J. L. Espinoza, J. A. Ramirez-Godinez, J. A. Jimenez and A. Florescows and growth of calves

Effects of calcium soaps of fatty acids on postpartum reproductive activity in beef

1995, 73:2888-2892.J ANIM SCI 

http://jas.fass.org/content/73/10/2888the World Wide Web at:

The online version of this article, along with updated information and services, is located on

www.asas.org

by guest on August 18, 2011jas.fass.orgDownloaded from

2888

1We gratefully acknowledge Dennis Hallford, Dept. of Anim. andRange Sci., New Mexico State Univ. for the progesterone assays andfor the preparation of this manuscript.

2Present address: Universidad Autonoma de B.C.S. ApartadoPostal 19-B, La Paz, B.C.S., Mexico, C.P. 23000.

3To whom correspondence should be addressed.Received October 4, 1994.Accepted June 1, 1995.

Effects of Calcium Soaps of Fatty Acids on Postpartum ReproductiveActivity in Beef Cows and Growth of Calves1

J. L. Espinoza2, J. A. Ramirez-Godinez3, J. A. Jimenez, and A. Flores

Facultad de Zootecnia, Universidad Autonoma de Chihuahua, Perif.Francisco R. Almada Km. 1, Apdo. Postal 4-28, C.P. 31031, Chihuahua, Chih. Mexico

ABSTRACT: Beef cows were used to determine theinfluence of calcium soaps of fatty acids (CSFA)incorporated in a range supplement on postpartumreproductive characteristics and growth of calves.Cows were assigned randomly to receive 0 (C, n = 68)or 125 g/d of CSFA (M, n = 66). Diets wereisonitrogenous (23%) and were used during 105 d,beginning at 61 ± 36 d (range) precalving. Two bloodsamples were collected monthly (7-d intervals).Weights of calves at 35, 50, and 90 d of age andweaning weight adjusted to 200 d of age were greaterin M than in C (46.8 vs 43.8 kg, P < .05; 56.0 vs 50.6kg, P < .01; 98.8 vs 91.8 kg, P < .01; and 186 vs 173 kg,P < .01, respectively). Body weights at 35 and 50 dpostcalving were greater in M than in C cows (334and 310 kg, P < .01; 329 and 300 kg, P < .01,

respectively). A similar tendency was observed inbody condition scores in the same postpartum periods(4.1 vs 3.4, P < .01 and 3.6 vs 2.5, P < .01 for M and C,respectively). Concentrations of total cholesterol,high-density lipoprotein cholesterol, low-densitylipoprotein cholesterol, very-low-density lipoproteincholesterol, and triglycerides were greater ( P < .01) inM than in C cows. Percentage of cycling (progesterone> 1 ng/mL) cows at 30 to 90 d postpartum was 38% inM and 22% in C ( P < .02). Percentage of pregnantcows during the first half of the breeding season wasgreater ( P < .02) in M (62.5%) than in C cows(35.5%). We concluded that CSFA incorporated in arange supplement during pre- and postpartum periodsimproved reproductive efficiency and growth of calves.

Key Words: Beef Cattle, Nutrition, Reproduction, Fat

J. Anim. Sci. 1995. 73:2888–2892

Introduction

Development of commercial products based oncalcium soaps of fatty acids ( CSFA) offers beef cattleproducers a method of increasing energy density inrange supplements without harming forage utilization(Hightshoe et al., 1990).

Feeding bypass fat (Megalac) to dairy cowsresulted in greater conception rates (Ferguson et al.,1988). The mechanism by which bypass fat influencesreproductive function is not well understood. Feedingfat may positively influence reproductive performanceof cows by promoting an earlier return to positiveenergy balance, earlier ovarian cycling postpartum,and higher conception rates at first service (Butlerand Smith, 1989; Carroll et al., 1990). In addition,

provision of linolenic acid (precursor to PGF2a) mayimprove follicular recruitment and conception rates(Lucy et al., 1991b). Feeding CSFA increased plasmaLH in beef cows after calf removal (Hightshoe et al.,1991). Addition of supplemental fat to dairy and beefcattle diets probably stimulates lipoprotein cholesterolexport by the intestine and increases circulatingplasma LDL and HDL cholesterol concentration(Talavera et al., 1985). Feeding diets high in lipidcontent (8%) to cows and heifers resulted in increasedconcentration of HDL in serum and follicular fluid(Wehrman and Williams, 1989).

