The objective of this study, published in Poultry Science by D.M. Paiva of Virginia Polytechnic Institute and State University and co-authors there and AB Vista Feed Ingredients, was to determine the influence of calcium source - highly soluble calcified seaweed (HSC) or limestone - phytase supplementation and dietary levels of calcium on bird performance and mineral digestibility (calcium and phosphorus) during a necrotic enteritis (NE) episode.

Cobb 500 male broilers were weighed and randomised into eight treatment groups (nine pens per treatment, 30 birds per pen) at day of hatch.

The 21-d trial was designed as a 2×2×2 factorial, which included two dietary levels of calcium (0.6 and 0.9 per cent), 2 calcium sources (limestone or HSC), and 2 levels of an Escherichia coli phytase (0 or 1,000 FTU/kg). One unit of phytase (FTU) is defined as the quantity of enzyme that releases 1μmol of inorganic phosphorus per minute from 0.00015mol per litre of sodium phytate at pH5.5 at 37°C.

Birds were placed on used litter from a previous flock that exhibited clinical signs of NE. Birds and feed were weighed on days 7, 14 and 21, and bodyweight gain, feed intake and feed conversion were calculated for each of these periods and cumulatively.

Mortality was recorded daily and pH of the gizzard and duodenum were measured on days 7, 14 and 21.

Ileal digesta (eight birds per pen) was collected on days 7, 14 and 21. Significance is reported at P<0.05.

Birds began exhibiting clinical signs of NE on day 9, and elevated NE-associated mortality persisted until the end of the trial. Significantly higher mortality was observed when broilers were fed diets with 0.9 per cent calcium from HSC compared with birds fed diets with 0.6 per cent calcium, regardless of calcium source.

Broilers fed 0.6 per cent calcium diets supplemented with phytase were heavier than the other treatments regardless of calcium source.

Broilers fed diets formulated with HSC had significantly higher feed conversion then broilers fed diets formulated with limestone.

The gizzard of broilers fed 0.9 per cent calcium in the diet was significantly less acidic than the gizzard of broilers fed 0.6 per cent calcium in the diet.

Broilers fed 0.6 per cent calcium in diets supplemented with phytase showed significant improvements in phosphorus and calcium digestibility.

Paiva and co-authors concluded that higher dietary calcium (0.9 per cent versus 0.6 per cent) had a negative effect on mortality associated with NE and on bird performance.

Reference

Paiva D.M., C.L. Walk and A.P. McElroy. 2013. Influence of dietary calcium level, calcium source, and phytase on bird performance and mineral digestibility during a natural necrotic enteritis episode. Poult. Sci. 92(12):3125-3133. doi: 10.3382/ps.2013-03298

January 2014