Nutrient requirements of cattle vary
widely throughout the year based on several factors:
-
Reproductive stage
-
Weight of the cow
-
Milking ability
-
Weather conditions
The Alliance Nutrition Year-Round
Range Program divides the cow reproductive phases into four stages
(Figure 9 and Table 5).
Figure 9 Brood Cow
Reproductive Phases
Table 5 Yearly Productive Stage for Beef Cows
Stage
|
Length in Days |
|
|
|
1 |
100 |
Weaning to 60
Days Before Calving |
|
|
2 |
60 |
60 Days Before
Calving to Calving |
|
|
3 |
82 |
Calving to End
of Breeding |
|
|
4 |
123 |
End of
Breeding to Weaning |
|
Stages 2 and 3 will typically be
consistent in the number of days during these stages. Stages 1 and
4 can have more variability in number of days based on when calves
are weaned. The nutrient requirements
vary widely among the stages based primarily on fetal growth rate
and lactation levels of the cow at that time (Table 6) and must be
considered when designing a Year-Round Range Program. Cows in
Stage 1 (weaning to 60 days before calving) have the lowest
nutrient requirements followed by Stage 2 (60 days before calving
to calving), making these stages the most cost-effective periods
for increasing body condition score. Increasing body condition
during Stage 3 (calving to breeding) should be avoided due to the
high nutritional requirements of lactation and recovery from
calving. During Stage 4 (end of breeding to weaning), the cow is
typically in a declining lactation phase and nutrient needs are
critical to optimize calf-weaning weights.
Net Energy Needs Adjustments
Table 6 takes into account such
factors as stage of production, weight, and lactation on the
nutritional requirements of cows. One factor not addressed in
Table 6 is the effect of weather on nutrient requirements.
Cattle perform best when the temperature is within their
thermoneutral zone, neither too hot nor cold. Table 7 shows the
critical temperatures (temperature below which they need to burn
energy to maintain body temperature) for cattle with Table 8
showing the adjustments needed to dietary net energy for
maintenance (NEm) to compensate for cold weather.
Table 7 Estimated
Lower Critical Temperatures for Beef Cattle
Coat Description
|
Critical Temperature |
|
Summer Coat or
Wet |
59°F |
|
Dry Fall Coat |
45°F |
|
Dry Winter
Coat |
32°F |
|
Dry Heavy
Winter Coat |
18°F |
Source: Kansas
State University
Table 8 Increased
NEm Requirement for Cattle Per Degree (F) Coldness Below Critical
Temperature
|
|
Cow Weight (lb) |
|
|
1000 |
1100 |
1200 |
1300 |
|
|
Percentage
Increase in NEm per Degree Coldness |
|
Summer Coat or
Wet |
2.0 |
2.0 |
1.9 |
1.9 |
|
Dry Fall Coat |
1.4 |
1.3 |
1.3 |
1.3 |
|
Dry Winter
Coat |
1.1 |
1.0 |
1.0 |
1.0 |
|
Dry Heavy
Winter Coat |
0.7 |
0.7 |
0.6 |
0.6 |
Source: Ames,
Kansas State University
Example:
Determining Net Energy Needs
(Use Tables 6, 7, and 8 to
determine net energy needs.)
-
1200 lb cow with dry winter coat;
temperature is 20º F and dry.
-
Table 7 shows the dry winter coat
critical temperature of 32º F.
-
Actual temperature is 20º F, 12º
below critical temperature.
-
Use the “winter coat” line in Table
8 and appropriate body weight (1200 lb), multiply 12 (degrees
below critical temperature) x 1.0 (percentage increase in NEm
per degree coldness).
-
Increase the NEm requirements by
12%.
-
Using Table 6, locate the stage and
NEm requirements for the stage the cow is in.
-
If the 1200 lb cow is in Stage 4
producing 20 lb of milk, the NEm is 12.22 Mcal/day. Multiply the
NEm by the increase in NEm requirement to obtain NEm for colder
weather: 12.22 x 1.12 = 13.69 Mcal/day meets the NEm
requirements.
The net energy system can also be used
to increase weight and BCS of cows. Table 9 shows the net energy
for maintenance, fetal growth (NEc), and lactation (NEl) of mature
beef cows. Table 10 (NEg Required for Cows of Differing BCS) can
be used in conjunction with Table 9 in the following manner to
determine NEm and NEg requirements to increase BCS:
Assumptions:
-
1000 lb cow
-
80 days to calving
-
Current BCS 3
-
Desired BCS 5
Application
-
NEm: 8.13 + 7.86 ÷ 2 = 8.00 Mcal/day
(Table 9 average of 1050 lb and 1100 lb cow)
-
NEc: 2.15 Mcal/day (Table 9)
-
NEl: 0 x 0.34 Mcal/lb milk
(Table 9 - non-lactating)
-
Total: 10.15 Mcal/day (NEm + NEc
+ NEl)
Diet Formulation
Table 9 NEm, NEc,
NEl Requirements of Mature Beef Cows
|
|
Cow Weight, lb
|
|
|
1000 |
1050 |
1100 |
1150 |
1200 |
1250 |
1300 |
1350 |
1400 |
|
NEm |
7.57 |
7.86 |
8.13 |
8.41 |
8.68 |
8.95 |
9.22 |
9.48 |
9.75 |
|
NEc |
2.15 Mcal/day
for a birth weight of 80 lb or 2.7 Mcal/day for a 95-100 lb
birth weight |
|
NEl |
0.34 Mcal/lb
of Milk |
Adapted from
Kansas State University (Wiltbank, 1982)
Table 10 NEg for
Cows of Different Body Condition Score
|
|
Desired Body Condition Score |
|
|
2 |
3-4 |
5 |
6-7 |
8 |
|
Current BCS |
NEg Mcal/lb of Weight Gain
|
|
2 |
1.17 |
1.45 |
1.74 |
2.02 |
2.31 |
|
3-4 |
|
1.73 |
2.02 |
2.30 |
2.59 |
|
5 |
|
|
2.30 |
2.59 |
2.87 |
|
6-7 |
|
|
|
2.87 |
3.16 |
|
8 |
|
|
|
|
3.44 |
Summary
Adjusting
the ration to take into account adverse weather, forage intake
based on forage quality, and desired body condition score of the
animal is critical to achieve the desired feeding objectives.
Ration adjustments for these factors has typically been made based
on forage TDN calculations. Research indicates adjusting for these
factors is better accomplished by utilizing energy mega-calories
instead of pounds of TDN.
By
determining forage intake and analyzing forage for nutrient
content, producers can make accurate assessments of
supplementation needs – eliminating costly over- and
under-supplementation. The result of a carefully planned
Year-Round Range Program is more efficient utilization of
available forage and maintenance of brood cows in moderate body
condition, which leads to optimum production.
See Calculating Nutrient
Requirements and Determining Supplementation Needs
