weight losses were greater for all cows ... samples of weighbacks were analyzed ..... rate both AI. 84.2 19. 76.2 21. 69.0 29. 51.5 33. First AI. 75.W 16. 25.0b 12.
Effect of Dietary Calcium Soaps on Milk Yield, Body Weight, Reproductive Hormones, and Fertility in First Parity and Older Cows D. SKLAN Faculty of Agriculture Hebrew University Rehovot 76-100, Israel M. KAIY, U. MOALLEM, and Y. FOLMAN Agriculhrral Research Organization PO Box 6 Bet Dagan, Israel ABSTRACT
The effects were determined of dietary Ca soaps of fatty acids fed to cows to 120 DIM on milk yield, BW, peripheral concentrations of reproductive hormones, and fertility in primiparous and multiparous cows. Milk yield was increased in primiparous and multiparous cows fed Ca soaps, and milk fat and protein yields were enhanced. Body weight losses were greater for all cows fed Ca soaps, and this trend was greater and longer lasting in primiparous cows than in multiparous cows. Plasma triglyceride concentrations were elevated in multiparous cows, but FFA tended to be higher in primiparous cows fed Ca soaps. Conception rate at first AI was lower for primiparous cows fed Ca soaps (33%) than for controls (74%), but differences were not significant for later AI or between multiparous groups. No differences were apparent for plasma progesterone or estradiol in the luteal or follicular phases preceding the fmt AI, and differences in mean luteinizing hormone concentrations were small in a 6-h window in the follicular phase. The differences in conception rate at fmt AI in primiparous cows could not be explained on the basis of changes in peripheral hormone concentrations. The enhanced negative energy balance in primiparous cows fed Ca soaps appar-
Received June 14, 1993. Accepted January 14, 1994. 1994 J Dairy Sci 77:1652-1660
ently was related to the decrease in their conception rate. (Key words: calcium soaps, milk yield, reproduction)
Abbreviation key: CSFA = calcium soaps of fatty acids, PG = prostaglandin, TG = triglyceride. INTRODUCTION
Dietary Ca soaps of fatty acids (CSFA), which are inert in the rumen, fed to high yielding lactating cows enhances ration energy density and energy intake, if DMI is not decreased, without compromising rumen cellulolytic bacterial activity (5, 12). Addition of CSFA has resulted in incmases in FCM yield when fed beginning at parturition (12, 17, 18, 19). In addition to enhanced milk yield, dietary CSFA resulted in decreases in BW or body condition following parturition that were greater for cows fed CSFA and reached a minimum later than that in controls (18, 19). Plasma FFA were higher for cows fed CSFA in early lactation, but after peak milk yield, plasma phospholipids and triglycerides (TG) were elevated by dietary CSFA (19). These results were obtained with multiparous cows; details of the effects on primiparous cows are not known. Multiparous cows fed CSFA had improved reproductive performance (8, 17, 18, 19). In a recent study, cows fed Ca soaps commenced ovarian cycling later after calving than did control cows. However, once cyclicity commenced, more cows fed fat than controls cows had normal cycle length (18 to 26 d) (19). Progesterone concentrations were higher in cows fed Ca soap in the luteal phase before AI 1652
1653
CALCIUM SOAPS PRODUCTION AND REPRODUffION
and were higher 9 and 24 d after AI in cows that conceived. Conception rate was higher for cows fed CSFA for second to fourth AI, a higher proportion of cows were pregnant at 150 d after calving, and the number of open days was reduced (19). In beef cows, dietary CSFA enhanced follicular growth and increased progesterone and LH during the luteal phase (7). The objectives of the present study were to examine the effects of dietary CSFA fed to primiparous cows on milk yield and to extend the understanding of the influence of CSFA on reproductive hormones and fertility. MATERIALS AND METHODS
TABLE 1. I n w e n t and chemical composition of diets in Experiment 1. Control
CSFAl
-(% of DM) Composition Barley Corn grain, ground Tapioca Wheat bran Rotein concentrate2 soybean meal
Rapeseed meal ceCO3, NaCl plus DCP3 CSFA Vetch hay Wheat silage Corn silage Cottonseeds Citrus pulp Analyses4 "EL,Mcal/kg of DM CP, %
8.7 13.8 6.8 8.4 6.4 3.9 2.0 2.2 0 6.4 14.3 15.3 6.8 4.9
8.6 13.5 6.1 8.3 6.3 3.9 2.0 2.0 2.5 6.3 14.1 15.1 6.7 4.6
