ANIMAL MODELS FOR THE STUDY OF LEISHMANIASIS IMMUNOLOGY

Leishmaniasis remains a major public health problem worldwide and is classified as Category I by the TDR/WHO, mainly due to the absence of control. Many experimental models like rodents, dogs and monkeys have been developed, each with specific features, in order to characterize the immune response to Leishmania species, but none reproduces the pathology observed in human disease. Conflicting data may arise in part because different parasite strains or species are being examined, different tissue targets (mice footpad, ear, or base of tail) are being infected, and different numbers (“low” 1×102 and “high” 1×106) of metacyclic promastigotes have been inoculated. Recently, new approaches have been proposed to provide more meaningful data regarding the host response and pathogenesis that parallels human disease. The use of sand fly saliva and low numbers of parasites in experimental infections has led to mimic natural transmission and find new molecules and immune mechanisms which should be considered when designing vaccines and control strategies. Moreover, the use of wild rodents as experimental models has been proposed as a good alternative for studying the host-pathogen relationships and for testing candidate vaccines. To date, using natural reservoirs to study Leishmania infection has been challenging because immunologic reagents for use in wild rodents are lacking. This review discusses the principal immunological findings against Leishmania infection in different animal models highlighting the importance of using experimental conditions similar to natural transmission and reservoir species as experimental models to study the immunopathology of the disease

Influence of feeding enzymatically hydrolysed yeast cell wall + yeast culture on growth performance of calf-fed Holstein steers

One hundred and sixty-eight crossbred steers (133 ± 7 kg) were used in a 336-d experiment to evaluate the effects of enzymatically hydrolysed yeast cell wall plus yeast culture (EHY) supplementation on growth performance and carcass characteristics. Treatments consisted of steam-flaked corn-based diet supplemented with 0, 195, 390 or 585 mg/kg EHY. Supplemental EHY enhanced overall (336-d) dry matter intake (DMI, P  .20), except for a slight lowering (0.7%, P = .04) in carcass yield. We conclude that throughout the growing-finishing period, supplemental EHY will enhance ADG, resulting in marked increases in final carcass weight. This effect is due to consistent increases in DMI, as supplementation did not affect gain efficiency or estimated dietary NE

Relación entre las concentraciones de IGF-1 y GH en plasma sanguíneo y el crecimiento de novillos Holstein

Insulin-like growth factor-1 (IGF-1) and growth hormone (GH) have been studied as indicators of growth potential in beef cattle, but these relationships had not been studied previously in Holstein steers. In this case 12 calves weaned at a mean age of 45 d and body weight (BW) of 54.6 kg were used to obtain, every 28 d during a 336-day experiment, BW data and blood samples. Ten blood samples collected at 30-minute intervals, from 0800 to 1300 h were mixed together and analyzed for concentration of IGF-1 and GH by radio-immuno assay. Linear regression and correlation analyses were performed to determine the relationship between average daily gain (ADG) and BW, and plasma IGF-1 and GH concentrations. The correlations between plasma IGF-1 and ADG or BW were consistently positive (0.47 and 0.48), but those between GH and ADG or BW were negative (-0.31 and - 0.37, respectively). Plasma concentration of IGF-1 explained 24% of the variation in ADG, but GH explained only about 10%. Concentration of IGF-1 showed a strong relationship with BW (R2 = 0.41) throughout a 336-day period of growth. These data indicate that plasma IGF-1 may be useful for predicting performance of Holstein steers.El factor de crecimiento ligado a la insulina (IGF-1) y la hormona de crecimiento (GH) se han estudiado como indicadores del potencial de crecimiento en bovinos de raza para carne, pero la relación entre éstos con el crecimiento y el desarrollo de novillos Holstein no se había estudiado previamente. En el presente trabajo 12 becerros de edad y peso corporal (BW) promedio de 45 d y 54.6 kg se usaron para obtener BW y muestras de sangre cada 28 d durante un experimento de 336 d. Se colectaron 10 muestras en intervalos de 30 min a partir de 0800 hasta 1300 h en cada fecha del muestreo. Las muestras del mismo día y animal se mezclaron y se analizaron para concentraciones de IGF-1 por la técnica de Radio Inmune Ensayo (RIA). Para determinar la relación de ganancia diaria promedio (ADG) y BW con las concentraciones plasmáticas de IGF-1 y GH (Conc. IGF-1 y Conc. GH), se aplicó análisis de regresión lineal y correlación simple. Las correlaciones entre Conc. IGF-1 y ADG o BW fueron consistentemente positivas (0.47 y 0.48), pero las de Conc. GH con ADG y BW fueron negativas (-0.31 y -0.37, respectivamente). La Conc. IGF-1 explicó 24% de la variación en ADG; en contraste, la Conc. GH explicó solamente cerca de 10%. La Conc. IGF-1 mostró una fuerte relación con BW (R2 = 0.41) durante los 356 d de crecimiento. Estos datos indican que aquella puede ser un predictor útil del potencial de crecimiento en novillos Holstein

