Effect of feeding different sources of rumen-protected methionine on milk production and N-utilization in lactating dairy cows

Objectives of this study were to quantify production responses of lactating dairy cows to supplying absorbable Met as isopropyl-2-hydroxy-4-(methylthio)-butanoic acid (HMBi), or rumen-protected Met (RPM, Smartamine M; Adisseo, Alpharetta, GA) fed with or without 2-hydroxy-4-(methylthio)-butanoic acid (HMB), and to determine whether Met supplementation will allow the feeding of reduced dietary crude protein (CP). Seventy cows were blocked by parity and days in milk into 14 blocks and randomly assigned within blocks to 1 of the 5 dietary treatments based on alfalfa and corn silages plus high-moisture corn: 1 diet with 15.6% CP and no Met source (negative control); 3 diets with 15.6% CP plus 0.17% HMBi, 0.06% RPM + 0.10% HMB, or 0.06% RPM alone; and 1 diet with 16.8% CP and no Met supplement (positive control). Assuming that 50% of ingested HMBi was absorbed from the gastrointestinal tract and 80% of the Met in RPM was absorbed at intestine, the HMBi and RPM supplements increased metabolizable Met supply by 9 g/d and improved the Lys:Met ratio from 3.6 to 3.0. After a 2-wk covariate period during which all cows received the same diet, cows were fed test diets continuously for 12 wk. Diet did not affect dry matter intake (mean ± SD, 25.0 ± 0.3 kg/d), body weight gain (0.59 ± 0.2 kg/d), or milk yield (41.7 ± 0.6 kg/d). However, feeding HMBi increased yield of energy-corrected milk and milk content of protein and solids-not-fat. Moreover, trends were observed for increased milk fat content and yield of fat and true protein on all 3 diets containing supplemental Met. Apparent N efficiency (milk N/N intake) was highest on the RPM treatment. Feeding 16.8% CP without a Met source elevated milk urea N and urinary excretion of urea N and total N and reduced apparent N efficiency from 34.5 to 30.2%, without improving production. Overall results suggested that feeding HMBi or RPM would give similar improvements in milk production and N utilization.     

Effects of feeding formate-treated alfalfa silage or red clover silage on the production of lactating dairy cows

In trial 1, 15 Holsteins were fed 3 total mixed rations (TMR) with 33% neutral detergent fiber in 3 × 3 Latin squares (28-d periods). Two TMR contained (dry matter basis): 40% control alfalfa silage (CAS) or 40% ammonium tetraformate-treated alfalfa silage (TAS), 20% corn silage (CS), 33% high-moisture shelled corn (HMSC), 6% solvent soybean meal (SSBM), and 18% crude protein (CP); the third TMR contained 54% red clover silage (RCS), 6% dried molasses, 33% HMSC, 6% SSBM, and 16.3% CP. Silages differed in nonprotein N (NPN) and acid detergent insoluble N (ADIN; % of total N): 50 and 4% (CAS); 45 and 3% (TAS); 27 and 8% (RCS). Replacing CAS with TAS increased intake, yields of milk, fat-corrected milk, protein, and solids-not-fat, and apparent dry matter and N efficiency. Replacing CAS with RCS increased intake and N efficiency but not milk yield. Replacing CAS or TAS with RCS lowered milk urea N, increased apparent nutrient digestibility, and diverted N excretion from urine to feces. In trial 2, 24 Holsteins (8 ruminally cannulated) were fed 4 TMR in 4 × 4 Latin squares (28-d periods). Diets included the CAS, TAS, and RCS (RCS1) fed in trial 1 plus an immature RCS (RCS2; 29% NPN, 4% ADIN). The CAS, TAS, and RCS2 diets contained 36% HMSC and 3% SSBM and the RCS1 diet contained 31% HMSC and 9% SSBM. All TMR had 50% legume silage, 10% CS, 27% neutral detergent fiber, and 17 to 18% CP. Little difference was observed between cows fed CAS and TAS. Intakes of DM and yields of milk, fat-corrected milk, fat, protein, lactose, and solids-not-fat, and milk fat and protein content were greater on alfalfa silage vs. RCS. Blood urea N, milk urea N, ruminal ammonia, and total urinary N excretion were reduced on RCS, suggesting better N utilization on the lower NPN silage. Apparent N efficiency tended to be higher for cows fed RCS but there was no difference when N efficiency was expressed as kilograms of milk yield per kilogram of total N excreted.     

Effect of dietary protein concentration and degradability on response to rumen-protected methionine in lactating dairy cows

An incomplete 8 × 8 Latin square trial (4-wk periods; 12 wk total) using 32 multiparous and 16 primiparous Holstein cows was conducted to assess the production response to crude protein (CP), digestible rumen-undegraded protein (RUP), and rumen-protected Met (RPM; fed as Mepron; Degussa Corp., Kennesaw, GA). Diets contained [dry matter (DM) basis] 21% alfalfa silage, 34% corn silage, 22 to 26% high-moisture corn, 10 to 14% soybean meal, 4% soyhulls, 2% added fat, 1.3% minerals and vitamins, and 27 to 28% neutral detergent fiber. Treatments were a 2 × 2 × 2 factorial arrangement of the following main effects: 15.8 or 17.1% dietary CP, with or without supplemental rumen-undegraded protein (RUP) from expeller soybean meal, and 0 or 9 g of RPM/d. None of the 2- or 3-way interactions was significant. Higher dietary CP increased DM intake 1.1 kg/d and yield of milk 1.7 kg/d, 3.5% fat-corrected milk (FCM) 2.2 kg/d, fat 0.10 kg/d, and true protein 0.05 kg/d, and improved apparent N balance and DM and fiber digestibility. However, milk urea N and estimated urinary excretion of urea-N and total-N also increased, and apparent N efficiency (milk-N/N-intake) fell from 33 to 30% when cows consumed higher dietary CP. Positive effects of feeding more RUP were increased feed efficiency and milk fat content plus 1.8 kg/d greater FCM and 0.08 kg/d greater fat, but milk protein content was lower and milk urea N and urinary urea excretion were elevated. Supplementation with RPM increased DM intake 0.7 kg/d and FCM and fat yield by 1.4 and 0.06 kg/d, and tended to increase milk fat content and yield of milk and protein.     

