Nutritive value and digestibility of macronutrients from sheep and alpaca skin hydrolysates as a new alternative in juvenile rainbow trout (Oncorhynchus mykiss) feeding

Abstract

Background: The protein source from fish meal is very important in trout feeding, but it is expensive and very scarce. Alternative nutrient sources are required to achieve sustainability as trout production rapidly grows in Peru. The objective of this research was to determine the proximate chemical composition and the apparent digestibility coefficient (ADC) of dry matter, organic matter, crude protein, crude fat, and digestible energy of hydrolyzed sheep (HSS) and alpaca (HSA) skins in juvenile rainbow trout. Methods: A total of 450 fishes were randomly distributed in nine digestibility tanks, with 60.0 ± 1.32 g of initial weight and 6.4 kg/m3 of stocking density. The water quality parameters were as follows: pH 8.4, temperature 11.5 °C, and dissolved oxygen 6.2 mg/l. The skin hydrolysates were treated at 130 °C with 15 psi pressure for 120 min. Fish were fed a reference diet and an experimental diet containing 70% reference diet and 30% skin hydrolysate. The ingredients of the diets were mixed and then extruded at 95 °C with 4-mm diameter (Extruder Khal® EE800). The ADC was determined by the indirect method using insoluble ash as a non-digestible marker. Results: The ADC in HSS and HSA was similar for dry matter (67.7 vs 69.1%), organic matter (66.9 vs 68.2%), crude protein (70.4 vs 70.1%), and digestible energy (3.35 vs 3.24 Mcal/kg DM), but crude fat values were different (12.3 vs 48.0%; p < 0.001, respectively). Conclusion: The hydrolyzed sheep and alpaca skins had a high content of macronutrients with an acceptable apparent digestibility of nutrients, making them a viable alternative to improve the nutritive value of more economical feeds for rainbow trout feed.