Dietary Glycerol Research Articles

Glycerol supplementation in farmed fish species: A review from zootechnical performance to metabolic utilisation

AbstractGlycerol, an abundant by‐product of biodiesel production, has gained attention due to its price and availability for potential commercial applications, and thus utilisation as an animal feed ingredient. This article comprehensively reviews glycerol utilisation in fish and its potential as a dietary ingredient for aquaculture. While dietary inclusion of glycerol may offer cost‐effective energy and metabolic intermediates, studies report inconsistent results regarding its effects on nutrient digestibility, zootechnical performance, and product quality. Recent studies however have demonstrated that dietary glycerol supplementation in fish induces metabolic shifts, such as alterations to gluconeogenesis and/or lipogenesis, modifying energy utilisation. Additionally, glycerol has been proposed to reduce protein catabolism, minimising nitrogen excretion and its environmental impact, but its influence on protein retention remains uncertain. Nevertheless, it is important to carefully consider the balance between feed palatability and these potential metabolic alterations when incorporating glycerol in aquafeeds. This review highlights the need for more studies to expand our understanding of glycerol metabolism in fish, since it does not seem to be metabolised by carnivorous species as much as omnivorous. Future research should explore the effects of glycerol supplementation on fish with different feeding habits and in developmental stages, as well as diverse environmental salinities and temperatures. Insight into the impact of impurities and the optimisation of glycerol inclusion in aquafeeds are recommended to support sustainable aquaculture practices and the utilisation of glycerol as a valuable resource.

Effects of dietary glycerol monolaurate on growth and digestive performance, lipid metabolism, immune defense and gut microbiota of shrimp (Penaeus vannamei)

The advancement of the Penaeus vannamei industry in a sustainable manner necessitates the creation of eco-friendly and exceptionally effective feed additives. To achieve this, 720 similarly-sized juvenile shrimp (0.88 ± 0.02 g) were randomly divided into four groups in this study, with each group consisting of three replicates, each tank (400 L) containing 60 shrimp. Four experimental diets were formulated by adding 0, 500, 1000, and 1500 mg kg−1 glycerol monolaurate (GML) to the basal diet, and the feeding trial lasted for 42 days. Subsequently, a 72-h White Spot Syndrome Virus (WSSV) challenge test was conducted. Polynomial orthogonal contrasts analysis revealed that with the increase in the concentration of GML, those indicators related to growth, metabolism and immunity, exhibit linear or quadratic correlations (P < 0.05). The results indicate that the GML groups exhibited a significant improvement in the shrimp weight gain rate, specific growth rate, and a reduction in the feed conversion ratio (P < 0.05). Furthermore, the GML groups promoted the lipase activity and reduced lipid content of the shrimp, augmented the expression of triglyceride and fatty acid decomposition-related genes and lowered the levels of plasma triglycerides (P < 0.05). GML can also enhanced the humoral immunity of the shrimp by activating the Toll-like receptor and Immune deficiency immune pathways, improved the phagocytic capacity and antibacterial ability of shrimp hemocytes. The challenge test revealed that GML significantly reduced the mortality of the shrimp compared to control group. The 16S rRNA sequencing indicates that the GML group can increases the abundance of beneficial bacteria. However, 1500 mg kg−1 GML adversely affected the stability of the intestinal microbiota, significantly upregulating intestinal antimicrobial peptide-related genes and tumor necrosis factor-alpha levels (P < 0.05). In summary, 1000 mg kg−1 GML was proven to enhance the growth performance, lipid absorption and metabolism, humoral immune response, and gut microbiota condition of P. vannamei, with no negative physiological effects.

