Assessing bioavailability of ruminally protected methionine and lysine prototypes

Met and Lys are essential AA that can limit lactational performance in dairy cattle fed protein-sufficient diets. Thus, there is industry demand for ruminally protected (RP) sources of Met and Lys. One method of providing ruminal protection for Met and Lys is lipid encapsulation. The objective of this work was to assess 3 lipid-encapsulated Met prototypes (P1, P2, and P3) and 1 Lys prototype (P4) to determine ruminal protection, small intestine absorption (experiment 1), and animal production responses (experiment 2). Ruminal protection was estimated from 8-h in situ retention during ruminal incubation and intestinal absorption from plasma appearance after an abomasal bolus of the in situ retentate. Blood samples were collected over time to determine plasma Met and Lys concentration responses compared with unprotected Lys and Met infused abomasally. The prototypes were not exposed to the total diet or subjected to typical feed handling methods before evaluation. The bioavailability of P1, P2, and P3 Met prototypes was found to be 14, 21, and 18% of the initial AA material, respectively. The RP-Lys prototype had a bioavailability of 45%. To evaluate production responses, 20 Holstein cows were randomly assigned to 2 trials (n = 10 each) in a replicated Latin square design with 14-d periods. The base diet was predicted to be deficient in metabolizable Met (?14.8 g/d) and Lys (?16.1 g/d) per the Cornell Net Carbohydrate and Protein System (version 6.55). In the Met trial, the base diet was supplemented with RP-Lys to meet Lys requirements, and treatments were as follows: no added RP-Met (NCM), NCM plus Smartamine M (SM; Adisseo, Alpharetta, GA), and NCM plus P1, P2, or P3 at 148% of the Met content of SM. In the Lys trial, the base diet was supplemented with RP-Met to meet the Met requirement, and treatments were as follows: no added Lys (NCL), NCL plus AjiProL (AL; Ajinomoto Heartland Inc., Chicago, IL), and NCL plus P4 at 55, 78, or 102% of the reported absorbed Lys in AL. All products were top dressed on the diet without prior mixing or extended exposure to the rest of the diet. Milk protein concentration significantly increased when diets were supplemented with P2, P3, or SM (3.12, 3.12, and 3.11%, respectively) compared with NCM (3.02%). Only P1 (3.04%) was significantly lower than SM. Prototype P2 had the greatest numerical milk protein output response among the 3 RP-Met prototypes, suggesting that it may have had the greatest efficacy when supplemented into these rations. There was a numerical milk protein concentration response to AL and a linear increase in milk protein concentration for P4. The P4 and AL treatments resulted in comparable milk protein production regardless of P4 dose.     

Relative availability of metabolizable methionine from 2 ruminally protected sources of methionine fed to lactating dairy cattle

Our objective was to evaluate the lactational responses of dairy cows to methionine provided from 2 ruminally protected sources of methionine activity. Twenty-one Holstein dairy cows [11 primiparous (634 kg of body weight, 140 d in milk) and 10 second-parity (670 kg of body weight, 142 d in milk)] were assigned to a treatment sequence in 4 replicated 5 × 5 Latin squares plus 1 cow, with 14-d periods. Treatments were as follows: control; 7.5 or 15 g/d of a ruminally protected product of 2-hydoxy-4-methylthio-butyric acid (NTP-1401; Novus International Inc., St. Charles, MO); or 7.5 or 15 g/d of a ruminally protected dl-methionine product (Smartamine M; Adisseo, Alpharetta, GA). The diet was predicted to meet metabolizable protein and energy requirements. Diets contained 16.1% crude protein, and the control diet was predicted to be deficient in metabolizable methionine (1.85% of metabolizable protein) but sufficient in lysine (6.8% of metabolizable protein). Feed intake and milk yield were measured on d 11 to 14. Blood was collected on d 14. Dry matter intake, milk yield, energy-corrected milk, milk fat yield and percentage, and efficiencies of milk and energy-corrected milk yield were not affected by treatment. Milk protein percentage and milk protein yield increased linearly with supplementation, without differences between methionine sources or interactions between source and level. Linear regressions of milk protein percentage and milk protein yield against supplement amount within source led to slope ratios (NTP-1401:Smartamine M) of 95% for protein percentage and 84% for protein yield, with no differences between sources for increasing milk protein. Plasma methionine concentrations were increased linearly by methionine supplementation; the increase was greater for Smartamine M than for NTP-1401. Plasma d-methionine was increased only by Smartamine M. Plasma 2-hydoxy-4-methylthio-butyric acid was increased only by NTP-1401. Our data demonstrated that supplementation with these methionine sources can improve milk protein percentage and yield, and the 2 methionine sources did not differ in their effect on lactation performance or milk composition.     

