Cumulative protein intake of pig genotypes, selected for high or low growth when fed diets differing in protein content

BSAS Annual Meeting, Scarborough 1999, paper no. 25

N.D. Cameron, C.C. McCorquodale, S. Welham and R. Thompson

IACR - Rothamsted, Harpenden, Hertfordshire, AL5 2JQ, England

In the study, three genotypes were tested on four isoenergetic dietary regimes to determine if a genotype with diet interaction existed for the pattern of cumulative protein intake and total protein intake. There were 150 Large White pigs from the lean, control and fat lines, with divergent selection for lean growth rate over seven generations. In each line, there were 10 full-sib groups and within each full-sib group, one pig was allocated to each of the high (H : 220 g crude protein (CP)/kg) or low (L : 120 g CP/kg) protein diets, a standard test diet (S : 195 g CP/kg) and the two remaining pigs were tested using the diet-choice procedure (DC), using the H and L diets. Pigs were performance tested from 30 to 85 kg, with individual penning.

Food intake was measured weekly and the number of measures per animal ranged from 9 to 16. Linear, quadratic and cubic orthogonal terms for the time on test were included in the model, with separate regression coefficients fitted for each genotype-diet subclass. Litter, animal and animal x regression coefficient(s) were fitted as random effects. Covariances between the animal effect and animal-regression coefficient(s) were incorporated in the model. Data was analysed using the AIREML algorithm.

When cumulative protein intake was regressed on week of test, the linear regression coefficient for each dietary regime (Table 1, s.e.d. 0.18) and the quadratic coefficient (0.11, 0.08, 0.05 and 0.04 kg²/week, s.e.d. 0.018) increased as the protein content of the diet increased. There were no between-genotype differences in the linear or quadratic regression coefficients, within each dietary regime, except for a significantly higher quadratic coefficient of the lean line tested on a standard test diet (0.13 v. 0.06, s.e.d. 0.03). In general, the shape of the cumulative protein intake curves were not significantly different for the three genotypes, when tested on each dietary regime.

The animal-linear regression coefficient was highly correlated with the animal effect (0.86) and the animal-quadratic coefficient (0.76), such that knowledge of the animal-linear regression coefficient simultaneously provides information on both the animal’s merit for protein intake and the shape of the cumulative protein intake curve.

Total protein intake of animals fed high protein and standard test diets were similar (28.6 and 27.3 kg, s.e.d. 1.1) and likewise for animals tested on the diet-choice and low-protein diets (21.2 and 19.5 kg). The only significant between-genotype differences in total protein intake were the 4.5 kg higher intake of the fat line relative to the lean and control lines, with testing on high protein or standard test diets.

For diet-choice animals, the effective dietary protein content (EDPC) was determined from the combination of H and L food consumed. The mean EDPC of the lean and control lines were significantly higher than the fat line (151 and 156 v. 133 g CP/kg, s.e.d. 5.7). The EDPC pattern with time differed between genotypes (Figure 1). The control line had a larger, although not significantly, linear-regression term than both the lean and fat lines (-3.8 v. -0.3 and -0.8, s.e.d. 1.89) and a significantly higher cubic term than the lean line (0.12 v. -0.08, s.e.d. 0.09). The quadratic- and cubic-regression terms of the fat line were essentially equal to zero (-0.02, s.e. 0.28 and -0.01, s.e. 0.06). The non-linear change in the EDPC pattern was greater for the control line than the lean line, while the EDPC of the fat line decreased linearly with time.

The lack of between-genotype differences for pattern of cumulative protein intake and the high correlations for the animal-linear regression coefficient with the animal effect and with the quadratic term indicate that only measurement of total protein intake on test is required when assessing animals for protein intake. The consistent increase in the linear regression term for cumulative protein intake with increasing dietary protein content demonstrated that animals were not attempting to achieve a constant daily protein intake. The higher effective dietary protein content of the lean line relative to the fat line was consistent with the higher rate of lean tissue deposition, but an explanation for the difference between the lean and control lines during the early test period is required.

Return to Publications

Return to Results Page

Return to Home Page