Abstract
The composition of milk was studied from purebred Tsigai sheep and F2 cross-breeds with Chios breed from 4th to 6th month of lactation, raised on a mountain pasture. The chemical analysis samples were taken from each sheep in the period of April-June. The content of fat, protein and amino acids was determined in individual samples and total sample formed by the milk yield from all animals, proportional to the daily milk yield from each individual. There is a tendency for higher milk yield and content of total protein and casein in milk of F2 cross-breeds of Chios in comparison with Tsigai sheep. Milk sheep from F2 crossbreeds of Chios had higher content of Lysine, as well as glutamic acid, methionine and leucine, in comparison to that form Tsigai sheep, respectively: 0.458?0.011. 1.389?0.040. 0.084?0.005 and 0.572?0.013. The milk chemical index in both groups of sheep was comparatively low and it constituted respectively 38.3% in Tsigai sheep and 35.4% in F2 cross-breeds, as a result of low concentrations of methionine and cysteine in milk. Biological value of milk obtained from Tsigai breed sheep and F2 milk cross-breeds of Chios had close values - respectively 92.01 and 91.87%. Results showed that the sward composition and the vegetation stage had an influence over the essential amino acids content in purebred Tsigai sheep and their cross-breeds with Chios breed.
Highlights
The amount of milk proteins and their amino acid content have been studied profoundly in different animal species
Biological value of milk obtained from Tsigai breed sheep and F2 milk cross-breeds of Chios had close values - respectively 92.01 and 91.87%
Results showed that the sward composition and the vegetation stage had an influence over the essential amino acids content in purebred Tsigai sheep and their cross-breeds with Chios breed
Summary
The amount of milk proteins and their amino acid content have been studied profoundly in different animal species. The differences among species in the amount of protein in the chemical composition are influenced by the nutritional requirements of the newborn, the difference in postnatal growth rate, stage of maturity, body composition at birth, the influence of environment etc. The interest for milk proteins is related to their biological and nutritional full value or degree of retention of nitrogen in body (Gachev, 1995). Amino acid composition of proteins in sheep milk has been studied in dairy sheep breeds by a number of authors (Velev, 1986; Tanev et al, 1986; Stancheva, 2002). Mihaylova et al (2006) found higher content of proline, valine and isoleucine, as well as higher biological value in the first breed
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