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Supplementation of Nicotinic Acid for Lactating Holstein Cows Under Heat Stress Conditions
Supplementation of Nicotinic Acid for Lactating Holstein Cows Under Heat Stress Conditions A. DI COSTANZO,1 J. N. SPAIN, and D. E. SPIERS Department of Animal Science, University of Missouri, Columbia 65211
ABSTRACT Twenty-six lactating Holstein cows (90 d of lactation) were blocked according to milk production, parity, and days of lactation for assignment to one of two dietary treatments. Diets included a control diet with no supplemental niacin and a diet supplemented with increasing concentrations of niacin (12, 24, or 36 g/d per cow over three consecutive 17-d periods. Cows were housed in a covered free-stall barn and were fed and milked twice daily. Mean maximum air temperatures and temperature-humidity indexes were 28.5, 31.4, and 25.2°C and 79.6, 85.1, and 75, respectively, for the three periods. Rectal temperature was measured with a rectal probe, tail and rump temperatures by infrared thermometry, and respiratory rate by visual observation. Measurements were made daily at 0800, 1600, and 2200 h. Rectal temperature was not affected by treatment. Comparison of skin temperatures for control cows and cows fed niacin showed higher temperatures at the tail (34.0 vs. 33.7°C at 0800 h; 35.1 vs. 34.8°C at 1600 h, respectively) and rump (34.1 vs. 33.7°C at 0800 h; 35.3 vs. 35.0°C at 1600 h, respectively) for control cows during period 1. No differences in thermal responses were observed during period 3. Niacin did not significantly increase milk production but decreased skin temperatures during periods of mild or severe heat stress. ( Key words: nicotinic acid, heat stress, vasodilation) Abbreviation key: Glc = glucose, NA = nicotinic acid, TCI = thermocirculatory index, THI = temperature-humidity index. INTRODUCTION Summer temperature and humidity conditions can decrease milk production from 10 to 35% below yearly means ( 9 ) . This depression may be mediated by a reduction in feed intake, which is reported to occur as ambient temperature rises above 27°C (15). An increase in body temperature usually accompanies this
Received December 27, 1995. Accepted September 27, 1996. 1Current address: Tampico, Tamaulipas, Mexico 89410. 1997 J Dairy Sci 80:1200–1206
rise in ambient temperature and may be a primary stimulus for reductions in both feed intake and milk production. Whole body heat content and body temperature are dependent on rates of heat gain and loss (16). These rates, in turn, are affected by thermal gradients among core, skin, and ambient sites. Any shift in peripheral or internal vasomotor activity may alter the heat loss process and affect body temperature. Therefore, a treatment that has the potential to increase body heat transfer could possibly ameliorate the effects of reduced feed intake and milk production that occur during summer. Nicotinic acid ( NA) , a B vitamin, elicits vasodilatory reactions that may be beneficial for cows under heat stress. Peripheral and internal vasodilation, caused by therapeutic concentrations of NA ( 1 ) , may enhance heat transfer from core to skin sites and generate a temperature gradient favoring heat loss from skin to environment. Thus, the objective of this experiment was to evaluate NA supplementation as a means of improving thermoregulatory responses of lactating Holstein cows during summer conditions. MATERIALS AND METHODS Twenty-six lactating Holstein cows (90 d of lactation) were utilized in a randomized complete block design and assigned to one of two dietary treatments: the control diet with no supplemental NA or a diet with NA supplemented at increasing concentrations over three consecutive 17-d periods (period 1 = 12 g/d, period 2 = 24 g/d, and period 3 = 36 g/d per cow). Diets were formulated to provide 18% CP and 1.74 Mcal/kg of diet with a forage to concentrate ratio of 55:45 (wt/wt) (Table 1). Cows were individually fed a TMR twice a day (0800 and 1500 h ) using electronic feeding gates (American Calan Inc., Northwood, NH). Orts were measured once a day. Feed samples were taken once a day for DM analysis, and composites were prepared weekly for N and ADF determination by AOAC ( 2 ) procedures. Milk weights were recorded at each milking (0030 and 1230 h). Weekly milk samples from two consecutive milkings were analyzed for fat and protein content (Multi-Spec Mark 1; Foss Food Technology, Min-
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NIACIN FOR LACTATING COWS UNDER HEAT STRESS TABLE 1. Percentage of ingredients and nutrient composition of the experimental diets. Dietary treatment Composition
Control1
NA
( % of DM) Ingredient Alfalfa haylage Corn silage Earlage Corn, cracked Cottonseed, whole Soybean meal (48% CP) Soybean hulls Blood meal Alifet2 Cottonseed meal Wheat midds NA,3 g/d Nutrient DM, % as fed ADF CP
8.0 31.5 10.0 16.8 11.0 11.5 1.5 1.5 0.2 4.2 1.5 0
8.0 31.5 10.0 16.8 11.0 11.5 1.5 1.5 0.2 4.2 1.5 12
56.5 22.0 18.5
57.2 23.0 18.2
1No
supplemental nicotinic acid (NA). USA, Inc. (Cincinnati, OH). 3For period 1, NA supplementation was 12 g/d per cow; for period 2, NA was increased to 24 g/d per cow; and, for period 3, NA was 36 g/d per cow. 2Alifet,
neapolis, MN) and SCC (Bentley Somacount 300; Bentley Instruments, Chaska, MN) by the Missouri DHIA Federation (Springfield). Both 4% FCM and energy-corrected milk (ECM) were calculated using the following equations (18): 4% FCM = (0.4 × MP) + (15 × FY) and ECM = MP × [(40.72 × FY) + (22.65 × PY) + 102.7]/340 where MP = milk production, FY = fat yield, and PY = protein yield. Body weight and body condition scores were recorded at the beginning of the study and at the end of each 17-d experimental period. Blood samples were collected from the coccygeal vein immediately before recording BW. Plasma was separated by centrifugation (2500 × g for 15 min) and subsequently stored frozen (–20°C ) until analysis. Plasma glucose ( Glc) was measured by hexokinase reactivity (Sigma Chemical Co., St. Louis, MO). Nonesterified fatty acids were quantified by a controlled oxidation method (NEFA kit; Wako Chemicals, Richmond, VA). Plasma urea N was measured using the procedures of Coulombe and Favreau ( 3 ) .
