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J. Anim. Sci. 2004. 82:2503-2515
© 2004 American Society of Animal Science

ANIMAL PRODUCTION

Productivity and hay requirements of beef cattle in a Midwestern year-round grazing system1,2

N. A. Janovick3, J. R. Russell4, D. R. Strohbehn and D. G. Morrical

Department of Animal Science, Iowa State University, Ames 50011


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Literature Cited
 
Our objective was to evaluate a replicated (n = 2) Midwestern year-round grazing system’s hay needs and animal production compared with a replicated (n = 2) conventional (minimal land) system over 3 yr. Because extended grazing systems have decreased hay needs for the beef herd, it was hypothesized that this year-round system would decrease hay needs without penalizing animal production. In the minimal land (ML) system, two replicated 8.1-ha smooth bromegrass-orchardgrass-birdsfoot trefoil (SB-OG-BFT) pastures were rotationally stocked with six mature April-calving cows and calves and harvested as hay for winter feeding in a drylot. After weaning, calves were finished on a high-concentrate diet. Six mature April-calving cows, six mature August-calving cows, and their calves were used in the year-round (YR) grazing system. During the early and late summer, cattle grazed two replicated 8.1-ha SB-OG-BFT pastures by rotational stocking. In mid-summer and winter, April- and August-calving cows grazed two replicated 6.1-ha, endophyte-free tall fescue-red clover (TF-RC) and smooth bromegrass-red clover (SB-RC) pastures, respectively, by strip-stocking. In late autumn, spring-calving cows grazed 6.1-ha corn crop residue fields by strip-stocking. Calves were fed hay with corn gluten feed or corn grain over winter and used as stocker cattle to graze SB-OG-BFT pastures with cows until early August the following summer. First-harvest forage from the TF-RC and SB-RC pastures was harvested as hay. Body condition scores of April-calving cows did not differ between grazing systems, but were lower (P ≤ 0.03) than those of August-calving cows from mid-gestation through breeding. Preweaning calf BW gains were 47 kg/ha of perennial pasture (P < 0.01) and 32 kg/cow (P = 0.01) lower in the YR grazing system than in the ML system. Total BW gains of preweaning calf and grazing stocker cattle were 12 kg/ha of perennial pasture less (P = 0.07), but 27 kg/cow greater (P = 0.02) in pastures in the YR grazing system than in the ML system. Amounts of hay fed to cows in the ML system were 1,701 kg DM/cow and 896 kg DM/cow-stocker pair greater (P < 0.05) than in the YR grazing system. Extended grazing systems in the Midwest that include grazing of stocker cattle to utilize excess forage growth will decrease stored feed needs, while maintaining growing animal production per cow in April- and August-calving herds.

Key Words: Beef Cows • Grazing • Rotational Stocking • Stockpiled Forage


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Literature Cited
 
Extending the grazing season by utilizing crop residues and/or stockpiled perennial forages in the fall and winter has reduced the amounts of hay required for winter feeding of beef cattle (Adams et al., 1994Go; Hitz and Russell, 1998Go; Hersom, 1999Go). Such systems must match cattle nutrient needs with the quantity and quality of forage available (Adams et al., 1996Go). Grazing of stocker cattle may complement extended grazing of beef cows by controlling excess spring forage growth associated with cool season species and utilizing the added pasture area needed in a stockpiled grazing system (Allen et al., 1992aGo, Hersom, 1999Go; Allen et al., 2000Go). However, this practice has the additional costs associated with the purchase or retention of the stocker cattle.

Nutrient requirements of cows are cyclic and depend on the physiological state of the cows (NRC, 1996Go). Therefore, the nutrient requirements of fall- and spring-calving herds may complement each other in a grazing system. Furthermore, the use of fall-calving herds has maximized the amount of weaned calf produced per cow (Bagley et al., 1987aGo,bGo), and decreased the area of summer rangeland needed to maintain these herds (Simms and Bailey, 1995Go). Extended grazing systems have been developed and evaluated for spring-calving herds (Allen et al., 1992bGo; Adams et al., 1994Go; Willms et al., 1998Go), but few studies have evaluated the use of extended grazing systems for fall-calving herds. The objectives of this experiment were to compare animal production and annual hay needs of April- and August-calving beef cows in a year-round grazing system to a conventional system of grazing and hay feeding for April-calving cows at land allowances adjusted to balance the amounts of hay harvested and fed to cattle in each system.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Literature Cited
 
