4.1. Donkey Meat
The live weight of Istrian donkeys is significantly higher than the live weight of Littoral Dinaric donkeys (+62.1 kg), which was also reflected in the greater mass of the cold carcass (+32.04 kg;
p < 0.001). The larger body frame of the Istrian donkey compared to the Littoral Dinaric donkey was also observed in an earlier study, with a difference of +24.17 cm in wither height. This difference can be attributed to their specific genetic constitution and the agroecological conditions of their rearing [
7]. Interestingly, local breeds in the Istrian peninsula area, such as the Istrian donkey, Istrian cattle, Istrian goat, and Istrian sheep, have a larger body frame and body mass compared to other local breeds of the same species in Croatia. This can be attributed to the unique environmental factors and centuries-old specific breeding strategies employed in the region. The Istrian donkey, due to its size, belongs to a group of medium to large donkey breeds, similar to the Italian breeds Ragusano, Pantelleria, Romagnolo, or Martina Franca. The Martina Franca breed was utilized in the selection process in Istria during the early 20th century to achieve the desired physical characteristics of the donkeys [
32]. On the other hand, the Littoral Dinaric donkey belongs to a group of smaller donkey breeds, with an average wither height of about 100 cm, similar to other donkey breeds commonly found in Southeastern Europe. The dressing percentage was higher in the Istrian donkey compared to the Littoral Dinaric donkey, with values of 50.25% and 49.52%, respectively. However, this was lower than the dressing percentage observed in donkeys from the Botswana region [
33] or the Martina Franca donkeys, which recorded a dressing percentage of 53.3% [
11]. In a study conducted by Polifori et al. [
13], crossbred male animals (Martina Franca × Ragusana; age 16 months) raised under extensive management conditions showed a dressing percentage of 51.3%. It is worth noting that the animals included in the present study did not receive additional concentrate and were older. Therefore, it can be concluded that the dressing percentage of the studied donkey breeds was relatively favorable and had the potential for improvement through selection or the implementation of an intensive feeding system [
13].
In the valorization and economic utilization of local donkey breeds, particularly in the context of slaughterhouses and restaurants offering gastronomic specialties, the percentage of deboned meat in the carcass serves as a crucial indicator. This percentage determines the purchase price of live donkeys, the price of the donkey carcass, and the sale price of meat categorized by primal cuts. The determined ratios between the weight of live animals and the weight of the carcass and boneless meat of the Istrian donkey (177.20:89.04:50.10 kg) and the Littoral Dinaric donkey (115.10:57.00:30.13 kg) served as references for establishing and optimizing the average market prices of “live donkeys/carcass/boneless meat”. It was observed that the proportion of boneless meat in relation to the live weight of donkeys was higher in the Istrian donkey compared to the Littoral Dinaric donkey (28.27% vs. 26.18%). The aforementioned findings regarding carcass usability indicated that it was justifiable to offer a higher price for Istrian donkeys, as the proportion of boneless meat in relation to live weight was approximately 2% higher compared to Littoral Dinaric donkeys. However, it is worth noting that the percentage of muscle tissue in the “rib section” (66.05–67.10%) was higher than the overall meat content in the whole carcass determined by the complete deboning of the entire carcass (54.39%, 55.64%). As a result, it can be challenging to accurately estimate the muscle/bone/fat and connective tissue ratio. For future studies, it would be necessary to precisely determine the anatomical position of the vertebral column in order to assess the proportions of meat, bone, fat and connective tissue in the donkey carcass. The values of “muscle/bone/fat and connective tissue” determined through the dissection of the “rib section” should not differ significantly from the values obtained through the dissection (deboning) of the entire carcass.
