Effects of Prepubertal Growth Rate and Diet on Lipid Metabolism in Lactating Holstein Cows1

Effects of Prepubertal Growth Rate and Diet on Lipid Metabolism in Lactating Holstein Cows1 P. J. GAYNOR,2 D. R. WALDO.3 A. V. CAPUCO,' R. A. ERDMAN,2 and L. W. DOUGLAS2 University of Maryland

College Park 20742 and USDA, Agricultural Research Service Beltsville, MD 20705

ABSTRACT

than when fed the control diet during second or third lactation. Increased deposition of fat in adipose and mammary tissues of cows with mean BW gain in excess of 950 g/d or fed a corn silage diet between 175 and 325 kg of BW did not result in more pronounced depression of milk fat percentage when cows were switched from a control diet to a high energy diet during second or third lactation. Overall, neither rate of BW gain nor type of silage fed between 175 and 325 kg of BW had a major influence on partitioning of excess dietary energy between synthesis of milk and BW gain during second or third lactation. (Key words: prepubertal, growth rate, diet, milk fat)

The objectives were to determine the effects of rate of BW gain and type of silage fed before puberty on the partitioning of excess dietary energy between synthesis of milk and BW gain in second or third lactation. Accordingly, 41 Holstein heifers weighing 175 kg were fed diets containing either alfalfa silage or corn silage to gain either 725 or 950 g/d until BW was 325 kg and two estrous cycles were observed. Puberty occurred near 281 kg of BW. During second (n = 36) or third (n = 5) lactation, the cows were fed a control diet (60% forage and 40% concentrate) and a high energy diet (20% forage and 80% concentrate) in a double-reversal experimental design with three 6-wk periods. The rate of BW gain before puberty did not affect the magnitude of changes in DMI, milk yield, milk composition, or concentrations of thyroid hormones, insulin, bST, glucose, or lipids in serum when cows were switched from a control to a high energy diet during second or third lactation. However, compared with cows fed a corn silage diet, cows fed alfalfa silage between 175 and 325 kg of BW had more depressed yields of fat, total solids, and FCM when fed the high energy diet

INTRODUCTION

Nutritional status between birth and puberty can exert a permanent effect on the ability of adult cows to produce milk (14, 30). Specific mechanisms underlying this effect have not been clearly established. However, factors affecting the number of secretory cells in developing mammary tissue may affect milk yield in subsequent lactations. For example, the DNA content of mammary tissue, used as an estimate of number of secretory epithelial cells, increased 3.5 times faster than the BW gain between 3 and 9 mo of age (92 to 229 kg of BW) for Holstein heifers in which puberty Received September 1, 1994. occurred at 7.4 mo or 195 kg of BW (26). Accepted March 10, 1995. Excessive intake of energy from the diet dur'Scientific Article A6494, Contribution Number 8701 of the Maryland Agricultural Experiment Station. No en- ing this allometric growth phase permanently reduced lactation potential (1, 9, 14, 16, 23). dorsements are herein implied. *Department of Animal Science, University of Mary- Specifically, high rates of BW gain before land. puberty were associated with younger age at 3Reprint requests: BARC-East, Building 200, Nutrient the onset of puberty (14), decreased concentraConservation and Metabolism Laboratory. 4Milk Secretion and Mastitis Laboratory, USDA-ARS. tion of bST in blood (23, 24), reduced growth 1995 J Dairy Sci 78:1534-1543

1534

1535

PREPUBERTAL GROWTH RATE AND DIET

of parenchyma in mammary tissue (5, 11, 25), impaired progression of primary ducts into the mammary fat pad (27, 28), and submaximal yield of milk during first and later lactations (9, 14, 16). In addtion, rate of BW gain and type of silage fed before puberty altered the composition of gain in empty body (31) and in mammary gland (6, 27). Specifically, heifers fed a corn silage diet compared with those fed alfalfa silage, and heifers grown at high (950 g) compared with those grown at low (725 g) rates of BW gain between 175 and 325 kg of BW had more fat in their empty bodies (31) and mammary glands (6. 27). Adipose tissue has an important role in lipid metabolism of lactating ruminants. Between 10 and 80% of metabolizable energy passes through adipose tissue of lactating dairy cows (8). For example, the estimated value is 32% for a 550-kg cow yielding 30 kg of milk/d (8). Further, rates of fatty acid synthesis in adipose and mammary tissues are usually inversely related (18). In addition, diets with a high

percentage of concentrate shift partitioning of nutrients away from synthesis of milk and toward synthesis of body fat (15). Our hypothesis was that increased deposition of fat in adipose and mammary tissues of heifers fed a corn silage diet, compared with those fed alfalfa silage or that gained at 950 compared with 725 gld between 175 and 325 kg of BW, may exert permanent effects on the partitioning of dietary energy between milk synthesis and BW gain. Thus, the objectives of this experiment were to determine whether the type of silage fed or the rate of BW gain before puberty affected magnitude of changes in synthesis of milk or BW gain when dietary energy was consumed at adequate versus excess amounts during second or third lactation. MATERIALS AND METHODS

