Effect of milking interval on milk partitioning between udder compartments, milk yield and milk composition in Maghrebi dairy camels

Abstract

Ten multiparous Maghrebi she-camels (Camelus dromedarius L.) were used to study the effects of 6 milking intervals (4, 8, 12, 16, 20 and 24h) at mid-late lactation (281±41 days in milk) on milk partitioning between udder compartments, milk yield and milk composition. Camels were kept in loose stalls, fed forage and concentrate, and hand milked twice-daily. Average milk yield during the experiment was 4.2±0.3l/day. Cisternal and alveolar milk were obtained by sequential milking, before and after inducing milk let-down with exogenous oxytocin, respectively. Udder cisterns volumes were measured by real-time ultrasonography before and after milk let-down. Backflow of milk from the cistern to the alveoli as consequence of udder elastic recoil was measured at 12-h milk interval by delaying milking for 90min after inducing milk let-down with oxytocin. On average, 44% of total milk volume was stored in the front udder quarters and 56% was stored in the rear udder quarters. Alveolar compartments accounted for 92% of milk volume and cisternal compartment for 8%. The volume of milk in the cistern (132±30ml) did not vary with increase in milking interval. Udder cisterns were visible by ultrasonography as small cavities that were dramatically engorged with milk after milk let-down. Milk secretion rate decreased linearly (ml/h=168.3−3.2 x; r2=0.90, P<0.05) upon increase of milking interval from 4 to 24h (from 168±28 to 105±10ml/h). Fat content in alveolar milk was 3.26±0.10% and protein content in alveolar milk was 3.39±0.08% .The content of fat and protein in the alveoli were greater across all milking intervals (P<0.05) than those measured in cisternal milk (2.22±0.10% for milk fat and 2.96±0.05% for milk protein). The concentration of fat and protein in milk decreased linearly with increase in milking interval (r2=0.98; P<0.05), except in the case of milk protein in cisternal milk, which did not change significantly with advancing milking intervals. Lactose concentration was steady across all milking intervals. A dramatic drop of milk secretion (62%) was observed when milking was delayed 90min after induced milk let-down, indicating the necessity of early milking after milk let-down. In conclusion, selection for large-cistern udders and twice-daily milking are recommended for improving the machine milking ability of this breed in order to increase its use for milk production.