Dietary cation-anion difference and dietary protein effects on performance and acid-base status of dairy cows in early lactation

Our objective was to examine the effects of dietary cation-anion difference (DCAD) with different concentrations of dietary crude protein (CP) on performance and acid-base status in early lactation cows. Six lactating Holstein cows averaging 44 d in milk were used in a 6 × 6 Latin square design with a 2 × 3 factorial arrangement of treatments: DCAD of −3, 22, or 47 milliequivalents (Na + K - Cl - S)/100 g of dry matter (DM), and 16 or 19% CP on a DM basis. Linear increases with DCAD occurred in DM intake, milk fat percentage, 4% fat-corrected milk production, milk true protein, milk lactose, and milk solids-not-fat. Milk production itself was unaffected by DCAD. Jugular venous blood pH, base excess and HCO₃⁻ concentration, and urine pH increased, but jugular venous blood Cl⁻ concentration, urine titratable acidity, and net acid excretion decreased linearly with increasing DCAD. An elevated ratio of coccygeal venous plasma essential AA to nonessential AA with increasing DCAD indicated that N metabolism in the rumen was affected, probably resulting in more microbial protein flowing to the small intestine. Cows fed 16% CP had lower urea N in milk than cows fed 19% CP; the same was true for urea N in coccygeal venous plasma and urine. Dry matter intake, milk production, milk composition, and acid-base status did not differ between the 16 and 19% CP treatments. It was concluded that DCAD affected DM intake and performance of dairy cows in early lactation. Feeding 16% dietary CP to cows in early lactation, compared with 19% CP, maintained lactation performance while reducing urea N excretion in milk and urine.     

Utilization of protein in red clover and alfalfa silages by lactating dairy cows and growing lambs

Feeding trials were conducted with lactating cows and growing lambs to quantify effects of replacing dietary alfalfa silage (AS) with red clover silage (RCS) on nutrient utilization. The lactation trial had a 2 × 4 arrangement of treatments: AS or RCS fed with no supplement, rumen-protected Met (RPM), rumen-protected Lys (RPL), or RPM plus RPL. Grass silage was fed at 13% of dry matter (DM) with AS to equalize dietary neutral detergent fiber (NDF) and crude protein contents. All diets contained (DM basis) 5% corn silage and 16% crude protein. Thirty-two multiparous (4 ruminally cannulated) plus 16 primiparous Holstein cows were blocked by parity and days in milk and fed diets as total mixed rations in an incomplete 8 × 8 Latin square trial with four 28-d periods. Production data (over the last 14 d of each period) and digestibility and excretion data (at the end of each period) were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). Although DM intake was 1.2 kg/d greater on AS than RCS, milk yield and body weight gain were not different. However, yields of fat and energy-corrected milk as well as milk content of fat, true protein, and solids-not-fat were greater on AS. Relative to AS, feeding RCS increased milk and energy-corrected milk yield per unit of DM intake, milk lactose content, and apparent N efficiency and reduced milk urea. Relative to AS, apparent digestibility of DM, organic matter, NDF, and acid detergent fiber were greater on RCS, whereas apparent and estimated true N digestibility were lower. Urinary N excretion and ruminal concentrations of ammonia, total AA, and branched-chain volatile fatty acids were reduced on RCS, indicating reduced ruminal protein degradation. Supplementation of RPM increased intake, milk true protein, and solids-not-fat content and tended to increase milk fat content. There were no silage × RPM interactions, suggesting that RPM was equally limiting on both AS and RCS. Supplementation of RPL did not influence any production trait; however, a significant silage × RPL interaction was detected for intake: RPL reduced intake of AS diets but increased intake of RCS diets. Duplicated metabolism trials were conducted with lambs confined to metabolism crates and fed only silage. After adaptation, collections of silage refusals and excreta were made during ad libitum feeding followed by feeding DM restricted to 2% of body weight. Intake of DM was not different when silages were fed ad libitum. Apparent digestibility of DM, organic matter, NDF, and hemicellulose was greater in lambs fed RCS on both ad libitum and restricted intake; however, acid detergent fiber digestibility was only greater at restricted intake. Apparent and estimated true N digestibility was substantially lower, and N retention was reduced, on RCS. Results confirmed greater DM and fiber digestibility in ruminants and N efficiency in cows fed RCS. Specific loss of Lys bioavailability on RCS was not observed. Based on milk composition, Met was the first-limiting AA on both silages; however, Met was not limiting based on production and nutrient efficiency. Depressed true N digestibility suggested impaired intestinal digestibility of rumen-undegraded protein from RCS.     