Pastures
All protocols were reviewed and approved by the Institutional Animal Care and Use Committee at Iowa State University. A 3-yr grazing experiment was conducted from November, 1998, through October, 2001, using the following: two 6.1-ha smooth bromegrass (Bromus inermis var. Barton)-red clover (Trifolium pratens var. Arlington) pastures, two 6.1-ha endophyte-free tall fescue (Festuca arundinacea var. Johnstone)-red clover pastures, two 6.1-ha corn (Zea mays) crop residue fields, and four 8.1-ha smooth bromegrass-orchardgrass (Dactylis glomerata var. Napier)-birdsfoot trefoil (Lotus corniculatus var. Norcen) pastures at the McNay Research and Demonstration Farm near Chariton, IA. These pastures had been established in 1988 through 1992 and were used in previous grazing experiments (Hitz and Russell, 1998Go; Hersom, 1999Go). Data from those experiments were used to estimate the annual carrying capacity in each system that maximized the length of the grazing season and provided all of the hay needed within that system.

Before grazing in the fall of 1998 (yr 1), 1999 (yr 2), and 2000 (yr 3), the two 6.1-ha stockpiled smooth bromegrass-red clover (SB-RC) pastures, stockpiled tall fescue-red clover (TF-RC) pastures, and corn crop residue fields were divided into four 1.53-ha strips to allow strip-grazing by cows in the year-round (YR) grazing system. For summer grazing in the YR grazing system, two 8.1-ha smooth bromegrass-orchardgrass-birdsfoot trefoil pastures (SB-OG-BFT) pastures were divided into eight 1.01-ha paddocks for rotational stocking. In the conventional (minimal land, ML) system, two 8.1-ha SB-OG-BFT pastures were divided into four 0.52-ha and six 1.01-ha paddocks for rotational stocking.

Grazing Management Systems
Minimal Land System.
To initiate winter management, 12 of 24 pregnant April-calving Angus cross cows (mean BW, 527 ± 7.9 kg; mean BCS, 5.3 ± 0.17; mean age, 6.0 ± 1.81 yr) were randomly allotted to two 0.12-ha drylots on November 11 of yr 1 (Figure 1Go). Cows were fed hay from SB-OG-BFT pastures to maintain a condition score of 5 on a 9-point scale (Neumann and Lusby, 1986Go). Initiation of the winter management systems in subsequent years occurred on October 28 and 18, respectively, with the same cows as yr 1, except for replacements for cows culled for impaired reproduction or health.



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  		Figure 1. Illustration of the minimal land grazing system. The arrows indicate movement of entire group of cows and/or calves. Each pasture within a management system was replicated twice.

 
At the initiation of summer grazing on April 22, April 26, and May 2 of yr 1, 2, and 3, respectively, April-calving cows with calves were assigned to one of the two SB-OG-BFT pastures and grazed the four 0.52-ha paddocks by rotational stocking (Table 1Go). First-harvest forage from the remaining six paddocks was removed as hay on May 24 and June 12 of yr 1 and 3, but only from five of six paddocks on May 28 in yr 2 because of low rainfall. Paddocks used for hay harvest were incorporated into the rotational stocking systems after a minimum of 28 d of regrowth. Assuming a standard livestock unit (SLU) of a 500-kg nonlactating cow (Minson and Whiteman, 1989Go), stocking densities of the pastures were 3.76 and 1.17 SLU/ha for periods of the grazing season before and after the paddocks used for hay harvest were stocked. Grazing intervals for each paddock varied so that approximately 50% of the initial live forage mass was removed, as estimated with a falling plate meter (4.8 kg/m2, Hermann et al., 2002Go) without correction for forage growth during the grazing interval. Cows were bred with two Angus bulls over a 45-d breeding season beginning on June 17, June 21, and June 18, in yr 1, 2, and 3, respectively. April calves were weaned and summer grazing was terminated on October 28, October 17, and October 26 in yr 1, 2, and 3 when the mean live forage DM mass of the SB-OG-BFT pastures was less than 730 kg/ha, as estimated with a falling plate meter. Weaned calves were moved to replicate pens in a feedlot at weaning and finished on a high-grain diet (Janovick, 2002Go).