The objectives of this study were to determine theinfluence of Megalac, as a source of CSFA, onreproductive efficiency during the postpartum periodin suckled beef cows maintained under pastureconditions and to determine the influence of CSFA oncalf growth.

Materials and Methods

Multiparous Angus and Hereford × Angus cows (n =134) ranging from 5 to 7 yr of age were blocked bybreed and age and assigned randomly to receive 1 kg/d

by guest on August 18, 2011jas.fass.orgDownloaded from

RESPONSE OF RANGE BEEF COWS AND CALVES TO BYPASS FAT 2889

Table 1. Weights of calves (kg) produced by cowsreceiving either a control diet or Megalac

a1 kg/d during 105 d, 68 cows with calf.b,dBased on 68 and 66 calves, respectively.cControl diet mixed with 125 g/d of Megalac during 105 d, 66

cows with calf.eAdjusted to 200 d of age.

Diet

Item Controla ± SEb Megalacc ± SEd P

Birth wt 30.6 ± .77 31.8 ± .70 > .05

Days of age35 (WC 1) 43.8 ± 2.67 46.8 ± 2.53 < .0550 (WC 2) 50.6 ± 2.47 56.0 ± 2.12 < .0195 (WC 3) 91.8 ± 4.01 98.8 ± 3.60 < .01

Weaning wte 173.0 ± 2.98 186.0 ± 2.72 < .01

of a control diet ( C, n = 68) containing grain sorghum(80%), meat meal (18%), and urea (2%) (ME = 3.12Mcal) or the same diet plus 125 g/d of Megalac ( M, n= 66; Church & Dwight Co., Princeton, NJ) as asource of CSFA (ME = 3.8 Mcal). Diets wereisonitrogenous (CP = 23%) and were fed during 105 d,beginning at 61 ± 3.9 d precalving. Birth weight ofcalves was recorded. At three postpartum periods (35,50, and 95 d), body condition scores ( BC1, BC2, andBC3 [Whitman, 1975]) and body weights ( BW1, BW2,and BW3) of cows were recorded. Weights of calves inthe same postpartum periods ( WC1, WC2, and WC3)and weaning weight ( WW) at 198 ± 6.0 d and 202 ±5.1 d of age in C and M calves, respectively, wererecorded. All cows were exposed to mature Herefordbulls (three bulls by group) that had passed breedingsoundness examinations (BIF, 1990) for a190-d breeding period on two pastures under a30-d rotational system. Two blood samples werecollected monthly from each cow (7-d intervals) ondifferent postpartum periods, for determination oftotal cholesterol ( CHOL) , high-density lipoproteincholesterol ( HDL) , low-density lipoprotein cholesterol( LDL) , very-low-density lipoprotein cholesterol( VLDL) , triglycerides ( TG) , and progesterone ( P4) .The percentage of cycling cows at 30 to 90 d and > 90 dpostpartum was determined by the P4 concentration(P4 > 1 ng/mL = cycling cow). Blood was collected intoevacuated tubes via jugular venipuncture, maintainedon ice, allowed to clot, and centrifuged within 12 hafter collection. Serum was harvested and stored at−20°C until P4 and lipids (CHOL, HDL, LDL, VLDL,and TG) were determined. Lipid profiles were deter-mined by a commercial laboratory using automated,enzymatic procedures. The CHOL was determined inserum after having been hydrolyzed and oxidizedenzymatically. In the oxidation process, H2O2 wasproduced. Its presence of peroxidase, by reaction with4-amino-antipirine and fenol, was transformed in acoloring of quinonimine (Merck-Mexico, S. A.). TheHDL were separated from chylomicrons, VLDL, andLDL by addition of a precipitating reagent (phos-photungstic acid-magnesium chloride) to serum. Aftercentrifugation, the cholesterol content of the HDLfraction remained in the supernatant and was deter-mined by the enzymatic colorimetric method usingcholesterol esterase, cholesterol oxidase, peroxidase,and the chromogen 4-aminophenazone/phenol (Sera-Pak, Ames Division). The LDL was determined bydifference between CHOL and HDL. The enzymaticcolorimetric method for TG determination is based onthe principle that glycerol released from hydrolysis oftriglycerides by lipoprotein lipase is converted byglycerolquinase into glycerol-3-phosphate, which isoxidized by glycerolphosphate oxidase to dihydrox-yacetone phosphate and hydrogen peroxide. In thepresence of peroxidase, hydrogen peroxide oxidizesthe chromogen 4-aminophenasone/N-ethyl-N-(3-sul-phopropyl)-m-anisidine to a violet-colored compound

