Milk production and composition responds to dietary neutral detergent fiber and starch ratio in dairy cows

Use of milk proteins as biomarkers of changes in the rumen metaproteome of Holstein cows fed low-fiber, high-starch diets

Dietary levels of undegraded neutral detergent fiber (uNDF240) and rumen-fermentable starch (RFS) can affect the rumen microbiome and milk composition. The objective of the study is to investigate the use of milk proteins as biomarkers of rumen microbial activity through a comparative evaluation of the rumen microbial and milk protein profiles produced by Holstein cows fed diets with varying contents of physically effective uNDF240 (peuNDF240) and RFS. Eight ruminally cannulated lactating Holstein cows were included in a larger study as part of a 4 × 4 Latin square design with 4 28-d periods to assess 4 diets varying in peuNDF240 and RFS content. For this experiment, cows received one of 2 dietary treatments: (1) low-peuNDF240, high-RFS (LNHR) diet or (2) high-peuNDF240, low-RFS (HNLR) diet. Within each period, rumen fluid samples were collected from each cow on d 26 (1400 h) and d 27 (0600 h and 1000 h), and milk samples were collected from each cow on d 25 (2030 h), d 26 (0430 h, 1230 h, and 2030 h), and d 27 (0430 h and 1230 h). Microbial proteins were isolated from each rumen fluid sample. For milk samples, milk proteins were fractionated, and the whey fraction was subsequently isolated. Isolated proteins within each rumen fluid or milk sample were isobarically labeled and analyzed by liquid chromatography-tandem mass spectrometry. Product ion spectra acquired from rumen fluid samples were searched using SEQUEST against 71 composite databases. In contrast, product ion spectra acquired from milk samples were searched against the Bos taurus database. Data were analyzed using the PROC MIXED procedure in SAS 9.4 to assess the effect of diet and time of sampling. To increase stringency, the false discovery rate-adjusted P-value (PFDR) was also calculated to account for multiple comparisons. Using the mixed procedure, a total of 129 rumen microbial proteins were quantified across 24 searched microbial species. Of these, the abundance of 14 proteins across 9 microbial species was affected due to diet and diet × time interaction, including 7 proteins associated with energetics pathways. Among the 159 quantified milk proteins, the abundance of 21 proteins was affected due to the diet and diet × time interaction. The abundance of 19 of these milk proteins was affected due to diet × time interactions. Of these, 16 proteins had the disparity across diets at the 0430 h sampling time, including proteins involved in host defense, nutrient synthesis, and transportation, suggesting that biological shifts resulting from diet-induced rumen changes are not diurnally uniform across milkings. The concentration of lipoprotein lipase (LPL) was statistically higher in the milk from the cows fed with the LNHR diet, which was numerically confirmed with an ELISA. Further, as determined by ELISA, the LPL concentration was significantly higher in the milk from the cows fed with the LNHR diet at 0430 h sampling point, suggesting that LPL concentration may indicate dietary carbohydrate-induced ruminal changes. The results of this study suggest that diet-induced rumen changes can be reflected in milk in a diurnal pattern, further highlighting the need to consider sampling time points for using milk proteins as a representative biomarker of rumen microbial activity.

Nutritional Value, Fermentation Characteristics and In Vitro Degradability of Whole Wheat Hay Harvested at Three Stages of Maturity

The nutritional value of whole crop wheat hay (WCWH) harvested at different maturation stages are different, and its feeding effects on dairy cows have not been thoroughly evaluated. In this study, the in vitro digestibility of whole wheat (Nongda 22) hay harvested during the flowering, late milk and dough stages were evaluated using batch culture technique. The neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents of whole wheat hay decreased by 35.5% and 40.4%, respectively, whereas the non-fibrous carbohydrates (NFC) content increased by 50.3% in WCWH harvested during the dough stage as compared to the flowering stage (p < 0.01). The pH of the fermentation liquid and acetate to propionate ratio was greatest in the wheat harvested during the flowering stage and lowest during the dough stage (p = 0.03), whereas the volatile fatty acid (VFA) concentration was greatest during the dough stage and lowest during the flowering stage (p < 0.01). The dry matter loss (DML) was 9.6% and 6.2% greater (p < 0.01) during the late milk stage than in the flowering or dough stages, and the NDF loss (NDFL; p = 0.01) and ADF loss (ADFL; p < 0.01) was greater in both the flowering and late milk stages. In conclusion, though the content of NDF was lower in the dough stage, and the starch to NFC ratio was greater, we determined that the optimal harvest stage should be the late milk stage due to the greater dry matter digestibility, the relatively greater NFC content and the shorter planting days.

