¹ Research program co-financed by "Università degli Studi di Parma" and "Ministero dell'Università e della Ricerca Scientifica e Tecnologica", 1998.
²Communication presented at the 2nd congress "Nuove acquisizioni in materia di alimentazione, allevamento e allenamento del cavallo sportivo", Campobasso, 13-14 October 2000.

³ Istituto di Zootecnica Alimentazione e Nutrizione, Università degli Studi, Via del Taglio 8, 43100 Parma.

Introduction

The foal, in the various phases of the suckling period, has at its disposal milk amounts that are sufficiently defined [1, 2], but rather variable [3], usually increasing during the first weeks of life. The availability of the nutrients varies considerably also in relation to the evolution of milk quality during the lactation cycle [4-6]. The knowledges, under this profile, with particular reference to the variables characterising the "plastic" and energy value of milk, are not well defined yet. There are several contrasting indications, for example, about the trend of fat content, as well as about the degree of protein and salt impoverishment in the milk, also in correspondence of the most tricky phases of development for the foal [4, 7-11].

Aim of this work was to give a contribution to the knowledge of the main properties of Haflinger nursing mare milk, with particular reference to their trend during 6 lactation months.

Materials and methods

The study was carried out on individual milk samples of 5 nursing mares of Haflinger Horse breed, reared in a stud in Brescia province (Northern Italy). The mares, from 7 to 14 years of age (4 ¸ 11 parities), live weight between 400 and 490 kg, were fed hay and perennial rye-grass, in prevalence, and lucerne, ad libitum. Concentrate was given occasionally, in moderate quantity (max. 3 kg), only to some mares during the 1^st and 4^th/5^th lactation month. Deliveries, all regular, happened in March (2), April (2) and May (1). Milk samplings (8 per mare) were collected at d 4, 20, 40, 60, 80, 120, 150 and 180 post-partum, for a total collection of 40 individual samples. Milk was taken by hand-milking from a single mammary gland, milked as deep as possible, in presence of the foal, that was previously prevented from suckling for 1 - 2 hours by a muzzle.

On the single milk samples the following analyses were carried out: pH by a potentiometer; titratable acidity (°SH) with 0.25N NaOH according to Soxhlet-Henkel method [12]; density at 15°C by means of Quevenne lactometer; freezing point by a thermistor cryoscope; total solids on 20 g milk at 102°C for 6 hours; fat and lactose by means of mid infrared lectures [13] with Milko-Scan 134A/B; total N and non protein N (NPN) by Kjeldahl [14]; ash on 20 g milk at 530 °C. Gross energy (kcal/kg) was calculated by coefficients reported by Oftedal et al. [15], in particular 9.11 for fat, 5.86 for true protein, 7.40 for non protein N and 3.95 for lactose. Data were analysed by two way ANOVA (fixed effect: lactation stage; random effect: mare) and least significant difference test application.

Results and discussion

a) Physico-chemical properties. - The values of density and freezing point have a specular trend (Table1). The density, starting from the 4^th day post-partum to the 60^th lactation day, decreases significantly (from 1.038 to 1.035). In the same period, the freezing point varies considerably (from - 0.536 to - 0.520 °C), going towards the water freezing point. In the following phases, until the 180^th lactation day, the values of these two properties tend to maintain a rather constant trend, precisely about 1.035 for the density and - 0.524 °C for the freezing point.

Milk produced near the partum has a low pH (6.60) and a fairly high titratable acidity (6.08 °SH at the 4^th day). During the following 2-3 weeks the values of both properties vary deeply in a specular way: pH markedly increases (6.93) and titratable acidity drastically decreases (3.40 °SH at 20^th day) (Fig. 1). In the following phases of the lactation the variations are moderate, but sufficient to indicate the tendency of a pH increase (7.11) and a titratable acidity decrease (2.01 °SH at 180^th day). Variations relative to the pH are in rather good agreement with those observed by Johnston et al. [16] during the first two weeks of lactation. Regarding titratable acidity values there is a substantial agreement with Storch [17], but not with the observations of Kulisa [18], that reports a quite peculiar trend, characterised by a considerable increase of the titratable acidity values from the 60^th (2.83 °SH) to the 150^th lactation day (3.61 °SH).

b) Chemical constituents. - Also for the chemical components, the most important variations are registered between the 4^th and the 20^th/40^th lactation day (Table 1; Fig. 1). All the main constituents decrease, except lactose, that, on the contrary, increases. In correspondence of the 20^th lactation day more significant variations are registered both for fat (- 37%), and for protein (- 32%), as well as for ash (- 18%) and for lactose (+5%). Crude protein and ash further decrease significantly, also in correspondence of the 40^th lactation day (- 18% and - 17%, with respect to 20^th day).

Fat content rather rapidly decreases during the first 60/80 days; subsequently there is a little increase of the values that, however, in correspondence of the 180^th day reaches the minimum value of the entire lactation (from 1.66 to 0.44 g per 100 g; decrease 73%). Such variations agree enough with data reported in literature [1, 8, 19-21] for lactations with a duration of at least 4 - 5 months. In other cases, instead, more moderate variations, or rather irregular trends [2, 17], were observed. The fat content increase, registered at the 4^th/5^th month, agrees with the observations of Kulisa [22] and Brzeski and Kulisa [23].