Prior History of Cows

Holstein heifers were fed a common diet and gained between 611 and 650 gld between

TABLE 1. Descriptive parameters for cows used in the current experiment that were fed alfalfa silage or a corn silage diet before puberty to achieve 725 or 950 g/d of BW gain. ~~

725 g/d

Cows, no. Actual BW gain,' g/d Calculated4 Empty BW gain, g/d Fat in EBWG.5 g/d Protein in EBWG? g/d Fat-free matter, gld Age at first calving, d Milk yield? kg/d Fat, 96 4% FCM, kgld Age at second calving, d

DIM7

950 gtd

Contrast'

Alfalfa

Corn

Alfalfa

Corn

SE2

I1 811

12 762

8 974

10 996

20.7

656 134 126 523 729 22.7 3.46 20.6 1199 114

642 145 114 493 744 23.9 3.43 21.1 1193 121

808 191 143 615 708 22.1 3.27 19.7 1229 108

873 233 148 639 708 22.5 3.31 19.9 1043

90

17.4 4.1 3.1 13.3 24 1.4 .I6 1.1 52 21

Diet @) Rate (R) D x R

.OOOl

.059

.09

.o001

.01

.ooO1

.o001

.OOO1

.oO01

,004

.OOO1

.02

'Diet = Alfalfa versus corn silage before puberty, rate = 725 versus 950 g of BW gaidd, and diet x rate = interaction between diet fed and rate of BW gain before puberty. 2For mean of eight samples. 3Between 175 and 325 kg of BW. Talculations based on body composition of contemporary heifers from same treatments applied before puberty and slaughtered near 325 kg of BW (31). 5Empty BW gain between 175 and 325 kg of BW. 6Through 301 d of first lactation. 'At beginning of current experiment. Journal of Dairy Science Vol. 78. No. 7. 1995

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GAYNOR ET AL.

100 and 175 kg of BW (32). At 175 kg of BW, heifers were randomly assigned to a 2 x 2 factorial arrangement of type of silage fed and rate of BW gain (31). Diets contained alfalfa silage alone or corn silage with protein, vitamins, and minerals added to meet requirements for growth (20). Planned rates of BW gain between 175 and 325 kg of BW were 725 and 950 g/d. Alfalfa silage fed before puberty contained 22% CP and 3.1 Mcal of digestible energylkg of DM, and the corn silage diet contained 16% CP and 3.4 Mcal of digestible energylkg of DM. Heifers were fed these diets at these rates of BW gain until individual BW were 325 kg and two or more estrous cycles were observed. Data that were collected during the experimental growth phase before puberty and during fust lactation were analyzed as a factorial design, with terms for prepubertal rate of gain (725 or 950 g/d), type of silage fed (alfalfa or corn), and the interaction. The random error term was used to test the significance of main effects. The percentage of BW gain that was empty BW gain (between 80.8 and 87.7%) for heifers fed alfalfa silage or a corn silage diet at either 725 or 950 g/d before puberty was different (31). Therefore, the actual rate of BW gain before puberty of each cow used in the current experiment was multiplied by corresponding percentages for contemporary heifers in a slaughter-balance experiment to estimate the rate of empty BW gain before puberty. Similarly, gains of protein, fat, and fat-free matter in empty BW gain were calculated (Table 1). At slaughter, the mammary gland was re-

moved, bisected, trimmed of skin and teats, and weighed. Fat was trimmed from the right half of the udder (based on color of tissue) and weighed. Weight of parenchyma was calculated as the difference in total mammary gland weight minus twice the weight of fat trimmed from the right half of the udder. Weights and composition of mammary glands of contemporary heifers assigned before puberty to treatments and killed at 325 kg of BW are presented in Table 2. After attaining BW of 325 kg and before first calving, heifers were fed according to NRC (20) recommendations and were housed as a group. During first lactation, cows were housed in tie stalls, milked twice daily, and individually fed a single diet that contained 35% corn silage, 20% alfalfa hay, and 45% concentrate for ad libitum consumption. The energy content of the diet fed during first lactation was 3.6 Mcal of digestible energylkg of DM, and the CP content was 17%. Milk weights were recorded daily, and percentage of fat in milk samples collected each week was determined by infrared analysis at a commercial laboratory (Environmental Systems Services, College Park, MD). Cows that were in third lactation in the current experiment were fed a diet that was balanced to meet NRC (20) nutrient requirements during second lactation and were not used in any other experiments in the interim. All cows were fed according to NRC (20) recommendations between calving and the beginning of the current experiment.

