The effect of cultivar and harvest date on the chemical composition and digestibility of fodder kale

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Abstract
The chemical composition and digestibility of seven marrow‐stem, three thousand‐head, and two curly kales were determined during the period from September to March. Differences between cultivars and between harvest dates were found for all of the characteristics assessed, but cultivar by harvest date interactions were not a serious problem. The largest differences in dry matter (DM) content were between the two curly kales (17.7%) and the other ten cultivars (14.0%), and between the mid‐September harvest (11.3%) and the three later harvests (15.8%). Then, expressed as a percentage of the DM, the main results were as follows. The organic matter (OM) content was low in the mid‐September (85.9 compared to 90.1) and contributed to a low digestible OM content (68.5 compared to 72.2). Amongst the marrow‐stem kales were the extremes for digestible OM, namely 68.6 in an un‐named marrow‐stem stock and 73.5 in Maris Kestrel. The crude protein content fell from 22.1 in mid‐September to 15.7 in mid‐November, and then rose to 17.4 in January and March. The S‐methyl cysteine sulphoxide (the haemolytic factor) content increased from 0.692 in mid‐September to 1.21 in January and March, when the curly kales had 41% higher contents than the marrow‐stem kales. The extreme thiocyanate ion (a goitrogen) contents occurred in mid‐November (0.0152) and mid‐January (0.0336), and ranged from 0.0157 in the marrow‐stem cultivar Merlin to 0.0334 in the dwarf thousand‐head cultivar Canson. Although not a yield trial, it was found that on average the DM yield of the curly kales was only 55% that of the marrow‐stem and thousand‐head kales.

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