Effect of Dietary Glycerol Addition on Growth Performance, Serum Biochemical Indexes, Carcass Traits, Fat Deposition, and Meat Quality in Fattening Period Kazakh Sheep

Effect of Dietary Glycerol Addition on Growth Performance, Serum Biochemical Indexes, Carcass Traits, Fat Deposition, and Meat Quality in Fattening Period Kazakh Sheep

EFFECT OF GLYCEROL ON MILK YIELD, ITS QUALITY AND BLOOD PARAMETERS OF HOLSTEIN COWS

The aim of this study was to investigate the effect of adding glycerol at different levels (T1 = control treatment without glycerol, T2 = 75 ml and T3 = 150 ml glycerol) on daily milk yield, milk components and some blood parameters of Holstein cows during the period of 60 days. Milk yield increased significantly (P≤0.05) at 15th day of the experiment, and highly significant (P≤0.01) at 30th and 60th days of the experiment in T3 group. Percentage of milk protein and lactose increased (P≤0.01) in T2 and T3 groups and the percentage of milk fat in the T3 group decreased at day 60 of the experiment. The blood glucose concentration increased (P≤0.01) in T2 and T3 groups at 30 and 60 days of the experiment. Triglyceride concentration increased (P≤0.01) in the blood of T2 and T3 treated cows at day 60. The concentration of cholesterol, NEFA and BHBA decreased (P≤0.01) in T3 treated cows at day 60 of the experiment. The concentration of phosphorous and magnesium were also affected as a result of glycerol treatment. It can be concluded that the addition of dietary glycerol 150 ml / day enhanced milk yield, protein and lactose percentage, and improved blood parameters by increasing blood glucose and reducing NEFA and BHBA concentrations of Holstein cows.

Growth performance and quality indicators of European seabass (Dicentrarchus labrax) fed diets including refined glycerol

Glycerol is a by-product of the biodiesel industry with growing availability and applicability in animal feeds. However, its use as a source of energy in aquafeeds has only been investigated in a small number of fish species. The effects of dietary refined glycerol inclusion rate on growth performance, nitrogen and energy balances, and fish quality were investigated in juvenile European seabass. Twelve fish were assigned to each of the nine tanks and used to test the experimental diets in triplicate. The diets comprised 0, 25, or 50 g kg−1 of refined glycerol (G0, G25, and G50, respectively), being not isoenergetic, although having similar digestible protein-to-energy ratios (22 mg kJ−1). Fish were fed twice a day to apparent satiation for 90 days. The G25 group displayed a higher absolute feed intake and a higher weight gain than the G0 or G50 groups, although feed efficiency and the use of protein as an energy source were similar between the three groups. Seabass fed the G25 diet also displayed a higher specific growth rate than fish fed the G50 diet. Higher hepato-somatic and visceral lipid-somatic indices of seabass were observed with increased levels of dietary glycerol, although proximal body composition remained similar across groups. The apparent digestibility coefficients for dry matter, crude protein, and energy increased with increasing dietary glycerol inclusion rate, whereas the apparent lipid digestibility coefficient was highest for the G25 group. No differences in the energy retained as protein, nitrogen efficiency, and total ammonia excretion rate were detected between seabass fed the different diets. At the end of the growth trial, physical and microbiological quality parameters of the skin and gill surfaces were assessed after 1 and 10 days of storage on ice. Fish quality decreased with storage time but was not affected by the dietary glycerol inclusion rate. In summary, the inclusion of refined glycerol in seabass diets may have economic benefits for feed manufacture and a positive effect on growth performance but does not change the efficiency of protein utilization in this carnivorous species.

Effects of dietary glycerol supplementation on meat quality, palatability, and lipid metabolism gene expression in the longissimus thoracis of Hanwoo steers

This study tested the hypothesis that dietary glycerol supplementation (GS) would affect growth of Hanwoo steers, beef marbling and palatability, and gene expression for lipid uptake and transport and lipogenesis in the longissimus thoracis (LT). Diets with or without 45.2 g daily glycerol supplementation/kg dry matter concentrate were tested in fourteen Hanwoo steers during a 16-week feeding trial. GS did not affect (P ≥ 0.40) the average daily gain or the gain-to-feed ratio. GS increased the LT marbling score (P = 0.01). GS enhanced (P ≤ 0.01) the sensory traits, including the flavor and overall acceptance of the LT. GS tended (0.05 < P ≤ 0.10) to upregulate mRNA levels of fatty acid translocase, lipoprotein lipase, and fatty acid binding protein 4 genes in the LT. These tendencies of upregulated expression of fatty acid uptake and cytosolic transport genes may, in part, contribute to the increased marbling by GS. The increased marbling degree caused by GS may improve palatability including the flavor and overall acceptance of the LT.

