Beta-carotene does not influence fertility in beef heifers

THERIOGENOLOGY

BETA-CAROTENE DOESNOT INFLUENCE FERTILITY IN BEEP HEIFERS L.G. Greenberg,’ P. Bristol,3 IB.D. Murphy,’ and B. Laarveld Biology University

Dfpartments of Animal and Poultry Science,1 and the Western College of Veterinary Medicine3 of Saskatchewan, Saskatoon, Sask., Canada S7N OWO

Received

for publication: Accepted:

February 26, 1986 August 22, 1986

ABSTRACT Eighty-four 18-month-old crossbred beef heifers, 3 to 4 months pregnant, were assigned by stratified randomization to either a high or low (control) B-carotene (B-car) diet to determine the effect of longterm supplementation of B-car on reproductive performance. The heifers were followed through pregnancy, calving and subsequent breeding. The basal diet consisted of barley, Heifers canola meal and barley straw. supplemented by B-car received 625 mg B-car per day in the concentrate. Vitamin A and D complex injections were given monthly to all heifers. Heifers were bred by artificial insemination after Day 60 postpartum. Throughout the study-heifers fed the B-car supplement had higher-levels of B-car in plasma ( > 300 un/dl) (P < 0.01) than the heifers fed the control diet- ( < 50. ug/dl). -Vitamin A status was satisfactory in all heifers throughout the study. Birth weight of calves, weight gain, and For the control incidence of mortality were not influenced by B-car. and B-car treatments, days postpartum to first normal luteal phase were 67.5 and 62.6 days; days postpartum to first detected estrus were 70.1 and 65.3, and services per conception were 1.24 and 1.29, respectively. B-car Long-term supplementation of increased prepartum plasma progesterone but had no effect on postpartum fertility. Key words: S-carotene,

fertility,

cattle,

beef heifers

Acknowledgements This study was funded by Saskatchewan Agriculture Research Fund, Farm Lab, Horned Cattle Trust Fund and the Department of Supply and Services, Government of Canada. Appreciation is expressed to Hoffman La-Roche for supplying Rovimix, Tuco-Upjohn for supplying Lutalyse and ICI Pharmaceuticals for supplying Estrumark. We thank Roseanne Halvorson and the Termuende Farm Staff for technical assistance. L.G. Greenberg was supported by a NSERCpostgraduate scholarship.

.

OCT ,BER 1986 VOL. 26 NO. 4

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THERIOGENOLOGY

INTRODUCTION Synthetic vitamin A has replaced the need for B-car, a provitamin A, in animal feeds. Vitamin A is essential for reproduction in cattle B-car by itself may also have a function in reproduction in cattle (1). (2, 3). Dairy cows fed little B-car may show an increased incidence of silent estrus, ovarian cysts, delayed ovulation, extended calving interval, lower conception rate, lower plasma progesterone level, and an increased incidence of embryonic mortality compared with cattle supplemented with B-car (2, 3). In contrast, there have been reports that cattle fed diets containing varying levels of B-car do not significantly differ in the incidence of silent estrus (4), ovarian cysts (5, 6), and postpartum anestrus (5, 7). Similarly, conception rate (4, 7-9) and plasma progesterone concentration (4, 5, 8) were not influenced by B-car. The importance of B-car in bovine reproduction is equivocal. In some studies (4, 7, 8), supplementation of B-car was limited since level of B-car in plasma did not exceed 300 ug/dl. A level of B-car lower than 300 ug/dl in plasma may not support normal fertility (10). Among reports there are variations in experimental conditions as well as differences in nutritional status of animals prior to and during the experiment and differences in herd and reproductive management (11). The objective of this study was to determine the effect of longterm supplementation of B-car on reproductive performance of beef heifers. We monitored these heifers during pregnancy, at calving, and during breeding. MATERIALSANDMETHODS Eighty-four 17-month-old Hereford and Hereford crossbred beef heifers, 2 to 3 months pregnant, from the University of Saskatchewan Termuende Farm were placed on a low B-car diet of rolled barley and barley straw. After 6 wk the heifers were assigned to four groups (n = 21) using stratified randomization based on breed and weight. Two treatments (control and B-car supplemented) and two replicates per treatment were used. Each group was randomly assigned to one of four adjacent pens for the duration of the study. Shelter was provided and animals had free access to cobalt iodized salt and water. Heifers were group-fed twice daily. The diet, which met the NRC (12) requirements for pregnant beef cattle, consisted of a barley and canola meal pelleted concentrate (Table 1). At the start of the experiment heifers were fed 3.2 kg of concentrate per day. As the stage of pregnancy progressed, this daily allowance was increased to 4.5 kg up to time of calving. Ruring lactation heifers were fed 7.7 kg of a different concentrate daily

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Table 1.