Production and nitrogen utilization in lactating dairy cows fed ground field peas with or without ruminally protected lysine and methionine

Previous research has shown that cows fed ≥24% of the diet dry matter (DM) as field peas decreased milk yield as well as concentration and yield of milk protein, possibly due to reduced DM intake and limited supply of Lys and Met. Twelve multiparous and 4 primiparous lactating Holstein cows were randomly assigned to 1 of 4 diets in a replicated 4 × 4 Latin square design. The diets contained (DM basis) 34.8% corn silage, 15.2% grass-legume silage, 5.9% roasted soybean, 2.4% mineral-vitamin premix, 2.0% alfalfa pellets, and either (1) 36% ground corn, 2.4% soybean meal, and 1.3% urea (UR), (2) 29.7% ground corn, 9.8% soybean meal, 0.13% ruminally protected (RP) Lys, and 0.07% RP-Met (CSBAA), (3) 25% ground field peas, 12.3% ground corn, and 2.4% soybean meal (FP), or (4) FP supplemented with 0.15% RP-Lys and 0.05% RP-Met (FPAA). Our objective was to test the effects of FP versus UR, FPAA versus CSBAA, and FPAA versus FP on milk yield and composition, N utilization, nutrient digestibility, ruminal fermentation profile, and plasma concentration of AA. Milk yield did not differ across diets. Compared with cows fed UR, those fed FP had greater DM intake, concentration and yield of milk true protein, apparent total-tract digestibility of fiber, urinary excretion of purine derivatives, and concentrations of total volatile fatty acids in the rumen and Lys in plasma, and less milk urea N and ruminal NH₃-N. The concentration of milk urea N, as well as the concentration and yield of milk fat increased in cows fed FPAA versus CSBAA. Moreover, cows fed FPAA had greater ruminal concentration of total volatile fatty acids, increased proportions of acetate and isobutyrate, and decreased proportions of propionate and valerate than those fed CSBAA. The plasma concentrations of His, Leu, and Phe decreased, whereas plasma Met increased and plasma Lys tended to increase in cows fed FPAA versus CSBAA. Concentration of milk true protein, but not yield, was increased in cows fed FPAA versus FP. However, cows fed FPAA showed decreased concentrations of His and Leu in plasma compared with those fed FP. Overall, compared with the CSBAA diet, feeding FPAA did not negatively affect milk yield and milk protein synthesis. Furthermore, RP-Lys and RP-Met supplementation of the FP diet did not improve milk yield or milk protein synthesis, but decreased urinary urea N excretion.     

Lactational response to soybean meal, heated soybean meal, and extruded soybeans with ruminally protected methionine

Seventy-three high producing Holstein cows were arranged in a 3 X 2 factorial to evaluate three protein supplements (soybean meal, heat-treated soybean meal, and extruded blend of soybeans and soybean meal) without or with 15 g/head/d of ruminally protected DL-methionine during wk 4 through 16 postpartum. Total mixed diets contained (DM basis) 30% corn silage, 15% alfalfa hay, and 55% of the respective concentrate mix. Milk production was higher when cows were fed either heated soybean product instead of soybean meal. Methionine supplementation increased production when fed with soybean meal (32.2 and 33.8 kg/d) but not when fed with heat-treated soybean meal (34.5 and 33.0 kg/d) or extruded soybeans (36.2 and 34.4 kg/d). Milk fat percentages were lower with extruded soybeans (3.01, 2.93, and 2.66) and were similar without (2.83) or with (2.90) supplemental methionine. Milk protein percentages were highest when fed soybean meal, lowest with extruded soybeans (3.02, 2.92, and 2.87), and higher with supplemental methionine (2.91 and 2.96). Dry matter intake was higher when fed supplemental methionine (20.0 and 21.3 kg/d). Production of milk in early lactation high producing dairy cows was increased by supplementing a soybean meal diet with ruminally protected methionine or by replacing the soybean meal with heat-treated soybean meal, soybeans, or a mixture of the two.     

