Several investigators have suggested that the conventional multicompartmental exponential analysis of in vivo glucose metabolism is arbitrary and possibly not the most accurate description of glucose kinetics, especially in the large animal. In support of that hypothesis, we found that in a systematic comparison of 3 methods, blood-specific radioactivity data in single-injection studies of glucose metabolism in lactating cows was better described graphically, or by a hybrid polynomial-biexponential curve fit, than by an exclusively exponential curve fit. We hypothesized that this finding was attributable to partial failure of linearity and steady-state assumptions that underlie the exponential model. Second, using both an irreversible tracer (3H-labeled glucose) and reversible tracer (14C-labeled glucose), we found that glucose carbon recycling had no effect during the first 2 hours, but became significant in lactating cows 7 hours after injection. Finally, we determined that approximately 52 to 55% of the glucose replacement rate was being used to generate lactose.

Hydrated sodium calcium aluminosilicate (HSCAS), an anticaking agent for agricultural feeds, was added to aflatoxin (AF)-contaminated diets of 3 lactating dairy cows and evaluated for its potential to reduce aflatoxin M1 (AFM1) residues in milk. During phase I, cows were fed alternating diets that consisted of 200 microgram of AF/kg of feed for 7 days, 0.5% HSCAS plus 200 microgram of AF/kg of feed for 7 days, and feed with the HSCAS removed for a final 7 days. The AFM1 milk concentrations from the intervals with HSCAS added to diets were compared with those times when HSCAS was absent. The presence of 0.5% HSCAS in feed containing 200 microgram of AF/kg reduced AFM1 secretion into the milk by an average of 0.44 microgram/L (from pretreatment of 1.85 microgram/L to 1.41 microgram/L with HSCAS, a 24% reduction). Following a 10-day period of noncontaminated feed consumption and no AFM1 residues in the milk, phase II of the study was begun. The same experimental design as phase I was used, but the dosages of HSCAS and AF were changed to 1.0% and 100 microgram/kg of feed, respectively. The addition of 1.0% HSCAS in feed containing 100 microgram of AF/kg decreased AFM1 content in the milk by an average of 0.40 microgram/L (from a pretreatment of 0.91 microgram/L to 0.51 microgram/L when HSCAS was present, a 44% reduction). These findings suggest that HSCAS, a high-affinity sorbent compound for AF in vitro, is capable of reducing the secretion of AFM1 into milk.

To compare the effects of milk stasis and milk flow on Brucella abortus infection of the mammary gland under the same systemic conditions, primiparous goats (n = 5) were inoculated IV with B abortus on the day of parturition, and suckling by their neonates was restricted to one mammary gland. Goats were euthanatized and necropsied at 3 weeks after inoculation, and milk, mammary glands, and supramammary lymph nodes were evaluated by bacteriologic, histologic, and immunoenzymatic staining techniques. Nonnursed mammary glands had high titers of brucellae in milk, moderate interstitial mastitis, and brucellar antigen in macrophages located primarily in alveolar and ductal lumina. Brucellae often filled the macrophage cytoplasm. In contrast, nursed mammary glands had fewer brucellae in milk, minimal inflammatory changes, and no detectable brucellar antigen in histologic sections. Hyperplastic changes were only seen in supramammary lymph nodes draining nonnursed mammary glands; these contained more brucellae than lymph nodes draining nursed mammary glands. These studies show that milk stasis may be the sole cause of increased susceptibility of nonnursed mammary glands to B abortus infection.

One hundred and fifty lactating Holstein cows from 2 genetic lines selected for high and average milk production were used in the study. Sera from 6 annual herd tests were analyzed by agar-gel immunodiffusion test for antibodies to bovine leukemia virus. Odds of being seropositive were analyzed by use of stepwise and backward logistic regression procedures. Analysis within birth year revealed that estimated ln odds increased by 0.19/year of age among cows of the high genetic line and by 0.43 among cows of the average genetic line. This was accompanied by a more important cohort effect among high producers than among average producers.

Naturally acquired gram-negative bacterial intramammary infections (n = 160) were studied in 99 cows over a 2-year period. Escherichia coli, Klebsiella spp, Serratia spp, Enterobacter spp, and unidentified gram-negative bacteria were isolated from 28.8, 39.4, 9.4, 5.0, and 11.2%, respectively, of infected mammary glands. A majority (61%) of intramammary infections were first detected during the nonlactating period. Gram-negative bacteria isolated during the first half of the nonlactating period were predominantly Klebsiella spp, Serratia spp, and Enterobacter spp. Onset of E coli intramammary infections was more prevalent during the second half of the nonlactating period and during the first 7 days of lactation. The majority (59%) of infections were <28 days in duration, but Klebsiella spp and Serratia spp infections were of significantly (P <0.05) greater duration than infections with E coli. The greatest percentage (47%) of gram-negative bacterial intramammary infections were first detected during the summer.

Milk samples were collected at onset of 508 episodes of clinical mastitis on a 1,700-cow dairy farm in Michigan. Daily milk production and disease events were recorded for all cows in the herd. Despite statistical association with severity of mastitis, this association was too weak for N-acetyl-beta-D-glucosaminidase (NAGase) activity to be of great value as a prognostic test for clinical mastitis. High milk NAGase activity was significantly (P < 0.0001) associated with: increased duration of treatment; increased duration of clinical signs of mastitis; decreased daily milk production; and increased risk of the cow being culled because of mastitis. The NAGase value was combined with days in milk production, baseline milk production before mastitis onset, parity, and season of onset to predict the outcome of clinical cases as measured by the first 3 aforementioned variables. Statistical models explained little of the variability among cows in duration of treatment (R2 = 0.11), duration of clinical signs of infection (R2 = 0.11), and milk production change (R2 = 0.09).