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Cows were housed in a covered free-stall barn and were provided with forced-air ventilation (wind velocity = 4 m/s) using 3-m diameter fans. Rectal temperatures were recorded using a stainless steel thermistor probe (Cole Parmer Instruments, Chicago, IL) attached to a recorder (Cole Parmer Instruments). Skin temperatures were measured on the tail and rump of each cow using a portable infrared thermometer (Linear Laboratories, Fremont, CA). Tail temperature was recorded at vulva height on a previously shaved spot. Rump temperature was measured at the central part of the right rump. Respiratory frequencies were recorded by visual observation and were reported as the number of breaths per minute. Temperatures and respiratory frequencies were determined twice daily for period 1 (0800 and 1600 h ) and three times daily for periods 2 and 3 (0800, 1600, and 2200 h). The additional time was added to monitor nighttime cooling based on the reported circadian rhythm of the core body temperature of cattle (19), which was important given the higher minimum temperature-humidity index ( THI) . Thermocirculatory index ( TCI) was calculated according to procedures of Ingram and Mount ( 8 ) and represented thermal conductance when heat was transferred from core body to peripheral tissues and from the periphery to the environment. The experiment was conducted from July 27 to September 15, 1993. Maximum and minimum air temperature and relative humidities were recorded by continuous chart psychrothermometer (CTH-532; Omega Instruments, Stamford, CT) located 1 m from the floor in the central part of the housing area in an empty free stall. Separate measurements of air temperature and relative humidity were made using a high precision temperature probe (digital hygrometer-thermometer; Fisher Scientific, Pittsburgh, PA) at the time of rectal and skin temperature measurements. Readings from the chart psychrothermometer were adjusted by regression analysis against readings from the high precision temperature probe to improve the accuracy of the daily maximum and minimum values for temperature and humidity. The THI, an indicator of the combined influence of temperature and humidity, was calculated as described by Igono et al. ( 7 ) . Results were analyzed using the general linear models procedure of SAS (14). The model was analyzed as a randomized complete block with repeated measurements over time and was tested for effects of date, treatment, and block within period. The rationale to utilize increasing concentrations of NA over time was to avoid refractory effects of the cow to the vitamin. As a consequence, ANOVA was conducted within the experimental period. Through Journal of Dairy Science Vol. 80, No. 6, 1997
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TABLE 2. Mean minimum and maximum ambient temperature and relative humidity ( R H ) per experimental period. Minimum
Maximum
Period
Temperature
RH
Temperature
RH
1 2 3
( °C ) 20.4 22.9 17.3
(%) 72.1 77.1 77.4
( °C ) 28.5 31.4 25.2
(%) 91.8 99.8 100.0
these tests, effects of dietary treatments were evaluated within period and not among periods. Significance was declared at P < 0.05 and trends at P < 0.20 unless otherwise indicated.
Figure 1. Changes in the daily temperature-humidity index (THI) during experimental periods. Temperature-humidity index at 0800 h ( - - -); THI at 1600 h ( — ) .
RESULTS Maximum and minimum ambient temperatures and relative humidity by experimental period are shown in Table 2. Calculated THI per experimental period are reported in Table 3. Period 1 had a mean maximum ambient temperature of 28.5°C and was designated as a period of mild heat stress. As summer progressed, period 2 was characterized by severe heat stress conditions; mean maximum ambient temperature and maximum relative humidity were 31.4°C and 99.8%, respectively. In contrast to period 2, period 3 was characterized with no heat stress conditions, even though the maximum relative humidity remained elevated. The changes in temperature and humidity across the experiment are illustrated in Figure 1. Table 4 shows the effect of NA supplementation on production responses across the three experimental periods. Milk production was numerically higher for cows fed diets supplemented with NA than for cows consuming the control diet. No statistical differences were found in any experimental period in milk production or 4% FCM between treatment groups. In addition, NA supplementation tended to increase
TABLE 3. Mean minimum and maximum temperature-humidity indexes (THI) per experimental period.1 THI Period
Minimum
Maximum
1 2 3
68.2 73.2 63.1
79.6 85.1 75.0
1Minimum
and maximum temperature and humidity values were recorded through a chart psychrothermometer and adjusted by a high precision THI probe. Journal of Dairy Science Vol. 80, No. 6, 1997
DMI during period 1 but decreased DMI in period 3 (21.2 vs. 20.0 kg/d per cow for control cows and cows fed diets supplemented with NA, respectively). Dietary treatment did not affect milk composition in any of the experimental periods (Table 4). Numerical trends for increased fat or protein yields were observed mainly as a consequence of increased milk production. Energy-corrected milk was not different
TABLE 4. Milk production, 4% FCM, and DMI per period. Dietary treatment Item
Control1
NA
SE
P
(kg/d) Period 1 Milk Fat, % Protein, % 4% FCM2 DMI ECM2,3 Period 2 Milk Fat, % Protein, % 4% FCM DMI ECM Period 3 Milk Fat, % Protein, % 4% FCM DMI ECM 1No
28.0 3.40 2.90 25.5 21.7 25.2
29.0 3.33 2.91 26.1 22.5 25.9
0.52 0.20 0.17 0.49 0.48 0.51
0.45 0.55 0.78 0.63 0.09 0.59
25.0 3.45 2.90 22.9 17.9 22.7
25.9 3.38 2.91 23.5 17.8 23.3
0.54 0.25 0.18 0.50 0.49 0.49
0.34 0.45 0.77 0.55 0.97 0.49
28.0 3.33 3.17 25.2 21.2 25.5
28.7 3.35 3.17 25.9 20.0 26.2
0.58 0.35 0.14 0.52 0.54 0.53
0.49 0.93 0.90 0.47 0.01 0.45
supplemental nicotinic acid (NA). as described by Tyrrell and Reid (18). 3Energy-corrected milk. 2Calculated
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NIACIN FOR LACTATING COWS UNDER HEAT STRESS TABLE 5. Changes in BW and body condition score1 (BCS) throughout the three experimental periods. Dietary treatment Control2
Item Period 1 BW Gain, kg/d BCS Change Period 2 BW Gain, kg/d BCS Change Period 3 BW Gain, kg/d BCS Change
NA
SE
P
0.91 0.13
0.67 –0.11
0.37 0.08
0.34 0.06
–0.82 0.14
–0.07 0.33
0.56 0.10
0.06 0.15
1.84 0.44
1.25 0.24
0.58 0.01
0.14 0.14
1Measured 2No
on a five-point scale where 1 = thin to 5 = fat. supplemental nicotinic acid (NA).
between treatments across the three experimental periods. Changes in BW and body condition score at the end of each experimental period are shown in Table 5. No statistical differences were observed for BW gain at the end of the first period. In contrast, BW losses in period 2 tended to be lower for cows fed diets supplemented with NA. Cows fed diets supplemented with NA tended to gain less BW during period 3 than did cows fed the control diet. Cows fed diets supplemented with NA lost more body condition during period 1 but appeared to gain more body condition during period 2 than did cows fed the control diet. In period 3, cows fed diets supplemented with NA tended to gain less body condition than did cows fed the control diet. Plasma metabolite concentrations at the end of each experimental period are reported in Table 6. No
TABLE 6. Plasma metabolite profile at the end of each experimental period.