Effect of ruminally protected methionine on splanchnic metabolism of amino acids in lactating dairy cows

The effect of ruminally protected Met (RPM) on splanchnic metabolism was measured in 3 primiparous and 3 multiparous Holstein cows. Doses of RPM (0, 36, and 72 g/d) were tested in a replicated 3 × 3 Latin square design, over 3 consecutive 14-d experimental periods. A mixed ration was fed in 12 equal meals per d (average dry matter intake: 17.5 ± 0.08 kg/d). Indwelling catheters were surgically implanted in the mesenteric artery and the portal and hepatic veins for blood collection, as well as in 2 distal branches of the mesenteric vein for infusion of p-aminohippurate to determine blood flow. On d 14 of each period, a temporary catheter was inserted into a mammary vein and 6 hourly blood samples were collected to determine plasma concentrations of metabolites, hormones, and their respective fluxes across the splanchnic bed and mammary glands. Yields of milk (32.8, 32.0, and 32.9 ± 0.92 kg/d) and protein (1,028, 1,053, and 1,075 ± 28.7 g/d) were unaffected by level of RPM. However, the true protein content in milk from primiparous cows increased linearly (2.92, 3.09, and 3.34 ± 0.077%). The addition of RPM linearly increased the net flux of Met across the portal-drained viscera, which resulted in increased arterial Met concentrations (25, 29, and 40 ± 1.1 μM). Although it had no significant effect on net portal and hepatic fluxes of other essential amino acids, RPM resulted in a linear increase in the total splanchnic output of Ile, Leu, Phe, and Thr. These results suggest that feeding RPM triggered a homeostatic response resulting in less utilization of certain essential amino acids through the gastrointestinal tract and liver. Net mammary uptake of Met did not change with the addition of RPM. However, mammary extraction of Met decreased in a linear fashion in response to increased arterial inflow.     

Corn distillers grains versus a blend of protein supplements with or without ruminally protected amino acids for lactating cows

In a replicated 4 x 4 Latin square design with 4-wk periods, we used 12 multiparous Holstein cows averaging 83 d postpartum to compare corn distillers grains (CDG) versus a blend (BLEND) of other protein sources with CDG (fish meal and soybean meal), and to determine the effectiveness of ruminally protected lysine and methionine (RPLM) in improving the utilization of CDG as a protein supplement for lactating cows. The 2 x 2 factorial arrangement of treatments was as follows: CDG diet, CDG diet plus RPLM, BLEND diet, and BLEND diet plus RPLM. All diets contained 30% corn silage, 20% alfalfa hay, and 50% the respective corn-based concentrate mixture. The array of amino acids available for absorption when cows were fed the BLEND diet was more desirable than for the CDG diet according to Milk Protein Score and Cornell Net Carbohydrate and Protein System. Dry matter intakes were similar among all diets. Milk yields (32.6, 31.7, 32.8, and 32.8 kg/d, respectively) were similar for cows fed all diets. Milk fat yields and percentages (3.72, 3.76, 3.67, and 3.63%) were unaffected by diet, but milk protein percentages (3.23, 3.26, 3.25, and 3.26%) tended to be higher when fed RPLM. Concentrations of most protein fractions in milk were similar for all diets, although beta-lactoglobulin was increased slightly when cows were fed BLEND diets. Lysine, Met, and Phe were indicated as the most limiting amino acids for all diets according to extraction efficiency and transfer efficiency of amino acid from blood by the mammary gland. Methionine status was apparently improved by RPLM supplementation; Lys status was improved by the BLEND diets. Milk yield and composition when cows were fed CDG were not further improved by feeding blends of protein sources or RPLM; however, such dietary changes improved Lys and Met status of the cows.     