Two dietary treatments, with and without CSFA, were compared with 56 primiparous 1.71 I .82 and 66 multiparous Israeli-Friesian cows per 16.1 16.1 group. Cows were kept under loose housing in 2.8 4.9 Fat, % 1 .o 1.o group pens; all cows in the pen were in the cas .48 .48 P. % trial. Cows were blocked according to parity, % 19.0 19.2 date of parturition, and previous lactation daily ADF, NDF % 32.2 32.5 FCM yield (multiparous cows). Cows calved 1Calcium soaps of fatty acids (CSFA; Koffolk Ltd.. within a 120-d period. The dietary treatments Pelttch-Tha, Israel) contained 86% fatty acids and 8.5% were designed to contain equal amounts of CP ca. and forage. Dietary ingredients were manipu1.83 Mcal of " E L k g of DM and 27.8% lated to provide equal amounts of ADF and CP Zcontained from 15.1% what, 27.1% wheat middlings, 10.9% NDF. Composition and analysis of diets are soybean meal, 3.4% corn gluten meal, 14.6% cottonseed presented in Table 1. The experimental diet meal. 13.1% raptseed meal, 12.3% feather meal, 2.1% contained 1.82 Mcal of NELAcg of DM com- soapstock, 1.1% Vitamin and mineral mix, and .3% pared with 1.71 for the control diet. All feeds CaCO3. 3Dicalcium phosphate. were mixed, weighed, and fed daily from a 4Parameters werc determined by analysis; NEL was mixing wagon. Weighbacks usually were less than 5% of feed offered, determined daily for calculated using NRC (11) values. each group throughout the experimental period, and removed before the a.m. feeding; samples of weighbacks were analyzed monthly. Thus, daily DMI was determined per Robertson (20). Fatty acid composition of Ca group. Diets were fed from calving to 120 soaps was determined following acid hydrolyDIM, after which all cows were transferred to sis by gas chromatography of the methyl esters on a packed column of 20% DEGS on Chrothe control diet. Cows were milked three times daily, and mosorb W using heptadecanoic acid as the yield was recorded electronically. Milk was internal standard (17). Cows were observed for sampled every 12 to 14 d from all three milk- signs of estrus for a 30-min period three times ings, and the samples were composited for fat, daily by the same technician who also insemiprotein, and lactose determinations by infrared nated all the cows. Cows were treated with two analysis. Cows were weighed on d 3 following injections of a prostaglandin (F'G) analogue parturition and at 10- to 14-d intervals until (estnunate; Coopers Animal Health Ltd.,Berkhemstead, England) given 14 d apart. The first 210 DIM and thereafter at 20-d intervals. Determination of DM, CP, ADF, Ca,and P injection was given to cows between 50 and 60 in feeds was by standard methods (I), and NDF DIM. Following the second PG injection, cows was determined as described by Van Soest and observed in estrus were inseminated. J o d of D a q Science Vol. 77. No. 6, 1994
1654
SKLAN
Blood was sampled from the jugular vein into heparinized vacutainers that were placed on ice, centrifuged, and stored at -18'C until analysis. Blood samples were collected weekly from 10 DIM until the first PG injection. For plasma progesterone and estradiol detenninations, cows were sampled at d 0, 2, 4, 8, 10, 12, 14, and 15 after the first injection of PG. In order to characterize the estradiol pattern during the follicular phase following the second PG injection, samples were collected at 8-h intervals from d 15 to 16 after estrus detection. After estrus and AI, blood samples for progesterone determination were collected every 2 to 3 d until conception. Conception was determined by rectal palpation 45 to 50 d following insemination. On d 10 and 15 after the first PG injection, blood samples were collected at 15-min intervals for LH determination. Conception rate was defined as the percentage of inseminated cows diagnosed as pregnant. The pregnancy rate was defined as the number of cows pregnant per total cows in the goup. Cows that did not show estrus after the PG treatment constituted less than 10% of total and did not differ between groups were bred at the next spontaneous estrus. Conception rate from frrst AI included cows that were inseminated after the PG treatment or after spontaneous estrus. Retained placenta was defined as the presence of fetal membranes after 24 h postpartum. Metritis was diagnosed according to the color, smell, amount, and consistency of the vaginal discharge and size, position, and tone of the uterus after rectal palpation and vaginal examination 7 to 10 d after calving. Lipids were extracted from plasma, and TG, phospholipids, cholesterol, and FFA were determined as previously described (19). Progesterone was determined in duplicate plasma samples by radioimmunoassay as previously described (14). Coefficient of variation was 12.2%. Estradiol-170 concentrations in plasma were determined using a solid-phase radioimmunoassay kit [Isodan Diagnostic Laboratories, Jerusalem, Israel (211. Minimum sensitivity was 2.5 pg per sample, and intraassay and interassay coefficients of variation were 16.8 and 29%, respectively. The LH concentrations also were determined by solidphase radioimmunoassay (13). Minimum sensitivity was .5 ng/ml, and the intraassay and interassay coefficients of variation both were 5.5%. Mean concentrations of LH in plasma Journal of Dairy Science Vol. 77, No. 6, 1994
ET AL.