Effect of alfalfa silage storage structure and rumen-protected methionine on production in lactating dairy cows

The objective of this study was to determine whether production and nutrient utilization differed when lactating cows were fed diets based on 1 of 3 sources of alfalfa silage (AS) and whether performance was altered by feeding rumen-protected Met (RPM; fed as Mepron). Thirty-six lactating Holstein cows were blocked by parity and days in milk, then assigned to a randomized complete block design and fed a 3 × 2 arrangement of diets formulated from alfalfa ensiled in bag, bunker, or oxygen-limited silos, and supplemented with either 0 or 8 g of RPM/d. After feeding a covariate diet for 3 wk, treatment diets were fed for the remaining 12 wk of the trial. Experimental diets averaged [dry matter (DM) basis] 41% AS, 24% corn silage, 24% high-moisture corn, 3.7% soybean meal, 4% roasted soybeans, 2% ground shelled corn, 1.0% minerals and vitamins, 16.7% CP, and 31% NDF. Alfalfa from the oxygen-limited silo was lower in ash, higher in lactate, nonfiber carbohydrate, and in vitro NDF digestibility, had lower pH and ammonia content, and gave rise to greater DM intake and ADF digestibility than silage from the other 2 silos, indicating a more effective fermentation that, in turn, resulted in greater nutrient preservation. However, the more favorable composition, intake, and digestibility of alfalfa from the oxygen-limited silo were not reflected in improved milk production, which was not different among alfalfa sources. There was increased apparent N efficiency and trends for improved feed efficiency and protein yield with RPM supplementation across all 3 silages. The National Research Council (2001) model predicted that feeding RPM reduced Lys:Met ratio from 3.5 to 2.9, indicating that the diets were limiting in Met.     

Lactation response to soybean meal and rumen-protected methionine supplementation of corn silage-based diets

Corn silage, an important forage fed to dairy cows in the United States, is energy rich but protein poor. The objectives of this experiment were to investigate the effects on production of milk and milk components of feeding corn silage-based diets with 4 levels of dietary crude protein (CP) plus rumen-protected methionine (RPM). Thirty-six cows were blocked by days in milk into 9 squares and randomly assigned to 9 balanced 4 × 4 Latin squares with four 4-wk periods. All diets were formulated to contain, as a percent of dry matter (DM), 50% corn silage, 10% alfalfa silage, 4% soyhulls, 2.4% mineral-vitamin supplement, and 30% neutral detergent fiber. Supplemental RPM (Mepron, Evonik Corp., Kennesaw, GA) was added to all diets to maintain a Lys:Met ratio of 3.1 in digested AA. Ground high-moisture corn was reduced and soybean meal (SBM) plus RPM increased to give diets containing, on average, 11% CP (28% corn, 31% starch, 6% SBM, 4 g of RPM/d), 13% CP (23% corn, 29% starch, 10% SBM, 8 g of RPM/d), 15% CP (19% corn, 26% starch, 15% SBM, 10 g of RPM/d), and 17% CP (14% corn, 24% starch, 19% SBM, 12 g of RPM/d). Data from the last 14 d of each period were analyzed using the mixed procedures in SAS (SAS Institute Inc., Cary, NC). With the exception of milk fat and milk lactose content, we found no significant effects of diet on all production traits. We did note linear responses to dietary CP concentration for intake, production of milk and milk components, and MUN. Cows fed the 11% CP diet had reduced DM intake, lost weight, and yielded less milk and milk components. Mean separation indicated that only true protein yield was lower on 13% CP than on 17% dietary CP, but not different between 15 and 17% CP. This indicated no improvement in production of milk and milk components above 15% CP. Quadratic trends for yield of milk, energy-corrected milk, and true protein suggested that a dietary CP concentration greater than 15% may be necessary to maximize production or, alternately, that a plateau was reached and no further CP was required. Although diet influenced apparent digestibility of DM, organic matter, and neutral detergent fiber, digestibility did not increase linearly with dietary CP. However, we observed linear and quadratic effects of dietary CP on acid detergent fiber digestibility. As expected, we found a linear effect of dietary CP on apparent N digestibility and on fecal and urinary N excretion, but no effect of diet on estimated true N digestibility. Ruminal concentrations of ammonia, total AA, peptides, and branched-chain volatile fatty acids also increased linearly with dietary CP. Quadratic responses indicated that 14.0 to 14.8% CP was necessary to optimize digestion and energy utilization. Overall results indicated that, when RPM was added to increase Lys:Met to 3.1, 15% CP was adequate for lactating dairy cows fed corn silage diets supplemented with SBM and secreting about 40 kg of milk/d; N excretion was lower than at 17% CP but with no reduction in yield of milk and milk components.     