Formulation of concentrates (4: air dry weight) containing a high or low level of B-carotene fed to heifers during pregnancy and lactation

Lactation

Pregnancy Control Barley Canola meal Dicalcium phosphate Limestone Mineral premix Cobalt iodized salt Rovimix

86.36 10.00

B-carotene 86.16 10.00

Control 81.97 15.00

81.89 15.00

1.70 1.00 O.lga

1.70 1.00 0. lga

1.70 0.30 0.28b

1.70 0.30b 0.28

0.75

0.75 0.20

0.75

0.75 0.08

a Mineral premix supplied per kilogram of concentrate: Zn, 112 mg; Hn, 95 mg; Mg, 0.7 gm, and 12, 2.3 mg. b

B-carotene

Mineral premix supplied per kilogram of concentrate: Zn, 54 mg; Mn, 37 mg; Mg, 1.2 gm, and 12, 2.0 mg.

Cu, 51 mg; Cu, 46 mg;

(Table 1). The B-car diet supplied 625 mg B-cars/head/day. Barley straw was fed ad libitum. During the last trimester of preqancy all heifers receivegd a single subcutaneous injection of selenite (5 ml). Vi tamin A and D complex was given monthly by intramuscular injections. At the same time animals were weighed and jugular blood samples were taken for analyses of B-car, vitamin A and progesterone. Immediately after collection, the blood samples were centrifuged (20 min; 2000 x g) and the plasma was stored at -2O’C pending analyses. Vitamin A status was repeatedly assessed in the same subpopulation of five heifers from each of the replicate groups. aRovimix - 10% Hoffmann-LaRoche Ltd.,

Brampton, Ontario.

b MU-SE injectable.

Schering

Canada Inc.,

‘Dominion

Vet Lab.,

Winnipeg,

Manitoba.

Per day equivalent IU of Vitamin E.

of 50,000

IU of Vitamin A; 7500 IU of Vitamin D and 5

d

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Pointe

Claire,

Quebec.

493

THERIOGENOLOGY

After calving, jugular blood samples for progesterone and B-car analyses were taken weekly from all animals. After Day 35 postpartum blood samples were taken twice weekly until time of breeding. After 30 d postpartum, heifers were observed for heat three times daily using visual Heifers in each observation with Estrumark paint as a detection aid. pen were observed for 30 min at 6 a.m., mid-day, and 7:30 p.m. All heat detection was conducted by the same two observers. To facilitate breeding, anipals were given a single intramuscular injection of 25 mg pros taglandin after Day 60 postpartum to synchronize estrus. F2P Heifers observed in estrus during the 5 d prior to the prostaglandin treatment were bred without estrus synchronization. All heifers were bred once by artificial insemination 12 to 15 h after the onset of estrus. Heifers in each treatment were equally assigned to either one of two bulls for all inseminations to reduce the possible confounding effect of differences in bull fertility. A single batch of semen from each bull was used. The inseminations were carried out by three experienced technicians with over 95% of the inseminations carried out by one technician. Jugular venous blood samples were taken for progesterone analysis 20 to 21 d postinsemination to determine success of conception. Pregnancy was confirmed by rectal palpation 40 to 45 days after insemination. Animals returning to estrus were rebred. Calves born during the course of the study were weighed monthly and jugular blood samples were taken for B-car and Vitamin A analyses. At the same time Vitamin A and DC complex intramuscular flank injections (l-ml dosage) were given.g This procedure continued until the calves were 2 to 3 mo old. Calves had free access to creep feed (oats) and water. Chemical Analyses B-car in plasma was extracted using the method of Brubacher and Vuilleumier (13). A modified high-performance liquid chromatography (HPLC) method was used to determine the concytration of B-car (14, 15). The HPLC apparatus consisted of 1) a Beckman isocratic 110 HPLC system with a loo-u1 injecter loop, 2) a Beckman Ultrasphere - Si straight phase column (4.6 mm i.d. x 250 mm (5~) wfith a 50-mm guard column), 3) a Beckman absorbance detector (Model 160) with a 436-nm filter, and 4) a eICI Pharmaceuticals, f

Lutalyse.

