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Responses of Primiparous and Multiparous Holstein Cows to Additional Energy from Fat or Concentrate During Summer¹

Department of Animal Sciences, University of Illinois, Urbana 61801

Corresponding author:
J. K. Drackley; e-mail:
drackley{at}uiuc.edu.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Supplemental fat has been advocated for use during hot weather and often increases milk yield of cows past peak production when energy intake should not be limiting. Relative responses of primiparous and multiparous cows to supplemental fat or isocaloric addition of concentrates under hot weather conditions have not been determined. Nine multiparous and nine primiparous Holstein cows (154 and 167 d in milk, respectively) were used in a replicated 3 x 3 Latin square design with 28-d periods. Diets were 1) control (35% alfalfa silage, 25% corn silage, and 40% concentrate, dry matter [DM] basis); 2) control plus 3% fat (HF); and 3) high concentrate ([HC] 15% alfalfa silage, 25% corn silage, and 60% concentrate). Diets were isonitrogenous; diets HF and HC were isocaloric (1.60 Mcal of net energy for lactation [NE_L] per kilogram DM) and higher energy than the control (1.52 Mcal/kg). No parity x diet interactions approached significance. DM intake (DMI) was greater when cows were fed HC than when they were fed HF (21.0, 20.1, and 21.3 kg/d for control, HF, and HC, respectively); intake of NE_L tended to be increased only for HC. Milk yield was increased by higher-energy diets, but milk fat content was decreased. Milk total protein content was decreased by HF and increased by HC. Yield of solids-corrected milk (SCM) was not different among diets. Efficiency of milk production, expressed either as total milk solids yield per kilogram of DMI or as kilograms of SCM per megacalorie of NE_L intake, was greater for HF than for HC. Plasma glucose was higher after feeding for cows fed HC; plasma nonesterified fatty acids were greater for HF. Respiration rate and rectal temperature were greater for HC than for HF. Regardless of parity, increased energy density from either fat or concentrate increased milk yield in midlactation cows, but diets caused energy to be partitioned differently among milk components and body storage. Supplemental rumen-active fat had modest advantages over additional starch-based concentrate during summer heat conditions.

Key Words: dietary fat • heat stress • primiparous cow

Abbreviation key: HC = high-concentrate diet, HF = high-fat diet, LCFA = long-chain fatty acids, THI = temperature-humidity index

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Supplemental fat has become a common feed ingredient to increase dietary energy density for dairy cows. Although responses of milk production to supplemental fat have been variable, energy balance of cows has been improved consistently (Chilliard, 1993). Supplemental fat has increased milk production in cows during midlactation even when intake of energy from unsupplemented diets exceeded requirements (Steele et al., 1971; DePeters et al., 1989; Knapp et al., 1991; Drackley et al., 1994; Schingoethe et al., 1996). Anecdotal evidence from the field has suggested that primiparous cows may have greater production responses to supplemental fat, perhaps because of their additional energy requirements for growth as well as for milk production. Available research data, however, indicate that production responses generally were similar between primiparous and multiparous cows (Schneider et al., 1988; DePeters et al., 1989; Canale et al., 1990; Knapp et al., 1991). Grummer et al. (1995) found that supplemental tallow increased milk yield by primiparous cows by about 1.5 kg/d after 7 wk of lactation.

A satisfactory mechanistic explanation for the stimulatory effect of supplemental fat on milk production in midlactation cows already consuming adequate energy has been elusive. At least part of the effect seems to result from increased energy density and increased energy intake. Feeding higher-energy diets made isocaloric through addition of fat or concentrate increased yields of milk over lower-energy control diets in some (Canale et al., 1990; Vasquez-Añon et al., 1997) but not all studies (Palmquist and Conrad, 1980; Grum et al., 1996). Yield of FCM often has been greater with high-fat diets than with isocaloric high-grain diets because of diversion of energy from milk fat to body fat deposition by the latter (Palmquist and Conrad, 1978; DePeters et al., 1989; Chow et al., 1990; Grum et al. 1996). Supplemental fat also might increase milk yield during midlactation by increasing energetic efficiency. The addition of fat decreases methane production (Chilliard, 1993), thereby increasing the proportion of metabolizable energy in the diet. Furthermore, incorporation of preformed long-chain fatty acids (LCFA) into milk fat or body fat is energetically more efficient than de novo synthesis of LCFA from acetate (Baldwin et al., 1980). Suppression of de novo synthesis of fatty acids in the mammary gland by LCFA (Storry et al., 1973) decreases oxidative use of glucose to furnish NADPH in support of milk fat synthesis, thereby sparing glucose for lactose production (Palmquist and Jenkins, 1980). Fat may also alter the endocrine profile in a manner that favors milk synthesis rather than body reserve replenishment (Grummer and Carroll, 1991). Determination of effects of supplemental fat on milk production is complex, therefore, because of the need to consider differences in energy intake, efficiency of energy use, and partitioning of energy into milk solids vs. body tissue storage.

