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Milk fatty acid metrics and their relationship to milk fat and true protein concentrations in tanks from US Jersey herds.

H. M. Dann



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Milk fatty acid metrics and their relationship to milk fat and true protein concentrations in tanks from US Jersey herds.
H. M. Dann*1, A. Pape1, D. M. Barbano2. 1William H. Miner Agricultural Research Institute Chazy, NY, 2Cornell University Ithaca, NY.

Our objective was to determine the relationship between milk fatty acid (FA) metrics and concentrations of milk fat and true protein (TP) in tanks from Jersey herds. Bulk tank or tanker milk samples were collected 3 to 7 d per mo for 1 yr from 28 US Jersey herds. Samples were preserved with bronopol and natamycin, refrigerated, and shipped with ice for testing. Samples were analyzed using mid-infrared (MIR) analysis (CombiScope FTIR 300 Hp; Delta Instruments) for fat, TP, de novo (DN: < C16), mixed origin (MO: C16 and C16:1), and preformed (PF: ≥C18) FA, and unsaturation index. Individual sample results were reduced to a monthly mean by herd. A subset of samples (n = 164) were selected, frozen, and analyzed by gas-liquid chromatography (GLC) for individual FA. Individual FA were summed by group and compared with MIR analysis results. Regression and correlation analyses were conducted with R 3.6.2. Fat and TP concentrations increased with increased concentrations of DN, MO, or DN + MO FA. In contrast, fat and TP concentrations were not related to PF FA concentration. Fat (y = −6.93x + 6.68; R2 = 0.36) and TP (y = −3.43x + 4.55; R2 = 0.22) expressed as a percentage were related negatively to the unsaturation index (x), expressed as double bonds per FA. The unsaturation index was correlated positively (r = 0.53) with C18:1 trans-10 FA expressed as g FA/100 g milk. There was good agreement between GLC and MIR results expressed as g FA/100 g milk for DN (r = 0.95), MO (r = 0.88), and PF (r = 0.77) FA (Table 1). These findings indicate that MIR analysis is a quick and cost-effective option for determining fatty acid metrics in milk from Jersey herds. Producers and consultants working with Jersey herds should focus on feeding and management practices that promote DN and MO fatty acids in milk to increase tank fat and TP concentrations.Table 1.

Y variable (%)X variable (g FA/100 g milk)EquationR2
FatDN FAy = 2.09x + 2.450.71
FatMO FAy = 1.53x + 2.210.72
FatDN + MO FAy = 1.03x + 1.870.84
FatPF FAy = 0.71x + 3.680.08
TPDN FAy = 1.30x + 2.140.66
TPMO FAy = 0.66x + 2.500.33
TPDN + MO FAy = 0.53x + 2.110.53
TPPF FAy = 0.04x + 3.60<0.01

Keywords: milk fat, milk protein, de novo fatty acids.