(Sera-Pak, Ames Division). The VLDL was calculatedto be 1/5 of TG (Sera-Pak, Ames Division). Serum P4was determined by RIA using a commercial kit(Diagnostic Products, Los Angeles, CA). Assays wereperformed by the Animal Science EndocrinologyLaboratory at New Mexico State University and thebetween- and within-assay coefficients of variationwere 5.2 and 8.1%, respectively.

Data for calf weight, weight and body conditionscore in cows, and lipid metabolites were analyzed byanalysis of variance in a completely randomizeddesign using the GLM procedure (SAS, 1988). Preg-nancy rates at the first and second half and at end ofthe breeding season were compared by chi-square(Steel and Torrie, 1980). The percentage of cyclingcows at 30 to 90 d and after 90 d postpartum wereanalyzed by the Catmod procedure (SAS, 1988).

Results and Discussion

Calf Weight. Calf weights from birth to weaning areshown in Table 1. The birth weight was similar ( P >.05) for calves from M (31.8 kg) and C (30.6 kg)groups. Even though diets were not isoenergetic, themetabolizable energy provided by 125 g of M was notsufficient to stimulate greater fetal growth. Similarresearch for birth weight in Hereford calves wasreported by Stuedemann et al. (1968). However, WC1was greater ( P < .05) in calves from the M group(46.8 kg) than in calves from the C group (43.8 kg)and was affected by sex, age, and birth weight ( P <.05). Male calves were heavier. A similar differencewas observed in WC2 ( P < .01), with values of 56.0and 50.6 kg for calves of M and C, respectively. TheWC3 and adjusted WW were greater ( P < .01) incalves of the M group, with a difference of 7 and 13 kgfor each variable, respectively (Table 1). Sex and ageof calf affected ( P < .01) WC3, WW, and gain frombirth to weaning (132.8 kg in M vs 120.8 kg in C,

by guest on August 18, 2011jas.fass.orgDownloaded from

ESPINOZA ET AL.2890

Table 2. Serum lipids (mg/dL) in cows fed either acontrol diet or a diet supplemented with Megalac

aCHOL = total cholesterol; HDL = high-density lipoproteincholesterol; LDL = low-density lipoprotein cholesterol; VLDL = very-low-density lipoprotein cholesterol; TG = triglycerides.

b1 kg/d during 105 d, 68 cows with calf.c,eBased on 32 and 38 samples, respectively.dControl diet mixed with 125 g/d of Megalac during 105 d, 66

cows with calf.

Diet

Metabolitea Controlb ± SEc Megalacd ± SEe P

CHOL 146.2 ± 7.62 186.6 ± 6.99 < .01HDL 67.8 ± 4.49 81.4 ± 4.12 < .02LDL 97.1 ± 9.4 130.1 ± 8.6 < .01VLDL 18.7 ± 1.25 26.0 ± 1.15 < .01TG 94.0 ± 6.27 130.0 ± 5.75 < .01

Table 3. Reproductive performance of cows fed acontrol diet or a diet supplemented with Megalac

a1 kg/d during 105 d, 68 cows with calves.bControl diet mixed with 125 g of Megalac during 105 d, 66 cows

with calves.cCycling cows at 30 to 90 d postcalving.dCycling cows after 90 d postcalving.ePregnant cows at first half of a 190-d breeding season.fPregnant cows at end of a 190-d breeding season.