TABLE 2. Weight and composition of mammary glands of heifers that were killed at 325 kg of BW.' 725 g/d

Heifers, no. Mammary gland, g Adipose, g Parenchyma, g

950 gJd

Contrast2

Alfalfa

Corn

Alfalfa

Corn

SE3

Diet (D)

Rate Oi)

D x R

8 1666 994 672

8 1939 1251 688

8 1881 1244 637

6 2625 1963 662

94 83 72

.ooO1

.OOO1 .OOO1

.025 ,013

.ooO1

'Heifers had been fed alfalfa silage or a corn silage diet before puberty to achieve 725 or 950 g/d of BW gain between 175 and 325 kg of BW. zDiet = Alfalfa versus corn silage before puberty, rate = 725 versus 950 g of BW gaidd, and D x R = interaction between diet fed and rate of BW gain before puberty. 3For mean of eight samples. Journal of Dairy Science Vol. 78, No. 7. 1995

PREPUBERTAL GROWTH RATE AND DIET Current Experiment: Control and High Energy Diets in Second or Third Lactatlon

During their second (n = 36) or third (n = 5 ) lactation, each cow was used once in a doublereversal experimental design and was alternately fed a control diet and a high energy diet in three 6-wk experimental periods. All cows completed all experimental periods. Incidence, severity, and duration of digestive upsets and mastitis were minor, and data were not adjusted for any reason. Ingredient and chemical composition of control and high energy diets fed during lactation are in Table 3. Cows were blocked according to date of calving. Initially, 12 cows in block 1 were 174 f 14 (mean k SE) DIM,14 cows in block 2 were 99 f 9 DIM, and 15 cows in block 3 were 67 f 8 DIM. Numbers of cows fed control and high energy diets in period 1 were 21 and 20, respectively. Cows were gradually accustomed to each lactation diet over 7 d at the beginning of each

1537

period. Housing was in a tie-stall barn, and milking was at 0630 and 1830 h daily. Orts were removed at 1400 h, and feeding began at 1430 h each day. Body weights were taken once weekly before feeding. Milk samples were collected at consecutive a.m. and p.m. milkings from each cow three times weekly during the last 3 wk of each experimental period. Fat, protein, lactose, and total solids contents in milk were determined by infrared analysis at a commercial laboratory (Environmental Systems Services). Samples of mixed diets and separate ingredients were collected daily and composited weekly for DM determinations. The control (n = 3) and high energy diets (n = 3) were subsequently composited within each of the three blocks, and chemical analyses were conducted at a commercial laboratory (Jefferson Laboratones, Jefferson, MD). Fatty acid composition of control (n = 3) and high energy diet (n = 3) composites was measured by GLC as described by Gaynor et al. (10).

TABLE 3. Ingredient and chemical composition of control and high energy diets fed during second or third lactation. Composition

Control

High energy

SE

SE

(% of DM)

Ingredient Corn silage' Alfalfa hay, chopped2 Corn, ground Soybean meal Barley, ground Sodium bicarbonate. Vitamins and minerals3 Chemical Samples analyzed, no. DM, % Fatty acids CP ADF NDF Ca P Mg K NEL,~McaVkg of DM

25 35 26.8 10 0 2 1.2 3 62.9 1.8 16 25.2 39.9

.I .4 .2 1.3 1.52

10 10

35 10 31.3 2 1.7

.2 .I .8 .6 1 .01 .a 1 .O 1 .06

3 16.7 2.4 15.9 13 26.1 .7 .4 .2 1.4 1.71

.4

.1 .9 .1 1.6 .04

.02

.o 1

.06

'Chop length between 1 and 1.5 cm. 2Chop length between 1.5 and 2.5 cm. 3Percentage of ingredients in dietary DM: .5% trace-mineral salt plus Se, .02% sulfur, .048% magnesium oxide, .OlZ% zinc oxide, ,04440 vitamin A, ,01646 vitamin D, ,04896 vitamin E control diet contained 3% monosodium phosphate (no limestone) and high energy diet contained 1.0% powdered limestone (no monosodium phosphate). 4Estimated (20). Journal of Dairy Science Vol. 78, No. 7, 1995

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GAYNOR ET AL.