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  		Table 1. Mean BW of cows (n = 6), calves (n = 6), and stockers (n = 6), and BCS of cows in the year-round and minimal-land systems at the initiation of the summer grazing season each yeara
 
Year-Round Grazing System.
Simultaneously with the initiation of winter hay feeding of cows in the ML system, the remaining 12 April-calving Angus cross cows were randomly allotted to the two 6.1-ha corn crop residue fields and 12 August-calving Angus cross cows (mean BW, 551 ± 7.1 kg; mean BCS, 5.2 ± 0.23; mean age, 5.8 ± 1.70 yr) with calves (mean BW, 97 ± 7.8 kg) were randomly allotted to two 6.1-ha stockpiled TF-RC pastures (Figure 2Go). On February 2, December 28, and January 17 of yr 1, 2, and 3, April-calving cows in the YR grazing system were moved to the two 6.1-ha stockpiled SB-RC pastures for the remainder of the winter. Corn crop residues and stockpiled grass-legume pastures in the YR grazing system were strip-grazed with new strips opened at 2- to 3-wk intervals, respectively, allowing cows to access the combined area of the opened strips. Smooth bromegrass-red clover and TF-RC hays harvested in the previous summer were fed as large round bales to maintain a mean BCS of 5 in April-calving cows, to maintain a BCS greater than 3 in a minimum of 50% of the August-calving cows, or if forage availability was inhibited by excessive snow and ice.



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  		Figure 2. Illustration of the year-round grazing system. Solid arrows indicate movement of entire group of cows and/or calves. Dashed arrows indicate animals remaining on pasture while other groups were moved. Each pasture within a management system was replicated twice.

 
On November 13, November 11, and November 4 of yr 1, 2, and 3, one Angus bull was added to each stockpiled TF-RC pasture to initiate a 45-d breeding season for August-calving cows. August calves were weaned on March 3 and March 2, as designed, in yr 1 and 2. Early weaning of August calves on January 17 of yr 3 was necessary because heavy snow and ice cover and cold temperatures resulted in BCS of 3 or lower in 50% of the August-calving cows. Weaned calves were maintained in a drylot on a hay and corn gluten feed or corn grain diet until the initiation of summer grazing (Janovick, 2002Go).

Simultaneously with the initiation of summer grazing in the ML system, the six April-calving cows with calves and six pregnant August-calving cows in each replicate of the winter treatments in the YR grazing system were assigned to each of the two remaining 8.1-ha SB-OG-BFT pastures (Table 1Go). In addition, 24 steer or heifer calves from the previous season’s April and August calf crops were assigned by age, sex, and weight to each SB-OG-BFT pasture to graze as stocker cattle.

For the first 57 d of grazing in yr 1 and 2 and 48 d in yr 3, April-calving cow-calf pairs and stocker cattle grazed by rotational stocking to remove approximately 34% of the live forage mass. These cows were followed by pregnant August-calving cows, which removed an additional 16% of live forage mass, as estimated with a falling plate meter (Hermann et al., 2002Go). Total stocking density was 2.68 SLU/ha. Depending on forage growth, a portion or all of the first-harvest forage from the replicated 6.1-ha TF-RC and SB-RC pastures used for winter grazing was harvested as hay in large round bales on May 24, May 28, and June 12 in yr 1, 2, and 3. On June 17, June 21, and June 18 of yr 1, 2, and 3, April-calving cow-calf pairs and August-calving cows were moved to the same 6.1-ha SB-RC and TF-RC pastures they grazed the previous winter to graze regrowth forage. In yr 1, these pastures were divided into four paddocks and strip-grazed for a total of 50 d. Because of low rainfall and forage productivity on SB-OG-BFT pastures in yr 2, cows grazed for 54 d on first-harvest forage in two paddocks in these pastures, followed by postharvest regrowth from the two paddocks from which hay was harvested. In yr 3, first-harvest forage from all paddocks in the TF-RC and SB-RC pastures was harvested as hay. But similar to yr 2, inadequate forage in the SB-OG-BFT pastures resulted in the cows being moved to these pastures 7 d after hay harvest to strip-graze regrowth for 14 d. Cows returned to the SB-OG-BFT pastures for 14 d, and returned to their respective TF-RC and SB-RC pastures to graze regrowth from hay harvest for 43 d. April-calving cows were bred with two Angus bulls over a 45-d breeding season beginning on the date grazing was initiated on the SB-RC pastures.

On August 5, August 2, and July 30 of yr 1, 2, and 3, stocker cattle were removed from the SB-OG-BFT pastures, and assigned by weight to two sets of replicated pens in a feedlot, and finished on a high-grain diet (Janovick, 2002Go). Simultaneously, April-calving cow-calf pairs and August-calving cows were returned to the SB-OG-BFT pastures to graze by rotational stocking at 2.00 SLU/ha. Forage in the SB-RC and TF-RC pastures was fertilized with 40 kg N/ha and stockpiled for a minimum of 83 d before initiation of winter grazing.

Grazing of summer pastures was terminated simultaneous to termination of grazing of pastures in the ML system. April calves were placed in one pen of a drylot, maintained on grass-legume hay and corn gluten feed or corn grain, and used as stockers the following summer (Janovick, 2002Go).

