Milk True Protein Research Articles

Eastern Gamagrass: Determining its Role in the Feeding of Lactating Cows

Cherney, D.J.R., Salon, P.R., Thompson, D. and Cherney, J.H. 2003. Eastern gamagrass: Determining its role in the feeding of lactating cows. J. Appl. Anim. Res., 23: 81–92. Two production trials were conducted to determine the role of eastern gamagrass (Tripsacum dactyloides (L.)L.) in the feeding of lactating cows. Two trials were conducted comparing eastern gamagrass total mixed ration (TMR) with corn silage TMR. At Cornell University, Ithaca, NY, a trial was conducted with 16 lactating Holstein cows (165.2±8.7 days in milk) milked three times daily. Twenty lactating Holstein cows milked twice daily were used at State University of New York (SUNY) Cobleskill. The Cornell University (CU) trial was a continuous trial with production parameters of the previous week used as a covariate. The SUNY Co leskill trial was a switchback design with 28d periods. Dry matter intake and milk production did not differ between the diets in either trial. Milk area nitrogen (MUN) was higher in the corn silage TMR than the eastern gamagrass TMR in the Cornell University trial. Milk fat, true milk protein and milk lactose did not vary in either trial. Results from this study indicate that eastern gamagrass can be used to replace the fiber coming from corn silage. This will result in considerably more grain being needed in the TMR, however, to offset the lower energy of eastern gamagrass. Whether or not this is economically or environmentally feasible will depend on the price of grain. Nutrient management aspects of possibly increasing feeds brought from off farm also needs to be considered.

Metabolizable protein supply (PDIE) and restricted level of ruminally degradable nitrogen (PDIN) in total mixed rations: effect on milk production and composition and on nitrogen utilization by dairy cows

Three levels of metabolizable protein supply (108, 98–95 and 85 g PDIE kg −1 DM) (PDIE: protein digested in the small intestine when rumen-fermentable energy is limiting) in the diet and three levels of difference between rumen-degradable energy and N (PDIE−PDIN=0, 10 and 20 g kg −1 DM) (PDIN: protein digested in the small intestine when rumen-fermentable nitrogen is limiting) were used in two trials with 24 and 32 dairy cows. Trials were conducted using Latin-square designs and all cows were fed a total mixed ration. Dry matter intake, net energy intake, and milk yield were significantly higher ( P<0.05) with increasing PDIE level. The PDIE level of the diet did not affect milk true protein content but the results for fat content were different for the two levels of PDIE increase: fat content decreased ( P<0.05) between the low and medium PDIE levels and did not vary between the medium and high PDIE level. Milk NPN and urea contents increased with the increased level of PDIE. The milk protein N yield/N intake ratio decreased ( P<0.10) as the level of PDIE in the diet increased. A difference of 10 g PDIN kg −1 DM between rumen-degradable N and energy affected neither dry matter, energy or PDIE intake, nor milk yield or composition. However, dry matter, energy and PDIE intake decreased ( P<0.10) for a rumen-degradable PDIN deficit of 20 g/kg DM. In this case, milk yield was not significantly affected but milk fat content increased significantly ( P<0.10) and milk true protein content decreased ( P<0.01). Milk NPN and urea contents decreased as the rumen-degradable PDIN deficit increased ( P<0.01). The milk protein N yield/N intake ratio increased with the increase in rumen-degradable PDIN deficit ( P<0.01).

The effect of protected lysine and methionine on milk yield and its composition in lactating dairy cows fed grass silage-based rations

1. Effect of rumen-protected methionine on feed intake, milk production, true milk protein concentration, and true milk protein yield, and the factors that influence these effects: A meta-analysis R.A. Patton Journal of Dairy Science CrossRef

Factors contributing to variation in the proportion of casein in cows' milk true protein: a review of recent INRA experiments.

The aim of this study was to identify and rank the various factors, in particular those involving feeding, that affect the proportion of caseins in milk true protein. Twenty-nine feeding trials involving 821 lactations were assessed, and lactoprotein genetic variants were known for 551 of these. The main factor affecting the casein: protein ratio was the genetic variant of beta-lactoglobulin: once corrected for other factors, the milk of BB type animals had a ratio nearly 30 g/kg total protein higher than AA animals. kappa-Casein variant B also had a positive effect (+12 g/kg in favour of BB relative to AA animals). Except in the last weeks of pregnancy and the first weeks of lactation, the casein: protein ratio varied little during lactation. It was significantly reduced when milk cell count exceeded 200,000 cells/ml, even in the absence of clinical mastitis. It also decreased slightly with parity. Among the various dietary factors studied (level and type of nitrogen and energy supplies, forage type and preservation method), none had any significant effect on the milk casein: protein ratio, except in drastic dietary situations. That ratio increased very slightly in parallel with the animals' milk yield and milk protein content. In practice, measuring the milk protein content in animals free from clinical mastitis remains a very precise predictor of casein content, accounting for 93% of its variation.

