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Amino acid exchange by the mammary gland of lactating goats when Histidine limits milk production

Bequette, B. J., Hanigan, M. D., Calder, A. G., Reynolds, C. K., Lobley, G. E. and MacRae, J. C. (2000) Amino acid exchange by the mammary gland of lactating goats when Histidine limits milk production. Journal of Dairy Science, 83 (4). pp. 765-775. ISSN 0022-0302

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To link to this item DOI: 10.3168/jds.S0022-0302(00)74939-3

Abstract/Summary

The aim of this study was to monitor amino acid (AA) exchange kinetics of the mammary gland in response to an imposed limitation on His supply for milk production. Lactating goats (n = 4, ∼120 DIM) were fed a low protein ration that provided only 77% of metabolizable protein and 100% of energy requirements for milk production. The protein deficiency was alleviated by infusion into the abomasum of an AA mixture (67 g/d) including (+H; 4.4 g/d) or excluding (−H) His. Goats were assigned to treatments (6 to 7 d) according to a switchback design. On the last day of the first two periods, [U-13C]AA were continuously infused i.v. for 7 h and arterial and mammary vein blood was withdrawn to determine plasma AA concentration and enrichment. Flow probes monitored mammary blood flow. The secretion and enrichments of AA in milk casein were monitored each hour. A threepool model of the gland was used to derive bi-directional rates of plasma AA exchange. Arterial plasma His concentration was lower during −H infusion (8 vs. 73 μM), but those of other AA changed little. Responses to low levels of plasma His were: 1) mammary blood flow increased by ∼33%; 2) the gland’s capacity to remove plasma His increased 43-fold, whereas the gland’s capacity for other AA declined by two- to threefold; and 3) influx and efflux of His by the gland decreased. Thus, as the reduction in His efflux was insufficient to offset the reduced influx, milk protein yield decreased from 118 to 97 g/d.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Life Sciences > School of Agriculture, Policy and Development > Food Production and Quality Division > Animal, Dairy and Food Chain Sciences (ADFCS)
ID Code:90821
Uncontrolled Keywords:amino acid, transporter, mammary gland, goats
Publisher:Elsevier

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