Effects of energy supplementation and season on serum immunoglobulin and protein levels in Moxoto goats

A study was conducted to determine the influence of various levels of energy supplementation and season on total serum immunoglobulin and protein levels of female goats grazing native range (caatinga) in Northeast Brazil. The energy supplement was whole sorghum grain. One hundred and twenty female Moxoto goats weighing 10 to 12 kg were randomly assigned to one of four treatment groups consisting of 30 animals. Grain was supplemented at: 0, 0.6, 1.2 and 1.8%/BW on an as fed basis. The quantity of supplement offered was adjusted bi-weekly using the mean BW of goats from each of the treatment groups. Grain was offered individually in headlock feeders twice a day, before and after grazing (6 a.m. and 5 p.m.). Goats rotationally grazed three pastures of 65 ha each. A mineral salt mixture was offered ad libitum. The four groups did not show a statistical difference in total serum immunoglobulin levels. All groups, however, showed a seasonal variation in immunoglobulin levels. Immunoglobulin levels were highest during June to December (dry season) and lowest during January to May (rainy season). The lower levels of serum immunoglobulin levels may be a partial explanation for the increased incidence of major diseases recorded during this period of the year in Northeast Brazil. Goats receiving no sorghum grain supplementation had statistically significantly lower levels of serum protein during 8 of 19 months of this study. The most marked difference was between these animals and those receiving the highest level of energy supplementation. Seasonal variations in serum immunoglobulin levels may be a reflection of varying periods of immunocompetence and be of potential significance when assessing responses to immunogens.