1999 NE Beef Cattle Report: Evaluation of Growth-Promoting Systems for Heifer Calves Finished in the Feedlot

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University of Nebraska Cooperative Extension MP 71

1999 Nebraska Beef Cattle Report

Evaluation of Growth-Promoting
Systems for Heifer Calves
Finished in the Feedlot

Mari Lubberstedt, Terry Mader, Jill Heemstra and Kelly Lechtenberg¹

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Optimum growth-promotant systems for finishing heifer calves include an initial implant with either Synovex-C or Synovex-H, followed by replanting with Synovex-H and Finaplix-H.

Summary

Two-hundred ten head of predominantly British and/or British x Continental cross heifers were assigned to six implant/reimplant treatment groups (five pens/treatment). In addition, melengestrol acetate (MGA) was provided to four treatment groups from day 28 until 48 hours prior to slaughter. Heifers not fed MGA had the greatest number of immature ovaries, although they were also the most efficient in feed conversion (lower feed to gain ratio). Heifers fed MGA and implanted with Finaplix were the least efficient in feed conversion.

Introduction

Generally, a recommended implant-reimplant program consists of an initial implant with estrogenic activity, followed by a second implant exhibiting both estrogenic and androgenic effects 70 to 100 days prior to slaughter. However, feeding melengestrol acetate (MGA) is another option for improving gain and efficiency in heifers. Issues concerning estrogen/androgen combinations and MGA feeding have not been fully addressed. Due to potential implant failure, and the possible additive effects of MGA in combination with an implant, producers may feed MGA plus implant cattle as well. The benefits of feeding MGA are primarily associated with heifers with functional, mature ovaries. The effects of implants on the development of the reproductive tract can vary. Characterization of implant effects on ovarian development are needed. Few studies provide data relevant to growth promoting systems for heifers fed more then 150 days, such as with heifer calves. Previous studies have found benefits to programs utilizing low dose (estrogenic) implants followed by high dose (estrogenic or estrogenic and androgenic) implants in long-fed steers and heifers. The objective of this study was to evaluate low dose/high dose implant systems when used in combination with the feeding of MGA for heifer calves finished in the feedlot.

Procedure

Two-hundred ten head of predominantly British and British x Continental cross heifers were eartagged and vaccinated for seven-way clostridial, IBR, PI3, BRSV and H. Somnus. Heifers were fed a receiving diet for approximately 10 days, after which time they were assigned to blocks based on their average initial weight and randomly assigned to pens (seven head/pen). The initial weight was the average of weights taken on two consecutive days before feeding. Pens were randomly assigned to six implant treatment (Trt) groups (five pens/treatment). On day zero, the heifers were weighed and implanted according to the treatment assignments; Synovex-C was implanted in groups 1 through 3 and Synovex-H was implanted in groups 4 through 6. On day 70, the heifers were implanted with Synovex-H and/or Finaplix-H, according to the experimental design (Table 1).

Table 1. Experimental design.

Study
Group Implant treatments^a MGA fed^b Replicates
(No. of pens) Animals
assigned
per pen

Day 0 Day 70

1 Synovex-C Synovex-H + Finaplix H none 5 7

2 Synovex-C Synovex-H + Finaplix-H yes 5 7

3 Synovex-C Finaplix-H yes 5 7

4 Synovex-h Synovex-H + Finaplix H none 5 7

5 Synovex-H Synovex-H + Finaplix-H yes 5 7

6 Synovex-H Finaplix-H yes 5 7

^aSynovex-C contains 10 mg estradiol benzoate and 100 mg progesterone; Synovex-H contains 20 mg estradiol benzoate and 200 mg testosterone propionate; Finaplix-H contains 200 mg trenbolone acetate.
^bMelengestrol acetate (MGA) was provided to all heifers at .45 mg/hd/day from day 28 to 48 hours prior to slaughter.

