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Effects of ruminally degraded protein and starch on gluconeogenic precursors in lactating cows.

A. Hruby

Abstract:

M22
Effects of ruminally degraded protein and starch on gluconeogenic precursors in lactating cows.
A. Hruby*, L. Campos, M. Li, J. Prestegaard, M. Hanigan. Virginia Tech Blacksburg, VA.

In lactating dairy cows, gluconeogenesis is vital to maintain glucose (Glu) levels for milk production. Propionate (Pr) produced by ruminal fermentation is the primary precursor for Glu synthesis, however, lactate and amino acids (AA) also contribute. The objectives of this study were to assess the relative contributions of these 3 substrates to gluconeogenesis when Pr and AA supplies are manipulated and to assess the validity of determining Pr production via isotope dilution in the blood pool. Two multiparous and 4 primiparous Holstein cows (247 � 26 and 166 � 61 DIM, respectively) were randomly assigned to 1 of 4 treatments. Treatments were arranged in a 2 � 2 factorial design consisting of high and low dietary concentrations of ruminally degraded protein (RDP), and high (HS) and low (HS) dietary concentrations of starch. Treatments were applied in a 4 � 4 Latin Square with 4, 14-d periods. [2—13C]-Pr was ruminally infused on d12. Jugular infusions of [1,2—13C]-Glu, [1—13C]-lactate, and [2—13C]-Pr were administered on d13 and [U-13C]-AA on d14. Jugular vein samples were taken during and following each infusion and assessed for substrate concentrations and isotopic enrichment. Blood samples were pooled and assessed for lactate, Pr, Glu, and AA concentrations. Met and Pro concentrations were greater for diets containing high starch; further, the latter was lower with high RDP (Table 1). Lactate concentrations were greater for the high RDP, HS treatment, and Pr concentrations tended to be greater with HS. Further, Pr appearance in blood through direct jugular infusions was assessed by isotope dilution in response to varying RDP and starch. Data from this experiment will allow preparation of an improved model for gluconeogenesis in lactating cows.Table 1. Least squares means of metabolite and AA concentrations in pooled blood plasma samples1

ItemLow RDPHigh RDPSEP-value2
LSHSLSHSRDPSRDP � S
Propionate entry rate (g/h)51.424.225.152.86.800.870.97<0.01
Propionate (μM)32.032.228.034.03.100.580.120.16
Lactate (mM)0.6190.6600.6500.5000.0500.120.180.03
Ala (μM)32734332831419.10.550.970.55
Ile (μM)20316014514112.3<0.010.030.07
Met (μM)22.927.122.828.41.190.56<0.010.46
Pro (μM)10411389.11026.30<0.01<0.010.56
Ser (μM)93.710891.81036.900.590.070.81
Val (μM)35330130228724.50.040.050.22
1S = starch; LS = low starch; HS = high starch.2Significance declared at P<0.05.

Keywords: stable-isotope, VFA, propionate.

Biography: Alexis Hruby is a direct PhD student in dairy science at Virginia Tech. A Florida native, she graduated from the nearby Auburn University with a degree in Animal Science in 2017. She hopes to postively impact the dairy industry with her research.