Abstract
In vivo digestibility and nitrogen balance were determined in a 3×3 Latin square trial with six non-lactating cows and six heifers of the Swedish Red breed fed three forages harvested from semi-natural grasslands. Total faecal collection and urinary spot-sampling were performed on all animals, and enteric methane emissions were measured in the cows by the tracer-gas technique. The forages were harvested from a wet shore meadow (WET), a naturalised cultivated grassland (NL) and a species-rich naturalised cultivated grassland (SNL). Neutral detergent fibre concentrations were similar between the forages. The WET forage had the highest organic matter (OM) and crude protein (CP) contents (947 and 118g/kg DM, respectively), but the lowest in vitro digestibility and hence metabolisable energy content (8.1MJ/kg DM). There was an interaction between forage and animal category with lower digestibility in heifers than in cows of DM (0.51 vs. 0.58), OM (0.54 vs. 0.60) and CP (0.52 vs. 0.60) for the WET forage. The CP digestibility in the cows was higher for the WET forage than for the other forages. The overall OM digestibility was 0.60 in vivo and 0.61 in vitro, respectively. Nitrogen balance in the animals differed between forage treatments (WET=21.3, NL=11.8 and SNL=26.9gN/day) but not between animal categories. The cows produced on average 53gmethane/kg digested OM, and no significant differences were found between forages. The digestibilities of the three forages studied are similar to those of other European extensively managed grasslands and nitrogen excretion routes in the cattle did not deviate from those of cattle indoor-fed standard rations. The results suggests that it is possible to use the standard Swedish in vitro method for estimation of in vivo digestibility of forages from semi-natural pastures when fed to cattle, even though this method was developed using other types of forages and ewes.
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