Crude protein oscillation in diets adequate and deficient in metabolizable protein: Effects on nutrient digestibility, nitrogen balance, plasma amino acids, and greenhouse gas emissions

Reducing dietary CP is a well-established means to improve N use efficiency. Yet, few studies have considered if transient restrictions in dietary CP could reduce the environmental footprint of late-lactation cows. We hypothesized that the effects of CP feeding pattern on digestibility and environmental outputs would be amplified at lower dietary CP. We tested CP levels below and near predicted requirements (low protein [LP], 13.8%; high protein [HP], 15.5%) offered in 2 feeding patterns: where diets alternated ±1.8 percentage units CP every 2 d (oscillating [OF]) or remained static. Our study used a 2 × 2 factorial design with 16 mid- to late-lactation Holsteins (mean = 128, SD = 12 DIM), divided into rumen-cannulated (n = 8) and noncannulated subsets (n = 8). For each 28-d experimental period, we recorded feed intake and milk production and took samples of orts (1×/d) and milk (2×/d) for 4 d. For the cannulated subset, we measured and sampled from the total mass of feces and urine production and collected plasma 2×/d across 4 d. For the noncannulated subset, we sampled carbon dioxide and methane emissions 3×/d for 4 d. For each subset, we fit linear mixed models with fixed effects for CP level, CP feeding pattern, the interaction of CP level and CP feeding pattern, period, and a random effect for cow. For plasma and urinary urea-N, we conducted time series analysis. Contrary to our hypothesis, we found no evidence that dietary CP level and CP feeding pattern interacted to influence N balance, nutrient digestibility, or gas emissions. Results showed HP resulted in similar milk N but increased manure N, reducing N use efficiency (milk true protein N/intake N) relative to LP. For OF, urea-N in urine and plasma peaked 46 to 52 h after the first higher-CP phase feeding. Nutrient digestibility and gas emissions were similar across treatments, except CO2 production was greater for OF-HP. In summary, measured variables were minimally affected by dietary CP alternating ±1.8 percentage units every 48 h, even when average dietary CP was fed below predicted requirements (LP). Although our findings suggest that mid- to late-lactation cows are resilient to oscillation in dietary CP, oscillating CP neither reduced the environmental footprint by improving nutrient use efficiencies nor reduced the potential for direct and indirect greenhouse gas emissions.

Effects of rumen-encapsulated methionine and lysine supplementation and low dietary protein on nitrogen efficiency and lactation performance of dairy cows

Low crude protein (CP) diets might be fed to dairy cows without affecting productivity if the balance of absorbed AA were improved, which would decrease the environmental effect of dairy farms. The aim of this study was to investigate the effects of supplementing ruminally protected Lys (RPL) and Met (RPM) at 2 levels of dietary CP on nutrient intake, milk production, milk composition, milk N efficiency (MNE), and plasma concentrations of AA in lactating Holstein cows and to evaluate these effects against the predictions of the new NASEM (2021) model. Fifteen multiparous cows were used in a replicated 3 × 3 Latin square design with 21-d periods. The 3 treatments were (1) a high-protein (HP) basal diet containing 16.4% CP (metabolizable protein [MP] balance of -130 g/d; 95% of target values), (2) a medium-protein diet containing 15% CP plus RPL (60 g/cow per day) and RPM (25 g/cow per day; MPLM; MP balance of -314 g/d; 87% of target values), and (3) a low-protein diet containing 13.6% CP plus RPL (60 g/cow per day) and RPM (25 g/cow per day; LPLM; MP balance of -479 g/d; 80% of target values). Dry matter intake was less for cows fed MPLM and LPLM diets compared with those fed the HP diet. Compared with the HP diet, the intake of CP, neutral detergent fiber, acid detergent fiber, and organic matter, but not starch, was lower for cows fed MPLM and LPLM diets. Milk production and composition were not affected by MPLM or LPLM diets relative to the HP diet. Milk urea N concentrations were reduced for the MPLM and LPLM diets compared with the HP diet, indicating that providing a low-protein diet supplemented with rumen-protected AA led to greater N efficiency. There was no significant effect of treatment on plasma AA concentrations except for proline, which significantly increased for the MPLM treatment compared with the other 2 treatments. Overall, the results supported the concept that milk performance might be maintained when feeding lactating dairy cows with low CP diets if the absorbed AA balance is maintained through RPL and RPM feeding. Further investigations are needed to evaluate responses over a longer time period with consideration of all AA rather than on the more aggregated MP and the ratio between Lys and Met.

