Meta-analysis of the effects of ionophores supplementation on dairy cows performance and ruminal fermentation

Abstract

A meta-analysis of 52 peer-reviewed papers was conducted to investigate the effects of ionophores (IOP) supplementation on the performance and ruminal fermentation of lactating dairy cows. We used random-effects models to examine the raw mean difference (RMD) between the IOP group (diets with IOP) and the control group (diets with no additives), weighed by inverse of the variance. We also evaluated the effects of the covariates IPO supplementation level dose groups (< 15; 15–20; 21–25; and > 25 mg/kg dry matter (DM) diet), IOP type (monensin or lasalocid), feeding system (total mixed ration or pasture) and days in milk (DIM) on RMD, by meta-regression and subgroup analysis. Overall, IOP supplementation (21.3 ± 8.3 mg/kg DM) reduced DM intake (DMI; RMD = - 0.39 ± 0.22 kg/d; P < 0.01; n = 82), but it increased milk yield (RMD = 0.43 ± 0.28 kg/d; P < 0.01; n = 87), and thereby increased feed efficiency. However, IOP supplementation reduced milk protein (RMD = -0.03 ± 0.02 g/100 g; P < 0.01; n = 79) and milk fat (RMD = -0.08 ± 0.05 g/100 g; P < 0.01; n = 70) contents. Overall, IOP supplementation had no effect on rumen pH (P = 0.29), NH3N (P = 0.63) and acetate concentrations (P = 0.08); however it enhanced the rumen concentration of propionate (P < 0.01) and reduced the rumen concentration of butyrate (P < 0.01). Most of the response variables analyzed herein had low and/or moderate heterogeneity (I2 < 25 and 26–50%, respectively). The ionophore dose was the major covariable impacting the IOP supplementation response (RMD) on animal performance. Ionophores supplementation at doses < 15 mg/kg DM had no effect on milk yield (P = 0.25). However, milk yield increased when cows received IOP doses ranging from 15- 20 mg/kg DM (RMD = 0.64 ± 0.55 kg/d; P < 0.02) and from 21- 25 mg/kg DM (RMD = 0.80 ± 0.54 kg/d; P = 0.03). In contrast, IOP supplementation at doses greater than 25 mg/kg DM reduced milk production (RMD = -0.93 ± 0.54 kg/d; P < 0.01). A positive effect on performance (P ≤ 0.05) was observed only with monensin supplementation and with cows ≤ 150 DIM, but IOP supplementation increased (P ≤ 0.05) performance regardless of the feeding system. Our study demonstrated that the effects of IOP supplementation on lactating dairy cows performance and ruminal fermentation are mainly dose-dependent. We recommend ionophores supplementation for lactating dairy cows at doses between 15 and 20 mg/kg DM diet.