This study investigated the physiological basis of differences in nutrient partitioning between the North American (NA) and New Zealand (NZ) strains of Holstein-Friesian @entity291 by determining the responses to homeostatic challenges at two stages of lactation. @entity413 tolerance tests, @entity1425 challenges and insulin challenges were carried out on consecutive days commencing on day 32    0.48 (mean    s.e.) of lactation (T1) and again commencing on day 137    2.44 of lactation (T2). The insulin and non-esterified @entity844 ( @entity3691 ) responses to @entity413 infusion did not differ between the strains. The NZ strain had a greater clearance rate (CR) of @entity413 (2.04% v. 1.66%/min) and tended to have a shorter (34.4 v. 41.1 min) @entity413 half-life (t  ) at T2 when infused with @entity413 . The NA @entity291 had a greater @entity413 response to @entity1425 infusion across T1 and T2, and tended to have a greater insulin response to @entity1425 infusion. Plasma @entity3691 concentration declined to similar nadir concentrations for both strains at T1 in response to insulin, though from a higher basal concentration in NA @entity291 , resulting in a greater (-2.29 v. -1.38) @entity3691 area under the response curve for NA @entity291 . @entity413 response to insulin varied with time, tending to be greater for NA at T1, but tending to be lower for NA at T2. The results indicated that NA @entity291 had a greater glycogenolytic response to @entity1425 , but both strains had similar lipolytic responses. The results also imply that higher basal circulating @entity3691 concentrations in the NA strain in early lactation were not due to diminished adipose tissue responsiveness to insulin. There were indications that @entity413 CR was greater in NZ @entity291 in mid-lactation, and may form the basis of increased body tissue accretion during mid- to late-lactation in this strain.

Responses of North American and New Zealand strains of Holstein-Friesian dairy XXXX to homeostatic challenges during early and mid-lactation.

@entity844 :: ('CHEBI:35366', 'Chemical') :: ['fatty acid'] @entity1425 :: ('MESH:D004837', 'Chemical') :: ['epinephrine'] @entity3691 :: ('MESH:D005230', 'Chemical') :: ['NEFA'] @entity291 :: ('9913', 'Species') :: ['cows', 'cattle'] @entity413 :: ('MESH:D005947', 'Chemical') :: ['glucose', 'Glucose']
@entity291 :: (9913,Species) :: ['cattle']
