Effects of replacing magnesium oxide with calcium-magnesium carbonate with or without sodium bicarbonate on ruminal fermentation and nutrient flow in vitro.

The objective of this study was to evaluate the effects of replacing magnesium oxide (MgO) with calcium-magnesium carbonate [CaMg(CO3)2] on ruminal fermentation with or without the addition of sodium bicarbonate (NaHCO3). Eight fermentors of a dual-flow continuous-culture system were distributed in a replicated (2) 4 × 4 Latin square design in a 2 × 2 factorial arrangement of treatments (magnesium sources × NaHCO3). The treatments tested were 0.21% MgO [MgO; dry matter (DM) basis; 144.8 mEq of dietary cation-anion difference (DCAD)]; 0.21% MgO + 0.50% NaHCO3 (MgO+NaHCO3; DM basis; 205.6 mEq of DCAD); 1.00% CaMg(CO3)2 [CaMg(CO3)2; DM basis; 144.8 mEq of DCAD]; and 1.00% CaMg(CO3)2 + 0.50% NaHCO3 [CaMg(CO3)2+NaHCO3; DM basis; 205.6 mEq of DCAD]. Diets were formulated to have a total of 0.28% of Mg (DM basis). The experiment consisted of 40 d, which was divided into 4 periods of 10 d each, where 7 d were used for adaptation and 3 d for sampling to determine pH, volatile fatty acids (VFA), ammonia (NH3-N), lactate, mineral solubility, N metabolism, and nutrient digestibility. The effects of Mg source [MgO vs. CaMg(CO3)2], NaHCO3 (with vs. without), and the interaction were tested with the MIXED procedure of SAS version 9.4 (SAS Institute). There was no Mg source × NaHCO3 interaction in the pH variables and mineral solubility, and Mg sources evaluated did not affect the variables related to ruminal pH and solubility of Mg. On the other hand, the inclusion of NaHCO3 increased the pH daily average, independent of Mg source, which led to a reduced time that pH was below 5.8 and decreased area under the curve. Total VFA and lactate concentration were similar among treatments regardless of NaHCO3 and Mg source; however, the molar proportion of isobutyrate and NH3-N concentration were lower in diets with CaMg(CO3)2 compared with MgO. Moreover, NaHCO3 inclusion increased NH3-N, total daily NH3-N flow, isobutyrate concentration, and acid detergent fiber digestibility. Our results showed that CaMg(CO3)2 leads to a lower NH3-N concentration and isobutyrate proportion. Therefore, because most of the tested variables were not significantly different between MgO and CaMg(CO3)2 when combined or not with NaHCO3, CaMg(CO3)2 can be a viable alternative source to replace MgO in dairy cow diets without affecting mineral solubility, ruminal pH, nutrient digestibility, total VFA, and the main ruminal VFA. Although Mg sources are known to have an alkalizing effect, NaHCO3 inclusion in diets with Mg supplementation allowed an increase in ruminal pH, as well as an increase in isobutyrate and NH3-N flow.

Proximal tibial osteophyte volumes are correlated spatially and with knee alignment: a quantitative analysis suggesting the influence of biochemical and mechanical factors in the development of osteophytes.

OBJECTIVE: To characterize the differences and correlations in osteophyte volumes between and within proximal tibial compartments, and to assess the correlations between osteophyte volumes and the femorotibial angle. DESIGN: CT scans of 73 knees with predominantly medial femorotibial osteoarthritis (21 K/L2, 28 K/L3, 24 K/L4) were retrospectively analyzed using a new, reproducible method measuring total and subregional osteophyte volumes in the medial and lateral compartments. Non-parametric statistics was used for comparison and correlation analyses. RESULTS: Total osteophyte volumes were larger in the medial than in the lateral compartment for all severity groups (p < 0.05). Additionally, statistically significant differences were observed among subregions of the lateral compartment in K/L3 and K/L4 knees. Statistically significant positive correlations were found between the medial and lateral total osteophyte volumes in K/L3 and K/L4 knees (ρ ≥ 0.44, p = 0.03), and among most subregional osteophyte volumes within each compartment in K/L3 knees. Markedly fewer statistically significant correlations were present in K/L2 and K/L4 knees. In K/L3 knees, the femorotibial angle was statistically significantly positively correlated with the total osteophyte volume in the medial compartment (ρ = 0.50, p = 0.01), with osteophyte volumes in most medial subregions, and with the osteophyte volume in the lateral posterior subregion (ρ = 0.40, p = 0.05). CONCLUSIONS: Quantitative assessment of osteophytes may bring insight on factors influencing their development. Positive correlations of osteophyte volumes found between and within compartments suggest the influence of biochemical mediators acting on the entire joint, while positive correlations between the femorotibial angle and osteophyte volumes suggest a role of mechanical factors. These hypotheses are to be further confirmed.

Effect of dietary fatty acid supplements, varying in fatty acid composition, on milk fat secretion in dairy cattle fed diets supplemented to less than 3% total fatty acids.