Effect of amount and ruminal degradability of soybean meal protein on performance of lactating dairy cows

Twenty-eight Holstein cows (4 with ruminal cannulas) were blocked by days in milk into 7 groups and then randomly assigned to 1 of 7 balanced 4 × 4 Latin square diet sequences. The diets contained [dry matter (DM) basis] 20% alfalfa silage, 35% corn silage, and 45% concentrate mainly from high-moisture corn and soybean meal. Diets differed in crude protein (CP) content and source of protein supplement: diet A) 15.6% CP, 3.7% solvent-extracted soybean meal (SSBM), 4.5% expeller soybean meal (ESBM); diet B) 16.6% CP, 9.6% SSBM, 0% ESBM; diet C) 16.6% CP, 4.6% SSBM, 5.9% ESBM; and diet D) 17.6% CP, 11.7% SSBM, 0% ESBM. Each experimental period consisted of 14 d for adaptation plus 14 d for collection of production data. Sampling of ruminal digesta and spot sampling of blood, feces, and urine was done on d 26 and 27 of each period. Planned contrasts compared included diet A vs. diet B, diet B vs. diet C, and diet B vs. diet D. There were no effects of diet on most of the production traits measured. However, milk yield tended to be higher for diet B vs. A. Trends were also detected for higher DM intake and weight gain and lower milk yield/DM intake in cows fed diet D vs. diet B. Milk lactose content was higher on diets A and C than on B. Ruminal NH₃ was higher on diet D vs. B, but other ruminal metabolites, apparent nutrient digestibility, and estimated bacterial CP synthesis did not differ across diets. Blood and milk urea-N were higher on diets C and D than on B; milk urea-N was higher on diet B than on A. Increasing dietary CP from 16.6% (diet B) to 17.6% (diet D) increased urinary N excretion by 54 g/d and reduced apparent N efficiency (milk N/N intake) by 2.5 percentage units, without altering yield. Under the conditions of this trial, milk production was not improved by feeding rumen-undegraded protein from ESBM or greater amounts of rumen-degraded protein from SSBM. Feeding more than 16.6% CP depressed N efficiency.     

Effect of two levels of crude protein and methionine supplementation on performance of dairy cows

Sixteen Holstein cows in midlactation were randomly assigned to treatments in a replicated 4 x 4 Latin square. Two levels of CP (16.1 vs. 18.8%) with or without supplemental methionine (0.07 g/100 g of DM) were tested in a 2 x 2 factorial arrangement of treatments. Dry matter intake, milk production, milk composition, and N excretion were determined. No interactions between CP level and methionine supplementation were observed. Milk production and dry matter intake were not different among treatments. Milk protein concentration increased from 3.17 to 3.26% with the addition of methionine and decreased from 3.24 to 3.17% with increased CP. No differences were observed among treatments in milk protein yield. Milk fat concentration was low across all diets, but was increased from 2.33% with 16.1% CP diets to 2.68% with 18.8% CP diets. No significant treatment effects were observed for SNF, lactose concentration in milk, or casein N as a fraction of skim milk N. Increased dietary CP increased milk urea N by 3.9 mg/dl. Methionine supplementation did not affect N excretion in urine or feces. The higher protein diets increased estimated urine volume by 2.9 L/d and increased N concentration by 1.7 percentage units in both urine and feces. Feeding higher protein increased milk urea and urine N excretion as expressed as a percentage of total N excreted (44 vs. 38% for 18.8 and 16.1% CP, respectively). Overall, feeding 16.1% CP produced milk and milk protein yields similar to feeding 18.8% CP, but reduced the N losses in urine and milk urea.     

Corn silage hybrid type and quality of alfalfa hay affect dietary nitrogen utilization by early lactating dairy cows

This experiment was conducted to determine the effects of corn silage (CS) hybrids and quality of alfalfa hay (AH) in high-forage dairy diets on N utilization, ruminal fermentation, and lactational performance by early-lactating dairy cows. Eight multiparous Holstein cows were used in a duplicated 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of dietary treatments. The 8 cows (average days in milk = 23 ± 11.2) were surgically fitted with ruminal cannula, and the 2 squares were conducted simultaneously. Within square, cows were randomly assigned to a sequence of 4 diets: conventional CS (CCS) or brown midrib CS (BMR) was combined with fair-quality AH [FAH: 46.7% neutral detergent fiber (NDF) and 18.4% crude protein (CP)] or high-quality AH (HAH: 39.2% NDF and 20.7% CP) to form 4 treatments: CCS with FAH, CCS with HAH, BMR with FAH, and BMR with HAH. Diets were isonitrogenous across treatments, averaging 15.9% CP. Each period lasted a total of 21 d, with 14 d for treatment adaptation and 7 d for data collection and sampling. Intake of DM and milk yield did not differ in response to CS hybrids or AH quality. Although feeding BMR-based diets decreased urinary N output by 24%, it did not affect fecal N output. Feeding HAH decreased urinary N output by 15% but increased fecal N output by 20%. Nitrogen efficiency [milk N (g/d)/intake N (g/d)] tended to increase for BMR treatments. Ruminal ammonia-N concentration was lower for cows fed BMR-based diets than for those fed CCS-based diets but was not affected by quality of AH. Feeding BMR-based diets or HAH decreased milk urea N concentration by 23 or 15%, respectively, compared with CCS-based diets or FAH. Total volatile fatty acid concentration increased with HAH but was not influenced by CS hybrids. Feeding BMR-based diets decreased urinary N-to-fecal N ratio (UN:FN), and it was further reduced by feeding HAH. Although cows fed the BMR-based diets tended to increase milk N-to-manure N ratio, the quality of AH did not affect the ratio. The lower ratio of UN:FN with a higher ratio of milk N-to-manure N ratio for the BMR-based diets indicates that feeding BMR may reduce manure ammonia-N by reducing excretion of urinary N and increasing secretion of milk N per unit of manure N excreted.     

