Ginkgo Biloba L. Residues Partially Replacing Alfalfa Hay Pellet in Pelleted Total Mixed Ration on Growth Performance, Serum Biochemical Parameters, Rumen Fermentation, Immune Function and Meat Quality in Finishing Haimen White Goats

Sixty castrated male Haimen white growing goats with an initial age of 100 days old and similar body weight (16 ± 1.5 kg) were selected and randomly allocated into five groups with three replicates in each group with four goats in each pen (5 m × 3.2 m). Goats in the control group (CG) were fed a basal pelleted total mixed ration supplemented with 30% alfalfa hay pellet, while experimental treatments (G6, G12, G18, or G24) were supplemented with four levels (6%, 12%, 18%, or 24%) of GBLR replacing alfalfa hay pellet in the diet, separately. Results showed that (1) the final body weight, average daily gain, and average feed intake of G18 was significantly higher (p < 0.05) than CG; in contrast, the feed conversion ratio of G18 was significantly lower than CG and G12 (p < 0.05); the feed cost per head per day of CG was significantly higher (p < 0.05) than that of G18 and G24, and exhibited obvious linearly decrease (p = 0.04) with increasing GBLR supplementation; and apparent total-tract digestibility of DM and NDF in GBLR treatments were significantly higher (p < 0.05) than CG; (2) alanine transaminase (ALT) concentration in the G18 group was significantly lower (p < 0.05) than those in the control group; aspartate transaminase (AST) concentration in the G24 was significantly lower (p < 0.05) than those in the control group, and an increase in dietary level of GBLR tended to result in a linear decrease (p = 0.09) in the concentration of serum AST; (3) the concentration of malondialdehyde (MDA) demonstrated a tendency to decrease (p = 0.06) linearly with increasing GBLR supplementation; however, glutathione peroxidase (GSH-PX) activity in G12 was significantly higher (p < 0.05) than CG, G6, and G24; in addition, superoxide dismutase (SOD) activity in G18 was significantly higher (p < 0.05) than CG and G6; concentration of immunoglobulin M (IgM), immunoglobulin G (IgG), and immunoglobulin A (IgA) were not affected by GBLR, but increasing dietary GBLR showed a tendency (p = 0.08) to linearly increase the IgG concentration; the content of interleukin 4 (IL4) was significantly higher (p < 0.05) in G12, G18, and G24 than that in CG and G6; (4) There were similar NH3-N, pH, TVFA, and butyrate for goats fed different levels of GBLR supplementation; the C2 (p = 0.07) and acetate: propionate (p = 0.06) demonstrated a tendency to increase linearly with increasing level of GBLR supplementation, separately; however, it was observed that concentration of propionate showed a tendency to decrease (p = 0.08) linearly in response to GBLR supplementation; and (5) Increasing dietary GBLR tended to linearly enhance the lightness (L*) (p = 0.07) and yellowness (b*) (p = 0.09) values of longissimus dorsi muscles; the redness (a*) value in G18 was significantly higher than that in CG (p < 0.05).