samples and frequency and amplitude of pulses of LH were determined using Pulsar software (10). Milk and fat outputs were utilized to calculate 3.5% FCM using the formula 3.5% F C M = milk yield x (.432 + .163 fat%). Analyses
Continuous variables were analyzed by the method of least squares ANOVA using the general linear models procedure of SAS (15). The model used was a general randomized model: yijklmn =
where
Y = all dependent variables presented, c c = overall mean of the population,
mi
= mean effect of treatment,
L j = mean effect of lactation number
(1 or 22), a covariance variable, effect of DIM, XI = a covariance variable, effect of dependent variable in the previous lactation (multiparous only), DAT, = a covariance variable, mean effect of date of observation, and E i j h = random residual assuming normal independent distribution.
Dk=
Frequency data were examined by the chisquare analysis procedure of SAS (15). Significance was at P < .05 unless otherwise stated. RESULTS
The group daily DMI were 20.6 f .8 kg/d of DM in control (mean daily DMI for 120 d f SD) and 20.3 f .9 kg/d for cows fed CSFA. Milk yield during the 120-d experimental period is shown in Table 2 and over the entire lactation in Figure 1. Cows fed CSFA produced 3.5 kg/d more milk and over 4 kgld more FCM than did controls (P < .OOOl). The increment for milk yield was slightly higher for primiparous cows than for multiparous cows. Fat yield was enhanced by CSFA in all cows, but milk fat percentage was increased
1655
CALCIUM SOAPS PRODUCTION AND REPRODUCTION
TABLE 2. Least squares means of milk and milk solids yields in cows fed Ca soaps of fatty acids during 120 DIM. ~
Primiparous
~~~~~~
Multiparous
Effect
Control
CSFAl
Control
CSFA
SE
P
T
27.9 3.14 3.00 ,881 .883 26.4
32.5 3.19 3.04 1.034 ,985 30.9
34.2 3.16 2.94 1.090 1.006 32.4
37.5 3.32 2.94 1.256 1.103 36.6
.3 .05 .02 .02 .01 .4
.o001
.o001
.I3 .19 .o001
.08 .12 .o001 .o001 .o001
P x T
TxDIM
P Milk, kg/d Fat, % Protein, % Fat, kg/d Protein, kg/d 3.5% FCM. kg/d
.o001 .o001
.22 .19 .56 .45 .31 .19
.o001 .o001 .o001 .o001
.OOol .o001
lCalcium soaps of fatty acids.
