ROTATIONAL GRAZING WITH DAIRY HEIFERS ON WICST:
b. Animal Performance Summary

Janet Hedtcke [1] and Josh Posner [2]

INTRODUCTION

In Wisconsin, there are nearly 2 million acres harvested for hay (WI Ag Stats, 2002) and another 2.5 million acres grazed (WI Ag Stats News Release, 2003).   In fact, according to WI Ag Statistic Service, grazed pasture ranks second in acreage just behind corn for grain production (2003).  Productive grass-legume pastures are key to most livestock systems.  Managed pastures provide high quality forage and offer an excellent, healthy environment for livestock.  Management-intensive grazing (MIG) is a low-input style of dairy herd management that can reduce feed, labor, equipment and other input costs.  It is estimated now that some form of MIG is practiced on 22% of Wisconsin dairy farms (PATS, 2001).  Reducing feed costs and labor relates directly to the ‘quality of life’ for the farm family.    MIG also offers less environmental risk with reduced erosion, minimal use of fertilizer and pesticide, and reduced barnyard runoff.  It can also offer wildlife habitat. 

Our objectives of this study are to compare the production, profitability and environmental impact across various cropping systems.  The pasture productivity summary can be found in the previous paper of this report entitled ‘Rotational Grazing with Dairy Heifers on WICST: a. Pasture Productivity and Quality’ and an economic summary is found in the next paper ‘Rotational Grazing with Dairy Heifers on WICST: c.  Economic Evaluation of MIG’.  The current paper deals with animal performance under MIG since 1992.

MATERIALS AND METHODS

Fencing Details

Fencing and water lanes for pastures at both locations were built during the spring of 1992.  At LAC, the forage was mechanically harvested until the spring of 1992 when grazing began.  At ARS, severe winterkill of the grasses required reseeding in 1992 and grazing began in the spring of 1993.  Fig. 1 shows an example of paddock layout at ARS, which was 0.70 acres; layout was similar at LAC but paddock size was 300’ x 120’ or 0.83 acres.  The perimeter fencing consists of three strands of high-tensile wire with wood posts energized by either a solar fencer or a battery powered fencer.  In recent years, pink ribbons have been tied on the wire around the perimeter of the plot to improve visibility of the fence to the heifers.  Polywire and plastic ‘pigtail’ posts have been used to subdivide each paddock.

Figure 1. Pasture layout at Arlington (similar at Lakeland)

 

Animal Details

Grazing details for years prior to 2001 have been reported in each of the previous WICST technical reports (2^nd-8^th).

Arlington 2001.  Ten heifers were selected for the study and initial weights were recorded on a shrunk-weight basis.  Six of the ten heifers were controls and remained in confinement with initial average weight of 548 lb.  The initial average weight of the four heifers in the pastured group was 516 lb.  Heifers were supplemented 2 lb of corn grain per hd per day until June 2 as heifers transitioned to a pasture diet.  As the grasses matured and became of lower quality, grain was increased to 4 lb per hd per day from June 2 to July 23.  The rest of the grazing season, grain was reduced again to 2 lb/hd/d.  In total, 347 lb (dry matter [DM] basis) grain/hd was supplemented for the season.  Midseason weights were not collected as one heifer escaped from the plots and it was decided not to pursue the effort once she was back in the plot.  Heifers were removed from the trial on October 2 due to cold and wet weather conditions. 

Arlington 2002.  Similarly to 2001, body weights were recorded for six control (confinement) and 4 pastured heifers.  Average size for the pastured heifers was 515 lb, about 100 lb larger than the controls.  The animals were supplemented 2 lb of corn grain per hd per day for the entire season except for the last 12 days when forage supply was running short and the weather was getting cold.  A total of 294 lb DM grain/animal was fed for the season.  Midseason weighing was forgone as it has been perceived as disruptive and stressful to the animals. 

Lakeland 2001.  Initial average shrunk weight of the four pasture heifers was 491 lb.  The confinement group averaged 556 lb/hd at beginning of season.  Heifers received 2 lb corn grain per day per hd for the entire season.  Total grain supplemented for the season was 269 lb DM grain/hd.  No mid-season weights were measured.  Controls did not get weighed at the end of the season.

Lakeland 2002.  Due to circumstances at the Walworth County Farm, heifers were obtained from a local farmer and raised on a contractual basis.  Grazing began May 17th and ended in November 6th.  Grain was supplemented at 2 lbs/day/hd for a total of 292 lb DM/hd for the season.  Three bales of hay (850 # each) were made from plot 408 in mid-July and fed back during September and October.

