THE OXIDATION AND UTILIZATION OF GLUCOSE AND ACETATE BY THE MAMMARY GLAND OF THE GOAT IN RELATION TO THEIR OVER-ALL METABOLISM AND MILK FORMATION

Abomasal infusion of branched-chain amino acids or branched-chain keto-acids alter lactation performance and liver triglycerides in fresh cows

BACKGROUND

Dairy cows are at high risk of fatty liver disease in early lactation, but current preventative measures are not always effective. Cows with fatty liver have lower circulating branched-chain amino acid (BCAA) concentrations whereas cows with high circulating BCAA levels have low liver triglyceride (TG). Our objective was to determine the impact of BCAA and their corresponding ketoacids (branched-chain ketoacids, BCKA) on production performance and liver TG accumulation in Holstein cows in the first 3 weeks postpartum.

METHODS

Thirty-six multiparous Holstein cows were used in a randomized block design experiment. Cows were abomasally infused for the first 21 d postpartum with solutions of 1) saline (CON, n = 12); 2) BCA (67 g valine, 50 g leucine, and 34 g isoleucine, n = 12); and 3) BCK (77 g 2-ketovaline calcium salt, 57 g 2-ketoleucine calcium salt, and 39 g 2-ketoisoleucine calcium salt, n = 12). All cows received the same diet. Treatment effects were determined using PROC GLIMMIX in SAS.

RESULTS

No differences were detected for body weight, body condition score, or dry matter intake averaged over the first 21 d postpartum. Cows receiving BCK had significantly lower liver TG concentrations compared to CON (6.60% vs. 4.77%, standard error of the mean (SEM) 0.49) during the first 3 weeks of lactation. Infusion of BCA increased milk yield (39.5 vs. 35.3 kg/d, SEM 1.8), milk fat yield (2.10 vs. 1.69 kg/d, SEM 0.08), and lactose yield (2.11 vs. 1.67 kg/d, SEM 0.07) compared with CON. Compared to CON, cows receiving BCA had lower plasma glucose (55.0 vs. 59.2 mg/dL, SEM 0.86) but higher β-hydroxybutyrate (9.17 vs. 6.00 mg/dL, SEM 0.80).

CONCLUSIONS

Overall, BCAA supplementation in this study improved milk production, whereas BCKA supplementation reduced TG accumulation in the liver of fresh cows.

Effect of glucose infusion on glucose and insulin metabolism in early- and mid-lactation ewes and goats fed diets differing in starch and highly digestible fiber concentration

This study aimed to test possible metabolic differences between ewes and goats in response to an intravenous glucose infusion. Thirty-six animals, 18 mature Sarda dairy ewes and 18 mature Saanen goats (from 15 to 150 ± 11 d in milk [DIM], mean ± SD; body weight: 49.8 ± 6.8 kg for ewes, 60.6 ± 7.3 kg for goats) were compared simultaneously. In early lactation, both species received the same high-starch diet (HS: 20.4% starch, 35.4% neutral detergent fiber [NDF], on dry matter [DM] basis), whereas from 92 ± 11 DIM both species were randomly allocated to 2 dietary treatments: HS (20.0% starch, 36.7% NDF, on DM basis) and low-starch (LS: 7.8% starch, 48.8% NDF, on DM basis) diets. At 50 and 150 ± 11 DIM, ewes and goats were challenged with an intravenous glucose tolerance test and peripheral concentrations of glucose and insulin were determined 15 min before and 5, 10, 15, 30, 45, 90, and 180 min after glucose infusion. In early lactation, baseline plasma glucose and insulin concentrations tended to be higher in ewes than in goats (glucose: 55.8 vs. 42.9 ± 7.3 mg/dL; insulin: 0.13 vs. 0.05 ± 0.04 µg/L). After glucose infusion, glucose and insulin concentrations were higher in ewes than in goats (278.6 vs. 247.6 ± 13.1 mg/dL; 0.82 vs. 0.46 ± 0.12 µg/L). In mid-lactation, the dietary treatment (HS vs. LS) did not affect glucose and insulin metabolism. Baseline plasma glucose was numerically highest in ewes, while baseline insulin was higher in ewes than in goats (0.39 vs. 0.12 ± 0.099 µg/L). After glucose infusion, glucose concentration did not differ between ewes and goats, while insulin concentration was highest in ewes. Compared with goats, ewes showed in both periods a higher peak insulin, insulin increment, linear insulin area under the curve, insulin resistance index, and lower insulin sensitivity indices. In conclusion, despite the limitations associated with the use of intravenous glucose tolerance test to assess glucose regulation mechanisms, this study indicated large species differences in both early and mid-lactation and a more evident anabolic status in the ewes compared with the goats.

Responses in splanchnic and mammary amino acid metabolism to short-term graded removal of methionine in lactating goats

Four multi-catheterized lactating goats were used in a 4 × 4 Latin square experiment to investigate the responses of amino acid metabolism in portal-drained viscera (PDV), liver, and mammary glands to short-term varying supplies of methionine (Met). During the last 45 h in each experimental period, goats were fasted for 12 h and then abomasally infused with an amino acid (AA) mixture plus glucose for 33 h. Treatments consisted of graded removal of Met from an infused AA mixture to achieve Met content in the infusate of 100% (complete), 60%, 30%, or 0% that in casein. Graded Met removal decreased the production of milk, milk protein, lactose, and fat linearly whilst also decreasing arterial Met concentration linearly (P < 0.05). Meanwhile, net PDV uptake and liver removal of Met decreased linearly (P < 0.05) due to decreased Met affinity of PDV and liver (P < 0.05). Net mammary uptake of Met (P > 0.1) was maintained as Met supply declined. This was achieved through increased mammary affinity (P < 0.05) and increased mammary blood flow (P < 0.05) totally offsetting the negative effect of decreased circulating Met concentration. Graded removal of Met from the infusate linearly decreased mammary uptake-to-milk output ratios of Met (P < 0.05) and tended to decrease essential amino acid (EAA) linearly (0.05 < P < 0.1). Treatments also linearly decreased circulating concentration of prolactin and linearly increased insulin concentration (P < 0.05). In conclusion, results of the present study indicated there were several mechanisms used to mitigate a Met deficiency, including reduced catabolism of Met in PDV, liver, and peripheral tissue (including mammary glands) and a linear increase in mammary blood flow. The observed decreases in milk protein production as Met supply decreased appear to be a result of regulatory events which may have been driven by decreased circulating prolactin, rather than as a result of decreased mammary Met uptake.

Assessing Amino Acid Metabolism in Splanchnic Tissues and Mammary Glands to Short-Term Graded Removal of Lys From an Abomasal-Infused Amino Acid Mixture in Lactating Goats

To investigate the responses of amino acid metabolism in portal-drained viscera (PDV), liver, and mammary glands (MGs) to a graded gradual decrease of post-ruminal Lys supply, four multi-catheterized lactating goats were used in a 4 × 4 Latin square experiment. Goats were fasted for 12 h and then received a 33-h abomasal infusion of an amino acid mixture and glucose. Treatments consisted of a graded decrease of Lys content in the infusate to 100 (complete), 60, 30, or 0% as in casein. Lys-removed infusions decreased the production of milk, milk protein, fat, and lactose linearly and also decreased arterial Lys concentrations linearly (p &lt; 0.05). Net PDV uptake decreased linearly (p &lt; 0.05) with decreasing PDV loss ratio (p &lt; 0.05). Although liver removal of Lys decreased linearly (p &lt; 0.05), the removal ratio relative to portal absorption changed small, which was about 10% in all four treatments. Reduced Lys supply resulted in a linear decrease in the utilization of Lys in the peripheral tissues (except mammary, p &lt; 0.05) and the release of more Lys in MGs. Although net mammary uptake of Lys declined linearly (p &lt; 0.05), lactating goats can partially offset the negative effect of decreased circulating Lys concentrations by increasing mammary affinity (p &lt; 0.05) and increasing mammary blood flow (p &lt; 0.05). Graded removal of Lys from the infusate linearly decreased mammary uptake-to-output ratios of Lys (p &lt; 0.05) suggesting that mammary catabolism of Lys decreased. Meanwhile, the treatments linearly increased circulating concentrations of glucagon and linearly decreased prolactin (p &lt; 0.05). In conclusion, the results of the present study indicated that there were several mechanisms used to mitigate a Lys deficiency, including reduced catabolism of Lys in PDV and peripheral tissues (including MGs) and linearly increased mammary blood flow and mammary affinity together with increased mammary uptake and U:O of branched-chain amino acids (BCAA). Given these changes, the decline in milk protein production could be attributed to the combined effect of mass action with Lys and hormonal status.

