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Feed intake and production responses of lactating dairy cows when commercially available fat supplements are included in diets: a meta-analysis
This analysis was performed to evaluate the effects of commercially available fat supplements on DMI and production responses of lactating dairy cows. Available data were collected from 133 peer-reviewed publications; of which 88 met our selection criteria, comprising 159 treatment comparisons. Calcium-salts of palm fatty acid distillate (PFAD; n=73), saturated prilled fats (PRILLS; n=37), and tallow (n=49) supplemented at ≤3% diet DM were compared to non-fat supplemented diets used as controls. Analysis was performed using Comprehensive Meta Analysis v2. software to calculate the effect size as the mean difference in least square means between control and fat supplemented treatments using a random effects model. Treatment comparisons were obtained from either randomized design (n=99) or crossover/Latin square design experiments (n=60). There were no differences in the overall effect of fat supplementation between randomized design and crossover/Latin square design experiments for any production parameter (all P>0.46). Therefore, all types of experimental design were analyzed together. Fat supplementation reduced DMI compared to control (0.30 kg/d, P<0.01). However, the response was dependent on fat type; PFAD and tallow reduced DMI (0.58 and 0.44 kg/d, P<0.01 and P=0.06, respectively), while PRILLS had no effect (P=0.71). Fat supplementation increased milk yield by 1.05 kg/d (P<0.01), with differences in the magnitude of response for PFAD (1.20 kg/d, P<0.01), PRILLS (1.19 kg/d, P<0.01), and tallow (0.70 kg/d, P<0.01). Fat supplementation increased milk fat yield by 0.04 kg/d (P<0.01) with increases of 0.05 and 0.06 kg/d for PFAD and PRILLS, respectively (both P<0.01) with no effect of tallow (P=0.72) compared to control. There was no overall effect of fat supplementation on milk fat concentration (P=0.84), although compared with control, tallow reduced milk fat by 0.08 percentage units (P=0.01), PFAD had no effect (P=0.25), and PRILLS increased milk fat by 0.08 percentage units (P=0.05). Milk protein yield was unaffected by PFAD and tallow (both P>0.31) and increased by 0.03 kg/d by PRILLS (P<0.01) resulting in an overall increase by fat supplementation of 0.01 kg/d (P<0.01). Milk protein concentration was reduced by all fat supplements (P<0.01 for PFAD and tallow; P=0.04 for PRILLS) for an overall reduction in milk protein concentration of 0.05 percentage units (P<0.01). In conclusion, fat supplementation has the potential to reduce DMI and increase the yield of milk and milk components. However, consideration should be given to the type of fat, as production responses were highly variable across fat supplements.
Keywords: fat supplementation, meta-analysis, production response