Evolution of udder morphology, alveolar and cisternal milk compartment during lactation and their relationship with milk yield in Najdi sheep

A total of 30 multiparous Najdi ewes were used to study the evolution of udder morphology traits and milk fractions in the udder during suckling (3rd, 6th, 9thwk) and milking (10th, 11th, 12thwk) periods. During suckling period, daily milk yield was estimated by using the double oxytocin injections method 4-h after milking. During milking period, ewes were hand-milked once daily. Udder and teat morphology traits for all ewes were measured 4-h after milking. Udder compartments were evaluated 8-h after milking by using atosiban and oxytocin; milk samples of each fraction were collected. Najdi ewes had a medium and healthy udders (CMT<1), with medium sized teats (length, 3.2±0.1 cm and width, 1.7±0.1 cm) attached at 35.7 ± 11º angle. Milk yield averaged 1.88±0.18 and 0.44±0.12 L d-1 during suckling and milking periods, respectively. A drop in milk yield (-75%, p<0.01) was found in the transition from suckling to milking. Udder traits, teats angle and width, and distance between teats declined (p<0.05) throughout lactation, whereas teat lengths did not show any change. Positive correlations (p<0.05) were observed between milk yield and udder depth (r=0.47-0.49), width (r=0.31-0.39) and distance between teats (r=0.26-0.39). The cisternal milk volumes decreased (p<0.05) after weaning, whilst the corresponding percentages increased (p<0.05). Cisternal milk accounted for 55% and 67% of the total udder milk during suckling and milking periods, respectively. Cisternal milk was positively correlated (r=0.93, p<0.05) with total milk yield. The percentages of protein and total solids in alveolar and cisternal milk increased significantly (p<0.05) after weaning, whilst fat percentages in cisternal milk did not change. In conclusion, the evaluated Najdi ewes showed medium sized cisterns and teats, which considered adequate for machine milking. Udder morphology traits had positive correlations with milk yield and hence, can be utilized in breeding programs