EFFECT OF PLANT GROWTH REGULATORS AND HARVEST DATE ON YIELD, BOTANICAL COMPOSITION, CHEMICAL CONSTITUTION, INTAKE AND DIGESTIBILITY OF CRESTED WHEATGRASS-ALFALFA HERBAGE BY SHEEP

Abstract

The effects of the plant growth regulators mefluidide (M) and maleic hydrazide (MH) were compared to untreated controls (C) at each of two harvest dates in 1987 (14 Aug. and 14 Sept.) and 1988 (27 June and 25 July). Plant growth regulators (PGR) were applied at rates of 0.28 kg active ingredient (a.i.) Mha−1 and 1.12 kg a.i. MH ha−1on 14 and 15 July 1987 and on 11 May 1988 to a mixed crested wheatgrass-alfalfa pasture. Application of PGR to the pasture reduced yield (P < 0.01) and increased (P < 0.05) the proportion of alfalfa in the mixture in 1987 only. Chemical composition of crested wheatgrass subsamples was largely unaltered by PGR treatment in 1987 but in 1988 crude protein (P < 0.01), in vitro organic matter disgestibility (P < 0.05) and ash (P < 0.001) were increased and neutral detergent fiber was decreased (P < 0.01). In 1987 the crude protein (P < 0.01) and ash (P < 0.05) contents of alfalfa were increased but were unaffected by PGR treatment in 1988. There were large differences in nutritional value between early- and late-harvest dates in 1987 when moisture was available but only small differences during the drought of 1988. In vivo digestibility of hay from treated plots in 1987 had lower organic matter digestibility (P < 0.001), hemicellulose digestibility (P < 0.001), cellulose digestibility (P < 0.05), acid detergent fiber digestibility (P < 0.05) and neutral detergent fiber digestibility (P < 0.01). In 1987, late-harvested material had lower digestible organic matter intake kg−0.75 and digestibilities of dry matter, organic matter, crude protein, hemicellulose, cellulose, acid detergent fiber, neutral detergent fiber and ash were significantly (P < 0.01) lower than for material harvested earlier. The improvements in forage quality were not sufficient to offset the large yield reductions which are likely to occur in a semi-arid environment. Key words: Plant growth regulators, mefluidide, maleic hydrazide, forage quality, sheep, intake