Dietary glycerol monolaurate protects Cherax quadricarinatus against white spot syndrome virus infection

Glycerol monolaurate (GML), one of the medium-chain fatty acid esters, is often used as an emulsifier or preservative. Its biological functions include antibacterial and antiviral activities. In this study, we examined the effects of dietary GML on the resistance of the red claw crayfish to WSSV infection. Crayfish fed with 4 g/kg GML showed higher survival rate and lower WSSV copy numbers than the control after WSSV infection. A RT–qPCR analysis showed that GML supplementation enhanced the expression of immune-related genes, especially JAK and caspase. Our data indicate that GML affects the immune parameters of crayfish, including the total hemocyte counts and phenoloxidase, acid phosphatase, superoxide dismutase, lysozyme, and peroxidase activities. After treatment with GML, the apoptosis of hemocytes increased significantly in both WSSV-infected and uninfected crayfish. In summary, GML reduced the mortality of WSSV-infected crayfish, perhaps by modulating the innate immunity of the crayfish. Our study shows that GML can be used to induce the innate immunity and enhance the immune protection of the red claw crayfish against WSSV infection, either therapeutically or as a preventive measure.

Dietary glycerol monolaurate improves bone growth through the regulation of IGF-1 in the fish model

Glycerol monolaurate (GML) has the potential of antibacterial and growth-promoting in food. Recent research reported that GML could significantly increase the body index of fish, but whether GML can exert growth-promoting ability via regulating bone metabolism remains unknown. This study explored the effects of GML on the bone growth of fish models and its mechanisms by analyzing the expression of insulin-like growth factor 1(IGF-1). The micro-CT scanning results showed that the dietary supplementation of 750 mg/kg GML significantly increased the body length and bone mineral density, and improved the bone microarchitecture parameters of the caudal vertebrae of zebrafish (Danio rerio). The centrum part of the vertebra was easier to respond to the regulatory effect of GML than the neural arch and the haemal arch. Mechanistically, the content of serum IGF-1, the expression of osteogenic differentiation-related genes, and genes involved in IGF-1/PI3K/Akt signaling pathway were significantly increased. The liver proteomic analysis showed the consistent results that GML supplementation could up-regulate the expression of hepatic IGF-1, and that energy metabolism and growth and development-related metabolic pathways were implicated in the GML bone growth boosting effects. These findings highlight that GML could be used as a functional food additive to improve bone growth and health.

Effects of Dietary Glycerol Monobutyrate Supplementation on Egg Performance, Biochemical Indices, and Gut Microbiota of Aged Hens

This experiment aimed to determine the effect of dietary supplementation with glycerol monobutyrate (GMB) on egg-laying performance, biochemical indicators, and gut microflora at the late stage of laying hens. A total of 252 healthy Dawu Golden Phoenix laying hens with no difference in body weight were selected and randomly divided into two groups: (1) control group (CG), corn-soybean meal diet, (2) 500 mg glycerol monobutyrate/kg added to the basal diet. Six replicates were set up for each treatment group, with 21 birds per replicate. The trial started at week 55 and lasted for 8 weeks. Compared to the control group, the supplementation with GMB increased egg weight (P = 0.03), shell thickness (P = 0.03) and decreased egg breaking rate (P = 0.04). There was no significant difference in egg production rate, feed-to-egg ratio, egg shape index, eggshell strength, and Haugh unit between the two groups. In addition, dietary GMB decreased the levels of aspartate aminotransferase (P = 0.03) and total bilirubin (P = 0.02) in serum, and increased total antioxidant capacity (P = 0.03) and total superoxide dismutase (P = 0.02). However, alpha diversity indices (Ace, Chao1, Shannon, Simpson, goods_coverage, and PD_whole tree) were not different between the two groups. Notably, dietary GMB significantly decreased the abundances of Proteobacteria at the phylum level and the abundances of Enterobacter at the genus level (P &amp;lt; 0.01), but there was no significant difference in the composition of other cecal microbiota. In summary, the present study revealed that supplementation with 500 mg/kg glycerol monobutyrate improved egg weight, eggshell quality, and antioxidant capacity in serum, but its effect on cecal microbiota composition was limited.

