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Factors affecting efficiency of AA and energy use in lactating dairy cows
When the concept of metabolizable protein (MP) was introduced to balance dairy rations, the efficiency of utilization of MP (EffMP) or essential AA (EffEAA) was considered fixed, independent of supply (e.g. NRC, 2001; CNCPS, Fox et al. 2004 AFST: 29). This assumption led to systematic over-prediction of milk protein yield (MPY) at high MP supply and under-prediction at low supply. Indeed, the marginal recovery of extra MP or AA supply into MPY decreases as supply increases, so that the overall efficiency decreases with supply (e.g. Hanigan et al. 1998 JDS: 3385; Doepel et al. 2004 JDS: 1279). This decreased EffEAA is linked to increased catabolism, mainly by the liver for Group-1 AA (His, Met, Phe, and Trp) or by the gut and peripheral tissues, including the mammary gland, for Group-2 AA (Ile, Leu, Lys and Val; Raggio et al. 2004 JDS: 3461). In fact, the hepatic removal of Group-1 AA seems to be related to liver inflow, directly linked to plasma AA concentrations (Hanigan. 2005 Anim. Sci: 23; Lapierre et al. 2005 Anim. Sci: 11): an increment in supply leading to an increment in plasma concentration will increase catabolism and therefore decrease the EffEAA. However, in studies where AA and energy supply were studied in a factorial design, infusion of glucose (Clark et al. 1977 JNutr: 631), or glucose precursor (Raggio et al. 2006 JDS: 4340), inclusion of fat in the diet (Cant et al. 1991 JDS: 211) or a higher energy supply with a diet change (Omphalius et al. ADSA 2018 # 487) increased the EffMP. Indeed, a closer look at the variation of EffMP and EffEAA also indicates a better relationship between the EffEAA and the ratio of AA supply/energy supply than with the AA supply alone (e.g. Lapierre et al. 2016 CNC: 205; van Amburgh 2018 ANCC: 90). Currently, the ratio of MP supply/energy supply is used by the European feeding systems to estimate the EffMP (e.g. the Scandinavian system (NorFor, 2011) and the Dutch DVE/OEB system). The new INRA (2018) system opted to predict first the MPY from a model including both MP and energy supply, Lys and Met as % of MP, and also the cow’s potential, and then estimate the EffMP using this prediction. Present work currently being done to improve North American models is presented. Using regression or Bayesian approach, the main factors influencing MPY or total export proteins are, in addition to MP or AA supply (quadratic), digestible energy intake (+), BW (+), days in milk (-), dietary starch (+) and fatty acid (+) concentrations (Hanigan et al. ADSA 2018 #492; Martineau et al. unpublished; Moraes et al. ADSA 2018 #512). Year of publication is also significant (+), probably as an indicator of increased genetic merit. Similarly, using a Bayesian approach, the EffEAA was influenced by digestible energy intake (+) and days in milk (-), in addition to the AA (-) supply (White et al. ADSA 2018 #T226). The positive impact of energy supply on EffMP and EffEAA might be related to a greater metabolic allowance to the energy-expensive protein synthesis, including milk-related enzymes and milk proteins themselves, and/or a sparing effect of energy on AA availability if less are used either for gluconeogenesis or oxidized to yield energy. The other factors are either related to energy supply or to the cow’s potential to produce milk.
Factors affecting efficiency of AA and energy use in lactating dairy cows
When the concept of metabolizable protein (MP) was introduced to balance dairy rations, the efficiency of utilization of MP (EffMP) or essential AA (EffEAA) was considered fixed, independent of supply (e.g. NRC, 2001; CNCPS, Fox et al. 2004 AFST: 29). This assumption led to systematic over-prediction of milk protein yield (MPY) at high MP supply and under-prediction at low supply. Indeed, the marginal recovery of extra MP or AA supply into MPY decreases as supply increases, so that the overall efficiency decreases with supply (e.g. Hanigan et al. 1998 JDS: 3385; Doepel et al. 2004 JDS: 1279). This decreased EffEAA is linked to increased catabolism, mainly by the liver for Group-1 AA (His, Met, Phe, and Trp) or by the gut and peripheral tissues, including the mammary gland, for Group-2 AA (Ile, Leu, Lys and Val; Raggio et al. 2004 JDS: 3461). In fact, the hepatic removal of Group-1 AA seems to be related to liver inflow, directly linked to plasma AA concentrations (Hanigan. 2005 Anim. Sci: 23; Lapierre et al. 2005 Anim. Sci: 11): an increment in supply leading to an increment in plasma concentration will increase catabolism and therefore decrease the EffEAA. However, in studies where AA and energy supply were studied in a factorial design, infusion of glucose (Clark et al. 1977 JNutr: 631), or glucose precursor (Raggio et al. 2006 JDS: 4340), inclusion of fat in the diet (Cant et al. 1991 JDS: 211) or a higher energy supply with a diet change (Omphalius et al. ADSA 2018 # 487) increased the EffMP. Indeed, a closer look at the variation of EffMP and EffEAA also indicates a better relationship between the EffEAA and the ratio of AA supply/energy supply than with the AA supply alone (e.g. Lapierre et al. 2016 CNC: 205; van Amburgh 2018 ANCC: 90). Currently, the ratio of MP supply/energy supply is used by the European feeding systems to estimate the EffMP (e.g. the Scandinavian system (NorFor, 2011) and the Dutch DVE/OEB system). The new INRA (2018) system opted to predict first the MPY from a model including both MP and energy supply, Lys and Met as % of MP, and also the cow’s potential, and then estimate the EffMP using this prediction. Present work currently being done to improve North American models is presented. Using regression or Bayesian approach, the main factors influencing MPY or total export proteins are, in addition to MP or AA supply (quadratic), digestible energy intake (+), BW (+), days in milk (-), dietary starch (+) and fatty acid (+) concentrations (Hanigan et al. ADSA 2018 #492; Martineau et al. unpublished; Moraes et al. ADSA 2018 #512). Year of publication is also significant (+), probably as an indicator of increased genetic merit. Similarly, using a Bayesian approach, the EffEAA was influenced by digestible energy intake (+) and days in milk (-), in addition to the AA (-) supply (White et al. ADSA 2018 #T226). The positive impact of energy supply on EffMP and EffEAA might be related to a greater metabolic allowance to the energy-expensive protein synthesis, including milk-related enzymes and milk proteins themselves, and/or a sparing effect of energy on AA availability if less are used either for gluconeogenesis or oxidized to yield energy. The other factors are either related to energy supply or to the cow’s potential to produce milk.
Factors affecting efficiency of AA and energy use in lactating dairy cows
Lapierre, Hélène (author) / Martineau, R. (author) / Ouellet, D. R. (author) / Hanigan, M.D. (author) / White, R.R. (author) / Moraes, L.E. (author) / Firkins, J.L. (author) / Kebreab, E. (author) / Lemosquet, Sophie (author) / Omphalius, Cléo (author)
2018-01-01
Reexamining amino acid and energy interactions in the dairy cow. 34th ADSA Discover conference. 2018; 34. ADSA Discover conference - Reexamining amino acid and energy interactions in the dairy cow, Itasca, USA, 2018-05-29-2018-06-06, 31-32
Conference paper
Electronic Resource
English
DDC:
690
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