Dietary fatty acids can affect both milk fat yield and fatty acid (FA) composition. This relationship is well established when the dietary level of FA exceeds 3% of diet dry matter (DM). We could find no reports directly examining the effects of dietary FA profile on milk fat at levels below 3%. Twenty-four primiparous and 36 multiparous lactating cows were paired by production (1 high with 1 low, within parity) to form 30 experimental units. Pairs were fed 6 diets in five 6×6 balanced Latin squares with 21-d periods, and data were collected during the last 5d of each period. Two control diets were fed: a corn control diet (CC; 29% corn silage, 16% alfalfa silage, 19% corn grain, and 8% distillers grain on a DM basis) containing 1.8% FA; and a low-oil control diet (LOC; 9% corn silage, 35% alfalfa silage, 20% food-grade corn starch, and 8% corn gluten feed on a DM basis) containing 1.2% FA. A portion of the food-grade corn starch in LOC was replaced with 4 different FA supplements to create the 4 treatment diets. Treatments were 1.7% (DM basis) of a 50:50 blend of corn oil and high-linoleic safflower oil (LO), 1.7% high-oleic sunflower oil (OO), 1.7% palm oil (PO), or 1.8% calcium salts of palm fatty acids (PFA). The resultant diets were thus enriched in linoleic (LO), oleic (OO), or palmitic acid (PO and PFA). Dietary treatments did not affect dry matter intake. Addition of any of the fat sources to LOC resulted in increased milk yield, but milk fat yields and milk FA composition were variable for the different treatments. The LO treatment resulted in lower milk fat yield, fat concentration, and C16:0 yield but increased both trans-10 C18:1 and trans-10,cis-12 C18:2 yields compared with the other added FA treatments. Diets PO and PFA resulted in increased milk C16:0 yield and decreased total milk C18 yield compared with OO. Regression analysis revealed a negative coefficient for dietary linoleic acid content over basal (LOC) for both milk short-chain FA yield and C16:0 yield. Dietary linoleic acid content also had a positive coefficient for milk trans-10 C18:1 and trans-10,cis-12 conjugated linoleic acid yield. These results demonstrate that even when total dietary FA are below 3%, free oils rich in linoleic acid can reduce milk fat yield by reducing secretion of milk FA with fewer than 18 carbons. Fatty acid composition of fat supplements is important even at this low level of total dietary fat.

Experimental cataracts in rats due to tryptophan-free diet.

A tryptophan-free diet induces posterior subcapsular cataracts and reversible corneal opacities in young Wistar rats. Compared to the controls there is a significant decrease of body weight, lens fresh weight, and water-soluble lens protein. Protein separation by isoelectric focusing shows diminished alpha-, beta-, and gamma-crystallin fractions. If tryptophan is restored to the diet after 24 days, new clear lens fibers are laid down again, indicating that the mechanism of protein synthesis has not been permanently damaged by tryptophan-deficiency.

Genes regulating glutathione concentrations in X-ray-transformed rat embryo fibroblasts: changes in gamma-glutamylcysteine synthetase and gamma-glutamyltranspeptidase expression.

The concentration of glutathione (GSH) and the expressions of gamma-glutamylcysteine synthetase and gamma-glutamyltranspeptidase (GGT) were assessed in rat embryo fibroblasts (REF) displaying various stages of X-ray-induced transformation. A secondary culture of REF cells was irradiated, and a normal-immortalized cell line (X-REF-23) was isolated. Chronic exposure of X-REF-23 cells to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) yielded cells (X-REF-23-TP) capable of benign tumor formation in nude mice. These cells exhibited GSH concentrations and gamma-glutamylcysteine synthetase heavy subunit mRNA levels that were approximately 50% less than those measured in X-REF-23 cells. Neither X-REF-23 nor X-REF-23-TP cells exhibited detectable GGT mRNA or activity. Administration of 3 Gy of X-rays followed by chronic TPA treatment yielded cells (X-REF-23-TPX) capable of malignant tumor formation in nude mice. These cells expressed GGT mRNA and Concanavalin-A minus GGT activity. One TPX clone (X-REF-23-TPX.1) was chosen for further characterization. Northern blotting of X-REF-23-TPX.1 cells indicated that gamma-glutamylcysteine synthetase heavy subunit mRNA levels were similar to those of X-REF-TP cells. X-REF-23-TPX.1 cells contained nearly the same amount of GSH as X-REF-23 cells. However, the ability of diethylmaleate (DEM) to deplete GSH was diminished in X-REF-23-TPX.1 cells compared with X-REF-23 cells. Furthermore, exposure of X-REF-23-TPX.1 cells to DEM stimulated GSH resynthesis such that the GSH concentration exceeded control values during exposure. The resynthesis of GSH during a DEM exposure was found to be dependent upon the expression of GGT, as demonstrated by inhibition with AT-125. These experiments indicate that ionizing radiation can lead to elevated constitutive expression of GGT in transformed REF cells and that expression of GGT activity was responsible for the increased rate of GSH repletion observed in X-REF-23-TPX.1 cells.