On the Utilization of Dietary Glycerol in Carnivorous Fish - Part I: Insights Into Hepatic Carbohydrate Metabolism of Juvenile Rainbow Trout (Oncorhynchus mykiss) and European Seabass (Dicentrarchus labrax)

Glycerol is a 3-carbon sugar alcohol successfully employed as an alternative feed ingredient for land-farmed animals and more recently for farmed fish. While most studies address zootechnical performance, few have delved into the metabolic utilization of dietary glycerol. A growth trial was performed using diets with increasing levels of glycerol (0, 2.5 and 5%) on two relevant species for aquaculture: rainbow trout (8-week trial; 3 tank per diet/25 fish per tank, on a 15 ± 1°C flow-through freshwater system); and European seabass (6-week trial; 5 tank per diet/6-8 fish per tank on a 21°C indoor saltwater RAS system). After this period, fish were subjected to a metabolic trial consisting of a 6-day residence in deuterated water (2H2O). Measurements of blood glucose and hepatic glycogen 2H-enrichments through Nuclear Magnetic Resonance, complemented by mRNA levels of key-enzymes for intermediary metabolism were used to evaluate the catabolic pathways of dietary glycerol. Dietary glycerol had no impact on plasma glucose, but hepatic glycogen levels increased significantly with increasing dietary glycerol levels in both species. While trout was able to regulate circulating glycerol plasma, seabass presented elevated levels on the glycerol-supplemented diets. Despite revealing some significant differences between sampling time (6 and 24 h), none of the enzymes’ mRNA levels responded to the dietary treatment. In trout, the main source of blood glucose was not labeled with 2H (~60%, likely from diet) while other contributors did not differ with glycerol supplementation. In seabass, the unlabeled contribution was approximately half of that observed in trout (~30%), accompanied by a significant increase of gluconeogenic contributions at the triose-phosphate level to the blood glucose with increasing dietary glycerol. In trout, labeling from 2H2O into hepatic glycogen revealed significant differences, with the contribution from the indirect pathway at the triose-phosphate level increasing with increased dietary glycerol. No such differences were found in seabass’ glycogen pool. These findings suggest that fish species are able to retain, catabolize glycerol and incorporate it into carbohydrates. The gluconeogenic utilization of exogenous glycerol differed between species and affected the synthesis of hepatic glycogen in trout and the appearance of blood glucose in seabass.

On the Utilization of Dietary Glycerol in Carnivorous Fish—Part II: Insights Into Lipid Metabolism of Rainbow Trout (Oncorhynchus mykiss) and European Seabass (Dicentrarchus labrax)

Glycerol is the by-product of biodiesel production and its utilisation in fish feed has recently gained relevance. As an important metabolic intermediate and structural component of triacylglycerol (TAG), it is still unclear whether its supplementation affects lipid utilisation and/or deposition in different tissues. Accordingly, a set of studies was aimed to evaluate how increasing levels of dietary glycerol (0, 2.5 and 5%) affect lipid synthesis in the liver, muscle and adipose tissue. After a growth trial with rainbow trout (8 weeks) and European seabass (6 weeks) fish were sampled at 6 and 24 h to assess mRNA levels of lipid metabolism-related enzymes. The remaining fish were subjected to a metabolic trial consisting of a 6-day residence in deuterated water (2H2O) for metabolic flux calculations. This study stands as the second part of a broader experiment that also aimed at evaluating the carbohydrate metabolism (Viegas et al., 2022). Dietary supplementation at 5% glycerol significantly increased plasma TAG levels in both species and liver TAG levels in seabass, with no repercussions on the perivisceral fat index. Despite responding as expected in a postprandial setting, only fas and Δ6-fad in trout and Δ6-fad in seabass responded significantly by increasing with the dietary supplementation of glycerol. In trout, the observed differences in the regulation of these enzymes were not reflected in the de novo lipogenic fluxes. The fractional synthetic rates (FSR) were overall low in all tissues with an average of 0.04, 0.02 and 0.01% d–1, for liver, muscle and perivisceral fat, respectively. In seabass on the other hand, and despite increased mRNA levels in Δ6-fad, the overall lipid profile in the liver muscle and perivisceral fat was higher in MUFA at the expense of lower PUFA. Moreover, glycerol supplementation altered the lipogenic capacity of seabass with hepatic fractional synthetic rates for TAG-bound FA increasing with increasing glycerol levels (0.32 ± 0.18, 0.57 ± 0.18, and 0.82 ± 0.24 for 0%, 2.5% and 5% glycerol supplementation, respectively). The findings of the present study suggest that supplementation up to 2.5% of glycerol did not severely impact the lipid metabolism nor increased lipogenic potential in liver, muscle and perivisceral fat accumulation.

