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Bovine embryonic trachea cells were hybridized with mouse A9 cells deficient in hypoxanthine phosphoribosyltransferase, and cattle-mouse hybrid cells clones were isolated after HAT/ouabain selection. In these interspecific cell hybrids, bovine glucose-6-phosphate dehydrogenase, alpha-galactosidase, and phosphoglycerate kinase were expressed concordantly with bovine HPRT. Their expression depended on the presence of bovine X chromosome. These data indicated that the genes for G6PD, PGK, and HPRT are linked and can be assigned to the bovine X chromosome.

Mineral analysis of hair samples was to assess its value as an indicator of excessive salt ingestion. Ten pregnant Holstein heifers averaging 499 +/- 32 kg were group-fed 9 kg of alfalfa hay cubes and 2 kg of a 14% dairy concentrate mix per head per day. Salt and dicalcium phosphate were available free choice. Prior to treatment animals received fresh water containing 450 ppm total dissolved salts. During treatment, sodium chloride was added to the fresh water at 3500 ppm. Hair samples together with blood and urine were taken immediately prior to start of the experiment and at 30 and 60 days after initiation. Hair samples from two previously marked areas were composited, washed with hot detergent, rinsed, dried with ethanol and then acetone, and wet-ashed. Blood electrolytes and hair and urinary minerals were measured by atomic absorption spectrophotometry. Analysis yielded no significant treatment effects for sodium, potassium, calcium, magnesium in hair and blood serum, and no correlations between hair, blood serum, and urinary minerals. Only urinary sodium reflected the increased sodium ingestion.

A premilking phase of positive-pressure pulsation was evaluated by comparing milk production, persistence, peak milk flow, average milk flow, and several indicators of udder health of two groups of high-producing Holstein cows. Forty-four cows, 21 controls and 23 test animals, completed at least 250 days of lactation. After a premilking wash-up regimen of 25 to 30 s, test cows were given an additional 45 s for positive-pressure pulsation. The group with positive-pressure pulsation maintained significantly more persistence during the last two-thirds of lactation, and this resulted in an 8% relative increase of milk production over controls. There were no differences of udder health between the two groups as measured by number of cases of clinical mastitis or California mastitis test.

The influence of lactation on beta-adrenergic receptor kinetics was studied with adipocytes from eight Holstein cows during two physiological states, dry period 30 days prepartum and 30 days postpartum or early lactation. Physiological state had no effect on binding kinetics of (--)-hydrogen-3 labeled dihydroalprenolol. Affinity rate constants (8.2 versus 7.2 X 10(7) min-1 M-1) and equilibrium dissociation constants (7.1 versus 7.9 nM) for both prepartum and postpartum periods were similar. In contrast, the apparent number of beta-adrenergic receptors varied with lactational state (42,154 versus 72,264 sites/cell) for dry and lactating status as estimated in assays containing 5 nM (--)-hydrogen-3 dihydroalprenolol. Glycerol release and adipocyte concentrations of adenosine-3',5'-cyclic phosphoric acid were assayed with or without 10 microM epinephrine. Epinephrine elicited greater release of glycerol in adipocytes from lactating than dry cows (3.91 versus 2.1 mumol/10(6) cells/120 min). The concentration of adenosine-3',5'-cyclic phosphoric acid rose during the first 5 min of incubation in the presence of epinephrine and then fell to base after 10 min. Maximum concentrations at 5 min were not different in adipocytes from dry and lactating cows (250 versus 280 pmol/10(6) cells).