statistical differences were observed for Glc, plasma urea N, or NEFA at the end of periods 1 or 2. Concentrations of Glc were higher for cows fed diets supplemented with NA at the end of period 3 than for cows fed the control diet. Thermal and respiratory responses for period 1 are shown in Table 7. No significant effects of dietary treatment on rectal temperatures at 0800 or 1600 h were observed. Tail temperature was lower for cows fed diets supplemented with NA than for cows fed the control diet at both the 0800 and 1600 h. Compared with cows fed the control diet, rump temperatures were lower at 0800 and 1600 h for cows fed diets supplemented with NA. Respiratory frequency was not affected by dietary treatment. Values for thermal and respiratory responses for period 2 are reported in Table 8. Rectal temperatures at 0800, 1600, and 2200 h were not affected by dietary treatments. In contrast, tail temperature at 0800 h was lower for cows fed diets supplemented with NA than for cows fed the control diet. Similarly, tail temperature at 1600 and 2200 h followed a decreasing trend in cows fed diets supplemented with NA. Rump temperatures at 0800 h also tended to be lower for cows fed diets supplemented with NA. However, rump temperatures at 1600 and 2200 h were not different statistically because of dietary treatment. Respiratory frequencies at 0800, 1600, and 2200 h numerically decreased because of NA supplementation. Values recorded for thermal and respiratory responses during period 3 are reported in Table 9. Rectal temperature, tail temperature, rump temperature, and respiratory frequencies at 0800, 1600, and 2200 h were not different statistically because of dietary treatment.
TABLE 7. Effect of nicotinic acid ( N A ) supplementation on thermal responses during period 1.
Dietary treatment Item Period 1 Plasma urea N, mg/dl Glucose, mg/dl NEFA, mM Period 2 Plasma urea N, mg/dl Glucose, mg/dl NEFA, mM Period 3 Plasma urea N, mg/dl Glucose, mg/dl NEFA, mM
Dietary treatment
Control1
NA
SE
P
23.3 60.3 133.4
23.9 65.1 136.7
0.82 2.3 7.9
0.62 0.19 0.78
16.1 67.2 133.7
16.5 64.5 131.6
0.84 1.8 1.8
0.78 0.32 0.93
20.9 64.3 140.5
20.1 66.4 156.2
0.65 0.70 1.9
0.40 0.05 0.29
1No supplemental nicotinic acid (NA). Means per treatment per period are presented as least squares means.
Control1
NA
SE
P
( °C ) 0800 h Rectal Tail Rump Resp.2 1600 h Rectal Tail Rump Resp. 1No
38.3 34.0 34.1 55.0
38.3 33.7 33.7 54.0
0.13 0.27 0.25 2.6
0.80 0.06 0.005 0.45
38.9 35.1 35.3 69.0
38.9 34.8 35.0 66.0
0.12 0.21 0.20 2.9
0.77 0.08 0.001 0.25
supplemental NA. rate, number per minute.
2Respiration
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TABLE 8. Effect of nicotinic acid ( N A ) supplementation on thermal responses during period 2.
TABLE 10. Effect of nicotinic acid ( N A ) supplementation on thermocirculatory index (TCI) during the three experimental periods.
Dietary treatment Control1
NA
Dietary treatment SE
P
( °C ) 0800 h Rectal Tail Rump Resp.2 1600 h Rectal Tail Rump Resp. 2200 h Rectal Tail Rump Resp. 1No
38.9 35.3 35.6 72
38.9 35.0 35.4 68
0.11 0.17 0.17 2.88
0.79 0.01 0.13 0.14
40.2 37.0 37.1 96
40.1 36.8 37.2 91
0.09 0.11 0.24 2.90
0.63 0.13 0.42 0.22
39.9 35.7 36.0 84
39.8 35.5 36.1 79
0.15 0.16 0.14 2.90
0.65 0.17 0.66 0.15
supplemental NA. rate, number per minute.
2Respiration
The TCI values are reported in Table 10. During period 1, cows fed diets supplemented with NA had lower TCI at rump skin sites at 0800 and 1600 h than did cows fed the control diet. The TCI for tail skin site tended to decrease in cows fed diets supplemented with NA compared with cows fed the control diet. In contrast, no treatment differences existed for TCI of rump values in period 2 at 0800, 1600, or 2200 h. The
TABLE 9. Effect of nicotinic acid ( N A ) supplementation on thermal responses during period 3. Dietary treatment Control1
Item
NA
SE
P
( °C ) 0800 h Rectal Tail Rump Resp.2 1600 h Rectal Tail Rump Resp. 2200 h Rectal Tail Rump Resp. 1No
38.1 31.2 31.6 46
0.08 0.25 0.21 1.64
0.93 0.26 0.57 0.54
38.5 34.0 34.2 56
38.5 33.9 34.2 53
0.07 0.10 0.12 1.80
0.38 0.26 0.84 0.31
38.4 33.0 33.3 53
38.4 33.0 33.2 50
0.09 0.13 0.34 2.32
0.94 0.84 0.88 0.36
supplemental NA. rate, number per minute.
Journal of Dairy Science Vol. 80, No. 6, 1997
Period 1 0800 h Tail Rump 1600 h Tail Rump Period 2 0800 h Tail Rump 1600 h Tail Rump 2200 h Tail Rump Period 3 0800 h Tail Rump 1600 h Tail Rump 2200 h Tail Rump
Control1
NA
SE
P
2.45 2.64
2.24 2.32
0.09 0.09
0.11 0.03
2.20 2.50
2.08 2.16
0.12 0.07
0.48 0.007
2.65 12.95
2.35 2.82
0.08 0.12
0.02 0.49
2.23 2.68
2.03 2.56
0.09 0.10
0.16 0.44
2.22 2.50
2.09 2.57
0.07 0.06
0.27 0.45
1.84 1.91
1.69 1.84
0.07 0.07
0.14 0.49
2.42 2.63
2.32 2.67
0.06 0.06
0.24 0.67
2.47 2.72
2.44 2.79
0.07 0.06
0.76 0.41
1No
supplemental NA. for TCI were calculated using tail or rump temperatures taken at 0800, 1600, or 2200 h. 2Values
TCI for tail temperature at 0800 h was lower for cows fed diets supplemented with NA than for cows fed the control diet during this period. The trend was similar for TCI of tail temperature at 1600 h, but not for tail temperature at 2200 h. No statistical differences of treatment were observed during period 3 for TCI of tail or rump temperatures at 0800, 1600, or 2200 h. DISCUSSION
38.1 31.4 31.7 47
2Respiration
TCI2
The first experimental period of this study showed mild heat stress conditions, as indicated by THI. During period 2, minimum mean THI values declined only to 73.2, suggesting conditions of severe heat stress. Ambient conditions were cooler during period 3. Johnson et al. ( 1 0 ) reported that THI greater than 72 decreased milk production of lactating Holstein cows. This phenomenon was observed specifically during period 2 when mean milk production per period was 12% lower than production in period 1. Cows fed diets supplemented with NA maintained a numerically, but not statistically, higher milk production across the three experimental periods than
NIACIN FOR LACTATING COWS UNDER HEAT STRESS
