Qualitative Characteristics of Jenny Milk

Producing jenny milk may be an interesting, profitable and alternative activity for farmers, mainly in southern marginal areas. However, in Basilicata, there are still few farmers that produce jenny milk. This is mainly due to poor farm consistency, which, in turn, makes it difficult to start this type of production. Moreover, the regional land conformation does not help the market of the milk, and the cost of production is much higher than cow milk for limited daily production. Overcoming these kinds of difficulties is fundamental to exploit all the commercial opportunities that jenny milk can offer.

Considering its unique nutrient profile, jenny milk may be easily employed to satisfy the nutritional requirements of newborn, heart and cholesterolemic patients. In particular, cow milk allergy, heart ageing and cholesterolemic diseases are considered to be increasing problems, and, for these reasons, the acquisition of new knowledge on jenny milk is very important in clinical and nutritional aspects. However, little is known about qualitative and quantitative characteristics of jenny milk. Although the species is a seasonal polyestrous, in south of Italy, jennies foal every season, probably because of small photoperiod oscillations between different seasons, and, consequently, milk is available all year (Giosue` et al. 2008). During lactation, this species has a low but constant daily production (Malacarne et al. 2002; Polidori et al. 2009a). Production level is influenced by several aspects, such as stage of lactation, milking technique, presence of the foal and foaling season (Dell'Orto et al. 1993; Oftedal et al. 1983). In particular, during milking, the presence of foal and the stage of lactation influence fat and protein content. Moreover, lactose content is constant during lactation, being independent of breed, milking time and stage of lactation (Guo et al. 2007). Jenny milk composition is similar among subjects from different continents, except for fat content (Blasi et al. 2008; Ivankovic´ et al. 2009).

Cosentino et al. (unpublished data) evaluated some aspects of donkey rearing that include the influence of lactation stage (30, 90 and 150 days from foaling) and of foaling season (spring and summer) on some qualitative aspects of jenny milk, in a farm situated at an altitude of 700 m a.s.l. in a protected area of Appennino Lucano National Park. The research was carried out on 23 jennies belonging to a local population and aged between 7 and 10 years. These jennies foaled in two different periods: spring and summer (12 and 14 jennies, respectively). Milk samples were collected monthly, in the periods March–August in spring group and July–November in summer group. During the trial period, jennies were confined in boxes with a large paddock, in order to avoid the effect of grazing on qualitative characteristics of milk. Animals were offered a diet consisting of ad libitum oat hay and of an integration of 3 kg of concentrate, characterised by the following mixture: 37 % flaked corn, 30 % oats, 9 % locust bean crushed, 8 % wheat bran, 8 % dehydrated alfalfa, 6 % beet pulp dried and 2 % minerals and vitamin supplement. Diet was dispensed twice a day: during milking and in the evening. From the second month after delivery, jennies were milked by mechanical milking (40 kPa vacuum level, 60 pulse per min), at 11:00 am. From 8:00 am to the end of milking, foals were separated from mares, but were kept in the adjacent box maintaining the visual and the acoustic contact.

Immediately after collection, on milk individual samples were measured: pH and titratable acidity, protein, fat, lactose, dry matter and ash content. In addition, somatic cell count (SCC), expressed as somatic cell score (SCS, log10n x 1,000/ mL), was determined.

The groups showed a milk production trend similar to that observed in literature by other authors (Giosue` et al. 2008; Santos and Silvestre 2008). Milk production, protein, ash, SCS and pH resulted highest in summer at 30 days; protein and pH resulted highest in summer also at 90 and 150 days, respectively (Table 1). Ash content in tendency decreased during lactation. The highest mineral content, at the start of lactation, is particularly important for the first growth stage of the young foal (Csap,o-Kiss et al. 1995). During lactation, pH values varied significantly between groups. SCS values observed from other authors ranged from 3.94 to

4.34 (Beghelli et al. 2009; Finocchiaro and Conte 2009; Ivankovic´ et al. 2009). In spring group, protein content was high at the start of lactation, decreased to a minimum at 90 days and increased at the end of lactation, as observed by Guo et al. (2007); instead, summer lactation showed two peaks at 30 and at 90 days. Protein content resulted lower than the values reported by other authors that studied the effects of seasons on jenny milk characteristics: 19.3 g/L in spring and 18.1 g/L in summer in Sicilian breeds (Giosue` et al. 2008) and 16.5 g/L in spring and 14.3 g/ L in summer in Croat breed (Ivankovic´ et al. 2009). Fat content was significantly highest in summer group at the end of lactation. The average fat content of jenny milk was similar to mare milk and was much lower than other mammals; other authors observed values in the range 0.01–1.8 %. Lactose content and dry matter resulted significantly the lowest in summer only at 30 days. In the other periods, lactose was not influenced by the considered factors, as reported in literature (Oftedal and Jenness 1988; Santos and Silvestre 2008); dry matter content was in agreement with values reported in the literature for equine milk (Malacarne et al. 2002; Miranda et al. 2004); Ivankovic´ et al. (2009) observed in Croat jenny values that ranged from 8.61 to 9.13 %. Titratable acidity (SHo) resulted highest in summer lactation at 90 and at 150 days, value lower than in cow's milk, attributable to the low content in casein and in phosphate (D'Auria et al. 2005; Guo et al. 2007).

Table 1 Jenny milk parameters (mean ± SE)

Means within periods with different superscripts significantly differ: a, b ¼ P < 0.05; A, B ¼ P < 0.01

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