Melengestrol acetate (MGA) was provided to groups 2, 3, 5 and 6 at .4 to .45mg/hd/day from day 28 until it was withdrawn from the feed 48 hours prior to slaughter. The feeding of MGA was delayed until day 28 when cattle were on the highest energy diet, a common practice in feedlots where supplement formulations and levels fed are designed for feeding in the final ration only.

At the start of the trial, all heifers were stepped-up to a high-energy finishing ration and were on full-feed by day 28 (Table 2). Heifers were fed Rumensin and Tylan throughout the 172 day feeding trial. Full-weights were taken on days 28, 70, 126 and prior to slaughter (day 172). Ovarian data, hot carcass weight and liver abscesses were determined on day of slaughter. Marbling score, fat thickness, percent kidney, pelvic and heart fat (KPH), yield grade, number of dark cutters and ribeye area were recorded following a 24-hour (minimum) chill. During the study, three heifers were removed due to death or health-related problems independent of treatment assignment and were not included in the statistical analysis.

Table 2. Diet Composition.

Diet number

Item 1 2 3 4 5A 5B 5C

Days fed 5 5 5 6 7 98 46

Diet, % DM 74.02 72.66 70.18 70.98 68.96 69.08 66.39

Ingredients, % diet DM

Corn silage - - - - - - 7.50

Alfalfa hay 37.60 25.70 15.77 7.19 - - -

Ground high-moisture ear corn 25.00 25.00 30.00 30.00 30.00 30.00 15.00

Ground high-moisture corn 17.42 22.61 24.31 28.18 31.63 30.59 34.34

Dry-rolled corn 17.42 22.61 24.31 28.18 31.62 30.58 34.33

Mineral-vitamin premix^a 1.25 0.92 0.54 - - - -

Rumensin supplement^b 1.31 1.31 - - - - -

Liquid supplement^d - 1.85 3.04 4.42 4.72 4.72 4.72

Rumensin/Tylan supplement^c - - 2.03 2.03 2.03 2.03 2.03

Control/MGA supplement^e - - - - - 2.08 2.08

Content, DM basis

Crude protein, % 12.55 12.50 12.00 12.00 12.03 12.08 12.12

Neg, Mcal/cwt 52.00 56.00 59.00 62.00 64.64 64.24 64.17

Nem, Mcal/cwt 80.74 85.16 88.59 91.95 94.95 94.46 94.12

Calcium, % 0.73 0.74 0.69 0.66 0.60 0.64 0.65

Phosphorous, % 0.34 0.34 0.34 0.34 0.35 0.35 0.34

Potassium, % 0.91 0.84 0.75 0.70 0.63 0.64 0.67

Magnesium, % 0.20 0.18 0.17 0.15 0.14 0.14 0.15

Sulfur, % 0.19 0.18 0.17 0.16 0.15 0.15 0.15

Salt, % 0.25 0.30 0.30 0.28 0.30 0.30 0.30

^aCorn based supplement containing on DM basis 19.85% salt, 14.21% Ca, 3.85% P, .21% K, .17% Mg, .27% S, .066 ppm Mn, .066 ppm Zn, .066 ppm Fe, .0066 ppm Cu, .002 ppm I, .00067 ppm Co, and 237,254 IU vitamin A/kg.
^bContained on DM basis 96.72% ground corn, 2.14 % molasses, 1.14 % Rumensin 60 (60g monensin/lb).
^cContained on DM basis 96.05% ground corn, 2.13 molasses, 1.14% Rumensin 60 and 0.68% Tylan 40 (40g Tylosin/lb).
^dContained on DM basis 50% CP, 47% NPN, 12.30% Ca, 6.3% salt, .79% P, 4.76% K, .15% Mg, .35% S, .0035% Zn, .0010% Fe, .0028% Mn, .0013% Cu, .0008% I, .0001% Co, 105,000 IU vitamin A/ kg, 24,500 IU vitamin D and 35 IU vitamin E/kg.
^eControl supplement contained on DM basis 36.51% ground corn, 30.62% soybean hulls, 19.96% wheat midds, 4.21% molasses, 5.61% limestone, and 3.10% soybean meal. MGA (melengestrol acetate 441 mg/kg) was put in at .5% of control supplement formulation to make the MGA supplement.

