D.M. Wang

Metabolomics of four biofluids from dairy cows: potential biomarkers for milk production and quality.

The fundamental understanding of the mechanisms regulating milk protein synthesis is limited. This study aimed to elucidate the metabolic mechanisms of milk production affected by forage quality through studying metabolites from four biofluids (rumen fluid, milk, serum, and urine) collected from 16 lactating cows fed alfalfa hay (AH, high-quality, n = 8) and corn stover (CS, low-quality, n = 8) using gas chromatography-time-of-flight/mass spectrometry. The cows fed AH exhibited higher milk yield (P < 0.01), milk protein yield (P = 0.04), and milk efficiency (P < 0.01) than those fed CS. A total of 165, 195, 218, and 156 metabolites were identified in the rumen fluid, milk, serum, and urine, respectively, while 29 metabolites were found in all four biofluids. In addition 55, 8, 28, and 31 metabolites in each biofluid were significantly different (VIP > 1 and P < 0.05) between the AH- and CS-fed animals. These metabolites were involved in glycine, serine, and threonine metabolism; tyrosine metabolism; and phenylalanine metabolism. Further integrated key metabolic pathway analysis showed that the AH-fed cows may have more comprehensive amino acid metabolisms, suggesting that these metabolite-associated pathways may serve as biomarkers for higher milk yield and better milk protein quality.

Effects of rumen-protected γ-aminobutyric acid on feed intake, lactation performance, and antioxidative status in early lactating dairy cows

The objective of this study was to investigate effects of rumen-protected γ-aminobutyric acid (GABA) on dry matter intake, milk performance, and serum metabolites in Chinese Holstein lactating cows. Thirty-nine multiparous cows were blocked based on days in milk (60 ± 6.3 d; mean ± SD) and milk production (30.9 ± 4.17 kg; mean ± SD), and were randomly assigned to 1 of 4 treatments, with rumen-protected GABA added at levels of 0, 0.8, 1.6, or 2.4 g/d, the actual predicted available amounts being 0, 0.30, 0.61, or 0.91 g of GABA/d, respectively. The experiment lasted for 8 wk, with the first week for adaptation. Milk yield and milk compositions were recorded weekly, and serum concentrations of GABA, neuropeptide Y, and biochemical and antioxidant variables were analyzed in the first, fourth, and seventh weeks of the study. Dry matter intake linearly increased in cows receiving added GABA compared with that for the control. Addition of 0.8 g of GABA/d was associated with higher milk yield than the other treatments, but contents of milk protein and fat did not differ across the treatments. Dietary GABA tended to quadratically enhance the serum content of GABA (23.6, 30.2, 29.8, or 28.3 mmol/L for 0, 0.8, 1.6, or 2.4 g/d, respectively), and increased neuropeptide Y, with the highest value (3.07 ng/L) for 0.8 g of GABA/d. Nonesterified fatty acid quadratically decreased with GABA addition, with the lowest value (218.1 μmol/L) for 0.8 g of GABA/d. Serum glutathione peroxidase and superoxide dismutase quadratically increased in cows fed GABA, whereas serum malondialdehyde was quadratically reduced for all GABA groups. Rumen-protected GABA quadratically improved N efficiency across all treatments, contributing to the enhanced production of milk and milk protein and reduced N emission to the environment. In conclusion, addition of rumen-protected GABA is beneficial for early lactation dairy cows in terms of feed intake, lactation performance, and animal health.

Systematic microRNAome profiling reveals the roles of microRNAs in milk protein metabolism and quality: insights on low-quality forage utilization

In this study, we investigated the molecular regulatory mechanisms of milk protein production in dairy cows by studying the miRNAomes of five key metabolic tissues involved in protein synthesis and metabolism from dairy cows fed high- and low-quality diets. In total, 340, 338, 337, 330, and 328 miRNAs were expressed in the rumen, duodenum, jejunum, liver, and mammary gland tissues, respectively. Some miRNAs were highly correlated with feed and nitrogen efficiency, with target genes involved in transportation and phosphorylation of amino acid (AA). Additionally, low-quality forage diets (corn stover and rice straw) influenced the expression of feed and nitrogen efficiency-associated miRNAs such as miR-99b in rumen, miR-2336 in duodenum, miR-652 in jejunum, miR-1 in liver, and miR-181a in mammary gland. Ruminal miR-21-3p and liver miR-2285f were predicted to regulate AA transportation by targeting ATP1A2 and SLC7A8, respectively. Furthermore, bovine-specific miRNAs regulated the proliferation and morphology of rumen epithelium, as well as the metabolism of liver lipids and branched-chain AAs, revealing bovine-specific mechanisms. Our results suggest that miRNAs expressed in these five tissues play roles in regulating transportation of AA for downstream milk production, which is an important mechanism that may be associated with low milk protein under low-quality forage feed.