Vascular sources of phenylalanine, tyrosine, lysine, and methionine for casein synthesis in lactating goats

The contribution to casein biosynthesis of peptides derived from blood was examined in late lactation goats (254 to 295 d in milk). Ratios of mammary uptake of free amino acids (AA) in blood to output of AA in milk protein and ratios of the enrichments of Phe, Tyr, Met, and Lys at isotopic plateau in secreted milk casein to the free AA in arterial and mammary vein blood were monitored during the last 5 h of a 30-h continuous i.v. infusion of [1-13C]Phe, [2H4]Tyr, [5-13CH3]Met, and [2-15N]Lys on two occasions: before (control) and on d 6 of an i.v. infusion of Phe (6 g/d). During the control, uptakes of free Phe and Met were less than their output in milk. This result was comparable with the labeling kinetic results, suggesting that vascular peptides contributed 5 to 11% of Phe and 8 to 18% of Met. Free Tyr and Lys uptakes during the control were sufficient for milk output; however, the labeling kinetics indicated that 13 to 25% of the Tyr and 4 to 13% of the Lys were derived from peptides. Infusion of Phe increased the uptake of free AA but reduced the contribution of peptides toward Phe (0 to 3%) and Tyr (8 to 14%) supply for casein synthesis. Whole body hydroxylation of Phe to Tyr increased from 10 to 18% with the infusion of Phe; within the mammary gland, this conversion was lower (3 to 5%). Results suggest that the mammary utilization of peptides containing Phe and Tyr appears to depend on the supply of free AA in blood.     

Studies on methionine derivatives as possible sources of protected methionine in ruminant rations

N-Oleoyl-D,L-methionine, D,L-methionine ethyl ester HCI and the methyl ester of methionine hydroxy analogue were examined for their ability to produce methyl mercaptan in the rumen of sheep. Results indicated that all derivatives were more stable than methionine. The derivatives were then examined for their ability, when fed in the diet, to increase the plasma methionine concentration of sheep. Methionine ethyl ester caused a marked rise. Further results suggested that while some of the methionine ester escaped ruminal degradation, it also passed through the rumen wall. The compound was found to be rapidly hydrolysed in the liver to yield methionine. The effects of the other derivatives tested on plasma methionine concentrations were small.     

Ruminal escape and intestinal digestibility of ruminally protected lysine supplements differing in oleic acid and lysine concentrations

This trial was conducted to determine the effect of the addition of 2 or 4% oleic acid to an hydrogenated fat coating applied to an experimental supplement with 55 or 58% lysine sulfate on ruminal escape and intestinal absorption of Lys. Two lactating Holstein cows (103 d in milk and 45.1 kg/d of milk) previously fitted with ruminal and duodenal cannulas were individually housed and fed a corn silage-based ration. In situ and mobile bag techniques were utilized to evaluate the 4 test products. Twenty bags of each product were incubated for 16 h in each cow to determine ruminal escape. After ruminal incubation, products were repackaged, soaked in pepsin/HCl solution for 2 h, inserted into the duodenum, and subsequently collected in the feces. The percentage of dry matter and fat escaping the rumen decreased as oleic acid increased from 2 to 4% or as the proportion of supplemental Lys increased. An interaction was observed because of a greater reduction of N and Lys escaping ruminal fermentation and flowing to the small intestine for the product with 58% supplemental Lys and 4% oleic acid compared with the other products. No differences were observed in intestinal digestibility of dry matter, N, Lys, or fat or in the amount of Lys digested in the small intestine. Increasing the proportion of oleic acid in the coating applied to supplemental Lys increased ruminal degradation. The extent of the degradation increased as the proportion of Lys in the product increased.     

Comparison of the in situ and in vivo intestinal disappearance of ruminally protected methionine

We designed a switchback expriment to compare the intestinal disappearance of ruminally protected Met determined in situ or in vivo over three consecutive periods. Four nonlactating Holstein heifers (477+/-36 kg) with cannulae in the rumen, duodenum, and ileum were fed a diet based on timothy silage to meet requirements for maintenance (dry matter intake = 8.72+/-0.15 kg). A total of 16 bags, containing 1.5 g of ruminally protected Met, were incubated in the rumen (4.5 h) of each cow and transferred to an acid-pepsin solution to simulate the abomasum (2.5 h). Following each incubation, bags were recovered and three bags were dried at 55 degrees C and analyzed for Met. Remaining bags were introduced directly into the duodenal or ileal cannula for the in situ method, while for the in vivo method, the content of remaining bags was transferred into gelatin capsules before their introduction in the duodenal or ileal cannula. Spot samples of digesta were collected during a 96-h period, with Co-EDTA and Cr-mordanted fiber used as indigestible markers to estimate in vivo digestibility. The disappearance of Met in the small intestine determined in vivo tended to be higher than in situ (74.45 vs. 43.65+/-1.79%). Our results indicate that when used to assess intestinal availability of ruminally protected Met, the mobile nylon bag technique can underestimate the true bioavailability of Met.     

