Transfer of passive immunity investigated in donkey foals

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Nearly a third of foals in the Italian study did not achieve full transfer of passive immunity, but they remained healthy.
Image by Les Bohlen

Research into the transfer of passive immunity from 20 donkeys to their foals revealed that the process was only partially completed in 30% of the studied births.

After birth, a foal’s immune system is immature and does not guarantee adequate protection, as it lacks circulating antibodies that do not cross from the placenta.

Colostrum, consumed in the first 24 hours after birth, provides immunity to the foal for the first few weeks of life until its own immune system kicks in.

The high protein content of colostrum reflects the concentration of immunoglobulins produced in late pregnancy.

Tiziana Nervo and her fellow researchers from the University of Torino in Italy set out to evaluate the transfer of passive immunity in donkeys using electrophoresis as the main diagnostic tool.

The study team enrolled a group of 20 Ragusano crossbreed jennies, aged 3 to 19, and their foals. All were kept on a farm that produces organic donkey milk for human consumption and cosmetics.

The jennies had all been mated naturally, showed uneventful pregnancies, and had natural deliveries.

The γ-globulin content of the jennies’ colostrum, as well as in the sera of the dams and foals, was measured. The study team, reporting in the Italian Journal of Animal Science, also looked for any effects on γ-globulin concentration related to the season of birth and age.

Nearly a third of foals in the Italian study did not achieve full transfer of passive immunity, but they remained healthy.
Image by H. Hach

Using the reference range used for horses, it was found that 70% of the donkey foals showed complete transfer of passive immunity, while 30% had a partial failure of passive transfer. None of the foals that achieved only partial transfer showed any signs of illness.

Age, nor the number of foals the jennies had previously produced, had any significant effect on passive immunity transfer, nor did the season. The authors noted that winter births were avoided to prevent the exposure of the newborns to extremely low temperatures.

Discussing their findings, they said the 30% of foals that achieved only partial transfer of immunity were all apparently healthy in the days following birth, and showed normal development. Even the foals with a very low immunoglobulin content 24 to 48 hours after birth showed no signs of problems.

“The association between a very low γ-globulin concentration and the absence of clinically evident neonatal diseases is extremely anomalous,” they said.

It was possible, they added, that the minimum antibody coverage that donkey foals require in the first days of life is lower than that needed by the horse foal.

“It would be interesting to evaluate serum immunoglobulin concentration of pathological foals to understand if the cut-off for defining the failure of passive immunity transfer in the donkey is different from that established for the horse.”

The researchers said much remains unknown about the transfer of passive immunity from jennies to their foals.

“Currently, there are no in-depth studies on the factors that can influence this delicate immune function.

“Apparently, this process is similar in horses and donkeys. However, it would be interesting to investigate the relationship between the donkey’s seasonality and its reproductive activity, referring to a larger population of animals.

“Comparing the donkey to the horse there is, in fact, the risk of not grasping the subtle differences that make the breeding of these two species completely different.”

The study team comprised Nervo, Alessia Bertero, Gian Guido Donato, Elena Panier Suffat and Leila Vincenti.

Tiziana Nervo, Alessia Bertero, Gian Guido Donato, Elena Panier Suffat & Leila Vincenti (2021) Analysis of factors influencing the transfer of passive immunity in the donkey foal, Italian Journal of Animal Science, 20:1, 1947-1956, DOI: 10.1080/1828051X.2021.1963863

The study, published under a Creative Commons License, can be read here

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