Longitudinal characterization of the metabolome of dairy cows transitioning from one lactation to the next: Investigations in blood serum

The objective of this study was to characterize changes in the serum metabolome and various indicators of oxidative balance in dairy cows starting 2 wk before dry-off and continuing until wk 16 of lactation. Twelve Holstein dairy cows (body weight 745 ± 71 kg, body condition score 3.43 ± 0.66; mean ± SD) were housed in a tiestall barn from 10 wk before to 16 wk after parturition. Cows were dried off 6 wk before the expected calving date (mean dry period length = 42 d). From 8 wk before calving to 16 wk after calving, blood samples were taken weekly to study redox metabolism by determining antioxidant capacity, measured as the ferric-reducing ability of plasma, reactive oxidative metabolites, oxidative stress index, oxidative damage of lipids, measured as thiobarbituric acid reactive substances, and glutathione peroxidase activity. According to these results, dairy cows had the lowest serum antioxidant capacity and greater levels of oxidative stress during the dry-off period and the early postpartum period. For metabolomics, a subset of serum samples including wk -7 (before dry-off), -5 (after dry-off), -1, 1, 5, 10, and 15 relative to calving were used. A targeted metabolomics approach was performed using liquid chromatography and flow injection with electrospray ionization triple quadrupole mass spectrometry using the MxP Quant 500 kit (Biocrates Life Sciences AG). A total of 240 metabolites in serum were used in the final data analysis. Principal component analysis revealed a clear separation by days of sampling, indicating a remarkable shift in metabolic phenotype between the dry period and late and early lactation. Changes in many non-lipid metabolites associated with one-carbon metabolism, the tricarboxylic acid cycle, the urea cycle, and AA catabolism were observed in the study, with changes in AA serum concentrations likely related to factors such as energy and nitrogen balance, digestive efficiency, and changing diets. The study confirmed an extensive remodeling of the serum lipidome in peripartum dairy cows, highlighting the importance of changes in acylcarnitine (acylCN), phosphatidylcholines (PC), and triacylglycerols (TG), as they play a crucial role in lipid metabolism. Results showed that short-chain acylCN increased after dry-off and decreased thereafter, whereas lipid-derived acylCN increased around parturition, suggesting that more fatty acids could enter mitochondria. Phospholipids and sphingolipids in serum showed changes during lactation. In particular, concentrations of sphingomyelins, PC, and lysoPC decreased around calving but increased in mid- and late lactation. In contrast, concentrations of TG remained consistently low after parturition. The serum concentrations of bile acids fluctuated during the dry period and lactation, with glycocholic acid, cholic acid, glycodeoxycholic acid, and taurocholic acid showing the greatest concentrations. These changes are likely due to the interplay of diet, liver function, and the ability of the gut microbiota to convert primary to secondary bile acids. Overall, these descriptive results may aid in hypothesis generation and in the design and interpretation of future metabolite-based studies in dairy cows. Furthermore, they contribute to our understanding of the physiological ranges in serum metabolites relative to the lactation cycle of the dairy cow.