Blood samples were collected from the coccygeal vein (vacutainer; Becton Dickinson, Princeton, NJ) at 0830, 1130, 1430 (before feeding), and 1930 h on 1 d during wk 4, 5, and 6. Serum was frozen at -2O'C preceding analyses. Concentrations of glucose (Yellow Springs Instruments, Yellow Springs, OH), NEFA (Wako Pure Chemicals Industries, Ltd., Osaka, Japan), as modified by McCutcheon and Bauman (17), and triacylglyceride (Wako) were determined in duplicate on all four samples collected during wk 6 of each period and on samples collected at 1130 h during wk 4 and 5. Concentrations of insulin, bST, triiodothyronine, and thyroxine in serum were measured by radioimmunoassay (3, 4). Intraassay and interassay coefficients of variation were between 2 and 13% for all laboratory analyses. Data from the current experiment were analyzed as follows. Concentrations of hormones and metabolites in serum samples collected during wk 6 (n = 4 per cow) were averaged within cow because responses at each sampling time were similar among treatments. The mean of this average and determinations from single samples (1 130 h sample) from wk 4 and 5 were analyzed using SAS (22). Data collected daily (milk weights and feed consumption) during wk 4, 5, and 6 were averaged and then analyzed with the following mathematical model for a double-reversal design adapted from Sanders and Gaynor (21):

+ block, + rate, + dietk (ratej x dietk) + COWlfijk) + x Prn(i3 + periodrn(i) + LA, + (LD, x rate,)

Yi,klmn = p

+ +

(LD, x dietk)

+

e i j b

where Yi.klmn= observed response of cow 1 in block i fkd prepubertal diet k at rate of BW gain j in period m receiving lactation diet n; p = overall mean; blocki = effect of block i (i = 1, 2, or 3); rate, = low or high BW gain before puberty; dietk = alfalfa silage or corn silage diet before puberty; COWl(ijk) = effect of individual cow 1 within block i, prepubertal BW gain j, and fed diet k before puberty; bi,u = partial regression coefficient of the response variable on period for cow 1 in block i, prepubertal rate of BW gain j, and prepubertal Journal of Dairy Science Vol. 78, No. 7, 1995

diet k; P,G) = (continuous variable) effect of period m within block i; periodme) = (class variable) effect of period m within block i; LD, = effect of lactation diet n (control or high energy); and q,umn= random error. The interaction term LD, x rate, x dietk was not significant for response variables presented and was pooled with the random error term. Influence of rate of BW gain before puberty and type of silage fed before puberty on the difference in responses between control and high energy lactation diets was evaluated using interaction terms LD, x rate, and LD, x dietk. Statistical significance was considered to be P I .05. RESULTS

Prior History of Cows

Actual rates of BW gain between 175 and 325 kg of BW averaged 81 1, 762, 974, and 996 g/d for treatments: low BW gain, alfalfa silage; low BW gain, corn silage diet; high BW gain, alfalfa silage; and high BW gain, corn silage diet, respectively (Table 1). Puberty occurred near 281 kg of BW (32); therefore, about 106 kg of BW gain were before puberty and 44 kg were after puberty for these heifers. Calculated composition of BW gain between 175 and 325 kg of BW is in Table l . These estimates should reflect composition of gain before puberty of cows used in the current lactation experiment. Compared with estimates for heifers fed alfalfa silage, these estimates suggest that heifers fed a corn silage diet before puberty gained more empty BW, more fat in empty BW gain, more protein in empty BW gain, and more fat-free matter at 950 than at 725 g/d. In addition, heifers fed a corn silage diet before puberty had more estimated fat in empty BW gain than heifers fed alfalfa silage before puberty. These estimates suggest that, compared with heifers fed to gain 725 g/d, heifers fed to gain 950 g/d gained more empty BW, more fat in empty BW gain, more protein in empty BW gain, and more fat-free matter. Age at first calving was similar among treatments (Table 1). Cows assigned to either alfalfa or corn silage diets at either 725 or 950 g/d of BW gain before puberty had similar mean daily milk yields through 301 d of first lactation. In addition, percentage of fat in milk in first lactation, FCM yield, age at second

1539

PREPUBERTAL GROWTH RATE AND DIET

calving, and DIM at initiation of the current experiment (either second or third lactation) were similar among treatments applied before puberty. Compared with heifers fed alfalfa silage before puberty, heifers fed a corn silage diet had greater weights of untrimmed mammary glands and physically dissected adipose tissue in mammary glands when fed to gain 950 g/d than when fed to gain 725 g/d (Table 2). In addition, weights of mammary glands and adipose in mammary tissue were greater for heifers fed a corn silage diet than for those fed alfalfa silage and for heifers fed to gain 950 g/ d than for those fed to gain 725 g/d. Weights of parenchyma were similar among treatments. Current Experiment: Control and High Energy Diets in Second or Third Lactation

In the current experiment, cows fed either an alfalfa silage diet or a corn silage diet before puberty had similar changes in DMI

when switched from a control diet to a high energy diet during second or third lactation (Table 4). For example, the difference in DMI between the high energy diet and the control diet was -.2 kg/d (19.9 minus 20.1 kg/d; Table 4) for cows fed alfalfa silage before puberty and 1.3 kg/d (21.4 minus 20.1 kg/d; Table 4) for cows fed a corn silage diet before puberty. The interaction between lactation diet and type of silage fed before puberty (P= .09; Table 4) tests if the difference between -.2 kg/d and 1.3 kg/d (1.5 kg/d) is different from zero. Compared with cows fed a corn silage diet, cows fed alfalfa silage before puberty had a smaller increase in amount of fatty acids consumed when switched from the control diet to the high energy diet during lactation (119 vs. 155 g/d; Table 4). Cows fed to gain either 725 or 950 g/d before puberty had similar changes in DMI and amounts of fatty acids consumed when switched from the control diet to the

