Effect of milk protein intake and casein-to-whey ratio in breakfast meals on postprandial glucose,satiety ratings,and subsequent meal intake

Whey and casein proteins differentially affect postprandial blood glucose and satiety mechanisms, with relevance for type 2 diabetes and obesity. Therefore, the purpose of this work was to investigate the effect of the casein-to-whey protein ratio and total protein concentration of milks consumed with cereal on postprandial blood glucose, appetite ratings, and subsequent food intake in a randomized, controlled, double-blinded study with healthy young adults (n = 32, 23.4 ± 3.1 yr, body mass index = 22.2 ± 2.5 kg/m²). Fasted participants consumed milk (250 mL) with either 80:20 or 40:60 (modified) casein-to-whey protein ratios at commercially normal (3.1%, wt) or high protein (9.3%, wt) concentration, or control (water with whey permeate), each along with 2 servings of oat-based breakfast cereal. Blood glucose concentrations were determined from finger prick blood samples and appetite was assessed using visual analog scales. Participants consumed a measured ad libitum pizza lunch at 120 min and blood glucose determination and appetite assessment continued following the lunch meal (140–200 min) to observe the second meal effect. Pre-lunch (0–120 min) incremental area under the curve (iAUC) and mean change from baseline blood glucose were reduced with consumption of all milk treatments relative to control. However, we found no differences between all treatments on pre-lunch appetite change from baseline and total area under the curve (tAUC) or lunch meal food intake. In terms of protein concentration results, high protein (9.3%, wt) treatments contrasted to normal protein (3.1%, wt) treatments lowered blood glucose change from baseline and iAUC, and post-lunch appetite change from baseline and tAUC. Protein ratio showed a modest effect in that modified (40:60) protein ratio lowered pre-lunch blood glucose change from baseline but not iAUC, and normal (80:20) protein ratio lowered pre-lunch appetite change from baseline but not tAUC. Therefore, high-carbohydrate breakfast meals with increased protein concentration (9.3%, wt) could be a dietary strategy for the attenuation of blood glucose and improved satiety ratings after the second meal.     

白面包搭配坚果油籽浆的餐后血糖反应

为研究不同坚果油籽浆对餐后血糖反应的影响,测定大豆(S)和黑芝麻(BS)、亚麻籽(LS)、巴旦木(A)打浆后搭配白面包(WB)食用的血糖指数(GI)及餐后240 min的血糖反应特征值,并与牛奶(M)的效果相比较.结果表明:M+WB和A+S+WB的GI值均为52,BS+WB的GI值和白面包同为74.LS+S+WB的血糖...     

Effect of stage of lactation and varying available energy intake on milk production, milk composition, and subsequent tissue enzymic activity

Twenty-four cows were allotted at parturition to receive one of four rations for 180 days. Rations were regular ad libitum (about 20% crude fiber), concentrate ad libitum (about 10% crude fiber), and restricted to recommended energy intake, and intermediate ration (14% crude fiber) ad libitum. Cows on concentrate consumed less dry matter, fiber and protein than intermediate and regular cows. Cows fed more forage gained more weight, had milk with higher protein and fat content, but were similar in milk production to those fed high concentrate. Fat test decreased to 4 wk in all treatments, and by 8 or 9 wk cows fed concentrate decreased to their lowest fat test. Concentrate restriction enhanced fat test beyond 8 wk. Ruminal propionate was higher and similar for both concentrate groups. Ruminal volatile fatty acids were higher, glucose slightly higher, and blood acetate lower for cows on ad libitum concentrate compared to intermediate. Mammary and adipose tissue from cows in midlactation were assayed for key enzymes of fatty acid synthesis. Activity of 6-phosphogluconate dehydrogenase tended higher for concentrate rations in adipose tissue, but mammary tissue was 21 to 28 times as active. Mammary tissue was 7 to 10 times as active as adipose tissue in fatty acid synthetase with no difference in rations.     