Environmental conditions may be another factor in responses of midlactation cows to additional energy. Because of the greater efficiency of LCFA use, less heat must be dissipated per unit of NE_Lintake from dietary fat than from concentrate or forage. Consequently, supplemental fat has been advocated for cows under heat-stress conditions (Moody et al., 1967), although benefits have not been demonstrated under controlled experimental conditions (Moody et al., 1967; Knapp and Grummer, 1991; Nianogo et al., 1991; Chan et al., 1997).

Our hypothesis was that cows in midlactation during summer heat conditions would respond to increased energy density from either supplemental unprotected fat or additional starch-based concentrate, but that fat supplementation should result in greater responses than additional concentrate. Furthermore, we postulated that effects of supplemental fat should be greater in primiparous cows than in multiparous cows because of their greater energy requirements for growth. Our objectives in this experiment were 1) to compare responses of midlactation cows during summer heat to increased dietary energy density either from supplemental fat or from additional concentrate, and 2) to compare responses of primiparous and multiparous cows to increased energy density.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
All procedures involving animals were approved by the University of Illinois Laboratory Animal Care Advisory Committee. Nine primiparous Holstein cows ( = 167 DIM, SD = 33, range 108 to 224) and nine multiparous Holstein cows ( = 154 DIM, SD = 23, range 132 to 201) were used in a replicated 3 x 3 Latin square design with 28-d periods. The first 23 d of each period were for adjustment to diets, and data were collected during the last 5 d of each period. Cows were housed in tie stalls in a mechanically ventilated barn and were allowed to exercise in an outside lot from approximately 0800 to 1000 h daily. Ventilation consisted of a series of overhead fans placed along the length of the barn, and a large fan directing outside air down the alley between the two rows of outward-facing cows. No sprinklers or misters were used. Cows were milked twice daily in a milking parlor.

Experimental diets (Table 1) were 1) a control diet containing 60% forage and no supplemental fat, 2) the control diet supplemented with 3% (DM basis) fat (HF) replacing a portion of the ground shelled corn and soybean hulls, and 3) a diet containing 40% forage and thus more concentrate (HC), achieved by decreasing the amount of alfalfa silage. The control diet was formulated to meet or exceed recommendations for all nutrients as specified by NRC (1989). Diets HF and HC were formulated to be isonitrogenous and isocaloric on an NE_Lbasis, as determined by the summative equation derived by Weiss et al. (1992) after chemical analysis of ingredients. Dietary NE_Lcalculated by this method was 1.572, 1.665, and 1.665 for control, HF, and HC diets, respectively. Diets HF and HC were formulated to be near practical limits for the amount of rumen-active fat addition and the forage-to-concentrate ratio, respectively.

All cows were fed the control diet for a 1-wk standardization period before the start of the experimental periods. Diets were fed as TMR twice daily in amounts to ensure 10% orts. Amounts of feed offered and refused were recorded daily. Corn silage and alfalfa silage were sampled weekly for DM determination, and rations were adjusted to maintain desired proportions of ingredients on a DM basis. Individual ingredients (alfalfa silage, corn silage, and concentrate mixtures) and final TMR were sampled daily during the last 5 d of each period and composited by period. Samples were stored frozen (-20°C) until they were dried in a forced-air oven (55°C) and ground through a 1-mm screen in a Wiley mill (Arthur H. Thomas, Philadelphia, PA). Ground samples were analyzed for DM (110°C for 24 h), ash (550°C for 8 h), CP (Kjeldahl analysis; AOAC, 1984), and NDF, ADF, acid detergent lignin, and cellulose (Van Soest et al., 1991). The TMR samples were analyzed for content of ether extract (AOAC, 1984).

Orts were sampled daily during the last 5 d of each period. The DM content was determined for calculation of daily DMI, and then daily samples for each cow in each period were pooled in proportion to daily DMI. Composited samples were ground through a 1-mm screen in a Wiley mill and analyzed for contents of CP, NDF, and ADF as described for feed samples.

