A modeling study evaluated the effects of milk production level on nutrient balance in March-and May-calving cows grazing Sandhills upland range during the breeding season. Forage quality of upland range peaks in June and steadily declines in July until November. In March-calving cows, metabolizable protein (MP) and energy were deficient by July 1 in all milking potential cows, which is exacerbated in greater milking potential cows. May-calving cows with 20 to 30 lbs of milk are predicted to enter the breeding season with a deficiency in MP and energy. In an effort to match cow type to environment in the Sandhills, producers should be selecting against high milk potential. With timing of forage quality decline and the start of breeding season in July, selecting for moderation in milk production becomes even more important in May-calving herds. Supplementation to meet MP deficiency with high ruminally undegradable protein supplements may be need in later breeding cows and younger cows in both March-and May-herds

Adams, Don C.

Mulliniks, Travis

English

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Nebraska Beef Cattle Reports Animal Science Department
2019
Evaluation of Lactation Demands on Nutrient
Balance in Two Calving Seasons in Range Cows
Grazing Sandhills Upland Range
Travis Mulliniks
University of Nebraska - Lincoln, travis.mulliniks@unl.edu
Don C. Adams
University of Nebraska - Lincoln, don.adams@unl.edu
Follow this and additional works at: http://digitalcommons.unl.edu/animalscinbcr
Part of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, and
the Veterinary Preventive Medicine, Epidemiology, and Public Health Commons
This Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It has
been accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.
Mulliniks, Travis and Adams, Don C., "Evaluation of Lactation Demands on Nutrient Balance in Two Calving Seasons in Range Cows
Grazing Sandhills Upland Range" (2019). Nebraska Beef Cattle Reports. 1043.
http://digitalcommons.unl.edu/animalscinbcr/1043
2019 Nebraska Beef Cattle Report · 21 
©  The Board Regents of the University of  
Nebraska. All rights reserved.
freeze- dried, ground, and analyzed for 
CP, in vitro dry matter digestibility, NDF, 
and ADF. Using the NRC model (NRC, 
2010), net energy for maintenance, rumen 
degradable protein (RDP), and metabo-
lizable protein balances were predicted for 
a March- and May- calving cow grazing 
Sandhills upland range during the breeding 
season. The nutrient values in the diet sam-
ples used in these analyses and the intake 
values used differ from those in another 
report (2019 Nebraska Beef Cattle Report, 
pp. 50–52). The primary differences are in 
diet TDN contents and estimated intake. 
These 2 factors tend to compensate across 
the 2 reports and estimate similar intakes of 
energy and protein.
Assumptions for the model were:
1. Cow body weight = 1200 lb
2. Body condition score = 5.0
3. Cow age = 48 months
4. Peak milk production = 20, 22, 24, 
26, 28, or 30 lb
5. Estimates of dry matter intake were 
based on NRC model estimations
6. No additional supplementation was 
included in any calculation
J. Travis Mulliniks
Don C. Adams
Summary with Implications
A modeling study evaluated the effects 
of milk production level on nutrient balance 
in March- and May- calving cows grazing 
Sandhills upland range during the breeding 
season. Forage quality of upland range peaks 
in June and steadily declines in July until 
November. In March- calving cows, metaboliz-
able protein (MP) and energy were deficient 
by July 1 in all milking potential cows, which 
is exacerbated in greater milking potential 
cows. May- calving cows with 20 to 30 lbs 
of milk are predicted to enter the breeding 
season with a deficiency in MP and energy. In 
an effort to match cow type to environment 
in the Sandhills, producers should be selecting 
against high milk potential. With timing of 
forage quality decline and the start of breeding 
season in July, selecting for moderation in 
milk production becomes even more import-
ant in May- calving herds. Supplementation 
to meet MP deficiency with high ruminally 
undegradable protein supplements may be 
need in later breeding cows and younger cows 
in both March- and May- herds.
Introduction
Selection for growth- oriented traits 
has been a focus in the beef industry in 
effort to maximize output. In doing so, 
cow- calf producers have tended to select for 
short- term traits such as growth and milk 
yield to increase weaning weights of calves 
for the potential to increase profitability. 
However, the economic value of repro-
duction is reported to be 5 times greater 
than growth or milk traits in beef cattle. 
