Evaluating igy recovery in rumen fluid and its potential role in performance and neutrophil function in lactating Holstein cows

A series of experiments were conducted to evaluate the effects of a spray dried egg (SDE) product from chickens vaccinated against mammalian enteric pathogens on in vitro disappearance of immunoglobulin Y (IgY) from rumen fluid and on performance of cows fed the product. In two separate in vitro experiments we incubated rumen fluid with SDE, an extract of SDE, or starch-encapsulated SDE for different amounts of time and used ELISA to measure IgY disappearance. The objectives of Experiment 1 were to determine IgY recovery from a SDE extract and SDE encapsulated with 50% starch following 6 h of incubation in rumen fluid. We also wanted to determine if recovery was influenced by the addition of total mixed ration (TMR) to the in vitro system. Recovery of IgY from the extract was 26% at 6 h, however, with the addition of TMR, 52% of IgY was recovered at 6 h. Recovery of IgY from starch-encapsulated SDE did not differ from recovery of IgY from the extract. Experiment 2 was conducted to determine IgY recovery from SDE incubated for up to 24 h in rumen fluid with TMR. Recovery of IgY decreased from 47% at 6 h to 25% at 12 h with numeric decreases to 15% and 14% at 18 h and 24 h, respectively. Based on this recovery data we predicted that approximately 50% of IgY from SDE should escape digestion in the rumen and be available to bind with intestinal pathogens.;We elected to evaluate the efficacy of this product on performance and neutrophil function of dairy cows. Thirty lactating Holstein cows (6 primiparous, 24 multiparous) were randomly assigned to a control diet or a diet supplemented with 45 g/d of SDE according to a crossover design with 6-week periods. Feed intake and milk yield were recorded daily and milk composition was determined weekly. Blood was collected every 3 weeks and neutrophils isolated to assess chemotaxis, phagocytosis and oxidative burst. No significant differences were observed in milk yield. There were trends for interactions between treatment and parity on milk yield (P = 0.10) and milk/DMI ( P = 0.06), with SDE numerically decreasing performance in primiparous cows and improving performance in multiparous cows. There were trends for a treatment effect on chemotaxis towards media only (P = 0.09) and an interaction between treatment x week on oxidative burst production in stimulated PMN (P = 0.10). In summary, although our in vitro experiments demonstrated that a substantial portion of IgY would likely pass from the rumen to the intestines, no benefits of dietary SDE on performance or neutrophil function were observed in this study.