2P = Parity; T = tleatment.
only for multiparous cows (Figure 2). Protein yield was enhanced by dietary CSFA, but milk protein percentage tended to decrease slightly. The elevation in milk and FCM yields observed during the experimental period was
maintained after cows were transferred to the control ration (Figures 1 to 3). Body weight changes are shown in Figure 4. Multiparous cows fed CSFA showed a consistent but nonsignificantly greater decrease in BW than control cows and minimum BW that was reached at similar DIM. Increases in BW were parallel in CSFA and control cows alPrimiparous though cows fed CSFA had lower BW between 120 and 220 DIM. Primiparous control cows BW was lowest at 35 DIM and did not increase until after 65 DIM; this increase was 4 5 7 1 slower than that of control cows until 170 DIM. Differences in BW between the two treatments for primiparous cows reached 40 kg at 140 DIM and decreased thereafter. The differences in BW change for primiparous cows were significant between 55 and 220 1 200 300 DIM. DIM Plasma lipid concentrations before the first Mu1tiparous PG injection are shown in Table 3. The TG concentrations at this time were higher in cows 45 fed CSFA and more pronounced in multiparous cows. No significant differences occurred in cholesterol or phospholipid concentrations. Concentrations of FFA tended to be higher in primiparous than in multiparous cows (P< .I) and were higher in primiparous cows fed CSFA than in multiparous cows fed CSFA (Table 3). Changes in FFA with DIM were examined (not shown); cows fed CSFA I 15 I had higher plasma FFA concentrations than 0 100 200 300 did control cows until 55 DIM, and this differDIM ence was more marked in primiparous cows. Conception rates were lower at first AI for Figure I . Milk yield of primiparous (top panel) and multiparous cows (bottom panel) fed either a control diet primiparous cows fed CSFA than for control (open symbols) or Ca soaps of fatty acids (CSFA) for 120 cows but not at the second AI (Table 4). PregDIM (filled symbols). Results are least squares means, and nancy rates from the first two AI were not bars are standard errors. Differences were significant for primiparuus cows fed CSFA at each DIM until 160 DIM different between the treatments. No signifiand for multiparous cows fed CSFA between 45 and 160 cant differences were apparent in conception rates from first AI, second AI, or pregnancy DIM and 200 and 260 DIM. 15
0
IO0
I
Journal of Dairy Science Vol. 77, No. 6, 1994
1656
SKLAN
rates in multiparous cows. Because of differences in the numbers of primiparous cows with postparturient reproductive disorders in the two treatments, data are presented comparing all cows as well as comparing only cows that were free of reproductive disorders. Plasma progesterone concentrations were similar in cows before estrus (Figure 5). However, following estrus, there was a significant treatment time by parity effect. Plasma concentrations were higher in primiparous control cows than in cows fed CSFA (cumulative 1 to 15 d progesterone concentrations, P < .08) and, in contrast, higher in multiparous cows fed CSFA than in controls (Figure 5, cumulative 1 to 15 d). Estradiol concentrations (not shown) after estrus were not significantly different with treatments although primiparous cows fed CSFA exhibited slightly higher plasma estradiol concentrations 64 to 32 h before estrus
(P < .11).
ET AL. Primiparous
45 15
0
200
ID0
JDO
DM
Mu1tmarous
45
B
p
3s
0 2s
1s
Pr lmiparous
P i p 3. Yield of 3.5% FCM of primiparous (top panel) and multiparous cows (bottompanel) fed either a control diet (opm symbols) or Ca soaps of fatty acids (CSFA) for 120 DIM (6Ued symbols). Results are least squares means, and bars are standard errors. Values were signiticantly higher for primiparous cows fed CSFA at
each DIM until 160 DIM and from 200 to 260 DIM, and for multiparous cows fed CSFA from 45 to 160 DIM and fmm 200 to 260 DIM. 0
200
100
yx)
MM
Mu1t IDarOuS
3.6
k I
0
200
100
300
ou
Figure 2. Milk fat percentage of primiparous (top panel) and multiparous cows (boaom panel) fed either a control diet (open symbols) or Ca soaps of fatty acids for 120 DIM (W symbols). Results are least squares means, and bars are standad errors. Journal of Dairy Science Vol. 77,No. 6, 1994
Determination of LH during the luteal phase did not reveal any significant differences in mean LH concentrations, number of pulses, or pulse amplitude (Table 5). Progesterone and estradiol plasma concentrations at the time of LH determination were not different between parities or treatments (Table 5). The LH concentrations 24 h after the second PG injection were lower for control versus CSFA diets fed to primiparous cows, but the inverse in LH concentrations occurred with multiparous cows. Mean progesterone or estradiol concentrations at this time did not differ between parities or treatments. DISCUSSION
In this study, response to dietary CSFA in primiparous cows was compared with the en-
1657
CALCIUM SOAPS PRODUCTION AND REPRODUCTION TABLE 3. Concentrations of plasma lipid fractions at 50 to 60 DIM. RimiparOUS
MdtiparoW
Control
CSFAl
Control
CSFA
12.5.b 164 181 166.b
12.8& 172 186 194a
11.2b 160 176 14Ob
13.5' 168 193 149b
Effect2
SE
Paritym
T2
.43 .48 .74 .22
.05 .29 .21 .66
P x T
0 TG,3 mg/dl PL.4 mg/dl Cholesterol, mgdl FFA, CrM
.8 9
IO 29
.07 .61 .34 .08
*sbMeans with different superscripts differ (P < .05) lCalcium soaps of fatty acids. 2P = Parity; T = treatmnt. 3Triglycerides. 4Phospholipids.
