A study of direct and correlated responses to selection for growth, feed efficiency and aspects of body composition in Japanese quail (Coturnix coturnix japonica) was conducted at the Veterinary Science Farm of the University of Queensland from March, 1999 to December 2001.
The study comprised of a selection experiment in which lines were selected for aspects of growth, feed efficiency and body composition, and contemporaneous studies were made of direct and correlated responses in these and related traits. In the final generation, measures were made of protein utilisation and reproductive performance in the lines. Birds in the base population were derived from an unselected control line of Japanese quail from a previous selection experiment. The base population of some 3000 birds generated from matings between 60 males and 180 females, were measured for aspects of growth, feed efficiency, abdominal fatness and breast area proportion across four hatches.
Sib analysis was used to calculate base population heritability and phenotypic and genetic correlation estimates between the measured traits. Heritability estimates for 35-d body weight varied from moderate to high, those for food conversion ratio and for abdominal fat proportion varied from low to moderate, and for breast area proportion (measured by ultrasound) ranged from low to high. Genetic correlation estimates between 35-day body weight and food conversion ratio varied from medium to high positive but the corresponding phenotypic correlation was low and negative. The genetic and phenotypic correlations between 35-day weight and abdominal fat proportion were positive and medium to high, whilst both genetic and phenotypic correlation estimates between 35-day weight and breast area proportion were negative and high.
Seven lines were derived from the birds in the base population. These were: (1) line HW, selected for high 35-day weight, (2) line FE, selected for decreased food conversion ratio, (3) line HF, selected for increased abdominal fat proportion (ABFP), (4) line LF, selected for decreased ABFP, (5) line HB, selected for increased breast area proportion (BAP), (6) line LB, selected for decreased (BAP) and (7) line C was a randombred control. Sib selection was used to produce the HF and LF lines, whilst ultrasound measures were used to develop the selection criteria used in the HB and LB lines. Each generation, lines were produced from matings between 10 males and 30 females selected from approximately 300 mixed-sex progeny across three hatches.
After 4 generations of selection, the average 35-day weight of HW line birds was increased by 52 g whilst the food conversion ratio in FE line was decreased by approximately 0.49. Selection for increased or decreased abdominal fat proportion resulted in divergent, although asymmetrical response. The increase in abdominal fat proportion in the HF line was approximately 60% from the initial abdominal fat proportion whilst the decrease in the LF line was approximately 40%. Direct selection for increased or decreased breast area proportion resulted in a moderate decrease in breast area proportion in the LB line but there was essentially no response in the HB line. These lines were terminated at generation 3.
There was a small positive correlated response in FCR in the HW line and a small correlated decrease in FCR in the LF line. In keeping with expectations, FCR in the HF line increased. The HW line showed essentially no correlated response in fatness to generation 3, but there was a moderate negative response by generation 4. Selection for improved feed efficiency in the FE line resulted in a substantial decrease in abdominal fat proportion, greater than that obtained in the LF line. Significant correlated increase in breast muscle proportion was found in the HW and FE lines, whereas the HF and LF line birds showed variable and inconsistent correlated response in this trait.
In the study of protein utilisation, birds were given isoenergetic (13.0 MJ ME/kg) diets varying in protein level (120 or 240 g CP/kg). In each of three experiments, approximately 16 birds per line were given either one or other of the two diets in single cages from 17 to 30 days of age. There were significant interactions between genotype and dietary protein for most of the measured traits. This was due largely to considerable difference in response between the FE and HF lines, responses in the other lines were in most cases intermediate, although the LF line tended to respond closer to the FE line. Growth and feed efficiency in the FE line birds were severely depressed on the low protein diet whereas the HF lines birds exhibited a much reduced depression. Protein retention efficiency was significantly improved in the FE line on both diets, but there was no difference between the control and HW lines in this regard. Selection for feed efficiency would thus appear to produce birds that require high protein diets, but which also utilise the protein in those diets efficiently.
Reproductive performance was measured during the matings and hatchings each generation and in two studies designed specifically to investigate correlated response in the lines. Egg production was significantly depressed in the HW line but unaffected in the three other selected lines. There was a moderate increase in egg weight in the HF line, but a substantial increase in the HW line. Egg weight was unaffected in the FE and LF lines. There was a large negative correlated response in hatchability in the HW line, a smaller negative response in the two fat lines from generations 1 to 3, but essentially no response in the FE line. Age at sexual maturity was significantly earlier in the two fat-selected lines than in the FE and HW lines, with the C line intermediate. The results suggest that selection for feed efficiency or low fatness in quail are likely to have little deleterious effect on reproductive performance, whereas selection for increased growth rate is likely to have deleterious effects on both egg production and hatchability.
The study has provided useful information on selection of quail for aspects of growth, feed efficiency and body composition for possible use by the commercial quail industry and, whilst demonstrating the usefulness of quail as a genetic model for broiler chickens in this regard, has provided information on a number of areas where physiological response in the two species differ.