Mississauga,

Tuco-Upjohn LTD., Orangeville,

gPer day equivalent of 1.6 IU of Vitamin E. h Beckman, Fullerton,

494

Ontario.

16,000

Ontario.

IU of Vitamin A; 2500 IU of Vitamin D and

CA.

OCTOBER 1986 VOL. 26 NO. 4

THERIOGENOLOGY

The mobile phase consisted of 90% Kipp and Zonen’ (BD41) chart recorder. n- hexane (HPLC nrade) and 10% methvl ethvl ketone (certified grade). Flow r te was 2YO mljmin. Commerc>al B-car standards prepared f rbm carrots “s were used. Vitamin A in plasma was analysed by HPLC (16). The HPLCapparatus was sin#lar to that for the B-car analysis except that a reversed-phase x 250 mm (5~) ) and a Beckman Ulkrasphere-ODS column (4.6 mm i.d. Perkin-Elmer W detector (LC-15B) were used. Plasma progesterone was analysed by radioimmunoassay (17). Based on 25 assays the coefficients of variation for intraassay and interassay Assay sensitivity was 10 pg/assay were 11.1 and 18.4X, respectively. tube or 100 pg/ml plasma. Determination

of Ovarian Function

Sequential plasma progesterone concentrations for each heifer during postpartum were plotted. A functional corpus luteum (CL) was than 1 ng/ml judged to exist when progesterone values were greater plasma. Elevation of plasma progesterone for more than 10 d was defined as a normal luteal phase, while an elevation of less than 10 d was An estimate of in vivo production of classified as a short luteal phase. progesterone was made from the area under the curvelfor the first normal luteal phase by means of a graph/pen sonic digitizer . Statistical

Analyses

Statistical analyses began with a one-way analysis of variance of Differences between group means were the replicated treatments (18). Within each group, determined by the Student-Newman-Keul method (19). analysis of variance for repeated measures (18) were calculated for B-car and body weight values. A one-way interaction between replicates for each variable was calculated and results not different were combined for analysis of variance (18). Comparison of conception rates was carried out by Chi-square (18). RESULTS During the study 13 heifers were removed from the experiment. Reasons were a) abortion during pregnancy (one control heifer and three ‘Kipp and Zonen, Utrecht,

Holland.

‘Sigma Chemical Company, St. k

Louis,

MO.

Perkin Elmer, Norwalk, CT.

1

Science

Accessories

OCTOBER

Corp.,

Southport,

1986 VOL. 26 NO. 4

CT.

495

THERIOGENOLOGY

B-car-supplemented heifers), b) calf death or rejection at birth (three control heifers and three B-car-supplemented heifers), c) calf death before 60 d of age (one control heifer and one B-car-supplemented heifer), and d) prolapsed uterus (one control heifer). In addition, two heifers in the control treatment and three in the B-car treatment showed few or no signs of ovarian activity as determined by rectal palpation throughout the study and therefore were not used in the breeding study. The chemical composition of concentrates and barley straw fed during pregnancy and lactation is presented in Table 2. The body weight of the heifers during the fourth month of gestation was similar for the control and B-car treatments (370.1 vs 372.4 kg; Figure 1). However, during the remainder of pregnancy, heifers fed B-car had higher body weights. Average daily gain was not different between treatments from 4 Beifers fed B-car were heavier (P < 0.05) during to 8 mo of pregnancy. the first and fourth months postpartum. Average daily gain from calving to 130 d postpartum did not differ. All heifers gained weight (P < 0.05) during pregnancy. The birth weight of calves was not different between the control and B-car supplemented treatments (Table 3). At 30 d of age, calves from heifers supplemented with B-car were significantly (P < 0.01) heavier, The incidence of mortality of calves at but this trend did not persist. birth and before 60 d of age was similar for each treatment. After 60 d of age, four calves (two per treatment) died but their dams were retained in the study. At 1 mo of age, calves born to dams supplemented with B-car had higher levels of B-car in plasma (18.1 ug/dl) than those from This significant trend the control group (7.3 ug/dl; P < 0.01). B-car levels in plasma increased (P continued during the 3 mo sampling. < 0.05) as the calves matured. The levels of B-car in plasma of the heifers during pregnancy and At all times B-car postpartum are presented in Table 4 and Figure 2. supplementation resulted in greater (P < 0.01) B-car values in plasma. Immediately prepartum and during early postpartum period, plasma B-car In heifers concentration declined in heifers for both treatments. B-car levels reached minimum supplemented with B-car, plasma concentration (229 ug/dl) during the first week post partum. By 3 to 4 wk postpartum, B-car levels were above 300 ug/dl in the heif ers supplemented with B-car. Throughout most of the study, heifers supplemented with B-car had higher (P < 0.05) concentrations of Vitamin A in plasma (Table 5). Heifers supplemented with B-car had greater (P < 0.05) levels of plasma progesterone during the last trimester of pregnancy (Table 6). Days postpartum to first short and first normal luteal phase, in vivo progesterone secretory response, days postpartum to first detected and concentration of progesterone estrus, in plasma associated with estrus activity were similar for both treatments (Table 7). The blood sampling protocol (twice weekly) did not enable us to determine length of

