Diet supplementation with canola meal improves milk production, reduces enteric methane emissions, and shifts nitrogen excretion from urine to feces in dairy cows

Graduate Student Literature Review: Concepts and challenges of amino acid supply and nitrogen metabolism in dairy cattle

Nitrogen utilization in dairy cows is crucial for maximizing production efficiency and minimizing environmental impacts. Ruminants possess a unique digestive system filled with microorganisms that work synergically to degrade feed particles and provide nutrients for both the microorganism and host metabolism. Dietary N, supplied as true protein and NPN, undergoes different degradation processes: a portion is degraded in the rumen, and another portion escapes ruminal degradation (i.e., RUP). Rumen-degraded protein is essential for microbial growth, contributing to the formation of microbial CP (MCP). Amino acids present in MCP and RUP that are digested and absorbed into the bloodstream and become available for animal metabolism (e.g., maintenance, growth, and production) constitute MP. Accurately assessing protein degradability and AA availability remains a challenge due to the limitations of current evaluation methods. In situ techniques are the most commonly used technique for this purpose, but they are not meant to predict MCP, RUP, and consequently the metabolizable AA supply of feed ingredients, which compromises diet formulation. Microbial CP growth is enhanced when both fermentable energy and N is available in the rumen. However, the extent of N recycling in sustaining microbial growth under low-protein diets is not adequately captured by MCP prediction models. Due to these limitations, several biases are added to protein models, resulting in protein overfeeding in an attempt to supply MP requirements and increasing both costs and N overload to the environment. Therefore, this review aims to synthesize fundamental information on the complex interplay of factors influencing ruminal protein degradation, MCP synthesis, AA supply, N metabolism, and N efficiency, and highlight the knowledge gaps that must be addressed to improve the accuracy of prediction models of AA supply in dairy cattle.

Effects of protein and forage source on performance and splanchnic and mammary net fluxes of nutrients in lactating dairy cows

This study was conducted to determine if the decreased MP supply predicted by the NRC (2001) when canola meal (CM) substitutes soybean meal (SBM) was supported by direct measurement of net portal absorption of AA or energy-yielding nutrients, plus the effect of the type of forage in CM-based rations. Nine Holstein cows with indwelling catheters in splanchnic blood vessels, 8 also with a ruminal cannula, were used to examine the effects of protein source in corn silage-based diets, comparing SBM versus CM, and forage source in CM-based diets, comparing corn versus grass silage. The cows were allocated to a triple 3 × 3 Latin square design with 21-d periods. The 3 experimental diets, formulated to be isoenergetic and isonitrogenous, were based on: (1) SBM and corn silage (SoCo); (2) CM and corn silage (CaCo) and (3) CM and cool-season grass silage (CaGr). Averages of intake, milk yield, and milk composition of the last 3 d of each period were used for statistical analyses. On d 21 of each period, 6 sets of arterial, portal, hepatic, and mammary blood samples and 2 ruminal fluid samples were collected. On d 12 of period 2, the protein sources were incubated in nylon bags to determine 16-h ruminal disappearance of DM and N and to obtain 16-h residues. Finally, 5 d after the completion of the Latin square design, the mobile bag technique was used to determine DM and N intestinal disappearance of the 16-h residues of SBM and CM. Pre-planned contrasts were used to compare the effect of the protein source in cows fed corn silage (i.e., SoCo vs. CaCo) and the effect of forage in cows fed CM (i.e., CaCo vs. CaGr). Data of the cow without a rumen canula could not be used because of health problem. In corn silage-based diets, substitution of SBM by CM tended to increase milk (6%) and milk fat (7%) yields. The 8% higher ruminal N disappearance and the 19% decreased MP supply from RUP predicted by NRC (2001) were not supported by the 25% decrease in ruminal ammonia concentration, similar net portal absorption of AA (except 22% higher for Met), and the 14% decrease in urea hepatic removal when CM substituted SBM. Ruminal incubation of CM in nylon bags does not appear suitable for adequate determination of the rumen by-pass of a protein source such as CM. Inclusion of grass silage rather than corn silage in CM-based diets tended to increase milk (6%) and increased milk lactose (8%) yields. Neither protein nor forage source resulted in variations of metabolism of energy-yielding nutrients that could explain observed increments in cow performance. The present study indicates no decreased AA availability when CM substitutes SBM. Therefore, substitution of SBM by CM in diets based on corn silage and CM in corn- or grass silage diets can be used successfully in high producing dairy cows.

