Abstract
Racer pigeons are renowned for their exceptional flying abilities, and Shiqi pigeons are
meat pigeons prized for their tender and nutritious meat. This study investigated the
physiological and metabolic differences between the two breeds under distinct breeding
objectives by examining their feeding habits, carcass performance, meat quality, and
intestinal development, thereby providing insights for pigeon breeding programs. Six racer
and six Shiqi pigeons, each aged 28 d, were selected. They were fed a basal diet until 35
d of age, after which they were slaughtered for testing. Racer pigeons had substantially
lower daily feed and pellet intake than Shiqi pigeons. There was no difference in the
proportion of the major grains consumed. Slaughter traits, including live, carcass,
semi-eviscerated weights, and weights of the spleen, gizzard, and bursa of Fabricius were
substantially lower in racer pigeons. Racer pigeons had substantially higher pectoral
muscle redness and yellowness at 45-min post-slaughter but lower pH values at 45 min and
24 h. Racer pigeons had substantially higher plasma GSH-Px activity and glucose
concentrations. Racer pigeons had a higher pectoral muscle triglyceride (TG) content,
greater duodenal weight and length, higher duodenal villus-to-lumen ratio, and elevated
catalase (CAT) activity. However, they had a lower pectoral muscle GLU content and reduced
jejunal weight and length. Compact racer pigeons are physiologically adapted for flight
and are characterized by a strong antioxidant capacity and a well-developed duodenum. In
contrast, the larger Shiqi pigeon, with a more developed jejunum and heavier pectoral
muscles, was optimized for digestion and meat yield. These distinct profiles highlight the
strong influence of genetic selection; the identified metrics offer valuable insights into
targeted breed development.
Introduction
Pigeon domestication has a long history and diverse applications ranging from ancient
communication and religious practices to modern pigeon racer, ornamental breeding, and meat
production[1]. As an approved sporting discipline,
pigeon racer has experienced rapid growth in China in recent decades, establishing itself as
the fastest growing market in the global pigeon racer industry[2]. In 2024, China’s meat pigeon output will exceed 800 million birds,
ranking first globally in production volume, with output values surpassing 10 billion
yuan[3]. China has nine officially-recognized meat
pigeon breeds, with Shiqi pigeons particularly favored for their excellent meat quality,
distinctive flavor, and rich nutritional value. Traditional racer pigeons consist of ten
breeds, with the Homer pigeon renowned for its swift flight and standardized physique.
However, modern meat pigeon breeding often uses inbreeding for selection, such as in the
Silver King pigeon, which has a high inbreeding coefficient. Consequently, genetic diversity
in these breeds is far less than that found in local varieties, such as the Shiqi and Tarim
pigeons[4]. Although racer pigeons have undergone
artificial selection, they retain a high degree of genetic diversity. Podbielska et
al.[5] assessed the genetic diversity of 519 racer
pigeons, finding that the genetic diversity within the racer pigeon population was at a
reasonably acceptable level (Ho = 0.623, He = 0.684). Smolucha et al.[6] conducted a study on the genetic diversity and population structure of
389 racer pigeons and concluded that racer pigeons possess complex ancestry and high genetic
diversity. Consequently, identifying diverse breeding materials and innovative breeding
methods is crucial for maintaining genetic diversity in domestic pigeon breeds and ensuring
sustainable development of the meat pigeon industry.