Effects of branched-chain amino acids on glucose uptake and lactose synthesis rates in bovine mammary epithelial cells and lactating mammary tissue slices

Even though supplementations of essential AA (EAA) are often related to increased lactose yields in dairy cows, underlying mechanisms connecting EAA availability to the mammary glands and lactose synthesis are poorly understood. The objective of this study was to examine the effects of branched-chain AA (BCAA) including Leu, Ile, and Val on (1) glucose transporter (GLUT1) abundance and glucose uptake, (2) the abundance of proteins regulating lactose synthesis pathway, and (3) fractional synthesis rates of lactose (FSR) using bovine mammary epithelial cells (BMEC) and mammary tissues slices (MTS). The BMEC (n = 4) were allocated randomly to regular Dulbecco's Modified Eagle Medium with Ham's F12 (DMEM/F12) media (+EAA) or +EAA deficient (by 90%) in all EAA (-EAA), all BCAA (-BCAA), only Leu (-Leu), only Ile (-Ile) or only Val (-Val). Western immunoblotting analyses, depletion of glucose in media, and a proteomic analysis were performed to determine the abundance of GLUT1 in the cell membrane, net glucose uptake, and the abundance of enzymes involved in lactose synthesis pathway in BMEC, respectively. The MTS (n = 6) were allocated randomly to DMEM/F12 media having all EAA and ¹³C-glucose at concentrations similar to plasma concentrations of cows (+EAA_p), and +EAA_p deprived of all BCAA (-BCAA_p) or only Leu (-Leu_p) for 3 h. The ¹³C enrichments of free glucose pool in MTS (E_Glu-free) and the enrichments of glucose incorporated into lactose in MTS and media [E_{Lactose-bound (T&M)}] were determined and used in calculating FSR. In BMEC, -BCAA increased the fraction of total GLUT1 translocated to the cell membrane and the fraction that was potentially glycosylated compared with +EAA. Among individual BCAA, only -Leu was associated with a 63% increase in GLUT1 translocated to the cell membrane and a 40% increase in glucose uptake of BMEC. The -BCAA tended to be related to a 75% increase in the abundance of hexokinase in BMEC. Deprivation of Leu tended to increase glucose uptake of MTS but did not affect E_Glu-free, E_{Lactose-bound (T&M)}, or FSR relative to +EAA_p. On the other hand, -BCAAp did not affect glucose uptake of MTS but was related to lower E_{Lactose-bound (T&M)}, or FSR relative to +EAA_p. Considering together, decreasing Leu supply to mammary tissues enhances GLUT1 and thus glucose uptake, which, however, does not affect lactose synthesis rates. Moreover, the deficiency of other BCAA, Ile, and Val alone or together with the deficiency of Leu seemed to decrease lactose synthesis rates without affecting glucose uptake. The data also emphasize the importance of addressing the effect of the supply of other nutrients to the mammary glands than the precursor supply in describing the synthesis of a milk component.

Supplementation of Spring Pasture with Harvested Fodder Beet Bulb Alters Rumen Fermentation and Increases Risk of Subacute Ruminal Acidosis during Early Lactation

Simple Summary

Fodder beet (FB) is widely used in grazing dairy systems of New Zealand to support early- and late-lactation milk production, however, the large fraction of water-soluble carbohydrate present in FB bulbs presents a risk of subacute and acute ruminal acidosis. Despite widespread use of FB across New Zealand, the incidence of ruminal acidosis using industry-recommended methods of feeding FB has not been investigated. This study analyzed the time-dependent changes to rumen fermentation, apparent dry matter intake, milk production, milk composition and plasma amino acid concentration of grazing dairy cows supplemented with moderate amounts (40% of dry matter intake) of FB during early lactation. Our findings indicate that incidence of subacute ruminal acidosis due to FB is greater than currently realized, as 25% of cows developed severe subacute ruminal acidosis following transition to target FB allocation (40% of daily intake). Across all cows, FB reduced rumen pH, feed conversion efficiency and was not advantageous to milk production. These results suggest methods for adapting cows to a diet containing FB require further evaluation to reduce the risk of subacute ruminal acidosis (SARA) experienced by individuals within the herd.

Abstract

In a cross-over design, eight rumen cannulated dairy cows were used to explore the industry-recommended method for dietary transition to fodder beet (FB: Beta vulgaris L.) on changes to rumen fermentation and pH, milk production, dry matter intake (DMI) and the risk of subacute ruminal acidosis (SARA) during early lactation. Cows were split into two groups and individually allocated a ryegrass (Lolium Perenne L.) and white clover (Trifolium repens L.) diet (HO) or the same herbage supplemented with 6 kg DM/cow of harvested fodder beet bulbs (FBH). Dietary adaptation occurred over 20 days consisting of: stage 1: gradual transition to target FB intake (days 1–12, +0.5 kg DM of FB/d); stage 2: acclimatization (days 13–17) and stage 3: post-adaption sampling (days 18–20). Response variables were analyzed as a factorial arrangement of diet and stage of adaption using a combination of ANOVA and generalized linear mixed modelling. Dietary proportion of FB represented 22, (stage 1), 32 (stage 2) and 38% (stage 3) of daily DMI. One cow during each period developed SARA from FB and the duration of low pH increased with FBH compared to the HO treatment (p < 0.01). Rumen concentrations of lactic and butyric acid increased with FBH but concentrations of acetate, propionate and total volatile fatty acids (VFA) declined by 9.3% at day 20, compared to the HO treatment (p < 0.01). Treatments did not affect milk production but total DMI with supplemented cows increased during the final stage of adaptation and feed conversion efficiency (FCE kg milk/kg DM) declined with the FBH treatment. The occurrence of SARA in 25% of animals fed FB suggest it is a high-risk supplement to animal health and further evaluation of industry-recommended methods for feeding FB at the individual- and herd-scale are needed.

