The frequency of unilateral milking alters leucine metabolism and amino acid removal by the mammary gland of lactating goats

• Published in: Journal of dairy science 2010-01, Vol.93 (1), p.162-169
• Main Authors: Bequette, B.J., Douglass, L.W.
• Format: Article
• Language: English
• Subjects: amino acid; amino acid metabolism; Amino Acids - metabolism; Animal productions; Animals; arteries; Biological and medical sciences; blood flow; blood veins; blood vessels; dairy animals; Dairying - methods; Female; females; Food industries; Fundamental and applied biological sciences. Psychology; goats; Goats - physiology; Lactation - metabolism; Lactation - physiology; leucine; Leucine - blood; Leucine - metabolism; mammary; mammary glands; Mammary Glands, Animal - blood supply; Mammary Glands, Animal - metabolism; Milk and cheese industries. Ice creams; milk protein yield; milking; milking frequency; oxidation; stable isotope; temporal variation; Terrestrial animal productions; Time Factors; Vertebrates
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2009-2459

The objective of this study was to test whether mammary AA metabolism and blood flow (BF) fluctuate in relation to changes in milk protein yield brought about by unilateral milking frequency. To investigate these relationships, the vascular systems of the mammary glands of 4 lactating goats were separated by ligation and flow probes were fitted around the external pudic artery of each gland. Goats were subjected to 3 consecutive periods (5 d each) during which 1) both glands were milked twice daily (2×; period 1); 2) glands were unilaterally milked, with gland A milked 8 times daily and gland B milked incompletely (30% of period 1 milk yield retained in the gland) once daily (8× vs. 1×; period 2); and 3) both glands milked twice daily (2×; period 3). On d 5 of periods 1 (2×) and 2 (8× vs. 1×), arteriovenous [1-13C]Leu kinetics were monitored for each gland. Milk protein yield was greater for gland A compared with gland B. After 2× milking resumed in period 3, yields for both glands returned to period 1 levels. Similarly, BF increased (19%) for gland A (8×), whereas BF was decreased (21%) for gland B (1×). For both glands, BF returned to previous levels when 2× milking resumed in period 3. Mammary net uptakes and oxidation of Leu were greater for the gland milked 8× compared with that milked 1×. Net uptakes from blood of Ile, Leu, Val, Lys, Pro, and Arg were greater (39–79%) for the 8× compared with the 1× gland. In conclusion, the excess removal and oxidation by the mammary gland of some amino acids appears an obligatory requirement to support increases or decreases in milk protein yield when milking frequency is altered.