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Effect of Supplemental Conjugated Linoleic Acids on Heat-Stressed Brown Swiss and Holstein Cows^*

Department of Animal Sciences, The University of Arizona, Tucson 85721

Corresponding author: Lance H. Baumgard; e-mail: baumgard{at}ag.arizona.edu.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Heat-stressed dairy cattle are bioenergetically similar to early-lactation cows in that dietary energy may be inadequate to support maximum milk and milk component synthesis. Study objectives were to evaluate whether conjugated linoleic acids- (CLA-) induced milk fat depression (MFD) during heat stress would allow for increased milk and milk component synthesis. In addition, CLA effects on production variables and its ability to induce MFD were compared between Holstein and Brown Swiss cows. Multiparous cows (n = 8, Holstein; n = 5, Brown Swiss) averaging 97 ± 17 d in milk were used in a crossover design during the summer (mean temperature-humidity index = 75.7). Treatment periods were 21 d with a 7-d adaptation period before and between periods. During adaptation periods, all cows received a supplement of palm fatty acid distillate (242 g/d). Dietary treatment consisted of 250 g/d of CLA supplement (78.9 g/d of CLA) or 242 g/d of palm fatty acid distillate to provide equal amounts of fatty acids. The CLA supplement contained a variety of CLA isomers (3.0% trans-8, cis-10; 3.4% cis-9, trans-11; 4.5% trans-10, cis-12; and 4.8% cis-11, trans-13 CLA). Treatments were applied 2 x/d with half of the supplement top-dressed at 0600 h and the remainder top-dressed at 1800 h. There was no overall treatment effect on dry matter intake (23.9 kg/d), milk yield (40.0 kg/d), somatic cell count (305,000), protein (2.86%), or lactose content (4.51%) or yields of these milk components. Supplementation with CLA decreased overall milk fat content and yield by 26 and 30%, irrespective of breed. The reduction of milk fat content and yield was greatest on d 21 (28 and 37%, respectively). Energy availability predicted by energy balance was improved with CLA supplementation compared with controls (3.7 vs. 7.1 Mcal/d, respectively). Respiration rate (78 breaths/min) and skin temperature (35.4°C) during maximum heat load were not affected by treatment. The group receiving CLA had higher total milk fat CLA concentration (9.3 vs. 4.9 mg/g). Supplementation with CLA induced MFD and altered milk fat composition similarly between breeds and improved calculated energy balance during heat stress, but had no effect on production measures under these conditions.

Key Words: conjugated linoleic acids • milk fat • heat stress • energy balance

Abbreviation key: bpm = breaths per minute, CLA = conjugated linoleic acids, EBAL = energy balance, MFD = milk fat depression, RI = rumen-inert, THI = temperature-humidity index

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Conjugated linoleic acids (CLA) are a group of linoleic acid isomers containing conjugated double bonds, and are primarily found in ruminant food products (Bauman et al., 2001). This family of fatty acids alleviates or improves symptoms or measures of many common human diseases in animal models, ranging from atherosclerosis to cancer (see reviews by Whigham et al., 2000; Belury, 2002). In addition, dietary CLA reduces carcass fat content in many rodent species and pigs (Thiel-Cooper et al., 2001; Terpstra et al., 2002) and CLA supplementation dramatically decreases milk fat synthesis in rodents, pigs, cattle, and women (see review by Bauman et al., 2001). Many studies confirmed that abomasally infused CLA caused milk fat depression (MFD; Loor and Herbein, 1998; Chouinard et al., 1999; Mackle et al., 2003) in lactating dairy cows and identified trans-10, cis-12 as a responsible CLA isomer (Baumgard et al., 2000; 2002a). Research utilizing rumeninert (RI) CLA supplements (Ca⁺⁺ salts) indicates that RI-CLA also decreases milk fat when fed to cows either consuming a TMR or rotationally grazed (Giesy et al., 2002; Perfield et al., 2002; Kay et al., 2004b; Moore et al., 2004). Therefore, RI-CLA may be a tool used to govern milk fat synthesis at times when energy required for production of milk fat could be used for the synthesis of additional milk or alternative milk components or to support a different physiological state (i.e., reproduction).