Short communication: Effect of glucose infusion dose and stage of lactation on glucose tolerance test kinetics in lactating dairy cows

The objective for this study was to determine the effect of glucose dose and days following peak milk yield on plasma glucose, serum insulin, and plasma nonesterified fatty acids (NEFA) kinetics during an intravenous glucose tolerance test (IVGTT) in lactating dairy cattle. Six lactating Holstein dairy cows (3 primiparous and 3 multiparous) were assigned to 2 squares and received 0.092, 0.15, or 0.3 g of glucose/kg of body weight (BW) during an IVGTT at 74 and 221 d in milk (DIM), representing early (post-peak) lactation and mid lactation, respectively. Treatments were applied in a replicated Latin square design using contiguous 7-d periods within each stage of lactation. Milk production and dry matter intake were determined daily during the first 6 d of each period. The IVGTT was performed on d 7. For the IVGTT, cows were prepared with indwelling catheters in each jugular vein, and blood samples were collected at -15, -10, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min relative to the glucose infusion. Samples were analyzed for plasma glucose, serum insulin, and plasma NEFA concentrations. Increasing the glucose dose during the IVGTT increased plasma glucose area under the curve (AUC), decreased glucose half-life, and increased maximal plasma glucose concentrations in plasma during the IVGTT. Greater glucose dose during the IVGTT elevated serum insulin AUC and increased nadir NEFA concentrations. Maximal plasma glucose concentration during the IVGTT was lower, whereas maximum NEFA concentration, NEFA AUC, and NEFA clearance rate were greater at 74 than at 221 DIM. Only glucose half-life was responsive to stage of lactation × glucose dose effects during the IVGTT, and the decrease in glucose half-life with increasing glucose dose was greater at 74 than at 221 DIM. Glucose AUC was greater and NEFA AUC lower for cows at 74 than at 221 DIM. For the doses tested, a glucose dose greater than 0.092 g/kg of BW resulted in peak blood glucose concentration that exceeded the previously reported renal glucose excretion threshold of 8.3 mM. There is a need for accompanying data to determine if this is the case for the glucose doses evaluated in this experiment. Based on maximal peak glucose concentrations and effects on glucose half-life, we identify 0.092 g of glucose/kg of BW (0.46 g/kg of metabolic body weight) as the preferred dose for the IVGTT for cows at 74 and 221 DIM in this study.

Effects of jugular infusions of isoleucine, leucine, methionine, threonine, and other amino acids on insulin and glucagon concentrations, mammalian target of rapamycin (mTOR) signaling, and lactational performance in goats

The supply and profile of absorbed AA may affect milk protein synthesis through hormonal changes and mammalian target of rapamycin (mTOR) signaling pathways; and Ile, Leu, Met, and Thr (ILMT) are the 4 AA that have been reported to have the greatest effect on mammary mTOR signaling. The extent to which ILMT and the other remaining AA (RAA) differ in their effects on milk protein synthesis needs to be systematically investigated. In this study, 5 lactating goats, averaging 120 ± 10 d in milk, fitted with jugular vein and carotid artery catheters, were fasted for 24 h, followed by intravenous infusions of a mixture containing AA and glucose for 8 h in a 5 × 5 Latin square design. The AA mixtures were formulated according to the profile of casein. The amounts of AA infused were calculated based on supplies of AA when metabolizable protein (MP) was at requirement (MR). Treatments were an infusate containing glucose without AA (NTAA); an infusate containing 3 × the MR of Ile, Leu, Met and Thr (3F0R); and infusates containing 3F0R plus 1, 2, or 3 × MR of RAA (3F1R, 3F2R, and 3F3R, respectively) according to amounts provided when fed to meet MP requirements for maintenance and lactation for each goat. Milk, arterial blood, and mammary tissue samples were collected immediately after halting the infusion. Relative to NTAA, supplementation of ILMT tended to increase milk protein production and plasma glucose concentrations, and increased milk and lactose production, but had no effects on production or content of milk fat. Graded supplementation of RAA tended to quadratically affect production of milk and lactose. Arterial glucose and glucagon concentrations decreased linearly, and plasma insulin concentrations decreased quadratically with increased RAA. Mammary p70-S6K1 phosphorylation was decreased by addition of ILMT compared with NTAA but increased linearly with increased RAA infusion. Furthermore, EIF4EBP1 gene expression was much lower for 3F-treated goats than for the NTAA treatment. Both MTOR and RPS6KB1 gene expressions were decreased quadratically with increased RAA supply. These results suggested that short-term milk protein yield tended to be increased by elevated ILMT availability, and this trend was not explained by variations in mammary mTOR signaling or pancreatic hormone secretions, whereas graded increase of RAA in combination with ILMT appeared to regulate the efficiency of conversion of glucose to lactose in a manner not involving milk protein production.

Standing on giant shoulders: a personal recollection of the lives and achievements of eminent animal scientists 1965–2015

This article is a compilation of pieces that are part biographical sketches and part personal recollections of 18 scientists with whom the author was acquainted in three continents over almost 50 years. The subjects, from Australia, the United States and the United Kingdom, will be recognisable to many in the field, especially more experienced scientists. For younger scientists, the article also is intended to put a human face on a generation of famous researchers who otherwise would be familiar only as somewhat anonymous authors of classic papers and reviews.

Peroxisome proliferator-activated receptor β/δ does not regulate glucose uptake and lactose synthesis in bovine mammary epithelial cells cultivated in vitro

The hypothesis of the study was that inhibition of PPARβ/δ increases glucose uptake and lactose synthesis in bovine mammary epithelial cells by reducing the expression of the glucose transporter mRNA destabiliser calreticulin. Three experiments were conducted to test the hypothesis using immortalised bovine mammary alveolar (MACT) and primary bovine mammary (PBMC) cells. In Experiment 1, the most effective dose to inhibit PPARβ/δ activity among two synthetic antagonists (GSK-3787 and PT-s58) was assessed using a gene reporter assay. In Experiment 2, the effect on glucose uptake and lactose synthesis was evaluated by measuring glucose and lactose in the media and expression of related key genes upon modulation of PPARβ/δ using GSK-3787, the synthetic PPARβ/δ agonist GW-501516, or a combination of the two in cells cultivated in plastic. In Experiment 3, the same treatments were applied to cells cultivated in Matrigel and glucose and lactose in media were measured. In Experiment 1 it was determined that a significant inhibition of PPARβ/δ in the presence or absence of fetal bovine serum was achieved with ≥ 1000 nm GSK-3787 but no significant inhibition was observed with PT-s58. In Experiment 2, inhibition of PPARβ/δ had no effect on glucose uptake and lactose synthesis but they were both increased by GW-501516 in PBMC. The mRNA abundance of PPARβ/δ target gene pyruvate dehydrogenase kinase 4 was increased but transcription of calreticulin was decreased (only in MACT cells) by GW-501516. Treatment with GSK-3787 did not affect the transcription of measured genes. No effects on glucose uptake or lactose synthesis were detected by modulation of PPARβ/δ activity on cells cultivated in Matrigel. The above data do not provide support for the original hypothesis and suggest that PPARβ/δ does not play a major role in glucose uptake and lactose synthesis in bovine mammary epithelial cells.

Effects of chronic dexamethasone administration on hyperglycemia and insulin release in goats

Background

Dexamethasone (Dex), a synthetic glucocorticoid, is among the most commonly used drugs worldwide in animals and humans as an anti-inflammatory and immunosuppressive agent. GC has profound effects on plasma glucose level and other metabolic conditions. However, the effect of prolonged use of Dex on glucose metabolism in ruminants is still unclear.

Results

Ten goats were randomly assigned to two groups: the control goats were injected with saline, and the Dex-treated goats were intramuscularly injected daily for 21 d with 0.2 mg/kg Dex. The results showed that plasma glucose and insulin concentrations were significantly increased after Dex administration (P < 0.05). Additionally, the content of hepatic glycogen was also markedly increased in Dex-treated goats (P < 0.01), while the content of glycogen in dorsal longissimus was unchanged by Dex (P > 0.05). The expression of several key genes, involved in blood glucose regulation, was detected by real-time PCR in the small intestine, skeletal muscle and liver. The expression of glucose transporter type 2 (GLUT2), sodium-glucose transporter 1 (SGLT1) and sodium-potassium ATPase (Na-K/ATPase) in the small intestine were generally increased by Dex, and GLUT2 mRNA expression was significantly up-regulated (P < 0.05). In liver, the expression of genes involved in gluconeogenesis including glucose-6-phosphatase catalytic subunit (G6PC), cytosolic form of phosphoenolpyruvate carboxykinase (PCK1) and pyruvate carboxylase (PC), were significantly down-regulated by Dex. However, the protein expression levels of PCK1 & PCK2 were significantly increased by Dex, suggesting a post-transcriptional regulation. In dorsal longissimus, the mRNA expression of genes associated with gluconeogenesis and the insulin signaling pathway were generally up-regulated by Dex, but the mRNA expression of two markers of muscle atrophy, namely F-box protein 32 (FBXO32/Atrogin1) and muscle RING-finger protein 1 (MuRF1), was not altered by Dex.