496

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1986 VOL. 26 NO. 4

87.10 86.33

87.32 87.16

89.90

Lactation Control -carotene

Barley straw

matter

% Dry

3.69

17.36 17.60

17.36 16.93

4: Crude protein

0.26

0.78 0.89

0.86 0.84

% Ca

0.05

0.60 0.61

0.82 0.78

4: P

0.14

0.36 0.38

0.24 0.26

XHg

-

0.58 0.56

0.55 0.57

%K

0.50 24.60

0.50 86.00

B-carotene (PPm)

Composition of concentrates and barley straw (X dry matter) low B-carotene diets during pregnancy and lactation

Pregnancy Control -car0 tene

Table 2.

3.60

52.73 54.73

91.03 85.20

(PE)

11.32

65.54

74.39

134.74 130.94

(PS

fed to heifers

29.21

58.39 56.37

133.68 128.20

(PZ)

on high or

THERIOGENOLOGY

CKI B-CAR fi CONTROL

500

350

t I

I

I

I

I

I

I

I

1

1

1

,

2 4 0 -4 -2 MONTHS PRE-AND POST-PARTUM

Figure

498

1.

Body weights (kg) during pregnancy and postpartum of heifers Data are mean + SE. fed diets high or low in B-carotene. *P < 0.05. Parturition occurred at 0 mo.

OCTOBER

1986 VOL; 26 NO. 4

THERIOGENOLOGY

Table

3.

Weights (kg) from birth to 3 mo of age, average daily gain of B-carotene in plasma (ug/dl) in (kg), and concentration calves from heifers fed diets high or low in B-carotene

Parameter

Control

B-carotene

Weightsa Birth Month 1 Month 2 Month 3 Daily

34.2 54.7 91.3 108.4

t ;.tb . T 12.1 ; 16.0

(39) I;:; (34)

34.1 62.1 82.3 97.3

+ 5 T T -

0.9 1.4** 2.1 3.9

(35)

+ T T 7

0.03** 0.05 0.05* 0.02

(34)

I::; (33)

Gain

Month 1 Month l-2 Month 2-3 Birth-Month

0.69 1.22 0.44 0.65

3

+ 5 5 ;

0.05 0.47 0.04 0.02

(35) :;i; (34)

0.94 0.67 0.59 0.73

I:;; (33)

Plasma B-carotene Month 1 Month 2 Month 3 a Month 3 represents b

19.8 weights

Mean -+ standard error.

i

5.1

18.1 18.7 48.5

+ 1.3** 7 2.0** i 8.3**

between 2.5 to 3 mo of age.

* P < 0.05;

OCTOBER 1986 VOL. 26 NO. 4

** P < 0.01 relative

to control.

499

I’HERIOGENOLOGY

Table 4.

Concentration of &carotene in plasma (ug/dl) during pregnancy in heifers fed diets high or low in B-carotene

5

40 -+ 4a,b

(41)

433 _+ 18

(38)

6

29 -+ 2

(41)

496 + 17

(39)

7

16 -+ 1

(41)

465 _+ 19

(39)

8

15 -+ 1

(40)

380 -+ 19

(39)

13 _+ lC

(40)

269 _+ 19

(38)

Days prior

to calving

a Mean + standard b

B-carotene

Control

Stage of Pregnancy (mo)

error.

