The effect of concurrent cecal coccidiosis infections on severity of Histomonas meleagridis (blackhead disease) in chickens was investigated in a series of experiments. Cecal lesions from H. meleagridis were severe in all inoculated control groups and did not appear to be affected by the introduction of Eimeria tenella infection. However, the severity of liver lesions and number of birds positive for liver lesions of H. meleagridis increased significantly with the presence of E. tenella. The increase was similar when 10(3) or 10(4) oocysts of E. tenella were given and was the same when oocysts were given at the same time as H. meleagridis or 4 days prior. The liver lesions increased directly as doses of H. meleagridis increased from 7.5 x 10(3) cells to 30, 100, or 300 x 10(3) when E. tenella was given along with H. melelagridis but not when H. meleagridis was given alone. Administration of a live coccidiosis vaccine containing very low levels of E. tenella also gave a significant boost to liver lesions but at a much lower level than that observed with larger doses of E. tenella. The positive relationship between infections of cecal coccidiosis and H. meleagridis in chickens suggests that such dual exposure may contribute to increased clinical outbreaks of blackhead disease in chickens under field conditions. 相似文献
1. After 5 generations of selection on income minus food cost between 21 and 40 weeks of age (SECR), a correlated genetic improvement of 14.5% and 16.3% of the base population mean could be observed for income minus food cost between 41 and 60 weeks (IF60) in two lines of laying hens. The total responses up to 60 weeks amounted to 17.2% and 17.3% of the base population mean. A heritability of 0.30 for IF60 and a genetic correlation of 0.61 between SECR and IF60 were estimated.
2. The correlated relative genetic responses for 5 traits of the period between 41 and 60 weeks of age for the two lines were: 4.3% and 5.2% in egg number, 5.8% and 7.4% in egg weight, 8.4% and 10.8% in egg mass, ‐2.7% and ‐0.6% in body weight at 60 weeks, and ‐5.2% and ‐6.3% in food efficiency.
3. The estimated heritabilities of these 5 traits from the whole data set were 0.36, 0.75, 0.34, 0.71 and 0.17. The estimated genetic correlations between SECR and the same 5 traits were 0.30, 0.46, 0.61, ‐0.22 and ‐0.49.
4. A high genetic correlation of income minus food cost with egg weight and a low one with egg number were found in pullets, but the relationships were reversed in older hens. 相似文献
1. A pause in egg production was induced in brown‐egg laying hens, aged 68 weeks, by feeding them whole oats for 7 d. Subsequently, these hens, together with control groups, were given laying diets with either 400 or 600 mg/kg iron. The 200 mg/kg of supplemental iron was added in the form of either ferrous sulphate or iron proteinate (chelated iron).
2. The feeding of whole oats halted egg production in 5.7 ±0.22 d and the duration of the pause was 8.3 ±0.78 d.
3. The induction of a pause improved the subsequent rate of egg production, egg output, efficiency of food utilisation, albumen quality, egg specific gravity and shell colour. It also increased food intake and body weight gain but neither egg weight nor the rate of mortality were affected.
4. Neither supplementation of the diet with iron nor its source had any significant effect on laying performance, egg quality or shell colour. 相似文献
1. Fourteen by‐products of oil refining, selected for their variability in free fatty acid and unsaponifiable contents, were analysed chemically with the objective of relating the determined ME values of the products to chemical composition by means of multiple linear regression analysis. Refined sunflower oil was included as a reference fat.
2. Twenty‐one 2‐week‐old chicks were used to determine fat digestibilities and AMEn values of diets, using the total collection method. Fats were included in a wheat‐soyabean meal diet at 100 g/kg. Multiple linear regression analysis was used to express the ME values of fats as functions of the parameters measured (moisture, gross energy, impurities, unsaponifiables, non eluted material, free fatty acid content, unsaturated: saturated ratio, peroxide value, TBA test).
3. The ME of the fat products lay in the range 12.62 to 24.35 MJ/kg, and 29.26 MJ/kg for refined sunflower oil. Free fatty acid content of the fats was shown to be a poor predictor of their ME values, whereas non eluted material (NEM) of the fat products showed a good correlation with their ME. A regression equation could be derived (R2 = 0.6548; SEE = 2–0064) with the unsaturated: saturated ratio (U:S) and NEM. An ME prediction equation based on the U:S, NEM and unsaponifiable content is also proposed (R2 = 0–7168; SEE= 1.9058). 相似文献