Different breeding objectives influence the carcass characteristics, intestinal
development, and biochemical indicators of livestock and poultry. For instance, in terms of
slaughter characteristics, broiler chickens bred for meat production exhibit pectoral and
thigh muscle ratios of approximately 20% and 22% respectively[7]. To enhance leg strength in fighting cocks, the leg muscle ratio is
approximately 24%, exceeding that of the pectoral muscle ratio[8]. In terms of intestinal development, Kinstler et al.[9] compared the modern broiler breed Cobb500 (Cobb) with
high-weight selection (HWS) and low-weight selection (LWS) lines and found that Cobb
chickens possessed the most efficient intestinal structure, characterized by short crypts
and long villi. The villus height to crypt depth ratio (VH:CD) serves is an indicator of
enhanced intestinal health and efficiency. Cobb chickens also exhibit increased Muc2
expression in goblet cells, demonstrating rapid and efficient growth. Regarding biochemical
indicators, Li et al.[10] observed that American King
pigeons exhibited elevated serum high-density lipoprotein cholesterol (HDL-C) levels,
reduced low-density lipoprotein cholesterol (LDL-C) and aspartate aminotransferase (AST)
activity, with higher antioxidant function indicators (such as superoxide dismutase, SOD;
catalase, CAT; and total antioxidant capacity, T-AOC) and lower malondialdehyde (MDA)
content. In contrast, European meat pigeons have lower levels of certain biochemical
indicators and overall antioxidant activity. This indicates that distinct breeding
objectives substantially influence differences in carcass traits, intestinal development,
and biochemical characteristics in poultry and livestock. However, no comparative studies
between racer and Shiqi pigeons have been conducted to date. Therefore, this study aimed to
compare the feeding preferences, carcass characteristics, intestinal development, and
biochemical indicators of racer and Shiqi pigeons to indicate differences between the two
breeds under distinct breeding objectives. This study will provide a scientific basis for
the conservation and development of domestic pigeon breeds.
Materials and Methods
Experimental design and feeding management
In this study, six female, 28-d-old racer pigeons (Racer Homers) and six Shiqi pigeons
were randomly selected. Shiqi pigeons were provided by Zhongshan Shiqi Pigeon Breeding
Co., Ltd (Zhongshan, Guangdong, China) and the Racer Pigeons were supplied by Huizhou
Fawell Biotechnology Co., Ltd. (Huizhou, Guangdong, China). The experimental site was
located in an animal room at Zhongkai University of Agricultural Engineering. Throughout
the experimental period, each pigeon was housed in a single cage with food, water, and
sand. The 28-d-old pigeons were raised for 7 d and then slaughtered at 35 d of age, with a
12-h pre-slaughter fasting period. The basal diet consisted of whole grains and pellets;
its composition and nutritional levels are detailed in Table 1. During this period, 200 g of feed was administered
daily at 09:00 each day, with a baffle plate installed to collect the spilled feed. The
feed remaining in the troughs and collected from the deflectors were retrieved at 09:00
the following day. The feed intake of all the pigeons was recorded. Feed statistics were
conducted once daily for six consecutive days, and the remaining amount of each feed type
was recorded daily to calculate feed preference. The average daily feed intake and
performance were calculated using the total and categorized weights recorded, following
the method described by Zhang et al.[11].
Table1 Feed formula and ingredient list (air-dried basis)
| Ingredients |
Ratio/% |
Nutrient levels 2) |
Content /% |
| Corn |
12.73 |
Dry matter |
87.97 |
| Sorghum |
16.85 |
Crude protein |
16.28 |
| Wheat |
13.29 |
Metabolizable energy (MJ/kg) |
15.66 |
| Soybean |
16.37 |
Crude lipid |
5.49 |
| Pellet1) |
40.76 |
Crude Ash |
2.59 |
| Total |
100.00 |
Calcium |
0.31 |
|
|
Total phosphorus |
0.41 |
1) The premix provided the following per kg of diets:Vitamin A, 14 200.00
IU; Vitamin D, 3,300.00 IU; Vitamin E, 22.50 mg; Vitamin K, 3.90 mg; Vitamin B1, 3.00
mg; Vitamin B2, 9.60 mg; Vitamin B6, 6.00 mg; niacin, 60.00 mg; calcium pantothenate,
18.00 mg; folic acid, 1.50 mg; vitamin B12, 0.03 mg; biotin, 0.06 mg; copper, 6.00 mg;
iron, 60.00 mg; zinc, 58.00 mg; manganese, 65.00 mg; iodine, 0.35 mg; selenium, 0.24
mg
2)All nutritional levels are calculated values
Blood was collected from all pigeons into heparin tubes (to prevent coagulation) from the
basilic vein after 12 h of fasting. The samples were then centrifuged at 3,000 ×
g for 10 min at 4 °C, after which the upper plasma was removed and
stored at −20 °C. Plasma was used to determine T-AOC, glutathione peroxidase (GSH-Px),
total superoxide dismutase (T-SOD), CAT, MDA, alanine aminotransferase (ALT), AST,
triglyceride (TG), total cholesterol (T-CHO), glucose (GLU), total protein quantitative
(TP), albumin (ALB), and uric acid (UA) using a Varioskan LUX multifunctional enzyme
marker (Thermo Fisher Scientific Ltd., Waltham, MA, U.S.A.). This was conducted using
commercial kits purchased from the Jiancheng Biological Engineering Research Institute,
Nanjing, China.