Conclusions

Taken together, these results indicate that chronic administration of a low dosage of Dex induces hyperglycemia mainly through gluconeogenesis activation in the goat liver.

Effects of graded removal of lysine from an intravenously infused amino acid mixture on lactation performance and mammary amino acid metabolism in lactating goats

To investigate responses of milk protein synthesis and mammary AA metabolism to a graded decrease of postruminal Lys supply, 4 lactating goats fitted with jugular vein, mammary vein, and carotid artery catheters and transonic blood flow detectors on the external pudic artery were used in a 4 × 4 Latin square experiment. Goats were fasted for 24 h and then received a 9-h intravenous infusion of an AA mixture plus glucose. Milk yield was recorded and samples were taken in h 2 to 8 of the infusion period; a mammary biopsy was performed in the last hour. Treatments were graded decrease of lysine content in the infusate to 100 (complete), 60, 30, or 0% as in casein. Lysine-removed infusions linearly decreased milk yield, tended to decrease lactose yield, and tended to increase milk fat to protein ratio. Milk protein content and yield were linearly decreased by graded Lys deficiency. Mammary Lys uptake was concomitantly decreased, but linear regression analysis found no significant relationship between mammary Lys uptake and milk protein yield. Treatments had no effects on phosphorylation levels of the downstream proteins measured in the mammalian target or rapamycin pathway except for a tended quadratic effect on that of eukaryotic initiation factor 2, which was increased and then decreased by graded Lys deficiency. Removal of Lys from the infusate linearly increased circulating glucagon and glucose. Removal of Lys from the infusate linearly decreased arterial and venous concentrations of Lys. Treatments also had a significant quadratic effect on venous Lys, suggesting mechanisms to stabilize circulating Lys at a certain range. The 2 infusions partially removing Lys resulted in a similar 20% decrease, whereas the 0% Lys infusion resulted in an abrupt 70% decrease in mammary Lys uptake compared with that of the full-AA mixture infusion. Consistent with the abrupt decrease, mammary Lys uptake-to-output ratio decreased from 2.2 to 0.92, suggesting catabolism of Lys in the mammary gland could be completely prevented when the animal faced severe Lys deficiency. Mammary blood flow was linearly increased, consistent with the linearly increased circulating nitric oxide by graded Lys deficiency, indicating mechanisms to ensure the priority of the mammary gland in acquiring AA for milk protein synthesis. Infusions with Lys removed increased mammary clearance rate of Lys numerically by 2 to 3 fold. In conclusion, the decreased milk protein yield by graded Lys deficiency was mainly a result of the varied physiological status, as indicated by the elevated circulating glucagon and glucose, rather than a result of the decreased mammary Lys uptake or depressed signals in the mTOR pathway. Mechanisms of Lys deficiency to promote glucagon secretion and mammary blood flow and glucagon to depress milk protein synthesis need to be clarified by future studies.

Effects of the standardized ileal digestible valine : lysine ratio on performance, milk composition and plasma indices of lactating sows

To determine the effects of standardized ileal digestible (SID) valine : lysine ratio on the performance, milk composition and plasma indices of lactating sows, 32 Large White × Landrace sows (219.78 ± 7.15 kg body weight; parity 1.82 ± 0.62) were allotted to one of four dietary treatments with eight sows per treatment based on parity, back fat thickness and body weight. The sows were fed corn-soybean meal-based diets containing 63, 83, 103 or 123% SID valine : lysine from day 107 of gestation until day 28 of lactation. The average daily feed intake of sows and daily weight gain of piglets increased linearly (P < 0.05) while back fat loss decreased linearly (P < 0.05) as the SID valine : lysine ratio increased. All of the analyzed amino acids in sow colostrum and valine concentrations of sow and piglet plasma increased linearly (P < 0.05) with the increasing SID valine : lysine ratio. In conclusion, 88 and 113% dietary SID valine : lysine ratios were optimal to achieve minimum back fat loss and maximum piglet growth rate using a linear-break point model which exceeds the requirement of 85% that is estimated by the National Research Council (2012).

RNA-Sequencing for profiling goat milk transcriptome in colostrum and mature milk

BACKGROUND

In this work we aimed at sequencing and assembling the goat milk transcriptome corresponding at colostrum and 120 days of lactation. To reconstruct transcripts we used both the genome as reference, and a de novo assembly approach. Additionally, we aimed at identifying the differentially expressed genes (DEGs) between the two lactation stages and at analyzing the expression of genes involved in oligosaccharides metabolism.

RESULTS

A total of 44,635 different transcripts, organized in 33,757 tentative genes, were obtained using the goat genome as reference. A significant sequence similarity match was found for 40,353 transcripts (90%) against the NCBI NT and for 35,701 (80%) against the NR databases. 68% and 69% of the de novo assembled transcripts, in colostrum and 120 days of lactation samples respectively, have a significant match with the merged transcriptome obtained using Cufflinks/Cuffmerge. CSN2, PAEP, CSN1S2, CSN3, LALBA, TPT1, FTH1, M-SAA3, SPP1, GLYCAM1, EEF1A1, CTSD, FASN, RPS29, CSN1S1, KRT19 and CHEK1 were found between the top fifteen highly expressed genes. 418 loci were differentially expressed between lactation stages, among which 207 and 122 were significantly up- and down-regulated in colostrum, respectively. Functional annotation and pathway enrichment analysis showed that in goat colostrum somatic cells predominate biological processes involved in glycolysis, carbohydrate metabolism, defense response, cytokine activity, regulation of cell proliferation and cell death, vasculature development, while in mature milk, biological process associated with positive regulation of lymphocyte activation and anatomical structure morphogenesis are enriched. The analysis of 144 different oligosaccharide metabolism-related genes showed that most of these (64%) were more expressed in colostrum than in mature milk, with eight expressed at very high levels (SLCA3, GMSD, NME2, SLC2A1, B4GALT1, B3GNT2, NANS, HEXB).

CONCLUSIONS

To our knowledge, this is the first study comparing goat transcriptome of two lactation stages: colostrum and 120 days. Our findings suggest putative differences of expression between stages and can be envisioned as a base for further research in the topic. Moreover because a higher expression of genes involved in immune defense response, carbohydrate metabolism and related to oligosaccharide metabolism was identified in colostrum we here corroborate the potential of goat milk as a natural source of lactose-derived oligosaccharides and for the development of functional foods.