did cows fed the control diet. Earlier experiments ( 1 1 ) conducted during summer conditions showed similar results when cows were fed diets supplemented with 6 g/d of NA; the higher milk production for the group treated with NA was reflected in higher 4% FCM production. In the present experiment, NA did not affect 4% FCM or energy-corrected milk. Dufva et al. ( 4 ) found that, for early lactating cows, supplementation of 6 or 12 g/d of NA to the diet increased blood Glc concentrations and milk production. Those same investigators ( 4 ) attributed the increase in milk production to a decrease in subclinical and clinical ketoacidosis. In the present experiment, cows were well past peak lactation. However, because of the energy-consuming mechanisms that were activated to deal with summer conditions, thermal challenge could have been an important stressor. Dry matter intake tended to increase in period 1 for cows fed diets supplemented with NA. Cows fed diets supplemented with NA consumed 3.6% more feed than did cows fed the control diet. Riddell et al. ( 1 2 ) reported slight increases of hay intake when NA was supplemented to lactating dairy cows that were past peak production. During period 2, DMI was not different between dietary treatments. In contrast to DMI of period 1, DMI during period 2 was 19.2% lower, mainly as a consequence of high ambient temperature and relative humidity. Holter and McGilliard ( 6 ) reported that DMI of multiparous Holstein cows was highly and negatively correlated with minimum THI during the day. During period 3, cows fed diets supplemented with NA decreased DMI by 5.6% compared with cows fed the control diet. This response might be attributable to a direct effect of palatability or to negative effects of the high concentrations of NA on the mucosa of the digestive tract. Plasma metabolites were not affected by diet in periods 1 or 2. Plasma Glc concentrations in cows fed diets supplemented with NA were significantly higher in period 3. Previous reports of Thornton and Schultz ( 1 7 ) indicated that administration of 6.5 to 17 g/d of NA to goats elevated blood Glc and insulin. This increase might be an indication of greater gluconeogenic activity promoted by the partial lipogenic suppression elicited by NA at the cellular level as reported by Ruegsegger and Schultz (13). Two possible explanations are available for the reduction in skin temperature but without a change in rectal or core temperature for cows fed diets supplemented with NA. The likely explanation is that heat transfer might have been reduced, in which case a comparable reduction in heat gain would be expected if the core temperature were to remain con-
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stant. Another explanation would be increased evaporative heat loss, which would cool the skin, lower temperature, and increase the thermal gradient for heat loss. If heat loss had taken place, then heat gain would have been controlled and would have allowed the cows to maintain a constant core temperature. Additional studies are needed to determine the specific changes in heat transfer that are produced by NA treatment. Further evaluation is also required to determine NA supplementation. Using different doses or treatment schedules could result in a significant improvement in production during periods of heat stress. CONCLUSIONS Seasonal decreases in milk production caused by heat stress conditions produced the need to seek alternative means to reduce the heat load of high producing lactating cows. The present experiment determined whether NA supplementation could modify the thermoregulatory ability of lactating Holstein cows during summer conditions. Results indicated that, during mild or severe heat stress conditions, NA supplementation did not affect rectal temperature. However, skin temperatures and TCI, as a measure of rate of heat transfer, were reduced during mild heat stress (maximum mean ambient temperature of 28°C and relative humidity of 90%). A trend toward reduced respiratory frequencies and rump temperature during severe heat stress conditions, followed by a lack of response of thermal parameters during thermoneutral conditions, supported a possible positive effect of NA supplementation on cows exposed to hot summer conditions. Measurements of blood flow and metabolic rate are necessary to determine the mechanism by which NA influences heat transport and cow comfort. REFERENCES 1 Altschul, R. 1994. Niacin in Vascular Disorders and Hyperlipemia. Charles C Thomas, Springfield, IL. 2 Association of Analytical Chemists. 1984. Official Methods of Analysis. 12th ed. AOAC, Arlington, VA. 3 Coulombe, J. J., and L. Favreau. 1963. A new simple semimicro method for colorimetric determination of urea. Clin. Chem. 9: 102. 4 Dufva, G. S., E. E. Bartley, A. D. Dayton, and R. O. Riddel. 1983. Effect of niacin supplementation on milk production and ketosis in dairy cattle. J. Dairy Sci. 66:2329. 5 Reference deleted in proof. 6 Holter, J. B., and M. L. McGilliard. 1994. Adjusting the prediction of ad libitum dry matter intake of lactating cows for depressing effect of heat stress. J. Dairy Sci. 77(Suppl. 1): 308.(Abstr.) 7 Igono, M. O., G. Bjotvedt, and H. T. Sanford-Crane. 1992. Environmental profile and critical temperature effects on milk Journal of Dairy Science Vol. 80, No. 6, 1997
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production of Holstein cows in desert climate. Int. J. Biometeorol. 36:77. 8 Ingram, D. L., and L. E. Mount. 1975. Man and Animals in Hot Environments. Springer-Verlag, New York, NY. 9 Johnson, H. D. 1987. Bioclimate effects on growth, reproduction and milk production. Page 35 in Bioclimatology and the Adaptation of Livestock. Elsevier Sci. Publ., Amsterdam, The Netherlands. 10 Johnson, H. D., A. C. Ragsdale, I. L. Berry, and M. D. Shanklin. 1963. Temperature-humidity effects including influence of acclimation on feed and water consumption of Holstein cattle. Univ. Missouri Agric. Exp. Stn. Res. Bull. 846. Univ. Missouri, Columbia. 11 Muller, L. D., A. J. Heinrichs, J. B. Cooper, and Y. H. Atkin. 1986. Supplemental niacin for lactating cows during summer feeding. J. Dairy Sci. 69:1416. 12 Riddell, D. O., E. E. Bartley, and A. D. Dayton. 1986. Effect of nicotinic acid on microbial protein synthesis in vitro and on dairy cattle growth and milk production. J. Dairy Sci. 64:782.
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13 Ruegsegger, G. J., and L. H. Schultz. 1986. Use of a combination of propylene glycol and niacin for subclinical ketosis. J. Dairy Sci. 69:1411. 14 SAS User’s Guide: Statistics, Version 5 Edition. 1985. SAS Inst., Inc., Cary, NC. 15 Schwab, C. G. 1983. Supplemental niacin for lactating cows. New England Dairy Feed Conf., Concord, NH. 16 Shearer, J. K., and D. K. Beede. 1990. Thermoregulation and physiological responses of dairy cattle in hot weather. AgriPractice 11:5. 17 Thornton, J. H., and L. H. Schultz. 1980. Effects of administration of nicotinic acid on glucose, insulin, and glucose tolerance in ruminants. J. Dairy Sci. 63:262. 18 Tyrrell, H. F., and J. T. Reid. 1965. Prediction of the energy value of cow’s milk. J. Dairy Sci. 48:1215. 19 Zhang, Q., D. E. Spiers, A. Al-Haidary, G. E. Rottinghaus, and G. B. Garner. 1994. Circadian rhythm of core body temperature in beef calves under cold and heat stress conditions. J. Anim. Sci. 72(Suppl. 1):154.(Abstr.)