All values between control different (P < 0.01).

and B-carotene

treatments

were

’ The mean sampling days were 7.8 + 0.7 and 7.6 + 0.6 d for control and bcarotene treatments, respectively.

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1986 VOL. 26 NO. 4

THERIOGENOLOGY

DAYS POSTPARTUM

Figure

2.

Concentration of @-carotene in plasma (ug/dl) at weekly intervals postpartum in heifers fed diets high or low in B-carotene. Data are mean -+ SE. All values were different between treatments.

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rHERIOGENOLOGY

Table 5.

Concentration of Vitamin A in plasma (ug/dl) ina b heifers fed the diets high or low in S-carotene ’

Date

41 + 2

(10)

(10)

46 -+ 2**

(10)

35 -+ 2

(10)

46 + 1**

(10)

February 22

33 + 1

(10)

34 -+ 1

(10)

March 22

24 + 3

(7)

33 -+ 2**

(10)

April

27 -+ 1

(8)

36 + 2**

(8)

May 30

43 + 1

(8)

39 + 1*

(9)

June 26

29 -+ 1

(8)

37 + 3

(8)

July 21

33 -+ 3

(8)

33 + 2

(9)

November 24

36 + 2’

(8)

December 21

39 + 1

January 18

19

a All heifers b

Analyses

received

Table 6.

Vitamin A injections

of same subpopulation

’ Mean + standard from control.

error.

monthly.

throughout

* P < 0.05;

the experiment.

** P < 0.01 different

Concentrations of progesterone in plasma (ng/ml) during the last trimester of pregnancy in heifers fed diets high or low in B-carotene s-carotene

Control

Stage Month 6

5.4 + 0.4a

(37)

8.3 -+ 1.3*

(31)

Month 7

8.4 -+ 0.9

(37)

12.9 -+ 0.8**

(38)

Month 8

4.5 -+ 0.4

(40)

6.7 + 0.7**

(36)

aMean + standard control.

502

B-carotene

Control

error.

* P < 0.05;

**

OCTOBER

P < 0.01 different

from

1986 VOL. 26 NO. 4

THERIOGENOLOGY

Table 7.

Postpartum fertility

of heifers

fed diets

Parametera

Control

Days postpartum phase

to first

short

Days postpartum phase

to first

normal luteal

Progesterone the first

high or low in B-carotene

luteal

b-carotene

49.3

-+ 2.0b

(30)

53.2

+ 2.4

(25)

67.5

-+ 3.1

(25)

62.6

+ 2.8

(21)

9.2

-+ 0.7

(11)

9.5

2 0.9

(12)

secretory response $uring normal luteal phase

Heifers (X) with more than one short luteal phase

20.0

(30)

13.8

(25)

Heifers (X) showing estrus before first normal luteal phase

66.7

(34)

57.1

(32)

Days postpartum estrus

70.1

(28)

65.3

to first

Plasma progesterone with estrus: Mounting

detected

(ng/ml)

-+ 2.2

+ 2.8

(28)

associated

Standing heat

0.44 -+ 0.04

(23)

0.51 + 0.04

(17)

0.46 -+ 0.06

(14)

0.53 + 0.04

(9)

These parameters were not under the influence

of prostaglandin

treatment.

Mean + standard error. Area (cm2) measured under the progesterone

OCTOBER

1986 VOL. 26 NO. 4

curve.

503

THERIOGENOLOGY

Table 8.

Reproductive B-carotene

performance

of heifers

Parameter

fed diets

Control

high or low in

B-carotene

Conception rate first artificial insemination (X)

64.7

(34)

59.4

(32)

Conception rate second artificial insemination (%)

63.6

(11)

61.5

(13)

Cumulative conception

85.3

(33)

84.4

(32)

1.24 -+ 0.08a

(30)

1.29 + 0.08

(27)

8.7

(28)

7.7

Services

rate

per conception

Plasma progesterone (ng/ml) 20-21 d postconception

(%)

