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Meta-analysis of the effect silage inoculation with homolactic or facultative heterolactic bacteria on the performance of dairy cows
Data from 13 peer-reviewed papers were summarized to examine the effect of silage inoculation with homolactic or facultative heterolactic bacteria (HAB) on the performance of dairy cows. The effects were compared by raw mean differences (RMD) between inoculant and control treatment means, and weighted by inverse variance using random-effect models. Heterogeneity sources evaluated by meta-regression and included as covariates crop species (grass, alfalfa, corn or mixtures of silages representing 68.8, 12.5, 6.3 and 12.5% of experiments, respectively), HAB species (L. plantarum or HAB combinations were each used in 50% of the studies), diet type (TMR vs. non TMR were used in 25 and 75% of the studies, respectively) and level of milk yield of Control cows (< or > 22 kg/d were produced in 56.3 and 43.7% of the studies). All studies had HAB application rates of 105 to 106 cfu/g fed. High heterogeneity was detected for DMI (I2 statistic = 71.5%), milk yield (I2 = 81.6%) and milk protein concentration (I2 = 88.7%), whereas moderate heterogeneity was detected for milk fat concentration (I2 = 49.1%). No interaction (P > 0.10) was detected between the covariates. Inoculation with HAB increased DMI (RMD = 0.66 (0.22, 1.10) kg/d, P < 0.01, n = 11), did not affect milk yield in cows producing < 22 kg of milk/d (RMD = -0.89 (-1.93, 0.13) kg/d, P = 0.09, milk yield for control cows = 19.60 ± 1.88 kg/d, n = 9), but increased milk yield in cows producing > 22 kg/d (RMD = 1.07 (0.26, 1.88) kg/d, P < 0.01, milk yield of control cows = 29.92 ± 8.64 kg/d, n = 6). Inoculation with HAB tended to increase milk fat concentration (RMD = 0.06 (-0.004, 0.11) % milk, P = 0.07, n = 15) and increased milk protein concentration (RMD = 0.10 (0.05, 0.15) % milk, P < 0.01, n = 13, n = 2 outliers). However, there was a trend for inoculation with a mixture of HAB species to give a higher milk protein response (RMD = 0.15 (0.02, 0.25) % milk, P = 0.02, n = 6) than inoculation with L. plantarum alone (RMD = 0.04 (0.01, 0.07) % milk, P < 0.01, n = 7). Inoculation with HAB with improved the performance of dairy cows producing more than 22 kg of milk/d but did not affect that of those producing lower quantities of milk.
Keywords: forage conservation