Fasting. Effects on immune response

During the last decades, infectious bronchitis in hens, (BIG), has caused enormous economic losses in the poultry industry. Its main prophylactic measure is based in the use of attenuated live vaccines, combined or not, with inactivated vaccines (Cavanagh & Naqi, 1997). In general terms, vaccination of flocks against the virus of infectious bronchitis in hens (VBIG) is performed at day one, after birth, (Mondal & Naqi, 2001) with the goal of obtaining an adequate condition of immune protection, which is normally associated to the systemic or local antibody levels. It is also known, that in the current poultry practices, birds may be subjected to long post-hatching fasting periods, which may interfere in their response to vaccination. Within this context, it was proven that birds fed with a deficient diet compromise the humoral immune response (Glick et al., 1981). Besides, prolonged fasting increases plasma levels of corticosterone, altering the count and functional activity of leukocytes, including lymphocytes T and B, which may damage immune responses in birds (Kubikova et al., 2001). On the other hand, we observed that reduced fasting periods, up to 24 hours, may favor both, the cellular immune response, as well as the humoral one (Klasing, 1988). The aim of this study was that of evaluating the effects of different fasting and water deprivation periods post-hatching (0, 12, 24, 48 or 72 h), on the humoral response to primary vaccination against the infectious bronchitis virus in hens (VBIG) in the local (lachrymal secretion) and systemic (serum) compartments.

Birds used in this study came from a commercial flock of Cobb 500 Slow^® grandmothers, 37 weeks old. They were subjected to a broad vaccination program, stressing, for the purposes of this study, immunization against BIG. Grandmothers were vaccinated with an attenuated live vaccine containing the ma5 strain of VBIG at days 1, 21, 42, 70 of age. The first dose was administered via the ocular route and the others by means of a spray. Besides, at 20 weeks of age, birds were intramuscularly vaccinated with a non activated vaccine ma5 strains and ma 274 variant. Finally, at week 23 of age, birds were vaccinated against BIG. Eggs from this grandmother's flock were incubated according to the routine procedures of the incubator of a commercial company. At the end of the incubation process, 360 breeders hatching within a maximum interval of 8 hours, were used for this experiment. Birds were kept in a climatic chamber and distributed into a DIC (totally random design) with five treatments (0, 12, 24, 48, or 72 fasting hours), with 4 replicates of 18 birds each. After housing, birds were vaccinated, via the ocular-nasal (1 /route) with a live lyophilized vaccine containing a H120 purified IBV. At the end of the fasting period applied to 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 of, one bird per experimental unit, were obtained to measure the IgG isotype antibody against VBIG, by Sandwich-ELISA method-Concanavalina A (Bronzoni et al., 2005). The titration of antibodies of isotype IgG was expressed by the value of the sample test ratio: sample of positive reference (A/P) (Bronzoni et al., 2005). Data were subjected to the variance analysis through the GLM procedure of the SAS^® program (2002) and in the case of significant difference (P<0,05), means were compared by the Tukey test at 5% of probability.

In tear secretion, fasting had an influence (p<0,05) over the mean titration of antibodies at day 5 and in the case of serum at day 14, nevertheless, serum conversion in response to the vaccine stimulus only happened in the local compartment at day 21 (Graphs 1 and 2). During the first interval, birds subjected to the 72 hours fasting presented an earlier immune humoral response and of greater magnitude than birds of other treatments, while at day 21 post vaccination, birds subjected to 48 hours fasting reached higher levels of antibodies of isotype IgG in tear secretion than those fed during housing, or after 72 hours of fasting. These results indicate that there was a positive immune modulator effect of 48 and 72 hours fasting on the immune humoral responses of the compartment of the mucosa of the superior respiratory tract and annexes, specially the ocular, nasal and tracheal mucosa which are the main entrance door for VBIG (Cavanagh, 2007). Regarding the immune-modulating action of fasting, Klasing (1988) had already verified the beneficial effect of short fasting periods (12 and 24 hours) on the cellular and humoral immune response, nonetheless, data gathered by this author, only refer to the alterations induced by fasting in the systemic behavior and not to the immune responses related to the mucosa, as this work concludes. Besides, the divergence prevailing between such works, in what has to do with the site of the response, most probably is due to the presence of maternal antibodies, due to the fact that broiler breeders coming from a flock of grandmothers which had received several doses of vaccination against VBIG were used; this brings along a further transference of maternal antibodies to their progeny. In this case, one should consider that maternal antibodies interfere in the post vaccine active immune response. As a matter of fact, Gelb et al. (1998), when measuring anti-VBIG total antibodies, found earlier responses with further magnitude to vaccines, in tear secretion and in the blood serum of birds SPF in comparison to commercial birds carrying maternal antibodies.

Graph 1. Kinetics of humoral immune response against  BIG, in serum of vaccinated broiler breeders, subjected to different post-hatching fasting periods.

 ^{a, b} Different letters, within each age, show the statistical differences for the Tukey Test at (5%).

Graph 2. Kinetics of humoral immune response against  BIG, in tear secretion of vaccinated broiler breeders, subjected to different post-hatching fasting periods.

^{a, b} Different letters, within each age, show the statistical differences for the Tukey Test at (5%).

On the other hand, at the end of the experiment, the immune vaccine response in the local compartment of fasting birds during 72 hours did not  differ from the ones fed during housing, showing that this fasting period was not enough so as to compromise the immune response of birds. These conclusions differ from those of Holt (1992), who verified that after 5 fasting days, there were s in the tritation of antibodies against Brucella abortus in birds previously immunized by means of this antigen. Such difference may be attributed to a more severe fasting that the one adopted for this study. In conclusion, we need to research, even more, the post-hatching fasting and the immune response against VBIG, with the end goal of adopting more effective measures in order to optimize the results of the immunoprophylactic schemes used against BIG.

Periods, up to 72 hours post-hatching, do not interfere in most of the intervals of the systemic humoral immune responses in commercial broilers vaccinated, at birth, against  VBIG. Nonetheless, there is a positive influence of the 48 and 72 fasting hours fasting periods in the level of antibodies produced in the compartments of the mucosa in the 5 and 21 day intervals post-hatching.

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