Palatability and effect on dairy cow milk yield of dried fodder from the forage trees Acacia boliviana, Calliandra calothyrsus and Leucaena leucocephala

Four groups of three Holstein–Friesian cows were supplemented with 1.5 kg of air-dried tree fodder of Acacia boliviana, Calliandra calothyrsus or Leucaena leucocephala, or 1.5 kg Rhodes grass hay as a control, mixed with 5 g of a commercial polyethylene glycol (PEG)-containing digestive modifier (Browse Plus). Cows on all treatments were fed a basal diet of maize silage, cottonseed cake and crushed maize grain, and had ad lib access to Rhodes grass hay from noon. A 2-week adaptation period was followed by a 2-week response period. Refusals of C. calothyrsus and grass hay were initially 12% and 32%, respectively, but their intake improved with time, and at the start of the response period practically all of the 1.5 kg was consumed for all the fodders. The highest milk yield of 13.19 kg day−1 was produced by cows receiving L. leucocephala (p < 0.001). Cows receiving A. boliviana produced 11.94 kg day−1, 0.58 kg day−1 more than with the grass hay control diet, but C. calothyrsus had no beneficial effect. Although L. leucocephala was judged not to be superior to the other tree fodders nutritionally with respect to protein and fibre content, its in vitro organic matter degradability (OMD) was higher, as was its 96 h gas production volume (p < 0.001). Despite being fed with PEG, it was concluded that anti-nutritional factors were operative with A. boliviana and C. calothyrsus. Amongst the tree forages, L. leucocephala had the lowest, and C. calothyrsus the highest, content of soluble polyphenolics and fibre-bound proanthocyanidins (PAs) (p < 0.001), though the former was still substantial in L. leucocephala, with the reverse occurring for OMD (p < 0.01). Soluble PA content and protein precipitating capacity were highest in A. boliviana (p < 0.001). There were strong negative relationships for both OMD and milk yield with tree fodder soluble phenolic and fibre-bound PA contents (r-values: OMD −0.88** and −0.96***, milk yield −0.96*** and −0.99***, respectively). The potential for use of C. calothyrsus conserved as hay is very limited, for A. boliviana only moderate, while for L. leucocephala it is apparently good.