THE ACTION OF VARIOUS PORTIONS OF FIBER ON THE DIGESTIBILITY OF NUTRIENTS AND RETENTION OF NITROGEN IN FEED MIXTURES FOR PIGS

The trials were aimed at the analysis of the action of various portions of fibre in feed mixtures for fattening pigs on the digestibility of organic nutrients and retention of nitrogen. Two balance trials were conducted in 9 young boars of White Meaty breed which were divided into three groups with three heads per group. At the beginning of the first trial the average live weight of animals was 40 kg, in the second trial it was 49 kg. The trial animals were placed in balance cages and they were fed moisty feed mixture two times daily (Tabs. I to IV). In the control group we used as the source of fibre wheat bran whereas in trial groups there were used buckwheat husks. The trial was divided into 7 days preparative period during which the animals were getting used to the environment and feed ration and into the main trial period with the duration of 7 days when the balance mass digestibility of organic nutrients was studied and the balance of nitrogen was determined. Urine and excrements were captured daily and the contents of nutrients were defined in average samples by means of chemical analyses. In trials up to 50 kg of live weight there was determined the significantly lower digestibility of dry-matter, nitrogen substances and N-free extract in animals of the IIIrd trial group only (P<0.05; Tab V) in comparison with the first control group. As to nitrogen balance, in the IIIrd trial group there was also investigated the significantly higher secretion of nitrogen through excrements (P<0.05) in comparison with the Ist group. In this group the lower digestibility of nitrogen in g was determined in comparison with the Ist and IInd groups. The other balance values were not statistically significant (Tab. VI). In the trials above 50 kg of live weight, the trial animals of the IIIrd group secreted significantly higher amount of nitrogen and digested lower amounts of nitrogen in g (P<0.01; Tab VIII) in their excrements. In this group the significantly lower amount of retained nitrogen in g and the portion of the utilization of received nitrogen were also determined, particularly in comparison with the Ist group (P<0.01) as well as with the IInd group (P<0.05). Like Morgan, Whittemore (1989) and Simon et al. (1987) we also found out that in the course of the increasing of fibre level the secretion of nitrogen through excrements increased, too. In accordance with the results of mentioned authors, the secretion of nitrogen through urine was decreased in the first trial too, which resulted in the more levelled balance of other values. In the second trial, however, the increase in the secretion of nitrogen through excrements was not accompanied by the decrease in the secretion of N through urine. This is the reason why both the amount of retained nitrogen in g and utilization of received nitrogen in per cent were significantly lower in the IIIrd group in comparison with the Ist and IInd ones. Chabeauti et al. (1991) ascertained that in the course of the increasing of fibre the digestibility of dry-matter, nitrogen substances and N-free extract increased, too, which was also proved in our trials. In the second trial, in comparison with the IInd groups, the IIIrd group also clearly manifested the decrease in the digestibility of fibre, mentioned by Munchov et al. (1986). The results obtained in the IInd group led us to the same conclusions like Zeman (1982) that the optimum upper limit of fibre for pigs with the live weight about 40 to 50 kg was 7 % and the for pigs above 50 kg of live weight it was 7.5 %.