Nitrogen metabolism of lactating ewes fed rumen-protected methionine and lysine

Twenty multiparous, crossbred, black-faced ewes and their newborn twin lambs were assigned to one of four dietary treatments in a 2 x 2 factorial experiment to examine the effects of increased supply of CP or a mixture of encapsulated methionine and lysine or both on the performance of ewes and their nursing twin lambs. Ewes were fed ad libitum amounts of either a 10.2% low CP diet or a 16.2% moderate CP diet with or without additional encapsulated amino acids. Nitrogen metabolism trials were conducted simultaneously on both ewes and lambs at wk 2, 4, and 8 of lactation. Analyses were conducted for blood urea N, plasma 3-hydroxybutyrate, lactate, NEFA, insulin, and amino acids (plasma, feed, and milk). Ewe DMI, BW, BW gain, and milk yield were not changed by dietary treatments. Balance of N and N digested were increased by moderate CP treatment. The portion of retained N used for milk synthesis was increased by low CP treatment. Methionine and total branched-chain amino acids were increased by encapsulated amino acids and by protein treatment. Gains in BW and N balance were increased in lambs nursing ewes fed protected amino acids. Increased growth of nursing lambs would be an important beneficial effect of supplementing diets of ewes with encapsulated methionine and lysine.     

Evaluation of calcium lignosulfonate-treated soybean meal as a source of rumen protected protein for dairy cattle

Four Holstein cows fitted with ruminal, duodenal, and ileal cannulae were used in a 4 x 4 Latin square design to measure ruminal protein degradation and small intestinal digestion of diets containing untreated soybean meal or soybean meal treated with heat and either water, xylose, or calcium lignosulfonate. Diets consisting of 40% corn silage, 10% alfalfa cubes, and 50% grain mix, and averaging 16.8% crude protein (DM basis) were fed four times daily. Approximately 50% of the total dietary protein was supplied by the respective soybean meal source. Ruminal protein degradation was 70.6, 69.6, 55.8, and 53.7% for diets containing untreated soybean meal, water-soybean meal, xylose-soybean meal, and calcium lignosulfonate-soybean meal, respectively. Duodenal non-NH3 N flow (g/d) and absorption of non-NH3 N (g/d) in the small intestine were generally not affected by treatment. Duodenal bacterial N flow (g/d) was lower with xylose-soybean meal and lignosulfonate-soybean meal than with untreated soybean meal. Treatment of soybean meal with xylose or calcium lignosulfonate was successful in decreasing ruminal protein degradation. However, it may be necessary to include a source of readily fermentable N in diets that contain protected proteins in order to supply adequate NH3 N for microbial protein synthesis.     

Evaluation of potato meal as a feedstuff for lactating dairy cows

Potato meal was ensiled with a grass-legume forage at 7.5% of fresh weight and substituted for ground corn in concentrate mixtures at 0, 15, and 30% fresh weight. Production, digestion, and nitrogen balance trials were conducted on 12 lactating Holstein cows fed individually for ad libitum intake. Potato meal was consumed readily in the quantities offered. Mean daily milk production for cows receiving the hay-crop silage ensiled with potato meal was 28.6 compared with 26.3 kg for cows consuming untreated silage. Molar percentages of acetate in rumen were lower and propionate higher for cows receiving hay-crop silage ensiled with potato meal. Digestibility coefficients for dry matter, organic matter, acid detergent fiber, neutral detergent fiber, crude protein, and gross energy all tended to be lower for the silage with added potato meal. Nitrogen balance was higher for cows consuming silage with potato meal. When potato meal was added to concentrate mixes replacing corn at 0, 15, and 30%, milk production was 27.5, 26.8, and 28.0 kg/day. Potato meal can be used advantageously as a silage additive and can be included in concentrate mixtures up to 30% of the fresh weight.     