Influence of supplemental tocopherol level (0, 250 and 500 IU RRR-α-tocopherol/d/steer) and injectable retinol form (retinyl propionate vs retinyl palmitate) on growth performance, carcass characteristics and plasma concentration in calf-fed Holstein steers

The influence of supplemental tocopherol level (0, 250 and 500 IU RRR-α-tocopherol/d/steer) and injectable retinol form (retinyl propionate vs retinyl palmitate) on growth performance, carcass characteristics and plasma tocopherol and retinol concentrations were evaluated in 108 Holstein steers fed a steam flaked corn-based finishing diet during 314-d feeding period. There were no treatment interactions (P > 0.10). During the initial 112-d period, dietary supplemental tocopherol tended to increase ADG (linear, P = 0.07) and DMI (linear, P = 0.06). Overall 314-d ADG, DMI, gain efficiency and carcass characteristics were not affected (P > 0.10) by dietary supplemental tocopherol. Overall DMI tended to be greater (3%, P ≤ 0.10) for steers injected with retinyl palmitate vs retinyl propionate. It is concluded that vitamin E supplementation above basal requirements may enhance growth performance during the initial 112-d phase. However, the overall effect on growth performance and carcass characteristics was not appreciable. Injectable retinol ester form did not affect overall ADG, gain efficiency, or dietary NE. Based on plasma retinol concentrations, the bioavailability of retinyl palmitate is greater than that of retinyl propionate

Influence of mixing supplements (dry or liquid) with monensin or soluble protein on the feeding value of finishing diets for feedlot cattle

The influence of supplement form (dry vs. liquid) on the feeding value of diets for feedlot cattle was evaluated. Treatments were: (1) dry supplement (DS); (2) liquid supplement (LS, all supplemental macro- and micro-minerals, salt, monensin and urea provided as a uniform blend with cane molasses; (3) LS minus monensin, that was provided in a 3% premix with dried distillers grains plus solubles before combination into a complete mixed diet (LS-MON) and (4) LS, except that condensed molasses solubles replaced 41% (DM basis) of the cane molasses solids (LSUF). In a 112-day trial involving 160 Holstein steers (473 ± 32 kg) cattle fed DS, LS, LS-MON and LSUF diets had similar (P > .10) ADG, DMI, feed efficiency and estimated dietary NE. The effects on characteristics of digestion were evaluate using four Holstein steers with cannulas in rumen and proximal duodenum. There were no treatment effects (P > .10) on ruminal digestion of OM, and feed N, microbial efficiency and ruminal N efficiency. It is concluded that the form of incorporation of minor dietary ingredients during batch mixing (dry premix or in combination with a liquid carrier) will not appreciably affect the feeding value of growing-finishing diets for feedlot cattle