SUMMARYPhosphorus requirements for maintenance and growth were assessed by giving to growing lambs and non-pregnant ewes diets low in P and to growing lambs a diet containing the quantity of P recommended by the Agricultural Research Council (1980).Seven 14-week-old lambs were given ad libitum a pelleted diet containing 1·88 (LP) or 2·75 (NP) g P/kg D. M. for 13 weeks. There was no effect of P intake on feed intake or growth during the first 8 weeks when the P intake of the LP groups was 1·07 of Agricultural Research Council (1980) requirements. During the last 5 weeks the P intake of the LP group was only 0·87 of Agricultural Research Council (1980) requirements and growth and feed intake were higher in the male but not female lambs in the NP group. From the 3rd week the plasma concentration of P was significantly lower (P <0·001) in the LP group. Mineralization of selected bones was less in the LP group.After 14 weeks on the diet, balance trials with 32 P were carried out on the lambs from each dietary group. P intakes ranged from 1 to 3 g/day. An additional balance trial was undertaken with eight 2-year-old female sheep consuming a hay diet (1·5 g P/day).The endogenous faecal excretion of P by the growing lambs on the LP diet and ewes was 12·2 ± 0·8 and 12·7 ± 1·00 mg/kg live weight/day respectively, very close to the value (12 mg/kg live weight/day) adopted by the Agricultural Research Council (1980). The absorbability of the P in the concentrate and hay diets was 0.71 ±0·267 and 0·74 ± 0·0218 respectively, the former agreeing with and the latter higher than the corresponding value for Agricultural Research Council (1980).
SUMMARYIn Expt 1 the efficiency of absorption of phosphorus in feedingstuffs was compared within four sets of 18-month-old, chimaera-derived triplets; 12 feedingstuffs were evaluated in four balance trials with 32P. Seven diets consisted of a P-rich ingredient mixed with a low-P basic diet and five of hay or pelleted dried grass or lucerne. The P ingredients tested were the protein-rich meals, rape, soya-bean, maize gluten, fishmeal and rice bran, and the cereals, barley and wheat.Sets of triplets absorbed dietary P with different (P < 0·001) efficiencies; the mean values were 0·72, 0·63, 0·76 and 0·79. The availability of P differed (P < 0·001) between diets, highest values being seen with the fishmeal (0·80), barley (0·78) and wheat diets (0·78) and the lowest with rice bran (0·63) and a perennial ryegrass hay (0·64). There was no evidence for an age effect on efficiency of absorption.Endogenous faecal excretion was positively related to intake (P < 0·001) and negatively related to efficiency of absorption of dietary P. Plasma concentration was positively related (P < 0·001) to both intake and, between sets, to the efficiency of absorption.Significant urinary excretion of P generally occurred when the efficiency of absorption was greater than 0·70. Two members of a set which absorbed P with high efficiency and excreted low volumes of urine died from urethral obstruction caused by calculi.In Expt 2 an estimate of the variation in the concentration of P in plasma of 48 ewes on a barley-based diet was assessed and the values for three of the chimaera sets fell within the top quartile.Safety factors were calculated from the animal and plant variations in the efficiency of absorption of dietary P and used to determine dietary allowances for different classes of sheep.
Balance trials were carried out in which different amounts of Mg (0-44-2-9 g/day) were infused alternatively into the rumen and into the omasum, abomasum or duodenum of sheep consuming a low Mg diet (0-2 g Mg/kg D.M.). Absorption from the region between the infusion sites was measured from the change in urinary excretion and apparent absorption caused by changing the site of infusion.Absorption was greater from a ruminal than from a comparable duodenal infusion. There was evidence, however, that the absorption mechanism within the stomach area was becoming saturated at the higher infusion rates in that the relationship between the amount absorbed and infused was curvilinear. The proportion of infused Mg which was absorbed from the stomach area fell from 0-61 to 0-14 as the infusion rate increased from 0-44 to 2-80 g/day.The main site of absorption within the stomach area was the rumen; a small amount was absorbed from the omasum, but none from the abomasum. Positive differences between omasal and duodenal infusions were seen in plasma concentration at the two lowest and in urinary excretion at all infusion rates.Increasing the amount of Mg infused into the duodenum caused an increase in plasma concentration and a linear increase in absorption.When the ruminal and duodenal infusions were repeated with the sheep consuming hay, the results were similar but the proportion of infused Mg absorbed was reduced.
Feeding and balance trials with 32 P were carried out to measure the true absorption of P in battery and broiler waste and to assess the risk of urolithiasis in sheep.Groups of six, 8-week-old Scottish Blackface lambs were given one of eight experimental diets containing barley and either 15, 30, 45 or 60 % of dried broiler or battery waste. After about 12 weeks on the diet, balance trials with 32 P were conducted on a sample of the female lambs from each dietary group. The phosphorus intakes ranged from 4-6 to 15-9g/day.Poultry waste was a good source of P. The proportion of dietary P absorbed by the lambs (A) ranged from 0-49 to 0-90 and was inversely related to the dietary intake of P (I). The relationship was A = 0-893 -0-02191. All lambs were in positive P balance (0-24-2-81 g/day), but only the bones from the lambs consuming the diets containing 45 and 60 % broiler waste were not osteoporotic.All lambs absorbed more P than they retained and the partition of the excess between urine and faeces were very variable.No clinical cases of urolithiasis were seen, but uroliths were found at post-mortem. The incidence was highest in lambs consuming broiler waste and in lambs consuming the diets containing 15% poultry waste. INTRODUCTIONMATERIALS AND METHODS
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