Production of rumen- and gastrointestinal-resistant nanoparticles to deliver lysine to dairy cows

Supplementing diets with rumen-protected lysine is a common strategy to meet the nutritional needs of high-producing dairy cows. This work addressed two separate but crucial issues: the lysine protection degree across the entire digestive tract as well as the production scalability of the proposed delivery systems. This was achieved by evaluating, in vitro or ex vivo, previously developed rumen-resistant lipid nanoparticles regarding their stability in the digestive tract and in the bloodstream of the dairy cow as well as how their production could be scaled-up. Results showed that the developed nanoparticles were able to resist digestion along the digestive tract but were degraded in the blood over 24 h. Thus, releasing their content to be used by the animal. In vitro viability assays were also performed, with the nanoparticles being found not to be inherently toxic when using nanoparticle concentrations up to 1 mg/mL. Results showed that neither the purity of the used lipids nor the production method significantly altered the nanoparticles' properties or their ruminal resistance. Furthermore, the shelf-life of these nanoparticles was assessed, and they were found to retain their properties and remain usable after at least 1 month of storage. Moreover, a pilot-scale production allowed the production of nanoparticles with similar properties to the previous ones made using standard methods. To summarize, the proposed rumen-resistant nanoparticles presented potential as orally ingested lysine delivery systems for dairy cattle supplementation, being capable of a large-scale production using cheaper components while maintaining their properties and without any efficiency loss. It should however be noted that these results were obtained mainly in vitro and further in vivo bioavailability and production experiments are needed before this technology can be confirmed as a viable way of delivering lysine to dairy cows.

Processed fava bean as a substitute for rapeseed meal with or without rumen-protected methionine supplement in grass silage-based dairy cow diets

Fava bean offers a sustainable home-grown protein source for dairy cows, but fava bean protein is extensively degraded in the rumen and has low Met concentration. We studied the effects of protein supplementation and source on milk production, rumen fermentation, N use, and mammary AA utilization. The treatments were unsupplemented control diet, and isonitrogenously given rapeseed meal (RSM), processed (dehulled, flaked, and heated) fava bean without (TFB) or with rumen-protected (RP) Met (TFB+). All diets consisted of 50% grass silage and 50% cereal-based concentrate including studied protein supplement. The control diet had 15% of crude protein and protein-supplemented diets 18%. Rumen-protected Met in TFB+ corresponded to 15 g/d of Met absorbed in the small intestine. Experimental design was a replicated 4 × 4 Latin square with 3-wk periods. The experiment was conducted using 12 multiparous mid-lactation Nordic Red cows, of which 4 were rumen cannulated. Protein supplementation increased dry matter intake (DMI), and milk (31.9 vs. 30.7 kg/d) and milk component yields. Substituting RSM with TFB or TFB+ decreased DMI and AA intake but increased starch intake. There were no differences in milk yield or composition between RSM diet and TFB diets. Rumen-protected Met did not affect DMI, or milk or milk component yields but increased milk protein concentration in comparison to TFB. There were no differences in rumen fermentation except for increased ammonium-N concentration with the protein-supplemented diets. Nitrogen-use efficiency for milk production was lower for the supplemented diets versus control diet but tended to be greater for TFB and TFB+ versus RSM. Protein supplementation increased plasma essential AA concentration but there were no differences between TFB diets and RSM. Rumen-protected Met clearly increased plasma Met concentration (30.8 vs. 18.2 µmol/L) but did not affect other AA. Absence of differences between RSM and TFB in milk production together with limited effects of RP Met suggest that TFB is a potential alternative protein source for dairy cattle.

Plasma essential amino acid concentration and profile are associated with performance of lactating dairy cows as revealed through meta-analysis and hierarchical clustering