Use of heated milk protein-sugar blends as antioxidant in dairy beverages enriched with linseed oil

Antioxidant preparations were obtained by heating aqueous dispersions of milk protein and sugars at 110 °C for 10 min. The milk protein-sugar blends contained 3.5 g/100 g protein and 10 g/100 mL sugar (with various proportions of lactose, sucrose and their monosaccharide mixtures glucose/galactose and glucose/fructose). These preparations were added at low concentration (5 mL/100 mL) to the formulation of sterilized dairy beverages containing ω-3 polyunsaturated fatty acids. Dairy beverages were also formulated with non heated protein-sugar blends. The total color difference and hydroxymethylfurfural content in dairy beverages increased (P < 0.01) with increasing monosaccharide concentration in the antioxidant preparation. These effects were more important when the protein-sugar blends were pre-heated. Non heated protein-sugar blends did not reduce lipid oxidation during sterilization while pre-heated blends containing monosaccharides were the most effective. Hexanal and propanal concentrations after sterilization were respectively reduced by 100 and 78% when the final concentration of monosaccharides in dairy beverages reached 0.4 g/100 mL. Adding a small fraction of milk protein as pre-heated protein-sugar blend in functional dairy beverage formulations is a promising approach to prevent the oxidation of ω-3 polyunsaturated fatty acids during sterilization treatment.     

In vivo and in vitro gastric emptying of protein fractions of milk replacers containing whey proteins.

In vivo and in vitro gastric emptying of protein fractions of three milk replacers containing either milk protein (control), a mixture (50:50 on a CP basis) of milk protein and native whey protein concentrate, or a mixture (50:50 on a CP basis) of milk protein and heated whey protein concentrate was studied. In vivo gastric emptying was measured in three preruminant calves fitted with reentrant duodenal cannulas and used in a 3 x 3 Latin square design. In vitro gastric emptying was determined after enzymatic digestion in an artificial stomach. In vivo and in vitro flow rates of protein N (12% TCA-insoluble N) and total N were higher for milk replacers containing whey proteins than for control. Gastric emptying of NPN (12% TCA-soluble N) was slightly higher for diets containing whey proteins than for that containing milk proteins. Gastric emptying of all protein fractions was similar for the two milk replacers containing whey proteins. In vivo and in vitro results were significantly correlated, suggesting that the in vitro method reproduced conditions for proteolysis and could be used to predict gastric digestion of protein fractions.     

Ready-to-drink protein beverages: Effects of milk protein concentration and type on flavor

This study evaluated the role of protein concentration and milk protein ingredient [serum protein isolate (SPI), micellar casein concentrate (MCC), or milk protein concentrate (MPC)] on sensory properties of vanilla ready-to-drink (RTD) protein beverages. The RTD beverages were manufactured from 5 different liquid milk protein blends: 100% MCC, 100% MPC, 18:82 SPI:MCC, 50:50 SPI:MCC, and 50:50 SPI:MPC, at 2 different protein concentrations: 6.3% and 10.5% (wt/wt) protein (15 or 25 g of protein per 237 mL) with 0.5% (wt/wt) fat and 0.7% (wt/wt) lactose. Dipotassium phosphate, carrageenan, cellulose gum, sucralose, and vanilla flavor were included. Blended beverages were preheated to 60°C, homogenized (20.7 MPa), and cooled to 8°C. The beverages were then preheated to 90°C and ultrapasteurized (141°C, 3 s) by direct steam injection followed by vacuum cooling to 86°C and homogenized again (17.2 MPa first stage, 3.5 MPa second stage). Beverages were cooled to 8°C, filled into sanitized bottles, and stored at 4°C. Initial testing of RTD beverages included proximate analyses and aerobic plate count and coliform count. Volatile sulfur compounds and sensory properties were evaluated through 8-wk storage at 4°C. Astringency and sensory viscosity were higher and vanillin flavor was lower in beverages containing 10.5% protein compared with 6.3% protein, and sulfur/eggy flavor, astringency, and viscosity were higher, and sweet aromatic/vanillin flavor was lower in beverages with higher serum protein as a percentage of true protein within each protein content. Volatile compound analysis of headspace vanillin and sulfur compounds was consistent with sensory results: beverages with 50% serum protein as a percentage of true protein and 10.5% protein had the highest concentrations of sulfur volatiles and lower vanillin compared with other beverages. Sulfur volatiles and vanillin, as well as sulfur/eggy and sweet aromatic/vanillin flavors, decreased in all beverages with storage time. These results will enable manufacturers to select or optimize protein blends to better formulate RTD beverages to provide consumers with a protein beverage with high protein content and desired flavor and functional properties.     

