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

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 +/- 0.3 liday. 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 90 min 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 +/- 30 ml) 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; r(2) = 0.90, P < 0.05) upon increase of milking interval from 4 to 24 h (from 168 28 to 105 10 ml/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 (r(2) = 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 90 min 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. (C) 2016 Elsevier B.V. All rights reserved.