Feeding Niashure at 12 gm/hd/day allowed cows challenged with a mild-heat-stress event to dissipate more body heat and allowed them to maintain a significantly lower core body temperature. The experiment (reported at 2007 ADSA meetings) was conducted with a small number of animals in environmental chambers at the University of Arizona. The current study involves a larger number of cows in a commercial dairy herd in Arizona from August through October 2007.

What

400 lactating primiparous and multiparous Holstein cows were randomly assigned to a switchback design (two 30-day periods) of either control (CON, no niacin, n = 200 cows) or Niashure™ (Trt, 12 gm/d, n = 200).

Parameters Monitored

Milk yields were recorded 3x and a monthly sample collected for milk components. Vaginal temperatures were collected using thermocron iButtons inserted into a random sub-sample of cows from each pen.

Key Results

1) Body core temperatures were reduced for Niashure Trt during times of peak thermal load.

2) Milk fat and protein percent were elevated for Niashure vs. CON group.

3) Fat- and energy-corrected milk yields were higher for Niashure Trt.

Implications

Supplementing lactating cows with Niashure during summer heat stress reduced body core temperature

and increased both milk protein and fat percent, in turn elevating fat- and energy-corrected milk yields.

Abstract

Effect of feeding rumen-protected niacin on core body temperature and milk production in lactating Holstein dairy cows during summer heat stress.

R. B. Zimbleman*, R. J. Collier, and T. R. Bilby, University of Arizona, Tucson.

Niacin has been shown to increase resistance to thermal stress in cattle by increasing whole body evaporative heat loss and cellular heat shock response to thermal stress in vitro. As raw niacin is extensively degraded in the rumen, this study utilized encapsulated niacin (NIASHURE™) to determine effects on body temperature, milk yield and composition. A total of 400 lactating primiparous and multiparous Holstein cows were randomly assigned to a switchback design (two 30d periods) of either control (C, no niacin n = 200) or rumen-protected niacin (RPN, cows supplemented with 12g/d/cow of encapsulated niacin, n = 200). Groups were balanced for DIM (166 +/–11), milk yield, and parity prior to start of the study which was conducted from August 7th thru October 7th, 2007, on a commercial dairy in Arizona. Milk yields were recorded 3X daily and a monthly milk sample was collected for milk components. Vaginal temperatures were collected using thermochron iButtons (MAXIM Integrated Products Inc., Sunnyvale, CA) temperature loggers attached to an intravaginal device and inserted into a random sub-sample of cows (n = 16) from each pen (n = 2) with similar DIM, milk yields, and parity for 7 d. Body core temperatures were decreased for the RPN group during periods of peak thermal load from 1300 to 1600 h (P < 0.01). Milk fat and protein percent was elevated in the RPN versus C groups (3.65 vs. 3.38 and 3.09 vs. 3.05%, respectively; P < 0.01). Subsequently both fat- and energy-corrected milk was greater for cows in the RPN group compared with cows in the C group (39.7 vs. 38.2 and 39.6 vs. 38.4kg, respectively; P < 0.01). In addition, both fat- and energy-corrected milk was increased in multiparous compared to primiparous cows (40.7 vs. 37.2 and 40.7 vs. 37.3 kg; P < 0.01). However, groups did not  differ in milk yield or DMI. In conclusion, supplementing lactating cows with rumen-protected niacin during summer heat stress reduced core body temperature and increased both fat and protein percent, in turn, elevating fat- and energy-corrected milk yields.