Milk was sampled from four consecutive milkings on d 26 and 27 of each period. Samples were composited according to milk weight at each milking and then split into three aliquots. One portion was analyzed for contents of fat and total (crude) protein using midinfrared methods (Dairy Lab Services, Dubuque, IA). A second portion was used to determine total solids content in our laboratory by a gravimetric procedure in which aliquots of whole milk were weighed before and after drying at 100°C. The third portion was frozen (-20°C) for later analysis of fatty acid profile (data not reported here). Yields of SCM (using contents of protein and fat in milk) were calculated according to equations given by Tyrrell and Reid (1965).

Cows were weighed at the beginning of the experiment and then daily on d 25 to 27 of each period. Body weights were averaged for each cow in each period for statistical analysis. BCS were assigned at the start of the experiment and on d 26 of each period by three experienced individuals, using a five-point scale (1 = thin to 5 = obese [Wildman et al., 1982]). Rectal temperatures and respiration rates were measured at 0700 and 1400 h on d 25 to 27 of each period. Respiration rates were determined for three separate 1-min intervals for each cow at each time and averaged before statistical analysis. Barn temperatures and humidity measurements were not available. Environmental temperature and humidity data were obtained from Illinois State Water Survey records for the Water Survey Research Center, Champaign. The experiment was conducted between June 25 and September 17, 1994.

Blood was sampled from a tail vein at 0800 h (before the a.m. feeding) and 1400 h (approximately 4 h after feeding) on d 26 of each period. Plasma obtained by centrifugation of heparinized blood was stored at -20°C until analysis for concentrations of NEFA (Drackley et al., 1991) and glucose (kit 315; Sigma Chemical Co., St. Louis, MO).

Repeated measurements (e.g., milk yield, DMI) were reduced to period means for each cow before statistical analysis. Data were subjected to ANOVA for a replicated Latin square design using the GLM procedure of SAS (1985). Square nested within parity was used as the error term to test the effect of parity. Effects of period, cow within square, diet, and the interaction of parity and diet were tested using the residual error. Interactions of parity and diet did not approach statistical significance for any measured variable (all P > 0.15), but all terms were retained in the model. Means were compared by use of orthogonal contrasts of 1) control vs. both high-energy diets—i.e., HF and HC—and 2) HF vs. HC. Significance was declared whenP 0.05.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Mean daily ambient temperatures during the week of experimental measurements in each period (d 21 to 28) were 24.4, 22.0, and 23.4°C for periods 1, 2, and 3, respectively. Mean daily maximum temperatures were 30.1 (range 27.8 to 34.4), 27.9 (range 23.3 to 33.3), and 30.1°C (range 25.6 to 32.8) for periods 1, 2, and 3, respectively. Mean daily minimum temperatures were 18.3 (range 15.6 to 21.1), 15.8 (range 12.8 to 22.2), and 16.3°C (range 14.4 to 18.9), respectively. Mean minimum relative humidity was 53.0 (range 38 to 72), 48.4 (range 44 to 56), and 45.5% (range 40 to 60), respectively. Temperatures were within ± 0.5°C of 30-yr averages for periods 1 and 2, but were about 4.6°C higher than historic averages for period 3. Consequently, environmental conditions were typical of summer at this location and are representative of summer heat conditions in much of the Midwest United States.

Estimates of the ambient (outside) temperature-humidity index (THI) were generated using the following formula (National Oceanic and Atmospheric Administration, 1976):

where td is dry-bulb temperature (in degrees Fahrenheit) and RH is relative humidity. When mean daily THI exceeds 72, cows are subject to some loss of DMI and milk yield from heat stress (Johnson et al., 1963). Estimates of mean THI (71, 68, and 70 for periods 1, 2, and 3, respectively) were conservative because we used mean daily temperature but mean minimum relative humidity for each sampling period. Cows were housed in a tie-stall barn with the exception of time in the milking parlor or holding pen twice daily and the 2-h morning exercise period; temperatures and relative humidity in the barn were not recorded, so the actual degree of heat stress cannot be calculated.

Analyzed composition of the total diets was similar to formulated values (Table 1). The exception was dietary NE_Ldensity. Subsequent to publication of the seventh revised edition ofNutrient Requirements of Dairy Cattle (NRC, 2001), dietary NE_Lvalues were recalculated using the assumptions and model therein. Values for dietary NE_Ldensity were lower than values used for formulation (1.525, 1.615, and 1.585 according to NRC [2001] vs. 1.572, 1.665, and 1.665 as formulated for control, HF, and HC diets, respectively). Although procedures for calculating digestible energy were similar between methodology used for formulation (Weiss et al., 1992) and that used by NRC (2001), the lower estimates of dietary NE_Ldensity overall and differences in dietary NE_Ldensity between HF and HC diets according to NRC (2001) resulted from the greater discounts applied for effects of increasing DMI and the fact that energy from supplemental fat is discounted less.

