Effects of level of intake and of available volatile fatty acids on the absorptive capacity of sheep rumen

Negative energy balance affects perinatal ewe performance, rumen morphology, rumen flora structure, and placental function

This study investigated the effects of negative energy balance (NEB) on perinatal ewes, with a focus on changes in growth performance, serum biochemical parameters, rumen fermentation, ruminal bacteria composition, placental phenotype-related indicators, and expression levels of genes related to placental function. Twenty ewes at 130 days of gestation were randomly allocated to either the positive energy balance (PEB) or NEB groups. In the experiment, ewes in the PEB group were fed the same amount as their intake during the pre-feeding baseline period, while ewes in the NEB group were restricted to 70% of their individual baseline feed intake. The experiment was conducted until 42 days postpartum, and five double-lamb ewes per group were selected for slaughter. The results demonstrated that NEB led to a significant decrease in body weight, carcass weight, and the birth and weaning weights of lambs (P < 0.05). Additionally, NEB caused alterations in serum biochemical parameters, such as increased non-esterified fatty acids and β-hydroxybutyrate levels and decreased cholesterol and albumin levels (P < 0.05). Rumen fermentation and epithelial parameters were also affected, with a reduction in the concentrations of acetic acid, butyric acid, total acid and a decrease in the length of the rumen papilla (P < 0.05). Moreover, NEB induced changes in the structure and composition of ruminal bacteria, with significant differences in α-diversity indices and rumen microbial community composition (P < 0.05). Gene expression in rumen papilla and ewe placenta was also affected, impacting genes associated with glucose and amino acid transport, proliferation, apoptosis, and angiogenesis (P < 0.05). These findings screened the key microbiota in the rumen of ewes following NEB and highlighted the critical genes associated with rumen function. Furthermore, this study revealed the impact of NEB on placental function in ewes, providing a foundation for investigating how nutrition in ewes influences reproductive performance. This research demonstrates how nutrition regulates reproductive performance by considering the combined perspectives of rumen microbiota and placental function.

A multi-species direct-fed microbial supplement alters the milk lipidome of dairy cows

The study evaluated the effects of supplementing a multi-species direct-fed microbial (DFM) on the milk lipidome of lactating dairy cows. Twenty-four multiparous Holstein cows (41 ± 7 d in milk) were used in a randomized complete block design with experimental duration of 91 d. Cows were blocked based on energy-corrected milk yield from a 14-d pretreatment period, and were assigned randomly within each block to the following treatments: (1) control (CON): corn silage-based total mixed ration without DFM; or (2) BOV+: basal diet top-dressed with a DFM containing a mixture of Lactobacillus animalis (LA-51), Propionibacterium freudenreichii (PF-24), Bacillus subtilis (CH201), and Bacillus licheniformis (CH200) at 11.8 × 109 cfu/d. Milk samples were taken from morning and evening milkings on 2 consecutive days of each week of the pretreatment and treatment periods. Separate composites of pretreatment period and treatment period samples were prepared for individual cows and used for lipidome analysis. Lipidome analysis of the milk samples was performed using an ultra-high-performance liquid chromatograph linked to a quadrupole time-of-flight mass spectrometer in both positive and negative ionizations. The relative concentrations of 14 lipid species, including long-chain polyunsaturated fatty acids (LC-PUFA) such as FA 20:8 and FA 28:7 and triacylglycerides (TG) such as TG 40:3 and TG 54:2, were increased [false discovery rate (FDR) ≤0.05], whereas 13 lipid species, including saturated FA 24:0 and TG 40:0 were decreased (FDR ≤0.05) by supplemental BOV+. The relative concentration of de novo FA in milk was greater, whereas that of preformed FA was lower in dairy cows supplemented with BOV+. Results from this study demonstrate the potential of a DFM containing L. animalis, P. freudenreichii, Bacillus subtilis, and B. licheniformis to alter the milk lipidome in lactating dairy cows toward increased relative concentration of LC-PUFA, which might offer a healthier profile of FA to consumers with its associated health benefits.