TABLE 4. Treatment means and interaction test for cows fed either alfalfa silage or a corn silage diet before puberty and a control diet and a high energy diet during second or third lactation. Alfalfa silage

Cow-periods, 110.3 DMI, kg/d Fatty acid intake, g/d Milk, kg/d Fat, % Fat, g/d Protein, 9% Lactose, % Total solids, % Total solids, g/d 4% FCM, kg/d BW,kg NEL balance.4 McaVd Concentrations in serum Glucose, mddl NEFA, cceq/ml Triacylglycerides, mg/dl Triiodothyronine, ng/ml Thyroxine, n g / d bST, n g / d Insulin. m U h

Control

High energy

29 20.1 340 23.5 3.70 857 3.24 4.77 12.43 2899 22.2

28 19.9 459 24.1 2.59 599 3.30 4.83 11.44 2728 18.6

Cam silage Control

High energy 33 21.4 494 24.7 2.65 642 3.44 4.89 11.70 2867 18.5 627 13.4 64.4 207 11.0 1.86 65.2 2.7 36.0

5.1

11.6

33 20.1 339 22.4 3.66 812 3.41 4.81 12.59 2812 21.2 618 5.7

60.0 24 1 12.6 1.88 65.5 3.5 24.0

64.6 219 12.2 1.91 67.0 3.2 32.1

61.3 22 1 12.4 1.79 62.5 3.6 25.6

602

606

SE' .5 9 .5

.09 22 .02 .02 .09 59 .4

2

.6 .7 6.5 .3 .03 1.4 .2 1.6

PZ .09 .04 .09 .56

.03 .35 .55 .58 .04 .02 .19 .29 .30 .51 .08 SO

.65 .12 .43

'For 28 samples. Probability level for interaction test of prepubertal diet and lactation diet. 3Number of cow-period observations used in each mean. 4Calculated using NRC (20) values. Journal of Dairy Science Vol. 78, No. 7, 1995

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GAYNOR ET A L

high energy diet during lactation (Table 5). Regardless of type of silage fed and rate of BW gain before puberty, cows had similar increases in milk yield and percentages of protein and lactose in milk and similar decreases in percentages of fat and total solids in milk when switched from the control diet to the high energy diet during lactation (Tables 4 and 5). Compared with cows fed a corn silage diet before puberty, cows fed alfalfa silage before puberty had greater declines in yields of fat in milk (grams per day) and 4% FCM when switched from the control diet to the high energy diet during lactation (-258 vs. -170 g of fat and -3.6 vs. -2.7 kg/d of 4% FCM, respectively; Table 4). Cows with BW gains of either 725 or 950 g/d before puberty had similar decreases in yields of milk fat (grams per day) and 4% FCM when switched from the control diet to the high energy diet during

lactation (Table 5). Yield of total solids in milk decreased -171 g/d for cows fed alfalfa silage before puberty and increased 55 g/d for cows fed a corn silage diet before puberty when cows were switched from the control diet to the high energy diet during lactation (Table 4). Cows with a BW gain of either 725 or 950 g/d before puberty had similar decreases in yield of total solids in milk when switched from the control diet to the high energy diet during lactation (Table 5). Regardless of type of silage fed and rate of BW gain before puberty, BW, estimated NEL balance, and concentration of glucose in serum increased similar amounts, and concentration of NEFA in serum decreased similar amounts when cows were switched from the control diet to the high energy diet during lactation (Tables 4 and 5). However, compared with cows fed a corn silage diet before puberty, cows fed alfalfa silage before puberty tended

TABLE 5. Treatment means and interaction test for cows grown at either 725 or 950 g/d before pubefly and fed a control diet and a high energy diet during second or third lactation. 725 g/d

COW-periods,110.3 DMI, kg/d Fatty acid intake, g/d Milk, kg/d Fat, % Fat, g/d Protein, % Lactose, % Total solids, % Total solids, g/d 4% FCM, kg/d BW, kg NEL balance.4 Mcal/d Concentration in serum Glucose, mg/dl NEFA, ceq/d

Triacylglycerides, mg/dl Triiodothyronine, n g / d Thyroxine, ng/ml bST, n g / d Insulin, mU/L