Table 1.  Supplemented grain and hay (‘as fed’ basis) per animal during each grazing season at each site (1992-2002)1.
	ARS		LAC
Year	lb feed mix/hd/yr	lb hay/hd/yr	lb feed mix/hd/yr	lb hay/hd/yr
1992	-	-	0	543
1993	485	0	195	390
1994	205	0	0	529
1995	300	0	308	275
1996	326	56	253	285
1997	338	0	-	-
1998	314	635	192	0
1999	368	0	158	0
2000	360	0	328	0
2001	408	0	316	0
2002	346	0	344	638

¹ Rates shown reflect supplement fed to animals that were on plots for entire season.

RESULTS & DISCUSSION

As a system for raising heifers, maximum weight gains of 1.8-2.0 lb/day (post-weaning) are desirable.  At this rate, animals are ready to be bred at 13-15 months (750-850 lb).  Prepuberty growth rates above 2.2 lb/d can inhibit mammary development and lead to permanent impairment of milk producing ability (Sejrsen, 1982).  Rates below 1.8 lb/day can lead to the hidden expense of delayed puberty, breeding and first calving (Fiez and Rimbey, 1983).  Of course, there is genetic variability between animals and gains from pasture have deviated above and below this ideal 1.8 lb/day rate of gain.

Arlington.  Average daily gain in 2001 was 1.63 lb/d/hd (ranging from 1.44 to 1.76 lb/day) for pastured animals and 1.72 lb/d/hd (ranging from 1.11 to 1.99 lb/day) for confinement.  The next year (2002) heifers on pasture had an average daily gain of 1.82 lb/ hd.  Weight gain ranged from 1.60 to 1.93 lb/d for pastured heifers and 1.99 to 2.67 lb/hd for confinement heifers. 

Lakeland.  Weights were recorded on a group weight basis in both 2001 and 2002 for simplicity sake.   Average daily gain of pastured heifers averaged 1.77 lb/hd in 2001.  Final weights in 2002 were less than ideal with animal gains of 1.05 lb/d.  Excess spring forage was not harvested for hay until mid-July (plot 408 only) which resulted in poor quality forage.  Hot, dry weather in June and July combined with poor forage quality negatively impacted heifer performance.  Furthermore, the animals were out too long in the fall without adequate supplementation when weather was getting cold and wet and when grasses typically have lower energy content.

In general, confinement animals gained 2.2 lb/d or about 20% faster rate than the heifers on pasture (data not shown).  This is in agreement with a study by Tobert and Linn (2002) who found that feedlot heifers gained 23% more weight per day than pastured heifers.  Lack of exercise and a higher calorie intake in confinement may account for this difference.  It should be noted that there has been no transition/adjustment period from confinement to pasture.  Ideally, the pastured animals would be on pasture for 10 days then weighed but existing facilities make that difficult.  Table 2 shows the current summary of animal performance at both LAC and ARS from 1992-2002.  It is apparent that the grazing days has been well below the expected 180 days at both sites over the years.  Grazing usually begins in early May but rarely extends beyond late September due to either lack of forage or difficult weather conditions.  Having no shelter or windblock can be very hard on dairy heifers in wet, cold weather because they don’t have a lot of extra body condition like beef cattle or sheep do.  Over the course of the trial, average daily gain was 1.78 lb/d at LAC and 1.65 lb/d and ARS for animals that were on pasture all season.  Animals taken off early (<60 d) showed little to no weight gain, which reflects a slow transition from confinement to pasture.

Table 2.  Summary of animal weight gain for WICST rotational grazing for 1992-20021.
	LAC		ARL
Year	lb/hd/day	# of Days	lb/hd/day	# of Days
1992	2.27	167	na	0
1993	1.64	152	1.76	137
1994	2.01	178	1.61	120
1995	1.91	154	0.78	60
1996	1.63	122	1.89	127
1997	na	0	1.75	125
1998	2.28	96	1.69	138
1999	1.83	148	1.79	134
2000	1.42	164	1.76	161
2001	1.77	158	1.63	153
2002	1.05	172	1.82	163

¹ data is for animals on pasture all season.