Effect of dietary N-carbamoylglutamate on milk production and nitrogen utilization in high-yielding dairy cows.

The objective of the current study was to investigate the effect of N-carbamoylglutamate (NCG) supplementation on milk production and nitrogen (N) utilization in Chinese Holstein dairy cows. Sixty multiparous cows (78±17.3 d in milk, 635±61.00kg of body weight, and 41.9±7.9kg/d milk yield; mean ± SD) were blocked by parity, days in milk, and milk yield and randomly allocated to 1 of 4 groups, each of which was fed a dietary treatment containing 0 (control), 10, 20, or 30g of NCG/d. Milk yield was recorded weekly. Dry matter intake, milk composition, plasma variables, and urea N contents in plasma, urine, and milk were determined every other week. Blood samples were collected from the coccygeal vein. Rumen microbial protein synthesis was estimated based on the purine derivatives in the urine. Dry matter intake was found to be similar between the treatments. Addition of 20g of NCG/d tended to increase milk yield (40.2 vs. 38.1kg/d) and increased the content (2.83 vs. 2.74%) and yield (1.12 vs. 1.02kg/d) of milk protein compared with the control. The yield and content of milk fat were similar between the treatments, whereas the contents of lactose and total solids increased linearly with an increase in NCG. Dietary supplementation of NCG linearly increased the plasma nitric oxide level and decreased the plasma ammonia N level. Compared with the control, the plasma Arg concentration in cows fed 10, 20, and 30g of NCG/d was increased by 1.1, 10.4, and 16.0%, respectively. The urea N concentrations in the milk, plasma, and urine decreased with the addition of NCG, although the lowest urea N concentrations were observed with the addition of 20g of NCG/d. The conversion of dietary crude protein to milk protein exhibited quadratic trends of improvement by NCG supplementation, with a peak at 20g of NCG/d. The rumen microbial protein synthesis was not altered by NCG supplementation, but the metabolizable protein tended to show a quadratic increase in cows fed 20g of NCG/d. In conclusion, supplementation of 20g of NVG/d may alter the plasma metabolites, optimize the AA profile, increase the metabolizable protein utilization, and thereby improve the lactation performance and N utilization of high-yielding dairy cows.

Effects of γ-aminobutyric acid on feed intake, growth performance and expression of related genes in growing lambs

This study was conducted to investigate the effects of rumen-protected γ-aminobutyric acid (GABA) on feed intake, growth performance and expression of related genes in growing lambs. A total of 24 lambs weaned at age of 50 days were divided into four block of six based on their BW, six lambs within a block were allocated to three pairs, which were then assigned randomly to three treatments with addition of rumen-protected GABA at levels of 0, 70 or 140 mg/day for 6 weeks. Dry matter intake was recorded weekly in three consecutive days, and BW was recorded every two weeks. At the end of the trial, four lambs from each group were slaughtered, and duodenum and ileum mucosa were obtained for measurement of mRNA abundance of GABA receptor and cholecystokinin receptor. Dry matter intake was higher (P<0.01) in the lambs fed 140 mg/day GABA than that in the control or 70 mg GABA-fed lambs. Average daily gain and nutrients digestibility were not different (P>0.05) among treatments. Lambs fed 140 mg/day GABA had higher mRNA abundance of GABA-B receptor (P<0.01) and lower mRNA abundance of cholecystokinin-2 receptor (P<0.01) in duodenum mucosa. Serum CCK content was lower (P<0.01) in lambs fed 140 mg/day GABA than that in control. It is indicated that GABA may enhance feed intake by regulating GABA- and cholecystokinin-related genes.

Short communication: Effects of dietary 5,6-dimethylbenzimidazole supplementation on vitamin B12 supply, lactation performance, and energy balance in dairy cows during the transition period and early lactation

The current study was conducted to investigate the effects of 5,6-dimethylbenzimidazole (DMB) supplementation to the feed during the transition period and early lactation on the vitamin B12 supply, lactation performance, and energy balance in postpartum cows. Twenty-four prepartum Holstein dairy cows were divided into 12 blocks based on their parity and milk yield at the last lactation and were then randomly allocated to 1 of 2 treatments: a basal diet without DMB (control) or a treatment diet that contained 1.5 g of DMB/d per cow. The study started at wk 3 before the expected calving day and ended at wk 8 postpartum. The feed intake and the lactation performance were measured weekly after calving. Blood parameters were measured on d -10, 0, 8, 15, 29, 43, and 57 relative to the calving day. Body weight was measured on the calving day and on d 57 after calving. The yields of milk, protein, and lactose in cows fed DMB were higher than in the control throughout the whole postpartum stage. On wk 8 postpartum, the vitamin B12 content in the milk and sera was greater in cows fed DMB than in the control. The overall body weight loss from wk 1 to 8 postpartum was less in cows fed DMB than in the control. The plasma content of nonesterified fatty acids and β-hydroxybutyric acid was significantly lower in cows fed DMB than in the control throughout the whole experimental stage. In conclusion, dietary DMB fed during the transition period and early lactation improved the vitamin B12 supply, milk production, and energy balance of postpartum dairy cows.

