USE OF BODY ENERGY RESERVES IN
BEEF COW-CALF NUTRITION
• Goals in feeding beef cows
– Optimize production efficiency
• Produce a calf that fits into an acceptable weight and quality
• Produce a calf every 365 days
– Post-partum interval must be no longer than 83 days
– Beef cows must produce 3 dominant follicles before observed
ovulation
– Therefore, first dominant follicle must be produced by 41 days postpartum
– Since first ovulation occurs 7 to 14 days after a cow comes out of
negative energy balance, positive energy balance must be achieved by
31 days post-partum
– Minimize feed costs
• Since 33 to 40% of the costs associated with beef cow-calf
production are required for stored feeds, grazing needs to be
optimized in relation to production/acre and length of season
– Maximize biological efficiency
RELATIONSHIP OF BIOLOGICAL
EFFICIENCY AND FEED AVAILABILITY
Maximum
efficiency
___Breed__
Red Poll
Angus
Hereford
Pinzgauer
Gelvieh
Braunvieh
Limousin
Simmental
DMI at Max
efficiency
gm calf
weaned/kg DMI/
cow exposed
47.1
41.3
35.1
46.9
44.5
39.4
39.4
41.5
kg/yr
3790
4111
4281
5473
5475
7031
7498
8609
DMI, kg/yr
3500
7500
gm calf
weaned/kg DMI/
cow exposed
47
24
39
17
30
13
38
44
29
36
33
42
33
42
26
42
• Effects of feed availability on biological efficiency
– Rebreeding rates
– Weaning weights
• Implications
– Biological type should match feed resources
– Feed to ‘optimize’ reproduction
FEEDING TO MAINTAIN REPRODUCTION
• Maintaining reproductive performance requires given
levels of body fat
– No less than 15.8% carcass lipid or 13.5% empty body fat at
parturition
• Can be as low as 12.4% empty body fat at parturition if fed at
130% of NRC energy requirement for 60 days post-partum
– Empty body fat at breeding should be 15% for optimal
pregnancy rates
– Cows should not exceed 20% carcass lipid or 17.8% empty
body fat
• Body weight
– Although NRC publications prior to 1996 used body weight,
most producers don’t weigh cows
– Body weights of pregnant cows can be confounded with
conceptus
USE OF CONDITION SCORING FOR BEEF COWS
• Systems
– 9-point visual system (NRC/Oklahoma)
– 9-point palpation system (Tennessee)
– 5-point visual system (Purdue)
• Limitations
– All systems are subjective
– Different systems make it difficult to standardize relative to
nutrient requirements
• Advantages
– Don’t require weighing of cows
– Less confounded by pregnancy than body weights
– Related to body weight
• Relationship with BW change
– Purdue
– NRC
1 BCS unit change = 68 kg (5-point system)
1 BCS unit change = 50 kg (9-point system)
• Relationship varies with age
– Mature cows 1 BCS unit change = 34 kg (9-point system)
– Primiparous heifers 1 BCS unit change = 68 kg (9 point system)
• Relationship of body condition score to body composition
Component
BCS
Change/BCS (5-point) BCS + BW
Carcass lipid
Carcass protein
Empty body lipid
Empty body protein
Hot carcass weight
Backfat
r
.63
.36
.48
.26
r
.70
.59
.74
.47
.95
.62
5.5-66% units
.2-1% units
.075-.29 cm
• Relationship of BCS from different systems to body lipid
BCS
System
9-pt 5-pt
NRC, 9-pt.
Texas, 9-pt.