Effects of feeding wheat or corn-wheat dried distillers grains with solubles in low- or high-crude protein diets on ruminal function,omasal nutrient flows,urea-N recycling,and performance in cows

A study was conducted to determine the effects of including either wheat-based (W-DDGS) or corn-wheat blend (B-DDGS) dried distillers grains with solubles as the major protein source in low- or high-crude protein (CP) diets fed to dairy cows on ruminal function, microbial protein synthesis, omasal nutrient flows, urea-N recycling, and milk production. Eight lactating Holstein cows (768.5 ± 57.7 kg of body weight; 109.5 ± 40.0 d in milk) were used in a replicated 4 × 4 Latin square design with 28-d periods (18 d of dietary adaptation and 10 d of measurements) and a 2 × 2 factorial arrangement of dietary treatments. Four cows in one Latin square were ruminally cannulated for the measurement of ruminal fermentation characteristics, microbial protein synthesis, urea-N recycling kinetics, and omasal nutrient flow. The treatment factors were type of distillers co-product (W-DDGS vs. B-DDGS) and dietary CP content [15.2 vs. 17.3%; dry matter (DM) basis]. The B-DDGS was produced from a mixture of 15% wheat and 85% corn grain. All diets were formulated to contain 10% W-DDGS or B-DDGS on a DM basis. No diet effect was observed on DM intake. Yields of milk, fat, protein, and lactose, and plasma urea-N and milk urea-N concentrations were lower in cows fed the low-CP compared with those fed the high-CP diet. Although feeding B-DDGS tended to reduce ruminal ammonia-N (NH₃-N) concentration compared with feeding W-DDGS (9.3 vs. 10.5 mg/dL), no differences were observed in plasma urea-N and milk urea-N concentrations. Additionally, dietary inclusion of B-DDGS compared with W-DDGS did not affect rumen-degradable protein supply, omasal flows of total N, microbial nonammonia N (NAN), rumen-undegradable protein, and total NAN, or urea-N recycling kinetics and milk production. However, cows fed the low-CP diet had lower N intake, rumen-degradable protein supply, ruminal NH₃-N concentration, and omasal flows of N, microbial NAN, and total NAN compared with those fed the high-CP diet. Feeding the low-CP compared with the high-CP diet also resulted in lower endogenous urea-N production, urea-N recycled to the gastrointestinal tract, and urea-N excretion in urine. In summary, our results indicate that both W-DDGS and B-DDGS can be included as the major protein sources in dairy cow diets without compromising nutrient supply and production performance. However, feeding the low-CP diet lowered omasal flows of microbial protein and metabolizable protein, which, in turn, resulted in lower milk production compared with feeding the high-CP diet.     

Effect of source of rumen-degraded protein on production and ruminal metabolism in lactating dairy cows

Twenty-eight (8 with ruminal cannulas) lactating Holstein cows were assigned to seven 4 × 4 Latin squares in a 16-wk trial to study the effects on production and ruminal metabolism of feeding differing proportions of rumen-degraded protein (RDP) from soybean meal and urea. Diets contained [dry matter (DM) basis] 40% corn silage, 15% alfalfa silage, 28 to 30% high-moisture corn, plus varying levels of ground dry shelled corn, solvent- and lignosulfonate-treated soybean meal, and urea. Proportions of the soybean meals, urea, and dry corn were adjusted such that all diets contained 16.1% crude protein and 10.5% RDP, with urea providing 0, 1.2, 2.4, and 3.7% RDP (DM basis). As urea supplied greater proportions of RDP, there were linear decreases in DM intake, yield of milk, 3.5% fat-corrected milk, fat, protein, and solids-not-fat, and of weight gain. Milk contents of fat, protein, and solids-not-fat were not affected by source of RDP. Replacing soybean meal RDP with urea RDP resulted in several linear responses: increased excretion of urinary urea-N and concentration of milk urea-N, blood urea-N, and ruminal ammonia-N and decreased excretion of fecal N; there was also a trend for increased excretion of total urinary N. A linear increase in neutral detergent fiber (NDF) digestibility, probably due to digestion of NDF-N from lignosulfonate-treated soybean meal, was observed with greater urea intake. Omasal sampling revealed small but significant effects of N source on measured RDP supply, which averaged 11.0% (DM basis) across diets. Increasing the proportion of RDP from urea resulted in linear decrease in omasal flow of dietary nonammonia N (NAN) and microbial NAN and in microbial growth efficiency (microbial NAN/unit of organic matter truly digested in the rumen). These changes were paralleled by large linear reductions in omasal flows of essential, nonessential, and total amino acids. Overall, these results indicated that replacing soybean meal RDP with that from urea reduced yield of milk and milk components, largely because of depressed microbial protein formation in the rumen and that RDP from nonprotein-N sources was not as effective as RDP provided by true protein.     

Effects of milk replacer composition on growth, body composition, and nutrient excretion in preweaned Holstein heifers

