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Untersuchungen zum Phosphor-Haushalt von Mastbullen bei Variation des Rohfasergehaltes in der Ration und Einsatz von Calciumchlorid

This
 investigation was carried out against the background of urolithiasis,
 one of the disorders frequently seen in intensive cattle fattening which is often
 caused by struvite concrements (magnesium ammonium phosphate hexahydrate), thought to be associated with a high renal
 phosphorus excretion and an alkaline urine pH. Aim of this study in fattening
 bulls was on the one hand the investigation of possible influences of feeding
 intensity on the P metabolism especially renal P excretion. On the other hand the effect of
 coated calcium chloride – which is an established agent against
 struvite in other species – was also investigated in fattening bulls.
 Five standard
 balance trials were conducted with three fattening bulls (A, B, C; beef
 cattle cross-bred, 270 ± 25 kg body weight at the beginning of trial, 386 ±
 31 kg at the end of trial). Rations were based on maize silage and soybean
 meal, supplemented with minerals and vitamins according to the animals’
 requirement. Crude fibre content varied between 14.8 % and 24.0 % of DM due
 to varying proportions of hay and barley; in two balances coated calcium
 chloride was used (75g/animal and day). In five consecutive balance trials
 (each with ten days adaptation and ten days collection of faeces and urine,
 then blood and saliva samples on the 21st day) influences on the
 macro mineral metabolism (apparent digestibility, faecal and renal excretion,
 retention, concentration in serum and saliva) were investigated, as well as
 on the acid-base-balance (pH-value in urine, faeces and blood, net acid base
 excretion (NSBA) with the urine). Phosphorus was analysed colorimetrically,
 calcium and magnesium by atomic absorption spectrometry, sodium and potassium
 by flame photometry and chloride by coulometric
 measurement mass analysis.
 The most
 interesting findings of this study can be summarised as follows:
 1.      Crude fibre content in the ration
 had no significant effect either on P concentration in urine or on absolute
 renal P excretion (g P/animal and day). In animal A only the ration with the
 highest crude fibre content (24 % of DM) caused a reduction in P excretion in
 urine (–48 %), the other animals showed the highest renal P excretion
 (B: + 22 %, C: + 107 %) under these feeding conditions.
 2.      Variations in renal P excretion
 between the three individuals exceeded differences caused by feeding strategy
 (crude fibre, calcium chloride) significantly. Bull A, which had always
 highest apparent digestibilities of phosphorus
 (47.5 – 57.1 %) and higher P concentrations in serum (2.43 –
 2.98 mmol/l), excreted 7 – 20 % of the
 ingested P in urine, the other bulls (apparent digestibilities
 of P: 30.6 – 45.5 %, P concentration in serum: 2.18 –
 2.60 mmol/l) less than 4 % at all times. P
 retention and P concentration in saliva were not influenced by the individual
 differences mentioned above.
 3.      Addition of calcium chloride
 resulted in a reduction of renal P excretion, however on individually
 different levels (A: –38 %, B: –43 %, C: –69 %). Calcium
 retention and faecal calcium excretion were elevated due to the forced
 calcium intake. Furthermore the calcium chloride supply modified the NSBA
 towards the negative range, blood pH-value was reduced and pH of the urine
 was lowered significantly from > 8 to < 6.5. The most significant
 acidification was measured in animal A’s urine. Results of
 this study show that variation in crude fibre content in rations –
 which might be practised under conventional feeding conditions in fattening
 bulls – does not effect the amount of
 renal P excretion significantly. Instead individual influence is of
 outstanding importance and indicates genetically based differences in P
 metabolism, well known and demonstrated in sheep, but of marginal advertence
 in cattle and without any attention paid to the genesis of struvite
 concrements. Presumably only those animals are disposed to struvite formation
 which absorb high amounts of P and excrete the P surplus via urine.
 The use of calcium chloride might be a useful dietetic measure in affected
 animals to avoid the formation of concrements and possibly dissolve them
 through the acidification of the urine. This would also result in an improved
 Ca/P ratio. The chosen dosage (75 g/animal and day, equals 20 g/100
 kg bodyweight) was adequate for the acidification of the urine and poses no
 threat to the animals’ health.