Short communication: Parameters of abomasal emptying and glucose-insulin dynamics in Holstein-Friesian calves at 2 ages and 2 levels of milk replacer intake

Elevated planes of nutrition in the preweaning period of dairy calf management can increase average daily gain, shorten age at puberty, and increase milk yield. In a previous study, 12 Holstein calves were fed 2 meals/d of 4 or 2 L milk replacer up to 7 wk of age. The objective of the current study was to estimate parameters of abomasal emptying and glucose-insulin dynamics in these calves by fitting a mechanistic model to postprandial appearances of plasma glucose, insulin, and the abomasal emptying marker acetaminophen measured at 4 and 7 wk of age. Higher intake of milk replacer resulted in longer bouts of abomasal emptying at a slower rate. Parameters of glucose and insulin dynamics were not affected by milk replacer intake. However, older calves had decreased insulin-stimulated glucose utilization indicating impaired insulin sensitivity, as well as increased pancreatic responsiveness. Neither of these effects were apparent from i.v. glucose tolerance tests on the calves and may have been related to postprandial gut hormone release. Effects of age on parameters of glucose-insulin dynamics were larger than effects of milk replacer intake. Conversely, effects of milk replacer intake on abomasal emptying were larger than effects of age.     

Adaptation of bovine milk towards mares’ milk composition by means of membrane technology for koumiss manufacture

This study was carried out to determine the physical, chemical, microbiological and organoleptic properties of koumiss made from bovine milk. The bovine milk was modified according to the composition of mares’ milk using ultrafiltration, microfiltration and nanofiltration. Koumiss made from modified bovine milk and mares’ milk were compared. In order to assess options for a consistent fermentation, a starter culture, instead of the prevailing spontaneous flora in traditional manufacture of koumiss, was used. Key compositional factors modified were the contents of dry matter, mineral, protein and lactose and the casein-to-whey protein ratio. Koumiss made from modified bovine milk and by starter cultures was found to be very similar to koumiss from mares’ milk in terms of pH, titratable acidity, alcohol, proteolytic activity, apparent viscosity, and microbiological composition, when assessed both in the freshly made product and that after 15 days storage at 4°C.     

Effect of milk protein composition and amount of β-casein on growth performance,gut hormones,and inflammatory cytokines in an in vivo piglet model

The objective of this work was to better understand the effect of differences in milk protein composition, and specifically, a change in β-casein to total casein in a milk-based matrix, on growth performance and metabolic and inflammatory responses using a piglet model. Three formulas were optimized for piglets, with similar metabolizable energy, total protein content, and other essential nutrients. Only the protein type and ratio varied between the treatments: the protein fraction of the control diet contained only whey proteins, whereas 2 other matrices contained a whey protein to casein ratio of 60:40, and differed in the amount of β-casein (12.5 and 17.1% of total protein). Piglets fed formula containing whey proteins and caseins, regardless of the concentration of β-casein, showed a significantly higher average daily gain, average daily feed intake, and feed efficiency compared with piglets consuming the formula with only whey protein. Consumption of the formula containing only whey protein showed higher levels of plasma glucagon-like peptide-1 and ghrelin compared with the consumption of formula containing casein and whey protein. A positive correlation was observed between postprandial time and glucagon-like peptide-1 response. The intestinal pro-inflammatory cytokine tumor necrosis factor α increased significantly in piglets fed the whey protein/casein diet compared with those fed whey protein formula. All formula-fed piglets showed a lower level of IL-6 cytokine compared with the ad libitum sow-fed piglets, regardless of composition. No significant differences in the anti-inflammatory IL-10 concentration were observed between treatment groups. Milk protein composition contributed to the regulation of piglets‘ metabolic and physiological responses, with whey protein/casein formula promoting growth performance and a different immune regulatory balance compared with a formula containing only whey protein. Results indicated no differences between treatments containing different levels of β-casein.     