Endogenous and exogenous factors influencing the concentrations of adiponectin in body fluids and tissues in the bovine

Adiponectin, one of the messenger molecules secreted from adipose tissue that are collectively termed adipokines, has been demonstrated to play a central role in lipid and glucose metabolism in humans and laboratory rodents; it improves insulin sensitivity and exerts antidiabetic and antiinflammatory actions. Adiponectin is synthesized as a 28 kDa monomer but is not secreted as such; instead, it is glycosylated and undergoes multimerization to form different molecular weight multimers before secretion. Adiponectin is one of the most abundant adipokines (μg/mL range) in the circulation. The concentrations are negatively correlated with adipose depot size, in particular with visceral fat mass in humans. Adiponectin exerts its effects by activating a range of different signaling molecules via binding to 2 transmembrane receptors, adiponectin receptor 1 and adiponectin receptor 2. The adiponectin receptor 1 is expressed primarily in the skeletal muscle, whereas adiponectin receptor 2 is predominantly expressed in the liver. Many of the functions of adiponectin are relevant to growth, lactation, and health and are thus of interest in both beef and dairy production systems. Studies on the role of the adiponectin protein in cattle have been impeded by the lack of reliable assays for bovine adiponectin. Although there are species-specific bovine adiponectin assays commercially available, they suffer from a lack of scientific peer-review of validity. Quantitative data about the adiponectin protein in cattle available in the literature emerged only during the last 3 yr and were largely based on Western blotting using either antibodies against human adiponectin or partial peptides from the bovine sequence. Using native bovine high-molecular-weight adiponectin purified from serum, we were able to generate a polyclonal antiserum that can be used for Western blot but also in an ELISA system, which was recently validated. The objective of this review is to provide an overview of the literature about the adiponectin protein in cattle addressing the following aspects: (1) the course of the adiponectin serum concentrations during development in both sexes, during inflammation, nutritional energy deficit and energy surplus, and lactation-induced changes including the response to supplementation with conjugated linoleic acids and with niacin, (2) the concentrations of adiponectin in subcutaneous vs visceral fat depots of dairy cows, (3) the protein expression of adiponectin in tissues other than adipose, and (4) the concentrations in different body fluids including milk.

Effects of glucose on lactose synthesis in mammary epithelial cells from dairy cow

Background

Lactose, as the primary osmotic component in milk, is the major determinant of milk volume. Glucose is the primary precursor of lactose. However, the effect of glucose on lactose synthesis in dairy cow mammary glands and the mechanism governing this process are poorly understood.

Results

Here we showed that glucose has the ability to induce lactose synthesis in dairy cow mammary epithelial cells, as well as increase cell viability and proliferation. A concentration of 12 mM glucose was the optimum concentration to induce cell growth and lactose synthesis in cultured dairy cow mammary epithelial cells. In vitro, 12 mM glucose enhanced lactose content, along with the expression of genes involved in glucose transportation and the lactose biosynthesis pathway, including GLUT1, SLC35A2, SLC35B1, HK2, β4GalT-I, and AKT1. In addition, we found that AKT1 knockdown inhibited cell growth and lactose synthesis as well as expression of GLUT1, SLC35A2, SLC35B1, HK2, and β4GalT-I.

Conclusions

Glucose induces cell growth and lactose synthesis in dairy cow mammary epithelial cells. Protein kinase B alpha acts as a regulator of metabolism in dairy cow mammary gland to mediate the effects of glucose on lactose synthesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0704-x) contains supplementary material, which is available to authorized users.

Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation

The demand for high-quality milk is increasing worldwide. The efficiency of milk synthesis can be improved by taking advantage of the accumulated knowledge of the transcriptional and posttranscriptional regulation of genes coding for proteins involved in the synthesis of fat, protein, and lactose in the mammary gland. Research in this area is relatively new, but data accumulated in the last 10 years provide a relatively clear picture. Milk fat synthesis appears to be regulated, at least in bovines, by an interactive network between SREBP1, PPARγ, and LXRα, with a potential role for other transcription factors, such as Spot14, ChREBP, and Sp1. Milk protein synthesis is highly regulated by insulin, amino acids, and amino acid transporters via transcriptional and posttranscriptional routes, with the insulin-mTOR pathway playing a central role. The transcriptional regulation of lactose synthesis is still poorly understood, but it is clear that glucose transporters play an important role. They can also cooperatively interact with amino acid transporters and the mTOR pathway. Recent data indicate the possibility of nutrigenomic interventions to increase milk fat synthesis by feeding long-chain fatty acids and milk protein synthesis by feeding amino acids. We propose a transcriptional network model to account for all available findings. This model encompasses a complex network of proteins that control milk synthesis with a cross talk between milk fat, protein, and lactose regulation, with mTOR functioning as a central hub.

Biology of glucose transport in the mammary gland

Glucose is the major precursor of lactose, which is synthesized in Golgi vesicles of mammary secretory alveolar epithelial cells during lactation. Glucose is taken up by mammary epithelial cells through a passive, facilitative process, which is driven by the downward glucose concentration gradient across the plasma membrane. This process is mediated by facilitative glucose transporters (GLUTs), of which there are 14 known isoforms. Mammary glands mainly express GLUT1 and GLUT8, and GLUT1 is the predominant isoform with a Km of ~10 mM and transport activity for mannose and galactose in addition to glucose. Mammary glucose transport activity increases dramatically from the virgin state to the lactation state, with a concomitant increase in GLUT expression. The increased GLUT expression during lactogenesis is not stimulated by the accepted lactogenic hormones. New evidence indicates that a possible low oxygen tension resulting from increased metabolic rate and oxygen consumption may play a major role in stimulating glucose uptake and GLUT1 expression in mammary epithelial cells during lactogenesis. In addition to its primary presence on the plasma membrane, GLUT1 is also expressed on the Golgi membrane of mammary epithelial cells and is likely involved in facilitating the uptake of glucose and galactose to the site of lactose synthesis. Because lactose synthesis dictates milk volume, regulation of GLUT expression and trafficking represents potentially fruitful areas for further research in dairy production. In addition, this research will have pathological implications for the treatment of breast cancer because glucose uptake and GLUT expression are up-regulated in breast cancer cells to accommodate the increased glucose need.

Effects of glucose availability on expression of the key genes involved in synthesis of milk fat, lactose and glucose metabolism in bovine mammary epithelial cells

As the main precursor for lactose synthesis, large amounts of glucose are required by lactating dairy cows. Milk yield greatly depends on mammary lactose synthesis due to its osmoregulatory property for mammary uptake of water. Thus, glucose availability to the mammary gland could be a potential regulator of milk production. In the present study, the effect of glucose availability on expression of the key genes involved in synthesis of milk fat, lactose and glucose metabolism in vitro was investigated. Bovine mammary epithelial cells (BMEC) were treated for 12 h with various concentrations of glucose (2.5, 5, 10 or 20 mmol/L). The higher concentrations of glucose (10-20 mmol/L) did not affect the mRNA expression of acetyl-CoA carboxylase, diacyl glycerol acyl transferase, glycerol-3 phosphate acyl transferase and α-lactalbumin, whereas fatty acid synthase, sterol regulatory element binding protein-1 and beta-1, 4-galactosyl transferase mRNA expression increased at 10 mmol/L and then decreased at 20 mmol/L. The content of lactose synthase increased with increasing concentration of glucose, with addition of highest value at 20 mmol/L of glucose. Moreover, the increased glucose concentration stimulated the activities of pyruvate kinase and glucose-6-phosphate dehydrogenase, and elevated the energy status of the BMEC. Therefore, it was deduced that after increasing glucose availability, the extra absorbed glucose was partitioned to entering the synthesis of milk fat and lactose by the regulation of the mRNA expression of key genes, promoting glucose metabolism by glycolysis and pentose phosphate pathway as well as energy status. These results indicated that the sufficient availability of glucose in BMEC may promote glucose metabolism, and affect the synthesis of milk composition.