Twenty-four newborn Holstein heifer calves were fed 1 of 4 milk replacers (MR): control (20% CP, 21% fat; MR fed at 441 g/d); high protein/low fat (HPLF; 28% CP, 20% fat; MR fed at 951 g/d); high protein/high fat (HPHF; 27% CP, 28% fat; MR fed at 951 g/d); and HPHF MR fed at a higher rate (HPHF+; 27% CP, 28% fat; MR fed at 1,431 g/d). Dry calf starter (20% CP, 1.43% fat) composed of ground corn (44.4%), 48% CP soybean meal (44.4%), cottonseed hulls (11.2%), and molasses (1.0%) was offered free choice. Heifers were obtained from a commercial dairy, blocked by groups of 8 in the order acquired, and randomly assigned to treatments within group. Upon arrival at the research farm, heifers were fed the control for 2 feedings. Treatments were imposed when heifers were 4 ± 1 d of age. Heifers were on study for 61 ± 1 d. Body weight and body size measures were taken weekly. Four-day total collection of feed refusals, feces, and urine was initiated at 57 ± 1 d of age. Heifers were slaughtered at the end of the collection period to evaluate body composition. Preplanned contrasts were used to compare control to all, HPLF to HPHF, and HPHF to HPHF+. Heifers fed the control diet consumed more starter than those fed other treatment diets, but their total dry matter intake and apparent dry matter digestibility were lowest. Fecal output was highest in heifers fed the control diet, whereas urine output and urine N excretion were lowest. Nitrogen intake and urine N excretion were greater for heifers fed HPHF+ compared with HPHF but were not affected by MR fat content (HPLF vs. HPHF). Retention (g/d) of N and P was greater in heifers fed all nutrient-dense diets compared with those fed the control diet, but was not improved by increasing fat in the milk replacer (HPLF vs. HPHF) or by increasing the amount fed. Addition of fat to the milk replacer (HPLF vs. HPHF) increased empty body weight fat content without improving average daily gain or frame measures. Increasing the volume fed (HPHF vs. HPHF+) increased growth rate and empty body weight, but HPHF+ heifers were neither taller nor longer and their carcasses contained more fat. Clear improvements in growth and nutrient retention were observed with more nutrient-dense diets, but most of the improvements were seen with the increased protein intake relative to the control MR; adding fat to the high protein MR did not further improve lean tissue gain.     

Varying protein and starch in the diet of dairy cows. II. Effects on performance and nitrogen utilization for milk production

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on the lactational performance and use of N for milk production. Sixty multiparous Holstein cows were used in a 210-d lactational trial with a completely randomized design with a 2 × 3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary CP (means = 14.8, 16.8, and 18.7%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25.0% corn silage, 20.0% alfalfa silage, 10.0% cottonseed, 26.7 to 37.0% corn grain, and 4.8 to 13.5% protein supplement, plus minerals and vitamins. Across the 210 d of lactation, the productive response of dairy cows to the source of supplemental CP depended on the concentration of CP in the diet. At 18.7% CP, cows fed SBM consumed more DM and produced more milk, 3.5% fat-corrected milk, fat, and true protein, but had lower efficiency of feed use and body condition score than cows fed AMB. At 16.8% CP, cows fed AMB produced more 3.5% fat-corrected milk, fat, and true protein than cows fed SBM. At 14.8% CP, cows fed SBM consumed more DM but produced less true protein and had lower feed efficiency than cows fed AMB. Across CP sources, cows fed 14.8% CP produced less fat-corrected milk and true protein than cows fed 16.8 and 18.7% CP. Across CP percentages, cows fed AMB produced more fat-corrected milk per kilogram of DM consumed than cows fed SBM. Despite these interactions, improvements in the gross efficiency of N use for milk production were achieved through reductions in the intake of N independently of the source of CP. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650 g daily if the source of RDP and RUP are properly matched with the source and amount of carbohydrate in the diet.     

Short communication: effects of 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester on milk production and composition of lactating Holstein dairy cows

Sixteen multiparous Holstein cows were used to determine the effects of 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester (HMBi: 0 vs. 1.26 g/kg of total ration dry matter (DM) and dietary crude protein (CP) concentration [14.7% (low) vs. 16.9% (standard), DM basis] on milk yield and composition using a replicated 4 × 4 Latin square design experiment with 4-wk periods. Cows were fed ad libitum a total mixed ration with a 1:1 forage-to-concentrate ratio (DM basis), and diets provided an estimated 6.71 and 1.86% lysine and methionine, respectively, in metabolizable protein for the low-protein diet and 6.74 and 1.82% in the standard protein diet. Dry matter intake, milk yield, and composition were measured during wk 4 of each period. There were no effects on DM intake, which averaged 24.7 kg/d. There was an interaction between dietary CP and HMBi for milk yield and 3.5% fat-corrected milk (FCM). Feeding HMBi decreased milk and FCM yield when fed with the low-CP diet but did not affect milk or FCM yield when fed with the standard CP diet. Feeding HMBi increased milk protein concentration regardless of diet CP concentration and increased milk protein yield when added to the standard CP diet but not the low-CP diet. The positive effect of HMBi on milk protein yield was only observed at the standard level of dietary CP, suggesting other factors limited the response to HMBi when dietary protein supply was restricted.     

Protein level for alfalfa and corn silage-based diets: II. Nitrogen balance and manure characteristics