Effect of amount and source of dietary nitrogen on milk fat depression in early lactation dairy cows

Twenty-four multiparous and 15 primiparous Holstein cows were fed a total mixed corn silage diet with one of three dietary treatments: 14% crude protein, 22% crude protein (all preformed), or 22% crude protein (preformed plus nonprotein N). Eight multiparous and 5 primiparous cows were randomly assigned to each treatment at calving. The diet contained 23% ADF during wk 1 to 4 postpartum and was lowered to 11% ADF for wk 5 to 12 postpartum. Treatment had no effect on the magnitude of depression in milk fat percentage or milk fat yield in multiparous cows. After fiber was lowered, changes in rumen acetate to propionate ratio, blood glucose, free fatty acids, and insulin were not influenced by treatment. Depression in milk fat percentage for primiparous cows was 19.7, 9.2, and 14.9% for low protein, high protein, and high protein with nonprotein N, respectively. When changed from high fiber to low fiber, the primiparous cows increased milk fat yield 9% for high preformed protein treatment but decreased fat yield for other treatments. Depression in acetate to propionate ratio and increase in blood glucose was least for the high preformed protein group.     

Blood responses of calves fed milk substitutes containing hydrolyzed fish protein and lime-treated corn flour

Two experiments involving 3- to 5-d-old dairy calves were carried out. In Experiment 1, lime-treated corn flour (Nixtamal) supplied 50 to 100% of carbohydrates in a milk substitute based on sodium caseinate, lard, and cerelose. In Experiment 2, partially hydrolyzed fish protein concentrate replaced 50% of 67% of proteins in milk substitutes based on skim milk powder, lard, and 35% Nixtamal. Increasing the proportion of carbohydrates supplied by Nixtamal was associated with a linear decrease of postprandial serum glucose and insulin. Postprandial fluctuations in blood glucose were less in calves fed Nixtamal than in controls. Nixtamal probably was trapped within the casein clot in the abomasum, leading to delayed rate of passage of Nixtamal carbohydrates into the intestine. Replacing skim milk protein with hydrolyzed fish protein in diets containing Nixtamal had no effect on blood glucose or insulin but elevated free essential amino acids, which promoted glucagon secretion. More uniform concentrations of blood essential amino acids and glucose were related to lower blood urea at 54 d in calves fed diets based on hydrolyzed fish protein and Nixtamal, than that of control calves. It is suggested that more uniform postprandial blood glucose concentrations might reduce amino acid degradation for energy purposes and stimulate protein synthesis. Young dairy calves may adapt to milk substitutes based on Nixtamal and hydrolyzed fish protein despite changes in the concentration patterns of several blood components.     

Influence of formaldehyde-treated soybean meal on milk production

Forty-eight Holstein cows were fed one of four diets containing 12.5% crude protein (negative control); 15.5% crude protein with untreated soybean meal; 15.5% crude protein with formaldehyde (.3%)-treated soybean meal; or 18% crude protein (positive control). Diets were 60% concentrate, 22% corn silage, 14% alfalfa hay, and 4% beet pulp (dry matter). Data were collected during the first 200 d of lactation. Dry matter intake, milk, and milk component yields did not differ among cows fed the untreated soybean meal, treated soybean meal, and positive control diets. Cows fed negative control diet consumed less dry matter and produced less milk than cows fed the other diets. Milk protein yield was lower for cows fed the negative control diet compared with the other diets. Nonprotein nitrogen content of milk increased as dietary protein increased.     

