diet selection and apparent total-tract digestibility among heifers … · 2016. 12. 11. · land...

Effect of stocking rate on performance,

diet selection and apparent total-tract

digestibility among heifers grazing cover

crops

B. R. Brunsvig*, D. W. Brake, A. J. Smart

and E. E. Grings

Land Usage Change

• U.S. Northern Great Plains

– 1,096,000 ha loss 2008 to 2012

• Iowa – 9,029 ha

• Minnesota – 5,042

• North Dakota – 4,012

• South Dakota – 10,983

– Total – 33,686 ha of new cropland (2011 to 2012)

Why The Change?

• Prices

– 2012 • Cattle- February Feeder USD $86.59 / kg

• Corn- August USD $7.63 / bu

– 2014 • Cattle- October Feeder USD $128.91 / kg

• Corn- April USD $4.71 / bu

– Current • Cattle- November Feeder Cattle USD $57.26 / kg

• Corn- July USD $3.53 / bu

Pasture Rent

0

50

100

150

200

250

2011 2012 2014 2015 2016

Do

lla

rs / h

a

USDA, NASS 2016

Impact on the cow-calf industry

• Segmented production of cattle and row crops.

• Could limit national cattle carrying capacity

• Increase Cow-calf production costs

Grazed vs Harvested Resources

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Grass

Pasture

Corn Corn

Silage

Grass Hay Alfalfa

Hay

Alfalfa

Silage

Do

lla

rs / M

ca

l N

Em

U.S. Cow Feed Costs By Region

Short, USDA, 2001

0

20

40

60

80

100

North West South

Fe

ed

C

ost, U

SD

How To Extend The Grazing Season?

• Graze crop residue

• Graze cover crops

– U. S. Department of Ag says…

• A cover crop is a crop generally recognized by agricultural

experts as agronomically sound for the area for erosion

control or other purposes related to conservation or soil

improvement.

Increase in U.S. Cover Crops

Adapted from Watts, SARE, 2015

0

50

100

150

200

250

2008 2009 2010 2011 2012 2013 2014 2015 2016

ha

, 1

x1

03

Where

Adapted from Watts, SARE, 2015

North American Wheat Production

Australian Center for International Ag Research

Stocking Rate and Performance

Adapted from Ackerman et al.,2001

0.55

0.60

0.65

0.70

0.75

300 500 700 900

AD

G, k

g/d

Stocking Rate, kg/ ha


Adapted from Ackerman et al., 2001

45

50

55

60

65

70

75

80

85

300 500 700 900

Ga

in

/h

a, k

g

Kg steer / ha


45

55

65

75

85

0.58

0.63

0.68

0.73

300 400 500 600 700 800 900

AD

G (k

g)

Kg steer / ha

Adapted from Ackerman et al., 2001

Stocking Rate

Adapted from Mott, 1973

Gain per Animal (g)

Gain per Unit Area (G) max

G

0 G

max g

0 g

Optimum

Range

u

Undergrazing Overgrazing

n

Grazing Pressure

0 n

m n

Objective

• Determine effect of stocking rate among heifers grazing a

cover crop mix

– Diet selection

– Diet digestibility

– Performance

Experimental Design

• 48 weaned heifers

• 67% Annual Ryegrass, 20% Radish, 13% Turnip

– 48d

• 3, 4 or 5 heifers

– 1.7, 2.3, 2.9 AUM/ha

Forage composition

Forage Consumption

0

20

40

60

80

100

Beginning Middle End

% B

ra

ssic

a S

ele

cted

Low

Medium

High

Forage Consumption

0

10

20

30

40

50

60

70

80

Beginning Middle End

% G

ra

ss S

ele

cted

Low

Medium

High

Nutrient Selection

Time Contrasts

% DM Initial Intermediate Final Linear Quadratic

OM 82.0 84.6 81.2 0.45 <0.01

NDF 48.2 35.5 42.8 0.11 <0.01

ADF 33.6 32.8 34.1 0.82 0.61

Stocking Rate, AUM × ha-1 Contrasts

% DM 1.7 2.3 2.9 Linear Quadratic

OM 82.7 82.1 83.0 0.90 0.71

NDF 41.2 41.2 44.1 0.25 0.52

ADF 33.4 33.2 34.0 0.48 0.49

Nutrient Selection

Digestibility


Item 1.7 2.3 2.9 Linear Quadratic

DMI, kg 6.0 9.1 8.2 0.07 0.05

Digest., %

DM 67.8 83.3 79.7 0.01 0.02

OM 76.7 87.7 84.8 <0.01 <0.01

NDF 69.0 80.0 80.0 <0.01 0.03

ADF 74.1 83.7 80.5 0.12 0.08

Period ADG


kg 1.7 2.3 2.9 Linear Quadratic

0-22d 0.3 0.1 0.1 0.05 0.24

22-48d 1.1 1.2 1.0 0.69 0.16

Cumulative ADG


kg 1.7 2.3 2.9 Linear Quadratic

0-22d 0.3 0.1 0.1 0.05 0.24

Overall 0.7 0.6 0.6 0.15 0.78

diet selection and apparent total-tract digestibility among heifers … · 2016. 12. 11. · land...

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