Histologic observations of mammary tissue samples from unbred heifers revealed that secretory parenchyma from uninfected quarters was undeveloped, exhibiting small alveoli with a limited luminal area and a large interalveolar stromal area. Tissues from quarters infected with Staphylococcus aureus were less developed, exhibiting less alveolar epithelial and luminal areas and more interalveolar stroma compared with tissues from uninfected quarters. Such quarters also demonstrated minimal secretory activity. Macroscopic and microscopic abscesses were observed in one quarter with S. aureus intramammary infection. Staphylococcus aureus-infected quarters showed greater leukocyte infiltration into mammary parenchymal components and cistern lining compared with uninfected quarters. Quarters infected with non-aureus staphylococci also exhibited greater leukocyte infiltration and greater percentages of interalveolar stroma compared with uninfected controls. Results demonstrated that presence of infection increased leukocytosis into the mammary gland and reduced secretory activity in heifers, suggesting a deleterious effect on future milk production.

Forty-two Holstein calves were used to study performance and metabolic responses when milk replacer and then postweaning starter were supplemented with 1 ppm of Cr as Cr-tripicolinate. From birth through 8 wk of age, supplemental Cr tended to improve the growth performance of bull calves but not of heifer calves. Starter intake and feed efficiency were not affected by supplemental Cr. From 1 to 5 wk of age, plasma cortisol concentrations sampled just prior to feeding decreased, and concentrations of insulin-like growth factor-I increased. All calves appeared to become less sensitive to insulin as they aged. From 1 to 5 wk of age, plasma glucose and insulin concentrations gradually diverged for all calves; glucose concentrations decreased, and insulin concentrations increased. In addition, glucose clearance rate, measured by i.v. glucose tolerance tests, was more rapid when calves were 2 wk of age than when calves were 8 wk of age. The glucose clearance rate was greater in heifer calves than in bull calves but was not affected by supplemental Cr. Entry of plasma glucose following an i.v. propionate load was also greater in heifer calves than in bull calves but was not affected by supplemental Cr. Plasma nonesterified fatty acids were lower in calves fed milk replacer or starter supplemented with Cr than in control calves, although this effect diminished as calves aged. This finding was considered to be indirect evidence of enhanced insulin sensitivity in calves fed milk replacer or starter supplemented with Cr. Overall, data suggested that supplemental Cr-tripicolinate had minor effects on the metabolism and growth performance of conventionally managed dairy calves. The most notable effects occurred during the initial few weeks of life.

Growth of fetuses, fetal membranes, and fetal fluids was characterized by least squares analysis for 254 conceptuses ranging from 25 to 278 days of gestation. Prior to 100 days of gestation, increases in allantoic fluid volume and chorio-allantoic membrane weight preceded those of fetal weight, amnio-allantoic membrane weight, and amniotic fluid volume. The relative rate of growth of components suggests a prerequisite of chorio-allantoic membrane expansion for subsequent fetal growth. Male fetuses were heavier than female fetuses as early as 100 days of gestation. Rate of growth of all fetuses was maximal at 230 days of gestation with a peak rate of greater than 200 g/day. Growth rate then declined to less than 100 g/day by term.

Clinical mastitis episodes occurring from 1962 through 1991 in the Louisiana State University Dairy Research Herd were studied to determine the distribution of clinical mastitis among quarters of the udder. Data were detailed records of all mastitis episodes that occurred during 1630 Holstein lactations. Incidence of episodes, categorized according to which quarters within a cow were clinical for a given case, were compared with mathematical expectations based upon the assumption that quarters were independent. Results indicated that quarters within a cow were more alike with respect to clinical mastitis than would be expected if quarters were independent. More episodes occurred in which either no quarters or all four quarters were clinical. Deviation of observed frequencies from expectation could have resulted from generalized cow differences, such as cow milk yield, immune competency, mammary type characteristics, and general health. Front quarters had less clinical mastitis than rear quarters when all episodes were considered. No difference was observed in incidence between front and rear quarters when only first episodes in first lactations were considered. No difference was observed between incidence in left and right quarters. Diagonal pairs occurred less often than expected and at about half the frequency of other pairs. Dependence between quarters should be taken into consideration when experiments are designed and analyzed.

A gel was developed and tested for cleaning and sanitizing cows teats for milking. Thirty lactating Holstein cows were divided into three groups of 10 each and assigned to three premilking hygiene treatments for 10 wk as follows: 1) cleaning teats with gel, allowing 30 s of contact time, and wiping residual gel off with paper towel; 2) washing teats with water and drying them with paper towel; 3) washing teats with water, drying with paper towel, predipping with .5% iodophor solution, allowing 30 s of contact time, and drying with paper towel. Individual cow composite milk and teat end swab samples were collected. The gel and predip treatments resulted in less bacterial contamination of milk and teat ends. The gel treatment had an advantage over wash and predip treatments in lower SCC and reduced mastitis. Parlor throughput was greatest for gel and wash treatments. The wash treatment group had highest SCC, bacteria in milk and on teat ends, and mastitis. Milk iodine content was low and similar for the three treatments. Daily milk production and fat and protein percentages were not affected by treatments. The gel treatment was effective, efficient, and provided good hygiene.