950 g/d High energy

Control

High energy

Control

35 20.2 342 23.5 3.71 852 3.35 4.15 12.52 291 1 22.2 617 5.1

34 21.3 489 25.3 2.70 650 3.39 4.83 11.63 2893 19.9 624 12.9

27 20.0 338 22.4 3.65 818 3.30 4.83 11.63 2800 21.2 602 5.7

23.6 2.54 592 3.35 4.90 11.51 2702 18.3 610 12.1

61.6 228 12.9 1.79 61.7 3.5 25.9

64.8 202 11.8 1.86 65.4 2.7 35.6

59.7 235 12.1 1.88 66.3 3.6 23.7

64.3 224 11.5 1.91 66.8 3.2 32.5

21 20.1

464

*For 27 samples. 2Probability level for interaction test of prepubertal BW gain and lactation diet, 3Number of cow-period observations used in each mean. 4Calculated using NRC (20)values.

Journal of Dairy Science Vol. 78, No. 7, 1995

SE1

P=

.5 10

.27 .24 .5 1 .56 .56 .76 .86 .56 .46 .41 .72 .25

.5

.10 23 .02

.M .09

61 .5

2 .6

.8 7 .3 .03 1.5 .2 1.6

.32 .21 31 .39 .24 .17

.I8

PREPUBERTAL GROWTH RATE AND DIET

1541

(P = .OS) to have a smaller decline in concentration of triacylglyceride in serum when they were switched from the control diet to the high energy diet during lactation (Table 4). Regardless of type of silage fed and rate of BW gain before puberty, cows had similar increases in concentrations of triiodothyronine, thyroxine, and insulin in serum and similar decreases in concentrations of bST in serum when switched from the control to the high energy diet during lactation (Tables 4 and 5).

greater milk fat yield during the first 10 wk of second lactation than did cows with a BW gain of 940 g/d before puberty (29). In contrast, Amir and Kali (1) concluded that the fat content of milk was greater for heifers reared on a high level of nutrition after reviewing 15 studies on relationships between growth rate before puberty and lactational performance. These opposing interpretations may reflect differences in the length of time that specified rates of BW gain were imposed on heifers before first calving. For example, treatments were continuously imposed between birth and DISCUSSION first calving in most experiments summarized Body weight gains in excess of 700 g/d by Amir and Kali (1). Thus, the possibility before puberty have been associated with exists that heifers with continuously high rates reduced milk yields in first and later lactations of BW gain had greater fat deposition before (1, 9, 14, 16, 23). Although actual BW and age calving and increased rates of fat mobilization, at which puberty occurred were quite different ketogenesis, and synthesis of milk fat after for heifers in the experiment of Sinha and calving. However, our data suggest that rate of Tucker (26), compared with those of heifers BW gain or carcass fat gain before puberty had used in this experiment (195 kg, 7.4 mo vs. no effect on decrease in milk fat percentage or 28 1 kg, 11.2 mo, respectively), treatments were yield of milk fat when cows were switched applied over approximately the same change in from a control to a high energy diet after peak BW before puberty (103 and 106 kg, respec- milk yield in second or third lactation. Further, tively). Milk yields through 301 d of first increased accretion of adipose tissue before lactation were not significantly affected for 76 puberty did not explain the differences in yield cows fed alfalfa or corn silage diets at 725 or of milk fat or FCM for cows fed alfalfa or corn 950 g/d of BW gain between 175 and 325 kg silage diets before puberty, because heifers of BW (Waldo et al., 1994, unpublished data). grown at high, rather than at low, rates of BW For 41 cows used in the current experiment, gain before puberty had greater accretion of fat milk yield, percentage of fat in milk, and 4% in the carcass, but did not have different yields FCM yield through 301 d of first lactation of milk fat or FCM in second or third lactawere similar. Collectively, these data suggest tion. Alternatively, quantity of DM consumed that accelerated rates of gain before puberty are possible without reducing lactation poten- has a strong positive relationship with amount tial (31). Johnsson (14) and Amir and Kali (1) of milk produced (7, 20). In addition, the perhave reviewed data that both support and re- centage of concentrate in dietary DM exerts fute the hypothesis that rate of gain before variable effects on quantity of DM consumed puberty affects milk yield in subsequent lacta- (19). Thus, the reason for increased DMI when cows fed corn silage before puberty were tions. The aim of the current experiment was to switched from a control to a high energy diet clarify the effects of rate of BW gain and type during lactation is not apparent. Compared of silage fed before puberty on the partitioning with cows fed alfalfa silage before puberty, of nutrients during subsequent lactations. Ef- cows fed corn silage before puberty had fects of rate of BW gain before puberty on the greater increases in DMI and fatty acid intake synthesis of milk fat in lactation have been when switched from the control to the high inconsistent. For example, Valentine et al. (29) energy diet during lactation. This, in turn, may reported that cows with BW gains of either have been the predominant reason why milk 180 or 620 g/d had greater milk fat yield yield increased more, and thus yield of fat in during the first 10 wk of first lactation than did milk declined less for cows fed a corn silage cows with BW gain of 940 g/d before puberty. diet than for cows fed alfalfa silage before Also, cows with BW gain of 180 g/d had puberty. Journal of Dairy Science Vol. 78, No. 7. 1995

