The research team, led by Hande Işıl Akbağ, worked with 114 one-day-old squabs drawn from three pigeon breeds: the Homing pigeon, prized for its long-distance flying ability, and two native Turkish breeds, the Takla and the Dolapçı, both famous for their acrobatic tumbling and spinning flight. For the first three days after hatching, all squabs were fed crop milk by their parents, ensuring that every chick received the same natural start. The birds were then randomly assigned to one of three feeding groups. A control group remained with their parents and continued to be fed naturally until 28 days of age. A second group was hand-fed a commercial artificial crop milk, diluted with water at a one-to-one ratio as the manufacturer recommends. The third group received the same artificial crop milk, but supplemented with kefir at 2 percent of daily feed intake, a level chosen so that the kefir’s own nutritional contribution would be negligible and its probiotic and bioactive effects could be assessed independently.

The logic behind the kefir trial was compelling. Kefir is a fermented milk beverage produced by kefir grains, complex symbiotic communities of lactobacilli, streptococci, and yeasts. During fermentation, these microbes generate not only lactic acid but also bioactive compounds such as kefiran, a heteropolysaccharide with documented antioxidant and antimicrobial properties. Previous work in broiler chickens had shown that kefir supplementation can improve growth performance, feed intake, and feed conversion. More importantly, natural pigeon crop milk itself harbors a rich microbiota, including Lactobacillus, Enterococcus, and Bifidobacterium species, which are thought to seed the squab’s developing gut and immune system. The researchers hypothesized that kefir, with its similar combination of beneficial microbes and bioactive molecules, might partially mimic what artificial crop milk lacks and bring hand-reared squabs closer to the performance of parent-fed birds.

Before any performance data could be interpreted, the team needed to understand what the squabs were missing. They collected crop milk samples from the parents three days after hatching and analyzed the chemical and microbiological composition. The results showed that breed made no difference to the macronutrient profile of the milk: crude protein, ether extract, ash, and water-soluble carbohydrates were statistically indistinguishable across the Takla, Dolapçı, and Homing lines. On a dry matter basis, the crop milk contained roughly 42.75 percent crude protein and an ether extract level consistent with earlier reports. The microbiological picture was more nuanced. Total aerobic bacteria and yeast counts were similar across breeds, but lactic acid bacteria levels differed significantly, with Homing pigeons producing milk with the highest counts at 3.96 log10 colony-forming units per gram, compared with 3.50 for Dolapçı and 3.24 for Takla birds. This variation in lactic acid bacteria, the authors suggest, may translate into differences in lactic acid production and possibly in the microbial environment that each breed’s chicks experience.

The growth results were unambiguous and, for anyone hoping for a kefir miracle, disappointing. By the end of the 28-day trial, parent-fed control squabs reached an overall body weight of 236.05 grams, dramatically outperforming both hand-fed groups. Squabs receiving kefir-supplemented artificial crop milk averaged 152.18 grams, while those on plain artificial crop milk reached only 146.02 grams. Feed conversion ratios told the same story: the control group converted feed into body mass with an overall efficiency of 2.61, whereas the kefir and artificial milk groups required 8.37 and 8.92 grams of feed per gram of gain, respectively. The gap was especially stark in the first ten days, when control squabs achieved a feed conversion ratio of 0.95 against 2.95 for the kefir group and 3.14 for the artificial milk group. Breed mattered as well, with Homing pigeons achieving the highest overall body weights, followed by Dolapçı and Takla birds, but no breed escaped the penalty of artificial rearing.

There was, however, one glimmer of breed-specific promise. Among Homing pigeons, squabs fed the kefir-supplemented diet showed higher feed intake and greater body weight than those fed plain artificial crop milk, suggesting that the response to kefir may depend on the genetic background of the bird. In the Takla and Dolapçı breeds, by contrast, the two hand-fed groups performed similarly. The authors caution against overinterpreting this pattern, but it hints that future attempts to optimize artificial rearing might need to account for breed-specific physiology rather than applying a one-size-fits-all formula. Notably, the artificial milk actually delivered more crude protein per feeding than natural crop milk when diluted as recommended, yet the hand-fed birds still grew poorly, underscoring that protein quantity alone cannot explain the superiority of parental feeding.