Hay Production and Feeding Measurements
Large round bales of hay harvested from the pastures on May 24, May 28, and June 12 in yr 1, 2, and 3, respectively, were weighed individually and core-sampled in two locations per bale at harvest for determination of total DM yield. During winter, each bale was weighed at feeding. Core samples were taken at depths of 0 to 22 cm and 22 to 76 cm in four locations around the bale monthly from a minimum of three bales to determine DM concentration by drying at 60°C for 48 h. Mean DM concentrations of the bales were calculated as the average of the measurements at the two depths, assuming that 50% of the forage volume is in the outer 22 cm of a bale with a 152-cm diameter (Brasche and Russell, 1988Go). To calculate hay balance for each system, the difference in the amounts of hay harvested in summer and fed during winter were calculated per cow (Hitz and Russell, 1998Go) and per cow-stocker pair.

Animal Management
Cows were replaced at the initiation of either the winter or summer grazing season if they failed to conceive, if a calf died, or if other health problems prevented a cow from being used in the experiment. Replacement cows were acquired from similar August- and April-calving herds at the McNay Research and Demonstration Farm and matched by weight and condition score to the cow being replaced. Cows had ad libitum access to trace mineral supplement blocks (180 ppm Mg, 200 ppm Cu, 350 ppm Zn, and 36 ppm Se; Harvest Brands Inc., Pittsburgh, KS) throughout the experiment. During winter, cows and calves from both systems were weighed without fasting at the initiation of winter grazing, at termination of corn crop residue grazing, at weaning of August calves, and at the end of the winter grazing season. Over summer grazing, cows, calves, and stocker cattle were weighed without fasting at the initiation of summer grazing and every 28 d thereafter. Body condition of cows was visually scored using a 9-point scale (Neumann and Lusby, 1986Go) by the same individual every 2 wk during winter treatments and at weighing during summer treatments.

Statistical Analyses
The design of this experiment was intended to allow comparisons to be made between two grazing management strategies. The YR system also allowed for calving season comparisons to be made within the system and for comparisons to be made for these calving seasons with the spring calving season in the ML system. Because two complementary calving seasons were used in the YR system, linear contrasts were created to compare the mean of the YR system to the mean of the ML system to determine whether the inclusion of two complementary herds in one system was feasible from a management standpoint. This contrast was used to answer questions about hay needs, cow performance, and growing animal production using both calving seasons compared with a single calving season, such as the traditional April-calving herd. Linear contrasts were also created to compare the calving seasons to one another in order to answer questions about the use of fall-calving compared with spring-calving cows in a YR grazing system. These contrasts allowed comparisons to be made between fall- and spring-calving cows in the YR system in addition to comparisons of the spring-calving cows in both systems.

Cow BW and condition scores; calf birth weights, weaning weights, and average daily gains; stocker cattle BW gains; and hay production, feeding, and balance were analyzed as a two-way analysis of variance using the GLM procedure (SAS Inst. Inc., Cary, NC) with the main effects of calving season within grazing system and year and the two-way interaction of calving season within grazing system and year included in the model. Body weight gains of stocker cattle while grazing pastures within the YR grazing system were analyzed as a two-way analysis of variance using the GLM procedure of SAS, with the main effects of calving season and year and the two-way interaction of calving season and year included in the model. The experimental unit in these analyses was each replicated group of animals within a calving season within a grazing system. Total growing animal production was defined as the sum of the body weight gains of all calves and stocker cattle produced within a replicate of either grazing system, and was also analyzed by the GLM procedure of SAS, with the main effects of grazing system and year and the two-way interaction of system and year. To test the effects of grazing system and calving season on hay production, feeding, and balance, data were also analyzed in a two-way analysis of variance using the GLM procedure of SAS, with main effects of grazing system and year and the two-way interaction of grazing system and year, using the sum of all cow groups within a grazing system as the experimental unit. For all these analyses, linear contrasts were created for the purposes outlined above to compare the means of the three cow groups and the means of the two grazing systems. When interaction occurred between cow group and year in all data sets, forage grazing system effects were tested in each year.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Literature Cited
 
