Strain effect on relative reproductive fitness of layer chickens in the tropics

The study investigated fitness in two layer-chicken strains reared in the Tropics. Twenty batches of Bovan Nera (BN) and Isa Brown (IB) parent-stock hens consisting of an average of 3254 hens and 400 cockerels per batch, reared on the deep-litter system, were evaluated for ten primary traits and eleven fitness traits in a completely randomized design. IB contributed more hatch-able eggs to progeny generation (HDP = 75.00 v 71.00, %, P < 0.0001) with higher reproductive cycle success (3.47 v 3.15, P < 0.0001) than BN. Bovan Nera contributed higher day-old cockerel chicks than IB (43.44 vs 41.60, %). Cockerel day-old chicks on fertile eggs (CDF) were highly correlated with hatchability of fertile eggs (HFE) and survivability of day-old chicks on fertile eggs (SDF) (rP = 0.52 - 0.97, P < 0.0001) in both strains. IB hens revealed a stronger relationship between hen-day egg production, hatchability of eggs set and viability of day-old chicks hatched with overall fitness (HDP, b = 1.0 vs 4.0; HES, d = 1.0 vs 1.5; VDC, e = 1 vs 1.5, units) than BN. In chicks, the BN strain reported similar coefficients for hatchability of fertile eggs set (HES, c = 1.00 v 1.10), while the IB strain demonstrated better coefficients of fertility of eggs set and viability of day-old chicks hatched (FES, b = -1.3 v 1.0; VDF, d = 1.0 vs 1.7, units) with overall fitness. Reproductive cycle success (RCS) was 3.2 and 3.5 for strains respectively. Isa Brown hens were superior to Bovan Nera hens in hen-day production, fecundity and reproductive cycle success, while Bovan nera was fitter than Isa brown in percent day-old cockerel chicks on fertile eggs and day-old chicks' fitness.