Heat stress negatively affects milk synthesis and impairs reproductive performance (West, 2003). As a consequence, heat stress is a significant financial burden in many dairy-producing areas of the United States and the world. The bioenergetic mechanism by which heat stress affects production and reproduction is partly explained by reduced feed intake, but also includes altered endocrine status, reduction in rumination and nutrient absorption, and increased maintenance requirements (Collier and Beede, 1985; Collier et al., 2005) resulting in a net decrease in nutrient/energy availability for production. This decrease in energy results in a reduction in energy balance (EBAL), and explains why cows lose significant amounts of body weight when subjected to heat stress. Dietary strategies to alleviate this energy deficit traditionally include increasing the energy density of the diet with concentrates or fat supplements (Knapp and Grummer, 1991; Chan et al., 1997; Drackley et al., 2003). An alternative method of improving EBAL during heat stress is to reduce milk fat synthesis, as this may attenuate or eliminate the deleterious effects of environmental heat on production and reproduction. Reducing the energy requirement for milk fat synthesis may allow for increased synthesis of milk or other milk components and could provide a signal to allow for improved reproduction. We hypothesized that reducing milk fat synthesis during heat stress, a time when nutrient availability may limit production, may allow for energy partitioning to support increased synthesis of milk and milk protein (Bauman et al., 2001; Baumgard et al., 2002b; Collier et al., 2005) as observed from cows on pasture in established lactation (Medeiros et al., 2000; Mackle et al., 2003). In addition to enhancing milk yield, inhibiting milk fat synthesis and thus improving EBAL may improve animal well being and reproductive success. Furthermore, this study was designed to characterize the effects of heat stress and CLA-induced MFD on Brown Swiss compared with Holstein cattle.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Design, Animals, and Treatments
The University of Arizona Institutional Animal Care and Use Committee approved all procedures involving animals. Thirteen multiparous cows (n = 8, Holstein and n = 5, Brown Swiss) averaging 97 ± 17 DIM and 730 ± 14 kg BW were used in a crossover design between July 24 and September 24, 2003, a time of the year when the combination of heat and humidity are typically at their maximum in Tucson, AZ. Treatment periods (n = 2) were 21 d with a 7-d adaptation before the first treatment period as well as between the 2 treatment periods. During the 7-d adaptation periods, all cows received (242 g/d) EnerGII (an RI supplement of palm fatty acid distillate; Bioproducts Inc., Fairlawn, OH; Table 1). Cows were maintained in a dry-lot pen and individually fed using the Calan Broadbent Feeding System (American Calan, Inc., Northwood, NH) for monitoring daily individual animal feed intake and application of different dietary treatments to cows housed in the same pen. The pen contained a corrugated sheet metal shade structure oriented North/South with an oscillating fan evaporative cooling system (Advanced Dairy System, Phoenix, AZ). Cows were moved to the pen, assigned to a Calan feeding door and allowed to acclimate to this feeding system for 10 d before trial initiation. Cows were individually fed a TMR twice daily (0600 and 1800 h) ad libitum, and orts were collected and recorded daily just before the morning feeding. The TMR was formulated to meet or exceed the predicted requirements (NRC, 2001) of energy, protein, minerals, and vitamins, using CPM-Dairy (Table 2). Alfalfa hay was the main forage source and steam-flaked corn was the primary concentrate. The TMR was sampled weekly, composited by period, and analyzed by wet chemistry methods for CP, ADF, NDF, NE_L, and minerals (Dairy One Cooperative Inc., Ithaca, NY). Dietary treatments consisted of 250 g/d of RI-CLA (82% lipid of which ~38% was mixed isomers of CLA; Bioproducts Inc.) or 242 g/d of EnerGII (85% lipid) to provide an equal amount of lipid (205 g/d). The CLA supplement contained a variety of CLA isomers (Table 1). Treatment was applied twice daily with half of the supplement top-dressed at 0600 h and half at 1800 h.