Forage Production using Estimated Dry Matter Intake Method

Although forage availability is a useful estimate of pasture production, it is not what the animal actually consumes as dry matter intake (DMI).   Forage availability does not account for trampled or refused forage and animals don’t graze evenly to ground level as is done to determine forage availability.  Actual forage consumption is difficult to determine for grazing studies without using invasive techniques such as surgically implanted fistulas.   We used animal energy consumption formulas, tables of feed composition, and animal nutrient requirements to estimate dry matter consumed by the grazing animals (Table 3).  Daily net energy for maintenance (NE_M) and net energy for growth (NE_G) requirements for the animals were determined by the standard formulas from the 1989 NRC Publication on Nutrient Requirements for Dairy Cattle (shown below) using average weight of each animal during the grazing period and their average rate of gain.

         NE_M (in Mcal/day) = .086 * (LW)^.75

and

        NE_G (in Mcal/day) = .035 * (LW)^.75  * (LWG/1000)^1.119 + 1.0 * LWG/1000

where LW is live weight in kg and LWG is live weight gain in g/day.

The pasture NE_M and NE_G (in Mcal/kg DM) used for ARS were an average of the following three values taken from the NRC feed energy tables:

            1) NE_M = 1.52 and NE_G = 0.93 for avg. of early and medium bloom red clover

            2) NE_M = 1.69 and NE_G = 1.08 for young orchardgrass

            3) NE_M = 1.48 and NE_G = 0.89 for avg. of early and medium maturity bromegrass

        Avg NE_M = 1.56 and NE_G = 0.97 for grass/clover mix pasture

Energy value of supplemented grain mix at Arlington is

             NE_M = 1.96 and NE_G = 1.30

Pasture NE_M and NE_G (in Mcal/kg DM) values used for Lakeland were taken from the NRC feed energy tables and are shown below:

            NE_M = 1.31 and NE_G = 0.74 for reed canarygrass

            NE_M = 2.06 and NE_G = 1.40 for barley supplement

Daily DMI was calculated using the following equation:

DMI (kg/d) = (daily NE_M requirement/ NE_M per kg ration) + (daily NE_G requirement/ NE_G per kg ration)

The actual NE_M and NE_G of the complete ration were calculated after determining the percent of daily DMI from the grain.  Forage consumption was then determined by subtracting off the grain from the daily DMI.  Then, we multiplied the number of days the animals were on pasture by the daily DMI per animal.  Total DMI per acre was determined by multiplying forage consumption per animal by the total number of animals plus any mechanically harvested hay, which is assumed to be used for winter feed.

Table 3.  Estimated Forage Production using Dry Matter Intake Calculations using NRC equations for maintenance and growth.   LAC ARL Year T DM/acre T DM/acre 1992 3.35 - 1993 2.46 2.16 1994 3.24 3.86 1995 2.54 1.89 1996 0.37 1.59 1997 - 2.06 1998 0.761 1.74 1999 1.63 1.36 2000 1.50 2.08 2001 1.86 1.88 2002 1.76 2.11 1Does not include growth before July 23.

CONCLUSION

Rotational grazing offers a low input system with good animal performance.  Excess forage growth should be harvested as hay or clipped in May and June to maintain high quality and intake.  Grain supplementation may not be necessary all year but it is a relatively inexpensive energy source that can improve condition in extreme weather.  Occasional hay supplementation may be necessary during periods of slow pasture growth such as in late July.  By managing both forage and animal needs, we can realize the potential of rotational grazing as a viable alternative to conventional heifer rearing.

CITATONS

Fiez, E.A., and N.R. Rmbey.  1983.  Optimum age for first calving.  Idaho Current Information Series No. 688.  University of Idaho-Ag. Extension Service, Moscow, ID.

National Research Council. 1989.  Nutrient requirements of dairy cows.  6^th edition.  National Academy Press.  Washing ton D.C. 1988.

Sejrsen, K. 1982.  Influence of nutrition on mammary development in pre- and postpubertal heifers.  J. Dairy Sci.  v. 65 (5) p. 793-800

Tobert and Linn. (agri-view article, June 12, 2003)

Wisconsin Agriculture Statistics Service. 2002.  USDA  p 35, 37, 49.

Wisconsin Agriculture Statistics Service News Release. 2003.  USDA

Wisconsin Family Farm Facts.  Program on Agriculture Technology Studies No.15, June 2001. ‘Technology Adoption among Wisconsin’s Dairy Farmers in the 1990s’.