Functional analyse of GLUT1 and GLUT12 in glucose uptake in goat mammary gland epithelial cells

Glucose transport, mediated by glucose transporters, is necessary for mammary gland development and lactation. GLUT1 and GLUT12 could both be expressed in the pregnant and lactating mammary gland to participate in the glucose uptake process. In this study, the goat GLUT1 and GLUT12 genes were cloned from Saanen dairy goats and transfected into goat mammary gland epithelial cells to assess their biological functions and distributions. The results showed that both goat GLUT1 and GLUT12 had 12 predicted membrane-spanning helices. Goat GLUT1 and GLUT12 each influenced the mRNA expression of the other transporter and increased the glucose consumption and lactose yield in GLUT1- and GLUT12-transfected goat mammary gland epithelial cells, respectively. The overexpression of GLUT1 or GLUT12 also increased the expression of amino acid transporters SLC1A5, SLC3A2 and SLC7A5 and affected genes expressions in GMGE cells. Using immunofluorescence staining, GLUT1 was detected throughout the cytoplasm and localized to the Golgi apparatus around the nuclear membrane, whereas GLUT12 was mainly distributed in the perinuclear region and cytoplasm. This study contributes to the understanding of how GLUT1 and GLUT12 cooperate in the incorporation of nutrient uptake into mammary gland epithelial cells and the promotion of milk synthesis in the goat mammary gland during lactation.

Regulation of leucine catabolism by metabolic fuels in mammary epithelial cells

Lactation is associated with elevated catabolism of branched-chain amino acids (BCAA) in mammary glands to produce glutamate, glutamine, alanine, aspartate, and asparagine. This study determined effects of metabolic fuels on the catabolism of leucine (a representative BCAA) in bovine mammary epithelial cells. Cells were incubated at 37 °C for 2 h in Krebs buffer containing 0.5 mM L-leucine and either L-[1-(14)C]leucine or L-[U-(14)C]leucine. The medium also contained 0-5 mM D-glucose, 0-2 mM L-glutamine, 0-4 mM DL-β-hydroxybutyrate, or 0-2 mM oleic acid. Rates of leucine decarboxylation were 60 % lower, but rates of α-ketoisocaproate production were 34 % higher, in the presence of 2 mM glucose than in its absence. All variables of leucine catabolism did not differ between 2 and 5 mM glucose or between 0 and 4 mM DL-β-hydroxybutyrate. Compared with 0-0.25 mM glutamine, 0.5 and 2 mM L-glutamine reduced leucine transport, transamination, and decarboxylation. In contrast, increasing the concentration of oleic acid from 0 to 2 mM dose-dependently stimulated leucine transamination, decarboxylation, and oxidation of carbons 2-6. Oleic acid also enhanced the abundance of cytosolic BCAA transaminase, while reducing the phosphorylated level (inactive state) of the E1α subunit of the mitochondrial branched-chain α-ketoacid dehydrogenase complex. Thus, hypoglycemia or ketosis in early lactation does not likely affect BCAA metabolism in mammary epithelial cells. Increasing circulating levels of BCAA and oleic acid may have great potential to increase the syntheses of glutamate, glutamine, aspartate, alanine, and asparagine by lactating mammary glands, thereby leading to enhanced production of milk for suckling neonates.

The oxidation and utilization of palmitate, stearate, oleate and acetate by the mammary gland of the fed goat in relation to their overall metabolism, and the role of plasma phospholipids and neutral lipids in milk-fat synthesis

1. Measurements were made of milk yield, mammary blood flow and arteriovenous differences of each plasma lipid fraction, and their specific radioactivities, during the infusion of [U-(14)C]stearate, [U-(14)C]oleate, [U-(14)C]palmitate and [1-(14)C]acetate into fed lactating goats. 2. Entry rates of fatty acids into the circulation were 4.2mg./min./kg. body wt. for acetate, and 0.18, 0.28 and 0.42mg./min./kg. for stearate, oleate and palmitate respectively. Acetate accounted for 23% of the total carbon dioxide produced by the whole animal, and contributed to the oxidative metabolism of the mammary gland to about the same extent. Corresponding values for each of the long-chain acids were less than 1%. 3. There were no significant arteriovenous differences of phospholipids, sterols or sterol esters, and their fatty acid composition showed no net changes during passage through the mammary gland. 4. There were large arteriovenous differences of plasma triglycerides, and their fatty acid composition showed marked changes across the gland. The proportions of palmitate and stearate fell, and that of oleate increased. 5. Arteriovenous differences of plasma free fatty acids (FFA) were small and variable, but a large fall in the specific radioactivity of each of the long-chain acids examined indicated substantial uptake of plasma FFA, accompanied by roughly equivalent FFA release from mammary tissue. The uptake of FFA was confirmed by the extensive transfer of radioactivity into milk. The FFA of milk were similar in composition and radioactivity to the milk triglyceride fatty acids, and quite unlike plasma FFA. 6. The formation of large amounts of oleic acid (18-21 mg./min.) from stearic acid was demonstrated. 7. During the terminal stages of the [(14)C]acetate infusion, milk triglyceride fatty acids of chain length C(4)-C(14) showed specific radioactivities that were 75-90% of that of blood acetate, and that of palmitate was roughly one-quarter of this value. Oleate and stearate were unlabelled. 8. The results confirmed that milk fatty acids of chain length C(4)-C(14) arise largely from blood acetate, and palmitate is derived partly from acetate and partly from plasma triglyceride, the latter fraction being almost the sole precursor of oleate and stearate.

Carnitine secretion into milk of ruminants

Total acid-soluble carnitine concentration in cow's, goat's and ewe's milk was 117, 101 and 872 nmol/ml respectively, of which acetylcarnitine made up 30% in goats, 10% in cows and 11% in ewes. The concentration of carnitine in the arterial blood of goats decreased significantly (P < 0·01) with the onset of lactation from 18·1 to 8·4nmol/ml and during lactation in goats and cows there was a significant arterio-venous difference of carnitine across the udder, with mean extractions of 14 and 5% respectively. Calculation of the udder uptake of carnitine, from these figures and from udder blood-flows, showed that in goats the amount lost in the milk was much less than that taken from the blood, but in cows about the same. Two groups of lactating ewes on low and high nutritional planes were sampled at 2-weekly intervals from 2 to 8 weeks of lactation. The concentrations of total acid-soluble carnitine and acetylcarnitine in the milk were similar in the 2 groups and remained relatively constant over this period, but the total acid-soluble carnitine concentration in jugular blood from the ewes on the low nutritional plane was significantly (P < 0·01) higher than from the ewes on the higher nutritional plane from the fourth week of lactation. The total acid-soluble carnitine concentration in liver of goats was 290 nmol/g wet wt; mammary gland, 324; kidney-cortex, 692; heart, 2030 and skeletal muscle, 14300. Carnitine acetyltransferase (E.C. 2.3.1.7) activity of mammary tissue from lactating ewes was 0·6 μmol per min per g wet wt of which approximately half appeared to be ‘latent’ or membrane bound. Acetate thiokinase (E.C. 6.2.1.1) activity in this tissue was found to be 1·5 μmol per min per g wet wt and was predominantly localized in the cytoplasm. Carnitine palmitoyltransferase (E.C. 2.3.1.21) activity in the same tissue was 0·8 μmol per min per g wet wt while no acetylcarnitine hydrolase activity could be detected. The results suggest that carnitine in mammary tissue is extracted from the blood for the oxidation of both acetate and long-chain fatty acids and that some is lost in the milk.

