The efficiency of conversion of metabolisable protein into milk true protein over a range of metabolisable protein intakes

Metcalf, J.A.; Mansbridge, R J; Blake, Jonathan S.; Oldham, J. D.; Newbold, J.R.

doi:10.1017/s1751731108002140

Cited by 33 publications

(41 citation statements)

References 11 publications

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“…Newbold (1994) discussed the need for different optimal ratios of MP : ME at different levels of ME intake. Metcalf et al (2008) reported responses to MP above optimal MP : ME ratios, but with decreasing efficiency of MP utilization. 7.…”

Section: Efficiency and Dietary Proteinmentioning

confidence: 97%

“…As the efficiency of conversion of MP and that of metabolisable amino acids into milk TP declines with both increasing supply of MP (Metcalf et al, 2008) and with Met and Lys (Vyas and Erdman, 2009), it follows that production responses to rumen protected forms of specific amino acids may increase at lower dietary protein levels so long as dietary energy intake and other amino acids do not become rate limiting. Most major protein sources contain less Met and Lys than does MCP, so that the proportion of these limiting amino acids in duodenal digesta decline at higher levels of dietary CP (Robinson, 2010).…”

Section: Cp and Intakementioning

confidence: 99%

“…3. Nitrogen efficiency is increased for low protein diets also by decreased catabolism of protein for energy (Metcalf et al, 2008) and for high protein diets by increased mobilisation of body fat reserves in cows that are fatter at calving (Garnsworthy and Jones, 1987). 4.…”

Section: Efficiency and Dietary Proteinmentioning

confidence: 99%

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Reducing dietary protein in dairy cow diets: implications for nitrogen utilization, milk production, welfare and fertility

Sinclair

Garnsworthy

Mann

et al. 2014

Animal

115

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In light of increasing global protein prices and with the need to reduce environmental impact of contemporary systems of milk production, the current review seeks to assess the feasibility of reducing levels of dietary CP in dairy cow diets. At CP levels between 140 and 220 g/kg DM there is a strong positive relationship between CP concentration and dry matter intake (DMI). However, such effects are modest and reductions in DMI when dietary CP is below 180 g/kg DM can be at least partially offset by improving the digestibility and amino acid profile of the undegradable protein (UDP) component of the diet or by increasing rumen fermentable energy. Level and balance of intestinally absorbable amino acids, in particular methionine and lysine, may become limiting at lower CP concentrations. In general the amino acid composition of microbial protein is superior to that of UDP, so that dietary strategies that aim to promote microbial protein synthesis in the rumen may go some way to correcting for amino acid imbalances in low CP diets. For example, reducing the level of NDF, while increasing the proportion of starch, can lead to improvements in nitrogen (N) utilisation as great as that achieved by reducing dietary CP to below 150 g/kg. A systematic review and meta-analysis of responses to rumen protected forms of methionine and lysine was conducted for early/mid lactation cows fed diets containing ⩽150 g CP/kg DM. This analysis revealed a small but significant ( P = 0.002) increase in milk protein yield when cows were supplemented with these rumen protected amino acids. Variation in milk and milk protein yield responses between studies was not random but due to differences in diet composition between studies. Cows fed low CP diets can respond to supplemental methionine and lysine so long as DMI is not limiting, metabolisable protein (MP) is not grossly deficient and other amino acids such as histidine and leucine do not become rate limiting. Whereas excess dietary protein can impair reproduction and can contribute to lameness, there is no evidence to indicate that reducing dietary CP levels to around 140 to 150 g CP/kg DM will have any detrimental effect on either cow fertility or health. Contemporary models that estimate MP requirements of dairy cows may require refinement and further validation in order to predict responses with low CP diets.Keywords: dairy cow, CP, milk yield, fertility, health ImplicationsReducing CP levels to around 140 g/kg DM in dairy cow diets increases the efficiency of N capture and reduces N excretion to the environment. Predicting milk yield responses, however, is complicated by the paucity of data for contemporary high-yielding cows. However, dietary strategies should aim to maximize the yield of microbial protein. Responses to additional essential amino acids such as methionine and lysine are variable and difficult to predict. No detrimental effects of low (i.e. 140 to 150 g CP/kg DM) CP diets on cow health and fertility are anticipated, but these require confirmation in contemporary hig...

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Section: Efficiency and Dietary Proteinmentioning

confidence: 97%

Section: Cp and Intakementioning

confidence: 99%

See 1 more Smart Citation

Reducing dietary protein in dairy cow diets: implications for nitrogen utilization, milk production, welfare and fertility

Sinclair

Garnsworthy

Mann

et al. 2014

Animal

115

View full text Add to dashboard Cite

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“…Van Amburgh et al (2009) stated that the first step in balancing for AA is to ensure that the model is capable of predicting MP-allowable milk with good accuracy and precision. In addition to the challenges of predicting MP and AA flows to the small intestine (NRC, 2001;Van Amburgh et al, 2009) and their intestinal digestibility (Boucher et al, 2009), the efficiency of use of the MP for lactation decreased from 77 to 50% as MP supply increased (Metcalf et al, 2008). Ruiz et al (2002) reported that with N-deficient diets, using an MP for lactation efficiency of 75% resulted in no bias with CNCPS prediction of milk production.…”