The pH
24 values of Istrian donkey and Littoral Dinaric donkey meat fell within the favorable range recommended by Wulf and Wise [
34], which suggests that the pH
24 of meat should ideally range from 5.3 to 5.7. The observed pH
24 values of 5.50 and 5.56 in the meat of Istrian donkeys and Littoral Dinaric donkeys indicated favorable degradation processes of glycogen that remains in the muscle after slaughter. A favorable pH
24 also indicates that there was no significant stress experienced by the animals before slaughter, which is beneficial for the meat’s sustainability and its suitability for processing. In a study by Polidori et al. [
11], a pH
24 value of 5.57 was determined in the meat of the Martina Franca donkey breed. The parameters of meat color did not show significant differences between the Istrian donkey and Littoral Dinaric donkey meat. Applying the recommendations for meat categorization according to Wulf and Wise [
34], based on the
L* value, the meat could be classified as dark meat (category 1;
L* < 33.5). However, considering the
b* value, it could be categorized as having favorable meat colors (category 8;
b* > 12.00). In a study by Polidori et al. [
13], color parameters (
L*,
a*,
b*) were observed in young male animals (16 months old) raised under extensive rearing conditions, resulting in values of 34.4, 12.1, and 7.6, respectively. Animals reared intensively exhibited slightly different color parameters, with values of 35.7, 11.4, and 7.7 for
L*,
a*, and
b*, respectively. Regarding the aforementioned research [
13], the lower values of the
L* color parameter and higher values of the
b* color parameter observed in the meat of Istrian donkeys and Littoral Dinaric donkeys could be primarily attributed to their older slaughter age and the extensive grazing rearing method.
Regarding the composition of the meat of the Istrian donkey and the Littoral Dinaric donkey, no significant differences were found in terms of moisture, protein, fat, and ash content. Pinto et al. [
14] confirmed the lower moisture, protein, and ash content, as well as the higher fat content in the meat of 12-month-old Martina Franca donkeys, which could be partially explained by their age and being fed with a higher energy meal (
Figure 1). In the meat of 12-month-old donkeys of the same breed, a higher moisture content and lower protein and fat content were determined [
13]. At 15 months of age, the meat showed lower contents of moisture, fat, and ash, but higher protein content [
11]. Additionally, the protein and fat contents in donkey meat were lower at 18 months of age [
12]. Under extensive management conditions, Polidori et al. [
13] found higher moisture and ash content, as well as lower protein and intramuscular fat content, in the meat of male crosses (Martina Franca × Ragusana). The observed variations in the meat composition can be explained by factors such as age, sex, breed, and management practices (including feeding), as supported by previous studies [
11,
13].
Regarding the individual fatty acids, four fatty acids dominated, including two saturated (C16:0, C18:0) and two unsaturated (C18:1n-9, C18:2n-6), which aligns with findings from previous studies [
13,
15]. When considering the fatty acids composition in the intramuscular adipose tissue of the Istrian donkey and Littoral Dinaric donkey, UFA dominated, with a higher proportion of MUFA compared to PUFA. Previous studies [
13,
14,
15] also reported a lower proportion of SFA compared to UFA (41.48% vs. 58.52%; 38.51 vs. 61.49%). The content of PUFA in the intramuscular fat tissue of Istrian donkey and Littoral Dinaric donkey meat (24.21%, 24.59%) was higher than the determined content in the Martina Franca donkey meat (13.02, 16.55%) [
14], but lower than the share of 28.08% in extensively reared Martina Franca × Ragusana crosses [
13]. The determined values of the atherogenic index (0.66, 0.70) were higher than those reported by Polidori et al. [
13], but lower than the values determined by Polidori et al. [
11]. The content of n-3 PUFA in the intramuscular adipose tissue of Istrian donkey and Littoral Dinaric donkey meat was higher than the values determined in previous studies [
13,
15]. From the nutritional and health perspectives, the overall indicators of meat composition and the fatty acids profile in the intramuscular adipose tissue of donkey meat indicated that it was a favorable food choice.
