Abstract
ObjectiveA meta-analysis was conducted to evaluate the effects of supplemental fat containing saturated free fatty acids (FA) on milk performance of Holstein dairy cows.MethodsA database was developed from 21 studies published between 1991 and 2016 that included 502 dairy cows and a total of 29 to 30 comparisons between dietary treatment and control without fat supplementation. Only saturated free FA (>80% of total FA) was considered as the supplemental fat. Concentration of the supplemental fat was not higher than 3.5% of diet dry matter (DM). Dairy cows were offered total mixed ration, and fed individually. Statistical analysis was conducted using random- or mixed-effects models with Metafor package in R.ResultsSub-group analysis showed that there were no differences in studies between randomized block design and Latin square/crossover design for dry matter intake (DMI) and milk production responses to the supplemental fat (all response variables, p≥0.344). The supplemental fat across all studies improved milk yield, milk fat concentration and yield, and milk protein yield by 1.684 kg/d (p<0.001), 0.095 percent unit (p = 0.003), 0.072 kg/d (p<0.001), and 0.036 kg/d (p<0.001), respectively, but tended to decrease milk protein concentration (mean difference = −0.022 percent unit; p = 0.063) while DMI (mean difference = 0.061 kg/d; p = 0.768) remained unchanged. The assessment of heterogeneity suggested that no substantial heterogeneity occurred among all studies for DMI and milk production responses to the supplemental fat (all response variables, I2≤24.1%; p≥0.166).ConclusionThe effects of saturated free FA were quantitatively evaluated. Higher milk production and yields of milk fat and protein, with DMI remaining unchanged, indicated that saturated free FA, supplemented at ≤3.5% dietary DM from commercially available fat sources, likely improved the efficiency of milk production. Nevertheless, more studies are needed to assess the variation of production responses to different saturated free FA, either C16:0 or C18:0 alone, or in combination with potentially optimal ratio, when supplemented in dairy cow diets.
Highlights
Supplementing fat in dairy rations to increase energy density has been extensively evaluated in numerous studies over the last a few decades
The supplemental fat was added to total mixed ration by replacing one ingredient at the same level of ration dry matter (DM); or by doing so, the diet was reformulated with multiple ingredients balancing for crude protein (CP); or the addition of the supplemental fat to control diet led all other ingredients diluted
The nutrient compositions of the experimental diets were notably variable among all studies, but no extremely high/low values of nutrients, especially total fatty acids (FA) due to the supplemental fat, in the diets occurred
Summary
Supplementing fat in dairy rations to increase energy density has been extensively evaluated in numerous studies over the last a few decades. There is a growing interest in understanding the effects of different fat sources, saturated free fatty acids (FA) on milk production and components [1]. Some meta-analysis have reviewed effects of fat addition to dairy cow diets on milk production and components [5,6,7]. In those meta-analyses several types of fat sources have been categorized, of which selected hydrolyzed tallow FA [5] or prilled fat [6,7] was identified as a type of fat sources differentiating it from others such as calcium salts, tallows, etc. The objective of the metaanalysis was to evaluate the effects of supplementing saturated free FA on milk performance of Holstein dairy cows
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