Iowa State University, McNay Memorial Research and Demonstration Farm ISRF00-35
Evaluation of Year-round Forage Management Systems for Spring- and Fall-Calving Beef Cows
N. A. Janovick, graduate assistant in animal
science,
J. R. Russell, professor of animal science,
D. Maxwell, beef herdsman, McNay Research
and Demonstration Farm, and
L. J. Secor, superintendent, McNay Research
and Demonstration Farm
Introduction
Stored feeds make up almost half the cost of
production for cow-calf enterprises in Iowa.
Therefore, any reduction in the amount of stored
feeds needed to maintain cows through the
winter can have an impact on overall costs of
maintaining the herd. Two resources that may
be used to reduce the use of stored feeds are
corn crop residues and stockpiled perennial
forages, which may be grazed during the winter.
The objective of this experiment was to design
and evaluate grazing systems to utilize such
resources.
Materials and Methods
A year-round grazing system for spring- and
fall-calving cows was developed to compare
animal production and performance, hay
production and feeding, winter forage
composition changes, and summer pasture yield
and nutrient composition with that from a
conventional, or minimal land system. Systems
compared forage from smooth bromegrassorchardgrass-
birdsfoot trefoil pastures for both
systems in the summer and corn crop residues
and stockpiled grass-legume pastures for the
year-round system to drylot hay feeding during
winter for the minimal land system. The yearround
grazing system utilized 1.67 acres of
smooth bromegrass-orchardgrass-birdsfoot
trefoil (SB-O-T) pasture per cow in the summer,
compared with 3.33 acres of SB-O-T pasture per
cow in the control (minimal land) system. In
addition to SB-O-T pastures, the year-round
grazing system utilized 2.5 acres of tall fescuered
clover (TF-RC) and 2.5 acres of smooth
bromegrass-red clover (SB-RC) per cow for
grazing in both mid-summer and winter for falland
spring-calving cows, respectively. Firstcutting
hay was harvested from the TF-RC and
SB-RC pastures, and regrowth was grazed for
approximately 45 days in the summer. These
pastures were then fertilized with 40 lbs N/acre
and stockpiled for winter grazing. Springcalving
cows in the year-round grazing system
also grazed corn crop residue (CCR) pastures at
an allowance of 2.5 acres per cow in late fall. In
the minimal land system, hay was harvested
from three-fourths of the area in SB-O-T
pastures and stored for feeding in a drylot
through the winter. Hay was supplemented
when the average condition score of springcalving
cows dropped below 5, the condition
score of half of the fall-calving cows dropped to
3 or forage allowance was limited by forage
mass or weather conditions. Summer grazing
was managed with rotational stocking for both
systems, and winter grazing of stockpiled
forages and corn crop residues by year-round
system cows was managed by strip-stocking.
Results and Discussion
There were no significant differences in hay
production between systems for year 1;
however, the amounts of hay needed to maintain
cows were 923, 1,373, and 4,732 lbs dry
matter/cow for year-round fall-calving, yearround
spring-calving, and minimal land springcalving
cows, respectively (Table 1). In year 2,
hay production per acre in the minimal land
system was greater (P<.05) than for the yearround
system, but the amounts of hay required
per cow were 0, 0, and 4,720 lbs dry matter/cow
for year-round fall-calving, year-round springcalving,
and minimal land spring-calving cows,
respectively.
Iowa State University, McNay Memorial Research and Demonstration Farm ISRF00-35
Average daily gains of fall calves in the yearround
system were 1.9 lbs/day compared with
weight gains of 2.5 lbs/day for spring calves
from both systems (Table 2). Yearly growing
animal production from pastures for both years
did not differ between systems when weight
gains of stockers that grazed summer pastures in
the year-round grazing system were added to
weight gains of suckling calves.
Acknowledgments
This project was funded, in part, by a grant from
the Leopold Center for sustainable Agriculture,
Iowa State University, Ames, IA. Special thanks
go to animal caretakers at the McNay Research
and Demonstration farm, and graduate and
undergraduate research assistants in our
research group.
Table 1. Year 1 and 2 hay production, feeding and balance for the year-round and minimal land systems.
System
Year-round Minimal land
Fall-calving Spring-calving System mean
Year 1
Hay production,
lb/harvested acc 1598 2035 1817 1171
lb/cow 3995 5088 4541 2926
Hay fed, lb/cow 923x 1373y 1148a 4732b
Hay balance, lb/cow 3071 3714 3393a -1805b
Year 2
Hay production,
lb/harvested acc 1481 1907 1694a 2883b
lb/cow 3703 4768 4236a 7206b
Hay fed, lb/cow 0 0 0a 4720b
Hay balance, lb/cow 3703 4768 4236 2486
abDifferences between means of systems with different superscripts are significant, P<.05.
xyDifferences between means of systems with different superscripts are significant, P<.05.
cHay was harvested from tall fescue-red clover and smooth bromegrass-red clover fields from 2.5 ac/cow for fall- and
spring-calving cows in the year-round grazing system and from smooth bromegrass-orchardgrass-birdsfoot trefoil
pastures at 1.67 ac/cow for spring-calving cows in the ML system.
Table 2. Birth weights, weaning weights, average daily gains, and growing animal production for calves and
stockers in both the minimal land and year-round grazing systems.
System
Year-round grazing Minimal land
Fall Calves Spring calves Spring calves
Birth weights, lbs
Year 1 -- 93.9 96.1
Year 2 100.4a 93.5 90.6b
Weaning weights, lbs
Year 1 415.4 498.7 480.7
Year 2 468.8 544.9 548.9
Average daily gain, lb/day
Year 1 1.8a 2.6b 2.5b
Year 2 2.0a 2.4b 2.5b
Total growing animal production, lb/ac
perennial pasturec Year-round grazing Minimal land
Year 1 115.5
Year 2
107.7
134.5 137.5
abDifferences between means with different superscripts are significant, P<.05.
cYear-round grazing system, 4.2 acres of perennial pasture per cow and 1.25 acres of cornstalks per cow. Minimal land
system, 3.3 acres of perennial pasture per cow. There was no significant difference between systems in total lb/acre
production, P>.05.