Effect of replacing peanut vine with extruded rape straw on growth, nutrient digestibility, energy metabolism, microbial crude protein synthesis, meat amino acid and fatty acid profiles of finishing lambs

Abstract

Peanut crop residues such as peanut vine are widely used to feed small ruminants as roughage in Asia, where the population of sheep and goat takes a large proportion in the world. Compared to peanut vine, straw is considered as a less nutritious but promising roughage source due to high availability and low price. Extrusion is a process to improve the palatability and digestibility of the feed. Here, we investigated the effects of replacing peanut vine with extruded rape straw on growth performance, apparent nutrient digestibility, energy metabolism, microbial crude protein (MCP) synthesis, and amino acid and fatty acid profiles in the longissimus thoracic (LT) of finishing lambs. Twenty-four 2-mo-old male Hu lambs of similar body weight (19.5 ± 1.0 kg) were fed two diets containing either peanut vine (CON, n = 12) or extruded rape straw (TRT, n = 12) as the only roughage source. The dietary concentrate to forage ratio was 70:30. Lambs were fed twice daily and had ad libitum access to feed and clean water. The experiment lasted 120 d, including a 30-d adaptation period. Lambs were weighed every 30 d. Digestibility trial was conducted during the 81 to 90 d of the experiment. At the end of the experiments, lambs were slaughtered for ruminal fluid and meat sample collection. Data were analyzed using mixed model with repeated measures, Student's t-test, or Wilcoxon signed-rank test. No difference in growth performance, apparent digestibility of nutrients, or energy utilization efficiency was observed, except for the apparent digestibility of ether extract, which was greater (P = 0.008) for lambs in the TRT group. In addition, the MCP estimated using urinary purine derivatives (P = 0.072) tended to be greater in the lambs of the TRT group. The concentration of most amino acids and fatty acids was not different in the LT sample of two groups of lambs, while the concentration of Met (P = 0.044) was greater, and that of myristoleic acid (C14:1) (P = 0.010), heptadecenoic acid (C17:1) (P < 0.001), trans-linoleic acid (C18:2n6t) (P = 0.003) and gamma-linolenic acid (C18:3n6) (P < 0.001) were lower in the LT sample of lambs from TRT group. In conclusion, extruded rape straw can effectively replace peanut vine in the diet of lambs without compromising health or nutrient utilization.

Keywords: amino acid; extruded rape straw; fatty acid; growth; lamb; peanut vine.

Figure 1.

Intake, body weight (BW), average daily gain (ADG), and feed conversion ratio (FCR) of lambs fed different sources of roughages. CON, peanut vine as the only roughage source; TRT, extruded rape straw as the only roughage source.

Figure 2.

Concentrations of total amino acids (TAA), essential amino acids (EAA), non-essential amino acids (NEAA), and the EAA/NEAA ratio in the longissimus thoracic muscle of lambs fed different roughage sources: peanut vine (CON) and extruded rape straw (TRT). Hedges’ g (effect size) for 2 comparisons (TRT vs. CON) is shown in the Cumming estimation plot. The raw data are plotted on the upper axes; each Hedges’ g is plotted on the lower axes as a bootstrap sampling distribution. Mean differences are depicted as dots; 95% CI are indicated. The unit of total and individual amino acid is expressed as g/100 g fresh sample. EAA is the sum of Val, Met, Ile, Leu, Phe, Lys, and Thr. NEAA is the sum of Asp, Ser, Glu, Pro, Gly, Ala, Tyr, His, and Arg.

Figure 3.

Concentrations of total fatty acids (TFA), saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) in the longissimus thoracic muscle of lambs fed different roughage sources: peanut vine (CON) and extruded rape straw (TRT). Hedges’ g (effect size) for 2 comparisons (TRT vs. CON) is shown in the Cumming estimation plot. The raw data are plotted on the upper axes; each Hedges’ g is plotted on the lower axes as a bootstrap sampling distribution. Mean differences are depicted as dots; 95% CI are indicated. The unit of total and individual fatty acid is expressed as g/100 g fresh sample. TFA is the sum of SFA, MUFA, and PUFA. SFA is the sum of C10:0, C12:0, C14:0, C15:0, C16:0, C17:0, C18:0, C21:0, and C24:0. MUFA is the sum of C14:1, C16:1, C17:1, C18:1n9t, and C18:1n9c. PUFA is the sum of C18:2n6t, C18:2n6c, C18:3n6, C18:3n3, C20:3n6, and C20:4n6.