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.

Expression of hepatic genes related to energy metabolism during the transition period of Holstein and F1 Holstein-Gir cows.

The aim of this study was to investigate the expression of genes encoding enzymes and other factors involved with carbohydrate and lipid metabolism in the liver of 2 genetic groups of dairy cows during the transition period. We analyzed the expression of glucose-6-phosphatase (G6PC), cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), methylmalonyl-CoA mutase (MUT), ß-hydroxybutyrate dehydrogenase-2 (BDH2), acetyl-CoA carboxylase (ACC), carnitine palmitoyltransferase-2 (CPT2), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), glucose transporter-2 (SLC2A2), and the transcription factor peroxisome proliferator-activated receptor α (PPARA). Blood concentrations of glucose, nonesterified fatty acids, and ß-hydroxybutyrate were also determined. Liver biopsies and blood samples were taken at d 15 prepartum and at d 6, 21, 36, 51, and 66 postpartum from Holsteins (n = 6) and F1 Holstein-Gir (n = 6) cows. Cows were kept under the same prepartum and postpartum management conditions. The results showed that the expression of G6PC, PEPCK-C, BDH2, ACC, CPT2, HMGCR, SLC2A2, and PPARA genes did not differ between genetic groups. Except for PEPCK-C, no interaction between genetic groups and the experimental period was observed. Within both groups of cows, G6PC and PEPCK-C gene expression decreased when comparing prepartum gene expression with 21 and 36 DIM, and increased in d 51 postpartum. MUT mRNA levels differed between the 2 genetic groups and displayed a significant increase after d 36 postpartum, whereas mRNA levels of HMGCR tended to increase when comparing d 21 and 36 to d 51 postpartum. Glucose concentrations also differed between genetic groups, being significantly higher in the plasma of F1 Holstein-Gir cows than in Holstein cows, but no differences were found within each group during the analysis period. ß-Hydroxybutyrate and nonesterified fatty acid concentrations did not differ between genetic groups, but displayed increased levels from prepartum to d 6 and 21 postpartum. Our results indicated that expression in the liver of genes involved with glucose and fatty acid metabolism were similar in both groups of cows and significant differences were observed between the 2 groups in the expression of MUT, a gene involved in propionate metabolism.

Alimentação de vacas F1 Holandês x Zebu com suplementos nitrogenados e monensina sódica: avaliação do consumo, parâmetros ruminais e produção de leite / Feeding F1 Holstein x Zebu cows with nitrogenated supplements and sodic monensin: feed intake, ruminal parameters and milk production

Avaliaram-se suplementos nitrogenados contendo ou não monensina sódica, adicionados à silagem, sobre o consumo de matéria seca (CMS), a digestibilidade da MS (DMS) e a produção de vacas F1 Holandês x Zebu. Vacas (n=15) com 21 dias em lactação, produzindo 19,2kg/dia, foram distribuídas em um delineamento quadrado latino 5X5, com três vacas por tratamento (T). Os T foram: 1- concentrado durante as ordenhas e silagem de milho após as ordenhas (C.SM); 2- C.SM + nitromineral (C.SMNM); 3- C.SM + nitroproteico (C.SMNP), 4- C.SMNM + monensina (C.SMNM+MO) e 5- C.SMNP + monensina (C.SMNP+MO). Os suplementos NP e NM adicionados à SM, (C.SMNP e C.SMNM) aumentaram o CMS (P<0,05). A adição de monensina não alterou o CMS nem a DMS (P>0,05). A suplementação proteica não aumentou o acetato (P>0,05), mas aumentou o propionato e o butirato (P<0,05). A adição de MO ao T C.SMNP reduziu o propionato e o butirato (P<0,05) em relação ao T C.SMNP. A concentração de nitrogênio amoniacal aumentou (P<0,05) no T C.SMNM em relação ao T C.SM e não diferiu dos demais. As produções de leite nos T C.SMNP e C.SMNPMO foram maiores do que no T C.SM (P<0,05). Vacas do T C.SM foram mais eficientes produzindo leite do que as do T C.SMNM (P<0,05).

The objectives of this study were to evaluate consumption, ruminal parameters and milk production of F1 Holstein x Zebu milking cows fed nitrogenated supplements with or without monensin added to the silage. Cows with 21 days on milk and producing initially 19.2kg of milk/day were distributed in a 5X5 Latin square design with three replicates per treatment. The treatments (T) were: 1- concentrate fed during the milking time and corn silage fed after milking (C.SM); 2- C.SM + nitromineral(NM) (C.SMNM); 3- C.SM + nitroproteico (NP) (C.SMNP); 4- C.SMNM + monensin (C.SMNM+MO) e 5- C.SMNP + monensin (C.SMNP+MO). The addition of NP e NM to the T C.SM increased the DMI when compared to C.SM (P<0.05). The addition of monensin did not change the DMI (P>0,05). The protein supplementation did not alter acetate (P>0,05), but increased propionate and butyrate concentrations. (P<0.05) The N-NH3 concentration increased (P<0.05) only in T C.SMNM (P<0.05). The addition of monensin to T C.SMNP decreased propionate and butyrate concentrations (P<0.05) related to T C.SMNP. The milk production was greater in the C.SMNP treatments than T C.SM (P<0.05). Cows in T C.SM produced milk more efficiently than cows fed C.SMNM (P<0.05), but did not differ from the others.