Carcass composition and meat quality of pigeons
According to the NY/T 823–2020 Terminology and Measurement Statistical Methods for
Poultry Production Performance published in China[12], pigeons were fasted for 12 h at 35 d of age. The pigeons were humanely
euthanized by cervical exsanguination, and the carcass weight after feather removal was
recorded as the slaughter weight. Subsequently, semi-eviscerated and eviscerated pectoral
muscle and abdominal fat weights were determined after slaughter to calculate the yield
percentage, semi-evisceration rate, evisceration rate, pectoral muscle rate, and abdominal
fat rate, following the methodology of Peng et al.[13]. The weights of the liver, pancreas, heart, glandular stomach, gizzard,
kidney, spleen, thymus, and bursa were measured to calculate organ-to-body weight ratios.
After slaughter, 7 g of the muscle tissue was excised from the left pectoral muscle of
each pigeon. The pH was determined according to the method described by
Hernández-Castellano et al.[14]. The right pectoral
muscle was collected and tested for pH and meat color (redness (a*), yellowness (b*), and
lightness (L*) values) using a portable pH meter (pH818M, Xima, Beijing, China) and
spectrophotometer (NS810, 3nh, Shenzhen, China), respectively. Measurements were taken 45
min and 24 h after testing in triplicate for each sample from different locations such
that average values could be calculated[15].
Intestinal length measurement and hematoxylin and eosin (HE)-based morphological
statistics
After slaughter, the entire intestine was carefully removed and its natural length was
measured using a ruler. The duodenum was measured from the posterior part of the pylorus
to the duodenojejunal flexure, the jejunum from the duodenojejunal flexure to the
vitelline diverticulum (the boundary between the jejunum and ileum), and the ileum from
the vitelline diverticulum to the end of the rectum. The intestinal segments were
separated and identified according to Peng’s anatomical descriptions of domestic animals
and fowls[16]. The excised intestine was rinsed
with physiological saline to remove the contents, blotted dry with filter paper, and
weighed using an electronic balance. Segments of approximately 1 cm were obtained from the
same location in the duodenum, jejunum, and ileum of each pigeon and fixed in 4% formalin.
The samples were sent to Wuhan Borf Biotechnology Co., Ltd.(Wuhan, Hubei, China) for
hematoxylin-eosin (HE) staining. The morphological structure of the intestinal tissue was
observed under a light microscope and five fields of view were selected per section for
statistical analysis. Villus height (VH) and crypt depth (CD) were measured and analyzed
according to the method described by Wilson et al.[17], and the villus height/crypt depth ratio (VH/CD) was calculated.
Tissue biochemistry indicators of pigeons
After slaughter, approximately 100 mg of pectoral muscle as well as samples of the
duodenum, jejunum, and ileum mucosa were collected from the same sites in all pigeons. The
biochemical indicators were measured using a Varioskan LUX Multifunctional Microplate
Reader (Thermo Fisher Scientific). The glycolipid metabolism parameters in the pectoral
muscle assays included T-CHO, GLU, TP, ALB, and TG. The T-AOC, CAT activity, T-SOD
activity, H2O2 concentration, and MDA content in the pectoral muscle
were determined using colorimetric assays. Intestinal mucosal analysis included T-AOC,
T-SOD, MDA, and CAT. All kits for the aforementioned assays were procured from Nanjing
Jiancheng Bioengineering Institute (Nanjing, Jiangsu, China), and measurements were
conducted in accordance with the manufacturer’s instructions provided with the kits.