hanced yield and reproduction previously observed in multiparous cows. Milk yield was enhanced similarly in primiparous and multiparous cows, but reproductive effects were different.
Milk yield increased with pari@ for all cows. Inclusion of CSFA in the ration increased milk yield of primiparous cows by 14.8% and multiparous cows by 8%. No interaction occurred between parity and treatment. Primiparous
Primiparous
._ 0
zoo
100
300
OM
Mu1t iparous
Mu1t iDarous
I 0
2oU
100
0
300
Figure 4. Body weight changes of primiparous (top panel) and multiparous cows (boaom panel) fed either a control diet (open symbols) or Ca soaps of fatty acids for 120 DIM (6lled symbols). Results are least quam mepos, and bars am standard e m . Trtahnent diffemnces were significant for primiparous cows at each DIM between 55 and 220 DIM.
2
4
1-
DM
8
101214 1 3 5 7 9 111315 aftf W S t PG cf after estrus M1
Figure 5. Plasma progesterone concentrations of primiparous (top panel) and multiparous cows (bottom panel) fed either a control diet (open symbols) or Ca soaps of fatty acids (filled symbols). Results are least squares means. and bars are standard errors. PGl and PG2 represent the time of adminhm'on of the. progesterone injectiOOS.
h u ~ ofl Dairy Science Vol. 77, No. 6, 1994
1658
SKLAN ET AL.
TABLE 4. Conception and pregnancy rates in cows from the first and second AI. Rimiparous
All cows2 Conception rates First AI Second AI First and second AI Pregnancy rate both AI Normal cows First AI Second AI First and second AI Pregnancy rate both A I
-Control X n
X
73.7. 19 33.3 6 64.0 25 84.2 19
33.3b 64.3 45.7 76.2
75.W 16 40.0 5 66.7 21 87.5 16
Multiparous
CSFA'
Control n
-X
21 14 35 21
25.0b 12 9 55.7 38.1 21 66.7 12
CSFA
n
-X
n
42.1 47.1 43.5 69.0
29 17 46 29
33.3 27.3 30.9 51.5
33 22 55 33
40.0 50.0 43.8 70.0
20 12 32 20
40.0 41.7 40.6 65.0
20 12 32 20
a,bMeansin rows with different superscripts differ (P < .05). lCalcium soaps of fatty acids. ZIncluding cows with postparturient reproductive disorders (retained placenta or metritis).
