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- Title
Effects of heat stress and rbST on production parameters and glucose homeostasis.
- Authors
Wheelock, J. B.; Sanders, S. R.; Shwartz, G.; Hernandez, L. L.; Baker, S. H.; McFadden, J. W.; Odens, L. J.; Burgos, R.; Hartman, S. R.; Johnson, R. M.; Jones, B. E.; Collier, R. J.; Rhoads, R. P.; VanBaale, M. J.; Baumgard, L. H.
- Abstract
Study objectives were to evaluate production parameters and glucose homeostatic variables in rbST-treated lactating dairy cattle during short-term heat stress (HS) or in pair-fed animals (UF). Twenty-two multiparous (99 DIM, 656 kg BW) Holstein cows [n=10 (HS), n=12 (UF)] were subjected to three experimental periods: 1) thermoneutral, ad libitum intake for 7d, 2) HS or UF for 7d, and 3) HS or UF with rbST (Posilac®, Monsanto, St. Louis MO, administered on d1 of P3) for 7d. All cows received an I.V. glucose (d5) and insulin (d6) challenge during each period. HS conditions were cyclic to mimic an AZ July day, with temperatures ranging from 29.7 to 39.2°C. Milk yield, DMI, EBAL and body temperature indices were measured daily. Heat stress reduced DMI by 30%, and by design, UF cows had similar intake reductions (28%). Rectal temperatures and respiration rates increased during HS (38.6 to 40.5°C and 44 to 89 breaths/min, respectively). During HS and UF, milk yield decreased by 27.5% (9.7 kg) and 15.3% (4.8 kg) respectively, indicating reduced DMI only accounted for 50% of the decreased milk production. Milk yield increased with rbST (~13%) in both HS and UF. Cows in both treatments were in positive EBAL (>3.7 MCal/d) but entered NEBAL during HS and UF (<-3.7 MCal/d). No effect of HS on the rate of glucose disposal (mg/dL/min or AUC) was detected, but UF and rbST caused mild insulin resistance (16-30%, based on mg/dl/min and AUC). HS and UF treatments decreased (11%) basal glucose concentrations without an additional effect of rbST. HS had no effect on basal NEFA levels; however UF (despite a similar calculated EBAL) had increased (60%) basal NEFA concentrations. We conclude that reduced nutrient intake accounts for only 50% of HS-induced decreases in milk yield and, based upon glucose challenge and basal NEFA data, increased extra-mammary insulin sensitivity may contribute to the additional reduction in milk yield.
- Subjects
SAINT Louis (Mo.); LACTATION in cattle; MONSANTO Co.; GLUCOSE; MILK yield; INGESTION; DAIRY cattle; HOMEOSTASIS
- Publication
Journal of Animal Science, 2006, Vol 84, p290
- ISSN
0021-8812
- Publication type
Article