Evaluating dynamic effects of dietary glycerol monolaurate on the productive performance and flesh quality of large yellow croaker (Larimichthys crocea)

The effects of GML (Glycerol monolaurate) supplementation with two level (0.5 and 1.0 g kg−1) on the productive performance and flesh quality of large yellow croaker (360 per group) were investigated during feeding (23,50-days) and fasting stage (23,70-days). The GML supplementation significantly increased body weight after 23-days and crude protein, inosinic acid, and yellowness after 50-days. Moreover, it increased hardness, springiness, and chewiness by increasing the collagen content, myofiber density, and decreasing myofiber diameter. The high GML supplementation increased the total free amino acids, delicate amino acids, monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (n-3 PUFA), and EPA + DHA, whereas it decreased the content of saturated fatty acids/unsaturated fatty acids (SFA/UFA). During fasting, better body shape and color were shown were shown at high GML supplementation. Conclusively, high dose GML supplementation exerted promising effects on the productive performance and flesh quality of large yellow croaker.

Complete replacement of corn grain with crude glycerin for dairy cows

The biodiesel process generates crude glycerin as a coproduct, which is primarily glycerol, but also includes varying amounts of other materials that may impact the value of crude glycerin as a feed for livestock. The response of dairy cows to the complete substitution of finely-ground mature corn with crude glycerin in diets containing a high content of non-forage fiber sources was evaluated. The goal was to maximize milk yield per unit of cultivated corn and to have a high replacement rate of corn starch by glycerol in the diet. Eighteen Holsteins (185±58 days in lactation) were housed in sand-bedded tie stalls and individually fed. Cows received a sequence of two treatments in a crossover design with 28-day periods. Treatments were: 1) control diet containing 14.8% ground corn (Control, CTL), or 2) a diet with complete substitution of ground corn with an isonitrogenous mixture of crude glycerin and soybean meal (Glycerin, GLY) at 12.3 and 2.7% of the ration dry matter (DM), respectively. Diets had (% of DM) 33.8% forage, 19.4% citrus pulp, and 8.6% whole cottonseeds. Crude glycerin contained 6.3% moisture, 76.2% glycerol, and 8,800 ppm of methanol, on an as-fed basis. No effect on DM intake (DMI, 16.7 kg/d) was observed, whereas GLY decreased milk yield from 23.4 to 21.3 kg/d. The daily secretion of lactose was lower (0.94 vs 1.05 kg/d) and there was a trend for total solids (2.57 vs 2.79 kg/d) to be lower for GLY than CTL. Plasma glucose concentration was decreased for cows fed the GLY diet (51.6 vs 58.3 mg/dL). Glycerin increased butyrate in rumen fluid (19.9 vs 15.6% of total volatile fatty acids) and decreased acetate (58.7 vs 64.6% of total volatile fatty acids) and the acetate to propionate ratio (2.79 vs 3.30). Total tract apparent OM digestibility was increased with GLY (74.1 vs 70.8% of intake). The ratios of milk yield to DMI (1.40 vs 1.30 kg milk/kg DMI) and milk energy secretion to digestible OM intake (DOMI) (1.47 vs 1.30 Mcal/kg) were decreased in GLY. There was no difference between treatments on rumen microbial yield, estimated by the daily excretion of urinary allantoin, and urinary allantoin per unit of DOMI. Eating time per unit of DMI was reduced for cows fed GLY (12.6 vs 14.2 min/kg DMI) and rumination rate did not differ between treatments (18.2 min/kg DMI). Overall, the substitution of ground corn with a crude glycerin and soybean meal mixture increased OM digestibility and decreased rumen acetate to propionate ratio, plasma glucose concentration, milk yield, and efficiencies of feed and energy utilization.

