ANEXO 2

The present work was based on six samples of PKE collected from only four sources over a period of only 36 months. Therefore, a larger number of samples from a wider range of sources, locations and times and places should be analysed to build a more robust and widely applicable database of PKE chemical composition, and confirm or deny the existence of a variation for this feed. These samples could also be subjected to analysis by near infrared reflectance spectroscopy (NIRS) in order to develop a reliable calibration curve that would make it possible to predict the chemical composition of PKE to be predicted quickly and cheaply.

Some of the samples should also be subjected to in saccoincubations, in order to assess their degradations and nutritive characteristics. Additionally, it has been reported in the literature that the prediction of PKE digestibility through enzymatic methods is very poor, and further research in this area should be carried out to facilitate the determination of the digestibility of PKE without the use of animals in expensive in vivo

digestibility trials.

The information presented here showed that PKE can be used as a supplement for grazing dairy cows in late lactation, but the responses were moderate but in the range of values found by other short-term experiments. Normally, carry over effects are not measured in short-term experiments, it would be interesting to evaluate the use of

PKE to supplement cows during a whole year, in which the availability of extra pasture that was saved during the supplementation period and the effects of the improved body condition would be taken into account in the final results. Also, the combination of other supplements (eg. maize silage, or barley grain) with PKE should be investigated in terms of diet balance and animal performance as farmers often feed more than one supplement to their cows, and associative effects may occur. Another interesting aspect to investigate is to evaluate the performance of grazing animals when PKE is supplemented during spring time, when the quality of pasture is good, as the results obtained here showed that lambs fed increasing amounts of PKE on a good quality pasture diet can reduce animal performance. But, it is important to note that results of grazing animals under supplementation will depend on the pasture allowance offered during the experiment, as explained above.

The effects on the environment due to the supplementation of PKE to grazing animals should also be examined in future research, as the in vivo results obtained here has shown that PKE supplementation can reduce nitrogen excretion of sheep fed high quality pasture with high protein content. Additionally, the determination of methane emissions of animals fed pasture and PKE could give useful information both for the determination of a more precise value of PKE metabolic energy and for environmental purposes, as the addition of fats and oil seeds (eg. palm kernel oil) in the diet of ruminants is one of the alternatives to reduce the emissions of methane (Beauchemin et al., 2008).

Last but not least, it would be interesting to look at the mineral balance of grazing animals supplemented with PKE, as PKE has a low ratio of calcium to phosphorus and a low sodium concentration, and therefore increasing amounts of this supplement could cause a deficiency of these two minerals in the diet. In addition, PKE has also a high copper content, which can cause chronic toxicity, primarily in sheep (Akpan et al., 2005) when fed in large quantities. However, in regions of New Zealand where the soil is deficient in copper (eg. the Northland soils; Sherrell and Rawnsley, 1982), supplementation of PKE to the diet of pasture may help to overcome this deficiency, and research about this topic may clarify availability of this mineral to the ruminant.

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