Methodological aspects of the microscopy of bovine liver biopsies

Liver transcriptomic networks reveal main biological processes associated with feed efficiency in beef cattle

BACKGROUND

The selection of beef cattle for feed efficiency (FE) traits is very important not only for productive and economic efficiency but also for reduced environmental impact of livestock. Considering that FE is multifactorial and expensive to measure, the aim of this study was to identify biological functions and regulatory genes associated with this phenotype.

RESULTS

Eight genes were differentially expressed between high and low feed efficient animals (HFE and LFE, respectively). Co-expression analyses identified 34 gene modules of which 4 were strongly associated with FE traits. They were mainly enriched for inflammatory response or inflammation-related terms. We also identified 463 differentially co-expressed genes which were functionally enriched for immune response and lipid metabolism. A total of 8 key regulators of gene expression profiles affecting FE were found. The LFE animals had higher feed intake and increased subcutaneous and visceral fat deposition. In addition, LFE animals showed higher levels of serum cholesterol and liver injury biomarker GGT. Histopathology of the liver showed higher percentage of periportal inflammation with mononuclear infiltrate.

CONCLUSION

Liver transcriptomic network analysis coupled with other results demonstrated that LFE animals present altered lipid metabolism and increased hepatic periportal lesions associated with an inflammatory response composed mainly by mononuclear cells. We are now focusing to identify the causes of increased liver lesions in LFE animals.

Expression and activity of key hepatic gluconeogenesis enzymes in response to increasing intravenous infusions of glucose in dairy cows

The present study aimed at investigating whether increasing concentrations of glucose supply have a depressive effect on the mRNA abundance and activity of key gluconeogenic enzymes in dairy cows. Twelve Holstein-Friesian dairy cows in mid-lactation were intravenously infused with saline (SI; n = 6) or a 40% glucose solution (GI; n = 6). For GI cows, the infusion dose increased by 1.25%/d relative to the initial NE(l) requirement until a maximum dose equating to surplus 30% NE(l) was reached on d 24. Cows receiving SI received an equivalent volume of 0.9% saline solution. Blood samples were taken every 2 d, and liver biopsies were collected every 8 d. A treatment x quadratic dose interaction (P < 0.01) was observed for the concentration of plasma glucose and serum insulin. The interactions were due to positive quadratic responses of the concentrations of glucose and insulin for GI cows, whereas the concentrations of glucose and insulin did not change over time for SI cows. The concentration of beta-hydroxybutyric acid (BHBA) and serum urea nitrogen (BUN) responded in a treatment x quadratic dose manner, such that greater decreases (P < 0.01) in BHBA and BUN concentrations were observed for cows receiving GI than SI as the dosage increased. Serum NEFA concentration tended to follow a similar pattern as serum BHBA and BUN; however, the interaction was not significant (P = 0.07). The mRNA abundance of gluconeogenesis enzymes followed a linear treatment x dose interaction (P < 0.05) for only pyruvate carboxylase (PC), which was paralleled by a trend for a linear treatment x dose interaction (P = 0.13) for PC enzyme activity. The least PC expression and activity were observed at the largest glucose dosage. The activity, but not mRNA abundance, of fructose 1,6-bisphosphatase (FBPase) showed treatment x quadratic dose interactions (P < 0.05) with decreasing activity at increasing glucose dose. Activities and expression of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase were not affected (P > 0.25) by treatment. In conclusion, hepatic gluconeogenic enzymes are only moderately affected by slowly increasing glucose supply, including a translational or posttranslational downregulation of FBPase activity and a decrease in the mRNA abundance of PC with possible consequences for PC enzyme activity.

Fat infiltration in liver and activity of lecithin:cholesterol acyltransferase in serum of dry and lactating dairy cows

To study the relationship between fat infiltration in the liver and the decrease in the activity of serum lecithin:cholesterol acyltransferase (LCAT), blood and liver samples were taken from 14 multiparous (MP) and 16 primiparous (PP) dairy cows four weeks and one week before, and one, four and eight weeks after calving. During the dry period, half the animals received a protein supplement. LCAT activity decreased significantly in all groups before parturition, but returned to the initial level within 1-4 weeks after parturition. There were no differences between the feeding groups, but after calving, the LCAT activity in the MP cows was significantly lower than in the PP cows. Fat infiltration was not detected in the PP cows, and in the MP cows fat infiltration was mild and fell within the physiological range. There was no correlation between liver fat content and the activity of LCAT in serum. These results suggest that shortly before and after parturition, the activity of LCAT in serum is limited by post-transcriptional regulation, possibly by the availability of amino acid for export protein synthesis in the liver.