The DMI was lower for cows fed HF than for those fed HC (Table 2). Differences among diets for DMI and dietary NE_Ldensity resulted in a weak tendency (P < 0.12) for NE_Lintakes to be greater for cows fed high-energy diets, although this effect was attributable only to cows fed HC (Table 2). Intakes of NDF, CP, and ADF (Table 2) followed those expected according to DMI and nutrient densities and indicated that sorting of ingredients in the TMR was minimal. Intakes of DM, NE_L, and other nutrient fractions were significantly lower for primiparous cows than for multiparous cows, as expected. However, DMI and NDF intake expressed as percentages of BW did not differ between primiparous and multiparous cows.

At least two explanations can be offered for the decreased DMI when cows were fed HF. First, the amount of unprotected fat used may have been excessive, resulting in decreased ruminal fiber digestion and thereby decreased DMI (Palmquist and Jenkins, 1980; Allen, 2000). Lower milk fat content (Table 3; discussed later) for cows fed HF indirectly supports an interference with ruminal fermentation. Cows fed the same fat source at 5% of dietary DM in a previous study had no alterations in ruminal fermentation characteristics, but DMI decreased by about 1 kg/d (Drackley et al., 1994). When Holstein steers were fed diets of similar composition and supplemented with 5% of the same fat source, the ruminal acetate-to-propionate ratio was decreased, but ruminal NDF digestion was unaffected (Elizalde et al., 1999). In contrast, Pantoja et al. (1994) reported that ruminal fermentation characteristics were not altered by supplementation of 5% animal-vegetable fat, yet ruminal NDF digestion was decreased by 15%; DMI was also decreased by about the same amount. Second, DMI may have been decreased by some factor or factors sensitive to intake of LCFA, as suggested by Drackley et al. (1992) and Palmquist (1994) and reviewed recently by Allen (2000). Unsaturated LCFA reaching the intestine decrease DMI (Drackley et al., 1992; Bremmer et al., 1998). Evidence has been presented for a role of increased concentrations of the gut hormones cholecystokinin (Choi and Palmquist, 1996) and glucagon-like peptide-1 (Benson and Reynolds, 2001) in response to LCFA reaching the intestine as mediators of decreased DMI.

Milk yield (Table 3) was increased (P < 0.002) by higher energy diets, with no difference between HF and HC. Similar responses were observed by Vazquez-Añon et al. (1997) when multiparous cows in midlactation were fed diets containing 1.70 Mcal of NE_L/kg compared with controls fed a diet containing 1.61 Mcal NE_L/kg. In that study, tallow was supplemented at 2.3% of dietary DM for the HF diet, and the high-grain diet contained 50% concentrate. Canale et al. (1990) noted a greater milk yield response when dietary energy density was increased by decreasing the dietary forage to concentrate ratio than by an isocaloric addition of dietary fat. Supplemental fat increased yield of 3.5% FCM compared with cows fed the isocaloric HC (Table 3), but yields of SCM did not differ significantly among diets. Milk fat content was lower for cows fed either high-energy diet, and was lower for cows fed HC than for cows fed HF. Lower milk fat content for cows fed HC was indicative of milk fat depression because yield of milk fat was also decreased by 0.07 kg/d (Table 3). In contrast, milk protein content was significantly higher for cows fed HC than for cows fed HF. The milk protein content was 0.10 percentage units lower for cows fed HF than for controls, which is commonly observed when supplemental fats are fed (Wu and Huber, 1994). Total solids content of milk was lower, but total solids yield was greater, when cows were fed high-energy diets (Table 3). Similar to milk protein, the content of SNF in milk was greater when cows were fed HC than when they were fed HF, but SNF yield was increased by either high-energy diet. In a previous experiment from our laboratory (Drackley et al., 1994), the same fat source was fed at 5% of dietary DM to Holstein and Jersey cows past peak milk yield; supplemental fat increased milk yield, but yields of FCM and SCM were unchanged because of corresponding decreases in concentrations of fat and protein in milk.

Efficiency of milk production was examined in two ways. First, on a mass input-output basis (kilograms of milk total solids per kilogram of DMI), efficiency was increased by high-energy diets, with cows fed HF being most efficient. Second, from an energetic standpoint, cows fed HF were more efficient in producing milk energy (kilograms of SCM) per megacalorie of NE_L intake than were cows fed HC. Lower apparent efficiency of milk energy secretion for cows fed HC likely arose from the depression of milk fat synthesis and consequent diversion of feed energy to fat deposition in adipose tissue (Tyrrell, 1980). However, differences in BW or BCS (Table 4)did not achieve statistical significance. Although Tomlinson et al. (1994) demonstrated that Latin square designs with 28-d periods are adequate for detection of milk production responses to supplemental fat, without carryover effects, such designs may not be sufficiently sensitive to detect diet-induced changes in BW or BCS (Drackley et al., 1994).