Statistical analyses for this trial were conducted using the GLM procedures of SAS (1991). Preplanned contrast included initial implant (IMP; group 1, 2, and 3 versus 4, 5 and 6); growth promotant regimen (GP; groups 1 and 4 versus 2 and 5 versus 3 and 6) and IMP x GP interaction except for characteristics which were compared using chi-square test. For those, the model included IMP, GP and a comparison between initial implant groups that received only MGA (Treatments 2 and 3 versus Treatments 5 and 6). In addition, contrasts were performed between treatment groups receiving MGA versus groups fed no MGA (Treatments 1 and 4 versus Treatments 2, 3, 5 and 6) and between Synovex-H in combination with Finaplix versus Finaplix alone (Treatments 3 and 6 versus 1, 2, 4 and 5). Liver abscesses, ovarian data, percent dark cutters and quality grade were analyzed by the frequency procedure of SAS (1991) using the chi-square option.

Results

The implantation of Synovex-H increased average daily gains and decreased feed required per unit of gain in the first 28 and 70 days of the study (Table 3). The addition of melengestrol acetate (MGA) to the diet at day 28 did not significantly affect average daily gains or dry matter intake. No differences in dry matter intake were observed among the growth-promotant treatments. Feed required per unit of gain was the least from zero to 70 days and over the entire trial for heifers not fed MGA. At the end of the trial, the least efficient in feed conversion were heifers fed MGA and implanted with only Finaplix.

Table 3. Initial implant (IMP) and overall growth promotant regimen (GP) effects on animal performance and carcass characteristics^a.

Treatment (Trt) group

Contrast P-Values by

Feed additive: None
MGA
None
MGA
treatment number

Implant (day 0):
Implant (day 70):
Trt No.: C
H/F
1 C
H/F
2 C
F
3 H
H/F
4 H
H/F
5 H
F
6 K L M N O

Total no. head (reps) 35 (5) 34 (5) 34 (5) 35 (5) 34 (5) 35 (5)

Weight, lb

Initial 614 615 616 614 616 616 .98 .99 1.00 .94 .95

28 d 701 702 703 714 710 711 .66 .99 .99 .97 .98

70 d 850 844 843 873 860 863 .45 .95 .99 .75 .89

Final (172 d) 1165 1171 1146 1196 1177 1163 .59 .79 .95 63 .51

Adj. final wt.^b 1168 1160 1131 1185 1165 1148 .69 .67 .98 .49 .42

ADG, lb

0-28 d 3.10 3.11 3.11 3.56 3.35 3.39 .02 .81 .75 .530 .84

28-70 d 3.55 3.39 3.33 3.78 3.59 3.63 .07 .40 .94 .181 .46

0-70 d 3.37 3.28 3.24 3.69 3.49 3.53 .02 .44 .91 .210 .53

70-172 d live wt 3.09 3.20 2.98 3.17 3.10 2.92 .84 .24 .75 .476 .01

70-172 d adj wt 3.08 3.06 2.79 3.03 2.96 2.77 .59 .12 .95 .183 .05
0-172 d live wt 3.20 3.23 3.08 3.38 3.26 3.18 .26 .32 .78 .272 .15