-+ 0.6

+ 0.5

(27)

a Mean + standard error. the first short and normal luteal phase accurately. We did observe that the first short luteal phase was not preceded by a typical estrus and that it was shorter than the first normal luteal phase. Fertility was not different between the two treatment groups (Table 8). Using prostaglandin F as a reproductive management tool, mean days postpartum to prostaglandir injection was 72.8 and 71.9 for the control and B-car treatments, respectively. Elevated progesterone in plasma at Day 21 postinsemination and pregnancy diagnosis by rectal palpation between Days 40 to 45 postinsemination indicated that there was no evidence of any embryonic death during this period of time. DISCUSSION The objectives of this study were to determine the effects of B-car status on pregnancy and on reproductive performance of beef heifers. In addition, the effects of maternal B-car status on calf performance were investigated. In comparison with many other studies a large number of heifers was used in uniform replicated experiment (ll), groups. Endocrine profiles were monitored, and uniform estrus detection was conducted. Almost all of the artificial insemination was done by one experienced technician. The diets fed were similar except for their content of B-car (the control diet was almost devoid of B-car). Furthermore, B-car and Vitamin A status of the heifers were well defined.

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THERIOGENOLOGY

The level of B-car in plasma of heifers supplemented with B-car were above the minimum level required to maintain normal reproduction as suggested by Friesecke (10) ( > 300 ug/dl plasma - good; 200 to 300 ug/dl > 200 ug/dl plasma-deficient). By the same criteria, plasma-suspect; the control heifers were severely deficient in B-car (lower than 50 The clearly defined difference in B-car status of our animals ug/dl). in B-car status contrasts with other studies (4, 6-8) where differences between treatment groups were often equivocal. The transient depression in level of B-car in plasma observed around time of parturition was also observed by Lotthammer (3) and Johnston and Chew (20), who reported Plasma B-car decreased plasma B-car levels around time of calving. levels in the heifers supplemented with B-car decreased at the end of the experiment. this decrease was due to some loss of B-car in the Possibly, concentrate during storage. Monthly injections of Vitamin status of all heifers (21). Vitamin supplemented with B-car were somewhat availability of B-car from the feed for

A resulted in adequate Vitamin A A levels in plasma from animals higher and may reflect a greater conversion to Vitamin A.

In this study, heifers supplemented with B-car were heavier during certain months of the last trimester of pregnancy and also during postpartum. However, birth weight of calves was not different between treatments; this finding leads us to suggest that the gain represents maternal weight gain. The body weight gain in beef heifers in this study is in agreement with results of Folman et al. (8), who also observed a higher growth rate in dairy heifers supplemented with B-car. During pregnancy the heifers supplemented with B-car had higher levels of progesterone in plasma. The significance of association of heavier body weights with higher levels of progesterone in plasma is not known. There were no differences in outcome of pregnancy and in birth weight of calves. Similarly, the incidence of dystocia was not different between treatments. Resumption of postpartum ovarian activity was similar between the treatments. The first estrous cycle postpartum for both treatments was of short duration and was not preceded by a normal estrus. This finding is in agreement with those of other studies (22-24). Subsequent luteal phases were of normal length and preceded by an estrus. Over 55% of the heifers in each treatment showed estrus before the first normal luteal phase. The interval from parturition to first detected estrus was similar between the two treatments and is similar to other studies (5, Postpartum reproductive performance for all groups was satisfactory 7). considering that visual estrus detection and artificial insemination were used. Cumulative conception rate for both treatments was high (85%). control results

The conception rate on first service was similar between the heifers and heifers supplemented with B-car and is similar to the in dairy cattle found by Larson et al. (5). There was no

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THERIOGENOLOGY

significant difference between treatments in overall conception rate in our study; this agrees with Folman et al. (8), who studied dairy heifers. Services per conception were not different between treatment groups; this finding is similar to others (7-9). Similar conception rate between treatments in our study contrasts with the findings of others in dairy cattle (2, 10, 25), where higher conception rate in animals supplemented . > r _.1_L n __._ _--...-.--> n -L.~.-~~~ &I~

THERIOGENOLOGY

6.

Marcek, J.M., Appell, L.H., Hoffman, C.C., Moredick, P.T. and Effect of supplemental E-carotene on incidence and Swanson, L.V. J. Dairy Sci. responsiveness of ovarian cysts to hormone treatment. 68~71-77 (1985).

7.

Bindas, E.M., Gwazdauskas, F.C., Aiello, R.J., Herbein, J.H., Reproductive and metabolic McGilliard, M.L. and Polan, C.E. characteristics of dairy cattle supplemented with B-carotene. J. Dairy Sci. g:1249-1255 (1984).

8.