Metabolomics Integrated with Transcriptomics Reveals a Subtle Liver Metabolic Risk in Dairy Cows Fed Different Crop By-products

Ruminants make large contributions to sustainable agriculture by converting crop by‐products into agricultural food. Multi‐omics integrative analysis helps to uncover the underlying molecular mechanisms. The liver metabolome‐transcriptome interface (LMTI) in dairy cows, including 3938 significant correlations (p < 0.01 and |ρ| > 0.6) among 772 genes, 306 metabolites, and 305 microRNAs, is first demonstrated. How different crop by‐products, corn stover (CS) and rice straw (RS), affect the liver metabolic functions based on the LMTI is further analyzed. Compared to the CS‐fed cows, 13 out of 24 metabolites have lower relative concentrations (variable importance projection > 1.0 and p < 0.05), and 51 out of 68 genes are downregulated in the RS group (p < 0.01 and fold change < –2). Integrated analysis of metabolomics and transcriptomics reveal that lipid metabolism is most enriched including 14 subpathways. The altered metabolites and genes revealed the enriched ketogenesis induced by the linoleic acid pathways (p = 0.017, topology value = 1), which is supported by blood and histomorphometric phenotypes. The above results indicate the foreseeable liver metabolic disorders when RS is fed to cows. These findings provide new insights into the liver metabolic mechanism and into crop by‐products utilization using integrative omics technologies.

Short communication: Effects of dietary addition of N-carbamylglutamate on milk composition in mid-lactating dairy cows

The present study was conducted to investigate the effect of N-carbamoylglutamate (NCG) on milk production and composition in mid-lactating Holstein dairy cows. Sixty multiparous cows with a mean body weight of 669 kg (standard deviation = 71) and 176 days in milk (standard deviation = 55) were blocked based on parity and milk production and randomly assigned into 4 treatments, a basal diet supplemented with 0, 10, 20, or 40 g of NCG/d per cow. Milk yield and composition were recorded weekly, whereas dry matter intake and plasma variables were determined every 2 wk. The results showed that the addition of NCG had no effect on the dry matter intake and milk yield of the cows. Milk fat content and yield increased linearly with NCG addition. The contents of milk protein and total solid also increased linearly in the cows fed NCG, whereas the yield of protein was not affected by the treatments. Conversely, dietary addition of NCG increased the plasma nitric oxide content in a quadratic manner. Moreover, addition of NCG linearly increased the plasma Arg content. Overall, the results indicate that dietary NCG addition increased the milk protein and fat contents, which improved the milk quality of lactating dairy cows.

Effect of dietary supplements of biotin, intramuscular injections of vitamin B12, or both on postpartum lactation performance in multiparous dairy cows

The current study was conducted to investigate the effects of dietary supplementation of biotin, intramuscular injections of vitamin B12 (VB12), or both beginning at the prepartum period on feed intake and lactation performance in postpartum dairy cows. Forty-eight dairy cows were allocated into 12 blocks, based on parity and milk yield of the previous lactation cycle, and randomly assigned to 1 of 4 treatments. Supplementation of VB12 (weekly intramuscular injections of 0 or 10 mg) and biotin (dietary supplements of 0 or 30 mg/d) were used in a 2 × 2 factorial arrangement in a randomized complete block design of 12 blocks with repeated measures. The study started at 3 wk before the expected calving date and ended at 8 wk after calving. Feed intake and lactation performance (milk yield and composition) were recorded weekly after calving. Blood variables were measured on d -10, 0, 8, 15, 29, 43, and 57 relative to calving. When VB12 was given, the cows had greater feed intake, better lactation performance and lower body weight loss in the postpartum period compared with animals without injection of VB12. The VB12-injected cows had lower plasma nonesterified fatty acids and β-hydroxybutyrate concentrations but higher plasma superoxide dismutase activity compared with cows without VB12. Cows fed a biotin supplement had higher milk protein yield (6 and 8 wk) and lactose yield (6-8 wk), compared with animals without biotin. However, under the present experimental conditions, we found no additive effect of a combined supplement of biotin and vitamin B12 on lactation performance of dairy cows.