ULTRA-STRUCTURE STUDY OF MAMMARY GLAND IN ZARAIBI GOATS DURING DIFFERENT STAGES OF LACTATION

ABSTRACT
This work was carried out on 32 Egyptian Nubian (Zaraibi) goats to investigate the effect of stage of lactation on the ultra-structure of secretory mammary cells and its relationship with milk production. Biopsies were taken surgically from the mammary gland from three goats for histological and fine structure studies. The histological structures of mammary gland showed clear differences between lactation stages, being more developed in the early and mid stages, compared to late stage of lactation. The number of alveolar secretory cells increased from early to mid stage of lactation by 17.6% then reduced at the late stage by 25% from that at mid stage. The milk yield increased by 32.2% from early to mid stage, and then reduced to 61.3% from mid to late stage. Ultra-structure features in mammary epithelial cells showed different features at successive stages of lactation. The nuclei of the active mammary epithelial cells were ovoid or nearly spheroid in shape and indentation in cells membranes. The stage of lactation had an effect on nucleus diameter and sectional area. The nucleus 
diameter was smallest during early and mid stages, while being greatest at late stage of lactation. The sectional area of the nucleus showed increased values in late stage of lactation than in other stages. The majority of cell organelles were distributed in the cytoplasm. These organelles showed different phenomenon during different stages of lactation.
The mitochondria showed a clear change in shape (ovoid or elongated), number and sectional area during different stages of lactation. The number of mitochondria per plate was maximal during mid-stage, followed by early stage (44.2 and 37.9, respectively). The total mitochondria sectional area at late stage was 27.9 um2. This area increased at early and mid stage of lactation by 3.8 and 37.9%, respectively. A well- developed laminated endoplasmic reticulum (ER) was frequently found in the cytoplasm of the mammary epithelial cells. Stage of lactation influenced the diameter of ER. At early and mid stages of lactation, the ER was well developed to occupy large part of the cell, with diameters of 0.55 and 51 μm, respectively. This value was minimal during the late stage of lactation (0.36 um2). Protein granules had an ovoidal shape and released in different sizes. The sectional area of the protein was the smallest during late lactation (0.05 μm2) and increased during early and mid stages of lactation (0.1 μm2). The lipid droplets were appeared in different sizes, the sectional area of the lipid droplets were the smallest during late lactation (1.46 μm2), and increased during early and mid lactation (4.52 and 2.58 μm2, respectively). In conclusion, the results of the present study indicated that stage of lactation influence the activity of mammary epithelial cells. The activity increases at early and mid lactation which is reflected on ultrastructure of epithelial cells of mammary gland of Egyptian Nubian (Zaraibi) goats.