Effects of Dietary Supplementation of Peanut Skins (Arachis hypogaea) on Performance, Digestibility, and Rumen Fermentation of Cattle: a Meta-Analysis

Abstract The objective of this study was to estimate the magnitude of effects of the dietary inclusion of Peanut skins (PS) byproduct (Arachis hypogea L.) on intake, total-tract digestibility, and rumen fermentation of cattle via meta-analysis. Data were collected following the PRISMA methodology. Nine manuscripts and a graduate thesis met the inclusion criteria from 1983 to 2010. The effect size was estimated by calculating the weighted raw mean differences (RMD) between PS vs. control diets. The RMD was compared with a robust variance estimation method followed by a meta-regression and a dose-response analysis fitting the diet characteristics like crude protein (CP), NDF content, ether extract content (EE), PS level in diet (0 to 40%), and tannin content as covariates. Dietary PS decreased (P < 0.01) total-tract CP digestibility (52.0 vs. 64.3%), final body weight (371.5 vs. 397.9 kg), and average daily gain (1.14 vs. 1.44 kg/d) among treatment comparisons. Likewise, PS decreased total VFA (92.6 vs. 107.6 mmol/L) and NH3N (8.22 vs. 12.1 mg/dL) among treatment comparisons, but no effects were observed on rumen pH (6.47 vs. 6.14), acetate (52.6 vs. 50.4%), propionate (31.9 vs. 33.1%), and butyrate (11.02 vs. 11.2%) molar proportions among treatment comparisons. Despite the between-cluster variance, dietary PS increased the ether extract digestibility (77.5 vs. 70.2%) among treatment comparisons. The subset and dose-response analysis revealed that PS should not exceed 8% (DM basis) in the diet to prevent negative effects on CP digestibility and animal performance. The tannin content in the diet strongly influenced the observed effects on rumen fermentation suggesting a low tolerance (> 3% in the diet) by cattle to tannins in PS. In conclusion, the results of this meta-analysis do not support the dietary inclusion of PS in cattle diets beyond 8%. However, low dietary levels of PS (up to 8%) could increase the incorporation of antioxidants and unsaturated fatty acids from PS in cattle.