EFFECT OF CRUDE GLYCEROL SUPPLEMENTATION VIA DRINKING WATER ON LAMBS PERFORMANCE, SOME BLOOD HAEMATOLOGY, AND BIOCHEMICAL METABOLITES

EFFECT OF CRUDE GLYCEROL SUPPLEMENTATION VIA DRINKING WATER ON LAMBS PERFORMANCE, SOME BLOOD HAEMATOLOGY, AND BIOCHEMICAL METABOLITES

Biodiesel‐derived glycerol as a dietary maize replacement for silver catfish ( Rhamdia quelen ) during the fattening phase

The aim of the present study was to assess the effects of crude biodiesel-derived glycerol on the zootechnical performance, carcass and fillet chemical composition, and blood parameters of silver catfish (Rhamdia quelen) during the fattening phase. A total of 150 adult silver catfish specimens (mean weight 188.89 ± 0.60 g) were distributed in thirty 1000 L-tanks containing a water recirculation system with mechanical filter and biofilter, in a completely randomized design comprising six treatments, 0%, 20%, 40%, 60%, 80% and 100% maize replacement by glycerol, with five repetitions each. The experiment was conducted for 206 days. Silver catfish morphometric parameters were not influenced (p > 0.05) by the glycerol maize replacement, although silver catfish standard length and width exhibited linear improvements (p < 0.05) with the dietary glycerol replacement. Fillet yield was affected (p < 0.05) by glycerol maize replacement, where the 80% replacement treatment led to better fillet yields (46.04%), differing only from the 20% replacement treatment (42.40% fillet yields). The blood plasma levels of glucose, pyruvic glutamic transaminase and triglycerides were influenced by the treatments (p < 0.05). The crude protein of fillet was influenced by the treatments (p < 0.05), where the highest value was observed in 100% glycerol maize replacement. Therefore, crude glycerol derived from biodiesel production is a suitable alternative energy source ingredient for silver catfish during their fattening phase, as it can replace maize in up to 100%.

Dietary Glycerol Monolaurate Improves Bone Growth Through the Regulation of Igf-1 in Fish Model

Dietary Glycerol Monolaurate Improves Bone Growth Through the Regulation of Igf-1 in Fish Model

Crude glycerin is an efficient alternative to corn in the diet of feedlot lambs.

The objective of this study was to evaluate the intake, digestibility, nitrogen balance, and performance of feedlot lambs fed diets containing crude glycerin. A total of 30 Ile de France lambs were confined to individual pens at an average age of 45 : 15.1 initial body weight and 32.2 final body weight. The animals were distributed in a completely randomized design and fed three diets containing fresh sugarcane as forage (50 %) and concentrate (50 %), with or without the inclusion of 100 and 200 vegetable crude glycerin per kilogram dry matter (DM) replacing corn. Dietary glycerin inclusion reduced the intake of ether extract () and total carbohydrates () as well as the apparent digestibility of ether extract (), but it had no effect on the intake and digestibility of the other nutrients nor on lamb performance. The apparent nitrogen balance of lambs on the three diets was positive. Although it does not affect the intake and digestibility of most nutrients, the inclusion of 100 and 200 of crude glycerin in the diet tends to worsen lamb performance, indicating that the ideal level of inclusion should be below 100 of crude glycerin.

The effect of dietary inclusion of crude glycerin on performance, ruminal fermentation, meat quality and fatty acid profile of beef cattle: Meta-analysis

