title: A dose-response evaluation of rumen-protected niacin in thermoneutral or heat-stressed lactating Holstein cows.
abstract: Twenty-four multiparous high-producing dairy cows (40.0±1.4kg/d) were used in a factorial design to evaluate effects of 2 environments [thermoneutral (TN) and heat stress (HS)] and a dose range of dietary rumen-protected niacin (RPN; 0, 4, 8, or 12g/d) on body temperature, sweating rate, feed intake, water intake, production parameters, and blood niacin concentrations. Temperature-humidity index values during TN never exceeded 68 (stress threshold), whereas temperature-humidity index values during HS were above 68 for 24h/d. The HS environment increased hair coat and skin, rectal, and vaginal temperatures; respiration rate; skin and hair coat evaporative heat loss; and water intake and decreased DMI (3.5kg/d), milk yield (4.1kg/d), 4% fat-corrected milk (2.7kg/d), and milk protein yield (181.7g/d). Sweating rate increased during HS (12.7g/m(2) per h) compared with TN, but this increase was only 10% of that reported in summer-acclimated cattle. Niacin supplementation did not affect sweating rate, dry-matter intake, or milk yield in either environment. Rumen-protected niacin increased plasma and milk niacin concentrations in a linear manner. Heat stress reduced niacin concentration in whole blood (7.86 vs. 6.89μg/mL) but not in milk. Reduced blood niacin concentration was partially corrected by dietary RPN. An interaction existed between dietary RPN and environment; dietary RPN linearly increased water intake in both environments, but the increase was greater during HS conditions. Increasing dietary RPN did not influence skin temperatures. During TN, supplementing 12g/d of RPN increased hair coat (unshaved skin; 30.3 vs. 31.3°C at 1600h) but not shaved skin (32.8 vs. 32.9°C at 1600h) temperature when compared with 0g/d at all time points, whereas the maximum temperature (18°C) of the room was lower than skin temperature. These data suggest that dietary RPN increased water intake during both TN and HS and hair coat temperature during TN; however, core body temperature was unaffected. Thus, encapsulated niacin did not improve thermotolerance of winter-acclimated lactating dairy cows exposed to moderate thermal stress in Arizona.
authors.affiliation: School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson 85721.
authors.forename: S
authors.initials: S
authors.lastname: Rungruang
authors.affiliation: School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson 85721.
authors.forename: J L
authors.initials: JL
authors.lastname: Collier
authors.affiliation: Department of Animal Sciences, Virginia Tech, Blacksburg 24061.
authors.forename: R P
authors.initials: RP
authors.lastname: Rhoads
authors.affiliation: Department of Animal Sciences, Iowa State University, Ames 50011.
authors.forename: L H
authors.initials: LH
authors.lastname: Baumgard
authors.affiliation: Balchem Corporation, New Hampton, NY 10958.
authors.forename: M J
authors.initials: MJ
authors.lastname: de Veth
authors.affiliation: School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson 85721. Electronic address: rcollier@ag.arizona.edu.
authors.forename: R J
authors.initials: RJ
authors.lastname: Collier
mesh_terms: D000818:Animals; D001130:Arizona; D001833:Body Temperature Regulation / Q000187:drug effects; D002417:Cattle; D004032:Diet / Q000662:veterinary; D004041:Dietary Fats / Q000032:analysis; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D005260:Female; D018869:Heat-Shock Response; D006813:Humidity; D007774:Lactation; D016014:Linear Models; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D008894:Milk Proteins / Q000032:analysis; D009525:Niacin / Q000097:blood / Q000494:pharmacology*; D056152:Respiratory Rate / Q000187:drug effects; D012417:Rumen / Q000187:drug effects* / Q000378:metabolism
chemical_list: D004041:Dietary Fats; D008894:Milk Proteins; D009525:Niacin
keywords: dose; heat stress; lactating dairy cow; niacin