Statistical Analysis
Preliminary data organization was conducted using Microsoft Excel. Differences between
groups were analyzed using Welch’s t-test (two-tailed, unequal variance)
in SPSS version 26.0. The P-value was used to determine statistical
significance; P < 0.05 indicated significant differences;
P < 0.01, highly significant differences; and P
> 0.05, no significant differences. All data in the tables are expressed as mean ±
standard deviation (SD).
Results
Feeding habits of pigeons
To investigate the feeding habits of racer and Shiqi pigeons, their feed intake and
preference was recorded during the experimental period. Racer pigeons consumed less feed
than Shiqi pigeons (P < 0.05), with a significant difference in pellet
feed intake rates (P < 0.01). No marked differences were observed in
the proportions of corn, wheat, sorghum, and soybeans consumed by racer and Shiqi pigeons
(P > 0.05) (Table
2).
Table 2 Feeding habits of racer and Shiqi pigeons
| Items |
Racer pigeon |
Shiqi pigeon |
SEM1 |
P-value |
| ADFI2/g |
60.57 ± 10.14 |
73.81 ± 6.39 |
0.818 |
0.023 |
| Corn% |
61.81 ± 20.26 |
69.13 ± 24.26 |
7.985 |
0.683 |
| Wheat % |
12.71 ± 1.01 |
11.54 ± 1.35 |
0.484 |
0.247 |
| Sorghum % |
16.85 ± 0.00 |
13.97 ± 2.68 |
0.925 |
0.121 |
| Pellet % |
10.90 ± 3.33 |
28.05 ± 3.18 |
3.64 |
0.002 |
| Soybean % |
13.16 ± 4.34 |
10.81 ± 1.96 |
1.183 |
0.454 |
P < 0.05 indicates a significant difference, P
< 0.01 indicates a highly significant difference, and P > 0.05,
no significant difference. n = 6 replicates per group
1 standard error of the mean
2ADFI, average daily feed intake
To elucidate the physiological differences between racer and Shiqi pigeons, their carcass
characteristics were compared. Racer pigeons had lower live, slaughter, semi-eviscerated,
spleen, gizzard, and bursa Fabricius weights than Shiqi pigeons (P <
0.05). No differences were observed in the semi-eviscerated, eviscerated, eviscerated,
pectoral muscle, pectoral muscle, abdominal fat, abdominal fat, liver, thymus, spleen,
pancreas, heart, gizzard, kidney, or brain weights (P > 0.05). The
liver and spleen percentages of racer pigeons were lower than those of Shiqi pigeons
(P < 0.05). However, no significant differences were observed in the
percentages of the thymus, pancreas, bursa of Fabricius, gizzard, or glandular stomach
(P > 0.05) (Table
3).
Table 3 Comparison analysis of carcass characteristics between racer and Shiqi
pigeons
| Items |
Racer pigeon |
Shiqi pigeon |
SEM1 |
P-value |
| Live body weight /g |
377.25 ± 40.16 |
440.25 ± 22.01 |
13.025 |
0.01 |
| Slaughter weight /g |
345.78 ± 38.35 |
394.67 ± 28.39 |
11.856 |
0.033 |
| Semi-eviscerated weight2 /g |
313.54 ± 31.24 |
368.02 ± 22.09 |
11.087 |
0.007 |
| Semi-eviscerated /% |
83.19 ± 2.88 |
83.58 ± 2.01 |
0.686 |
