Effect of forage quality on intake, chewing activity, faecal particle size distribution, and digestibility of neutral detergent fibre in sheep, goats, and llamas

This study investigated the effect of forage quality on intake, eating and ruminating activities, faecal particle size distribution, and neutral detergent fibre (NDF) digestibility in three ruminating species. The experimental design included ad libitum feeding of three ruminating species with two types of forage for two periods in a crossover design. The species included six adult, non-pregnant female Danish Landrace goats, Shropshire sheep, and Lama glama llamas with body weights of 45 ± 5, 75 ± 6, and 135 ± 20 kg (mean ± SD), respectively. Forage included chopped artificially dried grass hay (GH) and grass seed straw (GSS). The contents of NDF in dry matter (DM) and of in situ indigestible NDF (%NDF) were 58 and 15% for GH and 81 and 28% for GSS, respectively. Total faeces were collected for five days. The faecal samples were washed in nylon bags and freeze dried before being sorted into six sieving fractions with pore sizes in the 2.4–0.1 mm range and a bottom bowl. The dimension of each particle in sub-samples from each fraction was measured using image analysis. The DM intake per metabolic body weight (BW) was higher in sheep and llamas fed GH than in those animals fed GSS (P < 0.05). Sheep and goats had a higher NDF intake per kg BW than did llamas when fed GSS (P < 0.001). The mean and effective times spent eating per kg of DM intake, ruminating, and in total chewing per kg of DM and NDF intakes were higher when GSS was fed (P < 0.05). The total daily and effective time spent chewing was higher in sheep than in goats (P < 0.05). The mean daily and effective times spent chewing per kg of DM and NDF intakes were higher in goats than in sheep (P < 0.05). The ratio between the basic chewing rate during eating and ruminating was lower in llamas than in goats or sheep (P < 0.001) and was affected by forage type, species, and their interactions (P < 0.05). The proportions of small (<0.2 mm) and large particles (LP) (>1 mm) were significantly reduced by feeding GSS. Feeding GH rather than GSS resulted in lower most frequent particle size, length, and width values (P < 0.001) and a lower median particle size (P < 0.05). NDF digestibility was highest when GH was fed (P < 0.05). In conclusion, feeding low-digestible forage leads to a higher mean chewing time per kg of DM and NDF intakes and longer ruminating periods and cycles than when feeding medium-digestible forage. Feeding more digestible forage caused thinner and longer faeces particles than did feeding low-digestibility forage. The overall particle size, length, and width characteristics values in faeces did not differ between sheep, goats, and llamas, which indicates the same mechanism of selective retention of LP in the forestomach system. Across animal species and forage type, the mean particle size in faeces was negatively correlated with NDF digestibility.