Production and metabolic aspects of nonprotein nitrogen incorporation in lactation rations of dairy goats

Two lactation trials were conducted to evaluate the effects of dietary urea on milk production and metabolic criteria in dairy goats. In Experiment 1, 18 primiparous Alpine does (average BW 42kg) were fed one of three diets (65% TDN): NPC1, negative protein control (9.5% CP); PPC1, positive protein control (14% CP); and NPND, nonprotein N diet (14% CP, urea contributed 33% of the total dietary N). The lactation trial consisted of a 3 week adaptation and a 5 week collection period. Mean ADG, DM intake, milk yield, milk fat, and milk N were not affected by diet ( P > 0.10); however, milk noncasein N ( P < 0.02) and serum-derived protein N ( P < 0.05) were greater in the does fed the NPND diet compared with the does fed the NPC1 diet. Ruminal fluid ammonia N ( P < 0.01) and plasma urea N ( P < 0.001) were increased by dietary N level and NPN incorporation, and ruminal acetate:propionate molar ratio was lower ( P < 0.02) in does fed NPND compared with does fed PPC1. In Experiment 2, 20 multiparous Alpine does (average BW 55 kg) were fed one of four diets (65% TDN): NPC2, negative protein control (12.5% CP); PPC2, positive protein control (17% CP); LNPN, low nonprotein N (17% CP, urea contributed 25% of the total dietary N); and HNPN, high nonprotein N (16% CP, urea contributed 50% of the total dietary N). The lactation trial lasted 10 weeks following a 3 week adaptation period. Mean ADG, DM intake, milk yield, and milk fat were not affected by dietary treatment ( P > 0.10). Total milk N was affected ( P < 0.002) by diet. The NPN fraction was lowest ( P < 0.04), and the true protein N ( P < 0.005) and casein N ( P < 0.001) fractions highest in milk from does fed NPC2 compared with does fed PPC2. In addition, milk true protein N and casein N fractions were lowest in does fed the HNPN diet ( P < 0.005). Increasing dietary N levels and incorporation of NPN resulted in elevated ruminal fluid pH ( P < 0.10), ammonia N ( P < 0.02), and free, nonionized ammonia N ( P < 0.03). Ruminal fluid acetate:propionate molar ratio was lowest ( P < 0.001), and plasma ammonia N ( P < 0.04) and urea N ( P < 0.01) were elevated in does fed the HNPN diet. Plasma glucose, insulin, glucagon, and cortisol were not affected ( P > 0.10) by diet in either experiment. Incorporation of NPN in goat lactation diets can sustain milk yield during mid-lactation without the development of clinical hyperammonemia; however, milk N fractions, and hence, the milk processing properties may be affected at the higher levels of NPN incorporation.

Varying Degradation Rates of Total Nonstructural Carbohydrates: Effects on Ruminal Fermentation, Blood Metabolites, and Milk Production and Composition in High Producing Holstein Cows

Twelve multiparous Holstein cows (6 ruminally cannulated and 6 intact) at 56 to 77 d of lactation were used in an experiment with a 3×6 Latin square design. Cows were fed three total mixed rations that varied in degradation rates of total nonstructural carbohydrates (6.04, 6.98, and 7.94%/h). No interactions between treatment and square were detected. Higher ruminal degradation rates of dietary total nonstructural carbohydrates increased the nonammonia N (NAN) pool of the liquid fraction but did not alter the dry matter or volume of fractional pools, microbial NAN pools, or microbial composition. Treatment did not affect dry matter intake, total concentrations of volatile fatty acids, or fiber digestibility. As ruminal degradation rates of total nonstructural carbohydrates increased, the following effects were observed: 1) the turnover rates of solids increased linearly; 2) ruminal NH3 N concentrations and degradabilities of organic matter and N decreased, but propionate concentrations, bacterial efficiency, and total NAN flows tended to increase; 3) blood glucose and insulin concentrations were not affected, but blood urea N and nonesterified fatty acids were decreased; 4) intestinal and total tract digestibilities of organic matter and total nonstructural carbohydrates increased; and 5) milk production and milk true protein content and yield increased, but energetic efficiency of milk production did not change. The highest dietary ruminal degradation rate of total nonstructural carbohydrates increased the amount of nutrients digested in the intestine and increased milk production.

