2002, Number 1
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ABSTRACTA three-year grazing experiment was carried out in central Mexico in order to measure botanical composition, nutritional value and pasture growth rate, and to determine the relationship between pasture height and herbage mass of a mixed grass (Lolium perenne, Festuca arundinacea and Dactylis glomerata) legume (Medicago sativa and Trifolium repens) sward. The pasture was flood-irrigated, and grazed throughout the year by lactating Holstein dairy cows. The pasture’s botanical composition was determined using manual dissection techniques. The pasture’s nutritional value was determined through the in vitro dry matter (DM) digestibility (IVDMD), and its crude protein (CP) content. Energy content of pasture samples, expressed as megajoules (MJ) of metabolizable energy (ME) per kg of DM, was determined from the IVDMD values. Pasture growth rates were calculated from the monthly records of herbage mass determination, and the relationship between pasture’s height and herbage mass was determined using a linear regression. On average, the pasture’s botanical composition included 70% grass and 30% legumes. The relationship between pasture height and herbage mass was linear and, on average, pasture herbage mass increased 219 (r2 = 87.0, CV = 6%); 206 (r2 = 77.0, CV = 8%); 107.4 (r2 = 60.0, CV = 9%) kg DM by each centimeter increase in pasture’s height during spring, summer and autumn, respectively. On average, pastures yielded 17.22 tons DM/hectare/year during the three-year grazing experiment. The fastest pasture’s growth rates (38 to 63 kg DM/hectare/day) were obtained during the spring-autumn period, and the slowest ones (32 to 40 kg DM/hectare/day) during winter. Throughout the year for the three-year study, the pasture’s IVDMD, CP content, and ME concentration were 65%, 19.5%, and 9.6 MJ ME/kg DM, respectively. Variations observed on pasture’s production and nutritional value were due to an insufficient supply of irrigation water and low fertilizer doses applied, and not to adverse effects of the grazing animals on the pasture. It is concluded that under the conditions of this study the pasture’s nutritional value, botanical composition, and pasture growth rates were adequate for the feeding of lactating grazing dairy cattle.
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