Cow Body Weight and Condition Scores
Mean calving dates were April 21 and 22, April 18 and 11, and April 16 and 6 for April-calving cows in the ML and YR grazing systems and August 31, September 6, and August 28 for August-calving cows in the YR grazing system in yr 1, 2, and 3. Body weights of April-calving cows in either system did not differ (P > 0.05) in any month except March (Figure 3aGo), when the BW of cows in the ML system were greater (P < 0.01) than in the YR grazing system. Body condition scores of April-calving cows in either system did not differ (P < 0.05) in any month (Figure 3bGo). Although the BW of August-calving cows in the YR grazing system did not differ (P > 0.05) from April-calving cows in either grazing system at the initiation of winter grazing in late October or early November, the BW of the August-calving cows were lower (P < 0.05) than the April-calving cows in either grazing system in January and March until initiation of summer grazing. Body condition scores of August-calving cows were greater (P < 0.05) than April-calving cows in either system from the initiation of winter grazing until February, but lower (P < 0.05) than April-calving cows in the YR grazing system in February and in both grazing systems in March. Body weights and BCS of August-calving cows in the YR system were greater (P < 0.05) than April-calving cows in either system throughout the summer. Because of the loss of BW associated with calving and the lower forage allowance in September and October in the pastures in the YR grazing system (Janovick, 2002Go), the BW of August-calving cows in the YR grazing system decreased from August until the termination of grazing. This change resulted in no differences in BW between August-calving cows in the YR grazing system and April-calving cows in either grazing system at the termination of summer grazing. Body condition scores of August-calving cows in the YR grazing system also decreased during this period, but still were greater (P < 0.05) than April-calving cows in both systems at the termination of summer grazing.



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  		Figure 3. Mean BW (a) and BCS (b; 9-point scale) of August-calving cows in the year-round system (n = 6) and April-calving cows in either the year-round (n = 6) or minimal land (n = 6) grazing systems during the winter and summer grazing seasons over three years. a,bWithin months, differences between means of cow groups with different superscript letters differ, P < 0.05. The SEM for BW (kg) were 8.7, 5.3, 4.1, 4.5, 5.8, 5.1, 5.0, 4.2, 6.7, and 4.7 for November through September, respectively. The SEM for body condition score were 0.11, 0.09, 0.09, 0.12, 0.11, 0.12, 0.15, 0.17, 0.15, and 0.16 for November through September, respectively. October was the initiation of winter grazing. In January, April-calving cows in the year-round grazing system cows were taken off corn crop residue pastures. In April, August calves were weaned, winter grazing was terminated, and summer grazing was initiated. From May to October, monthly weights were taken while cattle grazed summer pastures.

 
Compared at similar production stages, April-calving cows in the ML grazing system had greater BW than April-calving cows in the YR grazing system at breeding (P < 0.05) and the April- or August-calving cows in the YR grazing system at weaning (P < 0.05; Figure 4aGo). However, BW at all other production stages and BCS (Figure 4bGo) at all production stages did not differ (P > 0.05) between April-calving cows in either grazing system. August-calving cows in the YR grazing system had greater (P < 0.05) BW than April-calving cows in either grazing system from the precalving through the prebreeding stage and greater (P < 0.05) BCS than April-calving cows in either system from mid-gestation through the breeding season. Body weights of August-calving cows in the YR grazing system were lower (P < 0.05) than April-calving cows in either grazing system at late lactation, but only lower (P < 0.05) than April-calving cows in the ML grazing system at weaning. Body condition scores of August-calving cows in the YR grazing system were lower (P < 0.05) than April-calving cows in either grazing system during late lactation and weaning. However, there were no differences in BW (P = 0.41) or BCS (P = 0.53) of cows between the three groups at a mean of 30 ± 13 d postweaning.



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  		Figure 4. Mean BW (a) and BCS (b; 9-point scale) of August-calving cows in the year-round system (n = 6) and April-calving cows in either the year-round (n = 6) or minimal land (n = 6) grazing systems over 3 yr analyzed by biological production stage of the cow. a,bWithin a production stage, differences between means of cow groups with different superscript letters differ P < 0.05. The SEM for BW (kg) were 5.4, 4.5, 4.7, 3.6, 6.2, —, 5.6, 6.7, 8.3, and 5.9 for production stages of precalving (PreC), calving (C), postcalving (PoC), breeding (B), postbreeding (PoB), late lactation (LL), weaning (W), postweaning (PoW), and midgestation (MG), respectively. The SEM for BCS were 0.10, 0.09, 0.08, 0.10, 0.13, 0.16, 0.17, 0.19, 0.13, and 0.11 for PreC, C, PoC, PreB, B, PoB, LL, W, PoW, and MG, respectively.

 
Mean rebreeding and replacement rates of cows in the experiment were 87.9% (SEM = 12.48, n = 18) and 12.8% (SEM = 13.60; n = 18) and did not differ (P = 0.20 and 0.45) between April-calving cows in the ML and YR systems or August-calving cows in the YR system. However, because of the low numbers of animals used in this experiment, the reproductive and replacement data should be interpreted with caution.