Section: Lactating Dairy Cowsmentioning

confidence: 99%

Models of protein and amino acid requirements for cattle

et al. 2015

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-Protein supply and requirements by ruminants have been studied for more than a century. These studies led to the accumulation of lots of scientific information about digestion and metabolism of protein by ruminants as well as the characterization of the dietary protein in order to maximize animal performance. During the 1980s and 1990s, when computers became more accessible and powerful, scientists began to conceptualize and develop mathematical nutrition models, and to program them into computers to assist with ration balancing and formulation for domesticated ruminants, specifically dairy and beef cattle. The most commonly known nutrition models developed during this period were the National Research Council (NRC) in the United States, Agricultural Research Council (ARC) in the United Kingdom, Institut National de la Recherche Agronomique (INRA) in France, and the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia. Others were derivative works from these models with different degrees of modifications in the supply or requirement calculations, and the modeling nature (e.g., static or dynamic, mechanistic, or deterministic). Circa 1990s, most models adopted the metabolizable protein (MP) system over the crude protein (CP) and digestible CP systems to estimate supply of MP and the factorial system to calculate MP required by the animal. The MP system included two portions of protein (i.e., the rumen-undegraded dietary CP -RUP -and the contributions of microbial CP -MCP) as the main sources of MP for the animal. Some models would explicitly account for the impact of dry matter intake (DMI) on the MP required for maintenance (MPm; e.g., Cornell Net Carbohydrate and Protein System -CNCPS, the Dutch system -DVE/OEB), while others would simply account for scurf, urinary, metabolic fecal, and endogenous contributions independently of DMI. All models included milk yield and its components in estimating MP required for lactation (MPl) and calf birth weight and some form of an empirical, exponential equation to compute MP for pregnancy (MPp). The MP required for growth (MPg) varied tremendously among the original models and their derivative works mainly due to the differences in computing growth pattern and the composition of the gain. The calculation of MCP differs among models; some rely on the total digestible nutrient (TDN; e.g., NRC, CNCPS level 1) intake to estimate MCP, while others use fermentable organic matter (FOM; e.g., INRA, DVE/OEB), fermentable carbohydrate (e.g., CNCPS level 2, NorFor), or metabolizable energy (ME; e.g., ARC, CSIRO, Rostock). Most models acknowledged the importance of ruminal recycled N, but not all accounted for it. Our Monte Carlo simulation indicated the prediction of most models for required MPl overlapped, confirming uniformity among models when predicting requirements for lactating animals, but a large variation in required MPg for growing animals exists.

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“…One aspect of nutrient partitioning, the relation between changes in nutrient supply and milk production and composition, has received a lot of attention. In particular, the effects of changes in either metabolizable protein (MP) (Vérité et al, 1987;Metcalf et al, 2008) or net energy (Coulon and Rémond, 1991) on milk outputs have been largely characterized. However, it is still unclear how to quantitatively combine the effects of changes in net energy and MP, including possible interactions between them, for predicting milk yield and milk composition responses.…”

Section: Introductionmentioning

confidence: 99%

Milk yield and milk composition responses to change in predicted net energy and metabolizable protein: a meta-analysis

Daniel

Friggens

Chapoutot

et al. 2016

animal

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Using a meta-analysis of literature data, this study aimed to quantify the dry matter (DM) intake response to changes in diet composition, and milk responses (yield, milk component yields and milk composition) to changes in dietary net energy for lactation (NE L ) and metabolizable protein (MP) in dairy cows. From all studies included in the database, 282 experiments (825 treatments) with experimentally induced changes in either NE L or MP content were kept for this analysis. These treatments covered a wide range of diet characteristics and therefore a large part of the plausible NE L and MP contents and supplies that can be expected in practical situations. The average MP and NE L contents were, respectively (mean ± SD), 97 ± 12 g/kg DM and 6.71 ± 0.42 MJ/kg DM. On a daily supply basis, there were high between-experiment correlations for MP and NE L above maintenance. Therefore, supplies of MP and NE L above maintenance were, respectively, centred on MP supply for which MP efficiency into milk protein is 0.67, and NE L above maintenance supply for which the ratio of NE L milk/NE L above maintenance is 1.00 (centred variables were called MP 67 and NE L100 ). The majority of the selected studies used groups of multiparous Holstein-Friesian cows in mid lactation, milked twice a day. Using a mixed model, between-and within-experiment variation was split to estimate DM intake and milk responses. The use of NE L100 and MP 67 supplies substantially improved the accuracy of the prediction of milk yield and milk component yields responses with, on average, a 27% lower root mean square error (RMSE) relative to using dietary NE L and MP contents as predictors. For milk composition (g/kg), the average RMSE was only 3% lower on a supply basis compared with a concentration basis. Effects of NE L and MP supplies on milk yield and milk component yields responses were additive. Increasing NE L supply increases energy partitioning towards body reserve, whereas increasing MP supply increases the partition of energy towards milk. On a nitrogen basis, the marginal efficiency decreases with increasing MP supply from 0.34 at MP 67 = −400 g/day to 0.07 at MP 67 = 300 g/day. This difference in MP 67 supply, assuming reference energy level of NE L100 = 0, equates to a global nitrogen efficiency decrease from 0.82 to 0.58. The equations accurately describe DM intake response to change in dietary contents and milk responses to change in dietary supply and content of NE L and MP across a wide range of dietary compositions.Keywords: dairy cow, milk composition, energy, protein, meta-analysis Implications Current feed evaluation systems are not suitable to predict animal responses to dietary changes. This paper quantifies average dry matter intake, milk yield and milk composition responses to change in net energy and metabolizable protein. The equations were derived from a meta-analysis of literature studies, which assembles a large number of dairy cow rations with a large range in dietary net energy and metabolizable protein contents.

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The efficiency of conversion of metabolisable protein into milk true protein over a range of metabolisable protein intakes

Cited by 33 publications

References 11 publications

Reducing dietary protein in dairy cow diets: implications for nitrogen utilization, milk production, welfare and fertility

Reducing dietary protein in dairy cow diets: implications for nitrogen utilization, milk production, welfare and fertility

Models of protein and amino acid requirements for cattle

Milk yield and milk composition responses to change in predicted net energy and metabolizable protein: a meta-analysis

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