Our aim was to explore whether changes in plasma essential AA (EAA) concentration ([EAA]_p) or profile (defined here as the molar proportion of individual [EAA]_p relative to the total [EAA]_p) may serve as an indicator of the EAA status of a cow. We undertook a meta-analysis with the objectives to determine if different plasma EAA profiles exist among cows and to explore the association of [EAA]_p or the profile of EAA with lactating cow performance and measures of N utilization. We hypothesized the existence of differences in [EAA]_p and different plasma EAA profile for cows with greater milk output, feed efficiency, and greater N use efficiency (NUE; milk true protein-N:N intake) compared with cows with lower milk output, feed efficiency, and lower NUE. The data set included 22 feeding trials and 96 dietary treatments. First, a mixed-effect model analysis was used to predict [EAA]_p in response to the categorical fixed effect of EAA, continuous fixed effect of National Research Council model-predicted metabolizable protein (MP) supply, continuous fixed effect of body weight, the fixed effect of EAA and MP supply interaction, the fixed effect of EAA and body weight interaction, and the random effect of study. Then, residuals of the model were standardized based on Z-score and clustered using the hierarchical method (Euclidean distance and Ward's minimum variance method) resulting in 2 clusters. Finally, a fixed-effect model was used to evaluate the significance with which clusters were associated with [EAA]_p, cow performance, feed efficiency, and NUE. The total concentration of [EAA]_p was lower (784 vs. 983 µM) and the concentration of each EAA was on average 22 µM lower for cows in cluster 1 compared with cluster 2 with the smallest and greatest difference found for Met (4 µM) and Val (59 µM), respectively. The percentage difference in [EAA]_p was the smallest for Thr (-5.3%) and the greatest for Leu (-37.1%). There was no difference between clusters for Arg, His, and Met molar proportions; however, cows in cluster 1 had a lower molar proportion of Leu and a tendency for lower molar proportion of Val compared with cows in cluster 2. Additionally, cows in cluster 1 had greater molar proportions of Ile, Lys, and Thr and a tendency for greater molar proportion of Phe compared with cows in cluster 2. The fixed-effect model analysis indicated that cows in cluster 1 had higher milk energy output (+3.2 Mcal/d), true protein yield (+87 g/d) and fat yield (+236 g/d), feed efficiency (milk Mcal:dry matter intake; +8% unit), and a tendency for greater MP efficiency (Milk true protein/MP supply; +2.3% unit) than cows in cluster 2. These results suggested greater use of EAA by the mammary gland (as reflected by greater milk protein synthesis) and lower hepatic catabolism of AA (as reflected by a tendency to greater MP efficiency) in cows of cluster 1 compared with cluster 2. Our findings should be evaluated further, including whether the relative molar proportions of plasma EAA might serve as a holistic indicator of the EAA status of cows as related to their productivity, feed efficiency and N utilization.

Effects of feeding rumen-protected methionine pre- and postpartum in multiparous Holstein cows: Lactation performance and plasma amino acid concentrations

Objectives were to evaluate the effect of feeding rumen-protected methionine (RPM) in pre- and postpartum total mix ration (TMR) on lactation performance and plasma AA concentrations in dairy cows. A total of 470 multiparous Holstein cows [235 cows at University of Wisconsin (UW) and 235 cows at Cornell University (CU)] were enrolled approximately 4 wk before parturition, housed in close-up dry cow and replicated lactation pens. Pens were randomly assigned to treatment diets (pre- and postpartum, respectively): UW control (CON) diet = 2.30 and 2.09% of Met as percentage of metabolizable protein (MP) and RPM diet = 2.83 and 2.58% of Met as MP; CU CON = 2.22 and 2.19% of Met as percentage of MP, and CU RPM = 2.85 and 2.65% of Met as percentage of MP. Treatments were evaluated until 112 ± 3 d in milk (DIM). Milk yield was recorded daily. Milk samples were collected at wk 1 and 2 of lactation, and then every other week, and analyzed for milk composition. For lactation pens, dry matter intake (DMI) was recorded daily. Body weight and body condition score were determined from 4 ± 3 DIM and parturition until 39 ± 3 and 49 DIM, respectively. Plasma AA concentrations were evaluated within 3 h after feeding during the periparturient period [d -7 (±4), 0, 7 (±1), 14 (±1), and 21 (±1); n = 225]. In addition, plasma AA concentrations were evaluated (every 3 h for 24 h) after feeding in cows at 76 ± 8 DIM (n = 16) and within 3 h after feeding in cows at 80 ± 3 DIM (n = 72). The RPM treatment had no effect on DMI (27.9 vs. 28.0 kg/d) or milk yield (48.7 vs. 49.2 kg/d) for RPM and CON, respectively. Cows fed the RPM treatment had increased milk protein concentration (3.07 vs. 2.95%) and yield (1.48 vs. 1.43 kg/d), and milk fat concentration (3.87 vs. 3.77%), although milk fat yield did not differ. Plasma Met concentrations tended to be greater for cows fed RPM at 7 d before parturition (25.9 vs. 22.9 µM), did not differ at parturition (22.0 vs. 20.4 µM), and were increased on d 7 (31.0 vs. 21.2 µM) and remained greater with consistent concentrations until d 21 postpartum (d 14: 30.5 vs. 19.0 µM; d 21: 31.0 vs. 17.8 µM). However, feeding RPM decreased Leu, Val, Asn, and Ser (d 7, 14, and 21) and Tyr (d 14). At a later stage in lactation, plasma Met was increased for RPM cows (34.4 vs. 16.7 µM) consistently throughout the day, with no changes in other AA. Substantial variation was detected for plasma Met concentration (range: RPM = 8.9-63.3 µM; CON = 7.8-28.8 µM) among cows [coefficient of variation (CV) > 28%] and within cow during the day (CV: 10.5-27.1%). In conclusion, feeding RPM increased plasma Met concentration and improved lactation performance via increased milk protein production.

