Ileal digestibility of amino acids in novel organic protein feedstuffs for pigs: Mussel meal(Mytilus edulis)

Summary

Abstract
The objective of this study was to determine the apparent total tract digestibility (ATTD) of nu-trients and the standardised ileal digestibility (SID) of amino acids in organically produced mus-sel (Mytilus edulis) meal in growing piglets. The use of mussel meal in pig feeding is not allowed for the time being, but feed legislation in the EU concerning the use of mussel meal for pigs is in progress.
The experiment was carried out with a total of 24 growing pigs, 13 gilts and 11 barrows, with the initial body weight of ca. 19 kg. The pigs were distributed in experimental groups from litters of Finnish Landrace or Finnish Yorkshire x Finnish Landrace sows inseminated with mixed semen from Duroc and Norwegian Landrace crossbred boars. Piglets were first fed in the farrowing pen with organic feed for piglets (period 0). The diet was changed to another organic diet when pig-lets were moved to the fattening unit (2piglets/pen) (period 1). Diets were switched to starch based diets for the determination of the SID of amino acids. There were two dietary treatments: 1) low-protein diet to determine the basal endogenous losses of amino acids, 2) diet in which only protein source was mussel meal, 30% (of diet DM). There were 10 piglets in group 1 and 14 piglets in group 2. Experimental design needed to be changed due to diarrhoea in piglets of the mussel meal group, and the mussel meal diet had to be diluted with a diet containing whey pro-tein concentrate (WPC). After modification of the experimental design there were 3 dietary treatments in pair feeding: 1) low-protein diet to determine the basal endogenous losses of amino acids, 2) mussel meal level 1 (12% mussel meal of diet DM) and 3) mussel meal level 2 (18% mussel meal of diet DM) and 8 pigs per treatment. 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 and the weight of empty stomach, liver and kidneys were measured.
Mussel meal contained 684 g crude protein, 105 g crude fat and 94 g ash per kg DM. There was 47.8 g of lysine, 17.0 g of methionine, 8.4 g of cystine and 29.8 g of valine per kg diet DM in mussel meal. The apparent ileal digestibility (AID) of essential amino acids was 69.9‒84.9% in diet with 12% mussel meal and 77.9‒87.2% in diet with 18% mussel meal. The variation of the AID of amino acids was clearly higher in the lower inclusion level of mussel meal compared to the higher inclusion level. The AID of the essential amino acids in mussel meal varied between 66.3‒88.5% (mussel meal level 1) and 71.8‒87.6% (mussel meal level 2). The AID of lysine and methionine was higher in diet with 18% mussel meal than in diet with 12% mussel meal.
In the present trial the basal endogenous losses of amino acids were remarkably high, and there-fore the mean values of the basal ileal endogenous losses of amino acids from three other di-gestibility trials in the ICOPP project were used for the calculation of the SID of amino acids in mussel meal. Due to high variation and several divergent values in the AID of amino acids in mussel in the lower inclusion level, the SID values for mussel meal were calculated only for the higher inclusion level. The SID of the essential amino acids in mussel meal varied between 80.9%‒92.5%. The SID values for lysine, methionine, cystine, threonine and valine were 89.7%, 89.1%, 71.3%, 80.9% and 89.7%, respectively.
Most of the piglets fed low-protein diet had severe gastric lesions in the oesophageal area which are expected to cause pain and reduce the welfare of the piglets. When mussel meal was added to the diets, 62.5 to 75.0% of the piglets had no gastric lesions or the lesions were only minor. Se-vere gastric lesions were found in approximately one third of piglets fed with mussel meal but no grade 3 lesions were found. The weight of kidneys and the weight of kidneys in relation to live weight increased when mussel meal was added to the diets.
In conclusion, results indicate that mussel meal provides highly digestible amino acids, which can improve the amino acid balance in organic feeds for piglets. The effects of mussel meal on the health of piglets need to be further explored in feeding trials. Mussel meal could diversify the protein supply for organic pig production, but the economic aspects of the production of mussel meal for pig feeding need to be explored. The fine-grained starch based feeds, especially the low-protein feed used for the determination of the basal endogenous losses of amino acids, caused gastric ulcers for the piglets. The research methods should be developed to minimize the disadvantages to animal welfare. The basal endogenous losses of amino acids in piglets also need further research.