Matching cow type or genetic potential 
to the production environment is and 
will be more important as cost of produc-
tion increases. The continual increase in 
Evaluation of Lactation Demands on Nutrient Balance in Two  
Calving Seasons in Range Cows Grazing Sandhills Upland Range
selection for milk production has resulted 
in range beef cows that are under greater 
nutritional stress in critical physiological 
periods, such as early lactation, that may 
ultimately reduce reproduction. Even in 
high feed quality environments, reproduc-
tion can be decreased in mature beef cows 
when peak milk production is greater than 
20 lb per day. In addition, when selection 
of production traits exceed the capacity of 
the production environment, production 
efficiency decreases. With that in mind, 
increasing efficiency of livestock grazing 
range or pasture settings has to be focused 
on managing and selecting animals that fit 
their given environment and management. 
Therefore, the objectives of this study were 
to demonstrate nutrient balance of lactation 
in both March- and May- calving cows graz-
ing Sandhills upland range with 20 to 30 lb 
of milk potential at peak lactation.
Procedure
Native range diets for this model were 
collected using esophageally- fistulated cows 
at the University of Nebraska’s Gudmund-
sen Sandhills Laboratory (1997 Nebraska 
Beef Cattle Report, pp. 3– 5). Samples were 
Figure 1. Laboratory analysis of range diet samples collected at Gudmundsen Sandhills Laboratory 
(Adapted from 1997 Nebraska Beef Report, pp 3– 5).
22 · 2019 Nebraska Beef Cattle Report
date has been utilized to match nutrient 
requirement of genetic potential for milk 
production with the greatest nutrient value 
of the forage. Figure 1 illustrates the season-
al changes in crude protein and digestibility 
for esophageal diet samples collected from 
upland native range pastures at Gudmund-
sen Sandhills Laboratory. Peak CP and 
digestibility occurs in June, which occurs 
this increase in production costs. This 
increases the need for producers to match 
cow size and milk production potential to 
forage resources in order to optimize forage 
utilization and reproductive efficiency. 
Matching nutrient availability of range 
with nutrient requirements of the cow has 
been recommended to efficiently utilize 
forage quality. In doing so, changing calving 
7. Breeding season started on June 1 for 
March- calving herd and July 20th for 
May- calving herd.
Results
Profit- motivated cow/calf operations 
must become more cost efficient to offset 
Figure 3. Evaluation of NEm (top graph), metabolizable protein (middle graph), 
and rumen degradable protein (bottom graph) balances for May- calving cow 
with milk production ranging from 20 to 30 lb of milk at peak lactation while 
grazing Sandhills upland range with a July 20th start of breeding date.
Figure 2. Evaluation of NEm (top graph), metabolizable protein (mid-
dle graph), and rumen degradable protein (bottom graph) balances for 
March- calving cow with milk production ranging from 20 to 30 lb of milk 
at peak lactation while grazing Sandhills upland range with a June 1st start of 
breeding date.
2019 Nebraska Beef Cattle Report · 23 
Moving cows from a spring- calving herd 
to a summer- calving herd matches calving 
date with increased quality forage to reduce 
feed costs compared to spring calving herds 
(2001 Nebraska Beef Cattle Report, pp. 8– 9). 
However, due to the sharp decline in nutrient 
requirement at peak lactation (approximately 
60 days postpartum) and during the breed-
ing season, milk potential of the cowherd 
may have to decline as well to match the 
environment as shown with the greater 
nutritional deficit during breeding from 
20 to 30 lbs of milk. In addition, drought 
conditions could exacerbate the deficiency 
in MP and energy in greater milk producing 
cows if forage conditions decline. Although, 
moving calving to a May- calving season may 
decrease winter feed cost, due to the forage 
quality during breeding, supplemental inputs 
during the breeding season may be greater in 
May- calving herds, especially in young range 
cows, to optimize pregnancy rates.
With current trends of selecting for in-
creased output- oriented traits in purebred 
and commercial herds in the US, average 
milk production at peak lactation has 
increased in the mid to high 20 lb. The con-
tinual increase in selection for milk produc-
tion in beef cows increases the nutritional 
stress in critical physiological periods, 
such as early lactation, and will ultimately 
reduce reproductive traits and/or increase 
production costs to maintain performance. 
This modeled dataset illustrates the need 
for future research focused on cow type (i.e. 
genetic potential for milk production) with-
in timing of calving to optimize cow herd 
production in the Nebraska Sandhills.