Effects of polymerization of casein and sources of lysine on amino acid bioavailability among calves fed liquid-based diets

Two experiments were conducted to evaluate the bioavailability of AA between polymerized and less polymerized or unpolymerized sources of AA. In the first experiment, 6 bull calves (53.8 ± 0.6 kg of body weight) were bottle-fed milk replacer that contained 0, 60, or 120 additional grams of AA from casein or acid hydrolyzed casein every 12 h. Plasma essential AA increased linearly with increasing intake of casein from either source. Branched-chain amino acids accounted for 74% of increases in essential AA, regardless of source of AA. Concentrations of nonessential AA increased linearly with increased intake of AA from acid hydrolyzed casein but only tended to increase in response to casein. Also, the rate of increase in total plasma AA concentration in response to acid hydrolyzed casein (4.3 µM increase per g of supplemental AA) tended to be 145% greater than casein (3.0 µM per g of supplemental AA). In a separate experiment, 6 additional bull calves (52.1 ± 0.9 kg of body weight) were bottle-fed milk replacer that contained 0, 4.8, or 9.6 additional grams of Lys from ε-polylysine or Lys-HCl each 12 h to measure Lys bioavailability between a polymerized and unpolymerized source of Lys. Plasma Lys concentrations increased linearly in response to greater Lys intake from Lys-HCl (slope = 13.51 µM/g Lys,), but plasma Lys concentrations did not change in response to increased intake of Lys from ε-polylysine. Plasma concentrations of Thr, Met, Glu, and Gln decreased linearly with increasing ε-polylysine intake, whereas concentrations of His, Val, Leu, and Ile increased linearly with increasing ε-polylysine intake. Data from these experiments suggest that the form of AA provided to calves should be considered when formulating diets to meet AA requirements.

A method of assessing essential amino acid availability from microbial and ruminally undegraded protein in lactating dairy cows