0.792 |
| Eviscerated weight3 /g |
246.70 ± 23.97 |
285.53 ± 43.93 |
11.364 |
0.095 |
| Eviscerated % |
65.46 ± 2.25 |
65.15 ± 11.22 |
2.228 |
0.949 |
| Pectoral muscle weight /g |
79.52 ± 9.05 |
82.56 ± 8.63 |
2.476 |
0.565 |
| Pectoral muscle ratio /% |
21.14 ± 2.21 |
18.76 ± 1.87 |
0.669 |
0.073 |
| Abdominal fat weight /g |
5.93 ± 2.02 |
5.85 ± 0.85 |
0.426 |
0.933 |
| Abdominal fat ratio /% |
1.56 ± 0.47 |
1.33 ± 0.21 |
0.106 |
0.316 |
| Liver /g |
8.35 ± 2.95 |
11.39 ± 3.37 |
0.985 |
0.128 |
| Liver indices /% |
2.18 ± 0.48 |
2.97 ± 0.39 |
0.178 |
0.018 |
| Thymus /g |
0.86 ± 0.46 |
0.88 ± 0.25 |
0.102 |
0.892 |
| Thymus /% |
0.23 ± 0.14 |
0.21 ± 0.06 |
0.029 |
0.634 |
| Spleen /g |
0.34 ± 0.11 |
0.63 ± 0.33 |
0.080 |
0.083 |
| Spleen /% |
0.09 ± 0.03 |
0.19 ± 0.09 |
0.024 |
0.039 |
| Pancreas /g |
1.05 ± 0.17 |
1.32 ± 0.41 |
0.095 |
0.171 |
| Pancreas /% |
0.28 ± 0.05 |
0.30 ± 0.08 |
0.019 |
0.586 |
| Heart /g |
5.34 ± 0.62 |
5.20 ± 1.02 |
0.233 |
0.781 |
| Gizzard /g |
7.25 ± 1.16 |
8.87 ± 0.94 |
0.380 |
0.025 |
| Gizzard /% |
1.99 ± 0.12 |
1.99 ± 0.14 |
0.038 |
0.520 |
| Glandular stomach /g |
0.72 ± 0.24 |
0.97 ± 0.15 |
0.066 |
0.058 |
| Glandular stomach /% |
0.19 ± 0.08 |
0.22 ± 0.03 |
0.018 |
0.298 |
| Kidney /g |
2.43 ± 0.56 |
2.76 ± 0.48 |
0.152 |
0.295 |
| Bursa /g |
0.80 ± 0.12 |
1.10 ± 0.27 |
0.073 |
0.040 |
| Bursa /% |
0.21 ± 0.04 |
0.22 ± 0.08 |
0.018 |
0.965 |
| Brain/g |
2.21 ± 0.40 |
2.11 ± 0.05 |
0.079 |
0.578 |
P < 0.05, significant difference; P < 0.01
denotes highly significant difference; P > 0.05, no significant
difference. n = 6 animals per group. The same applies to the table below.
1 Standard error of the means
2 Semi-eviscerated weight refers to the weight of the carcass after the
removal of the trachea, esophagus, crop, intestines, spleen, pancreas, gallbladder,
reproductive organs, stomach contents, and keratinized membranes
3 Eviscerated weight is defined as the semi-eviscerated weight minus the
weights of the heart, liver, glandular stomach, gizzard, lungs, abdominal fat, head,
and feet
To investigate the differences in meat quality traits between racer and Shiqi pigeons,
the pectoral muscle characteristics of the two breeds were compared. The redness (a*) of
the racer pigeon pectoral muscle after 45 min was higher than that in the Shiqi pigeon
(P < 0.01). The 45-min yellowness (b*) of the pectoral muscle of the
racer pigeons was also higher than that of the Shiqi breed (P < 0.05).
The pH of the racer pigeon pectoral muscle at 45 min and after 24 h was lower than that of
the Shiqi pigeon pectoral muscle (P < 0.01). No differences were
observed (P > 0.05) in the lightness (L*) of the pectoral muscles
after 45 min or 24 h or in the redness (a*) or yellowness (b*) of the muscles between
racer and Shiqi pigeons (Table 4).