This N balance study was completed with 48 multiparous Holstein cows (body weight [BW] = 653 kg; days in milk = 89) blocked by calving date and assigned to a 2 x 2 factorial arrangement of dietary treatments. The total mixed ration included alfalfa silage (AS) or corn silage (CS) as the primary forage source (41 and 14% vs. 14 and 41% of diet dry matter (DM), respectively) and were formulated for recommended (RP) or excessive (HP) amounts of rumen degradable protein (RDP) and rumen undegradable protein (RUP) according to the guidelines of the National Research Council (NRC). Crude protein (CP) averaged 16.5, 18.0, 16.4, and 17.3% for the AS-RP; AS-HP; CS-RP; and CS-HP diet, respectively (DM basis). Regardless of primary forage source, the reduction in dietary CP to the NRC guidelines tended to improve milk yield (43.4 vs. 41.0 kg/d) but did not alter 3.5% fat-corrected milk (37.0 kg/d) or milk true protein yield (1167 g/d). In this trial, cows fed the CS-based diets consumed less DM than those fed the AS-based diets in part because of rumen acidosis. The adverse effect of low rumen pH was accompanied by an increase in urinary N (UN) as a percentage of N intake, but did not alter milk yield. Notwithstanding partial confounding, fecal N (FN) was 49 g/d lower (213 vs. 164 g/d), UN was unchanged (229 g/d), but milk N tended to be higher (194 vs. 206 g/d) when cows were fed the CS-based diets compared with AS-based diets. Compared with the HP diets, cows fed the RP diets had similar FN (189 g/d) and milk N (200 g/d), but UN and urine urea N were reduced by 41 g/d (249 vs. 208 g/d) and 40 g/d (210 vs. 171 g/d), respectively. Fecal N concentration was higher for CS-based diets, but urinary N concentration was higher for AS-based diets. The reduction in dietary CP did not influence these concentrations but lowered urine volume. The metabolic relationships between energy and protein in determining the fate of excess dietary N (primarily in the form of excess RUP in this trial) was illustrated by a 17% increase in the UN to FN ratio for cows fed AS-HP compared with the AS-RP diet and a 42% increase in the UN to FN ratio for CS-HP compared with CS-RP diet, when cows' energy status was compromised because of rumen acidosis. In this trial, UN ranged from 150 to 320 g/d, and was best predicted as UN (g/d) = 0.0283 x BW (kg) x milk urea N (mg/dL). The NRC protein guidelines should not be exceeded to avoid unnecessary losses of manure N and, in particular, urine urea N.     

Effect of milk replacer program on digestion of nutrients in dairy calves

There are concerns with feeding young dairy calves amounts of milk solids approaching 0.9 kg of dry matter (DM) or more because of slumps in average daily gain (ADG) at weaning and low starter intakes. Additionally, programs feeding more than 0.6 kg of DM have not been thoroughly tested for success at different weaning ages. Four milk replacer (MR) programs were compared in trial 1. Program A was 0.44 kg of DM of a 21% crude protein (CP), 21% fat MR powder fed daily for 42 d. Program B was 0.66 kg of DM of a 27% CP, 17% fat MR powder fed daily for 42 d. Program C was 0.66 kg of DM of a 27% CP, 17% fat MR powder daily fed for 28 d. Program D was up to 1.09 kg of DM of a 29% CP, 21% fat MR daily fed for 49 d. Digestibility estimates were made and blood was sampled for serum constituents on d 53 to 56, and performance was measured for 84 d. Three programs feeding a 27% CP, 17% fat MR powder were compared in trial 2 over 56 d. Calves on program A were fed 0.66 kg of DM powder daily and weaned at 28 d. Calves on program B were fed 0.66 kg of DM powder daily and weaned at 42 d. Calves on program C were fed up to 1.09 kg of DM powder daily and weaned at 42 d. Digestibility estimates were made and blood was sampled for serum constituents d 21 to 24, d 36 to 39, and d 53 to 56. In trial 1, calves fed program A had the least overall ADG. Calves fed program D had the greatest ADG from 0 to 56 d, the least ADG from d 56 to 84, the least digestibility estimates, and the least concentrations of serum amylase. At 84 d, there were no differences in body weights of calves fed programs B, C, and D. In trial 2, calves fed program A had the greatest starter intake and greatest concentrations of serum amylase. Calves fed program C had the least estimates of digestibility from d 53 to 56 and the least serum concentrations of amylase. Calves fed up to 1.09 kg/d of 27 to 29% MR powders and weaned at 42 or 49 d had lower starter intakes, concentrations of serum amylase, and digestion of starter postweaning compared with calves fed conventional 21% CP, 21% fat MR powders fed at 0.44 kg/d. Calves fed 0.66 kg/d of a 27% CP, 17% fat MR powder and weaned at 28 or 42 d of age had no reductions in intake or digestion compared with calves fed conventional MR and gained as much total body weight from 0 to 84 d as calves stepped up to 1.09 kg of MR.     

Comparative evaluation of alternative forages to grass silage in the diet of early lactation dairy cows

