The interaction between proteins and tannins in ruminant and poultry feeds and effects on metabolism and growth were evaluated using both in vitro and in vivo methods.
Two in vitro studies were carried out to investigate the ability of particular proteins and polyethylene glycol (PEG, MW 4000) to potentially bind various types of tannins. The aim of the first study was to establish an assay technique for protein-tannin interaction in protein meals. Protein meals (fish, feather, meat and soy bean meal) and two pure proteins (bovine serum albumin and gelatine) were used as protein sources, and tannins extracted from the leaves of three plant species (Quebracho, Leucaena leucocephala and Leucaena pallida) were selected as tannin sources. Gelatine bound more tannin from Leucaena pallida than from
Quebracho and Leucaena leucocephala while fish meal was more soluble and more likely to bind to pallida tannins than any other protein source used. The second in vitro study aimed to investigate the effects of polyethylene glycol (PEG) on the digestibility of tannin containing forages. PEG improved digestibility of dry matter(DM), nitrogen (N) and the rate of ammonia-N production of all forages studied.
Subsequent in vivo studies evaluated the ability of proteins to ameliorate the deleterious effects of Quebracho tannin in broiler chickens and the effect of tannins from Leucaena pallida in wether sheep. The chicken trial showed that gelatine totally removed the negative effects of Quebracho tannin when included at the rate of 5% of the total diet DM. Fish meal moderately improved chicken performance and more effectively than either feather meal or soy-meat meal. In
chapter 6, sheep given Leucaena pallida leaves responded positively to fish meal supplementation but not to feather meal supplements. A similar response was found when PEG was included in the Leucaena pallida diet. Interestingly, PEG given to sheep consuming fish meal did not result in an improvement in N balance whereas PEG supplementation of sheep given feather meal resulted in a substantial improvement on N balance. It was concluded that fish meal has the ability to potentially ameliorate the anti-nutritional effects of tannin, while feather meal was not an effective ameliorant of tannin action.
A further experiment (chapter 7) was conducted with broiler chickens to investigate the effects of tannin (1%> in DM) type (from Leucaena pallida or Leucaena leucocephala) and ameliorant type (different proteins and PEG) on growth, bird health and feed conversion efficiency.
Surprisingly, chickens given the high astringency tannin (Leucaena pallida) performed better than those given the low astringency tannin source (Leucaena leucocephala), suggesting that factors other than tannin type may be affecting the metabolism of chickens in this study. Soybean meal and sunflower meal were the most effective protein sources, while chickens given fish meal performed poorly (depressed DM intakes and liveweight gains (LWG))when compared with all other treatments. The inclusion of PEG at the rate of 2% in dietary DM consistently improved intake, digestibility and the overall performance of chickens given both sources of tannins.
The last series of experiments was conducted to evaluated the effect of PEG supplementation on the steers grazing on Leucaena pallida, KX2 or Leucaena leucocephala cv Tarramba mixed with Bracharia decumbens. Steers consumed
62 g PEG/head/d and gained, on average, 543 g/dover the whole period off the trial. There was no significant effect of Leucaena type or PEG supplementation on either estimated daily DM intakes, DM and N digestibilities or on LWG of steers in the different treatments. However PEG supplements significantly (P<0.05) increased ruminal ammonia concentrations and increased the proportion of Leucaena leaf selected in their diet.
It was concluded that pure proteins, such as serum albumin and gelatine, and protein meals (fish meal, feather meal, meat meal, soybean meal) ameliorated the deleterious effects of tannins from a variety of sources in both monogastric and ruminant animals, the extent of amelioration depending on the sources and level of tannins in the diet and the types of proteins used. However, PEG was far superior to all protein sources as an ameliorant of tannin action, and is probably still the most effective way to overcome the deleterious
effects of tannins in animals consuming high tannin diets or forages.