Abstract
A plot study was conducted at the Gatton Research Dairy, Queensland, Australia, to quantify the effects of 5 regrowth periods (9, 11, 14, 16 and 18 days) and 4 vertical strata on the composition and nutritive value of kikuyu (Cenchrus clandestinus) pastures using a block factorial design with 4 replicates. Pasture samples were analyzed for crude protein (CP), ethanol-soluble carbohydrates (ESC), acid detergent fiber (ADF), neutral detergent fiber (aNDFom), in vitro indigestible neutral detergent fibre (iNDF240) and minerals. Metabolizable energy (ME) was then calculated from the concentrations of other nutrients. Regardless of the stage of regrowth, stems were located mainly in the bottom 1 or 2 strata, while leaves were present mainly in the top 2 or 3 strata. CP, ESC and ME declined, but aNDFom, ADF and iNDF240 increased with stage of regrowth and from top to bottom of the swards (P<0.05). While herbage quality variables were affected by both factors, vertical stratum had a much larger impact on quality than stage of regrowth. These results indicate that grazing management of kikuyu pastures should be based not only on stage of regrowth but also on level of defoliation, as both have strong impacts on the nutritive value of the consumed forage.
Highlights
These results indicate that grazing management of kikuyu pastures should be based on stage of regrowth and on level of defoliation, as both have strong impacts on the nutritive value of the consumed forage
Regardless of stage of regrowth, all pastures consisted of the same general structure, with stems predominantly located at the bottom of the sward and leaves at the top of the sward (Table 1)
The results are consistent with the study by Reeves et al (1996), who found that the proportion of stems increased with the stage of regrowth of kikuyu pastures
Summary
Previous studies examined the effects of stage of regrowth on herbage quality of leaves, stems and whole plants of kikuyu pastures (Reeves et al 1996) These early studies provided essential data for the understanding of factors driving herbage quality in kikuyu, such as differences in quality between plant parts at different stages of regrowth; these herbage quality results may not necessarily represent the quality of herbage consumed by animals grazing these pastures. It is well known from previous studies that beef and dairy cattle graze pastures in strata, and herbage quality declines from the top to the bottom of the swards (Ungar and Ravid 1999; Benvenutti et al 2016, 2017; Ison et al 2018). The aim of this study was to quantify the effects of stage of regrowth and vertical distribution in the sward on physical composition and nutritive value of kikuyu pastures
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