We used the NRC (2001) model to analyze nutrient intakes relative to predicted requirements. Primiparous and multiparous cows consumed 2.1 and 3.3 Mcal/d more NE_L, respectively, than required when the control diet was fed. Consequently, increased milk yield from feeding diets of higher energy density was not expected merely on the basis of increasing energy intake. The NRC (2001) model predicted slightly lower NE_L balance for primiparous and multiparous cows fed HF (1.7 and 2.8 Mcal/d, respectively), probably as a result of the lower DMI when fed HF. On the other hand, the NRC (2001) model predicted higher NE_L balance when primiparous (3.7 Mcal/d) and multiparous (5.2 Mcal/d) cows were fed HC. The model predicted metabolizable protein balances (supplied minus required) of 137, 19, and 338 g/d for multiparous cows fed control, HF, and HC diets, respectively, and 268, -87, and 175 g/d for primiparous cows fed control, HF, and HC diets, respectively. The Cornell Net Carbohydrate and Protein System (version 4.0.31; Cornell University, Ithaca, NY) predicted similar differences in metabolizable protein balance between control and HF diets. No parity x diet interactions were detected for any milk component or yield, which makes it unlikely that metabolizable protein supply actually limited responses of primiparous cows to any greater extent than multiparous cows.

Concentrations of glucose and NEFA in plasma are shown in Table 5. Glucose concentrations did not differ between primiparous and multiparous cows and were similar among diets in plasma sampled before the a.m. feeding. However, cows fed HC had greater glucose concentrations 4 h postfeeding, suggesting that propionate supply and energy balance were greater than for cows fed the control or HF diets. The concentration of NEFA was increased by HF, which also resulted in significant differences between high-energy diets and the control diet for both pre- and postfeeding samples. Supplemental fat increases the concentration of NEFA in blood (Grummer and Carroll, 1991). From an analysis of results from seven experiments in which multiple dietary fat concentrations were fed, Drackley (1999a) derived a regression equation that predicted an increase in plasma NEFA concentration of about 40 µM as dietary LCFA intake increased by 500 g/d, which approximates the increase in LCFA intake by cows fed HF. Primiparous cows had greater NEFA concentrations than multiparous cows, perhaps reflecting their slightly lower energy balance.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
For midlactation Holstein cows under conditions of moderate heat stress, increasing dietary energy density either by supplementation of unprotected fat (HF) or by increasing starch-based concentrate and decreasing forage (HC) resulted in greater milk yields; however, only cows fed HC had small increases in NE_L intakes. Production of SCM did not differ among the three diets because of contrasting changes of fat and protein production in milk between HF and HC relative to the control. Consequently, dietary energy was partitioned differently among diets. Measures of apparent efficiency of milk production (kg of milk solids/kg of DMI and kg of SCM/Mcal of NE_Lintake) were greater for HF than for HC. Improved efficiency resulted primarily from similar increases in milk production between HF and HC but decreased DMI when cows were fed HF. Greater morning respiration rates and rectal temperatures when cows were fed HC indicate that increased maintenance energy requirements resulting from greater expenditure of energy to dissipate heat load also may have been a factor in greater apparent efficiency for cows fed HF. No parity x diet interactions approached statistical significance in this study; consequently, first-lactation cows in midlactation responded to increased energy from either supplemental fat or increased concentrate in the same way as did multiparous cows. It must be noted, however, that evidence for a suboptimal ruminal environment was noted for cows fed either HF or HC. Consequently, future research should determine the effects of increasing dietary energy density by use of ruminally inert fat sources or by using nonforage fiber sources, such as soybean hulls, instead of cereal grains to replace forage during summer heat conditions.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The authors appreciate the assistance of G. C. McCoy and staff at the Dairy Research Unit for care of cows.

	FOOTNOTES

 
¹ Supported by state and federal funds appropriated to the Illinois Agricultural Experiment Station.

² Current address: R. R. 3 Box 206, Crawfordsville, IN 47933.

³ Current address: Land O’Lakes Feed, 1700 Bohm Drive, Little Chute, WI 54140.

Received for publication April 30, 2002. Accepted for publication August 15, 2002.

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TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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