Purdue, 5-pt
1
2
3
4
5
6
7
8
9
1
2
3
4
5
3.77
7.54
11.30
Empty body lipid, %
0
4
8
15.07
12
18.89
22.61
26.38
30.15
33.91
16
20
24
28
32
3.1
8.7
14.9
21.5
27.2
• Relationship of body condition score to reproduction
– Body condition score at calving is the primary factor related to
reestablishment of cyclic activity in beef cows
• Cows that calve at BCS > 5 (9-point system) will exhibit estrus
regardless of post-partum nutrition regime
• Feeding extra energy post-partum to cows that calve at BCS < 4 will
increase the percentage of cows exhibiting estrus in a finite
breeding season
Richards (1986)
Days to first estrus
Post-partum
nutrition
<4
High (+.45kg/d) 60
Mod. ( 0 kg/d)
60
Low (-.68 kg/d) 56
L/H (5 kg corn/d 67
14-d before
and through
breeding)
>5
51
46
50
49
Days to conception
Calving BCS
<4
>5
91
84
91
85
88
82
91
87
1st service conception
<4
67
65
54
75
>5
59
67
70
70
Houghton (1990)
(Pre- [last 90 days]) and Post- [through breeding]
energy intake
LL
LH
ML
MH
Parturition
BCS (5-point)
2.5
Empty body lipid 11.9
Post-partum
BCS
2.5
Empty body lipid
11.4
Post-partum interval, d 72.6
Cycling, % (60 days) 33.3
2.7
13.0
3.3
16.8
3.2
16.7
2.8
13.7
54.3
56.3
3.1
16.8
65.7
52.9
3.4
16.7
68.4
54.3
L = 70% NRC
M = Maintenance
H = 130% NRC
All cows started at condition score 3 on 5-point scale at 190 days of
gestation
– While high body condition scores at parturition may decrease
post-partum interval, high condition scores at breeding will
reduce conception rates
Post-partum BCS PPI, d Breeding BCS 1st service conception, %
2+
88.5
2+
100
369.7
394
3
59.4
3
80
3+
51.7
3+
70
430.6
467
Post-partum BCS change (5-point system)
< 3 with decreasing BCS
< 3 with increasing BCS
3 with no change in BCS
> 3 with decreasing BCS
> 3 with increasing BCS
Pregnancy rate, %
69
100
100
94
75
– Relying on post-partum energy supplementation may not be
effective because some breeds respond with greater milk
production
Angus
Braunvieh
Charolais
Gelvieh
Hereford
Limousin
Simmental
Peak milk
kg/kcal ME/BW.75
Intercept Slope
9.4
6.7
.027
6.4
.019
5.8
.030
8.5
6.9
.014
10.9
-
210-day total
kg/kcal ME/BW.75
Intercept Slope
929
3
501
7
568
4
477
6
1,191
-1,387
26
-1,495
30
– Although maximum rebreeding rate and gross return occurs at
condition score 5, maximum weaning rate occurs at condition
score 4.7 and maximum net return occurs at condition score
4.3.
BODY CONDITION SCORE EFFECTS ON
ENERGY RESERVES
• Energy in body condition
Body condition score (5-point system)
Mcal/kg BW change
1
2.57
2
3.82
3
5.06
4
6.32
5
7.57
– The reason for this difference is that weight change at
condition score 1 is 17% fat, but is 77% fat at condition score 5
– Implications
• It takes more energy to increase condition score at a higher condition
score than a lower condition score
• Loss of body condition at a high body condition provides more energy
than loss of body condition at a low body condition score
• Calculation of energy from body reserves
– Body composition from BCS
•
•
•
•
•
•
Proportion of empty body fat = AF = .037683CS
Proportion of empty body protein = AP = .200886 - .0066762CS
Proportion of empty body water = AW = .766637 - .034506CS
Proportion of empty body ash = AA = .078982 - .00438CS
Empty body weight, kg = EBW = .851SBW
Total ash, kg = TA = AA x EBW
– Calculation of total fat and protein reserves
•
•
•
•
•
•
•
•
AA1 = .074602
AF1 = .037683
AP1 = .194208
EBW1, kg = TA/ AA1
Total fat, kg = TF = AF x EBW
Total protein, kg = TP = AP x EBW
Total fat1, kg = TF1 = EBW1 x AF1
Total protein1, kg = TP1 = EBW1 x AP1
– Calculation of mobilizable energy
• Mobilizable fat = FM = TF - TF1
• Mobilizable protein = PM = TP – TP1
• Energy reserves, Mcal = ER = 9.4FM + 5.7PM
– During mobilization
• 1 Mcal ER substitutes for .8 Mcal of NEm
– During repletion
• 1 Mcal NEm will provide 1 Mcal ER
Example 1
•
•
•
•
If a beef cow with a shrunk BW of 485 kg at a BCS 4 has a NEm requirement of 10.46 Mcal/day
is consuming alfalfa hay with a NEm conc of 1.43 Mcal/day at 10.9 kg/d, how long will it take for
this cow to increase to a condition score of 5?