ABSTRACT Twenty-six lactating Holstein cows (90 d of lactation) were blocked according to milk production, parity, and days of lactation for assignment to one of two dietary treatments. Diets included a control diet with no supplemental niacin and a diet supplemented with increasing concentrations of niacin (12, 24, or 36 g/d per cow over three consecutive 17-d periods. Cows were housed in a covered free-stall barn and were fed and milked twice daily. Mean maximum air temperatures and temperature-humidity indexes were 28.5, 31.4, and 25.2°C and 79.6, 85.1, and 75, respectively, for the three periods. Rectal temperature was measured with a rectal probe, tail and rump temperatures by infrared thermometry, and respiratory rate by visual observation. Measurements were made daily at 0800, 1600, and 2200 h. Rectal temperature was not affected by treatment. Comparison of skin temperatures for control cows and cows fed niacin showed higher temperatures at the tail (34.0 vs. 33.7°C at 0800 h; 35.1 vs. 34.8°C at 1600 h, respectively) and rump (34.1 vs. 33.7°C at 0800 h; 35.3 vs. 35.0°C at 1600 h, respectively) for control cows during period 1. No differences in thermal responses were observed during period 3. Niacin did not significantly increase milk production but decreased skin temperatures during periods of mild or severe heat stress. ( Key words: nicotinic acid, heat stress, vasodilation) Abbreviation key: Glc = glucose, NA = nicotinic acid, TCI = thermocirculatory index, THI = temperature-humidity index. INTRODUCTION Summer temperature and humidity conditions can decrease milk production from 10 to 35% below yearly means ( 9 ) . This depression may be mediated by a reduction in feed intake, which is reported to occur as ambient temperature rises above 27°C (15). An increase in body temperature usually accompanies this
Received December 27, 1995. Accepted September 27, 1996. 1Current address: Tampico, Tamaulipas, Mexico 89410. 1997 J Dairy Sci 80:1200–1206
rise in ambient temperature and may be a primary stimulus for reductions in both feed intake and milk production. Whole body heat content and body temperature are dependent on rates of heat gain and loss (16). These rates, in turn, are affected by thermal gradients among core, skin, and ambient sites. Any shift in peripheral or internal vasomotor activity may alter the heat loss process and affect body temperature. Therefore, a treatment that has the potential to increase body heat transfer could possibly ameliorate the effects of reduced feed intake and milk production that occur during summer. Nicotinic acid ( NA) , a B vitamin, elicits vasodilatory reactions that may be beneficial for cows under heat stress. Peripheral and internal vasodilation, caused by therapeutic concentrations of NA ( 1 ) , may enhance heat transfer from core to skin sites and generate a temperature gradient favoring heat loss from skin to environment. Thus, the objective of this experiment was to evaluate NA supplementation as a means of improving thermoregulatory responses of lactating Holstein cows during summer conditions. MATERIALS AND METHODS Twenty-six lactating Holstein cows (90 d of lactation) were utilized in a randomized complete block design and assigned to one of two dietary treatments: the control diet with no supplemental NA or a diet with NA supplemented at increasing concentrations over three consecutive 17-d periods (period 1 = 12 g/d, period 2 = 24 g/d, and period 3 = 36 g/d per cow). Diets were formulated to provide 18% CP and 1.74 Mcal/kg of diet with a forage to concentrate ratio of 55:45 (wt/wt) (Table 1). Cows were individually fed a TMR twice a day (0800 and 1500 h ) using electronic feeding gates (American Calan Inc., Northwood, NH). Orts were measured once a day. Feed samples were taken once a day for DM analysis, and composites were prepared weekly for N and ADF determination by AOAC ( 2 ) procedures. Milk weights were recorded at each milking (0030 and 1230 h). Weekly milk samples from two consecutive milkings were analyzed for fat and protein content (Multi-Spec Mark 1; Foss Food Technology, Min-
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NIACIN FOR LACTATING COWS UNDER HEAT STRESS TABLE 1. Percentage of ingredients and nutrient composition of the experimental diets. Dietary treatment Composition
Control1
NA
( % of DM) Ingredient Alfalfa haylage Corn silage Earlage Corn, cracked Cottonseed, whole Soybean meal (48% CP) Soybean hulls Blood meal Alifet2 Cottonseed meal Wheat midds NA,3 g/d Nutrient DM, % as fed ADF CP
8.0 31.5 10.0 16.8 11.0 11.5 1.5 1.5 0.2 4.2 1.5 0
8.0 31.5 10.0 16.8 11.0 11.5 1.5 1.5 0.2 4.2 1.5 12
56.5 22.0 18.5
57.2 23.0 18.2
1No
supplemental nicotinic acid (NA). USA, Inc. (Cincinnati, OH). 3For period 1, NA supplementation was 12 g/d per cow; for period 2, NA was increased to 24 g/d per cow; and, for period 3, NA was 36 g/d per cow. 2Alifet,
neapolis, MN) and SCC (Bentley Somacount 300; Bentley Instruments, Chaska, MN) by the Missouri DHIA Federation (Springfield). Both 4% FCM and energy-corrected milk (ECM) were calculated using the following equations (18): 4% FCM = (0.4 × MP) + (15 × FY) and ECM = MP × [(40.72 × FY) + (22.65 × PY) + 102.7]/340 where MP = milk production, FY = fat yield, and PY = protein yield. Body weight and body condition scores were recorded at the beginning of the study and at the end of each 17-d experimental period. Blood samples were collected from the coccygeal vein immediately before recording BW. Plasma was separated by centrifugation (2500 × g for 15 min) and subsequently stored frozen (–20°C ) until analysis. Plasma glucose ( Glc) was measured by hexokinase reactivity (Sigma Chemical Co., St. Louis, MO). Nonesterified fatty acids were quantified by a controlled oxidation method (NEFA kit; Wako Chemicals, Richmond, VA). Plasma urea N was measured using the procedures of Coulombe and Favreau ( 3 ) .
