Feeding lactating primiparous sows to establish three divergent metabolic states: II. Effect on nitrogen partitioning and skeletal muscle composition
Clowes, E.J., Williams, I.H., Baracos, V.E., Pluske, J.R., Cegielski, A.C., Zak, L.J. and Aherne , F.X. (1998) Feeding lactating primiparous sows to establish three divergent metabolic states: II. Effect on nitrogen partitioning and skeletal muscle composition. Journal of Animal Science, 76 (4). pp. 1154-1164.
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We established an experimental model to study nitrogen (N) partitioning in lactating primiparous sows alimented to three levels of nutrient intake. Thirty-six sows fitted with a gastric cannula and fed a 15.4 MJ DE/kg and 18.6% CP diet were allocated to one of three treatments after farrowing: 1) ad libitum-fed; 2) restricted-fed to 55% of the ad libitum feed intake; and 3) superalimented to at least 125% of the ad libitum feed intake. These feed intakes were successfully achieved throughout lactation. Nitrogen balance was studied for three 5-d periods starting on d 2, 11, and 19 of lactation, and a triceps muscle biopsy was taken on d 26. For all treatments, N intake increased, milk N production increased, urinary N losses decreased, but fecal N losses increased as the 28-d lactation progressed. Restricted-fed sows had the lowest fecal N and urinary losses and mobilized the most maternal protein (-23.0 vs -7.4 +/- 6.5 g N/d for ad libitum-fed sows) during lactation. As a consequence of these economies, and extensive protein mobilization, restricted-fed sows were able to maintain milk N production similar to that of sows on the other treatments. Superalimented sows did not mobilize protein, had the poorest protein digestibility, directed the least digestible N toward milk (40.1 vs 78.3% in restricted-fed sows), and produced amounts of milk N similar to those produced by sows on the other treatments. The treatment differences in N retention measured by N balance were reflected in differences in skeletal muscle variables and urinary creatinine. Skeletal muscle cell size (protein:DNA ratio) and protein synthetic capacity (RNA:DNA ratio) increased in response to feed intake. The protein:DNA ratio increased (P < .01) linearly and the RNA:DNA ratio increased (P < .05) in a curvilinear manner. These data suggest that primiparous sows partition additional retained N toward their maternal reserves rather than milk N. They also suggest that sows fed inadequate N intakes maintain milk production by mobilizing maternal protein reserves. Such sows also conserve maternal N during lactation, possibly by reducing muscle protein synthesis.
|Publication Type:||Journal Article|
|Publisher:||American Society of Animal Science|
|Copyright:||© 1998 by American Society of Animal Science|
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