Calf and Stocker Cattle Production
There were no differences (P > 0.05) in the birth and weaning weights between April calves in either grazing system (Table 2Go). Birth weights of April calves born in the ML or YR grazing system were 3 kg lighter (P = 0.03) than August calves in the YR grazing system. However, August calves were 49 kg lighter (P < 0.01) at weaning than April calves in either grazing season. This difference in weaning weights between April and August calves was caused by differences in preweaning ADG and weaning age. However, 205-d adjusted weaning weights of August calves were lower (P < 0.01) than those of April calves. April calves from either grazing system gained 0.2 kg/d more than August calves in the YR grazing system (P < 0.01). There was no difference in the age at weaning between groups of April calves from either system (P = 0.39). But the mean age at weaning of August calves was 24 (P = 0.04) and 15 d younger (P = 0.16) than April calves in the YR and ML systems. These differences in weaning age largely resulted from the earlier weaning in yr 3 caused by the rapid decrease in BCS of August-calving cows attributable to excessively cold temperatures and snowfall. In yr 3, August calves were 44 kg lighter and 54 d younger than they had been at weaning the previous two years (group x year, P < 0.01).


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  		Table 2. Mean birth weights, weaning weights, and average daily gains for calves in the year-round (YR) and minimal-land (ML) grazing systems
 
Because of the lower preweaning weight gains of August calves and greater land requirements of the YR grazing system, calf production from the ML grazing system was 47 kg BW/ha of perennial pasture (P < 0.01) and 32 kg BW/cow (P = 0.01) greater than the YR grazing system (Table 3Go). However, the additional stocker cattle in the YR grazing system increased growing animal production by 35 kg BW/ha of perennial pasture and 55 kg BW/cow. Therefore, whereas the ML grazing system tended to have greater (P = 0.07) growing animal production per hectare of perennial pasture than the YR grazing system, the YR grazing system had 27 kg greater (P = 0.01) growing animal production per cow than the ML grazing system.


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  		Table 3. Mean total growing animal production per hectare and per cow for the year-round (YR) and minimal-land (ML) grazing systems over three years
 
Hay Production and Feeding
Over the 3-yr experiment, the SB-OG-BFT pastures in the ML system produced 1,312 kg DM/(harvested ha•yr) (P < 0.01) and 510 kg DM/(cow•yr) (P = 0.02) more hay than the mean of the TF-RC and SB-RC pastures in the YR grazing system (Table 4Go). Within the YR grazing system, TF-RC pastures produced less hay per hectare (P < 0.01) and per cow (P < 0.01) than the SB-RC pastures. In March of yr 2, total rainfall was 12.9 cm below the 30-yr average from March through May. As a result, only 83 and 75% of the total land area reserved for hay cutting was harvested as first-cutting hay in the ML and YR system, respectively. The remaining area was incorporated into the grazing systems. The low rainfall in yr 3 decreased the amount of hay DM harvested per hectare by 67.5, 37.3, and 53.1% from the TF-RC and SB-RC pastures in the YR grazing system and the SB-OG-BFT pastures in the ML systems compared with the preceding 2 yr (year, P < 0.01). Hay production per cow in these pastures was 83.7, 68.6, and 61.1% lower in yr 3 than the preceding 2 yr (year, P < 0.01).


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  		Table 4. Mean hay production, feeding, and balance per cow and per cow-stocker pair in the year-round (YR) and minimal-land (ML) grazing systems over three years
 
In the ML system, 1,701 kg DM/cow more hay/yr (P < 0.01) was fed than the mean amounts of hay fed to cows in the YR grazing system. The mean amount of hay fed to April-calving cows in the ML system was 2,234 kg/(cow•yr) and did not differ (P > 0.05) between years. In contrast, the amounts of hay fed to August- and April-calving cows differed considerably between years (group within calving season within grazing system x year, P < 0.01). In yr 1, August- and April-calving cows in the YR grazing system required 419 and 624 kg of hay DM/cow primarily after a 6.7-cm snowfall in November (Table 5Go). April-calving cows in the ML grazing system required 2,150 kg/cow. Because of mild temperatures (average, 2.9°C) and minimal snowfall (total precipitation and snowfall, 18.3 and 40.6 cm) from October through April in yr 2, no hay was fed to either August- or April-calving cows in the YR grazing system, but April-calving cows in the ML grazing system required 2,143 kg/cow. In yr 3, mean temperatures were –1.9°C and total precipitation and snowfall were 26.4 and 99.1 cm from October through April. Therefore, mean amounts of hay required by August- and April-calving cows in the YR grazing system were 1,061 and 1,096 kg DM/cow, whereas April-calving cows in the ML grazing system required 2,409 kg/cow.