Feed restriction reduces short-chain fatty acid absorption across the reticulorumen of beef cattle independent of diet

The objective of this study was to evaluate the effects of the forage-to-concentrate ratio (F:C) of diets fed before and during short-term feed restriction (FR) on rumen fermentation, absorptive capacity of the reticulorumen, and apparent total tract digestibility. Twenty ovariectomized and ruminally cannulated Angus × Hereford heifers were blocked by BW and individually penned in box stalls (9 m(2)), having free access to water throughout the study. Heifers were randomly assigned to 1 of 2 dietary treatments, receiving either a high forage diet (HF; F:C of 92:8) or a moderate forage diet (MF; F:C of 60:40). Diets were fed ad libitum for 14 d before 5 d of baseline measurements (BASE) followed by 5 d of FR where heifers were restricted to 25% of ad libitum DMI relative to BASE. Dry matter intake was measured daily and ruminal pH was recorded every 2 min throughout the study. Ruminal fluid and blood samples were collected on d 3 of BASE and FR whereas short-chain fatty acid (SCFA) absorption was assessed in vivo using the isolated washed reticulorumen technique on d 5 of BASE and FR. Indigestible NDF was used as a marker to estimate apparent total tract digestibility. Diet × period interactions (P = 0.030 and 0.025) were detected for DMI and ruminal SCFA concentration, respectively. The interaction was the result of greater DMI and numerically greater SCFA concentration for MF than HF during BASE, with a reduction observed for both during FR, although treatment effects were no longer present. Period effects (BASE vs. FR) but not treatment effects (P > 0.05) were detected for mean ruminal pH (P < 0.001) and the total SCFA absorption rate (mmol/h; P = 0.038). During BASE, mean pH was reduced (6.4 vs. 6.9) and the SCFA absorption rate was greater relative to FR (674.5 vs. 554.8 mmol/h). Diet (P < 0.001) and period (P < 0.001) effects were detected for DM and OM digestibility with greater digestibility occurring for heifers fed MF than HF (70.5 vs. 63.3% for DM and 73.0 vs. 66% for OM) and greater digestibility during FR than BASE (69.5 vs. 64.3% for DM and 71.7 vs. 67.2% for OM). During FR, NDF digestibility was also greater than during BASE (P < 0.001; 62.4 vs. 55.8%). The effect of FR on serum NEFA differed by diet (diet × period, P < 0.001) with NEFA being greater for heifers fed HF than MF during FR (474.4 vs. 377.7 μEq/mL, respectively) with no differences observed between HF and MF during BASE. It can be concluded that severe short-term FR had a negative impact on ruminal SCFA absorption and energy balance and that altering the F:C of the diet does not mitigate these effects.

Recovery of absorptive function of the reticulo-rumen and total tract barrier function in beef cattle after short-term feed restriction

Our objective was to determine if the severity of short-term feed restriction (FR) affects the timeline for recovery of the absorptive function of the reticulo-rumen and barrier function of the total gastrointestinal tract in beef cattle. Eighteen ruminally cannulated and ovariectomized Angus × Hereford heifers were housed in individual pens. Heifers were blocked by initial BW into 3 blocks and, within block, randomly assigned to 1 of 3 treatments that differed in the severity of FR: heifers were restricted to 75, 50, or 25% of ad libitum intake. Treatments were imposed during a 5-d period of FR followed by 3 consecutive wk of recovery (REC1, REC2, and REC3). Throughout the experiment heifers were fed the same diet (60% forage:40% concentrate) for ad libitum intake (except during FR) and water was available at all times. Dry matter intake was measured daily and ruminal pH was recorded every 2 min during FR and recovery periods. Ruminal fluid and blood samples were collected on d 3 of the FR and d 5 of REC1 and REC3. Short-chain fatty acid (SCFA) absorption rates were evaluated on the last day of FR, REC1, and REC3 using the temporarily isolated and washed reticulo-rumen technique. On d 2 of FR and d 4 of REC1 and REC3, a 1 L solution of Cr-EDTA (180 mM) was dosed into the rumen followed by 48 h of total urine collection. Dry matter intake (% BW) increased rapidly in REC1 for heifers restricted to 75 and 50%; however, heifers restricted to 25% needed at least 2 wk to recover (treatment × period; P < 0.001). Regardless of the severity of FR, the duration that pH < 5.5 was the highest during REC1 (period P < 0.001). However, an interaction was found for the acidosis index, with pH × min/kg of DMI being greatest in heifers restricted to 25% on d 1 of the recovery period. A treatment × period interaction was found for the absolute absorption rate (mmol/h) of total SCFA (P = 0.009). The total SCFA absorption rate was not different for heifers restricted to 75 and 50% across periods, whereas an increase from FR and REC1 to REC3 was detected for heifers restricted to 25% of ad libitum intake. A treatment effect was observed for urinary Cr output (P = 0.027) indicating that heifers previously restricted to 25% of ad libitum intake had greater Cr excretion in urine during FR and recovery. This study indicates that severe FR negatively affects the time required for recovery of reticulo-rumen absorptive function and total tract barrier function. Another important finding is that regardless of severity, FR increases risk for ruminal acidosis when heifers have free access to feed after FR.

