Effect of vacuum level on milk flow and vacuum stability in Alpine goat milking

摘要

Milking routine and settings of milking machine are crucial factors in influencing milk production, milking labour and teat condition. The aim of the study was to evaluate if different vacuum levels applied during goat milking can affect milk emission, vacuum stability, and teat measurements. At the university experimental farm, 29 Alpine dairy goats were milked once a day testing three different milking vacuum levels (30, 36 and 42 kPa). The study was divided in 4 periods during lactation, 3 weeks each, changing milking vacuum every week. Milk flow measurements were performed using Lactocorder devices (about 700 observations), while, to verify vacuum stability, Vadia devices were used collecting a total of 220 vacuum curves. Teat dimensions before and after milking were measured once a week. Classification of teat shapes was based on the ratio between diameter and length before milking. Milk flow curves were influenced by milking vacuum level. The highest values of peak and average milk flow were recorded using the highest vacuum level. Vacuum level affected the percentage of milk emitted in the first three minutes of milking; in particular, using the highest milking vacuum level, 92.5% of milk was released in the first three minutes. No differences were found in total milk production and milk somatic cell count using different vacuum levels. Both vacuum level at the short milk tube and vacuum level at mouthpiece chamber were significantly influenced by system vacuum level: as the system vacuum level raised, the first parameter increased while the second decreased. The percentage of curves characterized by irregular vacuum fluctuations, calculated as difference between maximum and minimum vacuum level (kPa) measured in the short milk tube during the main milking phase, was not different among vacuum levels (P = 0.562). Milk flow decreased from the first to the last period of trial, as lactation advanced, by 36.8%; 22.7%; 17.3% for 30, 36 and 42 kPa, respectively; this result impacts on milking performances in terms of duration of milking time and of the time in which teat is under vacuum force. The highest and lowest vacuum levels tested (42 and 30 kPa) caused more evident changes in teat dimensions pre and post milking in comparison with medium vacuum (36 kPa). Moreover, teat shape significantly influenced vacuum at the teat-end. In conclusion, medium vacuum level of 36 kPa seems to be less stressful for teat tissue and more efficient in terms of milking performances than the extreme vacuum levels.