The identified indicators of carcass and meat characteristics, such as pH, color, and chemical composition, play a crucial role in optimizing the production program and marketing of meat from local donkey breeds. These indicators help to ensure that the meat meets the preferences and expectations of consumers in regions where donkey meat is traditionally consumed. For instance, in the Istrian peninsula, which is the breeding area of the Istrian donkey, donkey meat has a long-standing tradition of consumption. On the other hand, in the breeding area of the Littoral Dinaric donkey, donkey meat consumption is not common. Modern consumers have shown a growing interest in leaner meat with low fat content, and also pay great attention to animal feeding management [
35]. Therefore, by considering these consumer preferences and aligning production practices accordingly, the marketability and acceptance of donkey meat can be enhanced. This includes ensuring appropriate feeding strategies to achieve desired meat characteristics and meeting the demand for lean and high-quality meat products. By responding to consumer expectations and preferences, local donkey breeds can effectively cater to the evolving market demands and promote their meat in a sustainable and consumer-friendly manner. The established quality indicators of local donkey breeds serve as valuable tools to educate existing consumers and attract new consumers to donkey meat. The objective is to promote the increased consumption of donkey meat, thereby boosting the demand for this type of meat. This increased demand not only contributes to the reproductive efficiency and self-sustainability of local breed populations, but also supports the overall viability of these breeds. To effectively promote donkey meat, it is important to utilize meat productivity indicators in determining the pricing of live animals intended for meat production, as well as the final meat products, taking into account the level of finishing. By incorporating these indicators into the pricing structure, the value and market positioning of donkey meat can be accurately reflected. By focusing on enhancing consumer awareness and understanding of the quality attributes of donkey meat, coupled with appropriate pricing strategies, the goal of increasing consumption and creating a sustainable market for donkey meat can be achieved. This, in turn, will contribute to the long-term preservation and viability of local donkey breed populations. Considering the ratio of live animal weight, carcass weight, and boneless meat for Istrian donkeys (SBW:CCW:BMW) as 100.00:50.25:28.27, the minimum price per kilogram of live weight, carcass and meat (excluding transport, slaughter, cutting, and other costs) would be 1.00:1.99:3.54. For Littoral Dinaric donkeys, using the same indicators (100.00:49.52:26.18), the minimum price ratio would be 1.00:2.02:3.82 for a kilogram of live weight, carcass, and meat (excluding additional costs). To illustrate with the example of Istrian donkeys, if the price of the live donkeys was set at 4.00 EUR/kg, the minimum price ratio for live weight, carcass, and meat would be 4.00:8.09:15.28 EUR/per kg. These production and quality indicators of local donkey breeds in meat production serve as valuable insights into the donkey breed’s potential, and can be utilized in a well-balanced program for its economic exploitation.
4.2. Donkey Milk
The significantly higher milk yield of Istrian donkeys compared to Littoral Dinaric donkeys can be primarily explained by the larger body size of Istrian donkeys [
7]. In a previous study [
23], Littoral Dinaric donkeys raised under extensive feeding conditions (hay and pasture without concentrate) yielded 180.7 mL/milking in the third month of lactation. However, in the current study, Littoral Dinaric donkeys fed a daily mixture of oats and barley ranging from 1.0 to 1.5 kg/day achieved a milk yield of 443.1 mL/milking. Salimei et al. [
21] reported a milk yield of 740 mL/milking for the Martina Franca and Ragusana breeds. Other studies have shown that the milk yield of Ragusana jennies ranged from 590 mL/milking to 1080 mL/milking [
17,
18,
19,
20,
21], and that of Amiatia jennies ranged from 379.08 mL/milking [
27] to 771.11 mL/milking [
28]. Various factors influence milk yield. Research has shown that extending the interval between milkings to 8 h instead of 3 h and conducting milking in the morning rather than in the evening results in a higher milk yield [
36]. The average milk yield per milking was highest when milking was carried out three times per day instead of once per day and when milking frequency was 3 h instead of 2 h [
37]. The pH of Istrian jennies’ and Littoral Dinaric jennies’ milk (7.05, 6.86) determines was lower than the values found in previous studies [
17,
20,
28,
38,
39], which ranged from 6.92 [
28] to 7.49 [
20].
Based on the composition analysis of milk from the Istrian jennies and the Littoral Dinaric jennies, the values of lactose, protein, fat, and ash content fell within the range of the previously determined values [
17,
18,
20,
21,
22,
23,
25,
26,
27,
28,
29,
38,
39,
40,
41]. These studies reported lactose content ranging from 5.75 to 7.25%, protein content ranging from 1.42 to 2.04, fat content ranging from 0.11 to 1.16%, and ash content ranging from 0.36 to 0.51% (
Figure 2).
The count of somatic cells and microorganisms in the milk of the Istrian jennies and the Littoral Dinaric jennies was relatively low, consistent with previous research findings. Malacarne et al. [
20] reported higher values of somatic cell count (SCC) and microorganism count (MC) in Ragusano jennies (4.82 log10 mL
−1 and 4.73 log10 mL
−1, respectively), whereas Alabiso et al. [
17] and Giosuè et al. [
18] found lower SCC values (3.89 log10 mL
−1 and 3.90 log10 mL
−1, respectively) in the same breeds. Milk from Arcadian jennies showed a low count of microorganisms and somatic cells, with an average of 4.4 log10 mL
−1 and 4.8 log10 mL
−1, respectively [
24]. A slightly higher SCC (4.09 log10 mL
−1) was observed in milk from Littoral Dinaric jennies in a previous study [
23]. These findings indicate a high level of hygiene in donkey milk, with no significant differences observed in the counts of somatic cells and microorganisms among the studied breeds.
