Effect Of Encapsulated Niacin On Resistance To Acute Thermal Stress In Lactating Holstein Cows
R. B. Zimbelman*, J. Muumba, L. H. Hernandez, J. B. Wheelock, G. Shwartz, M. D. O’Brien, L. H. Baumgard, and R. J. Collier, University of Arizona.
A physiological effect of niacin consumption is vasodilatation of blood vessels which facilitates dissipation of core body heat to the surface of the body. Previous work with feeding unprotected niacin in heat-stressed dairy cattle demonstrated a better ability to cope with heat stress by maintaining lower body temperatures and/or production levels.
Twelve multiparous cows were fed either 0 or 12 gm of Niashure™ rumen-protected niacin and were exposed to two environmental temperature patterns: thermo-neutral (TN) and heat stress (HS) of seven
days each. Studies were conducted in environment chambers. University of Arizona the temperature-humidity index (THI) range never exceeded 72 for the TN pattern. The HS pattern consisted of a circadian THI range exceeding 72 for 12 hours per day.
Respiration rate, surface temperatures of both shaved (S) and unshaved (U) areas, and rectal and vaginal temperatures. Vaginal temperatures were recorded at 15 min. intervals and averaged over the last 72 hours of the HS phase.
The average sweating rate for cows fed Niashure was higher (p <.0001) than for control cows during the daytime stress phase of the HS period. Cows fed the 12 gm/d of Niashure maintained lower (p < .0001) body core temperatures as indicated by vaginal temperatures, 38.0°C vs. 38.4°C (comparable to 1°F difference), vs. control cows.
Niashure at 12 gm/hd/day allowed cows challenged with a mild heat stress event to dissipate more body heat thus allowing them to maintain a lower body core temperature.
Abstract # 344
Twelve multiparous Holstein cows producing an average of 31.7 kg/d and balanced for parity and stage of lactation were randomly assigned to either 0 g encapsulated niacin/d (C) or 12 g niacin/d (NIASHURE™) (Trt) and were exposed to two environmental temperature patterns, thermoneutral (TN) and heat stress (HS). The temperature humidity index (THI) range of TN pattern never exceeded 72 while HS consisted of circadian THI temperature range exceeding 72 for 12 hours per day. Milk yields were recorded twice a day and milk sampled once a day for composition. Cows were fed twice a day and refusal and water intake was measured once a day. Respiration rates, surface temperatures of both shaved (S) and unshaved (U) areas were taken at the rump, (ST-R-S, ST-R-U) shoulder, (ST-S-S, ST-S-U), and tailhead (ST-T-S, ST-T-U), and sweating rates (SR) of the shoulder shaved (SR-S) and unshaved (SR-U) areas 4 x daily. Rectal temperatures (RT) were measured four times a day. Cows in Trt had increased DMI (40.7 vs 37.7, g/d) compared to cows in C. Surface temperatures were unaffected by Trt but were affected by shaving (32.5 shaved vs. 31.4°C unshaved). Cows given Trt had a tendency for higher average sweating rates when shaved (66.3 vs 57.8 g/M2/hr, P=0.11) and numerically for unshaved (57.4 vs 52.7 g/M2/hr) over the entire 24 hour period and these differences grew larger during periods of peak thermal stress along with the entire study (62.0° shaved vs. 55.0° unshaved). Between 11:00 AM and 4:00 PM average sweating rate for Trt group was higher than C (81.1 vs. 68.2 g/M2/hr shaved; P<0.0001 and 70.6 vs. 62.3 unshaved; P<0.0001). Vaginal temperatures recorded at 15 min intervals and averaged over last 72 hours of period 2 (HS) were lower (38.4 vs. 38.0°C; P < .0001) for cows given Trt compared to cows in C. We conclude that cows given encapsulated Niacin had higher sweating rates and lower core temperatures during acute thermal stress.
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