J. Travis Mulliniks, assistant professor, West 
Central Research and Extension Center, 
North Platte
Don C. Adams, emeriti professor, West 
Central Research and Extension Center, 
North Platte
are still growing and lactating with their 
first or second calf may drop out of the herd 
sooner in a May season due to decreased 
energy intake and reduced pregnancy 
rates. For instance, previous research has 
illustrated that pregnancy rates in mature 
cows from March or May- calving herd are 
similar (2001 Nebraska Beef Cattle Report, 
pp 8– 9); however, pregnancy rates in May- 
calving heifers are decreased compared to 
March- calving heifers (2017 Nebraska Beef 
Cattle Report, pp 8– 10). This may be par-
tially due to an imbalance of milk produc-
tion and environmental condition.
Conclusion
In general using the UNL diet mod-
el, the NRC predicted that a lactating 
March- and May- calving cow would not 
be deficient in RDP during the entire breed-
ing season. In March- calving herds, the 
deficiency in MP and NEm occurred after 
30 days of breeding when milk production 
was above 24 lb per day, which may create 
a situation that if cows don’t get bred early 
then reproductive performance may decline 
as the breeding season progresses. In May- 
calving herds, lactating cows were deficient 
in MP and NEm during the breeding 
season. Summer calving cows With RDP 
requirements in surplus during the breed-
ing season and as milk potential increases, 
there is a greater demand to supply supple-
mentation that would meet the energy and 
MP deficit. Supplementation with a high 
RUP supplement with added energy such 
as distillers grains may still be needed in 
young cows to meet the deficiency in MP. 
Supplements high in RDP will likely not 
correct the MP and energy deficiencies. In 
addition, complementary forage systems 
(i.e., regrowth sub- irrigated meadow) may 
be utilized to increase performance in 
young range cows.
with the onset of the breeding season for 
a March- calving herd. As the season pro-
gresses, CP and digestibility decline until 
November.
March- calving Results
At the start of breeding in the March- 
calving herd, cows across all milking poten-
tial levels are predicted to be in a positive 
energy, MP and RDP balances. For all milk 
production levels, RDP was predicted to 
be in excess of requirements with RDP 
balance plateauing in the second week of 
July. As the breeding season progressing in 
June and July, both with energy (NEm) and 
MP balances are linearly decreasing across 
milking levels. Cows milking in excess of 28 
lb of milk at peak lactation are in a negative 
energy balance by June 11th. By July 1st, 
all cows are predicted to be in a negative 
energy balance. With negative energy bal-
ance projected to occur within the first 30 
days of the breeding season, reproductive 
performance may decline in cows that did 
not conceive early in the breeding season. 
Similar to NEm by July 1st, cows milking 26 
lb or more at peak lactation would be in a 
deficit MP balance. By the end of breeding, 
only cows milking 20 lb of milk at peak 
were in a positive MP balance.
May- calving Results
Similar to March- calving herds, RDP 
balance was in excess and was predicted to 
be from 140 to 180 g/d above requirements 
during the entire breeding season. Howev-
er, both NEm and MP balances were in a 
deficit at the start of breeding. Coming into 
the breeding season in a negative energy 
balance creates a scenario that cows have 
to have the ability to mobilize and utilize 
stored body fat effectively to reproduce. The 
energy and MP deficient puts more stress 
on younger, lactating cows. Young cows that 


Evaluation of Lactation Demands on Nutrient Balance in Two
Calving Seasons in Range Cows Grazing Sandhills Upland Range

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnNebraska Beef Cattle Reports Animal Science Department2019Evaluation of Lactation Demands on NutrientBalance in Two Calving Seasons in Range CowsGrazing Sandhills Upland RangeTravis MulliniksUniversity of Nebraska - Lincoln, travis.mulliniks@unl.eduDon C. AdamsUniversity of Nebraska - Lincoln, don.adams@unl.eduFollow this and additional works at: http://digitalcommons.unl.edu/animalscinbcrPart of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, andthe Veterinary Preventive Medicine, Epidemiology, and Public Health CommonsThis Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It hasbeen accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.Mulliniks, Travis and Adams, Don C., "Evaluation of Lactation Demands on Nutrient Balance in Two Calving Seasons in Range CowsGrazing Sandhills Upland Range" (2019). Nebraska Beef Cattle Reports. 