NEm requirement, Mcal/day
= 10.46
NEm fed, Mcal/day
=1.43 x 10.9
= 15.59
NEm excess or deficient, Mcal/day
= fed-reqt
= 5.13
•
•
•
•
•
AF at CS4
AP at CS4
AA at CS4
EBW at CS4
Total ash at any BCS
=.037683 x 4
=.200886-.0066762 x 4
=.078982-.00438 x 4
=.851x485
=EBW x AA
= 0.1507
= 0.1742
= 0.0615
= 412.74
= 25.3675
•
•
•
•
AF at CS5
AP at CS5
AA at CS5
EBW at CS5
=.037683 x 5
=.200886-.0066762 x 5
=.078982-.00438 x 5
=25.3675/.0571
= 0.1884
= 0.1675
= 0.0571
= 444.26
•
•
•
•
Total fat at CS4, kg
Total protein at CS4, kg
Total fat at CS5, kg
Total protein at CS5, kg
=412.74 x .1507
=412.74 x .1742
=444.26 x .1884
=444.26 x .1675
=62.2000
=71.8993
=83.6986
=74.4136
•
•
•
•
Metabolizable fat, kg
Metabolizable protein, kg
Energy reserve needed, Mcal
Days to increase to CS5
=83.6986-62.2000
=74.4136-71.8993
=9.4 x 21.4986 + 5.7 x 2.5143
=216.42 x 1/ 5.13
=21.4986
= 2.5143
=216.42
= 42.19
Example 2
•If a beef cow with a shrunk BW of 485 kg at a BCS 4 has a NEm requirement of 10.46 Mcal/day is
consuming mature bromegrass hay with a NEm conc of 0.94 Mcal/day at 9.7 kg/d, how long will it
take for this cow to decrease to a condition score of 3?
•NEm requirement, Mcal/day
= 10.46
•NEm fed, Mcal/day
=0.94 x 9.7
= 9.12
•NEm excess or deficient, Mcal/day
= fed-reqt
= -1.34
•AF at CS4
•AP at CS4
•AA at CS4
•EBW at CS4
•Total ash at any BCS
=.037683 x 4
=.200886-.0066762 x 4
=.078982-.00438 x 4
=.851x485
=EBW x AA
= 0.1507
= 0.1742
= 0.0615
= 412.74
= 25.3675
•AF at CS3
•AP at CS3
•AA at CS3
•EBW at CS3
=.037683 x 3
=.200886-.0066762 x 3
=.078982-.00438 x 3
=25.3675/.0658
= 0.1130
= 0.1809
= 0.0658
= 385.52
•Total fat at CS4, kg
•Total protein at CS4, kg
•Total fat at CS3, kg
•Total protein at CS3, kg
=412.74 x .1507
=412.74 x .1742
=385.52 x .1130
=385.52 x .1809
=62.2000
=71.8993
=43.5638
=69.7406
•Metabolizable fat, kg
•Metabolizable protein, kg
•Energy reserve lost, Mcal
•Days to decrease to CS3
=43.5638-62.2000
=69.7406-71.8993
=9.4 x 18.6362 + 5.7 x 2.1587
=187.48 x .8/ 1.34
=-18.6362
= -2.1587
=-187.48
= 111.93
Mcal NE required for each CS at CS 5 mature wt of:
Condition score
450
550
650
2
126
154
182
3
141
173
204
4
162
198
235
5
186 227
269
6
217 266
314
7
267
314
371
8
309
378
446
9
377
461
545