Culture conditions for blastogenic responses of bovine mammary mononuclear cells

Several experimental parameters were examined to determine optimal conditions for proliferative responses of mammary mononuclear cells (MMC) obtained from six nonlactating dairy cows. These parameters were: pre-incubation of cells in medium prior to assay, mitogen concentration, assay incubation time, and type of culture medium. Response variables included viability of cells and the rate of proliferation as assessed by tritiated thymidine incorporation. Pre-incubation of cells in medium had no effect on the proliferative response of MMC. Whereas Concanavalin A (ConA; 3.3 or 6.6 micrograms/ml) and phytohemagglutinin (PHA; 1, 5, 10 micrograms/ml) did stimulate proliferation of MMC, the higher doses did not stimulate greater proliferation than the lower doses of mitogens. The greatest mitogenic response was obtained on days 2 and 3 of incubation. Proliferative responses were significantly higher at all mitogen levels tested in a 50-50 mixture of Rosewell Park Memorial Institute medium 1640 and Liebovitz-15 medium (RPMI/L-15) than in RPMI alone. Viability of MMC was also significantly higher in the RPMI/L-15 medium. To test whether the significant effect of media on blastogenesis was specific for mononuclear cells from the bovine mammary gland, peripheral blood lymphocytes (PBL) from four dairy cows were cultured with ConA and PHA in a mitogen assay in both RPMI and RPMI/L-15. Viability was measured on day of collection and on all culture days. PBL were stimulated equally in both media. PBL viability decreased significantly on day 1 in both RPMI and RPMI/L-15. These results suggest that the optimal culture conditions for blastogenic responses of mammary mononuclear cells and peripheral blood lymphocytes may differ.     

Reference values of the brainstem auditory evoked response of methoxyflurane anesthetized and unanesthetized dogs

The brainstem auditory evoked response (BAER) was recorded from 7 unanesthetized and 27 methoxyflurane anesthetized dogs. A 0.1 msec, 70 dB stimulus delivered at 10 Hz evoked the expected seven wave BAER. Mean peak wave latencies and standard deviations were calculated. Differences were not found between neither right and left ears, nor male and female dogs. The anesthetized dogs had a significantly longer latency for all waves, except wave I, than the unanesthetized dogs. Use of the BAER as a diagnostic technique for brainstem lesions is recommended.Publication No. 1702, School of Veterinary Medicine, Auburn University, AL 36849, USA     

Vascularization of cancellous chip bone grafts

Fresh autogenous, frozen allogeneic, and commercially prepared xenogeneic cancellous chip bone grafts were placed into plug holes in the tibia and into surgically simulated nonunion defects in the ulna of dogs. The microvascular and correlated histologic reactions were studied at given times up to 12 weeks after the graft implantation. Marked and characteristic differences were noted among the 3 graft materials. Fresh autogenous chips were extensively vascularized by 1 week, and subsequent microscopic healing was rapid. Allogeneic chips were incorporated into all defects, but vascularization and histologic healing rates were slower than those with the fresh autogenous graft material. The xenogeneic graft was poorly incorporated. A foreign body reaction was seen histologically, and corresponding vascularization of the graft was slow and incomplete.     

Effects of yard weaning and training on the behavioural adaptation of cattle to a feedlot

Two experiments were conducted to determine the effect of weaning in small yards, with or without a feed bunk training procedure, on the subsequent behaviour and performance of Bos taurus steers in a feedlot. A reduction in the incidence of bovine respiratory disease (BRD) was the primary objective. In each experiment, about 200 male beef calves (Angus × Hereford and Hereford) were separated from their mothers at 7–9 months of age and allocated to one of three matched weaning treatment groups. The treatments were (1) yard weaning with hay or silage, (2) yard weaning with hay or silage plus a novel handling procedure to train the animals to be able to find a grain ration in a trough, and (3) paddock weaning without supplement or handling according to common industry practice in southeastern Australia. Paddock weaning is the practice of abrupt separation of cows and calves followed by return to separate pasture paddocks, whereas yard weaning involves abrupt separation but the calves remain in the yards for several days. Experimental vaccines against the major BRD pathogens were given to half of each group 1–2 months prior to entry into a commercial feedlot. The yard weaned and yard trained cattle had a significantly greater weight gain in the first month and over the 90-day feeding period than the paddock weaned control groups. There was no difference between the groups in pre-feedlot weight gain. The yard trained groups showed greater feeding activity during the first few days in the feedlot, but were not significantly different in weight gain from yard weaned. The vaccination treatment also significantly improved the weight gain in the first month and over 80 days. The combination of yard weaning and vaccination produced the highest weight gains overall. There was consistently less morbidity in the yard weaned groups compared to paddock weaned controls. The morbidity in yard trained groups was intermediate between these two. Weaning in small yards and the appropriate use of effective BRD vaccines 1–2 months before feedlot entry are recommended for B. taurus feeder steers in southeastern Australia to minimise sickness and improve productivity in the feedlot. Associated benefits are reduced risks of antibiotic residues and of animal welfare problems.