Diet

Item Controla Megalacb P

Percentage cycling

30 to 90 dc 22.0 38.0 < .02> 90 dd 72.0 61.0 > .05FHBSe 37.5 62.5 < .02EBSf 84.7 90.9 > .05

respectively). The WW adjusted to 200 d of age wasgreater in M calves (186 kg) than C calves (173.8kg).

The increase in calf weights observed in the Mgroup can be explained possibly by a greater milkproduction of cows fed bypass fat (Coppock and Wilks,1991). However, in those studies dairy cows were usedand were fed greater levels of bypass fat. Moreover,Knapp and Grummer (1991) observed that milk fatpercentage was greater for Holstein cows fed 5 thanfor those fed 0% fat (3.46 vs 3.15%, respectively).

Weight and Body Condition Score in Cows. Bodyweight was greater ( P < .01) in M cows at 35 and 50 dpostpartum (BW1 = 334 vs 310 kg; BW2 = 329 vs 299kg). However, BW3 was similar ( P > .05) betweengroups (376 vs 360 kg in M and C, respectively). Thissimilarity at period 3 was expected because BW3 wasobtained 30 d after treatments ended, when cows wereon common pasture. Body condition scores (BC1, BC2,and BC3) followed a trend similar to that of BW (4.1vs 3.4, P < .01; 3.6 vs 2.25, P < .01; and 6.2 vs 5.9, P >.05, for M and C, respectively). Body condition scorechange between BC2 and BC3 was greater ( P < .01)in C than in M. Body condition score, body weight atsecond period, and body condition score changebetween BC2 and BC3 were affected ( P < .01) bypostpartum days. The tendencies in body weight andcondition scores at the start of the postpartum periodsupport observations that energy intake in this periodis less than required (Haresign, 1988). Williams(1989) found that body condition score remainedconstant through the first 100 d postpartum, and allcows exhibited a slight decrease (13.7 kg) in BW thatdid not differ between groups (8% vs 2.8% dietarylipid). However, in our study, feeding 125 g/d ofMegalac maintained a greater body weight and bodycondition score during the first 50 d postpartum.

Lipid Metabolites. Plasma concentrations ofcholesterol increased with ingestion of milk lipids bysuckling calves (Carroll and Hamilton, 1973). O’Kelly

(1975) reported that beef calves with greaterpreweaning growth had more serum cholesterol thandid calves that gained less rapidly. Furthermore,cholesterol in calves declined after weaning. Serumconcentration of lipid metabolites (CHOL, HDL, LDL,VLDL, and TG) were greater ( P < .01) in cows fedCSFA (Table 2). A similar response was observed byPeters and Corah (1993) in beef heifers fed .454 kg ofMegalac. Sklan et al. (1989) reported that serumlevels of CHOL and HDL were greater between 15 and29 d postpartum in CSFA-supplemented cows. Greaterconcentrations of CHOL, HDL, and TG were alsoobserved by Morgan and Williams (1989) in cows feddiets with elevated lipids. Williams (1989) observedthat mean concentrations of total CHOL and TG incontrol animals (2.8% dietary lipid) were lower thanin animals fed a high-lipid (8%) diet during the 4th,5th, and 6th wk after calving. By the 4th wk, plasmaconcentrations of CHOL and TG in cows supplementedwith a high-fat diet were greater than control valuesby 1.7- and 1.4-fold, respectively. The greater concen-tration of metabolites can be explained by increasedintestinal secretion of lipoproteins with a high contentof TG such as VLDL.

