# Inclusion of Sub-Antarctic Macroalgae (Gigartina skosttsbergii) as Feed Ingredient for Grazing Sheep

## TL;DR

This study shows that adding a type of red macroalgae to sheep feed can reduce methane emissions without affecting their weight gain.

## Contribution

The study is the first to evaluate the effects of Gigartina skottsbergii on methane emissions and sheep performance in both in vitro and in vivo settings.

## Key findings

- Gs inclusion at 450 g DM/d did not affect sheep body weight or average daily gain.
- Gs reduced in vitro methane emissions and gas production.
- Gs supplementation decreased blood glucose and albumin levels in sheep.

## Abstract

Macroalgae have been incorporated into livestock diets as novel protein and carbohydrate sources with bioactive compounds that could benefit both human and animal health. Recent studies demonstrated that macroalgae can reduce methane production in ruminants without affecting performance, supporting their use as a promising feed ingredient. In this study, we first evaluated the in vitro gas kinetic and methane emission of Gigartina skosttsbergii (red macroalgae), and secondly, we used in vivo assessment to obtain the effects of dietary Gigartina skottsbergii (Gs) supplementation for grazing sheep on growth performance and blood parameters. Our results showed that the dietary inclusion of Gs (at 450 g DM/d) for sheep did not alter body weight, average daily gain, and most of the blood parameters. The implementation of Gs mitigated enteric methane (CH4) emission, in vitro, at this inclusion rate; however, this was accompanied by lower in vitro gas production (IVGP) and in vitro dry matter degradability (IVDMD). Further research is needed to refine the potential impacts of Gs on ruminal fermentation, methane emission, and product quality.

Two experiments were carried out to evaluate the inclusion impacts of macroalgae Gigartina skottsbergii (Gs) for grazing sheep. Experiment (Exp.) 1 studied the effect of Gs on in vitro gas production (IVGP), dry matter (DM) digestibility (IVDMD), and methane (CH4) emission using three fistulated sheep and 96 h incubation of samples. In Exp. 2, ten Dohne Merino ewes [5-year-old; 47 ± 0.14 kg body weight (BW)] were randomly assigned to dietary treatments supplemented with Gs at 0 or 450 g DM/d per animal. The study lasted 31 days and was preceded by an adaptation period of 9 days. The BW, body conditional score (BCS), and blood were sampled at the first and the last day of the trial. The results of Exp. 1 showed that Gs supplementation reduced (MCP, p = 0.026) gas production (A), lag time (p = 0.013), and IVDMD (p = 0.071), while it enhanced partition factor (PF96; p = 0.004) and microbial crude protein (MCP) (p = 0.054). The concentration of CH4 decreased after 3 h (p = 0.0002), 6 h (p = 0.013), and 12 h (p = 0.010) with a tendency at 9 h (p = 0.109) and 24 h (p = 0.068). In Exp. 2, there were no diet effects on the initial BW (IBW, p = 0.77), final BW (FBW, p = 0.91), and average daily gain (ADG, p = 0.24) of ewes; however, Gs supplementation decreased BCS (p = 0.004). Of all blood parameters, only the concentration of glucose (p = 0.021) and albumin (p = 0.011) decreased in the Gs group. Overall, our results revealed that the dietary inclusion of Gs (at 450 g DM/d) affected neither the BW nor ADG of ewes; however, Gs was accompanied by lesser IVGP and CH4 emission.