Interactions of Ruminally Protected Methionine and Lysine with Protein Source or Energy Level in the Diets of Cows

Interactions between supplementation with ruminally protected Met and Lys and the nature of protein or energy concentration of the diet were studied using 16 and 12 multiparous lactating dairy cows in two trials of 8 and 12 wk, respectively, commencing on approximately d 40 of lactation. In trial 1, cows received a semicomplete diet plus concentrates. The diet consisted of 62 to 63% corn silage, 2.2% corn gluten meal, .4% urea, 11% soybean meal (untreated or treated with formaldehyde), and 23 to 24% barley. In trial 2, cows received a complete diet with corn silage, untreated and formaldehyde-treated soybean meal, and barley in the ratio 78:12:9:0 or 49: 13:4:33. All treatments were replicated in a 4 × 4 Latin square design.In both trials, Met plus Lys (10 g/d of intestinally available Met and 30 g/d of Lys) had no significant effect on DMI, milk yield, fat content, casein as a percentage of true protein, or urea content of the milk. Mean increase of milk protein yield was 46 g/d with Met plus Lys, and mean increase of true protein content was 1.1 g/kg of milk. The increase in content of milk true protein was greater for cows receiving the low energy diet. Protein source had no effect on milk yield or composition. Glucose, urea, NEFA, BHBA, and total free AA in plasma were unaffected by supplementation of ruminally protected Met plus Lys. However, concentrations of Met and Lys in blood were slightly, but not significantly, higher in supplemented cows.

Responses in Urea and True Protein of Milk to Different Protein Feeding Schemes for Dairy Cows

Four multiparous Holstein cows were used in a 4 × 4 Latin square to investigate the effects of protein concentration, degradability, and quality on plasma urea concentration and milk N constituents. Diets varied in the amount and proportion of RDP and RUP relative to NRC requirements: diet 1, excessive RDP, deficient RUP; diets 2 and 3, balanced for RDP and RUP; and diet 4, excessive RDP, balanced for RUP. Diet 3 was formulated for optimal AA balance as predicted by the Cornell Net Carbohydrate and Protein System. Diets contained 34% corn silage, 19% alfalfa haylage, and 49% concentrate (DM basis). Concentrates varied in amounts of urea and soybean, corn gluten, and fish and blood meals.Concentrations of urea N and NPN in milk varied among diets: diet 1, 19 and 34 mg/dl; diet 2, 16 and 31 mg/dl; diet 3, 15 and 30 mg/dl; and diet 4, 23 and 39 mg/dl, respectively. Increases in NPN concentration were attributed to increases in the urea fraction of NPN. Intake of RUP and AA balance influenced milk true protein content: diet 1, 2.89%; diet 2, 2.90%; diet 3, 3.01%; and diet 4, 2.95%. The proportions of true protein and urea in milk are influenced by CP concentration, protein type, and protein quality.

Dietary Protein Degradability Effects on Plasma and Milk Urea Nitrogen and Milk Nonprotein Nitrogen In Holstein Cows

Fifteen multiparous, midlactation Holstein cows were used in a 5 × 5 Greco-Latin square to investigate the effects of various amounts of ruminally degradable and undegradable protein on plasma urea and milk urea N and NPN constituents. Diets were designed to provide the following percentage of degradable and undegradable protein relative to NRC requirements: diet A, 80, 80%; diet B, 100, 100%; diet C, 120, 80%; diet D, 100, 120%; and diet E, 120, 120%. All cows were fed for ad Libitum intake a TMR consisting of 47% corn silage, 18% haycrop silage, and 35% concentrate (DM basis). Concentrate consisted of various amounts of dry corn plus soybean, fish, and blood meals to alter the degradability of protein. In situ measurements were used to determine grain protein degradability. Plasma urea N was increased across diets A to E, respectively: 8.2, 14.8, 16.5, 17.8, and 20.7 mg/dl. The within-cow coefficient of correlation between plasma and milk urea N was .88. The intake of undegradable protein elevated plasma and milk urea N to a similar extent as intake of degradable protein. Multiple regression analysis across all diets revealed a negative relationship of energy intake on plasma urea N. Diet significantly influenced milk true protein yield for diets A to E, respectively: .73, 30, .73, .78, and .81 kg/d. Milk true protein yield was influenced by milk yield, undegradable protein, and energy intake. Milk NPN concentration increased across diets A to E, respectively: 28.7, 33.9, 35.6, 36.8, and 39.8 mg/dl. The increase in milk NPN concentration across diets was attributed largely to an increase in the urea component of milk NPN.

Nonprotein Nitrogen and Protein Distribution in the Milk of Cows

The NPN content of milk represents only 5 to 6% of the total N in milk. However, the significance of this milk N fraction to energy and N metabolism in the dairy cow has not been well characterized. The single largest contributor to the NPN fraction of milk NPN is urea. Urea equilibrates in body water, and blood urea is the primary source of milk urea. The urea in milk can be derived from at least two sources: the end product of digestion and amino acid catabolism. Blood urea N was positively associated with intakes of ruminally degradable and undegradable protein and negatively associated with intake of net energy. Consequently, it might be possible to develop a system to evaluate the dietary protein and energy status of the lactating dairy cow employing milk urea in conjunction with milk true protein.