0-172 d adj wt 3.20 3.15 2.98 3.30 3.17 3.08 .42 .16 .92 .128 .08

DMI, lb

0-28 d 18.28 19.07 18.31 19.11 18.89 18.92 .52 .89 .80 .88 .75

28-70 d 19.09 19.13 19.02 19.58 9.76 19.62 .37 .98 .99 .94 .91

0-70 d 18.77 19.11 18.74 19.39 19.41 19.34 .42 .95 .97 .91 .84

70-172 d adj wt 20.30 21.30 20.16 21.08 21.23 21.98 .36 .55 .76 .70 .49

0-172 d adj wt 19.68 20.41 19.59 20.40 20.49 20.31 .37 .73 .86 .78 .62

Feed/gain

0-28 d 5.90 6.15 5.97 5.38 5.65 5.61 .03 .57 .94 .33 .91

28-70 d 5.37 5.67 5.73 5.19 5.52 5.42 .09 .08 .85 .03 .28

0-70 d 5.56^cd 5.84^d 5.80^d 5.25^c 5.56^cd 5.48^cd .01 .05 .98 .02 .39

70-172 d adj wt 6.37 6.38 6.60 6.48 6.61 6.95 .16 .18 .82 .22 .07

0-172 d adj wt 6.15^c 6.49^e 6.61^e 6.20^cd 6.45^de 6.60^e .96 .001 .89 .01 .01

^aC = Synovex-C, H= Synovex-H, F = Finaplix-H, and MGA = Melengestrol acetate, fed from day 28 to 170.
^bBased on hot carcass weight and 62% dress.
^cdeMeans within a row with different superscripts differ (P < .05).
K = IMP (1 2 3 vs 4 5 6)
L = GP 1 & 4 vs 2 & 5 vs 3 & 6)
M = IMP by GP Interaction
N = 1 & 4 vs 2 3 5 & 6
O = 3 & 6 vs 1 2 4 & 5

Heifers not fed MGA had the largest ribeye area, while heifers implanted with Finaplix only had the smallest ribeye area (Table 4). Lower yield grade was also observed for heifers not fed MGA. Heifers initially implanted with Synovex-H showed an increased occurrence of liver abscesses. No differences in quality grade were found.

Table 4. Initial implant and overall growth promoting regimen (GP) effects on carcass characteristics^a.

Treatment (Trt) group

Contrast P-Values by

Feed additive: None
MGA
None
MGA
treatment number

Implant (day 0):
Implant (day 70):
Trt No.: C
H/F
1 C
H/F
2 C
F
3 H
H/F
4 H
H/F
5 H
F
6 K L M N O R

Hot carcass weight, lb 723.9 720.0 702.0 734.8 722.2 711.9 .70 .68 .99 .49 .42 -

Dressing percentage 62.13 61.43 61.15 61.42 61.37 61.22 .48 .34 .58 .17 .26 -

Fat thickness, in 0.38 0.40 0.45 0.33 0.47 0.39 .68 .05 .09 .02 .36 -

KPH, % 2.37 2.31 2.41 2.10 2.25 2.40 .14 .20 .34 .20 .09 -

Rib-eye area, in 13.01^c 12.14^b 11.90^b 13.26^c 12.28^b 11.95^b .53 .01 .95 .01 .01 -

