Effect of slow-release somatotropin on the pattern of milk yield between and within injection intervals

The mammary gland in small ruminants: major morphological and functional events underlying milk production--a review

The importance of small ruminants to the dairy industry has increased in recent years, especially in developing countries, where it has a high economic and social impact. Interestingly and despite the fact that the mammary gland is the specialised milk production organ, very few authors studied the modifications occurring in the mammary gland through the lactation period in production animals, particularly in the small ruminants, sheep (Ovis aries) and goat (Capra hircus). Nevertheless, understanding the different mammary gland patterns throughout lactation is essential to improve dairy production. In addition, associating these patterns with different milking frequencies, lactation number or different diets is also of high importance, directly affecting the dairy industry. The mammary gland is commonly composed of parenchyma and stroma, which includes the ductal system, with individual proportions of each changing during the different periods and yields in a lactation cycle. Indeed, during late gestation, as well as during early to mid-lactation, mammary gland expansion occurs, with an increase in the number of epithelial cells and lumen area, which leads to increment of the parenchyma tissue, as well as a reduction of stroma, corresponding macroscopically to the increase in mammary gland volume. Throughout late lactation, the mammary gland volume decreases owing to the regression of the secretory structure. In general, common mammary gland patterns have been shown for both goats and sheep throughout the several lactation stages, although the number of studies is limited. The main objective of this manuscript is to review the colostrogenesis and lactogenesis processes as well as to highlight the mammary gland morphological patterns underlying milk production during the lactation cycle for small ruminants, and to describe potential differences between goats and sheep, hence contributing to a better description of mammary gland development during lactation for these two poorly studied species.

Bovine somatotropin administration to dairy goats in late lactation: effects on mammary gland function, composition and morphology

We investigated the effects of bovine somatotropin (bST) on mammary gland function and composition in the declining phase of lactation in goats. Sixteen Saanen goats, 180 +/- 11 days in milk (DIM), were divided equally into control and treated groups. The treated group received 120 mg/2 wk of slow-release bST for three cycles. Milk yield, milk composition, milk clotting measures, and plasmin-plasminogen activator activities were recorded weekly. Milk Na and K were determined in individual milk samples collected weekly during the third cycle. Blood samples were collected weekly during the second cycle and the plasma analyzed for nonesterified fatty acids (NEFA), glucose, and urea. At the end of the 6 wk, three goats from each group were slaughtered, and the udders were removed. Mammary gland weight, composition, and total DNA content were determined. The histological effects of bST on mammary tissue were investigated. The analyzed parameters included numbers of alveoli, corpora amylacea, apoptotic cells, and laminin fibronectin distribution and localization. An extensive morphological analysis on the epithelial and stromal components was performed. Milk yield was significantly higher in the treated group, fat content was not affected, but protein and nonprotein nitrogen were lower in treated goats milk. Treatment with bST did not influence milk pH but reduced coagulation time. Plasmin and plasminogen activator activities were not affected. Milk K levels were higher and the Na/K ratio was lower in treated animals. Plasma glucose, NEFA, and urea were unaffected. Mammary gland weight and total DNA were higher in treated than control animals, suggesting that with advancing lactation bST treatment maintains cells. Fat, protein, and collagen content of the mammary tissue did not differ between the groups. Treatment with bST significantly increased the number of lactating alveoli (LA) and significantly reduced the number of regressing alveoli (RA) and corpora amylacea, both within and outside the alveolar lumen. Laminin and fibronectin localization were not affected, and very few apoptotic cells were found in both treated and control samples. Our findings suggest that bST administration to dairy goats in late lactation can modulate mammary gland activity and improve lactation persistency; this is associated with maintained total mammary parenchyma weight and lactating alveoli.

Manipulation of milk production and quality by use of somatotropin in dairy ruminants other than cow

The ability of recombinant bovine somatotropin (BST) to enhance milk production is well established in cows and in other dairy ruminants. In dairy ewes, we found increased milk yield (20-30%) following treatment with BST, which did not negatively affect the gross composition or coagulating properties of milk, except in the advanced stage of lactation, when the percentages of milk protein and fat were reduced and the coagulation time was improved (shorter) compared with untreated animals. In dairy goats, administration of BST increased overall milk yield by 14-29%. Our studies and those of others on the Italian river buffalo showed that BST treatment increased milk yield by about 17%, or more, when associated with dietary protected fat, without affecting milk protein content. In general, studies on dairy ruminants show that treatment with BST increases milk production in the short term (immediate postinjection period) and that there is also a medium to long term effect on persistency of lactation. There is evidence that mammary gland involution can be at least partially reversed by BST administration, and this could be due to limitation in the decrease in mammary parenchyma as lactation progresses and/or to modulation of the plasmin-plasminogen system.

Effect of sustained-release somatotropin on performance and grazing behavior of ewes housed at different stocking rates

This study evaluated the effects of recombinant bovine somatotropin (bST; one injection of 320 mg per ewe) on milk production and composition and on the grazing behavior of multiparous ewes in the third to fourth lactation. Forty Comisana lactating ewes were divided into four groups: 1) untreated, grazing on natural pasture (botanical composition: 35% of Graminaceae, 49% of Fabaceae, 6% of Cruciferae, 10% of other families) at a low stocking rate (16 m2/d); 2) untreated, grazing at a high stocking rate (8 m2/d); 3) treated with bST, grazing at a low stocking rate; and 4) treated with bST, grazing at a high stocking rate. The diets of the ewes were supplemented with vetch and oat hay (500 g/d) and with concentrate (500 g/d). Treatment increased milk production (923.8 vs. 669.5 g/d) but had little effect on fat and protein contents. Administration of bST significantly increased herbage intake; the effect on intake was more marked at the high stocking rate. Under these grazing conditions, the treated ewes reduced selective intake behavior and, thus, achieved good feed intake despite the low biomass availability.