Fig. 1

Effect of increasing lipid supplementation to lactation diets on the increase in milk fat output when compared with no added lipid diets. Symbols represent the improvements of supplemental lipids relative to no added lipid diets from results reported in 7 studies published from 1989 to 2015 [21, 23–26, 36, 37]. Observations with response means greater than 2 standard deviations from the mean were considered outliers and excluded from the analysis. Linear and non-linear (quadratic, cubic) models were compared using goodness-of-fit tests. Minimum Bayesian information criterion (BIC), minimum root mean square error (RMSE), and maximum coefficient of determination (R²) techniques were used to select the best-fit model. Weighted models were constructed with sample size (n = 4 to 33 sows per data point) as weight