Reproductive Performance. The percentage of cyclingcows 30 to 90 d after calving was greater ( P < .02) inM (38%) than in C (22%). However, after 90 dpostpartum, the percentage of cycling cows wassimilar ( P > .05) between treatments (61 vs 72% forM and C, respectively [Table 3]).

The percentage of pregnant cows at end of thebreeding season was similar ( P > .05) betweentreatments (91 vs 84% in M and C, respectively);however, 62.5% of cows in M were pregnant during thefirst half of the breeding season, compared with 35.5%( P < .02) in the C group (Table 3). Similar resultswere reported by Ferguson et al. (1988), whoobserved greater conception rates and fewer open daysin dairy cows supplemented with bypass fat. Incontrast, cows fed CSFA (Sklan et al., 1991) initiated

by guest on August 18, 2011jas.fass.orgDownloaded from

RESPONSE OF RANGE BEEF COWS AND CALVES TO BYPASS FAT 2891

ovarian cyclicity later than controls; however, aftercyclicity began, more fat-fed cows than controls hadnormal cycle length (18 to 26 d). Conception rate wasgreater in cows fed CSFA and number of open dayswas reduced.

Feeding diets that contain fats and that are higherin energy may partially alleviate negative energybalance and stimulate ovarian function (Lucy et al.,1991b). Hypothetically, the additional dietary energy(and not the CSFA) stimulated the development offollicles and led to larger ovarian follicles in fat-fedcows. To test this hypothesis, Lucy et al. (1991a)conducted an experiment in which three diets wereformulated for postpartum lactating cows: a controldiet (no CSFA), a diet containing CSFA with energydensity equivalent to that of the control diet, and athird diet that contained both additional energy andCSFA. In that experiment, after 4 wk of feeding theexperimental diets, preovulatory follicles were largerin diameter in cows fed the CSFA diets with eithernormal or high energy levels than in cows fed thecontrol diet.

Although mechanisms have not yet been deter-mined, mean serum concentrations of LH measuredduring three periods surrounding calf removal weregreater in cows receiving CSFA than in controls(Hightshoe et al., 1991). Similar responses wereobserved by Lucy et al. (1989), who found that basalLH was increased in early postpartum dairy cowsreceiving CSFA. However, feeding fat (CSFA) did notinfluence the basal, smoothed mean concentration andaverage LH amplitude (Lucy et al., 1991b). Reports ofpituitary response to GnRH stimulation in intact beefcows consuming hyperlipidemic diets indicated thatneither GnRH-induced LH release nor tonic releasewas affected (Johnson et al., 1987; Morgan andWilliams, 1989). In contrast, De Luna et al. (1982)fed protected lipids to ovariectomized cows in the earlypostpartum period and observed greater concentra-tions of LH in response to exogenous GnRH.

In addition to their more obvious effects on energybalance, CSFA may increase postpartum release ofuterine prostaglandin F2a, which has been implicatedas an important modulator in the initiation of estrouscycles after calving (Madej et al., 1984). However,feeding fat (CSFA) did not influence 15-keto-13,14-dihydro-prostaglandin F2a (Lucy et al., 1991b).

Although the mechanisms by which changes in lipidmetabolism may influence ovarian function have notbeen determined, a wide array of potential pathwaysexists (Williams, 1989). The P4 production by lutealcells was greater with highest HDL and LDL in vitro(Carroll et al., 1992). Granulosa cells of heifers fedhigh-fat diets (8%) during 30 d released 2.1- to3.5-fold more pregnenolone and P4 in vitro, and theluteal activity was 18% greater (Wehrman et al.,1991). Based on these studies, we speculate that thegreater percentage of cycling cows at 30 to 90 d after

calving in our study may be related to a greater CHOLavailable for P4 synthesis in M cows. This speculationis based on a study in which 80% of lipid-fed femalesexhibited at least slight increases in baseline P4 beforeinduced estrous cycle with GnRH treatment, comparedwith 37% of controls (Williams, 1989). These observa-tions suggest that fat supplement affects the “quality”of the corpus luteum rather than the number orquantity of corpora lutea.

