CALCIUM, PHOSPHORUS AND MAGNESIUM IN THE MILK OF NURSING MARES FROM ITALIAN SADDLE HORSE BREED AND THEIR VARIATIONS DURING LACTATION*

F. Martuzzi, A.L. Catalano, A. Summer, P. Mariani

Istituto di Zootecnica, Alimentazione e Nutrizione, Università degli Studi, via del Taglio 8 - 43100 Parma

* Contributed paper at the 48th Annual Meeting of EAAP, Wien, 25-28 August 1997
This work was supported by MURST 60%

Introduction

The foal in the first two months of his life shows a particularly high growth rate (Doreau, 1994). The milk, in this critical period, especially during the first month, is the main feed of the foal, the source of all nutrients (Doreau et al., 1986; Martin et al., 1992). Mineral metabolism, particularly calcium and phosphorus metabolism, is of basic importance relating to the impressive skeletal development of the animal (N.R.C., 1989; Thatcher, 1991; Wolter, 1996).
The mineral composition of mare milk was studied by several Researchers (see reviews: Neuhaus, 1959; Doreau & Boulot, 1989). Regarding Ca and P contents the observed values appear quite variable, particularly that related to the P content. To a great extent, the variations are linked to the lactation stage (Neseni et al., 1958; Ullrey et al., 1966; Schryver et al., 1986; Smolders et al., 1990; Mariani et al., 1993). Nevertheless remarkable differences are noticed even in equal lactation stage (Ullrey et al., 1966; Schryver et al., 1986).
Beside the cited Authors (Neseni et al., 1958; Ullrey et al., 1966; Schryver et al., 1986; Smolders et al., 1990; Mariani et al., 1993), several other Authors studied Ca and P contents in the mare milk (Holmes et al., 1947; Baucus et al., 1989; Doreau et al., 1990; Doreau et al., 1992; Orlandi et al., 1992; Csapò-Kiss et al., 1995). Some of them with specific reference to the saddle breeds (Bouwman & Van der Schee, 1978; Miraglia et al., 1987; Smolders et al., 1990; Mariani et al., 1993).
Aim of this research was to study the basic mineral composition of the milk of nursing mares of the Italian Saddle Horse breed, as well as to consider its variations throughout the main phases of the lactation cycle.

Materials and methods

The study was carried out on milk samples of 21 nursing mares of the Italian Saddle Horse breed, reared in 8 different studs in Parma, Piacenza and Cremona provinces (North Italy). The mares, averaging 500-600 kg in body weight, aging from 3 to 20 years (1¸14 parities) were fed with hay ad libitum and 4-5 kg of commercial concentrate with 16% crude protein on dry matter.
The milk sample was obtained by manual milking of one gland, while the foal was suckling the other. In the 2 hours before the milking, the foal was prevented from suckling by a muzzle. Altogether, 54 individual milk samples were analyzed: 50 samples were collected between the 3^rd and the 120^th day of lactation, while 4 samples were taken from as many mares at drying-off (166¸196 d post partum) by injection of 20 IU of oxytocin.
Ash was determined in muffle at 530°C (Savini, 1946), Ca and Mg by atomic absorption spectrometry (Anon., 1982) and P by colorimetry (Allen, 1940). Statistical significance of the differences among the observed mean values was tested by ANOVA.

Results and discussion

In the table 1 the mean values of ash, Ca, P and Mg are reported. The ash content varies from 0.31 to 0.70 g per 100 g of milk. The mean value, equal to 0.467 g, is comparable to the values observed for the milk of other saddle breeds (Bouwman & Van der Schee, 1978) or similar breeds (Ullrey et al., 1966; Schryver et al., 1986; Martin et al., 1992). Ca, P and Mg contents result 106.5 mg, 63.5 mg and 7.6 mg per 100 g of milk respectively. All three elements show high variability. Ca varies from 66 to 167 mg and P from 31 to 118 mg. Ca:P ratio results equal to 1.68 (min. 1.15; max. 2.25).

In the table 2 the observed values are compared to those reported from other Authors, referring to the first lactation month. The mean value of Ca content is comparable to those found in the milk of Dutch Saddle mares (Bouwman & Van der Schee, 1978; Smolders et al., 1990) and similar breeds, like Thoroughbred, Arabian and Quarter Horse (Ullrey et al., 1966; Schryver et al., 1986). Recently Cauvin et al. (1997) in the milk of Italian Saddle mares found 123 mg of Ca per 100 ml. P content values result according to that of Dutch Saddle breed (Bouwman & Van Der Schee, 1978; Smolders et al., 1990), as well as to that of Thoroughbred (Schryver et al., 1986); while the values found by Ullrey et al. (1966) for Arabian and Quarter Horse appear definitely lower. The Mg data too are according enough to those found in the milk of some breeds comparable to the saddle breeds (Ullrey et al., 1966; Schryver et al. 1986; Baucus et al., 1989).

The mineral composition of the milk of the first 120 lactation days is shown in table 3. In the same table are reported the values of the milk taken at drying-off referring to 4 mares. Significant variations are observed. The milk produced from the 3^rd to the 15^th day of lactation results clearly richer of ash (0.601 g), Ca (135.5 mg), P (87.5 mg) and Mg (10 mg) than that produced in the following phases of the productive cycle. The milk at the beginning of the lactation results quite provided with P (Ca:P = 1.55); the values of the Ca:P ratio tend to increase throughout lactation, even though not significantly. The milk produced during the 2^nd lactation month contains 25% less Ca and 30% less P. The milk of the 4^th month contains 45% less Ca and 49% less P, always comparing to the first 2 weeks post partum. The milk of the last milking, taken at drying-off, results the poorest both in Ca (68.5 mg) and in P (35.7 mg).

