The effect of intestinal glucose supply on whole body rate of glucose appearance (WBGRa) and mammary utilization of glucose was studied in four lactating dairy cows. Glucose (0, 443, 963 and 2398 g/d) was continuously infused in the duodenum over 14-d periods using a Latin square design. A grass silage-based diet was formulated so that treatments were isoenergetic and isonitrogenous and contained 100 and 110% of energy and protein requirements according to INRA (1989). The WBGRa was measured by the [6,6-(2)H2]glucose dilution technique, and mammary glucose balance by arteriovenous differences and blood flow measurements. Duodenal glucose infusion increased arterial glucose concentrations linearly, whereas arterial concentrations of insulin, growth hormone, and glucagon were not changed. The WBGRa increased linearly with increasing glucose loads. The increase represented 42% of the intestinal glucose supplement. Mammary blood flow dramatically increased (up to 45%) and was associated with a significant increase of arterial insulin-like growth factor-1 concentrations. Mammary gland rate of glucose disappearance ([6,6-(2)H2]glucose measurement) increased linearly, whereas net mammary balance of glucose, lactose, and milk yields increased quadratically. Net mammary balance of glucose accounted for 60% of WBGRa, except for the greatest dose (47.6%). The decrease in milk yield with 2398 g/d of glucose may be explained by an imbalance in intracellular intermediate concentrations. The milk ratio of glucose-1-phosphate to glucose-6-phosphate decreased significantly at the greatest infusion of glucose. In conclusion, exogenous glucose supply to a grass silage-based diet increased WBGRa, mammary utilization of glucose and milk synthesis.

The objective of this study was to investigate the effects on plasma metabolites and rumen traits when butyrate was infused into the rumen or abomasum of lactating cows. Jugular catheters were inserted into 5 ruminally fistulated Holstein cows [94.2 ± 26.3 DIM; 717 ± 45 kg of body weight (BW); mean ± SD] in a 5 × 5 Latin square with 3-d periods. Cows were infused for 24 h with 1 of 5 treatments: water (CON), 1 g/kg of BW of butyrate infused into either the abomasum (A1) or rumen (R1), or 2 g/kg of BW of butyrate infused into either the abomasum or rumen. Sodium butyrate was the source of butyrate and NaCl was added to the CON, A1, and R1 treatments to provide the same amount of sodium as supplied by the sodium butyrate treatment in the 2-g treatments. Plastisol flanges were inserted into the abomasum to allow infusion to the abomasum and peristaltic pumps provided continuous infusion at 9.3 mL/min for all treatments. The concentration of NaCl and sodium butyrate was varied in the infusate to provide the correct infusion amount. Rumen fluid samples were collected at -2, -1, 0, 1, 2, 3, 4, 6, 8, 12, 18, 24, 28, and 32 h relative to start of infusion. Serial blood samples were collected at -2, -1, 0, 0.5, 1, 2, 3, 4, 6, 8, 12, 18, 24, 26, 28, and 32 h relative to start of infusion. Compared with CON, infusing butyrate increased both plasma butyrate and plasma β-hydroxybutyrate (BHB), whereas plasma glucose decreased. Increasing butyrate infusion from 1 to 2 g increased plasma butyrate, tended to decrease plasma glucose, and tended to increase plasma BHB. Compared with abomasal infusion, rumen infusion of butyrate increased rumen butyrate, did not affect plasma glucose, and tended to increase plasma BHB. Treatment had no effect on plasma insulin. Results demonstrated that site of infusion and amount of butyrate affected several plasma metabolites when butyrate was infused in lactating dairy cows over a period of 24 h.

Several studies have identified beneficial effects of butyrate on rumen development and intestinal health in preruminants. These encouraging findings led to further investigations related to butyrate supplementation in the mature ruminant. However, the effects of elevated butyrate concentrations on rumen metabolism have not been investigated, and consequently the maximum tolerable dosage rate of butyrate has not been established. Therefore, the first objective of this work was to evaluate the effect of a short-term increase in rumen butyrate concentration on key metabolic indicators. The second objective was to evaluate the source of butyrate, either directly dosed in the rumen or indirectly supplied via lactose fermentation in the rumen. Jugular catheters were inserted into 4 ruminally fistulated Holstein cows in a 4×4 Latin square with 3-d periods. On d 1 of each period, 1h after feeding, cows were ruminally dosed with 1 of 4 treatments: (1) 2L of water (CON), (2) 3.5g/kg of body weight (BW) of lactose (LAC), (3) 1g/kg of BW of butyrate (1GB), or (4) 2g/kg of BW of butyrate (2GB). Sodium butyrate was the source of butyrate, and NaCl was added to CON (1.34g/kg of BW), LAC (1.34g/kg of BW), and 1GB (0.67g/kg of BW) to provide equal amounts of sodium as the 2GB treatment. Serial plasma and rumen fluid samples were collected during d 1 of each period. Rumen fluid pH was greater in cows given the 1GB and 2GB treatments compared with the cows given the LAC treatment. Cows administered the 1GB and 2GB treatments had greater rumen butyrate concentrations compared with LAC. Those cows also had greater plasma butyrate concentrations compared with cows given the LAC treatment. Plasma β-hydroxybutyrate was greater and insulin tended to be greater for butyrate treatments compared with LAC. No difference in insulin was found between the 1GB and 2GB treatments. Based on plasma and rumen metabolites, singly infusing 3.5g/kg of BW of lactose into the rumen is not as effective at providing a source of butyrate as compared with singly infusing 1 or 2g/kg of BW of butyrate into the rumen. Additionally, rumen pH, rumen butyrate, plasma β-hydroxybutyrate, glucose, and plasma butyrate were less affected in cows administered the 1GB treatment than in cows given the 2GB treatment. This finding suggests that singly dosing 1g/kg of BW of butyrate could serve as the maximum tolerable concentration for future research.

