INTRODUCTION

Last decade, zoonotic viral diseases with high mortality have emerged, among these pathogens are the paramyxoviruses, to which Newcastle disease belongs (^{Xu et al., 2013}). This continues to be of great importance in the poultry industry due to its worldwide distribution, high virulence and economic repercussions it entails. The disease transmission has been prevented by vaccination; however, this method alone has not been efficient, since application methods of the vaccine and the cold chain maintenance must be considered, as well as different strains and variants present in the field, age of application, control of wild birds and the passive immunity that this causes, with a lower reaction to the vaccines applied. In the above lies the importance of searching for alternatives to generate a more efficient protection against these viruses (^{Darrell et al., 2012}; ^{Xu et al., 2013}; ^{Dimitrov et al., 2017}).

Multiple biological activities of sulfated polysaccharides have been described, within which antiviral, anticancer, antioxidant and anticoagulant activity are mentioned. The antiviral activity of polysaccharides was first described in 1958, from that date to the present day a large number of sulfated polysaccharides have been found, either synthetic or natural; both with antiviral activity (^{Xu et al., 2013}). Among these properties, sulfated polysaccharides have shown the ability to inhibit paramyxovirus infections, improve the survival rate against Newcastle disease by almost 20 % and allow blocking infections with high viral load so that possible treatments can be established (^{Xu et al., 2013}; ^{Xu et al., 2015)}.

The aim of the present work was to evaluate the effect of marine sulfur polysaccharides, obtained from algae of the genus Ulva, as a natural alternative that allows the efficiency of bird immune system before vaccination, and that in turn favors the increase of productive parameters.

MATERIAL AND METHODS

The present work was carried out in the broiler house of the Animal Production Department of the University Center of Biological and Agricultural Sciences of the Universidad de Guadalajara. Its location is Camino Ramón Padilla Sánchez No. 2100 Nextipac, Zapopan, Jalisco, Mexico; with coordinates 20°74'59.05", North Latitude and 103°50'96.38" West Longitude, and an altitude of 1670 m a.s.l (^{INEGI, 2020}). .

600 broilers of Cobb genetic line were used, 300 males and 300 females, one day old and vaccinated against Marek's disease. Birds were distributed in 4 treatments with 6 replicates of 25 birds; 1: control treatment without vaccine (C), 2: control treatment with polysaccharides (PC), 3: treatment with vaccine without polysaccharides (V) and 4: treatment with vaccine and polysaccharides (VP). The polysaccharides used were Olmix^© brand and they were used at a dose of 45 g per 500 L of water on days 2, 3, 7, 9, 10, 19, 21, 22, 34, 36 and 37.

Birds were housed in a house distributed in 2.5 m² pens; three pens for females and three pens for males for each treatment. Freeze-dried Lukert strain gumboro vaccine was administered to four treatments at 5 and 14 days of age; skim milk powder was used as stabilizer at a dose of 2.5 g per liter of water; this was left for 60 minutes in the drinkers. The Newcastle vaccine used was La Sota strain, which was administered ophthalmically at 8, 20 and 35 days of age of the birds; the samples for counting antibodies to the same virus were taken on days 9, 21, 28, 35 and 42, at treatment V and VP. Weekly feed rejections were weighed on an OHAUS^® model T21P scale with a precision of 50 grams and the average feed consumption was obtained. Feed conversion was obtained by the ratio of feed consumed per pen to the average weight gain per pen.

To measure Newcastle antibodies, on day 9, 0.3 mL of blood was taken from the jugular vein of 6 birds of each treatment; on days 21, 28, 35 and 42, 1 mL of blood was extracted from 24 birds of each treatment; sera were obtained and hemagglutination inhibition was performed to quantify antibody titers using the technique performed by ^{González (2012)}. A completely randomized statistical design was used using the following model:

y = µ +Vi + Rj + є

Where:

y = the variable to be measured. μ = the overall mean.

Vi = the ith level of polysaccharide utilization and vaccination. Rj = the jth repetition effect.

є = standard error.

The response variables were analyzed by ANDEVA and the comparison of means was analyzed by Fisher's method, both with a significance level of 5%. The Minitab 18 Copyright 2017^® program was used to analyze the data; mortality was also analyzed using the chi-square method.

RESULTS AND DISCUSSION

CONCLUSION

The production of antibodies against Newcastle virus was shown to be higher in the groups in which the vaccine was administered; however, polysaccharides showed no effect on the response to the vaccine. Sulfated polysaccharides showed no effect on feed intake, weight gain and feed conversion.