The effects of strain, age and sex of birds on the determined metabolisable energy of maize and fishmeal

The apparent metabolisable energy values for feedstuffs are not always constant, and may vary even when feedstuffs is fed to birds of the same type. Digestibility and utilisation of the nutrients in feed ingredients may also be dependent on the strain, age and sex of birds. These differences may be attributable to variations in the endogenous energy losses relative to the excreta energy of feed origin.

The age effect in the excretion of uric acid, ammonia and total nitrogen increases with age. The amount of FmE + UeE per unit body weight and size decreases with age, which would have the effect of increasing AME value. Knowing the degree of variability between two ages in the digestibility of a diet may help in isolating those dietary components that are more difficult to digest for the younger than the older chick. In the present study, metabolsable energy was determined using chromic oxide (Cr₂O₃) as an indicator. The objective of this study was to determine the effects of strain, age and sex on the AME and AMEn values for maize and fishmeal.

The chickens used in this experiment were 96 males and 96 females of two strains (Cornish and Rhode Island Red). All the one-d-old chicks were individually weighed and allotted to cages. The chickens were kept in rearing cages with wire floors (two chicks per cage). The environmental temperature was gradually lowered from 32°C at one day of age to 18°C at 6 weeks. All the chicks were fed on the same starter diet (AMEn 13·23 kJ/g and CP 230 g/kg) and the same finisher diet (AMEn 12·90 kJ/g and CP 194 g/kg). During the experimental period, fresh water and feed were constantly available. Weight changes and feed consumption data for the trial periods were recorded. The experimental diet was fed for a 4-d adaptation period followed by a 3-d collection period in which feed intake was recorded. The quantities of feed in the troughs were kept to a minimum to avoid wastage.

The effect of strain (meat and layer types) and sex on the apparent metabolizable energy (AME) and nitrogen–corrected AME (AMEn) of the maize (400 and 800 g/kg) and fishmeal (40 and 80 g/kg) are shown in Tables 1–3. The AME and AMEn values obtained for the maize and fishmeal ingredients were not significantly different between sexes of both strains (P > 0.05). These data are in agreement with those of Chwalibog et al. (1978) and Yaghobfar (2001). They found no differences among AME and AMEn values determined for male and female birds.

The result of the experiment indicated that the AME and AMEn values obtained for the meat type birds at 4 weeks of age were 12·93±1·42 and 12·38±1·40 (kJ/g), and at 8 weeks 13·55±0·33 and 12·93±0·37 (kJ/g). For layer types, the corresponding values were 13·51±1·05 and 11·97±1·50 kJ/g at 4 weeks and 13·26±0·92 and 12·72±0·96 kJ/g at 8 weeks respectively. There were no differences between the two strains. Washburn (1975) and Yaghobfar (2001) also found no differences between meat (Cornish) and layer (Rhode Island Red) type hens. However AME and AMEn values at 4 weeks of age were generally lower than AME and AMEn values at 8 weeks of age. There was no significant effect of age on AME and AMEn values for maize, while for fishmeal there was a significant (P < 0.0.5) effects of age on AME values. Thus, the AMEn values for fishmeal was not significantly different than those obtained at 4 and 8 weeks of age. It is interesting to note that the values for males were lower than females. The factorial analysis of variance indicated that there were a significant (P < 0.05) strain _* age _* feedstuffs (maize and fishmeal) interactions in AME and AMEn values.

It is generally accepted that nitrogen balance in birds is influenced by feed composition. As the data show, nitrogen balance was significantly (P < 0.05) different in the two strains and sexes between the ages. Nitrogen balance was significantly (P < 0.05) different between the two sexes of the Cornish, but this situation was not the same for the Rhode Island Red.