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Cows were housed in a covered free-stall barn and were provided with forced-air ventilation (wind velocity = 4 m/s) using 3-m diameter fans. Rectal temperatures were recorded using a stainless steel thermistor probe (Cole Parmer Instruments, Chicago, IL) attached to a recorder (Cole Parmer Instruments). Skin temperatures were measured on the tail and rump of each cow using a portable infrared thermometer (Linear Laboratories, Fremont, CA). Tail temperature was recorded at vulva height on a previously shaved spot. Rump temperature was measured at the central part of the right rump. Respiratory frequencies were recorded by visual observation and were reported as the number of breaths per minute. Temperatures and respiratory frequencies were determined twice daily for period 1 (0800 and 1600 h ) and three times daily for periods 2 and 3 (0800, 1600, and 2200 h). The additional time was added to monitor nighttime cooling based on the reported circadian rhythm of the core body temperature of cattle (19), which was important given the higher minimum temperature-humidity index ( THI) . Thermocirculatory index ( TCI) was calculated according to procedures of Ingram and Mount ( 8 ) and represented thermal conductance when heat was transferred from core body to peripheral tissues and from the periphery to the environment. The experiment was conducted from July 27 to September 15, 1993. Maximum and minimum air temperature and relative humidities were recorded by continuous chart psychrothermometer (CTH-532; Omega Instruments, Stamford, CT) located 1 m from the floor in the central part of the housing area in an empty free stall. Separate measurements of air temperature and relative humidity were made using a high precision temperature probe (digital hygrometer-thermometer; Fisher Scientific, Pittsburgh, PA) at the time of rectal and skin temperature measurements. Readings from the chart psychrothermometer were adjusted by regression analysis against readings from the high precision temperature probe to improve the accuracy of the daily maximum and minimum values for temperature and humidity. The THI, an indicator of the combined influence of temperature and humidity, was calculated as described by Igono et al. ( 7 ) . Results were analyzed using the general linear models procedure of SAS (14). The model was analyzed as a randomized complete block with repeated measurements over time and was tested for effects of date, treatment, and block within period. The rationale to utilize increasing concentrations of NA over time was to avoid refractory effects of the cow to the vitamin. As a consequence, ANOVA was conducted within the experimental period. Through Journal of Dairy Science Vol. 80, No. 6, 1997
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TABLE 2. Mean minimum and maximum ambient temperature and relative humidity ( R H ) per experimental period. Minimum
Maximum
Period
Temperature
RH
Temperature
RH
1 2 3
( °C ) 20.4 22.9 17.3
(%) 72.1 77.1 77.4
( °C ) 28.5 31.4 25.2
(%) 91.8 99.8 100.0
these tests, effects of dietary treatments were evaluated within period and not among periods. Significance was declared at P < 0.05 and trends at P < 0.20 unless otherwise indicated.
Figure 1. Changes in the daily temperature-humidity index (THI) during experimental periods. Temperature-humidity index at 0800 h ( - - -); THI at 1600 h ( — ) .
RESULTS Maximum and minimum ambient temperatures and relative humidity by experimental period are shown in Table 2. Calculated THI per experimental period are reported in Table 3. Period 1 had a mean maximum ambient temperature of 28.5°C and was designated as a period of mild heat stress. As summer progressed, period 2 was characterized by severe heat stress conditions; mean maximum ambient temperature and maximum relative humidity were 31.4°C and 99.8%, respectively. In contrast to period 2, period 3 was characterized with no heat stress conditions, even though the maximum relative humidity remained elevated. The changes in temperature and humidity across the experiment are illustrated in Figure 1. Table 4 shows the effect of NA supplementation on production responses across the three experimental periods. Milk production was numerically higher for cows fed diets supplemented with NA than for cows consuming the control diet. No statistical differences were found in any experimental period in milk production or 4% FCM between treatment groups. In addition, NA supplementation tended to increase
TABLE 3. Mean minimum and maximum temperature-humidity indexes (THI) per experimental period.1 THI Period
Minimum
Maximum
1 2 3
68.2 73.2 63.1
79.6 85.1 75.0
1Minimum
and maximum temperature and humidity values were recorded through a chart psychrothermometer and adjusted by a high precision THI probe. Journal of Dairy Science Vol. 80, No. 6, 1997
DMI during period 1 but decreased DMI in period 3 (21.2 vs. 20.0 kg/d per cow for control cows and cows fed diets supplemented with NA, respectively). Dietary treatment did not affect milk composition in any of the experimental periods (Table 4). Numerical trends for increased fat or protein yields were observed mainly as a consequence of increased milk production. Energy-corrected milk was not different
TABLE 4. Milk production, 4% FCM, and DMI per period. Dietary treatment Item
Control1
NA
SE
P
(kg/d) Period 1 Milk Fat, % Protein, % 4% FCM2 DMI ECM2,3 Period 2 Milk Fat, % Protein, % 4% FCM DMI ECM Period 3 Milk Fat, % Protein, % 4% FCM DMI ECM 1No
28.0 3.40 2.90 25.5 21.7 25.2
29.0 3.33 2.91 26.1 22.5 25.9
0.52 0.20 0.17 0.49 0.48 0.51
0.45 0.55 0.78 0.63 0.09 0.59
25.0 3.45 2.90 22.9 17.9 22.7
25.9 3.38 2.91 23.5 17.8 23.3
0.54 0.25 0.18 0.50 0.49 0.49
0.34 0.45 0.77 0.55 0.97 0.49
28.0 3.33 3.17 25.2 21.2 25.5
28.7 3.35 3.17 25.9 20.0 26.2
0.58 0.35 0.14 0.52 0.54 0.53
0.49 0.93 0.90 0.47 0.01 0.45
supplemental nicotinic acid (NA). as described by Tyrrell and Reid (18). 3Energy-corrected milk. 2Calculated
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NIACIN FOR LACTATING COWS UNDER HEAT STRESS TABLE 5. Changes in BW and body condition score1 (BCS) throughout the three experimental periods. Dietary treatment Control2
Item Period 1 BW Gain, kg/d BCS Change Period 2 BW Gain, kg/d BCS Change Period 3 BW Gain, kg/d BCS Change
NA
SE
P
0.91 0.13
0.67 –0.11
0.37 0.08
0.34 0.06
–0.82 0.14
–0.07 0.33
0.56 0.10
0.06 0.15
1.84 0.44
1.25 0.24
0.58 0.01
0.14 0.14
1Measured 2No
on a five-point scale where 1 = thin to 5 = fat. supplemental nicotinic acid (NA).
between treatments across the three experimental periods. Changes in BW and body condition score at the end of each experimental period are shown in Table 5. No statistical differences were observed for BW gain at the end of the first period. In contrast, BW losses in period 2 tended to be lower for cows fed diets supplemented with NA. Cows fed diets supplemented with NA tended to gain less BW during period 3 than did cows fed the control diet. Cows fed diets supplemented with NA lost more body condition during period 1 but appeared to gain more body condition during period 2 than did cows fed the control diet. In period 3, cows fed diets supplemented with NA tended to gain less body condition than did cows fed the control diet. Plasma metabolite concentrations at the end of each experimental period are reported in Table 6. No
TABLE 6. Plasma metabolite profile at the end of each experimental period.
