Some dairy traits of Istrian ewes kept in semi-intensive farming conditions

Istrian sheep has the highest milk yield among indigenous Croatian sheep breeds though originally belongs to a group of sheep of combined production traits. Since milk of Istrian sheep is traditionally processed into cheese and that processing possibilities of milk, among other things, are defined by its chemical composition and hygienic quality, the aim of this study was to determine the influence of some environmental factors (year, parity, stage of lactation, season (month) of lambing) on daily and lactation milk yield, lactation length, milk chemical composition and the somatic cell count (SCC) in the milk of Istrian ewes. A total of 83 purebred, dairy Istrian sheep, during three consecutive lactations (from 2012 to 2014), were involved in this research. Due to conditions of feeding, care and housing, all ewes were kept in identical (semi-intensive) farming conditions throughout the whole study period. During milking period of lactation regular milking controls were carried out (AT method) and, on these occasions, individual milk samples for chemical composition analysis and determination of somatic cell count were taken. During average lactation length of 206 days Istrian ewes produced on average 190.77 kg of milk, or 1.1 kg of milk per day. Milk of Istrian ewes on average contained 6.81% fat, 5.90% protein, 4.32% lactose, 18.08% total solids and 11.31% non-fat solids. The geometric mean of SCC was 316*103*mL-1 of milk (log 5.50±0.02). A significant (P < 0.001) effect of the year is determined on the milk yield and the lactation length, as well as the chemical composition of milk (with the exception of protein) and SCC. Ewes in the fourth lactation achieved the highest average daily (P < 0.001) and lactation milk yield (P < 0.05), while the first-lambing ewes produced milk with the highest content of total solids, milk fat and proteins. Stage of lactation significantly (P < 0.001) affected the daily milk yield, milk chemical composition, as well as the somatic cell count in ewe’s milk. Ewes born in December produced significantly (P < 0.001) more milk than ewes born in January and February. There was a negative correlation between SCC (log10) and daily milk yield (P < 0.001), while the SCC (log10) was positively correlated (P < 0.001) with the contents of total solids, milk fat and proteins