Protein content, instead, progressively decreases during the entire lactation (from 3.29 to 1.63 g per 100 g; decrease 50%). The protein impoverishment of the milk is confirmed by several Authors [2, 8, 19, 20, 24, 25], while in other ones the variations appear more gradual [1, 11, 22, 26, 27], or rather irregular [17]. Rather analogous is the trend of ash content, that, however, in the first phases of the lactation shows a less accentuated decrease (from 0.57 to 0.27 g per 100 g; decrease 53%) than the protein content. This trend is substantially confirmed by other observations [1, 8, 19-21, 28].

Lactose content, on the contrary, increases progressively until the 180^th day (from 6.36 to 6.88 g per 100 g; increase 8%), in particular during the first lactation weeks, to partially counterbalance the losses of total solids. Several studies tend to confirm that mare milk during lactation becomes rich of carbohydrates [1, 8, 11, 19-21, 29], also if there are some contrasting indications [22, 30]. Kulisa [29], at the end of the lactation (5^th month), registers a decrease of lactose that confirms the observations of Krasnova [30] for the 4^th/6^th month; this fact, however, is in contrast with Sonntag et al. [11], that at the end of the lactation found markedly increasing lactose values.

c) Gross energy. - The variations of energy value of milk reflect those relative to organic components, precisely true protein and fat that decrease and lactose that increases (Table 1; Fig. 1). Total energy significantly decreases between 4^th and 20^th day (- 18%), but registers a further decrease also in correspondence of the 40^th day (- 8%). From 4^th to 180^th lactation day, milk energy value, despite of the higher contribution of lactose, decreases progressively and in a significant way (from 583 to 398 kcal per kg; decrease 32%). Such variations are in agreement with the observations of Ullrey et al. [20], Burns et al. [31] and Mariani et al. [8]. Analogous indications, but relative only to the first 2 months of lactation, are reported also by Oftedal et al. [15], Doreau et al. [5] and Martin et al. [32], while Doreau et al. [33], in the same period, don't find any considerable variation.

Conclusions

Physico-chemical properties, chemical composition and energy value of Haflinger nursing mare milk significantly modify during 6 lactation months. The most important variations concern the initial phases of the lactation, such as to deeply affect the plastic and energetic value of the milk, the only nutritional source for the young foal in full development. In little more than 1 month, fat (- 51%), protein (- 45%) and ash (- 32%) contents decrease drastically. Consequently, also energy value of the milk decreases (- 24%), despite of the increase of lactose content. Protein supply, equal to 33 g per kg milk at the 4^th day, in correspondence of the 40^th day is reduced to 18 g; fat supply, likewise, varies from 17 to 8 grams.

Key words: Haflinger Horse, nursing mares, lactation stage, milk characteristics.

Parole chiave: Cavallo Avelignese, giumenta, stadio lattazione, caratteristiche latte.

Mots clés: Cheval Avelignais, jument, stade de la lactation, caractéristiques du lait.

SUMMARY - The trend of the main characteristics of the milk of Haflinger nursing mares in the course of the entire lactation was studied. Density, pH, titratable acidity, total solids, fat, protein, lactose and ash varied significantly, while the freezing point showed modifications statistically not significant. The contents of protein, fat and ash diminished; also the gross energy value tended to reduce, despite of the lactose content increase. The individual differences and the variations of the composition of milk in relation to the lactation stage appeared important for the effects on the ability to development of the foal, in special way in the first weeks of life, when the feeding is exclusively or mostly milk.

RIASSUNTO - Caratteristiche chimico-fisiche e valore energetico del latte di cavalle di razza Avelignese nel corso di 6 mesi di lattazione.

È stato studiato l'andamento delle principali caratteristiche del latte di cavalle nutrici di razza Avelignese nel corso dell'intera lattazione. Densità, pH, acidità titolabile, sostanza secca, grasso, proteina, lattosio e ceneri variano significativamente. Diminuiscono i contenuti di proteina, grasso e ceneri; anche l'energia grezza tende a diminuire, nonostante l'aumento di contenuto in lattosio. Le differenze individuali e le variazioni della composizione del latte in rapporto allo stadio di lattazione appaiono importanti per gli effetti sulle capacità di sviluppo del puledro, in special modo nelle prime settimane di vita, quando l'alimentazione è esclusivamente o prevalentemente lattea.

RÉSUMÉ - Caractéristiques chimico-physiques et valeur énergétique du lait de jument de race Avelignaise pendant 6 mois de lactation.

On a étudié l'évolution des principales charactéristiques du lait de jument de race Avelignaise pendant une entière lactation. Densité, pH, acidité de titration, matière seche, matière grasse, matière azotée, lactose et cendres montrent une significative variation. Se réduisent les teneurs de matière azotée, matière grasse et cendres; la valeur énergétique, aussi, tend a décroitre, malgré l'augmenter du lactose. Les différences individuelles et les variations de la composition du lait in relation au stade de la lactation semblent importantes pour les effets sur les capacités de développement du poulain, sourtout pendant les prémières semaines de vie, quand l'alimentation est exclusivement ou pour la plupart constituée de lait.

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