Implications

The calcium soaps of fatty acids may be used inrelatively small amounts in beef cow diets on range toimprove reproductive efficiency during the postpartumperiod. In this study, feeding Megalac resulted in morecows cycling at 30 to 90 d postpartum and more cowspregnant during the first half of the breeding season.These effects would result in older calves during thenext production cycle and a greater efficiency in theherd. Moreover, calves produced by Megalac-sup-plemented cows were heavier than those produced bycontrols, which could justify addition of Megalac topre- and postpartum cattle diets.

Literature Cited

BIF. 1990. Guidelines for Uniform Beef Improvement Programs(6th Ed.). Beef Improvement Federation, Oklahoma StateUniv., Stillwater.

Butler, W. R., and R. D. Smith. 1989. Interrelationship betweenenergy balance and postpartum reproductive function in dairycattle. J. Dairy Sci. 72:767.

Carroll, D. J., R. R. Grummer, and F. C. Mao. 1992. Progesteroneproduction by cultured luteal cells in the presence of bovine lowand high density lipoproteins purified by heparin affinity chro-matography. J. Anim. Sci. 70:2516.

Carroll, D. J., M. J. Jerred, R. R. Grummer, D. K. Combs, R. A.Pierson, and E. R. Hauser. 1990. Effects of fat supplementationand immature alfalfa to concentrate ratio on plasma progester-one, energy balance, and reproductive traits of dairy cattle. J.Dairy Sci. 73:2855.

Carroll, K. K., and R.M.G. Hamilton. 1973. Plasma cholesterol levelsin suckling and weaned calves, lambs, pigs and colts. Lipids 8:635.

Coppock, C. E., and D. L. Wilks. 1991. Supplemental fat in high-energy rations for lactating cows: Effects on intake, digestion,milk yield, and composition. J. Anim. Sci. 69:3826.

De Luna, C. J., W. H. Brown, D. E. Ray, and T. N. Wagner. 1982.Effects to protected fat supplement on GnRH induced LHrelease in ovariectomized and early postpartum beef cows. J.Anim. Sci. 55(Suppl. 1):348 (Abstr.).

Ferguson, J. D., T. L. Blanchard, and W. Chalupa. 1988. Protein,fats and fertility in dairy cows. Bovine Proc. 20:112.

Haresign, W. 1988. Condicion corporal, produccion de leche yreproduccion en el ganado vacuno. En: W. Haresign and D.J.A.Cole (Ed.) Avances en Nutricion de los Rumiantes. p 1.Acribia, Spain.

Hightshoe, R. B., R. C. Cochran, L. R. Corah, D. L. Harmon, and E.S. Vanzant. 1990. Influence of level and source of rumen-escapelipid in a supplement on forage intake and digestibility. J.Anim. Sci. 68(Suppl. 1):571 (Abstr.).

by guest on August 18, 2011jas.fass.orgDownloaded from

ESPINOZA ET AL.2892

Hightshoe, R. B., R. C. Cochran, L. R. Corah, G. H. Kiracofe, D. L.Harmon, and R. C. Perry. 1991. Effects of calcium soaps of fattyacids on postpartum reproductive function in beef cows. J.Anim. Sci. 69:4097.

Johnson, M. S., T. N. Wagner, and D. E. Ray. 1987. Effects ofelevated serum lipids on luteinizing hormone response togonadotrophin releasing hormone challenge in energy deficientanestrous heifers. Theriogenology 27:421.

Knapp, D. M., and R. R. Grummer. 1991. Response of lactating dairycows to fat supplementation during heat stress. J. Dairy Sci.74:2573.

Lucy, M. C., R. L. De La Sota, C. R. Staples, and W. W. Thatcher.1991a. Effect of dietary calcium salts of long chain fatty acids(CaLCFA), energy intake, and lactation on ovarian folliculardynamics in Holstein dairy cows. J. Anim. Sci. 69(Suppl. 1):451 (Abstr.).