Intestinal disappearance and mesenteric and portal appearance of amino acids in dairy cows fed ruminally protected methionine

An experiment was conducted to compare the rates of disappearance of amino acids (AA) from the small intestine and their net appearance in the blood draining only the small intestine (mesenteric-drained viscera) and the whole gastrointestinal tract (portal-drained viscera) of cows fed a silage-based diet supplemented or not with ruminally protected Met. Five lactating dairy cows (118+/-4 DIM) equipped with duodenal and ileal cannulae (n = 2) or a duodenal cannula only (n = 3), two of which were multicatheterized, were fed a TMR top dressed with 0 or 72 g of ruminally protected Met per day. The addition of ruminally protected Met to the diet increased the duodenal flux of Met leading to a higher apparent digestibility of Met in the small intestine. Sixty-six percent of Met from ruminally protected Met bypassed the rumen and 82% of that Met disappeared from the small intestine. Arterial plasma Met concentrations numerically increased with ruminally protected Met (45 vs. 18 microM), while total AA concentration decreased. Feeding ruminally protected Met resulted in higher concentrations of urea-N and glucose in arterial plasma. Milk production and milk composition were unaffected. The disappearance of essential AA across the small intestine was equivalent (101%) to their flux through the mesenteric-drained viscera while the portal:mesenteric-drained viscera flux ratio for each essential AA varied from 38% for Thr to 76% for Phe. The portal:mesenteric-drained viscera flux ratio for Met was 66%. These results confirm observations made with pigs and sheep.     

Fava beans can substitute soybean meal and rapeseed meal as protein source in diets for lactating dairy cows

The effect of replacing mixtures of wheat and soybean meal and wheat and rapeseed meal by toasted fava beans, and the effect of toasting fava beans on feed intake, milk yield, and composition of milk and feces were investigated using 40 Holstein cows in each of two 4 × 4 Latin square design trials conducted simultaneously. In trial 1, the 4 treatment concentrates were untreated fava beans, toasted fava beans, 42% soybean meal + 58% rolled wheat, and a 21, 29, and 50% mix of soybean meal, rolled wheat, and toasted fava beans, respectively [on dry matter (DM) basis]. In trial 2, the 4 experimental treatments were untreated fava beans, toasted fava beans, 64% rapeseed meal + 36% rolled wheat, and a 32, 18, and 50% mix of rapeseed meal, rolled wheat, and toasted fava beans, respectively (on DM basis). In each trial, 16 primiparous and 24 multiparous cows were fed the treatment concentrates as part of a partial mixed ration, of which the forage consisted of 50% corn silage and 50% grass-clover silage. Substitution of soybean meal and wheat or rapeseed meal and wheat with toasted fava beans did not affect total DM intake, and no linear effects were observed on milk yield or energy-corrected milk (ECM) yield. However, in trial 2, a quadratic effect was observed on milk yield when substituting rapeseed meal and wheat with toasted fava beans. In both trials, substitution of soybean meal and wheat or rapeseed meal and wheat with toasted fava beans increased milk lactose concentration and decreased milk protein yield and concentration of protein in milk. In both trials, fecal concentration of starch increased linearly when substituting soybean meal and wheat or rapeseed meal and wheat with toasted fava beans. In trial 2, fecal concentration of P decreased when substituting rapeseed meal and wheat with toasted fava beans. In situ investigations showed increased rumen undegradable protein concentration and thereby increased estimated metabolizable protein supply when toasting fava beans. However, in both trials, milk protein yield and concentration decreased when cows were fed toasted compared with untreated fava beans. Furthermore, when cows were fed toasted compared with untreated fava beans in trial 1, milk yield, ECM yield, and nitrogen efficiency decreased. We conclude that toasted fava beans could substitute soybean meal and wheat or rapeseed meal and wheat with regard to ECM yield. However, milk protein yield decreased when substituting soybean meal and wheat or rapeseed meal and wheat with toasted fava beans. Compared with untreated fava beans, toasting had no positive effect on milk production and nitrogen efficiency.     

Chick bioassay of available methionine and methionine plus cystine. Assay of whole egg, fish meal and caseins.