Effects of dietary supplements of algae,containing polyunsaturated fatty acids,on milk yield and the composition of milk products in dairy ewes

Thirty-two lactating Karagouniko ewes were allocated at random to four groups for 6 weeks, to examine the effect of four diets: C (control treatment, ration without algae); LA (ration with low level of algae); MA (ration with medium level of algae) and HA (ration with high level of algae); containing 0, 23.5, 47 and 94 g algae, respectively, on the enrichment of milk and dairy products. Addition of algae reduced (P < 0.001) DM intake for treatments MA and HA. Milk yield did not differ between treatments but milk composition was significantly affected by dietary inclusion of algae. Milk fat content was significantly increased (P < 0.001) for treatment HA whereas milk protein content was significantly increased (P < 0.001) for all treatments containing algae. Milk from treatments LA, MA and HA was significantly enriched in the following PUFA: C20:5 (n-3) (0.4-2.1%), C22:5 (n-6) (0.8-4.1%), C22:6 (n-3) (4.3-12.4%) (P < 0.001) and C22:5 (n-3) (2.1-3.1%) (P < 0.05), which were not detected in control milk. Feta cheese and yogurts produced from the enriched milk had identical composition with the milk, and would be characterized as healthy foods. The ratio of n-6 to n-3 fatty acids was 2.5-4.5.     

Effect of dipotassium phosphate and heat on milk protein beverage viscosity and color

Our objective was to determine the effect of addition of dipotassium phosphate (DKP) at 3 different thermal treatments on color, viscosity, and sensory properties of 7.5% milk protein-based beverages during 15 d of storage at 4°C. Micellar casein concentrate (MCC) and milk protein concentrate (MPC) containing about 7.5% protein were produced from pasteurized skim milk using a 3×, 3-stage ceramic microfiltration process and a 3×, 3-stage polymeric ultrafiltration membrane process, respectively. The MCC and MPC were each split into 6 batches, based on thermal process and addition of DKP. The 6 batches were no postfiltration heat treatment with added DKP (0.15%), no postfiltration heat without added DKP (0%), postfiltration high-temperature, short time (HTST) with DKP, postfiltration HTST without DKP, postfiltration direct steam injection with DKP, and postfiltration direct steam injection without DKP. The 6 MCC milk-based beverages and the 6 MPC milk-based beverages were stored at 4°C. Viscosity, color, and sensory properties were determined over 15 d of refrigerated storage. MCC- and MPC-based beverages at 7.5% protein with and without 0.15% added dipotassium phosphate were successfully run through an HTST and direct steam injection thermal process. The 7.5% protein MCC-based beverage contained a higher calcium and phosphorus content (2,425 and 1,583 mg/L, respectively) than the 7.5% protein MPC-based beverages (2,141 and 1,338 mg/L, respectively). Pasteurization (HTST) had very little effect on beverage particle size distribution, whereas direct steam injection thermal processing produced protein aggregates with medians in the range of 10 and 175 μm for MPC beverages. A population of casein micelles at about 0.15 μm was found in both MCC- and MPC-based beverages. Larger particles in the 175-μm range were not detected in the MCC beverages. In general, the apparent viscosity (AV) of MCC beverages was higher than MPC beverages. Added DKP increased the AV of both MCC- and MPC-based beverages, while increasing heat treatment decreased AV. The AV of beverages with DKP increased during 15 d of 4°C of storage for both MCC and MPC, whereas there was very little change in AV during storage without DKP and a similar effect was observed for sensory viscosity scores. The L value of beverages was higher with higher heat treatment, but DKP addition decreased L value and sensory opacity greatly. Sulfur-eggy flavors were detected in MPC beverages, but not MCC-based beverages.     