Perspectives on ruminant nutrition and metabolism. II. Metabolism in ruminant tissues

The discovery of the dominance of short-chain fatty acids as energy sources in the 1940s and 1950s, as discussed in part I of this review (Annison & Bryden, 1998) led to uncertainties concerning the interrelationships of glucose and acetate in ruminant metabolism. These were resolved in the following decade largely by use of14C-labelled substrates. Although only small amounts of glucose are absorbed in most dietary situations, glucose availability to ruminant tissues as measured by isotope dilution was shown to be substantial, indicating that gluconeogenesis is a major metabolic activity in both fed and fasted states. Studies with14C-labelled glucose and acetate revealed that in contrast to non-ruminants, acetate and not glucose is the major precursor of long-chain fatty acids in ruminant tissues. Interest in the measurement of energy metabolism in livestock grew rapidly from the 1950s. Most laboratories adopted indirect calorimetry and precise measurements of the energy expenditure of ruminants contributed to the development of new feeding systems. More recently, alternative approaches to the measurement of energy expenditure have included the use of NMR spectroscopy, isotope dilution and the application of the Fick principle to measure O2consumption in the whole animal and in defined tissues. The refinement of the classical arterio-venous difference procedure in the study of mammary gland metabolism in the 1960s, particularly when combined with isotope dilution, encouraged the use of these methods to generate quantitative data on the metabolism of a range of defined tissues. The recent introduction of new methods for the continuous monitoring of both blood flow and blood O2content has greatly increased the precision and scope of arterio-venous difference measurements. The impact of data produced by these and other quantitative procedures on current knowledge of the metabolism of glucose, short-chain fatty acids and lipids, and on N metabolism, is outlined. The role of the portal-drained viscera and liver in N metabolism is discussed in relation to data obtained by the use of multi-catheterized animals. Protein turnover, and the impact of stress (physical, social and disease related) on protein metabolism have been reviewed. The growth of knowledge of mammary gland metabolism and milk synthesis since the first quantitative studies in the 1960s has been charted. Recent findings on the regulation of amino acid uptake and utilization by the mammary gland, and on the control of milk secretion, are of particular interest and importance.

Expression and regulation of glucose transporters in the bovine mammary gland

Glucose is the primary precursor for the synthesis of lactose, which controls milk volume by maintaining the osmolarity of milk. Glucose uptake in the mammary gland plays a key role in milk production. Glucose transport across the plasma membranes of mammalian cells is carried out by 2 distinct processes: facilitative transport, mediated by a family of facilitative glucose transporters (GLUT); and sodium-dependent transport, mediated by the Na+/glucose cotransporters (SGLT). Transport kinetic studies indicate that glucose transport across the plasma membrane of the lactating bovine mammary epithelial cell has a K(m) value of 8.29 mM for 3-O-methyl-D-glucose and can be inhibited by both cytochalasin-B and phloretin, indicating a facilitative transport process. This is consistent with the observation that in the lactating bovine mammary gland, GLUT1 is the predominant glucose transporter. However, the bovine lactating mammary gland also expresses GLUT3, GLUT4, GLUT5, GLUT8, GLUT12, and sodium-dependent SGLT1 and SGLT2 at different levels. Studies of protein expression and cellular and subcellular localizations of these transporters are needed to address their physiological functions in the mammary gland. From late pregnancy to early lactation, expression of GLUT1, GLUT8, GLUT12, SGLT1, and SGLT2 mRNA increases from at least 5-fold to several hundred-fold, suggesting that these transporters may be regulated by lactogenic hormones and have roles in milk synthesis. The GLUT1 protein is detected in lactating mammary epithelial cells. Its expression level decreases from early to late lactation stages and becomes barely detectable in the nonlactating gland. Both GLUT1 mRNA and protein levels in the lactating mammary gland are not significantly affected by exogenous bovine growth hormone, and, in addition, GLUT1 mRNA does not appear to be affected by leptin.

The recycling of carbon in glucose, lactate and alanine in sheep

Pregnant ewes with catheters implanted in an artery and the uterine and recurrent tarsal veins were infused at a constant rate with U-(14)C-labelled glucose, alanine or bicarbonate. Measurements were made of the overall and local fractional contribution of glucose and alanine to CO(2) production and of the extent of interconversion of these metabolites. In the whole animal, by coupling the results with the authors' previous study of lactate metabolism, a solution was obtained to an open unrestricted 4-compartment model of the exchange of carbon between glucose, lactate, alanine and CO(2). A more limited study was made with non-pregnant sheep because complete data for lactate interactions with alanine were not available. Our analysis of glucose/lactate/alanine/CO(2) interactions in pregnant sheep suggests that about two-thirds of the glycogenic carbon was oxidised fairly directly to CO(2). There was relatively little recycling of glucose carbon through lactate and alanine so that most of the remaining glycogenic carbon was stored as product with relatively long turnover time. It is possible that much of this was in the form of muscle glycogen, and analysis of glycogenic carbon exchange across the hind limb muscle was consistent with this conclusion. In non-pregnant ewes, the findings, although incomplete, suggested that there were no great differences from the findings in pregnant ewes.

Glucose metabolism in crossbred Holstein cattle feeding on two types of roughage at different stages of lactation

An experiment was performed to study the glucose kinetics of crossbred Holstein cattle feeding on either hay or 5% urea-treated rice straw during early lactation (30 days post partum), mid-lactation (120 days post partum) and late lactation (210 days post partum). Two breeds: Holstein FriesianxRed Sindhi (50:50 = 50% HF) and Holstein FriesianxRed Sindhi (87.5:12.5 = 87.5% HF) were used. In early lactating 87.5% HF animals feeding on either hay or urea-treated rice straw, the high milk yields and lactose secretion were related to glucose uptake by the udder and udder blood flow as compared with those of 50% HF animals. Marked decreases in udder blood flow, glucose uptake, lactose secretion and milk yield were apparent in mid- and late lactation of both groups of 87.5% HF animals. In contrast, both groups of 50% HF animals showed no significant changes in udder blood flow, udder glucose uptake, lactose secretion and milk yields throughout the course of lactation. Total glucose entry rate using 3-[3H] glucose infusion, recycling of glucose carbon and plasma glucose clearance significantly increased during late lactation for 50 and 87.5% HF animals feeding on urea-treated rice straw. The utilization rates of glucose using [U-(14)C] glucose infusion were not significantly different among groups of animals and periods of lactation. It can be concluded that 87.5% HF animals have the genetic potential for a higher milk yield, but a shorter peak yield and poorer persistence in comparison with 50% HF animals. Changes in the utilization of glucose by the mammary gland for milk production in both groups of crossbred animals during feeding on either hay or urea-treated rice straw would be dependent on intramammary changes.

Glucose metabolism in vivo in crossbred Holstein cattle feeding on different types of roughage during late pregnancy and early lactation

An experiment was carried out to study the glucose kinetics of crossbred Holstein cattle feeding on either hay or 5% urea treated rice straw during late pregnancy (21 days prepartum) and early lactation (30 days postpartum). In all 16 pregnant heifers (23-25 months of age) were selected for the experiments, including eight animals of two breed types, Holstein Friesian x Red Sindhi (50:50 = 50% HF) and Holstein Friesian x Red Sindhi (87.5:12.5 = 87.5% HF). They were divided into four groups of four animals each. Animals from the same breed type in each group were fed with either rice straw treated with 5% urea or pangola hay (Digitaria decumbens) as the source of roughage throughout the experiments. The glucose turnover rate in both types of crossbred Holstein cattle was determined using a continuous infusion of [U-14C] and 3-[3H]glucose during late pregnancy and early lactation. Total glucose entry and utilization rates increased significantly during lactation for all groups. Recycling of [C]glucose was, approximately 20% in both crossbred cattle fed either hay or urea treated rice straw and was unaffected by the stage of late pregnancy or early lactation. Comparing 50 and 87.5% HF animals, arterial plasma glucose concentrations were slightly higher during pregnant periods but significantly higher in lactating periods in 50% HF animals. The ratio of specific radioactivity of arterial blood bicarbonate relative to that of arterial blood [14C]glucose in the lactating period, significantly decreased in 50% HF animals fed either urea treated rice straw or hay. An increase in udder blood flow during early lactation was significantly higher in 87.5% HF animals than in 50% HF animals. The uptake, arteriovenous differences and extraction ratio for glucose across the udder, significantly increased in the lactating period for all crossbred animals. Glucose uptake by the udder of 87.5% HF animals accounted for 65% of the total glucose turnover rate compared to a value of 46% in the lactating 50% HF animals. It can be concluded that both crossbred cattle fed either urea treated rice straw or hay exhibit the same body glucose turnover rate. The 87.5% HF animal has the genetic potential for a high milk yield and has high body and udder glucose metabolisms compared with 50% HF animals.