Effects of diet and osmotic pressure on Na+transport and tissue conductance of sheep isolated rumen epithelium

The intention of this study was to determine the effects of mucosal osmotic pressure on transport and barrier functions of the rumen epithelium of sheep, which were fed various diets: hay ad libitum, or 600, 1200 or 1800 g day(-1) of a supplemented diet plus hay ad libitum. The experiments were conducted by using the conventional Ussing chamber technique. Mucosal osmolarity was adjusted to 300 (control), 375 or 450 mosmol l(-1). Feeding of a supplemented diet led to a significant increase of mucosal to serosal Na+ transport and net Na+ transport, probably because of an increase of apical Na+-H+ exchange activity. An increase in mucosal osmotic pressure: (a) reduced net Na+ transport in all feeding groups, the remaining net Na+ transport being higher in tissues of sheep fed a supplemented diet; (b) increased transepithelial tissue conductance, this rise being smallest with a high intake of the supplemented diet; and (c) enhanced the serosal to mucosal Na+ transport in tissues of hay-fed sheep and sheep fed with 600 g day(-1) of the supplemented diet, while higher intakes of the supplemented diet (1200 and 1800 g) did not produce any effect. All these changes indicate a diet-dependent adaptation to luminal hypertonicity.

Sodium Transport Across the Isolated Epithelium of Sheep Omasum is Influenced by Luminal Ammonia

Ammonia is a physiological fermentation product in the forestomachs and is absorbed from the rumen and omasum. Cellular uptake of ammonia affects the intracellular pH of polar and non-polar cells. The effect of the uptake on the pH of the cytosol depends on the predominant form of ammonia. NH(3) uptake and its intracellular protonation tend to alkalinize the cytoplasm, whereas the uptake of NH(4)(+) acidifies the cytoplasm by reversing this reaction. Consequently, the absorption of ammonia across the omasal epithelium could cause a change of the intracellular pH and pH-dependent transport mechanisms like Na/H exchange. Because no information is available about the form of ammonia absorbed in the omasum and, hence, possible modulation of Na transport by ammonia, the effect of increasing luminal ammonia concentrations (0, 5, 15 and 30 mmol/l) on Na transport were studied. In epithelia of hay-fed animals, ammonia linearly inhibited Na transport in a dose-dependent manner, at a luminal pH of 7.40, but not at a pH of 6.40. Ammonia did not influence Na transport in epithelia of concentrate-fed animals. Because luminal ammonia did not consistently change the short circuit current or tissue conductance absorption of ammonia as NH(4)(+) appears to be unlikely. The predominant form of ammonia absorbed in the omasum is probably NH(3), which is protonated in the cytosol. The reduced availability of protons may be the cause of inhibition of Na transport via Na/H exchange.

Effects of volatile fatty acid supply on their absorption and on water kinetics in the rumen of sheep sustained by intragastric infusions1

Three sheep fitted with a ruminal cannula and an abomasal catheter were used to study water kinetics and absorption of VFA infused continuously into the rumen. The effects of changing VFA concentrations in the rumen by shifting VFA infusion rates were investigated in an experiment with a 3 x 3 Latin square design. On experimental days, the animals received the basal infusion rate of VFA (271 mmol/h) during the first 2 h. Each animal then received VFA at a different rate (135, 394, or 511 mmol/h) for the next 7.5 h. Using soluble markers (polyethylene glycol and Cr-EDTA), ruminal volume, liquid outflow, apparent water absorption, and VFA absorption rates were estimated. There were no significant effects of VFA infusion rate on ruminal volume and water kinetics. As the VFA infusion rate was increased, VFA concentration and osmolality in the rumen were increased and pH was decreased. There was a biphasic response of liquid outflow to changes in the total VFA concentration in the rumen, as both variables increased together up to a total VFA concentration of 80.1 mM, whereas, beyond that concentration, liquid outflow remained stable at an average rate of 407 mL/h. There were significant linear (P = 0.003) and quadratic (P = 0.001) effects of VFA infusion rate on the VFA absorption rate, confirming that VFA absorption in the rumen is mainly a concentration-dependent process. The proportion of total VFA supplied that was absorbed in the rumen was 0.845 (0.822, 0.877, and 0.910 for acetate, propionate, and butyrate, respectively). The molar proportions of acetate, propionate, and butyrate absorbed were affected by the level of VFA infusion in the rumen, indicating that this level affected to a different extent the absorption of the different acids.