Fat yield was enhanced by similar proportions in cows of both parities by CSFA, and thus the increment in FCM yield was proportionally greater for primiparous cows fed CSFA, and the interaction between parity by treatment was significant (P < .OS). However, data for primiparous cows may possibly contain some bias because of potential group differences at the start of the trial. Energy intake during the experimental period on a group basis was approximately 2.4 Mcal/d higher in cows fed CSFA, and yield of FCM was enhanced by 4.2 and 4.4 kg/d in primiparous and multiparous cows, respectively. Thus, cows fed CSFA were under a greater negative energy balance of about .6 McaYd. Thus, as previously described, CSFA (18, 19) or CSFA with cottonseeds (8) increased the use of body reserves. In primiparous cows fed CSFA, the results of the negative energy balance appeared to be a greater use of body tissue, as shown by the decreases in BW (Figure 4). This result is illustrated by the increase of 5 kg from the minimal BW that occurred 27 d later (95 vs. 70 d) in primiparous cows fed CSFA and 10 d later (80 vs. 90 d) in multiparous cows. The greater mobilization of body reserves is confirmed by the plasma FFA, which were considerably increased in primiparous cows fed CSFA. Other plasma lipid fractions tested were Journal of Dairy Science Vol. 77, No. 6, 1994
not differentially affected between parities by dietary CSFA. In a previous study, CSFA fed to multiparous cows improved conception rate, especially at the second AI, and delayed resumption of cyclicity and progesterone production (19). In the present study, conception rate at the first AI was depressed in primiparous cows fed CSFA, and differences in multiparous cows were not significant at first or second AI. The major factor that complicates the comparison between this study and the previous study is that here cows were synchronized beginning at 60 d. This procedure did not enable the AI of cows at their spontaneous estrus and may have shortened the postpartum interval to AI in cows with a greater negative energy balance (i.e., primiparous cows fed CSFA). This "forced" AI may have reduced the conception rate in primiparous cows fed CSFA. No differences in plasma concentrations of progesterone or estradiol were observed before estrus, and the small differences in progesterone following estrus may not have been sufficient to support the different conception rates. Decreased energy intake appeared to suppress the increase in LH pulse frequency that was necessary for follicular growth to the preovulatory stage (16). However, the differences in LH pulsations in the luteal phase do not appear to explain the lower conception in primiparous cows fed
1659
CALCIUM SOAPS PRODUCTION AND REPRODUCTION
TABLE 5. Plasma LH, progesterone, and estradiol concentrations on d 10 following the first prostaglandin (PG) injection (luteal phase) and d 1 following the second PG injection (follicular phase). Rimiparous Control
CSFAl
Multiparous Control
CSFA
Effect2 SE
T
P
P x T
- (P4 Luteal phase Mean3 LH Number of pulses Pulse amplitude p44 E2 Follicular phase Mean LH Number of pulses Pulse amplitude p4 E2
4.1 3.0 1.7
3.6 .7 4.7b .6 .3 .4
.9
5.3
.7 1.7 3.5 1.o 5.98 .3 .5 .3 1.7
5.3 1.2 1.3
3.1 I .o 5.7“ .7 .7 .4
1.6
.73 .54
4.6 2.2 .9 3.1 .9
.6 .5 .5 .2
.66
4.9b
.5 .2 .5 .1 .5
.6 1.2 .4 1.5
.2
.42
.69 .84 .35 .45 .73
.18 .10 .68 .57 .86
.87
.53
.59 .22
.88
.65 .38 .75
.45
.36
.01 .76 .73 .54 .73
.75
*pbMeans in rows with different superscripts differ (P e .05). lCalcium soaps of fatty acids. *P = Parity; T = treatment. 3Mean LH values of 25 determinations over 6 h as calculated by the. Pulsar software (10). 4Progesterone (p4) and estradiol (E?) determined at the same time as LH.
CSFA, although the LH “window” examined here may not have been optimal. However, previous studies feeding CSFA to early postpartum cows did not alter LH kinetics but increased follicle size (9). Several hypotheses have been suggested to explain the positive influences of dietary fat on reproductive performance (6). One theory proposed that improved energy balance resulted from an earlier return to postpartum ovarian cycling (3). A second theory proposed that increased linoleic acid may provide increased PGF2, and stimulate the return to ovarian cycling and improved follicular recruitment (9). A third hypothesis suggested that progesterone secretion increased either from improved energy balance (21) or from altered lipoprotein composition from dietary fat, which stimulated progesterone production (4), thus improving fertility. The major body of evidence does not support the first two hypotheses (17, 19). In contrast, enhanced progesterone secretion explains some of the observed data. Previous studies also have indicated that energy balance and conception rate were correlated negatively (3), but the mechanism of this effect has not been clearly defined. Thus, augmented energy supply from CSFA apparently led to increased milk and milk
solids yields while it enhanced the negative energy balance more in primiparous than in multiparous cows, and this greater negative energy balance adversely affected conception rate. ACKNOWLEDGMENTS
This study was supported in part by The Israeli Milk Marketing Board. REFERENCES 1 Association of Official Analytical Chemists. 1990.
