Supplementation of palm kernel expeller to grazing dairy farms in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
This thesis is composed of a series of studies to assess the nutritional value and characteristics of palm kernel expeller (PKE) for grazing ruminants. The chemical composition of PKE has shown high concentrations of neutral detergent fibre (NDF) (70.1±0.39 g/100g DM) and fat (9.0±0.37 g/100g DM), and a moderate content of crude protein (16.2±0.42 g/100g DM), with very low concentrations of starch and sugar (0.3%) and reasonable gross energy content (18.6±0.33MJ/kg DM). In sacco digestion kinetics of PKE and pasture showed that PKE presented lower values for the soluble fractions in dry matter (DM), crude protein (CP) (25-27% and 37-38%, respectively) than pasture (41 and 52%), and the majority of the NDF in PKE was also present in the slowly degradable fraction (58-59%). The values for mixtures of pasture plus PKE were generally intermediate to those of the two feeds alone and the rate of degradation (k) for DM and fibre fractions did not differ significantly between feeds. But the rate of degradation for CP in PKE was about three to four times lower than that in pasture (6.7-9.8%/h and 33.8-48.4%/h, respectively), and the addition of PKE with pasture reduced the rate of protein degradation for the mixture to a rate similar to that of PKE alone (around 10%/h). In vitro net ammonia (NH3) production decreased as the amount of PKE increased in the mixture with pasture, while PKE was only able to maintain a surplus of NH3 for a short period of time; in contrast volatile fatty acids (VFA) yields were increased, with butyrate percentage being higher at the expense of acetate. In the in vivo trial with lambs, daily pasture DM intake was reduced as the amount of PKE plus molasses (PKEM) was increased in both periods, but total DM intake was not increased with the addition of PKE, except when the values were converted to DM intake per kg of metabolic liveweight. Independent of the pasture quality offered, there was a linear decrease in the apparent digestibility of DM and CP with the addition of PKEM in the diet; however NDF digestibility of the diet was only decreased when PKEM was fed with good quality pasture (period 1). The apparent digestibilities of PKEM of DM, CP, and NDF for PKEM were around 63.0%, 52.0% and 68.5%, respectively, with the estimated concentration of digestible energy (DE) of PKEM being approximately 12.8 MJ /kg DM. Addition of PKEM caused a decrease in the diet’s DE concentration with high quality pasture (period 1), but an increase with low quality pasture (period 2). Faecal nitrogen (N) increased and urine N decreased when increasing
amounts of PKEM were fed in the diet, however, N retention and VFA concentrations were only increased by the addition of PKEM to the low quality pasture (period 2). The supplementation of either 3 or 6 kg of PKE to cows in late lactation grazing a restricted pasture allowance (20 kg DM/cow/day) decreased pasture intake, but overall total DM intake increased. Cows actually consumed only 2.7 and 3.6 kg PKE/cow of the 3 and 6 kg PKE offered/cow and presented substitution rates of 0.30 kg/kg and 0.54 kg/kg, respectively. Supplemented cows produced 0.86 to 0.94 kg milksolids/cow daily, respectively, while cows offered restricted pasture allowance only produced 0.76 kg milksolids/day. Supplemented cows had higher concentrations of milk fat than cows offered pasture only, and marginal returns of 42 and 53 g of milksolids/kg of PKE to cows offered 3 and 6 kg of PKE, respectively.