This meta-analysis was carried to evaluate the effect of the use of crude glycerin in diets for beef cattle on the ruminal fermentation, animal performance, physical and chemical characteristics, and fatty acid profile of meat through meta-analysis. Data from forty-eight peer-reviewed publications with 170 treatments means was included in the data set. The effect glycerin in diet were evaluated by examining the weighted mean differences (WMD) between glycerin treatment (diets with crude glycerin) and control diet (without crude glycerin). Heterogeneity was explored by meta-regression and subgroup analysis using genetic type, treatment period, crude glycerin in the diet (g/kg DM), feed systems (pasture or total mixed ration), and concentrate in the diet (g/kg DM). The inclusion of crude glycerin had no effect on the average daily gain, but increased feed efficiency by 3.15% while reducing subcutaneous fat thickness by 3.13%. Inclusion of crude glycerin reduced meat cholesterol by 9.13%, and total saturated fatty acids by 1.05%, and increased total unsaturated (2.02%), monounsaturated (3.17%) fatty acids. However, it did not affect the concentrations of conjugated linoleic acid and omega-3. Crude glycerin inclusions up to 200 g/kg DM did not promote a negative effect on animal performance, carcass and physical-chemical characteristics of meat, and supported an increase in total monounsaturated (1.73%), oleic acid (12.29 mg) and palmitoleic acid (1.24 mg), while reducing myristic acid (3.08 mg), stearic acid (12.00 mg) in beef cattle meat.

Effects of Dietary Crude Glycerin Concentration on Testicular Morphology and Oxidative Stress Markers and on Plasma Testosterone Concentrations

We evaluated the effects of feeding 6%, 12% or 18% crude glycerin, containing 80.5% glycerol, on testicular histomorphometry and markers of oxidative stress and on plasma testosterone concentrations in lambs. Body weight, testicular biometric measurements, gonadosomatic index and net weight of the testicles were higher for the treated groups (P<0.05) compared with a control group that did not receive dietary glycerin. The mean total length of seminiferous tubules was higher in the 6% group (P<0.05), while the mean total tubular and seminiferous epithelium volumes increased in all treated groups (P<0.05). The volume of Leydig cells increased in the 12% group, while their number per gram of testicle decreased (P<0.05). There was a decrease in mean nuclear diameter and mean volume of Leydig cells, and an increase in the mean number of these cells per gram of testicle, in the 18% group (P<0.05). Plasma testosterone concentrations were unaffected. There was desquamation of seminiferous epithelium and vacuolation of Sertoli cells in the treated groups. Variable degrees of spermatocyte necrosis and the presence of giant cells were seen in all groups and there was intense vacuolation of Sertoli cells in the 12% and 18% groups. Superoxide dismutase and catalase production increased most in the 12% and 18% groups (P<0.05), while glutathione production was higher in the 18% group (P<0.05). Mean nitric oxide concentration decreased in all treated groups (P<0.05), while malondialdehyde production was higher in the 18% group than in the control and 6% groups (P<0.05). We conclude that the inclusion of 6% glycerin in the diet of lambs results in changes in testicular morphology that have been previously associated with improved reproductive function, but without evidence of oxidative stress.

Dietary glycerol monolaurate improved the growth, activity of digestive enzymes and gut microbiota in zebrafish (Danio rerio)

Microbial recurrent infections and antimicrobial resistance have motivated the researchers to explore bioactive compounds as safe alternative antimicrobials to target pathogenic microorganisms. Interest in finding new biologically active substances to replace conventional antibiotics in aquatic feed has rapidly increased, since the misuse or overuse of antibiotics produced antibiotic resistance. Glycerol monolaurate (GML), has attracted attention of researchers due to its growth-promoting and immunomodulatory potential by exerting beneficial effects on the gut microbiota and host health. This study aimed to evaluate the effects of dietary GML using as a feed additive on the growth performance, blood lipid profile, hepatic lipid deposition, body composition, digestive enzymes, serum anti-inflammatory activities, and gut microbiota of zebrafish. The study’s findings showed that diet supplemented with 750 mg kg−1 of GML, significantly improved the growth performance, feed utilization and intestinal lipase activity, as well as body crude lipid content without inducing hepatic fat accumulation. GML supplementation also promoted the serum anti-inflammatory potential by elevating the level of TGF-β1 and IL-10. Moreover, dietary supplementation of GML positively restructured the intestinal microbial ecology by improving the relative abundance of several favorable bacteria, including Cetobacterium, Shewanella, and Vibrio at the genus level. Conclusively, study’s findings suggest that GML supplementation contributes in improving the growth, digestive enzymes activities, anti-inflammatory potential, and gut microbiota, indicating GML promising potential as a feed additive in aquaculture nutrition.