Effect of short-term underfeeding on weight of splanchnic organs in ewes

We assessed the effect of short-term underfeeding on weight and protein mass of splanchnic tissues in adult ewes submitted to a factorial experimental design. In a pre-experimental period, 18 ewes divided into 2 groups of 9 were fed a second cut of natural grassland hay during 4 weeks at 112 or 38% of their energy maintenance requirements. Three ewes of each group were then fed the same hay during 4 weeks at either low (group L), moderate (group M) or high intake (group H), corresponding to 38, 75 or 112% of their energy maintenance requirements, respectively, then slaughtered. Fresh weight and protein mass of splanchnic organs were measured. No carry-over effect of the pre-experimental level of intake on weight and protein mass was observed for any splanchnic organs. Splanchnic tissues contributed at 10.7 and 8.6% to the decrease in live weight for groups M and L, respectively. The decrease in weight of splanchnic tissues (-15%) was mainly attributed to reticulorumen (-23%), liver (-21%), and at a lesser extent small intestine (-11%). No large change in the mass ratio between mucosa and muscular-serosa in both dorsal and ventral sacs occurred in the rumen wall. These results are discussed together with previous published results on long-term underfed ewes, and suggest that the decrease in energy expenditure in whole animal induced by underfeeding is mainly related to the decrease in splanchnic weight at short-term, and to the decrease in other tissues at long-term, splanchnic weight being stabilized.

Mechanisms of Mg(2+) transport in cultured ruminal epithelial cells

Net Mg(2+) absorption from the rumen is mainly mediated by a transcellular pathway, with the greater part (62%) being electrically silent. To investigate this component of Mg(2+) transport, experiments were performed with isolated ruminal epithelial cells (REC). Using the fluorescent indicators mag-fura 2, sodium-binding benzofuran isophthalate, and 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, we measured the intracellular free Mg(2+) concentration ([Mg(2+)](i)), the intracellular Na(+) concentration ([Na(+)](i)), and the intracellular pH (pH(i)) of REC under basal conditions, after stimulation with butyrate and HCO(-)(3), and after changing the transmembrane chemical gradients for Mg(2+), H(+), and Na(+). REC had a mean resting pH(i) of 6.83 +/- 0.1, [Mg(2+)](i) was 0.56 +/- 0. 14 mM, and [Na(+)](i) was 18.95 +/- 3.9 mM. Exposure to both HCO(-)(3) and HCO(-)(3)/butyrate led to a stimulation of Mg(2+) influx that amounted to 27.7 +/- 5 and 29 +/- 10.6 microM/min, respectively, compared with 15 +/- 1 microM/min in control solution. The increase of [Mg(2+)](i) was dependent on extracellular Mg(2+) concentration ([Mg(2+)](e)). Regulation of pH(i) has been demonstrated to be Na(+) dependent and is performed, for the most part, by a Na(+)/H(+) exchanger. The recovery of pH(i) was fully blocked in nominally Na(+)-free media, even if [Mg(2+)](e) was stepwise increased from 0 to 7.5 mM. However, an increase of [Mg(2+)](i) was observed after reversing the transmembrane Na(+) gradient. This rise in [Mg(2+)](i) was pH independent, K(+) insensitive, dependent on [Mg(2+)](e), imipramine and quinidine sensitive, and accompanied by a decrease of [Na(+)](i). The results are consistent with the existence of a Na(+)/Mg(2+) exchanger in the cell membrane of REC. The coupling between butyrate, CO(2)/HCO(-)(3), and Mg(2+) transport may be mediated by another mechanism, perhaps by cotransport of Mg(2+) and HCO(-)(3).