statistical differences were observed for Glc, plasma urea N, or NEFA at the end of periods 1 or 2. Concentrations of Glc were higher for cows fed diets supplemented with NA at the end of period 3 than for cows fed the control diet. Thermal and respiratory responses for period 1 are shown in Table 7. No significant effects of dietary treatment on rectal temperatures at 0800 or 1600 h were observed. Tail temperature was lower for cows fed diets supplemented with NA than for cows fed the control diet at both the 0800 and 1600 h. Compared with cows fed the control diet, rump temperatures were lower at 0800 and 1600 h for cows fed diets supplemented with NA. Respiratory frequency was not affected by dietary treatment. Values for thermal and respiratory responses for period 2 are reported in Table 8. Rectal temperatures at 0800, 1600, and 2200 h were not affected by dietary treatments. In contrast, tail temperature at 0800 h was lower for cows fed diets supplemented with NA than for cows fed the control diet. Similarly, tail temperature at 1600 and 2200 h followed a decreasing trend in cows fed diets supplemented with NA. Rump temperatures at 0800 h also tended to be lower for cows fed diets supplemented with NA. However, rump temperatures at 1600 and 2200 h were not different statistically because of dietary treatment. Respiratory frequencies at 0800, 1600, and 2200 h numerically decreased because of NA supplementation. Values recorded for thermal and respiratory responses during period 3 are reported in Table 9. Rectal temperature, tail temperature, rump temperature, and respiratory frequencies at 0800, 1600, and 2200 h were not different statistically because of dietary treatment.
TABLE 7. Effect of nicotinic acid ( N A ) supplementation on thermal responses during period 1.
Dietary treatment Item Period 1 Plasma urea N, mg/dl Glucose, mg/dl NEFA, mM Period 2 Plasma urea N, mg/dl Glucose, mg/dl NEFA, mM Period 3 Plasma urea N, mg/dl Glucose, mg/dl NEFA, mM
Dietary treatment
Control1
NA
SE
P
23.3 60.3 133.4
23.9 65.1 136.7
0.82 2.3 7.9
0.62 0.19 0.78
16.1 67.2 133.7
16.5 64.5 131.6
0.84 1.8 1.8
0.78 0.32 0.93
20.9 64.3 140.5
20.1 66.4 156.2
0.65 0.70 1.9
0.40 0.05 0.29
1No supplemental nicotinic acid (NA). Means per treatment per period are presented as least squares means.
Control1
NA
SE
P
( °C ) 0800 h Rectal Tail Rump Resp.2 1600 h Rectal Tail Rump Resp. 1No
38.3 34.0 34.1 55.0
38.3 33.7 33.7 54.0
0.13 0.27 0.25 2.6
0.80 0.06 0.005 0.45
38.9 35.1 35.3 69.0
38.9 34.8 35.0 66.0
0.12 0.21 0.20 2.9
0.77 0.08 0.001 0.25
supplemental NA. rate, number per minute.
2Respiration
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TABLE 8. Effect of nicotinic acid ( N A ) supplementation on thermal responses during period 2.
TABLE 10. Effect of nicotinic acid ( N A ) supplementation on thermocirculatory index (TCI) during the three experimental periods.
Dietary treatment Control1
NA
Dietary treatment SE
P
( °C ) 0800 h Rectal Tail Rump Resp.2 1600 h Rectal Tail Rump Resp. 2200 h Rectal Tail Rump Resp. 1No
38.9 35.3 35.6 72
38.9 35.0 35.4 68
0.11 0.17 0.17 2.88
0.79 0.01 0.13 0.14
40.2 37.0 37.1 96
40.1 36.8 37.2 91
0.09 0.11 0.24 2.90
0.63 0.13 0.42 0.22
39.9 35.7 36.0 84
39.8 35.5 36.1 79
0.15 0.16 0.14 2.90
0.65 0.17 0.66 0.15
supplemental NA. rate, number per minute.
2Respiration
The TCI values are reported in Table 10. During period 1, cows fed diets supplemented with NA had lower TCI at rump skin sites at 0800 and 1600 h than did cows fed the control diet. The TCI for tail skin site tended to decrease in cows fed diets supplemented with NA compared with cows fed the control diet. In contrast, no treatment differences existed for TCI of rump values in period 2 at 0800, 1600, or 2200 h. The
TABLE 9. Effect of nicotinic acid ( N A ) supplementation on thermal responses during period 3. Dietary treatment Control1
Item
NA
SE
P
( °C ) 0800 h Rectal Tail Rump Resp.2 1600 h Rectal Tail Rump Resp. 2200 h Rectal Tail Rump Resp. 1No
38.1 31.2 31.6 46
0.08 0.25 0.21 1.64
0.93 0.26 0.57 0.54
38.5 34.0 34.2 56
38.5 33.9 34.2 53
0.07 0.10 0.12 1.80
0.38 0.26 0.84 0.31
38.4 33.0 33.3 53
38.4 33.0 33.2 50
0.09 0.13 0.34 2.32
0.94 0.84 0.88 0.36
supplemental NA. rate, number per minute.
Journal of Dairy Science Vol. 80, No. 6, 1997
Period 1 0800 h Tail Rump 1600 h Tail Rump Period 2 0800 h Tail Rump 1600 h Tail Rump 2200 h Tail Rump Period 3 0800 h Tail Rump 1600 h Tail Rump 2200 h Tail Rump
Control1
NA
SE
P
2.45 2.64
2.24 2.32
0.09 0.09
0.11 0.03
2.20 2.50
2.08 2.16
0.12 0.07
0.48 0.007
2.65 12.95
2.35 2.82
0.08 0.12
0.02 0.49
2.23 2.68
2.03 2.56
0.09 0.10
0.16 0.44
2.22 2.50
2.09 2.57
0.07 0.06
0.27 0.45
1.84 1.91
1.69 1.84
0.07 0.07
0.14 0.49
2.42 2.63
2.32 2.67
0.06 0.06
0.24 0.67
2.47 2.72
2.44 2.79
0.07 0.06
0.76 0.41
1No
supplemental NA. for TCI were calculated using tail or rump temperatures taken at 0800, 1600, or 2200 h. 2Values
TCI for tail temperature at 0800 h was lower for cows fed diets supplemented with NA than for cows fed the control diet during this period. The trend was similar for TCI of tail temperature at 1600 h, but not for tail temperature at 2200 h. No statistical differences of treatment were observed during period 3 for TCI of tail or rump temperatures at 0800, 1600, or 2200 h. DISCUSSION
38.1 31.4 31.7 47
2Respiration
TCI2
The first experimental period of this study showed mild heat stress conditions, as indicated by THI. During period 2, minimum mean THI values declined only to 73.2, suggesting conditions of severe heat stress. Ambient conditions were cooler during period 3. Johnson et al. ( 1 0 ) reported that THI greater than 72 decreased milk production of lactating Holstein cows. This phenomenon was observed specifically during period 2 when mean milk production per period was 12% lower than production in period 1. Cows fed diets supplemented with NA maintained a numerically, but not statistically, higher milk production across the three experimental periods than
NIACIN FOR LACTATING COWS UNDER HEAT STRESS
