis when dietary supply increased. Microbial activity could have also reduced degradation of thiamine, riboflavin, and niacin, which is supported by (1) the negative correlation between ARS of these vitamins and ruminal pH or microbial N duodenal flow; and (2) the positive correlation between ARS and ruminal concentrations of volatile fatty acids. Folate ARS followed the opposite correlation pattern. Nevertheless, in spite of differences in intake and ARS, with both forages, decreasing particle length of silages had limited effects on the amounts of B vitamins reaching the sites of absorption in the small intestine of dairy cows.

Choline absorption and evaluation of bioavailability markers when supplementing choline to lactating dairy cows

The metabolites of choline have a central role in many mammalian biological processes, and choline supplementation to the periparturient dairy cow improves hepatic lipid metabolism. However, variability in responses to choline supplementation has highlighted a lack of understanding of choline absorption in the lactating dairy cow. Our objective was to determine net choline absorption by measuring net portal fluxes of choline and choline metabolites in cows receiving either dietary supplements of rumen-protected choline (RPC) or abomasal delivery of choline (ADC). We also evaluated markers for choline bioavailability by examining relationships between net portal absorption of choline and choline metabolites in plasma and milk. Five late-lactation Holstein cows were used in a 5×5 Latin square design, with 5-d treatment periods and a 2-d interval between periods. Treatments were (1) control (0g/d of choline), (2) 12.5g/d of choline fed as RPC, (3) 25g/d of choline fed as RPC, (4) 12.5g/d of choline provided as ADC, and (5) 25g/d of choline provided as ADC. At the end of each 5-d period, milk was sampled and 9 blood samples were collected simultaneously from an artery and portal vein at 30-min intervals. Plasma, milk, and feed ingredient concentrations of acetylcholine, betaine, free choline, glycerophosphocholine, lysophosphatidylcholine, phosphatidylcholine, phosphocholine, and sphingomyelin were quantified by hydrophilic interaction liquid chromatography-tandem mass spectrometry. With an increasing dose of ADC, the net portal flux of free choline increased and regression analysis indicated 61% net absorption of the infused dose. Among the choline metabolites, only concentrations of betaine, free choline, and phosphocholine increased in both arterial plasma (3.9, 1.9, and 0.4 times, respectively) and milk (2.5, 1.4, and 1.0 times, respectively) with 25g/d of ADC relative to the control. For RPC, the net portal flux of free choline was low relative to ADC (13%), which was similar to the relative difference observed in the concentrations and yields of milk free choline and betaine (averaged 21%). When evaluating markers for choline bioavailability, betaine was the leading candidate. Betaine in plasma and milk (alone or in combination with phosphocholine) was strongly associated with net free choline portal flux (coefficient of determination ranging from 0.64 to 0.79). In summary, free choline supply to the lactating dairy cow increases only specific choline metabolites in plasma and milk, which can be potential markers for choline bioavailability.

High-concentrate diets based on forages harvested at different maturity stages affect ruminal synthesis of B vitamins in lactating dairy cows.

Effects of plant maturity on apparent ruminal synthesis and post-ruminal supply of B vitamins were evaluated in two feeding trials. Diets containing alfalfa (Trial 1) or orchardgrass (Trial 2) silages harvested either (1) early cut, less mature (EC) or (2) late cut, more mature (LC) as the sole forage were offered to ruminally and duodenally cannulated lactating Holstein cows in crossover design experiments. In Trial 1, conducted with 16 cows (569±43 kg of empty BW (ruminal content removed) and 43.7±8.6 kg/day of 3.5% fat-corrected milk yield; mean±SD) in two 17-day treatment periods, both diets provided ~22% forage NDF and 27% total NDF, and the forage-to-concentrate ratios were 53 : 47 and 42 : 58 for EC and LC, respectively. In Trial 2, conducted with 13 cows (588±55 kg of empty BW and 43.7±7.7 kg/day of 3.5% fat-corrected milk yield; mean±SD) in two 18-day treatment periods, both diets provided ~25% forage NDF and 31% total NDF; the forage-to-concentrate ratios were 58 : 42 and 46 : 54 for EC and LC, respectively. Thiamin, riboflavin, niacin, vitamin B6, folates and vitamin B12 were measured in feed and duodenal content. Apparent ruminal synthesis was calculated as the duodenal flow minus the intake. Diets based on EC alfalfa decreased the amounts of thiamin, niacin and folates reaching the duodenum, whereas diets based on EC orchardgrass increased riboflavin duodenal flow. Daily apparent ruminal synthesis of thiamin, riboflavin, niacin and vitamin B6 were correlated negatively with their intake, suggesting a microbial regulation of their concentration in the rumen. Vitamin B12 apparent ruminal synthesis was correlated negatively with total volatile fatty acids concentration, but positively with ruminal pH and microbial N duodenal flow.