Table 4 Comparison analysis of pectoral muscle traits between racer and Shiqi
pigeons
| Items |
Racer pigeon |
Shiqi pigeon |
SEM1 |
P-value |
| 45 min L2* |
39.59 ± 4.05 |
39.82 ± 3.49 |
1.041 |
0.611 |
| 45 min a3* |
17.86 ± 1.43 |
13.95 ± 1.94 |
0.754 |
0.031 |
| 45 min b3* |
13.89 ± 0.81 |
12.07 ± 1.28 |
0.403 |
0.036 |
| 24 h L* |
43.03 ± 3.18 |
44.95 ± 3.44 |
0.956 |
0.889 |
| 24 h a* |
17.25 ± 1.45 |
15.38 ± 2.86 |
0.684 |
0.423 |
| 24 h b* |
15.91 ± 2.34 |
15.67 ± 2.56 |
0.676 |
0.512 |
| PH 45min |
5.71 ± 0.25 |
6.29 ± 0.07 |
0.101 |
< 0.001 |
| PH 24h |
5.58 ± 0.06 |
6.15 ± 0.06 |
0.088 |
< 0.001 |
Standard error of the mean2 brightness
3 redness
4 yellowness
To investigate the differences in biochemical indicators between racer and Shiqi pigeons
with distinct breeding objectives, plasma biochemical indicators were measured in both
groups. The racer pigeons had higher plasma GSH-Px activity than Shiqi pigeons
(P < 0.05) (Figure 1A).
Racer pigeons also had higher plasma T-AOC activity than Shiqi pigeons, though this
difference was not statistically significant (P = 0.093) (Figure 1B). The plasma glucose level in racer
pigeons was higher than in Shiqi pigeons (P < 0.05) (Figure 1C), and the TG level in racer pigeon plasma
was higher than in Shiqi pigeons (P < 0.01) (Figure 1D). However, no statistical differences were observed in
the plasma MDA, ALB, T-CHO, UA, and TP levels or ALT, AST, CAT, and T-SOD activities
between the two groups (P > 0.05) (Figure 1E–M).
Comparison of pectoral muscle biochemistry indicators
Biochemical indicators of the pectoral muscles were determined in both breeds. The TG
content of the pectoral muscles of racer pigeons was higher than that of Shiqi pigeons
(P < 0.05) (Figure 2A),
whereas GLU levels were lower in racer than in Shiqi pigeons (P <
0.05) (Figure 2B). No marked differences were
observed between the two breeds in H2O2, MDA, ALB, T-CHO or TP
levels, or in the activity of CAT, T-SOD and T-AOC (P > 0.05) (Figure 2C–J).
Comparison of the intestinal morphology of pigeons
To investigate the intestinal development of racer and Shiqi pigeons, the length and
weight of different intestinal segments, villus heights, crypt depths, and villus-to-crypt
ratios were measured. The duodenum of racer pigeons was heavier than that of Shiqi pigeons
(P < 0.05), and the duodenum of racer pigeons was longer than that
of Shiqi pigeons (P < 0.01) but the jejunum was shorter than that of
the Shiqi pigeons (P < 0.01). There were no marked differences in
ileum weight, length, or colon length in racer and Shiqi pigeons (P >
0.05) (Figure 3A–C). The villus-to-crypt ratio
of the duodenum was higher in racer than in Shiqi pigeons (P < 0.05).
There were no marked differences in the villus length or crypt depth between the two
pigeon types (P > 0.05) (Figure
3D). Similarly, there were no significant differences in villus length, crypt
depth, or villus-to-crypt ratio of the jejunum or ileum between the two pigeon types
(P > 0.05) (Figure 3E,
F).
The biochemical indicators of different intestinal segments in both groups were tested
and compared. The CAT enzyme activity was higher in the duodenum of racer than in Shiqi
pigeons (P < 0.05) (Figure
4A). Activities of T-SOD and T-AOC and MDA content in the duodenum of racer and
Shiqi pigeons were similar (Figure 4B–D). No
marked differences were observed in CAT, T-SOD, and T-AOC activities or MDA content in the
jejunum or ileum of racer or Shiqi pigeons (P > 0.05) (Figure 4E–L).
Discussion
Racer pigeons prefer whole grains to stone-ground pigeon feed. Feed intake and preferences
are influenced by breed and physiological characteristics[18]. Pigeons prefer whole grains, with corn being the most preferred[19]; accordingly, both pigeon breeds in our study
consumed more than 60% corn. Fekete et al.[20]
reported marked differences in feed intake per body weight. In the present study, racer
pigeons had substantially lower total feed and pellet intake, body weight, and stomach
weight than Shiqi pigeons, which partly explains their reduced intake. Dietary composition
also varies by breed: racer pigeons are typically fed whole grains (including corn, wheat,
peas)[21]. However, meat pigeons, such as Shiqi,
receive different diets, which may account for their lower pellet intake. Shiqi pigeons
consumed more pellets, indicating higher acceptance of this feed type.