The objective of this study was to extend a stable isotope-based assessment of AA absorption from rumen-degradable protein (RDP) sources to include determination of essential AA (EAA) availability from microbial protein (MCP). To demonstrate the technique, a study using a 2 × 2 factorial arrangement of treatments applied in a repeated 4 × 4 Latin square design was undertaken. Factors were high and low rumen-degradable protein and high and low starch. Twelve lactating cows were blocked into 3 groups according to days in milk and randomly assigned to the 4 treatment sequences. Each period was 14 d in length with 10 d of adaption followed by 4 d of ruminal infusions of ¹⁵N-labeled ammonium sulfate. On the last day of each period, a ¹³C-labeled AA mixture was infused into the jugular vein over a 6-h period to assess total AA entry. Rumen, blood, urine, and milk samples were collected during the infusions. Ruminal bacteria and blood samples were assessed for AA enrichment. Total plasma AA absorption rates were derived for 6 EAA from plasma ¹³C AA enrichment. Absorption of 6 EAA from MCP was calculated from total AA absorption based on ¹⁵N enrichment in blood and rumen bacteria. Essential AA absorption rates from total protein, MCP, and rumen-undegradable protein were derived with standard errors of the mean of 6, 14, and 14%, respectively. An average of 45% of absorbed EAA were from MCP, which varied among 6 EAA and was interactively affected by starch and RDP in diets. Microbial AA availability measured by isotope dilution method increased with the high RDP diets and was unaffected by starch level, except for Met, which decreased with high starch. Microbial protein outflow, estimated from urinary purine derivatives, increased with RDP and was not significantly affected by starch. This was consistent with measurements from the isotope dilution method. Total AA absorption rates measured from isotope dilution were similar to estimates from CNCPS (v. 6.55), but a lower proportion of absorbed AA was derived from MCP for the former method. Compared with the isotope and CNCPS estimates, the Fleming model underestimated microbial EAA and total EAA availability. An average of 58% of the absorbed EAA was converted into milk, which varied among individual AA and was interactively affected by starch and RDP in diets. The isotope dilution approach is advantageous because it provides estimates of EAA availability for individual EAA from rumen-undegradable protein and MCP directly with fewer errors of measurement than can be achieved with intestinal disappearance methods.

Effects of rumen-protected lysine and histidine on milk production and energy and nitrogen utilization in diets containing hydrolyzed feather meal fed to lactating Jersey cows

Hydrolyzed feather meal (HFM) is high in crude protein, most of which bypasses rumen degradation when fed to lactating dairy cows, allowing direct supply of AA to the small intestine. Compared with other feeds that are high in bypass protein, such as blood meal or heat-treated soybean meal, HFM is low in His and Lys. The objectives of this study were to determine the effects of supplementing rumen-protected (RP) Lys and His individually or in combination in a diet containing 5% HFM on milk production and composition as well as energy and N partitioning. Twelve multiparous Jersey cows (mean ± SD: 91 ± 18 d in milk) were used in a triplicated 4 × 4 Latin square with 4 periods of 28 d (24-d adaptation and 4-d collection). Throughout the experiment, all cows were fed the same TMR, with HFM included at 5% of diet DM. Cows were grouped by dry matter intake and milk yield, and cows within a group were randomly assigned to 1 of 4 treatments: no RP Lys or RP His; RP Lys only [70 g/d of Ajipro-L (24 g/d of digestible Lys), Ajinomoto Co. Inc., Tokyo, Japan]; RP His only [32 g/d of experimental product (7 g/d of digestible His), Balchem Corp., New Hampton, NY]; or both RP Lys and His. Plasma Lys concentration increased when RP Lys was supplemented without RP His (77.7 vs. 66.0 ± 4.69 µM) but decreased when RP Lys was supplemented with RP His (71.4 vs. 75.0 ± 4.69 µM). Plasma concentration of 3-methylhistidine decreased with RP Lys (3.19 vs. 3.40 ± 0.31 µM). With RP His, plasma concentration of His increased (21.8 vs. 18.7 ± 2.95 µM). For milk production and milk composition, no effects of Lys were observed. Supplementing RP His increased milk yield (22.5 vs. 21.6 ± 2.04 kg/d) and tended to increase milk protein yield (0.801 vs. 0.772 ± 0.051 kg/d). Across treatments, dry matter intake (18.5 ± 0.83 kg/d) and energy supply (32.2 ± 2.24 Mcal of net energy for lactation) were not different. Supplementing RP His did not affect N utilization; however, supplementing RP Lys increased N balance (25 vs. 16 ± 9 g/d). The lack of production responses to RP Lys suggests that Lys was not limiting or that the increase in Lys supply was not large enough to cause an increase in milk protein yield. However, increased N balance and decreased 3-methylhistidine with RP Lys suggest that increased Lys supply increased protein accretion and decreased protein mobilization. Furthermore, His may be a limiting AA in diets containing HFM.