Body weight was recorded weekly. Net EBAL was calculated using the following equation: EBAL = net energy intake –(net energy for maintenance + net energy for lactation). Net energy intake was calculated by multiplying the daily DMI by the net energy of the diet plus the net energy value of the supplement [calculated using NRC (2001) energy values for calcium soaps of fat]. Digestibility and absorbability were assumed to be similar between the 2 fat supplements. Net energy for maintenance was calculated according to NRC (2001) using the following equation: net energy for maintenance = (0.08 x BW^0.75) x 1.2 to account for increased maintenance due to heat stress (NRC, 1981). Net energy for lactation was calculated according to NRC (2001) by the following equation; NE_L = [(0.0929 x fat %) + (0.0547 x CP %) + (0.0395 x lactose %)] x milk production. Solids-corrected milk was calculated according to Tyrrell and Reid (1965), and production efficiency was calculated according to Drackley et al. (2003).

The Arizona Meteorological Network recorded weather data daily and this information was used to calculate the temperature-humidity index (THI). The maximum, minimum, and mean THI was calculated: {THI = (dry bulb temperature, °C) + [(0.36 x dew point temperature, °C) + 41.2)]; Buffington et al., 1981} each day as well as the THI at 1600 h. Respiration rates were determined each day at 1600 h by counting the number of breaths in a 15-s period and multiplying this by 4 to determine breaths per minute (bpm). Surface temperatures were recorded daily at 1600 h at the point of the left paralumbar fossa with a Raynger MX infrared thermometer (Raytek RAYMX4PU, Santa Cruz, CA).

Fatty Acid Analysis
Milk fat from samples collected on d 1, 3, 5, 14, and 21 were extracted according to Hara and Radin (1978) and fatty acid methyl esters were prepared by the transmethylation procedure described by Christie (1982) with modifications (Chouinard et al., 1999). Fatty acid methyl esters were quantified using a gas chromatograph (Hewlett Packard GC system 6890; Wilmington, DE) equipped with a flame ionization detector and a CP-7420 fused silica capillary column (100 m x 0.25 mm i.d. with 0.2 µm film thickness; Varian, Walnut Creek, CA). Initial oven temperature (50°C) was held for 1 min then increased at 5°C/min to 160°C, held for 42 min, and then increased at 5°C/min to 190°C, and held for 22 min. Inlet and detector temperatures were maintained at 250°C and the split ratio was 100:1. Hydrogen carrier gas flow rate through the column was 1 mL/min. Hydrogen flow to the detector was 30 mL/min, airflow was 400 mL/min, and the nitrogen make-up gas flow was 25 mL/min. Peaks in the chromatogram were identified and quantified using pure methyl ester standards (GLC60; Nuchek Prep, Elysian, MN; Matreya, Inc., Pleasant Gap, PA, anhydrous milk fat; R.T. Corporation, Laramie, WY) and the CLA profile identified as previously described (Roach et al., 2002). A butter oil reference standard (anhydrous milk fat; R.T. Corporation) was used to determine recoveries and correction factors for individual fatty acids (Baumgard et al., 2000).

Statistical Analyses
Milk yield, DMI, and EBAL were analyzed with the repeated measures PROC MIXED procedure of SAS (SAS Institute, 2001) with week of treatment as the repeated effect. The model contained period, breed, treatment, week of treatment, and all possible interactions. Milk components and fatty acid profiles were also analyzed with the repeated measures PROC MIXED procedure of SAS (SAS Institute, 2001) with day of treatment as the repeated effect. The model contained period, breed, treatment, day, and all possible interactions. Both models used the autoregressive of order 1 covariance structure.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
The maximum (83.6), mean (76.2), and THI at 1600 h (81.7; the time of respiration rate and skin temperature measurements) did not differ for the 2 treatment periods (Figure 1). Minimum THI was decreased (P < 0.02) in the second treatment period compared with the first treatment period (70.2 vs. 67.6). Respiration rate (78 bpm) and skin temperature (35.4°C) were not affected by treatment (Table 3). Respiration rate was increased (P < 0.01) in Brown Swiss compared with Holsteins (81 vs. 75 bpm), but there was no effect of breed on skin temperature.

