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Predicting the yield of milk fat and milk fatty acid sources from fatty acid intakes in lactating dairy cows: A meta-analysis.

J. M. dos Santos Neto

Abstract:

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Predicting the yield of milk fat and milk fatty acid sources from fatty acid intakes in lactating dairy cows: A meta-analysis.
J. M. dos Santos Neto*1, J. de Souza2, A. L. Lock1. 1Michigan State University East Lansing, MI, 2Perdue AgriBusiness Salisbury, MD.

We performed a meta-analysis to evaluate the effect of intake (_i) of C16:0, C18:0, C18:1, C18:2, and C18:3 on the yields of milk fat and milk fatty acid (FA) sources. Our analysis used 1,339 individual cow observations from 16 studies at Michigan State University. Diets (% DM) contained (mean � SD) 30.1 � 2.47 NDF, 26.6 � 3.17 starch, and 4.03 � 0.78 total FA. Total FA_i averaged 1,126 g/d � 296 and ranged from 308 to 2,248 g/d. Statistical analyses were performed using the PROC MIXED of SAS, including random effects of study, period within study, and cow within study. Individual FA_i (g/d) were used as independent variables, the yields (g/d) of milk fat and milk FA were used as dependent variables. Independent variables were removed from the model using backward elimination with significance criteria of P > 0.10. Total FA intake was not used as an independent variable in the model to avoid multicollinearity. We classified milk FA by source as de novo (<16 carbons), mixed (16 carbons), and preformed milk FA (>16 carbons). C16:0_i linearly increased the yield of milk fat [1,552 � 70.9 + 0.30 � 0.04 x C16:0_i, P < 0.01; RMSE = 1.30]; C18:3_i tended to linearly decrease the yield of de novo milk FA [373 � 18.8 - 0.04 � 0.03 x C18:3_i, P = 0.10; RMSE = 19.3], C16:0_i linearly increased mixed milk FA [468 � 19.7 + 0.22 � 0.01 x C16_i, P < 0.01; RMSE = 14.5], and C18:1+C18:2_i tended to linearly increase preformed milk FA [486 � 48.9 + 0.33 � 0.12 x C18:1_i + 0.13 � 012 x C18:2_i, P = 0.06; RMSE = 22.4]. C18:0_i had no effect on milk FA yield (P > 0.10). Among individual de novo milk FA, C16:0 tended to linearly decrease milk FA from 10 to 14-carbons (P = 0.07), had no effect on C8:0 (P = 13), and linearly increased the yields of C4:0 [43.6 � 2.94 + 0.009 � 0.001 x C16:0_i, P < 0.01; RMSE = 1.61] and C6:0 [29.5 � 1.55 + 0.002 � 0.001 x C16:0_i, P = 0.02; RMSE = 0.96]. In conclusion, the yields of milk FA by source were dependent on the profile of FA ingested. Overall, C16:0_i was associated with increasing milk fat yield. C16:0 increased C4:0 and C6:0, which can be associated with the role of these FA in maintaining milk fluidity, given their low melting point.

Keywords: fatty acid, meta-analysis, milk fat.