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  		Table 5. Mean monthly temperature, precipitation, and snowfall at the McNay Research and Demonstration Farm, near Chariton, IA
 
Over 3 yr, mean hay production in the ML system was 232 kg DM/(cow•yr) less than required to maintain April-calving cows. In contrast, hay production from SB-RC and TF-RC pastures were 1,152 and 766 kg DM/(cow•yr) greater than required for April- (P < 0.01) and August-calving (P < 0.01) cows in the YR grazing system. As a result, mean amounts of hay produced in the YR grazing system were 958 kg DM/(cow•yr) greater than that fed (P < 0.01). This difference in hay balance for the two grazing systems resulted exclusively from the use of extended grazing with supplemental hay feeding in the YR system compared with exclusive hay feeding in the ML system, thus meeting the objective of reducing hay needs for cows.

During winter backgrounding, April- and August-born stocker cattle required 1,305 and 305 kg hay DM/(stocker•yr) (P < 0.01) from weaning to the initiation of summer grazing (Janovick, 2002Go). When added to the hay requirements of the cows, mean hay requirements for the April- and August-calving cows and their retained calf crops in the YR grazing system were 1,877 and 798 kg DM/(cow-stocker pair•yr), respectively (P < 0.01). In spite of these added hay needs, the mean total amount of hay needed by cow-stocker pairs in the YR grazing system was 896 kg DM/(cow-stocker pair less•yr) (P < 0.05) than cows in the ML system. The additional hay needs of the stocker cattle resulted in a deficit of 152 kg DM/(cow-stocker pair less•yr) in the amounts of hay produced and fed for April-calving cows and stockers (P < 0.05) but left an excess of 461 kg DM/(cow-stocker pair less•yr) in the amounts of hay produced and fed to August-calving cow and stockers (P < 0.05) in the YR grazing system. As a result, hay balance did not differ (P > 0.05) between the YR or ML grazing systems in any year.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Literature Cited
 
Winter weather can affect the success of strategies used to extend the grazing season (Adams et al., 1986Go) and must be considered to use resources effectively. In the current study, the amounts of supplemental hay fed to cow and calf groups in the YR grazing system varied with differences in annual snowfall and ambient temperature. However, as designed, the amounts of hay required by both groups of cows in the YR grazing system were less than those required for cows fed hay in a drylot during winter in the ML system over 3 yr. Grazing 1.01 ha of corn crop residues and 1.01 ha of stockpiled SB-RC pastures per cow over approximately 180 d decreased the amount of hay required to maintain April-calving cows by 1,611 kg/(cow•yr) in the current study. The amounts of hay required to maintain spring-calving cows have been reduced by 646 kg/cow by grazing TF-RC at 0.33 ha/cow over 141 d (Allen et al., 1992bGo), 1,050 kg/cow by grazing stockpiled TF-RC or SB-RC at 0.82 ha/cow over 139 d (Hitz and Russell, 1998Go), or 2,692 kg/cow by grazing 0.61 ha of corn crop residue and 1.22 ha TF-RC or SB-RC/cow over 185 d (Hersom, 1999Go). In addition to hay savings, the YR grazing system using perennial pastures and corn crop residues in this study supported ADG of calves and BCS of April-calving cows comparable to those of the ML system. However, because of the added land area required for the stockpiled pastures, calf production for April calves in the YR grazing system was reduced per unit of pasture area.

August-calving cows underwent greater changes in BCS than April-calving cows in either system over their production cycle. Excessive BCS in August-calving cows at calving likely contributed to the changes in BCS late in the summer, as fatter cows tend to lose more condition than those in moderate condition (Houghton et al., 1990Go). However, allowing cows to go through cyclic changes in body weight has improved the efficiencies of energy and nitrogen utilization (Freetly and Nienaber, 1998Go). Furthermore, Freetly et al. (2000)Go reported that cows losing condition in the second trimester of pregnancy, and then regaining condition before calving had calf production and reproductive performance similar to those of cows that were maintained at the same condition over the entire pregnancy. Therefore, the increased efficiency of utilizing body energy reserves contributed to the lower amounts of supplemental hay needed for August-calving cows than April-calving cows. Furthermore, calving date affects the cost of feeding cows by matching the cow more closely with forage resources and providing a weaned calf crop at a time of year when calf prices are highest (May et al., 1999Go). However, because of lower ADG, earlier weaning age, and the added land area of the YR grazing system, BW gains of August calves were only 126 kg/August cow and 37 kg/ha of perennial forage in the present experiment.