View larger version (27K): [in this window] [in a new window]   Figure 1. Temporal pattern of maximum, minimum, mean, and 1600 h temperature-humidity index (THI) over the trial period. Dashed boxes indicate treatment periods.

View larger version (16K): [in this window] [in a new window]   Figure 2. Temporal pattern of milk fat content (A) and milk fat yield (B) from cows fed a control diet with 242 g/d of EnerGII or control diet supplemented with 250 g/d of conjugated linoleic acids (CLA) during heat stress. Values are means, n = 13 for both treatment groups; SEM averaged 0.16 and ranged from 0.159 to 0.164%, and averaged 72 and ranged from 71 to 78 g/d for milk fat content and yield, respectively.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

In agreement with other trials feeding RI-CLA to mid- and late-lactating cows (Medeiros et al., 2000; Giesy et al., 2002; Perfield et al., 2002), milk fat content and yield were decreased (26 and 30%, respectively). We hypothesized that reducing milk fat during periods of heat stress, a time when nutrient availability may be limiting (due to decreased DMI), would allow for spared energy to be partitioned for increased production of milk or milk components (Bauman et al., 2001; Baumgard et al., 2002b; Collier et al., 2005). An increase in milk production and protein content has been observed on pasture-fed, CLA-supplemented dairy cows, which are frequently limited by nutrient (especially energy) availability (Medeiros et al., 2000; Mackle et al., 2003; Kay et al., 2004b). Supplementation with CLA did not affect protein or total milk synthesis under the heat stress conditions during this trial (Table 3), even though approximately 3.5 Mcal of additional energy was available due to the CLA-induced MFD. This trial was not designed to determine the effects of CLA on reproduction, but it is conceivable that improving EBAL could alleviate some of the poor reproductive performance associated with heat stress.

Holstein cows produced more milk (4 kg/d; Table 3) and SCM (1.7 kg/d; Table 3) than Brown Swiss cows. This increase in milk yield was independent of DMI, resulting in Holsteins producing milk more efficiently [SCM/NE_L intake (kg/Mcal)]. The decreased efficiency of Brown Swiss can, partially, be attributed to the fact that they were, on average, 45 kg heavier (P < 0.04; data not shown) than the Holsteins, resulting in increased energetic cost for maintenance of approximately 1.2 Mcal/d. This increased maintenance cost accounts for approximately 50% of the increased energy output in milk by Holsteins and helps explain why Brown Swiss had a similar EBAL compared with Holsteins even though they produced less milk while consuming a similar amount of feed (Table 3).

Use of RI-CLA increased the milk fat content of total CLA by 90%, and tended to increase cis-9, trans-11 CLA (P < 0.07; Table 4). The changes in total and specific CLA content were independent of breed, although Brown Swiss had 29% greater cis-9, trans-11 CLA content then Holsteins, independent of treatment. This is in contrast to previous data from the same herd that indicated Holsteins have a slightly higher cis-9, trans-11 CLA content than the Brown Swiss (Kelsey et al., 2003). Reasons for the discrepancies in these 2 data sets are not clear, but most likely are due to methods of collecting data. The present study used repeated measurements of milk fat composition (n = 8) on each cow, where as the previous trial (Kelsey et al., 2003) used data from a single sample taken on a single day. cis-9, trans-11 CLA is predominantly synthesized through endogenous conversion of trans-11 18:1 via ⁹-desaturase (Corl et al., 2001; Kay et al., 2004a). In the present study there was no breed effect on the ⁹-desaturase system (based on the overall ⁹-desaturase index; Table 4). However, Brown Swiss had a higher milk fat trans-11 18:1 and lower 18:0 content, indicating the increased cis-9, trans-11 CLA levels in Brown Swiss milk fat is probably due to biohydrogenation differences resulting in an increased supply of trans-11 18:1 (the cis-9, trans-11 CLA precursor) to the mammary gland as experimentally increasing the supply of trans-11 18:1 increases the amount of cis-9, trans-11 CLA (Corl et al., 2001).