Racer pigeons have a poorer slaughter performance than Shiqi pigeons; however, their
muscular structure is better suited for long-distance flights. Live, slaughter, and dressed
weights are key carcass metrics for assessing the growth, body size, and breeding value of
livestock and poultry[22]. Lin et al.[23] showed that lean- and fat-type Beijing ducks differ
in growth; lean-type ducks have higher body weight and greater pectoral muscle mass, whereas
fat-type ducks have more subcutaneous fat rich in monounsaturated fatty acids, indicating
that breeding goals shape carcass traits. Consistent with this notion, racer and Shiqi
pigeons exhibit distinct carcass and organ characteristics associated with their different
breeding purposes. Organ indices in poultry are crucial for evaluating growth, development,
immune function and health status[24]. Liver indices,
for example, can be used to assess lipid metabolism in poultry, whereas spleen size reflects
immune capacity[25,26]. This study found that racer pigeons had substantially lower liver and spleen
indices than Shiqi pigeons, which may reflect differences in the metabolic and immune
characteristics between the two breeds. However, further functional studies are required to
determine whether these differences correspond to the variations in lipid metabolism and
immune capacity.
The meat color index (a* redness, b* yellowness, and L* lightness) reflects the
physiological and biochemical changes in muscle tissue; its values depend mainly on the
state and concentration of myoglobin, oxygenated myoglobin, and ferrihemoglobin[27]. Marked differences in meat color have been reported
between different muscle types in poultry, with higher redness (a*) values in leg than
breast muscle because of its greater myoglobin content[28]. Ranjith et al.[29] found that a higher
proportion of myoglobin in completely-bled muscles was correlated with higher meat redness.
In the current study, racer pigeon pectoral muscles had a substantially higher a* value
45-min post-slaughter than Shiqi pigeons, which was hypothesized to be due to higher
myoglobin content in breed-specific muscle types. Holloszy et al.[30] reported that red (slow-twitch) muscle contained more mitochondria
for aerobic metabolism and higher myoglobin, whereas white (fast-twitch) muscle had abundant
glycogen and glycolytic enzymes, relied on anaerobic glycolysis, and contained less
myoglobin. High myoglobin levels also increase muscle oxygen content and aerobic
metabolism[31]. The b* (yellowness) can be
influenced by the poultry breed[28] and dietary
carotenoids[32]. The current study found that the
proportion of corn consumed by racer and Shiqi pigeons was similar, suggesting that the
observed difference in pectoral muscle yellowness between the two breeds is unlikely to be
explained by differential corn (carotenoid) intake and was more likely breed-related.
The pH reflects post-slaughter glycogenolysis rate and muscle acid–base status. Anaerobic
glycogen breakdown produces lactic acid, which lowers pH[33]. In the current study, racer pigeon pectoral muscles had a substantially lower
pH than Shiqi pigeons 45-min and 24-h post-slaughter. This suggests that Shiqi pigeons
exhibit weaker anaerobic respiration or slower glycolysis, leading to less lactic acid and a
slower decline in pH. In contrast, racer pigeons exhibited rapid glycogenolysis and vigorous
anaerobic respiration, accelerating lactic acid accumulation.
Racer pigeons have a stronger antioxidant system than Shiqi pigeons. Oxidative stress
reflects the antioxidant capacity. Glutathione peroxidase (GSH-Px) catalyzes the conversion
of GSH to water or alcohols to protect cells[34]. Liu
et al.[35] reported a breed-dependent serum
antioxidant capacity in chickens, with Xianju being the strongest and Silky-feathered Silkie
the weakest. In the present study, racer pigeons had substantially higher plasma GSH-Px
activity and total antioxidant capacity (T-AOC) than Shiqi pigeons; however, no differences
were observed in the pectoral muscle. Thus, racer pigeons may possess a stronger circulatory
antioxidant system, which is possibly linked to flight adaptation and higher physiological
demands, whereas Shiqi pigeons have a lower basal plasma antioxidant capacity. The lack of
muscle differences warrants investigation of tissue-specific antioxidant regulation.