A dose–response evaluation of freeze‐dried strawberries independent of fiber content on metabolic indices in abdominally obese individuals with insulin resistance in a randomized,single‐blinded,diet‐controlled crossover trial

Scope : This study evaluated the dose–response relationship of strawberries, an anthocyanin‐rich fruit, on postprandial glucose and insulin concentrations in individuals with insulin resistance (IR), including changes in plasma anthocyanins, markers of oxidative stress, and inflammation. Methods and Results : In a randomized controlled, four‐arm, dose–response, crossover trial, 21 adults with IR consumed a high‐carbohydrate, high‐fat meal with one of four beverages containing 0 g freeze‐dried whole strawberry powder (0g FDS, control), 10, 20, or 40 g FDS, controlled for fiber. Blood was collected at 0 min and at 30 min intervals postmeal until 2 h, then hourly until 6 h. Postmeal insulin concentrations (6 h) were significantly reduced after the 40‐g FDS beverage compared to other beverages (p < 0.05). Postmeal 6 h glucose concentrations were not different, although mean insulin:glucose ratio was significantly different among beverages (p < 0.05). Pelargonidin‐glucuronide was inversely associated with mean insulin concentrations after the 20 and 40 g FDS (p < 0.05). Oxidized low‐density lipoprotein was reduced after 20 g FDS (p < 0.05) and IL‐6 was not different among treatments. Strawberry intake reduced the insulin demand to manage postmeal glucose in obese individuals with IR, which was related to plasma anthocyanin/pelargonidin concentrations. Conclusion : The data support a role of strawberries in improving insulin sensitivity in people with IR.     

Effects of intravenous infusion of amino acids and glucose on the yield and concentration of milk protein in dairy cows

To test the hypothesis that the availability of glucose or its precursors can influence the response of milk protein concentration to the intravenous infusion of amino acids, five cows were used in a 5 x 5 Latin square design with period lengths of 7 d. The five treatments were the basal diet of grass silage ad lib. plus 5 kg/d of a cereal-based supplement containing feather meal (Basal); Basal plus 4 g/d histidine, 8 g/d methionine and 26 g/d lysine (4H); Basal plus 8 g/d histidine, 8 g/d methionine and 26 g/d lysine (SH); and these two amino acid mixtures together with 600 g/d of gluctose (4HG and 8HG respectively). Earlier experiments with this basal diet had shown that histidine was first-limiting for secretion of milk protein, followed by methionine and lysine. The yield of milk protein was increased progressively with the amount of histidine infused. The efficiency of transfer of histidine into milk protein was 0.42 for the 4H and 4HG and 0.35 for the 8H and 8HG treatments, and the concentration of milk protein was increased over Basal by all infusion treatments. However, milk protein concentrations were higher, and lactose concentrations in the milk were lower, in the absence of added glucose. Concentrations of insulin in blood plasma were not affected by treatment. It is concluded that, with the treatments without added glucose, a shortage of glucose prevented an increase in lactose secretion, and hence limited the increase in milk yield, leading to an increased concentration of protein in the milk.     

Nutritional effects of including different levels and sources of protein in milk replacers for calves

Two digestibility and nitrogen balance experiments were carried out with groups of young calves given high-fat milk replacers reconstituted with water and fed in liquid form. In the first experiment six different milk replacers with crude protein contents ranging from 12.7 up to 27.6% in the dry matter were compared, the differences in protein content being brought about by adjustments to the level of separated milk protein used in the replacers. The apparent digestibility of organic matter was very high on all the treatments and unaffected by level of protein. Although the crude protein fraction showed an increase in apparent digestibility with increase in level of protein, its true digestibility was estimated to be virtually 100% on all the treatments. Retention of nitrogen expressed as a percentage of total intake remained fairly constant for diets containing from 18.8 to 27.6% of crude protein and the weight of nitrogen retained increased with each successive increase in level of dietary protein. In the second experiment the effects of replacing half of the milk protein in a control milk replacer by different forms of animal protein were studied. The true digestibilities of the total dietary protein on the treatment containing only separated milk protein and on the other treatments containing partial substitution by dried delactosed whey, dried blood, white fish meal and meat meal were found to be 94.1, 90.9, 85.4, 91.1 and 86.6%, respectively. Their biological values were 74.7, 70.3, 69.1, 66.0 and 65.5%, respectively. A sixth treatment in which the meat meal was provided with an enzyme supplement did not effect any significant change in either digestibility or biological value. Retentions of nitrogen expressed as percentages of intake were significantly lower on all the treatments containing partial replacement of separated milk protein by the other sources of protein than on the control treatment.     