Production of monoclonal antibodies and enzyme immunoassay to bovine retinol-binding protein and determination of retinol-binding protein serum levels and retinol concentrations in serum and liver in dairy cows before and after parturition

To study vitamin A transport in dairy cows and heifers around parturition, an enzyme immunoassay for bovine retinol binding protein (RBP) was developed and serum levels determined. Serum and liver concentrations of retinol were assayed by HPLC. Four weeks before expected calving the cows and heifers were divided into two groups each, and half of the animals received a protein supplementation during the dry period. The mean serum RBP concentration 4 weeks before calving was 42 mg l-1 for the cows and 44 mg l-1 for the heifers. The serum retinol concentrations were 0.53 mg l-1 for the cows and 0.42 mg l-1 for the heifers, and the liver retinol concentrations 0.30 mg l-1 and 0.13 mg g-1, respectively. In the groups without protein supplementation there was a significant decrease in serum RBP at sampling 1 week before parturition compared to initial values. The measurement of serum RBP may prove useful in assessment of amino acid availability in dairy cows.

Ultrastructure of the liver of reindeer calves under different nutritional conditions

A total of 12 reindeer calves were divided into two groups and the volume densities of liver cytoplasmic structures were counted using TEM. The six animals in group 1 were allowed to graze freely while those in group 2 were kept in pens and fed with lichens. All of them had a negative energy balance and lost weight from November to April, group 1 by 14.9% and group 2 by 24.8%. In spite of the weight losses, no significant changes in volume densities occurred during the winter. Glycogen remained fairly steady and there was no fatty infiltration into the hepatocytes. The very low incidence of Golgi apparatus in the hepatocytes may have been due to the inhibition of protein and lipid synthesis during the winter. These results point to substantial adaptation to extreme environmental conditions. The animals in group 1 apparently moved about more, which may have caused a greater breakdown of glycogen, resulting in turn in a lower volume density of glycogen in January and March.

Liver histology of reindeer calves during the winter season

Seventeen reindeer calves were divided into three groups and liver biopsies were taken during the winter. Group 1 consisted of 6 animals allowed to graze freely under natural conditions, those in groups 2 (n = 5) and 3 (n = 6) were kept in pens and fed with lichens, the diet being designed to achieve a slight (group 2) or moderate (group 3) weight loss. Weight losses from November to April averaged 14.9%, 13.2% and 24.8% in the three groups respectively. The relative volumes of the different structures in the liver were determined by light microscopic morphometry. The mean size of the hepatocytes was slightly greater in March than in January in groups 1 and 2, and slightly smaller in group 3 (no statistical differences) and then decreased markedly. These changes could also be seen in the sinusoidal lumina. The decrease in the size of the hepatocytes may reflect a shortage of amino acids in the cells or it may be hormone-mediated. Unlike the situation in cows, there was no fatty accumulation in the hepatocytes. This may be a species adaptation to an annual period of starvation.

Ultrastructural changes of the liver in spontaneously ketotic cows

The ultrastructure of the liver in normal, mildly ketotic and severely ketotic cows was studied using stereological methods. In the liver of severely ketotic cows there is: (1) a significant increase in the volume fraction of hepatocytes and a decrease in the volume fraction of sinusoids, and (2) an increase in the volume fraction of lipid and smooth endoplasmic reticulum and a decrease in the volume fraction of glycogen and Golgi in parenchyma. A decrease in the profile density of mitochondria per 1 mm2 field and an increase of the volume occupied by mitochondria were not significant nor was the decrease in the volume density of rough endoplasmic reticulum. The degree and duration of negative energy balance obviously affect the morphological changes of the fatty liver. However, additional work is needed to determine the significance of ultrastructural changes in liver function.

Fatty infiltration of liver in spontaneously ketotic dairy cows

The purpose of this study was to ascertain 1) fatty infiltration of the liver in spontaneously ketotic cows and 2) the most appropriate blood components to aid diagnosis of ketotic fatty liver. Liver biopsies and blood samples were obtained under field conditions. Cows were divided into three groups (healthy, mildly ketotic, and severely ketotic) by their blood ketone body concentrations. Severely ketotic cows had a greater percent fat in the liver than healthy cows. The mildly ketotic group fell between the other two groups and was significantly different from only the severely ketotic group. There was a positive correlation between fatty infiltration and blood ketone body concentrations but a negative correlation with glucose concentrations. Liver-specific enzymes were positively correlated with fatty infiltration. Only ornithine carbamoyltransferase and iditol (sorbitol) dehydrogenase could be used to separate healthy cows from those with severe ketosis. The best equation to explain the variation of percent fat in liver included concentration of beta-hydroxybutyrate (BHB) and logarithm of ornithine carbamoyltransferase concentration (Log-OCT): % Fat = -6.15 + 2.39 (BHB) + 11.7 (LogOCT) Although this equation explained 39.5% of the variation, it could not be used to predict reliably percent fat in the liver. Liver biopsy seems still to be the only reliable method of measuring of fatty infiltration in the liver.