Folman, Y., Ascarelli, I., Herz, Z., Rosenberg, M., Davidson, M. and Halevi, A. Fertility of dairy heifers given a commercial diet free of B-carotene. Br. J. Nutr. e:353-359 (1979).

9.

Bremel, D.H., Hemken, R.W., Heersche, G., Jr., Edgerton, L.A. and Olds, D. Effects of S-carotene on metabolic and reproductive J. Dairy Sci. 65 (Suppl. 1): parameters in lactating dairy cows. 78 abstr. (1982). The significance of beta-carotene in ruminant H. field results Europe. In: Importance of for Bovine Fertility. Roche. Symp. London. 1978, pp.

10.

Priesecke. nutrition: Beta-carotene 53-72.

11.

Stowe, H.D. on Continuing (1984).

12.

NRC. Nutrient Requirements of Domestic Animals, No. 4. Nutrient Fifth Revised Ed. National Academy of Requirements of Beef Cattle. Sciences - National Research Council, Washington, DC., 1976.

13.

Brubacher, G. and Vuilleumier, J.P. Carotene in blood plasma. In: Hoffmann-LaRo&, Manz, U. (ed.). Beta-carotene Assay Methods. Basle, Switzerland. 1980, pp. 15-16.

14.

High performance Thompson, J.N., Hatina, G. and Maxwell, W.B. of vitamin A in margarine, liquid chromatographic determination J. Assoc. Off. Anal. milk, partially skimmed milk and skimmed milk. Chem. e:894-898 (1980).

15.

Stancher, B. and Zonta, F. High-performance liquid chromatographic determination of carotene and vitamin A and its geometric isomers in foods . J. Chromatography -238:217-225 (1982).

16.

Catigani, G.L. and Bieri, J.G. Simultaneous determination of serum or retinol and a-tocopherol in plasma by liquid chromatography. Clin. Chem. g:708-712 (1983).

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Beta carotene Education for

and bovine reproduction. The Compendium the Practicing Veterinarian -6: S167-S175

1986 VOL. 26 NO. 4

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THERIOGENOLOGY

17.

Rutter, L.M., Carruthers, T.D. and Manns, J.G. The postpartum induced corpus luteum: functional differences from that of cycling cows and the effects of progesterone pretreatment. Biol. Reprod. 2:560-568 (1985).

18.

Nie, D.H.

19.

Steel, R.G.D. Statistics.

20.

Johnston, L.A. and Chew, B.P. Peripartum changes of plasma and milk vitamin A and bcarotene among dairy cows with or without mastitis. J. Dairy Sci. g:1832-1840 (1984).

21.

Thompson, S.Y. Role of carotene and vitamin World Rev. Nutr. Dietetics e:224-280 (1975).

22.

Peripheral Donaldson, L.E., Bassett, J.M. and Thornburn, G.D. plasma progesterone concentration of cows during puberty, oestrous cycle, pregnancy and lactation, and the effects of undernutrition or exogenous oxytocin on progesterone concentration. J. Endocrinol. %:599-614 (1970).

23.

Schams, D. , Schallenberger, E., Menzer, C., Stangl, J., Zottmeier, K., Hoffman, B. and Karg, H. Profiles of LH, FSH and progesterone in postpartum dairy cows and their relationship to the commencement of cyclic functions. Theriogenology 0:453-468 (1978).

24.

Manns, J.G., Humphrey, W.D., Flood, P.F., Hapletoft, R.J., Rawlings, N. Endocrine functional and Cheng, K.W. profiles and characteristics of corpora lutea following onset of postpartum ovarian activity in beef cows. Can. J. Anim. Sci. 63:331-347 (1983).

25.

Cooke, B.C. A study of the relationship between beta-carotene and fertility problems in dairy cows. In: Importance of Beta-carotene for Bovine Fertility. Roche, Symp. i&rdon. 1978, pp. 45-52.

26.

Bonsembiante, H., Andrighetto, and bovine fertility: further Anim. !:199-212 (1983).

508

N.H., Hull, C.H., SPSS. McGraw Hill

Jenkins, J.G., Book Co., N.Y.,

Steinbrenner, 1975.

K. and Bert,

and Torrie, J.H. Principles and Procedures McGraw Hill Book Co., N.Y., 1980.

A in animal

I. and Bittarte, G. experimental results.

OCTOBER

of

feeding.

Beta-carotene Zoot. Nutr.

1986 VOL. 26 NO. 4