Effects of supplementing rumen-protected lysine and methionine during prepartum and postpartum periods on performance of dairy cows

An experiment was conducted to examine effects of prepartum, postpartum, or continuous prepartum and postpartum supply of rumen-protected lysine (RPLys) and rumen-protected methionine (RPMet) on performance and blood metabolites of transition cows. The experiment consisted of a prepartum (3 wk), postpartum (3 wk), and carryover (10 wk) period. Eighty-eight prepartum cows (36 primiparous and 52 multiparous cows) were blocked by parity and expected calving date and assigned to 1 of 4 treatments arranged factorially. Treatments were a prepartum diet (12% crude protein on a dry matter basis) without (Pre-) or with supplemental RPLys (10 g of digestible Lys/cow per day) and RPMet (4 g of digestible Met/cow per day; Pre+) followed by postpartum diets (16% crude protein on a dry matter basis) without (Post-) or with supplemental RPLys (26 g of digestible Lys/cow per day) and RPMet (11 g of digestible Met/cow per day; Post+). Prepartum, only 2 treatments were applied, but postpartum cows received treatments of Pre-Post-, Pre-Post+, Pre+Post-, or Pre+Post+. During the prepartum period, treatment did not affect dry matter intake and body weight. During the postpartum period, milk protein content was greater (3.23 vs. 3.11%) for Post+ compared with Post- independent of prepartum treatment. However, dry matter intake, body weight, milk yield, and yields of milk components were not affected by Post+ versus Post-. No effects of prepartum treatment or interactions between pre- and postpartum treatments were observed on postpartum performance of cows. No effects of pre- and postpartum supplementation of RPLys and RPMet on performance during the carryover period were found except prepartum supplementation of RPLys and RPMet decreased somatic cell count (4.60 vs. 4.83; log₁₀ transformed) compared with Pre- in the postpartum period and this effect continued during the carryover period [i.e., 4.42 and 4.55 (log₁₀ transformed) for Pre+ and Pre-, respectively]. Prepartum supplementation of RPLys and RPMet increased or tended to increase plasma concentration of Lys, Met, and branched-chain AA compared with Pre- in prepartum cows. Cows on Post+ tended to have greater plasma Lys concentration compared with Post-, but plasma Met concentration was not affected. Health events of postpartum cows were not affected by treatments. In conclusion, we did not observe positive effects of supplementing with RPLys and RPMet on performance of prepartum and postpartum cows. However, prepartum supply of RPLys and RPMet may have potential to improve udder health and immune status of fresh cows.

Does blending canola meal with other protein sources improve production responses in lactating dairy cows? A multilevel mixed-effects meta-analysis

The objective of this meta-analysis was to evaluate the effect of blending canola meal (CM) with other protein sources on production responses in lactating dairy cows. To evaluate this effect, a data set was assembled containing 22 studies reporting at least 3 isonitrogenous dietary treatments (total of 74 treatment means). Each study needed to report 1 diet with CM <0.3 kg/d, 1 or more diets consisting of CM blended with another protein source, and 1 diet with CM as the main protein source in the protein supplement (>85%). The crude protein (CP) concentration of CM averaged 37.4 ± 3.09% (dry matter basis), and the predictor of interest was the intake of CP from CM, which averaged 0.46 ± 0.413 kg/d among studies. The maximal CP from CM ranged from 0.47 to 1.55 kg/d among studies. The quadratic relationship between CP from CM and responses in milk true protein concentration was significant, the maximum response (3.19%) being reached at 0.79 kg of CP from CM; the quadratic relationships were not significant for the other dependent variables. Responses in dry matter intake; yields of milk, energy-corrected milk, and milk true protein; and apparent N efficiency were related positively to CP from CM and negatively for responses in milk fat and milk urea N concentrations. Remembering that diets were isonitrogenous within studies, this indicates no nutritional benefit of blending CM with another protein source. Taken together, the results indicate that the whole-body N utilization efficiency by the dairy cow improved and that more dietary protein was used to synthesize milk protein when CM was used as the sole protein source in the protein supplement up to 1.55 kg/d.