Lucy, M. C., C. R. Staples, F. M. Michel, W. W. Thatcher, and D. J.Bolt. 1991b. Effect of feeding calcium soaps to early postpartumdairy cows on plasma prostaglandin F2 alpha, luteinizing hor-mone and follicular growth. J. Dairy Sci. 74:483.

Lucy, M. C., W. W. Thatcher, F. J. Michel, and C. R. Staples. 1989.Effect of dietary calcium soaps of long chain fatty acids(Megalac) on plasma prostaglandin F metabolite (PGFM),LH, energy balance, and follicular populations in early postpar-tum dairy cattle. J. Anim. Sci. 67(Suppl. 1):389 (Abstr.).

Madej, A., H. Kindahl, W. Woyno, L. E. Edquist, and R. Stupnicki.1984. Blood levels of 15-keto-13,14-dihydro-prostaglandin F2alpha during the postpartum period in primiparous cows.Theriogenology 21:279.

Morgan, A. R., and G. L. Williams. 1989. Effects of body conditionand postpartum dietary lipid intake on lipid metabolism andpituitary function of beef cows. J. Anim. Sci. 67(Suppl. 1):385(Abstr.).

O’Kelly, J. C. 1975. Growth and lipid metabolism in geneticallydifferent types of calves in a tropical environment. Growth 39:125.

Peters, C. W., and L. R. Corah. 1993. Effect of rumen-escape lipid onendocrine profiles, lipid metabolites and follicular dynamicsduring estrus synchronization in primiparous beef heifers. J.Anim. Sci. 71(Suppl. 1):72 (Abstr.).

SAS. 1988. SAS/STAT User’s Guide (Release 6.03). SAS Inst. Inc.,Cary, NC.

Sklan, D., E. Bogin, Y. Avidar, and S. Gur-Arie. 1989. Feedingcalcium soaps of fatty acids to lactating cows: Effect on produc-tion, body condition and blood lipids. J. Dairy Res. 56:675.

Sklan, D., U. Moallem, and Y. Folman. 1991. Effect of feedingcalcium soaps of fatty acids on production and reproductiveresponses in high producing lactating cows. J. Dairy Sci. 74:510.

Steel, R.G.D., and J. H. Torrie. 1980. Principles and Procedures ofStatistics: A Biometrical Approach (2nd Ed.). McGraw-HillPublishing Co., New York.

Stuedemann, J. A., J. J. Guenther, S. A. Ewing, R. D. Morrison, andG. V. Odell. 1968. Effect of nutritional level imposed from birthto eight months of age on subsequent growth and developmentpatterns of full-fed beef calves. J. Anim. Sci. 27:234.

Talavera, F. C., C. S. Park, and G. L. Williams. 1985. Relationshipsamong dietary lipid intake, serum cholesterol and ovarian func-tion in Holstein heifers. J. Anim. Sci. 60:1045.

Wehrman, M. E., T. H. Welsh, and G. L. Williams. 1991. Diet-induced hyperlipidemia in cattle modifies the intrafollicularcholesterol environment, modulates ovarian follicular dynamicsand hastens the onset of postpartum luteal activity. Biol.Reprod. 45:515.

Wehrman, M. E., and G. L. Williams. 1989. Effect of dietary lipidintake on serum and ovarian follicular lipid metabolites and onfollicular populations in beef females. Proc. So. Sect. Am. Soc.Anim. Sci. p 59 (Abstr.).

Whitman, R. W. 1975. Weight change, body condition and beef cowreproduction. Ph.D. Dissertation. Colorado State Univ., FortCollins.

Williams, G. L. 1989. Modulation of luteal activity in postpartumbeef cows through changes in dietary lipid. J. Anim. Sci. 67:785.

by guest on August 18, 2011jas.fass.orgDownloaded from

Citationshttp://jas.fass.org/content/73/10/2888#otherarticlesThis article has been cited by 3 HighWire-hosted articles:

by guest on August 18, 2011jas.fass.orgDownloaded from