Ruminal solubility of N, K, P, Ca, Mg and S were measured for three forages at six growth stages. The three forages were Kentucky 31 tall fescue (TF), Kenhy fescue (KN) and a red clovertall fescue mixture (RC). Disappearance parameters were measured by means of the dacron bag technique using cannulated steers. Exposures were for 48 h ; maximum extent of disappearance for all elements occurred before this time. High proportions (>60%) of P, K and Mg were released from all three forages during the first 3 h of incubation, with small losses thereafter. Amounts of N and S released during the first 3 h ranged between 40 to 75%. Ca had the lowest initial disappearance. Forages differed (P<.05) in extent of mineral disappearance after 3-and 48-h incubations and in rate of disappearance (K d) of the potentially available, slowly solubilizing, fraction of N, Ca and S. Across growth stages, TF had generally the lowest extent and rate of disappearance. With increasing maturity, K d for Mg, Ca and S decreased (P<.05). For each element, K d was not correlated with herbage concentration or initial (3 h) disappearance. Partial correlations between disappearance of N, K, Ca, Mg and S after the 48-h incubation and herbage concentration were significant. Solubilization values corrected for rate of passage (ERS) showed significant differences among forages for K, Ca and S. Average ERS values for S and K were highest for KN; RC herbage had higher ERS values for Ca. Increases in forage maturity lowered (P<.001) ERS for all elements. The results indicate that for all growth stages, ruminal solubility and potential availability of N and minerals from the three forages was high. The rate of release differed among elements and may have affected efficiency of microbial fermentation. Although ruminal solubility of minerals from TF was generally lower than from the other two forages, the difference was not sufficient to explain fully the lower apparent availability observed in previous studies.

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SummaryThree experiments were conducted to determine the value of foliage from three tropical legume trees as low level protein supplements to napier grass diets for growing ‘Kacang’ goats. The average crude protein concentration in the napier grass was 12%.Napier grass and foliage of the legume trees Gliricidia maculata, Leucaena leucocephala and Sesbania grandiflora were subjected to in situ microbial fermentation and subsequent treatment with acid-pepsin solution. The levels of N solubilized after 2 h incubation were 46 and 43% for napier grass and sesbania respectively, which were higher (P < 0·05) than those for gliricidia and leucaena (27%). Rates of protein disappearance between 2 and 24 h incubation in the rumen averaged 2·6%/h for the legumes and 1·0%/h for napier grass. The proportion of water-insoluble, rumendegradable protein from the legumes was larger (P < 0·05) than that from napier grass.Napier grass intake by goats supplemented with gliricidia or leucaena at 15% of the dry-matter intake from napier grass was lower (P < 0·05) than that of controls receiving no legume supplement. Napier grass intake did not differ between controls and sesbania-supplemented goats. There was no difference among diets in total dry-matter intake, intake of cell wall constituents or digestibility. Average daily gain for control goats was – 1 g/day as compared with 21 g/day for supplemented goats.The feeding of formaldehyde-treated soya-bean meal (F-SBM) as a supplement to either napier grass or napier grass–legume diets increased (P < 0·05) intake of dry matter and weight gain of goats. Napier grass intake of animals supplemented with only F-SBM was higher (P < 0·05) than that of control animals. The efficiency of N utilization from F-SBM was higher than that in the legumes, but replacement of legumes by F-SBM above 4% F-SBM feeding had no effect on weight gain or efficiency of utilization.It was concluded that napier grass of 6–8 weeks' regrowth with 12% crude protein did not provide sufficient protein for growing goats owing to inefficient protein utilization. The increase in efficiency of protein utilization on supplemented diets is mainly associated with the larger proportion of water insoluble, rumen degradable protein and possibly acid-pepsin soluble protein in tropical tree legumes.

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