Mortality data added another layer of concern. No deaths occurred in the parent-fed control group, but 23.8 percent of squabs in the artificial milk group and 19.5 percent in the kefir group died between days 3 and 28. Although the statistical difference between the two hand-fed groups was not significant, and the kefir group fared marginally better, the overall mortality in both hand-reared groups was high compared with figures of around 2 to 4 percent reported in some earlier studies using different artificial feeding protocols. The authors note that the timing of separation from parents matters greatly: previous research found mortality rates of 26.7 percent when squabs were separated at hatching, but only about 3 percent when separation occurred at 7 days of age. Because parents produce pure crop milk only until roughly the third day after hatching, after which its composition gradually shifts, the three-day separation point used in this study may represent a particularly vulnerable window.

The serum biochemistry results provided a window into the metabolic state of the birds. At 28 days of age, blood samples revealed that total protein and albumin were the only serum parameters significantly affected by feeding treatment, with the control group showing the highest concentrations of both. Elevated total protein and albumin are generally interpreted as markers of greater anabolic activity, consistent with the superior weight gain observed in parent-fed birds. Breed, meanwhile, influenced nearly every measured parameter except aspartate aminotransferase. Homing pigeons had the lowest serum glucose, which the authors link to their long-distance flight capacity and larger body size, while the smaller Takla and Dolapçı breeds showed higher glucose levels, in line with the general avian pattern that smaller species maintain higher blood sugar. Cholesterol concentrations were higher in the larger Dolapçı and Homing breeds, plausibly reflecting their greater energy requirements.

What does this all mean for the future of intensive pigeon production? The study’s conclusion is clear: kefir, at least at the 2 percent inclusion level tested, did not rescue the growth performance or survival of hand-reared squabs. The problem appears to lie deeper than the absence of probiotics. Natural crop milk contains a complex array of bioactive proteins, growth factors, and immunomodulatory compounds that industrial formulations have yet to replicate, and the frequency and manner of parental feeding may also play a role that hand-feeding protocols cannot easily mimic. The authors also flag a methodological caveat: feed intake in the control group was estimated by weighing squabs before and after feeding, and because parent birds may feed their chicks more frequently than the twice-daily schedule imposed on the hand-fed groups, actual intake in the control group may have been underestimated. Even accounting for this, the magnitude of the growth gap is difficult to dismiss.

The research opens several avenues for follow-up. The authors suggest that compensatory growth processes in squabs after weaning from artificial diets, and the effects of artificial crop milk formulations with different nutrient compositions on later growth and reproductive traits, remain largely unexplored. The breed-dependent response to kefir, particularly the improved performance of Homing squabs, deserves targeted investigation with larger sample sizes and possibly higher inclusion rates. For now, the message for pigeon breeders is that there is still no substitute for the real thing. The crop milk produced by parent pigeons, a substance so distinctive that scientists have compared its function to mammalian lactation, remains an irreplaceable foundation for healthy squab development, and closing the artificial rearing gap will require far more than a splash of fermented milk.

Subject of Research: Effects of kefir supplementation on growth performance and serum biochemistry of artificially reared pigeon squabs

Article Title: Can kefir supplementation influence the growth performance and serum biochemistry of artificially reared squabs of three pigeon breeds?

Article References: Akbağ, H. I., Şensoy, A., Erdem, H., Yiğit, S., Tölü, C., & Savaş, T. (2026). Can kefir supplementation influence the growth performance and serum biochemistry of artificially reared squabs of three pigeon breeds?. Archives Animal Breeding, 69(3), 529-539. https://doi.org/10.5194/aab-69-529-2026

Image Credits: AI Generated

DOI: 10.5194/aab-69-529-2026

Keywords: pigeon, squab, crop milk, kefir, probiotics, artificial rearing, growth performance, serum biochemistry, animal nutrition, poultry science, microbiota, feed conversion ratio