Inclusion of stocker animals in the YR grazing system resulted in masses and nutritional values of forage in SB-OG-BFT pastures that did not differ from pastures used for grazing and hay harvest in the ML grazing system (Janovick, 2002Go). Furthermore, the addition of stockers from the April and August calves increased growing animal production by 19 and 17 kg/ha perennial forage. However, during winter postweaning, stockers from the April and August calves required 1,305 and 305 kg hay DM/(stocker animal•yr). Therefore, although the mean amount of hay produced was 958 kg of DM in excess of each cow’s needs, the mean amount of hay produced was decreased to 154 kg of DM in excess of each cow-stocker pair’s needs. Grazing stockpiled pasture (Allen et al., 1992aGo, 2000Go) or corn crop residues (Klopfenstein et al., 1987Go) may be options to decrease the amount of stored feeds used to maintain growing animals over winter. In contrast to the YR grazing system, hay production of first-cutting forage from 0.84 to 1.01 ha/cow of SB-OG-BFT pasture in the ML grazing system was inadequate to maintain cows in the drylot in yr 1 and 3. Although this production was 232 kg DM/cow less than was needed for feeding cows, this deficiency was much lower than in previous studies by Hersom (1999)Go and Hitz and Russell (1998)Go, from which hay was harvested from 0.5 and 0.81 ha/cow.

Conclusion
In conclusion, the YR grazing system—using grass-legume pastures and corn crop residues—decreased the amounts of hay needed to feed cows and calves over winter compared with feeding hay in the drylot and provided risk management for summer grazing in drought years. Inclusion of August-calving cows and calves in an extended grazing system using cool-season grass-legume pastures in the upper Midwest is possible to complement forage utilization in grazing systems with April-calving cows. August-calving cows were able to regain condition during summer and provide a source of stocker calves that required less stored feed after weaning compared with April calves. Although retaining weaned calves increased the amount of stored feeds needed for winter, grazing stocker cattle with cows increased growing animal production per cow.


   Footnotes
 
1 Journal paper of the Iowa Agric. and Home Econ. Exp. Stn., Ames. Project No. 3810. Research was funded, in part, by a grant from the Leopold Center for Sustainable Agriculture, Iowa State Univ., Ames. Back

2 The authors gratefully acknowledge the assistance of L. J. Secor, D. R. Maxwell, M. L. Hermann, M. J. Hersom, and the animal caretakers at the McNay Research and Demonstration Farm for assistance in conducting this experiment and P. M. Dixon for assistance in the statistical analysis of the data. Back

3 Present address: Dept. of Anim. Sci., Univ. of Illinois, Urbana 61801. Back

4 Correspondence: 337 Kildee Hall (phone: 515-294-4631; fax: 515-294-3795; e-mail: jrussell{at}iastate.edu).

Received for publication July 23, 2003. Accepted for publication April 13, 2004.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Literature Cited
 


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Allen, V. G., J. P. Fontenot, and R. A. Brock. 2000. Forage systems for production of stocker steers in the upper south. J. Anim. Sci. 78:1973–1982.[Abstract/Free Full Text]

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Allen, V. G., J. P. Fontenot, D. R. Notter, and R. C. Hammes, Jr. 1992b. Forage systems for beef production from conception to slaughter: I. Cow-calf production. J. Anim. Sci. 70:576–587.[Abstract]

Bagley, C. P., J. C. Carpenter, Jr., J. I. Feasel, F. G. Hembry, D. C. Huffman, and K. L. Koonce. 1987a. Effect of forage system on beef cow-calf productivity. J. Anim. Sci. 64:678–686.[Abstract/Free Full Text]

Bagley, C. P., J. C. Carpenter, J. I. Feasel, F. G. Hembry, D. C. Huffman, and K. L. Koonce. 1987b. Influence of calving season and stocking rate on beef cow-calf productivity. J. Anim. Sci. 64:687–694.[Abstract/Free Full Text]

Brasche, M. R., and J. R. Russell. 1988. Influence of storage methods on the utilization of large round bales by beef cows. J. Anim. Sci. 66:3218–3226.[Abstract/Free Full Text]

Freetly, H. C., C. L. Ferrell, and T. G. Jenkins. 2000. Timing of realimentation of mature cows that were feed-restricted during pregnancy influences calf birth weights and growth rates. J. Anim. Sci. 78:2790–2796.[Abstract/Free Full Text]

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Hermann, M. L., J. R. Russell, and S. K. Barnhart. 2002. Evaluation of hay-type and grazing-tolerant alfalfa cultivars in season-long or complementary rotational stocking systems for beef cows. J. Anim. Sci. 80:768–779.[Abstract/Free Full Text]

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