THE INCORPORATION OF CARBON DIOXIDE INTO MILK CITRATE IN THE ISOLATED PERFUSED GOAT UDDER

1. Isolated perfused goat udders supplied with glucose, acetate and amino acids were infused for several hours with NaH(14)CO(3). 2. Lactose, milk-fat fatty acids and glycerol had very little radioactivity. The specific radioactivity (counts./min./mg. of C) of milk citrate was 9-16% that of the carbon dioxide in the perfusion fluid and 19% that estimated for tissue carbon dioxide. The specific radioactivity of tissue citrate resembled that of milk citrate. 3. The radioactivity in citrate was predominantly in C-6, suggesting some carboxylation of alpha-oxoglutarate in addition to carboxylation of C(3) compounds. 4. [1-(14)C]Glutamate was infused in a similar experiment, and milk citrate radioactivity was predominantly in C-1+C-5. 5. The results are discussed in relation to the contribution of glucose and acetate carbon to citrate. The implications of the carboxylation of alpha-oxoglutarate are considered.

Localization and gene expression of glucose transporters in bovine mammary gland

Glucose uptake in the mammary gland is a rate-limiting step in milk synthesis. To study glucose transporters in the bovine mammary gland, the erythrocyte-type glucose transporter (GLUT1) and the insulin-responsive glucose transporter (GLUT4) proteins were assessed by Western blotting and immunohistochemical staining, using polyclonal antibodies against the C-terminal peptide of GLUT1 and GLUT4. Our results demonstrated that the bovine mammary gland expressed a relatively high level of GLUT1 protein, whereas GLUT4 protein was not detected in the mammary gland of either lactating or dry cows. The absence of GLUT4 may indicate that glucose transport is not regulated by insulin in the lactating and dry bovine mammary gland. The anti-GLUT1 antibody strongly stained the single layer of epithelial cells of mammary alveoli. The expression of GLUT1 mRNA was similar in the mammary gland of late lactation and non-lactating cows. However, a smaller molecular weight species (38 kDa) of GLUT1 protein was detected in the mammary gland of non-lactating cows where its abundance in crude membrane preparation was 80% higher than in lactating animals. There were no significant differences in GLUT1 mRNA in bovine mammary gland at 118 d and 181 d postpartum, however, GLUT1 protein expression tended to be greater at 118 d postpartum.

Changes in mammary glucose and protein uptake in relation to milk synthesis during lactation in high- and low-yielding goats

1. Glucose and protein uptake were measured in both mammary glands of two low- and two high-yielding dairy goats during lactation. 2. Low-yielding goats tended to have higher arterial glucose concentrations, but approximately 40% lower arterio-venous differences (AV) and extraction rates (E) for glucose than high-yielding goats. 3. AV and E for glucose (but not protein) were linearly related to yields of both lactose, milk protein and fat. 4. Mammary uptake of glucose is determined primarily by mammary glucose metabolism, not glucose supply; lower intracellular glucose concentration in mammary cells of genetically superior animals thus explains the more efficient mammary uptake.

Effects of decreased availability of glucose for dairy cows

After a preliminary trial to establish dose responses to phlorizin, five Holstein cows at 6 wk postpartum were used to test the response of cows in negative energy balance to a sudden decrease in availability of glucose caused by phlorizin. Cows were fed equal amounts of feed twice daily to supply 100% of NRC recommendations for protein and 90% of NRC recommendations for NEL and were in negative energy balance throughout the experiment. Phlorizin at 0, 2, and 4 g/d was injected subcutaneously in equal amounts every 6 h for 48 h and caused excretion of 0, 225, and 337 g/d of glucose in urine. Milk production was not decreased, but percentage of milk fat increased linearly (3.34, 3.56, and 3.70%) with increasing phlorizin. Concentrations of glucose (64.2, 62.6, and 59.4 mg/dl) and insulin (518, 432, and 329 pg/ml) in blood plasma decreased linearly, whereas beta-hydroxybutyrate (6.11, 8.88, and 9.98 mg/dl) and NEFA (181, 220, and 271 mu eq/L) increased linearly. The changes were most dramatic during the final 12 h of the 48-h injection interval. Healthy, early lactation cows in negative energy balance seem to have the capacity to make metabolic adjustments to provide adequate substrates for maintenance and milk synthesis and to compensate for short-term increased needs for glucose.

Protein synthesis and degradation in the mammary gland of lactating goats

Lactating goats were given a close arterial infusion of [1-14C]leucine and [4,5-3H]4-methyl-2-oxopentanoic acid into one half of the mammary gland at 2-3 weeks and 34-39 weeks after kidding. Rates of protein synthesis, degradation and net output were determined from measurements of arteriovenous difference and blood flow using a model of leucine metabolism previously developed for muscle (Oddy & Lindsay, 1986). Protein leucine output in milk (Y mumol/min) correlated well with the difference between synthesis and degradation (X mumol/min) derived from the model: Y = 1.30 + 1.24X (r2 = 0.9; n = 9, P less than 0.01). There was substantial synthesis and degradation of protein within the mammary gland. Although only an approximate value could be obtained for the partitioning of protein synthesis and degradation between tissue and milk proteins, there was evidence of appreciable turnover of both. There was no significant difference between mammary leucine and protein metabolism in early and late lactation other than that imparted by a greater mass of mammary tissue in early lactation, although there was a tendency for greater oxidation of leucine in late lactation.

Effect of season and stage of lactation on plasma insulin and glucose following glucose injection in Holstein cattle

Changes in plasma glucose and insulin concentrations following glucose injection in dairy cows (six per stage of lactation per season) were characterized during early, middle, and late lactation in winter, spring, and summer. Blood samples were collected 60, 45, 30, 20, 15, 10, 5, and 0 min (period 1) before glucose injection (.1 g/kg body weight) and at 5, 10, 15, 20, 30, 45, and 60 min (period 2) after injection. Plasma insulin concentrations were affected by season, period, season by period interaction, and time within period. Plasma glucose was affected by period, time within period, and stage of lactation by period interaction. Insulin was lowest in summer. Magnitude of insulin response to glucose was highest in spring. Both plasma glucose and insulin increased significantly 5 min following glucose injection. Peak glucose concentrations increased with advancing lactation. Results indicate alterations in glucose metabolism as well as changes in insulin sensitivity to glucose in various seasons and stages of lactation.

Blood glucose kinetics in whole body and mammary gland of lactating goats exposed to heat

Whole-body and mammary kinetics of blood glucose were measured in lactating goats exposed to thermoneutral, moderate hot, and severe hot environments for 4 d. Milk yields were reduced by 3 and 13% during moderate and severe heat exposure, but heat production was unchanged during the experiment. Concentrations of plasma glucose and free fatty acids did not change during heat exposure. Concentration of thyroxine tended to decrease and concentration of prolactin increased with increasing temperature. Whole-body turnover of blood glucose decreased significantly during both moderate and severe heat exposure. Blood glucose oxidation rate and contribution of blood glucose to total carbon dioxide production were not influenced by heat exposure. Mammary glucose uptake tended to decrease during heat exposure, and this reduction may account for the decreased whole-body turnover of blood glucose. The lactose concentration in milk was decreased on the 4th d of severe heat exposure. A relatively low production of milk lactose was apparently derived from blood glucose. These results suggest that the whole-body turnover of blood glucose decreases in step with a decrease in mammary glucose uptake during heat exposure in lactating goats.