1043.http://digitalcommons.unl.edu/animalscinbcr/10432019 Nebraska Beef Cattle Report · 21 ©  The Board Regents of the University of  Nebraska. All rights reserved.freeze- dried, ground, and analyzed for CP, in vitro dry matter digestibility, NDF, and ADF. Using the NRC model (NRC, 2010), net energy for maintenance, rumen degradable protein (RDP), and metabo-lizable protein balances were predicted for a March- and May- calving cow grazing Sandhills upland range during the breeding season. The nutrient values in the diet sam-ples used in these analyses and the intake values used differ from those in another report (2019 Nebraska Beef Cattle Report, pp. 50–52). The primary differences are in diet TDN contents and estimated intake. These 2 factors tend to compensate across the 2 reports and estimate similar intakes of energy and protein.Assumptions for the model were:1. Cow body weight = 1200 lb2. Body condition score = 5.03. Cow age = 48 months4. Peak milk production = 20, 22, 24, 26, 28, or 30 lb5. Estimates of dry matter intake were based on NRC model estimations6. No additional supplementation was included in any calculationJ. Travis MulliniksDon C. AdamsSummary with ImplicationsA modeling study evaluated the effects of milk production level on nutrient balance in March- and May- calving cows grazing Sandhills upland range during the breeding season. Forage quality of upland range peaks in June and steadily declines in July until November. In March- calving cows, metaboliz-able protein (MP) and energy were deficient by July 1 in all milking potential cows, which is exacerbated in greater milking potential cows. May- calving cows with 20 to 30 lbs of milk are predicted to enter the breeding season with a deficiency in MP and energy. In an effort to match cow type to environment in the Sandhills, producers should be selecting against high milk potential. With timing of forage quality decline and the start of breeding season in July, selecting for moderation in milk production becomes even more import-ant in May- calving herds. Supplementation to meet MP deficiency with high ruminally undegradable protein supplements may be need in later breeding cows and younger cows in both March- and May- herds.IntroductionSelection for growth- oriented traits has been a focus in the beef industry in effort to maximize output. In doing so, cow- calf producers have tended to select for short- term traits such as growth and milk yield to increase weaning weights of calves for the potential to increase profitability. However, the economic value of repro-duction is reported to be 5 times greater than growth or milk traits in beef cattle. Matching cow type or genetic potential to the production environment is and will be more important as cost of produc-tion increases. The continual increase in Evaluation of Lactation Demands on Nutrient Balance in Two  Calving Seasons in Range Cows Grazing Sandhills Upland Rangeselection for milk production has resulted in range beef cows that are under greater nutritional stress in critical physiological periods, such as early lactation, that may ultimately reduce reproduction. Even in high feed quality environments, reproduc-tion can be decreased in mature beef cows when peak milk production is greater than 20 lb per day. In addition, when selection of production traits exceed the capacity of the production environment, production efficiency decreases. With that in mind, increasing efficiency of livestock grazing range or pasture settings has to be focused on managing and selecting animals that fit their given environment and management. Therefore, the objectives of this study were to demonstrate nutrient balance of lactation in both March- and May- calving cows graz-ing Sandhills upland range with 20 to 30 lb of milk potential at peak lactation.ProcedureNative range diets for this model were collected using esophageally- fistulated cows at the University of Nebraska’s Gudmund-sen Sandhills Laboratory (1997 Nebraska Beef Cattle Report, pp. 3– 5). Samples were Figure 1. Laboratory analysis of range diet samples collected at Gudmundsen Sandhills Laboratory (Adapted from 1997 Nebraska Beef Report, pp 3– 5).22 · 2019 Nebraska Beef Cattle Reportdate has been utilized to match nutrient requirement of genetic potential for milk production with the greatest nutrient value of the forage. Figure 1 illustrates the season-al changes in crude protein and digestibility for esophageal diet samples collected from upland native range pastures at Gudmund-sen Sandhills Laboratory. Peak CP and digestibility occurs in June, which occurs this increase in production costs. This increases the need for producers to match cow size and milk production potential to forage resources in order to optimize forage utilization and reproductive efficiency. Matching nutrient availability of range with nutrient requirements of the cow has been recommended to efficiently utilize forage quality. In doing so, changing calving 7. Breeding season started on June 1 for March- calving herd and July 20th for May- calving herd.ResultsProfit- motivated cow/calf operations must become more cost efficient to offset Figure 3. Evaluation of NEm (top graph), metabolizable protein (middle graph), and rumen degradable protein (bottom graph) balances for May- calving cow with milk production ranging from 20 to 30 lb of milk at peak lactation while grazing Sandhills upland range with a July 20th start of breeding date.Figure 2. Evaluation of NEm (top graph), metabolizable protein (mid-dle graph), and rumen degradable protein (bottom graph) balances for March- calving cow with milk production ranging from 20 to 30 lb of milk at peak lactation while grazing Sandhills upland range with a June 1st start of breeding date.2019 Nebraska Beef Cattle Report · 23 Moving cows from a spring- calving herd to a summer- calving herd matches calving date with increased quality forage