Milk yield and mammary growth effects due to increased milking frequency during early lactation.

Increased milking frequency (IMF) at the beginning of lactation has been shown to increase milk yield not only during IMF but also after its cessation. The objectives of this experiment evaluated the effects of increased milking frequency initiated during early lactation on mammary growth and effects on milk yield (MY). Thirty-one cows were divided into treatment groups: 1) 2X: cows milked twice daily (2X) beginning at parturition (d 1), 2) IMF1: cows milked four times daily (4X) from d 1 to 21 postpartum (PP) and 3) IMF4: cows milked 2X d 1 to 3 and 4X d 4 to 21 PP. The 4X cows were milked immediately before 2X cows and again approximately 3 h later, at the end of the normal milking routine. All cows were milked 2X from d 21 to 305 postpartum. Milk yields were 34.5, 37.8 and 37.6 kg/d during wk 1 to 44 for 2X, IMF1 and IMF4, respectively. Mammary biopsies from four cows per treatment were obtained on d 7 and 14 PP to evaluate mammary cell proliferation. Tritiated-thymidine incorporation tended to increase on d 7 in IMF1 cows, and arithmetic means of the percentage of cells expressing Ki-67 proliferation antigen were consistent with a proliferative response to IMF though not significant. Blood was sampled three times per wk during the first 2 wk and then once per wk during wk 3, 4, 5, 6, 8, and 10. Plasma insulin-like growth factor-1 (IGF-1) averaged 20.1 ng/ml in IMF cows vs. 24.2 in 2X but was not accompanied by a change in bST. Prolactin was also not affected by treatment. Neither milk yield nor potential effects on mammary cell proliferation were correlated with systemic IGF-1. Implementing an IMF routine increases MY during treatment and elicits a carryover effect on the remainder of lactation. Milk yield responses after an IMF routine may be the result of increased mammary cell proliferation.

Lactation persistency: insights from mammary cell proliferation studies.

A persistent lactation is dependent on maintaining the number and activity of milk secreting cells with advancing lactation. When dairy cows are milked twice daily, the increase in milk yield from parturition to peak lactation is due to increased secretory activity per cell rather than to accretion of additional epithelial cells. After peak lactation, declining milk yield is due to loss of mammary epithelial cells by apoptosis. During lactation, only 0.3% of mammary cells proliferate in a 24-h period. Yet this proliferative rate is sufficient to replace most mammary epithelial cells by the end of lactation. Management practices can influence lactation persistency. Administration of bovine somatotropin may enhance persistency by increasing cell proliferation and turnover, or by reducing the rate of apoptosis. Increased photoperiod may also increase persistency of lactation by mechanisms that are as yet undefined. Increased milking frequency during the first weeks of lactation increases milk yield, even after return to less frequent milking, with increases of approximately 8% over the entire lactation. A mammary cell proliferation response to frequent milking during early lactation appears to be involved. Conversely, advanced pregnancy, infrequent milking, and mastitis increase death of epithelial cells by apoptosis. Regulation of mammary cell renewal provides a key to increasing persistency. Investigations to characterize epithelial cells that serve as the proliferative population in the bovine mammary gland have been initiated. Epithelial cells that stain lightly in histological sections are evident through all phases of mammary development and secretion and account for nearly all proliferation in the prepubertal gland. Characterization of these cells may provide a means to regulate mammary cell proliferation and thus to enhance persistency, reduce the effects of mastitis, and decrease the necessity for a dry period.

Analysis of the swing phase dynamics and muscular effort of the above-knee amputee for varying prosthetic shank loads.

The purpose of this study was to determine the effect of varying prosthetic shank mass, while maintaining the mass centre location and moment of inertia, on the swing phase kinematics, kinetics and hip muscular effort of free speed above-knee (AK) amputee gait. Six AK amputees, wearing similar prosthetic designs, had three load conditions applied to their prosthetic shank: 1) Load 0-unloaded (X = 39.1% sound shank mass), 2) Load 1-75%, and 3) Load 2-100% sound leg mass. Despite increases in shank mass from 1.33 to 3.37 kg the AK amputee was able to maintain a consistent swing time and walking speed. As load increased, there were significant changes in the maximum knee and hip displacements, as well as phasic shifting. The prosthetic knee Resultant Joint Moment (RJM) was negligible while the shank was accelerating (periods 1 and 2), but was a major contributor during shank deceleration (periods 3 and 4). During periods 1 and 2 the principle contributors to the shank acceleration (forces resisting excessive knee flexion) were the gravitational moment (S-G) and the moment due to thigh angular acceleration (S-AT). During the periods of shank acceleration (sections 1 and 2), there was not a significant increase in the hip muscular effort. However, during sections 3 and 4, the periods associated with shank deceleration, there were significant increases in the hip muscular effort. The hip muscular effort for the complete swing phase increased as load increased by 36.7% and 71.3% for loads 1 and 2. Despite the significant increases in hip muscular effort, four of the six subjects preferred load 1 condition.

Antihypertensive thiadiazoles. 2. Vasodilator activity of some 2-aryl-5-guanidino-1,3,4-thiadiazoles.

Some 2-aryl-5-guanidino-(or N-substituted guanidino)-1,3,4-thiadiazoles and closely related analogues were found to lower blood pressure in metacorticoid (DOCA) hypertensive rats. In the unsubstituted guanidines that exhibited low toxicity, optimum activity resulted when the aryl group was a 2-methylphenyl ring (11). Modifications to the guanidine group did not increase antihypertensive activity, but, in the 2-methylphenyl series, the N-n-butyl- and N-(2-methoxyethyl)guanidines (63 and 78) and the related iminoimidazolidine 93 were of comparable activity to that of the unsubstituted guanidine 11. The iminoimidazolidine 93 showed a somewhat longer duration of action than the guanidine derivatives. Preliminary studies in a pithed rat preparation indicated that these thiadiazole derivatives (11, 63, and 93) lowered blood pressure by a direct relaxant effect on vascular smooth muscle.