Acid-insoluble ash is a better indigestible marker than chromic oxide to measure apparent total tract digestibility in pigs

The aim of this study was to determine the apparent total tract digestibility(ATTD)of nutrients in cottonseed meal(CSM)and soybean meal(SBM)in simple carbohydrate and more complex wheat-based diets using 2 indigestible markers and total faecal collection.Twenty-five Large White×Landrace boars(57.8 kg)were randomly allocated to either a pure wheat diet,40%CSM or SBM in either a sugar-starch-(1∶1)or wheat-based diet for 18 d.Acid-insoluble ash(AIA)and chromic oxide(Cr2O3)were included in all diets as indigestible markers.Diets were offered(1,800 g/d per pig)in 3 meals/d from d 1 to 11 and 8 meals/d from d 12 to 17.On d 9,the pigs were moved to individual metabolism cages to allow total faecal collection.On d 18,the pigs were fed hourly for 8 h.After the 8th meal,pigs were anaesthetized and digesta sampled from the terminal ileum and rectum before lethal injection.There were no differences between ATTD of nitrogen(N)determined using AIA as a marker and measured by total faecal collection.On the other hand,the ATrD of N of diets containing CSM in sugar-starch-or wheat-based diets and the pure wheat diet determined using Cr2O3 as a marker was less(-3.11%,-4.46%and-6.59%;P<O.001)than that measured by total faecal collection.The ATTD of N determined using AIA as a marker was highly correlated with that measured using total faecal collection(P<0.001;R2=0.95).Similarly,the ATTD of N determined using Cr2O3 as a marker was correlated with that measured using total faecal collection,although the correlation was not quite as strong as using AIA(P<0.001;R2=0.87).Also,the slope of the regression line and the intercept were closer to unity and zero for the relationship when the ATTD of N was determined using AIA compared to Cr2O3 as an indigestible marker.The ATTD of organic and dry matter behaved similarly.These data demonstrate that the basal diet and choice of indigestible marker can substantially influence the ATTD and that the use of AIA as an indigestible marker is more suitable than Cr2O3 in digestibility studies in pigs.

Basal diet and indigestible marker influence apparent digestibilities of nitrogen and amino acids of cottonseed meal and soybean meal in pigs

This study was to determine the apparent ileal nitrogen(N)and amino acid digestibilities of cottonseed meal(CSM)and soybean meal(SBM)in simple carbohydrate-based and more complex wheat-based diets.Twenty five Large White × Landrace boars(40.9 kg)were randomly allocated to one of 5 dietary treatments:a wheat diet,40% CSM in either a sugar:starch(1:1)or wheat-based diet,or 40% SBM in either a sugar:starch or wheat-based diet for 14 d.All diets contained vitamins,minerals,and contained acid-insoluble ash(AIA)and Cr2 O3 as indigestible markers.Rations were offered(1,800 g/pig per d)in3 meals/d on d 1-11 and 8 meals/d on d 12-13.On d 14,the pigs were fed hourly for 8 h.After the 8 th meal,pigs were anaesthetised with isoflurothane,and ileal and faecal digesta sampled from the terminal ileum and rectum before lethal injection of barbiturate.Apparent ileal digestibility(AID)of N was greater(12.1%)when CSM was fed in the wheat-based diet as compared to the simple carbohydrate-based diet,whereas apparent ileal N digestibility of SBM was slightly lower(-4.5%)in the wheat-based diet as compared to the sugar:starch-based diet.Apparent ileal amino acid digestibility generally respondeds similarly to N.Therefore,while there was a wide difference in apparent N and amino acid digestibilities of SBM and CSM when they were fed in the sugar:starch-based diets,these differences were less apparent when they were fed the wheat-based diet.There was an apparent net release of N into the hindgut of pigs fed CSM in both base diets.Conversely,there was quite substantial apparent digestion of N in the hindgut of pigs fed SBM in both base diets.The use of Cr2 O3 as an indigestible marker resulted in lower apparent ileal and faecal digestibilities than using AIA,particularly for diets containing CSM.These data demonstrate that the basal diet and choice of indigestible marker can substantially influence the estimate of apparent N digestibility,this response can differ for different protein meals.