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Variations in Mammary Metabolism During the Natural Filling of the Udder with Milk over a 12-h Period Between Two Milkings¹

M. C. Thivierge^*,2, D. Petitclerc, J. F. Bernier^*, Y. Couture and H. Lapierre

^* Département des sciences animales, Pavillon Paul-Comtois, Université Laval, Sainte-Foy, QC, Canada, G1K 7P4
Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Lennoxville, QC, Canada, J1M 1Z3
Faculté de médecine vétérinaire, Université de Montréal, St-Hyacinthe, QC, Canada, J2S 7C6

Corresponding author:
H. Lapierre; e-mail:
lapierreh{at}em.agr.ca.

Two groups of four Holstein cows, one in their second and the other in their third or fourth lactation, were used to study temporal variations of mammary metabolism over a 12-h period between two milkings. Blood samples were collected every 30 min from an artery and a mammary vein during a 12-h interval between two milkings. Isoleucine, leucine, lysine, methionine, and phenylalanine mammary net fluxes varied or tended to change over time after milking with a similar pattern between whole blood and plasma. For these amino acids, whole blood and plasma net fluxes reached their maximum over the first 8 h after milking. Simultaneously, respiratory quotients decreased linearly and varied from 2.31 to 2.01 during the first 8 h of the period, suggesting active mammary lipogenesis. From 8 to 12 h after milking, mammary amino acid net fluxes decreased, while mammary oxygen uptake tended to increase with a concomitant decrease in the respiratory quotient reaching 1.84 to 1.40. These findings suggest that, beginning 8 h after milking, mammary uptake of amino acids starts to decrease and catabolic processes appear promoted; this phenomenon could help to explain the increase in milk production reported in the literature with increased milking frequency.

Key Words: amino acid • mammary gland • uptake • nutrient

Abbreviation key: AV = arteriovenous, FIL = feedback inhibitor of lactation

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