did cows fed the control diet. Earlier experiments ( 1 1 ) conducted during summer conditions showed similar results when cows were fed diets supplemented with 6 g/d of NA; the higher milk production for the group treated with NA was reflected in higher 4% FCM production. In the present experiment, NA did not affect 4% FCM or energy-corrected milk. Dufva et al. ( 4 ) found that, for early lactating cows, supplementation of 6 or 12 g/d of NA to the diet increased blood Glc concentrations and milk production. Those same investigators ( 4 ) attributed the increase in milk production to a decrease in subclinical and clinical ketoacidosis. In the present experiment, cows were well past peak lactation. However, because of the energy-consuming mechanisms that were activated to deal with summer conditions, thermal challenge could have been an important stressor. Dry matter intake tended to increase in period 1 for cows fed diets supplemented with NA. Cows fed diets supplemented with NA consumed 3.6% more feed than did cows fed the control diet. Riddell et al. ( 1 2 ) reported slight increases of hay intake when NA was supplemented to lactating dairy cows that were past peak production. During period 2, DMI was not different between dietary treatments. In contrast to DMI of period 1, DMI during period 2 was 19.2% lower, mainly as a consequence of high ambient temperature and relative humidity. Holter and McGilliard ( 6 ) reported that DMI of multiparous Holstein cows was highly and negatively correlated with minimum THI during the day. During period 3, cows fed diets supplemented with NA decreased DMI by 5.6% compared with cows fed the control diet. This response might be attributable to a direct effect of palatability or to negative effects of the high concentrations of NA on the mucosa of the digestive tract. Plasma metabolites were not affected by diet in periods 1 or 2. Plasma Glc concentrations in cows fed diets supplemented with NA were significantly higher in period 3. Previous reports of Thornton and Schultz ( 1 7 ) indicated that administration of 6.5 to 17 g/d of NA to goats elevated blood Glc and insulin. This increase might be an indication of greater gluconeogenic activity promoted by the partial lipogenic suppression elicited by NA at the cellular level as reported by Ruegsegger and Schultz (13). Two possible explanations are available for the reduction in skin temperature but without a change in rectal or core temperature for cows fed diets supplemented with NA. The likely explanation is that heat transfer might have been reduced, in which case a comparable reduction in heat gain would be expected if the core temperature were to remain con-
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stant. Another explanation would be increased evaporative heat loss, which would cool the skin, lower temperature, and increase the thermal gradient for heat loss. If heat loss had taken place, then heat gain would have been controlled and would have allowed the cows to maintain a constant core temperature. Additional studies are needed to determine the specific changes in heat transfer that are produced by NA treatment. Further evaluation is also required to determine NA supplementation. Using different doses or treatment schedules could result in a significant improvement in production during periods of heat stress. CONCLUSIONS Seasonal decreases in milk production caused by heat stress conditions produced the need to seek alternative means to reduce the heat load of high producing lactating cows. The present experiment determined whether NA supplementation could modify the thermoregulatory ability of lactating Holstein cows during summer conditions. Results indicated that, during mild or severe heat stress conditions, NA supplementation did not affect rectal temperature. However, skin temperatures and TCI, as a measure of rate of heat transfer, were reduced during mild heat stress (maximum mean ambient temperature of 28°C and relative humidity of 90%). A trend toward reduced respiratory frequencies and rump temperature during severe heat stress conditions, followed by a lack of response of thermal parameters during thermoneutral conditions, supported a possible positive effect of NA supplementation on cows exposed to hot summer conditions. Measurements of blood flow and metabolic rate are necessary to determine the mechanism by which NA influences heat transport and cow comfort. REFERENCES 1 Altschul, R. 1994. Niacin in Vascular Disorders and Hyperlipemia. Charles C Thomas, Springfield, IL. 2 Association of Analytical Chemists. 1984. Official Methods of Analysis. 12th ed. AOAC, Arlington, VA. 3 Coulombe, J. J., and L. Favreau. 1963. A new simple semimicro method for colorimetric determination of urea. Clin. Chem. 9: 102. 4 Dufva, G. S., E. E. Bartley, A. D. Dayton, and R. O. Riddel. 1983. Effect of niacin supplementation on milk production and ketosis in dairy cattle. J. Dairy Sci. 66:2329. 5 Reference deleted in proof. 6 Holter, J. B., and M. L. McGilliard. 1994. Adjusting the prediction of ad libitum dry matter intake of lactating cows for depressing effect of heat stress. J. Dairy Sci. 77(Suppl. 1): 308.(Abstr.) 7 Igono, M. O., G. Bjotvedt, and H. T. Sanford-Crane. 1992. Environmental profile and critical temperature effects on milk Journal of Dairy Science Vol. 80, No. 6, 1997
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production of Holstein cows in desert climate. Int. J. Biometeorol. 36:77. 8 Ingram, D. L., and L. E. Mount. 1975. Man and Animals in Hot Environments. Springer-Verlag, New York, NY. 9 Johnson, H. D. 1987. Bioclimate effects on growth, reproduction and milk production. Page 35 in Bioclimatology and the Adaptation of Livestock. Elsevier Sci. Publ., Amsterdam, The Netherlands. 10 Johnson, H. D., A. C. Ragsdale, I. L. Berry, and M. D. Shanklin. 1963. Temperature-humidity effects including influence of acclimation on feed and water consumption of Holstein cattle. Univ. Missouri Agric. Exp. Stn. Res. Bull. 846. Univ. Missouri, Columbia. 11 Muller, L. D., A. J. Heinrichs, J. B. Cooper, and Y. H. Atkin. 1986. Supplemental niacin for lactating cows during summer feeding. J. Dairy Sci. 69:1416. 12 Riddell, D. O., E. E. Bartley, and A. D. Dayton. 1986. Effect of nicotinic acid on microbial protein synthesis in vitro and on dairy cattle growth and milk production. J. Dairy Sci. 64:782.
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13 Ruegsegger, G. J., and L. H. Schultz. 1986. Use of a combination of propylene glycol and niacin for subclinical ketosis. J. Dairy Sci. 69:1411. 14 SAS User’s Guide: Statistics, Version 5 Edition. 1985. SAS Inst., Inc., Cary, NC. 15 Schwab, C. G. 1983. Supplemental niacin for lactating cows. New England Dairy Feed Conf., Concord, NH. 16 Shearer, J. K., and D. K. Beede. 1990. Thermoregulation and physiological responses of dairy cattle in hot weather. AgriPractice 11:5. 17 Thornton, J. H., and L. H. Schultz. 1980. Effects of administration of nicotinic acid on glucose, insulin, and glucose tolerance in ruminants. J. Dairy Sci. 63:262. 18 Tyrrell, H. F., and J. T. Reid. 1965. Prediction of the energy value of cow’s milk. J. Dairy Sci. 48:1215. 19 Zhang, Q., D. E. Spiers, A. Al-Haidary, G. E. Rottinghaus, and G. B. Garner. 1994. Circadian rhythm of core body temperature in beef calves under cold and heat stress conditions. J. Anim. Sci. 72(Suppl. 1):154.(Abstr.)