title: Feeding lactating primiparous sows to establish three divergent metabolic states: II. Effect on nitrogen partitioning and skeletal muscle composition.
abstract: 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.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Canada.
authors.forename: E J
authors.initials: EJ
authors.lastname: Clowes
authors.forename: I H
authors.initials: IH
authors.lastname: Williams
authors.forename: V E
authors.initials: VE
authors.lastname: Baracos
authors.forename: J R
authors.initials: JR
authors.lastname: Pluske
authors.forename: A C
authors.initials: AC
authors.lastname: Cegielski
authors.forename: L J
authors.initials: LJ
authors.lastname: Zak
authors.forename: F X
authors.initials: FX
authors.lastname: Aherne
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000145:classification / Q000378:metabolism; D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D015331:Cohort Studies; D004247:DNA / Q000032:analysis; D004435:Eating / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D007774:Lactation / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry*; D009584:Nitrogen / Q000378:metabolism*; D010298:Parity; D011506:Proteins / Q000032:analysis; D012313:RNA / Q000032:analysis; D013552:Swine / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D011506:Proteins; D012313:RNA; D004247:DNA; D009584:Nitrogen