Saturated fatty acids are more represented in the milk fat of Istrian jennies and Littoral Dinaric jennies, which aligns with findings from previous studies [
21,
29,
42,
43,
44]. A higher share of UFA was detected in the milk fat of Zamorano-Leonese and Nordestina breeds [
26,
39] (
Figure 3). The prevalence of MUFA over PUFA was consistently observed in several earlier studies [
21,
26,
29,
39,
42,
43]. The dominant fatty acids were two saturated fatty acids (C14:0 and C16:0) and two unsaturated fatty acids (C18:1n-9 and C18:2n-6) [
38,
39,
42]. Notably, a significant content of linoleic fatty acids (C18:3n-3) was found in the milk of donkeys of Zamorano-Leonese and Nordestina breeds (12.32% and 6.51%, respectively) [
26,
39]. Some studies [
26,
38,
42,
45] reported significant levels of C8:0, C10:0, and C12:0 fatty acids, which were not observed in the milk fat of Istrian jennies and Littoral Dinaric jennies.
Indices commonly used as indicators of the health benefits of donkey milk to consumers include the UFA/SFA ratio, PUFA/SFA ratio, n-6/n-3 PUFA ratio, atherogenicity index (AI), and the thrombogenicity index (TI). The content of n-3 PUFA fatty acids in milk fat (5.50, 3.07) further confirms the favorable fatty acid profile for consumer health. Martemucci et al. [
43] found lower values for the n-6/n-3 PUFA ratio, AI and TI (1.81, 1.16, and 0.70, respectively), and higher values for UFA/SFA and PUFA/SFA ratios (0.92, 0.39) in Martina Franca jennies’ milk. Cavalcanti et al. [
26] observed lower index values for n-6/n-3 (1.19), AI (0.85), and TI (0.59) in Nordestina jennies’ milk. Ragona et al. [
29] reported lower values for UFA/SFA, PUFA/SFA, and n-6/n-3 ratios (0.80, 0.37, 1.65) in the Amiatia donkey breed, and the same indices were lower (0.48, 0.25, 0.86) in the milk of Ragusana jennies [
20]. Lazarević et al. [
40] observed similar UFA/SFA, PUFA/SFA, and n 6/n-3 indices in Balkan jennies’ milk (0.81, 0.27, 1.03). The reported indices for Zamorano-Leonese jennies’ milk were 1.25, 0.62 and 1.16, respectively [
39].
Donkey milk has been valued for its nutritional properties for thousands of years. Its composition, particularly in terms of protein and lipid content, closely resembles human milk, making it historically used in infant feeding. Donkey milk contains lower amounts of casein and β-lactoglobulin, which are potential allergenic components, making it a suitable alternative for individuals with a cow’s milk allergy [
46,
47]. The high concentration of unsaturated fatty acids in donkey milk holds importance in preventing cardiovascular, autoimmune, and inflammatory diseases [
42]. Wolter [
48] highlights the beneficial effects of milk on osteogenesis, atherosclerosis treatment, and the rehabilitation of patients with cardiac problems and diseases. Lysozyme, lactoperoxidase, and lactoferrin present in donkey milk are known as antimicrobial and bacteriostatic agents [
39,
49,
50], offering potential benefits for intestinal health, particularly in individuals with weakened immune systems such as children, the elderly, and convalescents. In Croatia, donkey milk has been traditionally used for centuries to treat respiratory diseases, especially whooping cough in children, which has colloquially been referred to as “donkey cough” due to its association with the treatment. The identified indicators of local donkey breeds’ milk production potentially highlight their significant value. To fully exploit this potential, it is crucial to promote the preference for donkey milk consumption, emphasizing its potential functional and health benefits. Although donkey milk production per milking is relatively modest compared to cows, sheep, or goats, its high market price (EUR 35/kg in Croatia) has sparked interest in this type of production. It is important to note that donkey milk production is closely tied to reproduction, as new offspring are necessary for both milk and meat production. Therefore, the production of donkey milk and donkey meat should be considered in conjunction.