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Another possibility is that increased lipogenic activity in adipocytes before puberty influenced their functioning in lactation. Jensen et al. (13) reported that lipoprotein lipase in mammary tissue of mice was derived from adipocytes that were depleted of lipid. In addition, Baldwin et al. (2) reported that activities of lipogenic enzymes were higher in adipose tissue and lower in mammary tissue of cows fed a diet that caused depression of milk fat percentage compared with those of cows fed a control diet. Although the experiment of Baldwin et al. (2) was not designed specifically to test relationships between growth rate before puberty and performance during lactation, the possibility was discussed that cows with greatest depression of milk fat percentage and related changes in activity of lipogenic enzymes in mammary and adipose tissues may have gained BW at higher rates before puberty (R. L. Baldwin, 1986, personal communication). If differences in composition of mammary tissue observed before puberty persisted through second and third lactations, then the potential for altered yield and composition of milk existed. For example, increased removal of lipid from triaclyglycerides by adipose and mammary tissues of cows fed a corn silage diet before puberty may have alleviated depressed yield of milk fat concurrent with increased BW. Finally, Hansson et al. (12) hypothesized that “differences in rearing intensity create persistent differences in the endocrine system,” which in turn influence synthetic activity in mammary tissue. Data from the current experiment do not support the hypothesis that rate of BW gain or type of silage fed before puberty alters differences in concentrations of insulin, bST, triiodothyronine, or thyroxine in serum when control and high energy diets are fed. CONCLUSIONS

Rate of BW gain before puberty had no influence on differences in responses measured when control and high energy diets were fed in a double-reversal experimental design during second or third lactation. However, compared with cows fed a corn silage diet before puberty, cows fed alfalfa silage before puberty tended to have lower increases in DMI and milk yield, more reduced yields of fat and total Journal of Dairy Science Vol. 78. No. 7. 1995

solids in milk, and lower 4% FCM yield when fed the high energy diet than when fed the control diet during second or third lactation. Thus, increased deposition of fat in adipose and mammary tissue of cows fed a corn silage diet between 175 and 325 kg of BW or with BW gain in excess of 950 g/d between 175 and 325 kg of BW did not result in more pronounced depression in percentage of milk fat when a high energy rather than a control diet was fed during lactation. Overall, neither rate of BW gain nor type of silage fed between 175 and 325 kg of BW had a major influence on partitioning of excess dietary energy between synthesis of milk and BW gain during second or third lactation. REFERENCES

1 Amir, S., and J. Kali. 1974. influence of plane of nutrition of the dairy heifer on growth and performance after calving. Dairy Science Handbook. AgriServ. Found., Clovis. CA 7:183. 2 Baldwin, R. L., H. J. Lin, W. Cheng, R. Cabrera, and M. Ronning. 1969. Enzyme and metabolite levels in mammary and abdominal adipose tissue of lactating dairy cows. J. Dairy Sci. 52:183. 3 Barnes, M. A., G. W. Kaymer, R. M. Akers, and R. E. Pearson. 1985. Influence of selection for milk yield on endogenous hormones and metabolites in Holstein heifers and cows. J. Anim. Sci. 60271. 4Capuc0, A. V., J. E. Keys, and J. J. Smith. 1989. Somatotrophin increases thyroxine-5’-monodeiodinase activity in lactating mammary tissue of the cow. J. Endocrinol. 121:205. 5Capuc0, A. V., J. J. Smith, and D.R. Waldo. 1986. Influence of diet and prepubertal growth rate of Holstein heifers on mammary gland growth and concentration of growth hormone and prolactin in serum. J. Dairy Sci. 69(Suppl. 1):202.(Abstr.) 6Capuc0, A. V., J. J. Smith, D. R. Waldo, and T. H. Elsasser. 1988. Effect of diet and prepubertal growth rate of Holstein heifers on mammary gland growth and milk production. J. Dairy Sci. ’Il(Supp1. 1): 229.(Abstr.) 7 Chase, L. E. 1993. Developing nutrition programs for high producing dauy herds. J. Dairy Sci. 76:3287. 8Emery. R. S. 1979. Deposition, secretion, transport and oxidation of fat in ruminants. J. Anim. Sci. 48: 1530. 9 Foldager, J., and K. Sejrsen. 1991. Rearing intensity in dairy heifers and the effect on subsequent milk production. Rep. Natl. Inst. Anim. Sci., Denmark 693: 1. lOGaynor, P. J., R. A. Erdman, B. B. Teter, J. Sampugna, A. V. Capuco. D. R. Waldo, and M. Hamosh. 1994. Milk fat yield and composition during abomasal infusion of cis or trans-octadecenoates in Holstein cows. J. Dairy Sci. 77:157.

