Vacuum level for opening the teat sphincter and the change of the teat end wall thickness during the machine milking of mountainous Greek breed (Boutsiko) ewes

The aim of this work was to study some of the teat characteristics involved in the milking ability of dairy ewes, such as the vacuum level of the milking machine that is required for the opening of the teat canal sphincter, and the changes in the teat end wall thickness induced by milking. After weaning, 48 ewes of the mountainous Greek breed, Boutsiko (16 ewes of the first, 16 of the second and 16 of the third and subsequent lactations) were milked for 12 weeks. Every 14 days, during the morning and evening milking, milk fractions and composition were recorded. The vacuum level that is required for the opening of teat sphincter (VOTS) was also measured before milking. The measurement of teat end wall thickness (TEWT) was performed before and after milking and the milk flow was monitored during the morning milking only. The results of this study show that during the experimental period, the ewes had a mean daily milk yield of 862.9 ml, of which the 173.3 ml corresponded to the machine stripped milk (MSM). The mean VOTS was 16.59 ± 0.7 kPa and tended to decrease as the stage of lactation progressed. The TEWT (4.75 ± 0.04 mm) was not modified by milking. A continuous and significant decrease in teat thickness (from 5.03 to 4.3 mm, P < 0.05) was observed, which suggests a reaction to intramammary pressure and milk quantity in the gland. Parity was affected significantly (P < 0.001) only the TEWT. The type of birth did not influence the VOTS and TEWT. Phenotypic correlations showed that by increasing the VOTS, the machine stripped milk increased as well, and so did the TEWT. These results give rise to the need for a possible reduction of the current vacuum level (44 kPa), which should be applied in the milking of this particular mountainous Greek breed of sheep.