The variations related to the lactation stage are according with those observed by other Authors for saddle breeds (Smolders et al., 1990; Mariani et al., 1993), for saddle-like breeds (Ullrey et al., 1966; Schryver et al., 1986), as well as for other breeds (Neseni et al., 1958; Doreau et al., 1990; Doreau et al., 1992; Csapò-Kiss et al., 1995). Nevertheless, there are partially contrasting observations (Holmes et al., 1947; Bouwman & Van der Schee, 1978; Baucus et al., 1989).
In table 4 individual variability in the mineral composition is shown, limited to the milk produced by 5 nursing mares. Ca content varies to a great extent (from 83 mg of the mare 2 to 118.7 mg of the mare 3). P variability results important too (from 56.7 to 71 mg). Ca:P ratio values move from 1.38 to 1.86.

Conclusions

Ca content in the milk of Italian Saddle mares appears very similar to that of other saddle breeds or saddle-like breeds, as Thoroughbred, Quarter Horse and Arabian. P content tends to agree only with the values observed in other saddle breeds, while there are disagreements both with saddle-like breeds and other breeds, generically defined "light" or "heavy".
The milk produced in the first 2 weeks post partum, after the short colostral phase, results the richest of Ca and P in relation to the considerable mineral requirements of the young foal in strong weight growth. In this stage the value of Ca:P ratio tends to be lower than in the following phases. Also the milk of the second half of the first lactation month appears fairly provided of Ca (a little less of P). Afterwards the mineral supply of the milk decreases considerably.
Due to the remarkable individual variability (i.e. for the Ca) we think that the knowledge of milk composition can be useful for right foal feeding, particularly in the first and in the second month of his life.

Keywords: Italian Saddle Horse, nursing mare, lactation stage, milk composition, mineral content.

Parole chiave: Cavallo Sella Italiano, giumenta, stadio lattazione, composizione latte, contenuto minerale.

SUMMARY. -The mineral composition of the milk of Italian Saddle mares was studied. 54 individual milk samples from 21 nursing mares were analyzed. 50 samples were collected from the 3rd to the 120^th day of lactation, and 4 were taken at drying-off (166¸196 d). Milk was obtained through complete hand milking of one gland. The mares, ranging in weight 500¸600 kg and in age 3¸20 years (1¸14 parities) were fed with hay ad libitum and 4-5 kg of concentrate. Ash was determined in muffle at 530°C, Ca and Mg by atomic absorption spectrometry and P by colorimetry. Data were analyzed by means of ANOVA. The following mean values were observed (±SE) per 100 g of milk: ash 0.467±0.013 g; Ca 106.5±3.5 mg; P 63.5±2.4 mg; Mg 7.6±0.3 mg. The milk produced from the 91^st to the 120^th day of lactation contains less Ca (74.8±4.2 mg) and less P (44.6±2.4 mg) compared to the milk produced from the 3^rd to the 15^th day of lactation (Ca 135.5±5.4 mg; P 87.5±5.1 mg). The milk collected at drying-off appears poor in Ca (68.5±1 mg) and in P (35.7±2 mg). Also the Ca:P ratio modifies, varying from 1.55±0.09 (beginning of lactation) to 1.92±0.11 (at drying-off).

RIASSUNTO. Contenuti di calcio, fosforo e magnesio nel latte di giumente di razza Cavallo Sella Italiano e variazioni durante la lattazione. E’ stata studiata la composizione chimica del latte di giumente di razza Cavallo Sella Italiano. Sono stati analizzati 54 campioni di latte individuale prelevati da 21 cavalle nutrici allevate presso 8 scuderie del nord Italia. 50 campioni sono stati raccolti tra il 3° ed il 120° giorno di lattazione, mentre 4 sono stati prelevati in corrispondenza della messa in asciutta (166¸196 d) di altrettante cavalle. Il latte è stato ottenuto mediante la mungitura manuale completa di una mammella in presenza del puledro, cui è stata impedita la suzione per 2 ore mediante l’applicazione di museruola. Le cavalle, di 500-600 kg di peso vivo, di età compresa tra i 3 ed i 20 anni (1¸14 parti), erano alimentate con fieno polifita ad libitum e 4-5 kg di concentrato al 16% di proteina grezza sul secco. Le ceneri sono state determinate in muffola a 530° C, il Ca ed il Mg mediante spettrofotometria in assorbimento atomico ed il P per via colorimetrica. Sono stati osservati i seguenti valori medi (±ES) per 100 g di latte : 0.467±0.013 g di ceneri, 106.5±3.5 mg di Ca, 63.5±2.4 mg di P e 7.6±0.3 mg di Mg. I valori si modificano profondamente nel corso della lattazione (P<0.001). Il latte prodotto dal 91° al 120° giorno di lattazione contiene meno calcio (74.8±4.2 mg) e meno P (44.6±2.4 mg) rispetto a quello prodotto dal 3° al 15° giorno di lattazione : 135.5±5.4 mg di Ca e 87.5±5.1 mg di P. Il latte prelevato in corrispondenza della messa in asciutta risulta povero sia di Ca (68.5±1 mg) sia di P (35.7±2 mg). Si modifica anche il rapporto Ca:P che varia tra 1.55±0.09 (inizio lattazione) e 1.92±0.11 (messa in asciutta).

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