Marbling score^e 506 520 514 495 532 512 .97 .24 .73 .15 .98 -

Quality gradef 18.20 18.32 18.36 18.00 18.58 18.40 .90 .39 .65 .85 .80 -

Yield grade 2.20^c 2.38^cd 2.52^d 1.91^b 2.24^c 2.30^cd .07 .02 .90 .01 .04 -

Liver abscesses, %^g 0.00 0.00 5.71 5.71 2.86 14.29 .05 .04 - .34 .01 .15

Dark cutter, %^g 40.00 52.38 43.81 42.86 38.09 45.71 .63 .87 - .60 .84 .45

Quality grade, %^g

Prime (Pr) 0.0 2.9 0.0 0.0 0.0 0.0 .31 .36 - .47 .48 .31

Choice 54.3 58.8 61.8 57.1 64.7 57.1 .24 .60 - .50 .92 .42

Select 45.7 38.2 35.3 40.0 35.3 42.9 .47 .43 - .50 .92 .44

Standard (Std) 0.0 0.0 2.9 2.9 0.0 0.0 1.00 .59 - .63 .62 .31

Choice+Pr 54.3 61.7 61.8 67.1 64.7 57.1 . 27 .66 - .44 1.00 .45

Select+Std 45.7 38.2 38.2 42.9 35.3 42.9 .23 .48 - .44 1.00 .41

^aC = Synovex-C, H = Synovex-H, F = Finaplix-H, and MGA = Melendgestrol acetate, fed from day 28 to 170.
^b,c,dMeans within a row with different superscripts differ (P < .05).
^e450 = Slight average, 550 = Small average, 650 = Modest average.
^f17 = Select average, 18 = Select high, 19 = Choice low.
^gP-values based on chi-square analysis.
K = IMP (1 2 3 vs 4 5 6)
L = GP (1 & 4 vs 2 & 5 vs 3 & 6)
M = IMP by GP Interaction
N = 1 & 4 vs 2 3 5 & 6
O = 3 & 6 vs 1 2 4 & 5
R = 2 & 3 vs 5 & 6

There was an unusually large incidence of dark cutter carcasses. This could not be attributed to any one experimental treatment, but possibly was caused by factors, including weather. The two days prior to slaughter, for example, were abnormally hot and humid. In addition, heifers were held overnight at the packing plant prior to slaughter and were not fed MGA 48 hours prior to slaughter. Heifers were not segregated by treatment at the packing plant.

Ovarian data (Table 5) indicate implanting with Finaplix alone reduced the number of immature ovaries and number of mature ovaries with no follicle, but increased the number of mature ovaries with graafian follicles. Heifers not fed MGA had the greatest number of immature ovaries. However, these heifers were the most efficient in feed conversion (lower feed to gain ratio).

Data suggest optimum growth promotant systems for heifer calves, managed under the above-mentioned conditions, includes an initial implant with either Synovex-C or Synovex-H, followed by reimplant with Synovex-H and Finaplix-H.

Table 5. Effect of initial implant (IMP) and overall growth promoting regimen (GP) on ovary development and function^a.

Treatment (Trt) group

Feed additive: None
MGA
None
MGA
Chi-square (P-values) by treatment number

Implant (day 0):
Implant ( day 70):
Trt No.: C
H/F
1 C
H/F
2 C
F
3 H
H/F
4 H
H/F
5 H
F
6 GP
I MP
(1 2 3 vs 4 5 6) (1 & 4 vs 2 & 5 vs 3 & 6) 1 & 4 vs 2 3 5 & 6 3 & 6 vs 1 2 4 & 5 2 & 3 vs 5 & 6

Missing, % 0.0 0.0 0.0 2.9 0.0 0.0 .31 .35 .15 .48 -

Very immature,(<15mm),% 0.0 0.0 0.0 0.0 0.0 0.0 - - - - -

Immature, (15-20mm), % 5.7 0.0 0.0 5.7 5.9 0.0 .36 .08 .05 .08 .14

Mature, (>20mm, no follicle), % 28.6 35.3 17.6 34.3 38.2 20.6 .66 .41 .35 .02 .49

Mature (graafian follicle), % 60.0 61.8 82.4 54.3 52.9 73.5 .36 .37 .39 .01 .21

Mature (multiple follicle), % 5.7 2.9 0.0 2.9 2.9 5.9 .67 .83 .54 .79 .26

Mature (Corpus Luteum), % 0.0 0.0 0.0 0.0 0.0 0.0 - - - - -

^aC= Synovex-C, H = Synovex-H, F = Finaplix-H, and MGA = Melengestrol acetate, fed from day 28 to 170.

Mari Lubberstedt, research technician, Northeast Research and Extension Center, Concord;
Terry Mader, professor, Animal Science, Northeast Research and Extension Center, Concord;
Jill Heemstra, former research technician, Northeast Research and Extension Center, Concord;
Kelly Lechtenberg, Consultant Midwest Veterinary Research, Oakland, Nebraska.

File MP71 under: BEEF
Issued January 1999; 3,000 printed.

Electronic version issued February 1999
pubs@unl.edu

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Elbert C. Dickey, Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.

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