Fifty-six autumn-calving Holstein-Friesian cows, blocked on the basis of days in milk (27.6 ± 10.65 d), lactation number (3.1 ± 2.21), and preexperimental milk yield (28.4 ± 6.69 kg) were used to examine the effects of replacing 330 g/kg of dry matter (DM) of first-cut perennial ryegrass silage with either fermented whole-crop wheat (WCW), urea-treated processed WCW, or corn silage on subsequent feed intake, milk production, and efficiency of nitrogen utilization. The DM (g/kg), crude protein (CP, g/kg of DM) and in vitro DM digestibility (g/kg) of the forages were 204, 179, and 762 for grass silage; 389, 90, and 711 for fermented WCW; 795, 141, and 768 for urea-treated processed WCW; and 346, 93, and 783 for corn silage, respectively. Four forage treatments were evaluated as follows: 1) grass silage as the sole forage (GS); 2) a mixture of grass silage and fermented WCW silage, (F-WCW); 3) a mixture of grass silage and urea-treated processed WCW, (UP-WCW); and 4) a mixture of grass silage and corn silage (CS). In all cases, the alternative forages comprised 67% of the forage mix on a DM basis. Isonitrogenous diets were formulated by offering all cows 8 kg of concentrate as fed, formulated to different CP concentrations. Cows were offered these diets from 28 to 104 d in milk. Total DM intake and milk yield were greater on UP-WCW (20.0 and 30.2 kg/d) and CS (18.3 and 33.2 kg/d) than on GS (13.5 and 26.5 kg/d). Although DM intake was greater on F-WCW (17.1 kg/d) than on GS, milk yield was not significantly greater (+2.7 kg/d). Milk protein concentration was greater on F-WCW (30.5 g/kg), UP-WCW (31.3 g/kg), and CS (30.7 g/kg) than on GS (28.5 g/kg). However, there was no difference between treatments in milk fat or lactose concentrations. Body weight change was greater for cows offered GS (−0.27 kg/d) than for those offered UP-WCW (−0.01 kg/d) and CS (+0.05 kg/d) but not compared with those offered F-WCW (−0.06 kg/d). There was no effect of treatment on plasma glucose, nonesterified fatty acids, β-hydroxybutyrate, urea, or total protein at d 64 ± 17.4 and d 92 ± 17.4 postpartum. Efficiency of N utilization was greatest for CS with 0.36 of N intake being recovered in milk compared with 0.28, 0.32, and 0.26 for GS, F-WCW, and UP-WCW, respectively. There was no effect of treatment on milk urea N concentration or the urinary allantoin N to creatinine N ratio. The results of this experiment indicate that corn silage is a more suitable supplementary forage to grass silage than fermented or urea-treated processed WCW, with advantages realized in milk production and more efficient N utilization.     

Utilization of phosphorus in lactating cows fed varying amounts of phosphorus and sources of fiber

This study was undertaken to determine the effect of dietary P content and fiber source on P utilization. Four dietary treatments were formed in a 2 × 2 factorial arrangement. The P content was 0.32 or 0.44%, and the fiber source was varied by substituting 10% soyhulls for 6% alfalfa hay on a dry matter (DM) basis. Diets also contained approximately 50% corn silage and alfalfa silage for all treatments. The diets were fed to 32 early to midlactation Holsteins for 10 wk. Fecal P excretion was estimated using indigestible acid detergent fiber marker determined with 12-d in situ incubation and grab sampling. Milk yield was high, averaging 43 kg/d across treatments, and 42.1 and 44.0 kg/d for the 0.32 and 0.44% P diets, respectively. Milk fat content was also high, averaging 3.68 and 4.12% for the 0.32 and 0.44% P diets, respectively. Milk protein yield averaged 1.240 and 1.323 kg/d. Differences in milk production were associated with 1.5 kg/d less DM intake for the lower P diets on average. Based on lactation performance, 0.32% P appeared inadequate for this level of production, whereas the calculated (National Research Council) requirement was 0.37%. Fecal P concentration increased linearly with P intake, and based on this relationship, reducing dietary P from 0.44 to 0.37% would reduce fecal P excretion by 12%. Partial substitution of soyhulls for alfalfa hay did not affect feed intake or milk production, but reduced fecal P excretion, partially because of increased P apparent digestibility. The reduction in fecal P excretion resulting from reduced P intake or substitution of soyhulls for alfalfa hay was apparently through reductions in the regulated portion of fecal P. Cows producing 43 kg/d of milk appeared to need > 0.32% P, whereas the requirement assessed from National Research Council data was 0.37%. Using highly digestible nonforage fiber sources in place of forage fiber sources in the diet may allow less P to be fed while still meeting the requirement.     

Effect on Production of Replacing Dietary Starch with Sucrose in Lactating Dairy Cows

Replacing dietary starch with sugar has been reported to improve production in dairy cows. Two sets of 24 Holstein cows averaging 41 kg/d of milk were fed a covariate diet, blocked by days in milk, and randomly assigned in 2 phases to 4 groups of 6 cows each. Cows were fed experimental diets containing [dry matter (DM) basis]: 39% alfalfa silage, 21% corn silage, 21% rolled high-moisture shelled corn, 9% soybean meal, 2% fat, 1% vitamin-mineral supplement, 7.5% supplemental nonstructural carbohydrate, 16.7% crude protein, and 30% neutral detergent fiber. Nonstructural carbohydrates added to the 4 diets were 1) 7.5% corn starch, 0% sucrose; 2) 5.0% starch, 2.5% sucrose; 3) 2.5% starch, 5.0% sucrose; or 4) 0% starch, 7.5% sucrose. Cows were fed the experimental diets for 8 wk. There were linear increases in DM intake and milk fat content and yield, and linear decreases in ruminal concentrations of ammonia and branched-chain volatile fatty acids, and urinary excretion of urea-N and total N, and urinary urea-N as a proportion of total N, as sucrose replaced corn starch in the diet. Despite these changes, there was no effect of diet on microbial protein formation, estimated from total purine flow at the omasum or purine derivative excretion in the urine, and there were linear decreases in both milk/DM intake and milk N/N-intake when sucrose replaced dietary starch. However, expressing efficiency as fat-corrected milk/DM intake or solids-corrected milk/DM intake indicated that there was no effect of sucrose addition on nutrient utilization. Replacing dietary starch with sucrose increased fat secretion, apparently via increased energy supply because of greater intake. Positive responses normally correlated with improved ruminal N efficiency that were altered by sucrose feeding were not associated with increased protein secretion in this trial.