Forty Israeli-Holstein 5-d-old calves were used to determine the effect of increasing calf body weight (BW) and skeletal size during the nursing period on age and skeletal size at puberty and on skeletal size and performance during first lactation. The calves were randomly allotted to 2 experimental groups as follows: milk replacer (MR) [calves were given 0.450 kg/d dry matter of milk replacer for the first 50 d of life] and milk-fed (MF) [calves had free access to milk in two 30-min meals/d]. From weaning to 180 d of age, all calves were fed the same diet. At 180 d of age, the MR and MF calves were each divided into 2 equal subgroups: one subgroup from each treatment was given only growing ration, and the other was given the same ration supplemented with fish meal to supply 2% crude protein (CP) (treatments MR + CP and MF + CP, respectively). Finally, at 270 d of age, all calves were housed together and fed a growing heifer's ration until first calving. During the entire nursing period, the MF calves consumed 9.8% more DM, 39.7% more CP, and 52.4% more metabolizable energy than the MR calves. At 60 d of age, BW and all skeletal parameters were higher in the MF calves than in the MR calves. During the entire rearing period (60 to 550 d), the average BW of the MF calves was greater by 16 kg than the BW of the MR calves. Nursing management did not affect differences in skeletal parameters at calving. Average age at puberty onset was 272 +/- 26.8 d; MF calves reached puberty 23 d earlier than MR calves. Yields of milk (kg/305 d) and fat-corrected milk (FCM, kg/d) were greater for the MF + CP heifers than for the MR heifers. It was concluded that nursing by ad libitum milk, as compared with milk replacer, affected BW but not skeletal size of the adult animal, decreased age of puberty onset, and increased FCM yield at first lactation. Supplementing the diet with 2% CP during the prepubertal period increased BW but not skeletal size of the adult animal and 305-d milk and FCM yields during first lactation.

Albumin is a well-characterized product of the liver. In the present study, objectives were to determine if the albumin gene is also expressed in various nonhepatic tissues in the bovine; whether mammary gland epithelial cells synthesize albumin; and how its synthesis is affected by bovine mastitis. Albumin expression was monitored using reverse transcription-polymerase chain reaction. Tissues examined were: liver, mammary gland, tongue, intestine, lymph gland, testicle, ovary, and uterus. All tissues except the ovary expressed the albumin gene, albeit less so than the liver. The highest level of expression (other than liver) was found in the lymph nodes but expression was also found in the mammary gland. Incubation of mammary gland explants with the labeled amino acid L-[(35)S] methionine resulted in formation of labeled immunoprecipitable albumin, newly synthesized in the explant. Immunoprecipitable albumin in the medium verified that newly synthesized albumin was also secreted into the medium. This shows that the gland itself is a source of milk albumin. Albumin mRNA expression was approximately 4 times higher in mammary gland tissue from 6 mastitic cows compared with expression in mammary tissue from 6 healthy glands. Further, secretion of albumin was increased 3.5-fold from explants of mastitic mammary glands compared with secretion from explants of healthy mammary glands. Addition of lipopolysaccharide increased the synthesis and secretion of albumin in mammary gland cells in a dose-dependent manner. Exposure to lipopolysaccharide accelerated albumin synthesis in a time-dependent manner up to 48 h. These results lead us to suggest that the secretion of albumin by the mammary gland is part of the innate nonspecific defense system.

We examined the effect of calving month (CM) on the production of milk and milk protein by Israeli Holstein dairy cows located in the main climatic zone of Israel during their third and fourth lactations, and found it to be significant. Cows that calved in December produced the highest milk and milk protein yields, and those that calved in June produced the lowest, 92.8% of the maximum. The combined effect of the environmental average temperature and day length accounted for 0.96 of the variability in average milk production during lactation and 0.93 of that in average protein production during lactation. Average milk production was reduced by 0.38 kg/degree C and average protein production was reduced by 0.01 kg/degree C. Elongation of daylight increased average milk production by 1.2 kg/h and average protein production by 0.02 kg/h of daylight. Analysis of the temperature pattern effect on milk and protein yield during lactation indicated that cows at the second month (the pike of their milk yield) are more vulnerable to the negative temperature effect than cows on the ninth month of lactation.

-Dexamethasone was injected in dairy cows in order to get a better insight into the effects of corticosteroids on milk secretion and composition. A single intramuscular dose of 40 mg dexamethasone caused a 45% reduction in milk yield after 24 h; full recovery took 5 d. The secretion of fat, casein and magnesium was not affected by the treatment. Consequently, the concentration of fat, total protein, total casein, magnesium and phosphorus increased then decreased in direct proportion to the changes in milk yield. The secretion of total protein, calcium and phosphorus decreased as a result of the treatment. The concentration of lactose and the monovalent ions (sodium, potassium, and chlorine) was unaffected, and as a result their secretion decreased and returned to pretreatment level in direct inverse proportion to the changes in milk yield. Whey protein secretion decreased for 48 h and was responsible for the decrease in total protein secretion for 48 h. The most profound effect of dexamethasone is the reduction in the secretion of the osmotic components. milk yield / dairy cows / stress / corticosteroids Résumé -Effet de la dexaméthasone sur la production et la composition du lait chez les vaches laitières. La dexaméthasone a été injectée à des vaches laitières afin de mieux comprendre les effets des corticostéroïdes sur la sécrétion et la composition du lait. Une dose unique intramusculaire de 40 mg de dexaméthasone a réduit de 45 % la production de lait après 24 h ; le retour total à la production antérieure a pris 5 jours. La sécrétion des lipides, des caséines et du magnésium n'a pas été affectée par le traitement. En conséquence, la concentration des lipides, des protéines totales, des caséines totales, du magnésium et du phosphore a augmenté puis a diminué proportionnellement aux changements de production laitière. La sécrétion des protéines totales, du calcium et du phosphore a diminué à la suite du traitement. La concentration du lactose et des ions monovalents (sodium, potassium et chlore) est restée inchangée ; leur sécrétion a diminué et est revenue au niveau initial dans une proportion inverse aux modifications de la production laitière. La sécrétion des protéines du lactoserum a diminué pendant 48 h et a été responsable de la diminution de la sécrétion des protéines totales

Active transport of glutamate by Escherichia coli K-12 requires both Na+ and K+ ions. Increasing the concentration of Na+ in the medium results in a decrease in the Km of the uptake system for glutamate; the capacity is not affected. Glutamate uptake by untreated cells is not stimulated by K+. K+-depleted cells show a greatly reduced capacity for glutamate uptake. Preincubation of such cells in the presence of K + fully restores their capacity for glutamate uptake when Na+ ions are also present in the uptake medium. Addition of either K+ or Na+ alone restores glutamate uptake to only about 20% of its maximum capacity in the presence of both cations. Changes in K-+ concentration affect the capacity for glutamate uptake but have no effect on the Km of the glutamate transport system. Ouabain does not inhibit the (Na+-K+)-stimulated glutamate uptake by intact cells or spheroplasts of E. coli K-12.