Effect of monensin on milk production of Holstein-Friesian dairy cows

We examined the effects of monensin on feed intake and milk production in Holstein-Friesian cows receiving a total mixed rations in two experiments. In experiment 1, 60 individually fed cows consumed, during wk 7 to 26 of lactation, 1 kg/d of supplement containing either 0, 150,300, or 450 mg of monensin. In experiment 2, 98 group-fed cows also received 1 kg/d of a supplement with either 0 or 300 mg/d of monensin for two consecutive lactations. In lactations 1 and 2, treatment started at wk 8 and 3 wk prior to calving, and continued for 32 wk. In experiment 1, 150, 300, and 450 mg of monensin/d produced a small decrease in feed intake and milk yield responses of 2.8, 2.5 and 1.5 kg/d, respectively. In experiment 2, milk yield responses of 0.8 and 1.1 kg/d were recorded in lactations 1 and 2. Milk fat and milk protein content declined in experiments 1 and 2, lactations 1 and 2 by 0.46, 0.38 and 0.27%, and 0.16, 0.16 and 0.11%, respectively. Yield of milk constituents was unaffected. Efficiency of milk production was increased by 5% in experiment 1. In experiment 2, lactation 2, monensin decreased beta-hydroxybutyrate and acetoacetate but increased blood glucose concentration.     

Effect of dietary starch level and high rumen-undegradable protein on endocrine-metabolic status,milk yield,and milk composition in dairy cows during early and late lactation

Diet composition defines the amount and type of nutrients absorbed by dairy cows. Endocrine-metabolic interactions can influence these parameters, and so nutrient availability for the mammary gland can significantly vary and affect milk yield and its composition. Six dairy cows in early and then late lactation received, for 28 d in a changeover design, 2 diets designed to provide, within the same stage of lactation, similar amounts of rumen fermentable material but either high starch plus sugar (HS) content or low starch plus sugar content (LS). All diets had similar dietary crude protein and calculated supply of essential amino acids. Dry matter intake within each stage of lactation was similar between groups. Milk yield was similar between groups in early lactation, whereas a higher milk yield was observed in late lactation when feeding HS. At the metabolic level, the main difference observed between the diets in both stages of lactation was lower blood glucose in cows fed LS. The lower glucose availability during consumption of LS caused substantial modifications in the circulating and postprandial pattern of metabolic hormones. Feeding LS versus HS resulted in an increase in the ratio of bovine somatotropin to insulin. This increased mobilization of lipid reserves resulted in higher blood concentrations of nonesterified fatty acids and β-hydroxybutyrate, which contributed to the higher milk fat content in both stages of lactation in the LS group. This greater recourse to body fat stores was confirmed by the greater loss of body weight during early lactation and the slower recovery of body weight in late lactation in cows fed LS. The lower insulin to glucagon ratio observed in cows fed LS in early and late lactation likely caused an increase in hepatic uptake and catabolism of amino acids, as confirmed by the higher blood urea concentrations. Despite the higher catabolism of amino acids in LS in early lactation, similar milk protein output was observed for both diets, suggesting similar availability of amino acids for peripheral tissue and mammary gland. The latter could be the result of sparing of amino acids at the gut level due to starch that escaped from the rumen, and to the balanced amino acid profile of digestible protein. This last aspect appears worthy of further research, with the aim to enhance the efficiency of protein metabolism of dairy cows, reducing environmental nitrogen pollution without affecting milk yield potential.