Mare milk nitrogen fractions during lactation and determination by reversed-phase HPLC of the major whey proteins

Abstract

P. 2005. Mare milk nitrogen fractions during lactation and determination by reversed-phase HPLC of the major whey proteins. Can. J. Anim. Sci. 85: 93-99. The aim of this research was to describe the changes of the nitrogen fractions in milk of Haflinger nursing mares and in particular to determine the whey protein content and distribution, and their evolution throughout the first 6 mo of lactation. Samples were collected by hand-milking on days 4, 20, 40, 60, 80, 120, 150 and 180 post-partum. Nitrogen fractions were determined by Kjeldahl on 80 samples from 10 mares, while HPLC separation of whey proteins was conducted on 40 samples from 5 mares. The total N, casein N, and true whey protein N contents showed a statistically significant decrease from day 4 to day 40, and then remained unvaried. In general, the nitrogen distribution of mare's milk significantly changed between day 4 and day 20 and then remained almost unchanged until day 180 (except for the day 150 value, which showed a statistically significant increase for CN × 100/TN). β-Lactoglobulin and serum albumin contents showed a marked reduction, of 27 and 45.5%, respectively, between day 4 and day 20, and then remained unchanged; α-lactalbumin and immunoglobulins contents had a reduction of 24.7 and 38.3%, respectively, between day 4 and day 20, and another decrease between day 20 and day 40, of 20 and 32.8%, respectively. All whey proteins, expressed as a percentage on the total sum of the four whey proteins considered, did not vary significantly during lactation. However, the sum on the two whey proteins of mammary gland origin (β-Lg + α-La) increased between day 4 and day 20 by 6.3%, and between day 20 and day 40 by 3.8%; the sum of the whey proteins of blood origin (SA + Ig) showed an opposite trend, with a decrease by 14.5% between day 4 and day 20 and by 11% between day 20 and day 40. Mots clés: Lait de jument, stade de la lactation, distribution des protéines du lactosérum, HPLC en phase inverseThe duration of lactation in mares is 5-8 mo , and in Italy it is usually about 180 d. The colostral period of mares is much shorter than that of cows, and the colostrum shows significant differences from normal milk only on the first day after foaling (Neseni et al. 1958;Ullrey et al. 1966;Csapó et al. 1995). 93Abbreviations: HPLC, high pressure liquid chromatography; N, nitrogen; TN, total nitrogen; CN, casein nitrogen; NCN, non-casein nitrogen; NPN, non-protein nitrogen; d, day of lactation; β-Lg, β-lactoglobulin; α-La, α-lactalbumin; SA, serum albumin; Ig, immunoglobulin; CV, coefficient of variation Can. J. Anim. Sci. Downloaded from www.nrcresearchpress.com by 52.36.4.81 on 05/11/18For personal use only.

Equid milk for human consumption

“…The protein content decreases by 20e25% from d 28 to d 150 in horse (Doreau & Martin-Rosset, 2011;Mariani et al, 2001;Martuzzi, Summer, Formaggioni, & Mariani, 2004;Summer, Tirelli, Formaggioni, Malacarne, & Mariani, 2005;Ullrey, Struthers, Hendricks, & Brent, 1966) and donkey milk (Giosuè et al, 2008;Guo et al, 2007;Salimei et al, 2004a). In equids, the milk nitrogen fractions are also reported to be influenced by the length of the lactation period.…”

“…In equids, the milk nitrogen fractions are also reported to be influenced by the length of the lactation period. The casein content declines by approximately 20e30% in horse (Mariani et al, 2001;Martuzzi et al, 2004;Summer et al, 2005) and donkey milk (Fantuz, Maglieri, Varisco, La Manna, & Salimei, 2009b;Giosuè et al, 2008) while results on the non-protein nitrogen (NPN) milk content during lactation are not conclusive. No significant trends are reported for horse milk NPN by Mariani et al (2001) and Summer et al (2005) but not by Martuzzi et al (2004), who observed a significant decline during lactation, consistent with reports by Guo et al (2007) for donkey milk.…”

5’-flanking variants of the equine α-lactalbumin (<i>LALBA</i>) gene – relationship with gene expression and mare’s milk composition

“…However, it should be underlined that noticeable differences in equine milk α-LA occur between various investigations. For example, in a study by Summer et al (2005) the mean concentration of α-LA was 1.6 g/l, while in the experiment by Markiewicz-Kęszycka et al (2013) this protein was more abundant (2.2 g/l). Moreover, a significant variability in α-LA content was observed between various mares analysed in the same study.…”

Genes encoding equine β-lactoglobulin (LGB1 and LGB2): Polymorphism, expression, and impact on milk composition

“…It seems that selected equine LGB gene variants can be considered potential markers for these particular traits; however, further studies with larger animal groups of different horse breeds are necessary. Associations between β-lactoglobulin polymorphisms and total milk protein and/or fat concentration have previously been described for cattle [12,42,43] and sheep [44,45]. We have also recorded a relationship between genotypes in rs1151091548 (LGB1) and rs1147750066 (LGB2) SNPs and the milk lactose level of PPH and PCH mares, respectively.…”

“…However, some different values have been found by different investigations. For example, Summer et al (2005) [12] found the mean concentration of LGB in equine milk to be 2.8 g L -1 , while Markiewicz-Kęszycka et al (2013) [13] recorded a slightly lower value (2.6 g L -1 ).…”