Apparent ruminal synthesis of B vitamins in lactating dairy cows fed diets with different forage-to-concentrate ratios

Effects of the forage-to-concentrate ratio on apparent ruminal synthesis of thiamine, riboflavin, niacin, vitamin B6, folates, and vitamin B12 were evaluated in an experiment using 14 ruminally and duodenally cannulated Holstein cows. The experiment was a crossover design with two 15-d treatment periods and a 14-d preliminary period in which cows were fed a diet intermediate in composition between the treatment diets. Treatments were diets containing low-forage (44.8% forage, 32.8% starch, 24.4% neutral detergent fiber) or high-forage (61.4% forage, 22.5% starch, 30.7% neutral detergent fiber) concentrations. Both diets were formulated with different proportions of the same ingredients. Concentrations of B vitamins were analyzed in feed and duodenal digesta. Apparent ruminal synthesis of each B vitamin was calculated as the duodenal flow minus the intake. The high-forage diet had the highest concentrations of riboflavin, niacin, vitamin B6, and folates, whereas the low-forage diet had the highest thiamine concentration. Vitamin B12 in the diets was under the level of detection. Consequently, despite a reduction in dry matter intake when the cows were fed the high-forage diet, increasing dietary forage concentration increased or tended to increase intakes of riboflavin, niacin, and vitamin B6 but reduced thiamine and folate intakes. Increasing dietary forage concentration reduced apparent ruminal degradation of thiamine and apparent ruminal synthesis of riboflavin, niacin, and folates and increased ruminal degradation of vitamin B6, but had no effect on ruminal synthesis of vitamin B12. As a consequence, increasing the forage-to-concentrate ratio had no effect on the amounts of thiamine, riboflavin, and vitamin B12 reaching the small intestine but decreased the amounts of niacin, vitamin B6, and folates available for absorption. Apparent ruminal syntheses of riboflavin, niacin, folates, and vitamin B12 were correlated positively with the amount of starch digested in the rumen and duodenal flow of microbial N, whereas these correlations were negative for thiamine. Apparent ruminal syntheses of thiamine and vitamin B6 were negatively correlated with their respective intakes, whereas folate intake was positively correlated with its synthesis in the rumen.

Short communication: Effect of fatty acid supplements on apparent ruminal synthesis of B vitamins in lactating dairy cows

The effect of fat supplements (FS) providing different proportions of saturated (SFA) and unsaturated (UFA) fatty acids on supply, apparent ruminal synthesis (ARS), and duodenal flow (DF) of some B vitamins (thiamine, riboflavin, niacin, vitamin B6, folates, and vitamin B12) were evaluated in an experiment using 8 ruminally and duodenally cannulated lactating Holstein cows. The experiment was a replicated 4 × 4 Latin square design with 21-d treatment periods. The 4 treatments were a control diet without fatty acid supplement and 3 diets with 2.5% additional fatty acids from supplements containing (1) SFA, (2) an intermediate mixture of SFA and UFA, or (3) UFA. All diets were served as a total mixed ration once daily at 115% of the expected intake. B-vitamin concentrations were analyzed in feed and duodenal digesta. Apparent ruminal synthesis of each B vitamin was calculated as the DF minus the intake. B-vitamin concentrations were similar among the 4 treatments; consequently, daily intake of the vitamins followed the same pattern as dry matter intake. Adding FS decreased B-vitamin intakes (except vitamin B12), as did increasing the proportion of UFA. Riboflavin and niacin DF and ARS, expressed as total daily amount or per unit of dry matter intake, were not affected by FS, but increasing the proportion of UFA decreased riboflavin and niacin DF and ARS. Fat supplements decreased DF of vitamin B6, expressed either as total daily amount or per unit of dry matter intake. No treatment effects were observed on total daily folate DF and ARS. However, when expressed per unit of dry matter intake, folate DF and ARS were greater when cows were fed FS and they increased linearly with the proportion of UFA in the supplement. Inclusion of fat supplements into the dairy cow diet had a limited effect on the fate of most B vitamins in the rumen although increasing the proportion of UFA in the FS linearly decreased apparent synthesis of riboflavin and niacin in the rumen and the amounts of these vitamins reaching the small intestine.

Corrigendum to “Effects of dietary nitrogen levels and carbohydrate sources on apparent ruminal synthesis of some B vitamins in dairy cows” (J. Dairy Sci. 99:2730–2739)

In this paper, we used erroneous values for the molecular weight of thiamin and vitamers of vitamin B6. This error had limited effects on the overall results or statistical significance; however, several values reported in text and in tables are incorrect. The error affected statements in the Thiamin (page 2735) and Vitamin B6 (page 2737) subsections of the Results and Discussion, as well as values of thiamin and vitamin B6 reported in Table 1 (page 2732), Table 2 (page 2735), and Table 3 (page 2735), and correlation coefficients for ARS of vitamin B6 in Table 4 (page 2736). A revised version of this paper containing the corrections noted above has been published as supplementary data (see file below). The authors regret the errors.

Short communication: Apparent ruminal synthesis of B vitamins in lactating dairy cows fed Saccharomyces cerevisiae fermentation product

Apparent ruminal synthesis and duodenal flow of thiamin, riboflavin, niacin, vitamin B6, folates, and vitamin B12 were evaluated in an experiment using 15 ruminally and duodenally cannulated lactating Holstein cows fed a basal diet, according to a crossover design, supplemented or not with 56 g/d of Saccharomyces cerevisiae fermentation product. Duration of the treatment period was 28 d. The basal ration had 28% neutral detergent fber, 30% starch and 16.5% crude protein; forages were corn silage (67% of forage dry matter) and alfalfa silage (33% of forage dry matter). Concentrations of B vitamins were analyzed in feed and duodenal digesta. Apparent ruminal synthesis of each B vitamin was calculated as the duodenal flow minus the intake. Under the present experimental conditions, a dietary supplement of Saccharomyces cerevisiae fermentation product had no effect apparent synthesis of B vitamins in the rumen or on the amounts of these vitamins reaching the duodenum and available for absorption by the dairy cow.