PREPUBERTAL GROWTH RATE AND DIET 1I Grieve, D. G.,P. J. Visser, and B. W. McBride. 1986. Effect of forage source and feeding level on growth and mammary development of Holstein calves. J. Dairy Sci. 69(Suppl. 1):132.(Abstr.) 12 Hansson, A., E. Briinnhg, and L.-E. Liljedahl. 1967. Studies on monozygous cattle twins. XIX. The interaction of heredity and intensity of rearing with regard to growth and milk yield in dairy cattle. Lantbrukshtigsk. Ann. 33643. 13 Jensen, D. R., D. H. Bessensen, J. Etienne, R. H. Eckel, and M. C. Neville. 1991. Distribution and source of lipoprotein lipase in mouse mammary gland. J. Lipid Res. 32:733. 14 Johnsson, I. D. 1988. The effect of pnpubeltal nutrition on lactation performance by dairy cows. Page 171 in Nutrition and Lactation in the Dairy Cow. P. C. Gamsworthy, ed. Buttenvorths, London, England. 15 Jorgensen, N. A., L. H. Schultz, and G. R. Barr. 1965. Factors influencing milk fat depression on rations high in concentrates. J. Dairy Sci. 48:1031. 16 Little, W., and R. M. Kay. 1979. The effects of rapid rearing and early calving on the subsequent performance of dairy heifers. Anim. Prod. 29:131. 17 McCutcheon, S. N., and D. E. Bauman. 1986. Effect of chronic growth hormone treatment on responses to epinephrine and thyrotcopin-releasing hormone in lactating cows. J. Dairy Sci. 69:44. 18 McNamara, J. P.. D. C. McFarland, and S. Bai. 1987. Regulation of bovine adipose tissue metabolism during lactation. 3. Adaptations of hormone-sensitive and lipoprotein lipases. J. Dairy Sci. 70:1377. 19 National Research Council. 1987. Predicting Feed Intake of Food-Producing Animals. Natl. Acad. Sci., Washington, DC. 20 National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC. 21 Sanders, W. L.. and P. J. Gaynor. 1987. Analysis of switchback data using Statistical Analysis System, Inc. software. J. Dairy Sci. 70:2186. 22SAS" User's Guide: Statistics, Version 5 Edition. 1985. SAS Inst., Inc., Cary, NC.

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23SeJrsen, K. 1978. Mammary development and milk yield in relation to growth rate in dairy and dualpurpose heifers. Acta Agric. Scand. 28:41. 24 Sejrsen, K..J. Foldager, M.T. Sorensen, R. M. Akers. and D. E. Bauman. 1986. Effect of exogenous bovine somatotropin on pubertal mammary development in heifers. J. Dairy Sci. 69:1528. 25Sejrsen. K., J. T. Huber, H. A. Tucker, and R. M. Akers. 1982. Influence of nutrition on mammary development in pre- and postpubertal heifers. J. Dairy Sci. 65:793. 2 6 S i n k Y. N., and H. A. Tucker. 1969. Mammary development and pituitary prolactin level of heifers kern birth through puberty and during the estrous cycle. J. Dairy Sci. 52:507. 27Smith. J. J., A. V. Capuco, and D. R. Waldo. 1986. Influence of diet and prepubertal growth rate of Holstein heifers on mammary gland histology. J. Dairy Sci. 69(Suppl. l):ZM.(Abstr.) 28Swanson. E. W. 1960. Effect of rapid growth with fattening of dairy heifers on their lactational ability. J. Dairy Sci. 43:377. 29Valentine. S. C., R. C. Dobos, P. A. Lewis, B. D. Bartsch and R. B. Wickes. 1987. Effect of live weight gain before or during pregnancy on mamfnary gland development and subsequent milk production of Australian Holstein-Friesian heifers. Aust. J. Exp. Agric. 27:195. 30Widdowson. E. M., and D. Lister. 1991. Nutritional control of growth. Page 67 in Growth Regulation in Farm Animals. A. M. Pearson and T. R. Dutson, ed. Elsevier Appl. Sci., London, England. 31 Waldo, D.R. 1988. Protein and energy deposition in growing Holstein heifers. Page 111 in Wissenschafleliche Zeitschrift Der Wilhelm-Pieck-Universitl Rostock Natunvissenschaftliche Reihe. Eur. Assoc. Anim. Prod. Publ. 37 (Patt 2). 32 Waldo, D. R., A. V. Capuco, and C. E. Rexroad, Jr. 1989. Replacement heifer growth rate affects milk producing ability. Feedstuffs (Nov. 27):15. Miller Publ. Co., Minnetonka. MN.

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