Effects of grass moisture on utilization of forage by grazing animals. 1. Availability of grasses to grazing animals for three different sward heights

摘要

Moisture is a major component of fresh herbage. We studied seasonal changes in yield and the nutrient and moisture contents of Orchardgrass (OG, Dactylis glomerata L.), Tall fescue (TF, Festuca arundinacea Schreb.), and Perennial ryegrass (PRG, Lolium perenne L.) in swards with three different grass lengths (20, 30, 40 cm) to determine whether the dry matter and nutrient intake of grazing animals were restricted by forage moisture. The moisture content in the grasses was higher for short sward heights than for long sward heights, except for OG in summer. Dry matter yields increase with sward height, but most occur in the lower part of the canopy. The spatial distribution of the standing crop in the canopy does not favor dry matter ingestion by grazing animals, because they are unable to graze on the grass in the lower part of the canopy. Furthermore, the plant tissues with high moisture content are in the upper part of the canopy, and grazing animals are obliged to ingest the high-moisture forage. Consequently animals necessarily ingest large quantities of water as grass moisture, which leads to restricted dry matter and nutrient intake. The grass moisture is held in the plant tissue, and is not released in the animal gut unless the plant tissues are destroyed by mastication or ruminal digestion. This study suggests that if animals grazed on shorter swards, grass moisture might restrict animal dry matter and nutrient intake.