Effect of different glucogenic to lipogenic nutrient ratios on rumen fermentation and bacterial community in vitro

Aims

This study was to investigate the effect of different ratios of glucogenic to lipogenic nutrients on rumen fermentation and the corresponding ruminal bacterial communities.

Methods and Results

Four diets, including glucogenic diet (G), lipogenic diet (L), two mixed diets: GL1 (G: L = 2 : 1) and GL2 (G:L = 1 : 2), served as substrates and were incubated with rumen fluid in vitro. The results revealed that the gas production, dry matter digestibility and propionate proportion were significantly increased by the G diet than others. The G diet increased the bacterial genera of Succinivibrionaceae_UCG_002, Succinivibrio, Selenomonas_1 and Ruminobacter but decreased some cellulolytic bacteria including the Eubacterium and several genera in family Ruminococcaceae than others.

Conclusions

When the glucogenic nutrient was above 1/3 of the dietary energy source among the four diets, the in vitro incubation had a higher feed digestibility and lower acetate to propionate ratio. Bacterial genera, including Selenomonas, Succinivibrio, Ruminobacter, certain genera in Ruminococcaceae, Christensenellaceae_R‐7_group and Eubacterium, were more sensitive to the glucogenic to lipogenic nutrients ratio.

Significance and Impact of the Study

The present study provides a new perspective about the effect of dietary glucogenic to lipogenic ingredient ratios on rumen metabolism by comparing end‐products, gas production and bacterial composition via an in vitro technique.

Non-Invasive Indicators Associated with Subacute Ruminal Acidosis in Dairy Cows

The aim of the study was to characterize the interrelationship between decreased ruminal fluid pH during subacute ruminal acidosis (SARA) and concentrations of principal constituents of milk and biochemical indices associated with nitrogen utilizations such as rumen ammonia nitrogen (RAN), blood urea nitrogen (BUN) and milk urea nitrogen (MUN). Ruminal fluid samples were obtained by rumenocentesis from 305 cows representing 13 dairy herds. The cows were divided according to ruminal fluid pH into three groups: low, moderate, and high rumen pH cows. The herds were divided into three groups on the basis of the percentages of cows with an assigned value of ruminal fluid pH: SARA-positive, SARA-risk and SARA-negative. SARA-positive herds were characterized by higher concentrations of RAN (12.6 vs. 6.9 mg/dL), BUN (16.2 vs. 10.1 mg/dL) and MUN (12.4 vs. 9.1 mg/dL) compared to SARA-negative herds. Similarly, low-rumen pH cows had greater concentrations of RAN, BUN and MUN than high-rumen pH cows (11.9 vs. 5.8 mg/ dL, 19.9 vs. 14.1 mg/dL, and 12.3 vs. 9.5 mg/dL, respectively). Moreover, SARA-positive herds and low-rumen pH cows had the highest lactose and the lowest fat concentrations in milk. The study demonstrated that the concentration of milk urea nitrogen could be considered one of the indirect and non-invasive indicators of the occurrence of subacute ruminal acidosis in dairy herds.

Estimation of between-Cow Variability in Nutrient Digestion of Lactating Dairy Cows Fed Corn-Based Diets

Simple Summary

Cow variability present in nutrient digestibility studies differs for different diets and nutrients. It is a major factor determining adequate sample size so that studies are not under-powered or over-powered. The objective of the current study was to develop cow variability estimates that can be used to determine the optimal sample size for digestibility trials having randomized block designs using mid-lactation dairy cows when fed corn-based diets having different neutral detergent fiber:starch ratio (0.7, 1.0, and 1.3). Cow variability is greater for digestibility of fiber and dry matter and less for starch. Estimated cow variability as standard deviations for digestibility of dry matter, neutral detergent fiber and starch were 3.8 g/kg, 5.1 g/kg and 3.3 g/kg, respectively. A major implication of this study is that cow variability is greatest for fiber digestibility and the use of a minimum of 12 cows per dietary treatment is adequate to reliably detect treatment effects on the digestibility of fiber, starch and dry matter using lactating dairy cows fed in groups with randomized block design under current experimental conditions.

Abstract

The objective of this study was to estimate cow variability that can be used to determine the optimal sample size for digestibility trials using lactating dairy cows. Experimental design was randomized complete block design having three blocks and three dietary treatments. Three similarly managed nearby intensive farms were considered as blocks, and three diets were formulated to have 0.7, 1.0, and 1.3 neutral detergent fiber (NDF): starch ratio. In each farm, 18 cows were assigned for each dietary treatment and five sample sizes per each treatment group were simulated by simple random sampling of data from 18, 15, 12, 9 and 6 cows respectively. Intake was not affected by diet or sample size (p > 0.05). Estimated cow variability (as standard deviation) for digestibility of dry matter, NDF and starch were 3.8 g/kg, 5.1 g/kg and 3.3 g/kg, respectively. A major implication of this study is that cow variability is greatest for NDF digestibility and the use of a minimum of 12 cows per dietary treatment is adequate to reliably detect treatment effects on the digestibility of NDF, starch and dry matter using cows fed in groups with randomized block design under these experimental conditions.