to reduce feed costs compared to spring calving herds (2001 Nebraska Beef Cattle Report, pp. 8– 9). However, due to the sharp decline in nutrient requirement at peak lactation (approximately 60 days postpartum) and during the breed-ing season, milk potential of the cowherd may have to decline as well to match the environment as shown with the greater nutritional deficit during breeding from 20 to 30 lbs of milk. In addition, drought conditions could exacerbate the deficiency in MP and energy in greater milk producing cows if forage conditions decline. Although, moving calving to a May- calving season may decrease winter feed cost, due to the forage quality during breeding, supplemental inputs during the breeding season may be greater in May- calving herds, especially in young range cows, to optimize pregnancy rates.With current trends of selecting for in-creased output- oriented traits in purebred and commercial herds in the US, average milk production at peak lactation has increased in the mid to high 20 lb. The con-tinual increase in selection for milk produc-tion in beef cows increases the nutritional stress in critical physiological periods, such as early lactation, and will ultimately reduce reproductive traits and/or increase production costs to maintain performance. This modeled dataset illustrates the need for future research focused on cow type (i.e. genetic potential for milk production) with-in timing of calving to optimize cow herd production in the Nebraska Sandhills.J. Travis Mulliniks, assistant professor, West Central Research and Extension Center, North PlatteDon C. Adams, emeriti professor, West Central Research and Extension Center, North Platteare still growing and lactating with their first or second calf may drop out of the herd sooner in a May season due to decreased energy intake and reduced pregnancy rates. For instance, previous research has illustrated that pregnancy rates in mature cows from March or May- calving herd are similar (2001 Nebraska Beef Cattle Report, pp 8– 9); however, pregnancy rates in May- calving heifers are decreased compared to March- calving heifers (2017 Nebraska Beef Cattle Report, pp 8– 10). This may be par-tially due to an imbalance of milk produc-tion and environmental condition.ConclusionIn general using the UNL diet mod-el, the NRC predicted that a lactating March- and May- calving cow would not be deficient in RDP during the entire breed-ing season. In March- calving herds, the deficiency in MP and NEm occurred after 30 days of breeding when milk production was above 24 lb per day, which may create a situation that if cows don’t get bred early then reproductive performance may decline as the breeding season progresses. In May- calving herds, lactating cows were deficient in MP and NEm during the breeding season. Summer calving cows With RDP requirements in surplus during the breed-ing season and as milk potential increases, there is a greater demand to supply supple-mentation that would meet the energy and MP deficit. Supplementation with a high RUP supplement with added energy such as distillers grains may still be needed in young cows to meet the deficiency in MP. Supplements high in RDP will likely not correct the MP and energy deficiencies. In addition, complementary forage systems (i.e., regrowth sub- irrigated meadow) may be utilized to increase performance in young range cows.with the onset of the breeding season for a March- calving herd. As the season pro-gresses, CP and digestibility decline until November.March- calving ResultsAt the start of breeding in the March- calving herd, cows across all milking poten-tial levels are predicted to be in a positive energy, MP and RDP balances. For all milk production levels, RDP was predicted to be in excess of requirements with RDP balance plateauing in the second week of July. As the breeding season progressing in June and July, both with energy (NEm) and MP balances are linearly decreasing across milking levels. Cows milking in excess of 28 lb of milk at peak lactation are in a negative energy balance by June 11th. By July 1st, all cows are predicted to be in a negative energy balance. With negative energy bal-ance projected to occur within the first 30 days of the breeding season, reproductive performance may decline in cows that did not conceive early in the breeding season. Similar to NEm by July 1st, cows milking 26 lb or more at peak lactation would be in a deficit MP balance. By the end of breeding, only cows milking 20 lb of milk at peak were in a positive MP balance.May- calving ResultsSimilar to March- calving herds, RDP balance was in excess and was predicted to be from 140 to 180 g/d above requirements during the entire breeding season. Howev-er, both NEm and MP balances were in a deficit at the start of breeding. Coming into the breeding season in a negative energy balance creates a scenario that cows have to have the ability to mobilize and utilize stored body fat effectively to reproduce. The energy and MP deficient puts more stress on younger, lactating cows. Young cows that 

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Evaluation of Lactation Demands on Nutrient Balance in Two Calving Seasons in Range Cows Grazing Sandhills Upland Range

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