The dynamics of fat digestion and metabolism in ruminants depends on the dietary fatty acid (FA) profile and microbial metabolism of FA in the rumen. Digestion of FA can vary widely between dietary fat sources. A meta-analytic study was conducted to estimate the apparent total-tract digestibility coefficients of FA (DCFA_TTa) in dairy cows. A total of 31 studies (142 treatment means) that reported digestion of FA were used. Data for diet composition, intake, and digestibility, were collected from 357 cows (BW = 597 ± 74.9 kg, DM intake = 20.3 ± 4.92 kg/d, milk yield = 31.4 ± 8.28 kg/d). Dietary sources of fat were grouped into 11 categories. The digestible FA intake was then regressed on FA intake. The mixed model included the random effect of study. Studies were weighted according to the inverse of their variance (SE). DCFA_TTa was influenced (P < 0.001) by the source of dietary fat; however, the intercept was not significant (P > 0.01). Fat supplements with high levels of palmitic, stearic acids, or hydrogenated triglycerides, had markedly lower FA digestion compared with those that are rich in unsaturated FA (Table 1). Overall, cows that were fed higher levels of saturated FA had lower FA digestion. Digestion coefficients of FA are useful to estimate the amount of dietary FA that could potentially be digested by dairy cows. Future studies should focus on individual FA digestion in lactating dairy cows. Table 1. Coefficients of apparent total tract digestibility of fatty acids (DCFA_TTa)

Classes	DCFATTa, g/g	SE
Basal diet	0.73	0.026
Oil seeds	0.73	0.041
Oil1	0.70	0.033
Blended triglycerides2	0.63	0.027
Tallow3	0.68	0.029
Mildly hydrogenated tallow triglycerides4	0.61	0.037
Hydrogenated triglycerides5	0.44	0.030
Ca-salts of palm FA6	0.76	0.027
Partially hydrogenated tallow FA7	0.69	0.022
Palmitic acid, ~85%8	0.73	0.077
Palmitic or stearic acid > 90%9	0.31	0.046

¹>20% PUFA and > 65% UFA. ²<20% PUFA and >56% UFA. ³>36% MUFA and <56% UFA. ⁴>25% MUFA and <36% UFA. ⁵<20% MUFA and <25% UFA. ⁶>30% MUFA. ⁷<15% MUFA and <20% UFA. ⁸>7% MUFA and <10% UFA. ⁹<2% MUFA and <2% UFA.