Examination of stability,and its effect on the nutritive value,of fish silage in diets for growing pigs

Fish silage was manufactured by the addition of formic acid (85% solution) to whole mackerel at a rate of 35 g kg⁻¹ wet weight (ww)]. During 112 days of storage, the peroxide value of the silage declined from 164.3 meq O₂ kg⁻¹ oil on Day 1 to 55.0 meq O₂ kg⁻¹ oil by Day 42 and thereafter remained stable; microbial activity persisted at 10 colonies g⁻¹ silage ww. Four diets of similar crude protein, digestible energy and mineral concentrations were formulated with 0, 50, 100 or 150 g fish silage kg⁻¹ diet dry matter (DM). The diets were given to 72 Landrace × (Landrace × Large White) pigs (boars, gilts and castrated males) from 25 kg to slaughter at 55 kg.Animals on fish silage diets grew faster than those given no fish silage owing to an improved food conversion ratio (FCR); 100 g fish silage kg⁻¹ diet DM effected best performance (daily liveweight gain, 725 g; FCR, 1.96). Carcass measurements did not vary between dietary treatments. Soft, yellow fat was observed in carcasses from pigs given 150 g silage kg⁻¹ diet DM. Growth rates were similar between sexes; boars and gilts had less backfat than castrated males.