畜牧生产中营养物质转化规律及其影响因素

本文以生长猪、鸡为对象,着重探讨了品种间对饲料能量与球白质在消化、代谢、合成过程中的效率异同;研究了某些微量元素及其有关酶对能量、蛋白质及其它物质利用的影响。

MODE AND VARIABILITY OF METABOLIC DYNAMICS IN RELATION TO SWINE AND POULTRY PRODUCTION

A grant was received from the Scientific Foundation of Academia Sinica in 1983～1987. Following is a summary of 20 research projects accomplished.A. Metabolism on growth of swine and poultry1. SwineComparisons were made between the indigenous Min Zhu and the improved Harbin White(HW)breeds, as also of 3-way crosses on feed intake, growth rate, body composition and digestion and utilization of nutrients. Min Zhu ate 10～20% less feed than improved or crossbred hogs and grew 15～20% less rapidly. Under ad libitum feeding of rations of conventional energy density, intake of digestible energy(DE) amounted to 3 times maintenance(W~(·63)), against 3.3 for crossbreds, the latter being equivalent to 85% of that stipulated by the Agricultural Research Council of England(ARC).Min Zhu exceeded the HW in digestibility of energy, crude protein and crude fiber by ca. 5～10 percentage units. Digestibility of the reciprocal cross F_1 progenies were similar to their parental mean, suggesting an intermediate inheritance. Taking the total intake of energy and crude protein as 100, digestive coefficients were 89.3 and 83.8%, metabolic rate 86.7 and 61.0, conversion rate 38.0 and 29.9% respectively. Ratio between DE and ME was 100 : 96, that between ME and NE 100 : 44. Partial efficiency of protein was 44.5 against 45% from literature average. That for fat was 81.5 against 75% from literature average. There was no difference in gross efficiency between the Min and HW.Min Zhu proved to be more resistant to hunger stress, lost less weight and less body fat during partial fasting. Following realimentation, gain of the HW contained more water(55% against 50% for the Min). No difference was disclosed in protein and fat accretion.Min Zhu had larger and heavier colon than HW of similar liveweight. This could be associated with more total volatile fatty aeids(VFA) fermented, hence more energy recovered from the hindgut.The maintenance energy requirement of Min Zhu inclined to be lower than the HW.Throughout the growing period, changes in body protein and body fat content could be estimated by the following allometrie equations.Minprotein(kg) = 0.147x~(1.004)fat(kg) = 0.038x~(1.480)HWprotein(kg) = 0.080x~(0.844)fat(kg) = 0.036x~(1.530)2. ChickenEmphasis was put on comparisons between the light(represented by White Leghorn) and the heavy (represented by the White Rock) types during the first 10 weeks of life.Feed intake of the heavy-type was 1.6～1.8 times that of the light-type, but growth rate was 1.85～2.15 times. Obviously, higher feed intake could not account for all the merit. For, even when limit-fed to equal intake, heavy- type chicks still grew 35% faster. Gross energy efficiency of the heavy-type was 10 percentage units higher than the light-type (+38.5% actual): partial efficiency surpassed by 8 percentage units(+14.9% actual).Somatic energy, protein and retention rate(Y) were linearly related to age (X in days). Empty body of the heavy-type chicks contained 10.89% more energy(kcal/g) due to more fat content. Light-type chicks required more crude protein(23～20%)than the heavy-type (20～17.7%) during the first 10 weeks of life. Light-type chicks did nor consume more feed of higher energy density, but the heavy-type inclined to eat more.Protein level of diet would not influence the body protein content but could alter its fat content.B. On the Zinc and Selenium requirements of swine and poultry1. Swinea. ZincWith growth rate as the sole criterion, 34ppm Zn would be sufficient. Taking physiological responses into consideration (serum AKP activity, serum protein level), 100ppm would be more appropriate. Listed below are current stipulations on Zn requirements:liveweight (kg) 5～10 10～20 20～50NRC (1988) 100ppm 80 60China (1985) 104 78 110b. SeleniumDiets with Se from 0.0185 to 2.5ppm fed to 8.5～25kg piglets did not affect feed intake nor growth rate. Neither deficiency nor toxic symptoms were observed. 12.5 ppm adversely affected intake and growth although still without acute symptom. There existed close linear relationship between Se intake(X) and serum Se and hair Se contents(Y);Serum Se ppm=0.5432+0.3252lgXhair Se ppm = 2.0306+ 1.2555 lgXSerum GSH-Px rose gradually on diets with 0.0185～0.1185 ppm, but dropped at higher levels showing a parabolic curve model. Parallel trials with rats revealed similar pattern only more responsive to excessive allowance with occurances of death at both lower and higher levels. The lower threshold could be set at 0.0385ppm for piglets and 0.1185 for rats.Current standards for Selenium are: liveweight (kg) 5～10 10～20 20～50NRC (1988) 0.30ppm 0.25 0.15China (1985) 0.17 0.14 0.252. Poultrya. ZincAn extended trial including the growing, rearing and laying phases on two Ca and three Zn levels was conducted for 500 days with the following results:Wide range Zn levels (29-1229ppm) and low-high Ca (0.69～v0.88—1.36～1.76%) level crisscross treatments did not affect feed intake or growth rate of layer-type chicks during growing phase (0～20 weeks). But low Zn (29ppm) delayed the development of the oviduct and thus extended sex maturity 5～15 days. Ultrahigh Zn intake promoted oviduct length and weight increase. 69ppm and up elevated serum AKP activity and serum and tibia-ash Zn contents.Addition of Zn could raise egg yolk Zn concentration without effect on egg white. High Zn level adversely affected shell thickness and weight only during the late laying period. Low Zn (29ppm) decreased egg fertility and hatchability. Serum AKP activity of progeny also were depressed. Current regulations for Zn requirements are:age (wk) 0～6 7～20 21～40 40 and upNRC (1984) 40ppm 35 40 60China (i984) 40 35 50(table) 50(table) 65(hatching) 65(hatching)b. SeleniumThree experiments were conducted on basic diets with 0.029-0.038ppm Se with additions from 0 to 250ppm. 0.029～0.038ppm could not sustain chick health with death rates of 20～100% during the first 6 weeks. Exudative diathesis and muscular dystrophy occurred decreasingly at Se levels from 0.038 to 0.088ppm reaching normality at 0.129-0.179ppm. Death reappeared at 0.539 ppm reaching 40% at 20ppm and 100% at 50ppm. Se levels either below 0.088 or above 20ppm were both unfavorable to feed intake or growth rate. Relationship between GSH-x and diet Se level could be demonstrated as linear between 0.038 and 0.388ppm and asymptotic beyond 0.388.Supplementation with methionine to low Se diet could alleviate deficiency symptom and reduce mortality. At normal Se range (0.15～0.03), methionine proved to be still effective. Up to 1.00ppm, methionine was still effective in reducing death loss. At 20ppm it was inaffective. As for relationship between dietary Se level and Se contents of several organs, there appeared two inflec- tions, one at 0.338 and another at 1.00ppm, which could be fitted to a fourth degree polynomial equation.Requirements of Se for chicks could be set at 0.13～0.33ppm, tolerent level at 1.0ppm and toxic level at 20ppm. Current standards stipulated are.age (wk) 0～6 7～20 layer broilerNRC (1984) 0.15ppm 0.10 0.10 0.15China (1984) 0.15 0.10 0.10 0.15