The effect of calcareous marine algae, with or without marine magnesium oxide, and sodium bicarbonate on rumen pH and milk production in mid-lactation dairy cows

Two experiments were carried out to evaluate different dietary buffers and their influence on (1) rumen pH in dairy cows and (2) milk production in dairy cows. The supplements included were calcareous marine algae (CMA; Lithothamnion calcareum), with or without marine magnesium oxide (MM; precipitated magnesia derived from seawater), and sodium bicarbonate (SB). Dietary treatments in experiment 1 consisted of the control [32.9% starch and sugar, and 19.9% neutral detergent fiber from forage per kg of dry matter (DM)] including no dietary buffer (CON); the control plus 0.45% DM CMA (CMA); the control plus 0.45% DM CMA and 0.11% DM MM (CMA+MM); the control plus 0.9% DM SB (SB). Diets were formulated to a dry matter intake (DMI) of 18 kg per cow/d. Dietary treatments in experiment 2 also consisted of CON (28.3% starch and sugar, and 23% neutral detergent fiber from forage per kg of DM), CMA, CMA+MM, and SB and were formulated to achieve identical intakes of experimental ingredients (80 g of CMA, 80 g of CMA plus 20 g MM, and 160 g of SB per cow/d) with a DMI of 22.6 kg per cow/d. Experiment 1 used 4 rumen-cannulated dairy cows in a 4 × 4 Latin square design. Rumen pH was measured over five 2-h periods, following feeding, using rumen pH probes. In experiment 2, 52 multiparous and 4 primiparous cows (62.7 ± 3.4 d in milk) were assigned to 4 experimental treatments for 80 d. Both CMA treatments maintained a greater mean rumen pH than the CON during 4 of the 5 periods following feeding and the CON had a greater number of hours below rumen pH 5.5 compared with all other treatments. Dry matter intakes tended to be higher on the SB compared with CON. The CMA treatment increased the production of milk fat and protein yield (kg/d) compared with all other treatments. Both CMA and CMA+MM increased milk fat yield compared with CON but were similar to each other and SB. Protein yield was highest in the CMA treatment compared with CON, CMA+MM, and SB. All 3 buffer treatments increased milk fat concentration compared with CON but did not differ from each other. The SB treatment reduced milk protein concentration and milk production efficiency, energy-corrected milk per kilogram of DMI. Results indicate that the addition of CMA can benefit milk fat and protein production when included in diets based on typical feedstuffs of the northern European region. The use of CMA when compared with SB, in such diets, can increase milk protein production and milk production efficiency.

Short communication: Effects of different selenium supplements on rumen fermentation and apparent nutrient and selenium digestibility of mid-lactation dairy cows

The aim of this study was to evaluate the dose-dependent effects of a hydroxy-analog of selenomethionine (HMSeBA) on rumen fermentation, apparent nutrient digestibility, and total selenium absorption in mid-lactation dairy cows, and to compare the effects with those of sodium selenite (SS). Fifty mid-lactation dairy cows with similar milk yields, days in milk, and parity were randomly assigned to 1 of 5 treatments according to a randomized complete block design. The cows were fed a basal diet containing 0.06 mg/kg dry matter (DM) of Se (control) or the same basal diet supplemented with SS, yielding 0.3 mg of Se/kg of DM (SS-0.3), or HMSeBA, yielding 0.1, 0.3, or 0.5 mg of Se/kg of DM (SO-0.1, SO-0.3, and SO-0.5, respectively), during the experimental period. The final content of Se in control, SS-0.3, SO-0.1, SO-0.3, and SO-0.5 was 0.06, 0.34, 0.15, 0.33, and 0.52 mg of Se/kg of DM. The experiment lasted for 10 wk, with a pretrial period of 2 wk. Supplementation with HMSeBA altered rumen fermentation by linearly increasing total volatile fatty acids and the molar proportions of propionate and butyrate but decreasing rumen pH, ammonia content, and the ratio of acetate to propionate. Compared with SS, HMSeBA enhanced the molar proportion of propionate in the rumen and the apparent digestibility of crude protein, neutral detergent fiber, acid detergent fiber, and selenium. We demonstrated that HMSeBA promoted rumen fermentation, apparent nutrient digestibility, and selenium absorption, implying that HMSeBA has a greater apparent absorption than SS.