The effects of RI-CLA on milk fat synthesis, yield, and fatty acid profile were similar to results reported by others (Giesy et al., 2002; Perfield et al., 2002; Moore et al., 2004) and followed expected patterns indicating no breed effect on response to CLA-induced MFD. The decrease in milk fat did not allow for a subsequent increase in milk yield or yield of other milk components as we hypothesized. Although cows in this study were experiencing significant heat stress, the magnitude of heat stress may not have been extensive enough to induce severe negative energy balance (i.e., –10 to –15 Mcal/d). Controls in this experiment had an estimated negative energy balance of 3.7 Mcal/d (Table 3) and therefore milk and milk component synthesis may not have been limited by energy availability, or limited enough to detect or measure improvements in production.

Estimating EBAL during heat stress introduces 2 problems independent of those inherent to normal EBAL estimations (Vicini et al., 2002). First, considerable evidence suggests that increased maintenance costs are associated with heat stress (7 to 25%; NRC, 1981); however, due to complexities involved in predicting upper critical temperatures, no universal equation is available to adjust for this increase in maintenance (Fox and Tylutki, 1998) when calculating EBAL in heat-stressed animals. Not incorporating a heat-stress correction factor results in overestimating EBAL and inaccurate prediction of energy status. In this paper, we used data provided by the NRC (1981), which suggests an increased maintenance requirement of 20% for cows experiencing 35°C or greater for more than 6 h/d. Secondly, a proportionate decrease in milk yield causes calculated EBAL to remain slightly positive and thus appears adequate because of adjusted level of production. However, despite the calculated positive EBAL, irrespective of treatment, cows lost approximately 18 kg of BW during this trial (data not shown). In agreement, cows in established lactation from semi-arid environments (e.g., Arizona, Middle East) will typically lose approximately 20 kg of body weight during the course of a summer (Dennis Armstrong, personal communication, 2004). The loss of body weight indicates cows in this trial were in negative energy balance, and illustrates the difficulty in accurately estimating EBAL during heat stress.

We believe it is likely that these cows were limited by energy availability to produce milk to their genetic potential. Furthermore, cows were already heat stressed at trial initiation and it is possible the deleterious effects of heat stress were too severe for CLA to overcome. It is of interest to determine if CLA-induced MFD could prevent (rather than remedy) the negative effects of heat stress, if provided to thermal-neutral animals before initiation of heat stress.

	CONCLUSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Cows in this trial were heat stressed as indicated by THI, respiration rate, and skin temperature. Feeding RI-CLA during heat stress to induce MFD alleviated estimated EBAL, but had no effect on milk yield or yield of other components. Rumeninert CLA inhibited milk fat synthesis similarly in Brown Swiss and Holstein cows, whereas Brown Swiss had higher cis-9, trans-11 and total CLA content than Holstein cows.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
The authors express their appreciation to Dan Luchini and Bioproducts Inc. (Fairlawn, OH) for the donation of calcium salts of CLA and EnerGII. The technical advice of Dairy Nutrition Service (Chandler, AZ) and the assistance of Henry Hafliger, III, Octavio Mendivil, Sara Sanders, Mike Dwyer, and Steve and Nancy Faber is also greatly appreciated.

	FOOTNOTES

 
^* This work was partially supported by the University of Arizona Experiment Station #ARZT-136339-H-24-130.

Received for publication August 31, 2004. Accepted for publication January 11, 2005.

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TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 


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