A chick bioassay procedure¹ has been used to determine the relative potency of several animal protein concentrates based on live-weight gains, food conversion efficiency (FCE) or nitrogen retention. In general, the assays were statistically valid and the majority had 95% fiducial limits as narrow as 88–114%. Expressing response as FCE or nitrogen retention did not give better precision than using weight gain alone. The results showed that there are wide differences in available methionine and SAA in fish meals marketed under same the name.     

Evaluation of rumen-protected methionine sources and period length on performance of lactating dairy cows within Latin squares

Multiparous Holstein cows (n = 16) were used in a replicated (n = 4) Latin square design with 2-wk periods to determine whether length of the experimental period chosen within Latin square designs would influence experimental outcomes for performance-related variables. Cows were fed a basal TMR formulated to supply Lys in excess of the predicted requirements and either no rumen-protected Met (RP-Met; control), or 6 (M6) or 12 (M12) g/d of RP-Met (Mepron), or 12 (S12) g/d of RP-Met (Smartamine M). Performance outcomes were evaluated separately using data collected at the end of each week of each period, and as overall means for each period. Milk yield was not affected by treatment in any period. Supplementation of RP-Met from all sources tended to increase milk fat percentage when evaluated using wk-1 data, but responses evaluated using wk-2 data only were not significant. Supplementation of M12 and S12 tended to increase milk fat percentage over the entire experimental period. Supplementation of M6 and M12 tended to increase milk true protein percentage when evaluated using wk-1 data only; however, responses to treatments during wk 2 were not significant. All supplemental RP-Met treatments either tended to increase (M6 and S12) or increased (M12) milk true protein content over the entire experimental period relative to the control treatment. Yields of fat and true protein were not affected by treatment. Carryover effects of treatment on production variables were largely not significant. Predictions of nutrient supply with 3 models used in dairy ration formulation and evaluation (CPM-Dairy, AminoCow, and 2001 NRC Dairy) indicated that energy, protein, and Met all were supplied in excess of requirements for all treatments. Overall, results suggest that interpretation of performance outcomes can vary depending on selection of the experimental period in Latin squares, and responses to increased Met supply based on ratio-based formulation may not be independent of the grams of Met supplied.     

Evaluation of maize gluten meal—peruvian fish meal mixtures as protein supplements for egg production

Maize gluten meal protein was used to replace 25, 50, 75 and 100% of the protein supplied by Peruvian fish meal (14.25%) in a cereal-based diet for caged hens. When the level of maize gluten meal was increased to provide 50% of the supplementary protein, egg production dropped from 80% on the fish meal control diet to 75%, and fell to 53.4% when all the supplementary protein in the diet was provided by maize gluten meal. Mean egg weight dropped significantly when the dietary maize gluten meal supplied 75% and 100% of the supplementary protein. The best food conversion efficiencies were obtained on the two diets with the highest content of Peruvian fish meal. The energetic efficiency for egg production fell slightly when the contribution of dietary protein from the maize gluten was equal to that from the Peruvian fish meal, and fell markedly at the two highest levels of dietary maize gluten meal. The conclusion is reached that satisfactory egg production can be maintained when up to 25% of the protein of the fish meal control diet is replaced by maize gluten meal protein, and that the efficiency of utilisation of energy for egg production is not adversely affected.     

Short communication: Canola meal as a substitute for cottonseed meal in diet of midlactation Holsteins

The growing demand by humans for monounsaturated vegetable oils has provided canola meal (CM) for use in dairy diets because it possesses an excellent nitrogen profile for rumen microbes. Six midlactation cows were used in a replicated 3 × 3 Latin square design with 3 periods of 20 d each. Treatments included diets with 1) CM, 2) 50% CM + 50% cottonseed meal (CSM), and 3) CSM. Total crude protein (CP), nonprotein nitrogen, and rapidly degradable true protein (% of CP) were greater in CM than in CSM. The neutral and acid detergent fibers, slowly degradable true protein, and unavailable CP were lower in CM than in CSM. Daily feeding of 3.4 kg of CM instead of 5.6 kg of CSM enhanced milk percentage of protein and SNF, and improved total tract digestibility of dry matter and CP. Therefore, CM offers an economical substitute for CSM in midlactation diets when commercial access, cost, and quality of CSM are variable.