Fasting. Effects on materanl antibodies

Infectious bronchitis in hens (BIG), caused by an avian corona virus, the virus of infectious bronchitis in hens (VBIG), is a highly infectious disease, causing huge economic losses in the poultry section, even in Brazil. The protection of newly born chicks against this agent, depends of the innate immunity and of the maternal antibodies, acquired, in a passive manner, through the yolk sac (Tizard, 2009). It was proven that maternal antibodies of isotope IgG, transferred from the grandmothers vaccinated against  BIG to their chicks, are capable of protecting chicks against the VBIG challenge, for a period of up to 4 weeks (Darbyshire & Peters, 1985), due to the fact that maternal immunoglobulines (Igs) deposited in the yolk sac, may be transferred to chicks by two ways. In the first place, during the final third of the incubation period, through the direct passage from the yolk to the blood circulation of the embryo (Kramer & Cho, 1970; Kowalczyk et al., 1985). Secondly, Igs may be acquired by means of the intestinal absorption of the chicken during their first hours of life after hatching. (Rose & Orlans, 1981; Loeken & Roth, 1983; Kaspers et al.,1996). Nevertheless, prolonged fasting may negatively interfere in the absorption of Igs, because, in order to take care of their physiologic needs, birds under a prolonged fasting period, may use the metabolization of Igs of the yolk sac in order to obtain energy (Dibner et al., 1998). This work was done with the objective of evaluating the effect of different post hatching water and food fasting periods (0, 12, 24, 48 or 72 h), regarding the profile of decay of antibodies versus VBIG, in the local (tear secretion) and systemic (serum) compartments.

Birds used in this study came from a commercial batch of Cobb 500 Slow^® grandmothers, 37 weeks old. The batch was subjected to a broad vaccination program, being, the most outstanding one for this research, that of immunization against BIG. Grandmothers were vaccinated, with a live ma5 strain of VBIG, attenuated vaccine, during days 1, 21, 42 and 70. The first dose was administered by means of an ocular administration, and the rest, by spray. Furthermore, at week 20, birds received an intramuscular inactivated vaccine, containing ma5 strains and a ma 274 variant. Finally, as of week 23ª, birds were weekly vaccinated against BIG in drinking water, with the same attenuated vaccine, previously used. Eggs, from this batch of grandmothers were incubated according to the routine procedures of the incubating commercial company. At the end of the incubation process, 360 breeders that hatched within a maximum interval of 8 h, were used for this experiment. Birds were kept in a climatic chamber and DIC distributed (totally random design) into five treatments (0, 12, 24, 48, or 72 fasting hours), with 4 replicates of 18 birds each. At the end of the fasting period used in each treatment, birds were fed ad libitum with a corn and soybean bran based diet, taking care of the nutritional demands of NRC (1994). At days 3, 5, 7, 14 and 21, serum and tear secretion samples were obtained of one bird of each experimental unit for the measurement of antibodies of isotope IgG against VBIG, by the method of Sandwich-ELISA-Concanavalina A (Bronzoni et al., 2005). The titer  of the antibodies of IgG isotope was expressed by the values of the sample test ratio: sample of a positive reference (A/P) (Bronzoni et al., 2005). Data were subjected to the variance analysis by means of the GLM procedure of the SAS^®  program (2002) and in the case of the significant difference (P<0,05), means were compared by the Tukey test at a 5% of probability.

Periods up to 72 hours of post hatch fasting, do not damage the decay of maternal antibodies of anti-VBIG in the local and systemic compartments of broiler breeders, with the expectation of a punctual alteration observed at the third day in the serum (Graphs 1 and 2), when the titer of antibodies in the serum  of these birds, measured by the A/P ratio, surpassed the titer of the birds fed at housing (Graph 1). These results indicate that post-hatching fasting, does not interfere with the amount of IgG transferred from the breeder to its chicks, suggesting that the degradation of IgGs of the yolk sac, used as a nutrient source, does not depend on the fasting period of the birds. As a matter of fact, it is considered that the total amount of IgG in the newly born chicken is that of 2 or 3 mg, while the yolk, has around 100 to 400 mg of that Ig isotope (Kowalczyk et al., 1985). According to Carlander (2002), these data indicate that most of the IgGs are used as a nutrient source during the development of the embryo.

Besides, the increase in the titer of antibodies of the fasting birds, during 72 hours, was probably due to a reduction in the plasmatic volume as a consequence of the chronic deprivation of water. Other observed alterations in the hemogram and in the biochemical evaluation of plasmatic proteins (non shown data), stress the occurrence of hemoconcentration in these birds.

Graph 1. Kinetics of the decay of IgG anti-VBIG maternal antibodies in the serum of non vaccinated broiler breeders subjected to different post hatching fasting periods.

^a,b Different letters, per age, show the statistical difference by means of Tukey test at (5%).

Graph 2. Kinetics of the decay of IgG anti-VBIG maternal antibodies, in the tear secretion of non vaccinated breeders subjected to different post hatching fasting periods.

The absorption of maternal IgGs from the yolk sac is not influenced by post hatching fasting.

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