Digestibility of nutrients in novel organic protein feedstuffs for pigs: grass pea seeds, dehulled sainfoin seeds and soybean pulp (okara)

Summary

Abstract
The objective of this study was to determine the apparent total tract digestibility (ATTD) of nutrients and the standardised ileal digestibility (SID) of amino acids in three organically produced protein sources: grass pea seeds, dehulled sainfoin seeds and wet soybean pulp (okara) in growing pigs. The experiment was carried out with a total of 40 individually housed growing pigs (50% gilts and 50% barrows) with initial body weight of ca. 43 kg. The pigs came from litters of Finnish Landrace or Finnish Yorkshire x Finnish Landrace sows inseminated with mixed semen from Duroc x Norwegian Landrace crossbred boars. The experiment was carried out according to a randomized complete block design, where blocks were formed from five pigs of similar body weight. Within a block pigs were randomly allotted to the dietary treatments. Collection of faecal spot samples was done at the end of period 1 on days 14‒16. After that pigs were gradually switched to the starch based diets of period 2 for the determination of the SID of amino acids. The basal feed in period 1 consisted mainly of cereals, rapeseed expeller and whey protein concentrate (WPC). Of the experimental diets 10 or 20% was replaced by grass pea seeds or 20% by dehulled sainfoin seeds or okara on dry matter (DM) basis. Period 2 lasted for 7 d and the starch based basal diet was replaced by 15 or 30% of grass pea seeds, 45% of dehulled sainfoin seeds or 45% wet okara on DM basis. Titanium dioxide (3g/kg feed DM) was used as indigestible marker. The basal endogenous losses of amino acids were determined by feeding starch based low-protein diet, which contained 5% WPC. At the end of the trial, 3.5 h after the morning feeding, the pigs were stunned by bolt pistol, bled and ileal digesta was collected for digestibility determination. Stomachs were visually estimated for gastric ulcers. The weight of empty stomach, stomach contents, liver and kidneys were measured.
The crude protein content in grass pea seeds, dehulled sainfoin seeds and okara was 295, 396 and 345 g/kg DM, respectively. The content of lysine was 18.5, 20.0 and 20.7 g/kg DM, the content of threonine was 10.9, 13.2 and 13.9 g/kg DM and the content of methionine was 3.7, 7.2 and 5.9 g/kg DM, respectively. Replacing the basal organic diet with the experimental feedstuffs did not affect the ATTD of dry matter and organic matter. Okara and dehulled sainfoin seed diets had the highest crude protein digestibility, 73.5 and 72.9% (p<0.05). The crude protein digestibility in the diet with 10% grass pea seeds did not differ from that of dehulled sainfoin seed diet. Crude protein, crude fat and crude fibre digestibility for grass pea seed diets did not differ from each other or from the basal organic diet. Crude fat digestibility was the highest in okara diet, 68.2% (p<0.01).
Nutrient digestibility in the experimental feedstuffs was calculated by difference method, when the digestibility of the experimental diet differed from the digestibility of the basal organic diet. In cases of no difference in the digestibility, the digestibility value of the diet was used as the digestibility value of the feedstuff (mean value of the two inclusion levels for grass pea seeds). The crude protein digestibility in okara, dehulled sainfoin seeds and grass pea seeds was 81.5, 79.0 and 67.9%, respectively. The crude fat digestibility was the highest in okara (82.1%).
The apparent ileal digestibility (AID) of essential amino acids was the highest in okara (87‒95%) and it did not differ from the values of grass pea seeds (73‒84%). The AID of most of the essential amino acids in dehulled sainfoin seeds was clearly lower (41‒55%). The basal losses of endogenous amino acids were high in this trial, which resulted in high SID values for essential amino acids especially in okara, over 98%. The SID of essential amino acids in grass pea seeds and dehulled sainfoin seeds was 80‒95% and 53‒64%.
All pigs fed starch based low-protein diet had severe gastric ulcers. Also 38‒50% of the pigs fed starch based diets with grass pea seeds and dehulled sainfoin seeds had severe gastric ulcers. No severe gastric ulcers were detected in pigs fed okara diet.
The results indicate that the ileal digestibility of amino acids in pigs is better in grass pea seeds than in dehulled sainfoin seeds. The ileal digestibility of amino acids in okara is very high. The use of okara in feeding promotes gastric health in pigs which is important for the welfare of the animals. The experimental feedstuffs can diversify protein source supply in organic pig feeding. More research is needed to define the optimal level of grass pea seeds and dehulled sainfoin seeds in diets for pigs and also the effects of the anti-nutritional substances in these legumes need to be further explored.