Glucose and lipid metabolism indicators (ALB, GLU, T-CHO, and TG) are important in
assessing the health and metabolism of poultry[36].
GLU is the main energy source that affects growth, immunity, and protein synthesis in
muscles, whereas TG reflects fat storage and utilization efficiency[37]. The current study found that racer pigeons had higher plasma GLU,
lower pectoral muscle GLU, and higher pectoral muscle TG than Shiqi pigeons, which is
consistent with their long-distance flight traits. Zhang et al.[38] showed that elevated blood GLU levels support high-intensity flight
(e.g., take-off) via glycogenolysis and gluconeogenesis. Dixit et al.[39] reported that migratory birds accumulate fat reserves to fuel
long-distance flight.
Racer pigeons have shorter digestive tracts than Shiqi pigeons; however, their foreguts are
more developed. The gut is the largest digestive and immune organ in poultry; it secretes
enzymes and harbors mucosal immunity[40]. The small
intestine is comprised of the duodenum (initial digestion), jejunum (main absorption of
nutrients), and ileum (absorption of bile salts and vitamin B12)[41]. The current study found that racer pigeons had longer and heavier
duodenums but shorter jejuna and ileums than Shiqi pigeons, reflecting different digestive
strategies[42]. A longer duodenum may enhance
enzymatic digestion and the assimilation of lipids/proteins for flight, whereas a shorter
jejunum/ileum reduces intestinal mass and body weight, which is beneficial for flight[43]. Shiqi pigeons exhibit the opposite pattern,
resulting from a sedentary lifestyle[44]. Racer
pigeons had a greater duodenal villus length and villus-to-lumen ratio, possibly
compensating for the reduced absorptive area from the shorter jejunum/ileum. Further studies
are required to clarify the functional implications.
The measurement of intestinal oxidative stress indicators can indicate breed differences in
digestion, gut health, and stress responses, thereby offering insights into nutrient
metabolism during flight in racer pigeons. In the present study, racer pigeons had
substantially higher duodenal CAT activity than Shiqi pigeons, possibly reflecting enhanced
antioxidant regulation to counter oxidative stress from sustained flight. Increased CAT
helps decompose hydrogen peroxide, reducing oxidative damage to intestinal cells[45]. Further physiological and metabolic studies are
required to determine whether these differences translate into improved nutrient absorption
or flight performance.
In conclusion, racer pigeons are smaller but exhibit stronger oxidative muscle
characteristics, including darker meat color and higher antioxidant capacity, which may
support rapid flight and environmental adaptation. Shiqi pigeons are larger with a more
developed jejunum, heavier pectoral muscle, and superior meat quality, reflecting their
selection for meat production. These findings highlight the role of genetic selection in
shaping breed-specific physiological traits, and may inform future breeding strategies for
domestic pigeons.
Ethical Approval
All experimental procedures were approved by the Animal Management and Ethics Committee of
Zhongkai University of Agricultural Engineering (approval number: ZHKUMO-2022-055).
Funding
This study was supported by Central Government Guided Local Science and Technology
Development Fund Projects(Project No.: 2024B0202010014).
Acknowledgements
The authors acknowledge Zhongkai University of Agricultural Engineering for providing the
experimental sites.
Author Contributions
Haopeng Lu and Ziying Li: Writing – review and editing, Writing – original draft,
Investigation, Formal analysis, Data curation, Software. Yanhua Huang and Yayan Liang:
Writing-review and editing, Conceptualization, Project administration. Shiqi Zheng, Wuhao
Chen, Shuangyan, Mo, Guohua Tan: Investigation & Methodology. Yantao Lv and Wei Wang:
Writing – review, editing, and methodology. Chuanshang Cheng and Xiu Zhang: Investigation.
Kai Yan, Shuo Zhou, and Jie Peng: Writing, review and editing, Supervision, Project
administration
Data availability statement
Not Applicable
Conflicts of Interest
The authors declare that they have no competing financial interests or personal
relationships that may have influenced the work reported in this study.
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