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IEPL; International audience; It has been previously shown that the long-term inhibition of milking-induced prolactin (PRL) release by quinagolide (QN), a dopamine agonist, reduces milk yield in dairy cows. To further demonstrate that PRL is galactopoietic in cows, we performed a short-term experiment that used PRL injections to restore the release of PRL at milking in QN-treated cows. Nine Holstein cows were assigned to treatments during three 5-d periods in a 3 × 3 Latin square design: 1) QN: twice-daily i.m. injections of 1 mg of QN; 2) QN-PRL: twice-daily i.m. injections of 1 mg of QN and twice-daily (at milking time) i.v. injections of PRL (2 µg/kg body weight); and 3) control: twice-daily injections of the vehicles. Mammary epithelial cells (MEC) were purified from milk so that their viability could be assessed, and mammary biopsies were harvested for immunohistological analyses of cell proliferation using PCNA and STAT5 staining. In both milk-purified MEC and mammary tissue, the mRNA levels of milk proteins and BAX were determined using real-time reverse-transcription PCR. Daily QN injections reduced milking-induced PRL release. The area under the PRL curve was similar in the control and PRL injection treatments, but the shape was different. The QN treatment decreased milk, lactose, protein, and casein production. Injections of PRL did not restore milk yield but tended to increase milk protein yield. In mammary tissue, the percentage of STAT5-positive cells was reduced during QN but not during QN-PRL in comparison with the control treatment. The percentage of PCNA-positive cells was greater during QN-PRL injections than during the control or QN treatment and tended to be lower during QN than during the control treatment. In milk-purified MEC, κ-casein and α-lactalbumin mRNA levels were lower during QN than during the control treatment, but during QN-PRL, they were not different from the control treatment. In mammary tissue, the BAX mRNA level was lower during QN-PRL than during QN. The number of MEC exfoliated into milk was increased by QN injections but tended to be decreased by PRL injections. Injections of PRL also increased the viability of MEC harvested from milk. Although PRL injections at milking could not reverse the effect of QN treatment on milk production, their effects on cell survival and exfoliation and on gene expression suggest that the effect of QN treatment on the mammary gland is due to QN's inhibition of PRL secretion.

High-quality colostrum is an important factor influencing neonatal calf health, and quality assessment is essential to obtain good health results. This research evaluated the effects of the calf’s sex, the parity of the cow and the hour of colostrum harvest after parity on the fat, nonfat solids, protein and Ig contents in Holstein colostrum for cows under high grazing conditions in the tropics. The effects of the calf’s sex and parity on somatic cell count (SCC) at the first milking postpartum were determined. A comparison was made between a laboratory method and a farm method for the estimation of the fat and protein content of colostrum. Thirty-three cows were sampled in the study. The calf’s sex was shown to have an effect on the amount of colostrum, on the concentration of fat, and on the amount of milk produced by lactating Holstein cows; all were higher in cows that gave birth to a female calf. Colostrum protein decreased after the first hour postpartum, and the Ig concentration had a tendency to decrease after 4 h. The cows that had parity 1–2 had lower Ig concentrations and total production of Igs, and higher SCC at the first milking postpartum. Ekomilk was a reliable method to measure the colostrum fat on the farm. COL0009556