Biomechanical analysis of single- versus double-screw fixation in slipped capital femoral epiphysis at physiological load levels.

Slipped capital femoral epiphyses in 12 pairs of bovine femora were pinned with a single screw on one side and two screws on the other. The specimens were subjected to physiological shear loads across the epiphysis (100 cycles at 1.1 Hz; 400 N for slow walking, and 900 N for fast walking). The rates of creep were decreased 23% with double screws compared to single screws at slow walking, and 30% at fast walking; this was not statistically significant. Single-screw fixation in slipped epiphyses is thus recommended, because the small gains in resistance to cyclic creep at physiological loading were not statistically different, and did not offset the increased risks of complications with multiple screws.

Single versus double screw fixation for treatment of slipped capital femoral epiphysis: a biomechanical analysis.

Slipped capital femoral epiphyses (SCFE) were created in 10 pair of bovine femurs. Each pair was pinned with a single screw on one side and two screws contralaterally. The specimens were reloaded to failure. Double pin fixation yielded only a 33% increase in stiffness as compared with single pin fixation. Resistance to further slip was not proportional to screw number. The stiffness of neither double nor single screw fixation approximated that of the intact physis. Single screw fixation in slipped epiphyses is recommended because the small gains in stiffness with a second screw do not offset the risk of complications.

Effect of relaxin on mammary development in ovariectomized pregnant gilts.

The role of relaxin in mammary development was studied between days 80-110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. To obtain an objective measurement of lobulo-alveolar (parenchymal) composition, mammary glands were cut in cross-section through the teat, and the area of parenchymal tissue on the exposed face of the gland was determined. Ovariectomy on day 80 or 100 followed by progesterone replacement therapy resulted in a dramatic reduction in the rate of growth of mammary parenchymal cross-section area on days 100 and 110 of gestation, respectively, compared to that in controls. In contrast, progesterone plus relaxin therapy, with highly purified porcine relaxin, restored the mammary parenchymal cross-section area to control values in ovariectomized gilts. Morphometric analysis of mammary tissue on day 110 of pregnancy indicated that both the absence of relaxin after ovariectomy and replacement therapy with porcine relaxin in ovariectomized gilts had little if any effect on the percentages of the lumen, stroma, or epithelial that comprised the mammary parenchyma. It is concluded that relaxin has a stimulatory effect on the growth of mammary parenchymal tissue during late gestation in the pig.

Recent developments in the roles of vitamins and minerals in reproduction.

Vitamins and minerals affect reproductive function. Vitamin A deficiency has long been known to affect reproductive function in cattle. More recently, a role has been proposed for the vitamin A percursor, beta-carotene, in reproductive efficiency. Dietary supplementation with vitamin E and selenium may reduce the incidence of retained placenta, but these nutrients may also affect reproductive function in other ways. Calcium and phosphorus deficiencies affect reproduction in cattle, and vitamin D may directly affect reproductive function in addition to its role in calcium and phosphorus metabolism. Dietary manipulation of a number of other vitamins and minerals also influences reproductive function. However, the specific roles of nutrients in reproductive tissues are not well-defined in dairy cattle, and nutrient requirements for optimal reproductive efficiency in modern dairy cattle deserve careful reevaluation. This review provides a background of the effect of vitamins and minerals on reproduction and it attempts to provide a basis for further investigation of specific mechanisms by which reproductive function is affected. The interface between nutritional science and reproductive physiology provides considerable potential for optimizing reproductive efficiency in dairy cattle.

Duration of experimentally induced Corynebacterium bovis colonization of bovine mammary glands during the lactating, nonlactating, and peripartum periods.

Bovine mammary glands were inoculated intracisternally with a streptomycin-resistant (SR) strain of Corynebacterium bovis to determine the number of colony-forming units (CFU) required to induce colonization and to maintain persistence of C bovis colonization throughout lactation and involution. Streptomycin resistance was used as a strain marker. Uninfected quarters in cows during midlactation were challenge exposed with successively higher numbers of SR C bovis until all quarters became colonized. Inoculum containing 790 CFU of SR C bovis established colonization in only 7 of 38 quarters. Colonization persisted in only 4 of these quarters by 23 days after inoculation. Eleven quarters were reinoculated with higher numbers of SR C bovis, and all became colonized by the time challenge-exposure inoculum contained 8 X 10(4) CFU. Colonization persisted throughout the 93-day experimental period. Somatic cell counts were significantly (P less than 0.01) higher in SR C bovis-colonized quarters after inoculation than before. Sixteen additional quarters were inoculated with a mean number of 8 X 10(4) CFU of SR C bovis 7 days before suppression of lactation. All quarters became colonized, and SR C bovis was shed during the experimental period; throughout the nonlactating and peripartum periods, high numbers of SR C bovis in pure culture were shed from 13 of 16 quarters.

Experimental infection of lactating bovine mammary glands with Streptococcus uberis in quarters colonized by Corynebacterium bovis.

Twenty-seven quarters of 18 lactating dairy cows were inoculated intramammarily with 3.6 X 10(4) colony-forming units (CFU) of a strain of Streptococcus uberis isolated from a cow with clinical mastitis. Before quarters were inoculated, 22 were considered as naturally colonized with Corynebacterium bovis, and 5 were considered bacteriologically negative. Streptococcus uberis was isolated from all quarters within 2 days after inoculation, and all quarters developed clinical mastitis by 3 days after inoculation. Mastitis was acute, and most cows had increased rectal temperatures. The number of somatic cells increased significantly (P less than 0.05), and milk production decreased significantly. In many cows, rectal temperatures remained increased, and Str uberis was isolated from infected glands after intramammary and systemic antimicrobial treatments were given. A decreased number (110 CFU) of the same strain of Str uberis caused equally severe mastitis in 3 quarters colonized with C bovis and in 1 bacteriologically negative quarter in 2 cows. Streptococcus uberis was isolated from all inoculated quarters, and all quarters developed clinical mastitis by 2 days after inoculation. Two quarters colonized with C bovis and 2 bacteriologically negative quarters were inoculated once with 25 CFU and once with 240 CFU of a different strain of Str uberis (ATCC 27958). Streptococcus uberis was never isolated from inoculated quarters, and changes in milk yield or number of somatic cells were not observed.