Linkage of in situ ruminal degradation of crude protein with ruminal degradation of amino acids and phytate from different soybean meals in dairy cows

The objectives of this study were to determine the range in ruminal degradability of crude protein (CP) and intestinal digestibility of rumen undegradable protein in commercial soybean meal (SBM) and to investigate the range in in situ ruminal AA and phytate (InsP6) degradation and their relationship to CP degradation. An in situ study was conducted using 3 lactating Jersey cows with permanent rumen cannulas. Seventeen SBM variants from Europe, Brazil, Argentina, North America, and India were tested for ruminal CP and AA degradation, and in vitro intestinal digestibility of rumen undegradable protein. Nine variants were used to investigate the ruminal degradation of InsP6. The estimated rapidly degradable fraction (a) of CP showed an average value of 4.5% (range: 0.0%-9.0%), the slowly degradable fraction (b) averaged 95% (91%-100%), and the potential degradation was complete for all 17 SBM variants. The degradation of fraction b started after a mean lag phase of 1.7 h (1.1-2.0 h) at an average rate (c) of 10% per hour, but with a high range from 4.5% to 14% per hour. Differences in the degradation parameters induced a considerable range in CP effective degradation at a rumen passage rate of 6% per hour (CPED6) from 38% to 67%; hence, the concentration of rumen undegradable protein varied widely from 33% to 62%. The range in AA degradation between the SBM variants was high, with Ser showing the widest range, from 28% to 96%, and similar for the other AA. The regression equations showed close relationships between CP and AA degradation after 16 h of in situ incubation. However, the slopes of the linear regressions were significantly different between AA, suggesting that degradation among individual AA differs upon a change in CP degradation. The concentrations of InsP6 and myo-inositol pentakisphosphate in bag residues in the in situ study decreased constantly with longer ruminal incubation times. The ruminal degradation parameters of InsP6 ranged from 11% to 37% for fraction a, 63% to 89% for fraction b, and from 7.7% to 21% per hour for degradation rate c, with average values of 21%, 79%, and 16% per hour, respectively. The calculated InsP6 effective degradation at a rumen passage rate of 6% per hour (InsP6ED6) varied from 61% to 84% among the SBM variants. Significant correlations were detected between InsP6ED6 and CPED6 and between InsP6ED6 and chemical protein fractions A, B1, B2, B3, and C. Linear regression equations were developed to predict ruminal InsP6 degradation using CPED6 and chemical protein fractions B3 and C chosen by a stepwise selection procedure. We concluded that a high range in CP, AA, and InsP6 degradation exists among commercial SBM, suggesting that general degradability values may not be precise enough for diet formulation for dairy cows. Degradation of CP in SBM may be used to predict rumen degradation of AA and InsP6 using linear regression equations. Degradation of CP and InsP6 could also be predicted from the chemical protein fractions.

Effects of faba bean, blue lupin and rapeseed meal supplementation on amino acid metabolism of dairy cows fed grass silage-based diets

Information about the amino acid (AA) supply of locally produced protein supplements to dairy cow metabolism is needed to design sustainable diets for milk production. In this dairy cow experiment, grass silage and cereal-based diets supplemented with isonitrogenous amounts of rapeseed meal (RSM), faba beans (FB) and blue lupin seeds (BL) were compared with a control diet (CON) without protein supplementation. The diets were arranged as a 4 × 4 Latin Square using periods of 21 days, and four rumen-cannulated Nordic Red dairy cows were used in the experiment. The intake of all AAs increased in response to protein supplementation and was for many individual AAs higher when RSM rather than the grain legumes FB and BL were fed. The total AA flow at the omasal canal was 3 026, 3 371, 3 373 and 3 045 g/day for cows fed CON, RSM, FB and BL, respectively, but only RSM resulted in higher milk protein output. This may be explained by the higher provision of essential AA for milk protein synthesis when RSM was fed. The cows fed FB showed some positive features such as a tendency for greater omasal flow of branched-chain AA compared with BL. Overall, low plasma methionine and/or glucose concentrations in all treatments suggest that their supply was possibly limiting further production responses under the dietary conditions of the current study. It seems that the benefits of grain legume supplementation are limited when high-quality grass silage and cereal-based diets are used as the basal diet, but higher responses in amino acid supply and subsequent production responses can be expected when RSM is used.