Official Methods of Analysis. 15th ed.AOAC, Arlington, VA. 2Bor. A., R. Braw-Tal, and E. Gootwine. 1992. Monitoring ovarian response of booroola Asaf ewe lambs to PSMG using ultrasonography and serum estradiol. Theriogenology 38645. 3Butler. W. R., and R. D. Smith. 1989. Interrelationships between energy balance and postpartum reproductive function in dairy cattle. J. Dairy Sci. 72: 767. 4Carrol1, D. J., R. R. Grummer, and M. K. Clayton. 1992. Stimulation of luteal cell progesterone production by lipoproteins from cows fed control or fatsupplemented diets. J. Dairy Sci. 75:2205. 5 Chalupa. W., B. Vecchiarelli, A. H. Elser, D. S. Kronfeld, D. Sklan,and D. L. Palmquist. 1986. Rumen fermentation in vivo as influenced by long chain fatty acids. J. Dairy Sci. 69:1293. 6Ferguson. J. D., D. Sklan. W. Chalupa, and D. S.
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Kronfeld. 1990. Effects of hard fats on the in vitro and in vivo rumen fermentation, milk production and reproduction in dairy cows. J. Dairy Sci. 73:2864. 7 Hightshoe, R. B.. R. C. Cochran, L. R. Corah, G. H. Kiracofe. D. L. Harmon, and R. C. Ferry. 1991. Effects of calcium soaps of fatty acids on postpartum reproductive function in bccf cows. J. Anim. Sci. 69: 4097. 8 Holter, J. B.. H. H. Hayes, W. E. Urban, Jr., and A. Duthie. 1992. Entrgy balance and lactation response in Holstein cows supplenmted with cottonseed with or without calcium soap. 1. Dairy Sci. 75:1480. 9Lucy. M. C., C. R. Staples, F. M. Michel. W. W. Thatcher, and D. J. Bolt. 1991. Effect of feeding dietary calcium soaps to early postpartum dairy cattle on plasma prostaglandin F h , luteinizing hormone. and follicular growth. J. Dairy Sci. 74483. IOMemam, G. R., and K. W. Wachter. 1982. Algorithms for the study episodic hormone secretion. Am. J. Physiol. 243:E310. 11 National Research Council. 1989. Nutrient Requirements of Diury Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC. 12 Palmquist, D.L. 1984. Use of fats in diets for lactating dairy cows. Page 357 in Fats in Animal Nutrition. J. Wiseman, ed. Butterworthc. London, England. 13Roscnberg. M..D. Amir, and Y.Folman. 1987. The effect of active immunization against progesterone on plasma concentrations of total and fnx progesterone.
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ET AL estradiol 178, and LH in the cyclic ewe. Theriogenology 28:417. 14 Rosenberg, M., Z. Hen. M.Davidson, and Y.Folman. 1977. Seasonal variation in postpartum plasma progesterone levels and conception in primiparous and multiparous dairy cows. J. Reprod. F e d . 51:3163. 15 SAWSTAT@for Personal Computers, Version 6.04. 1989. SAS Inst., hc., Cary, NC. 16Schillo. K. K. 1992. Effects of dietary energy on control of luteinizing hormone secretion in cattle and shcep. J. Anim. Sci. 70:1271. 17 Schneider, P., D. Sklan, W. Chalupa, and D. S. Kronfeld. 1988. Feeding calcium salts of fatty acids to lactating cows. J. Dairy Sci. 71:2143. 18Sklan. D., E. Bogin, Y. Avidar. and S. Gur-Arie. 1989. Feeding calcium soaps of fatty acids to lactating cows: effect on production, body condition and blood lipids. J. Dairy Res. 56:675. 19 Sklan. D., U. Moallem, and Y.Folman. 1991. Effect of f d i g calcium soaps of fatty acids on production and reproductive responses in high producing lactating cows. J. Dairy Sci. 74510. 20Van Soest, P. J.. and J. B. Robeltson. 1985. Analysis of Forage and Fibrous Feeds. A Laboratory Manual. Cornel1 Univ.. Ithaca, NY. 21 Villa-Gcdoy, A., T. L. Hughes, R. E. Emery, L. T. Chapin, and R.L. Fogwell. 1988. Association between energy balance and luteal function in lactating dairy cows. J. Dairy Sci. 71:1063.
