Impact of Herbage Allowance on Lactating Beef Cows Grazing Stockpiled Tall Fescue By L.E. Meinhardt and R.L. Kallenbach

Efficient forage utilization by beef cattle is essential for optimum economic production and performance in a cow-calf operation. The most efficient way to utilize forage is by grazing; however, forage growth is dormant between late autumn and early spring. During this period, producers commonly rely on stored feed even though it is expensive. Use of stored feed accounts for 70 percent of the annual beef cow maintenance cost. Research at the University of Missouri found extending the grazing season into winter reduces dependence on stored feed and decreases winter-feeding costs by one-third to one-half (Bishop-Hurley and Kallenbach, 2001). One way to extend the grazing season is to utilize stockpiled tall fescue (Festuca arundiacea Schreb).

Tall fescue, the predominant forage in the transition zone, lends itself well to stockpiling. It produces more autumn growth, maintains yield and quality throughout the winter, and responds to nitrogen fertilization better than other coolseason grasses. A great deal of research has been conducted on stockpiled tall fescue, although much of this research has been done on yield, quality, fertilization, defoliation, and accumulation (Berry and Hoveland, 1969; Collins and Balasko, 1981a, b; Fribourg and Bell, 1984; Kallenbach et at., 2003). There have also been several successful stockpile-grazing studies with gestating, spring calving beef cows and stocker calves (Allen et al., 1992a, b; Hitz and Russell, 1998; Tucker et al., 1989; Waller et al., 1988). In recent years, producers are switching to fall calving operations, and as a result more cows are lactating over winter. Only a few studies have documented using stockpiled tall fescue with lactating fall calving cows. Animals in these studies were typically allocated feed equal to three percent of their body weight each day with 70 percent utilization. Remarkably, the scientific basis for this allowance is largely unknown, yet the literature indicates that it is widely accepted.

As fall calving gains popularity, the importance for an appropriate herbage allocation level increases. Lactating cows have much higher nutrient requirements than gestating cows (NRC, 2000) and may require higher herbage allowances. On the other hand, it may be economical for cows to loose body condition in the winter, when forage supplies are limited, and regain weight when lush spring growth occurs. However, research is needed to evaluate the most economical herbage allowance of stockpiled tall fescue for lactating fall calving beef cows.

It is less expensive to maintain a lactating cow on lower herbage allocation levels than higher allocations; however, this does not mean that the lower allocations are the most economical. Forcing high utilization rates with low allocation levels may limit cow intake causing excessive weight loss, decrease reproductive performance, and decreased milk production resulting in reduced calf gain. Spring regrowth may also be adversely affected by low allocation levels. Some studies show that spring growth is not affected by grazing stockpiled during the winter (Allen et al. 1992a; Riesterer et al., 2000) while other studies report decreases in spring yield (Hall et al., 1998). Research is limited on why these contradictions occur. Animal performance when consuming tall fescue herbage is often hindered due to a fungal endophyte, Neotyphodium coenophialum [(Morgan-Jones and Gams) Glenn, Bacon and Hanlin]. The endophyte infection results in an accumulation of toxic alkaloids know to cause a series of animal health disorders, costing the United States livestock industry an estimated $609 million annually (Hoveland, 1993). Resent research indicates endophyte toxicity should be less severe in stockpiled tall fescue. However, there is insufficient evidence on the effects of grazing infected stockpiled tall fescue on cow-calf performance.

The objectives of this trial are: 1) establish optimum daily herbage allowance for lactating beef cows and their calves wintered on stockpiled tall fescue, 2) estimate dry matter utilization rate of stockpiled tall fescue at different herbage allocation levels, 3) observe the impact of grazing endophyte infected tall fescue over-winter on animal performance, and 4) determine the effect of herbage allocation level on spring regrowth. Conventional winter hay-feeding practices will also be evaluated for an economical comparison with stockpiling tall fescue. Answering these objectives is necessary to maintain a profitable fall calving herd throughout winter.

Materials and methods
The experiment was conducted in a randomized complete block design with three replications and four stockpiled tall fescue at herbage allowances treatments; 2.25, 3.00, 3.75, and 4.50 percent of cow and calf body weight per head per day (BW hd^-1 d^-1). Sixty, cow-calf pairs were stratified into twelve groups and then assigned to treatments at random. The first year of the experiment began on 2 December 2004 and ended 24 February 2005. Stockpiled tall fescue was strip-grazed with forage allocated every 3.5 days. Pre-grazing herbage mass was determined at the beginning of the experiment and every 21 days thereafter, by clipping ten, 32 inches x 15 feet strips from each pasture. Strips were cut to as near as ground level as possible. Cows and calves were weighed and body condition scored at the beginning of the experiment and every 21 days thereafter. All cows were maintained on hay from 24 February until weaning on 20 April 2005. The experiment will be repeated again this winter.

Year one project summary
The first year of allocation data collection has been completed. Cows allocated herbage at 2.25 percent of BW hd^-1 d^-1 lost the most weight (avg. daily loss of 2.3 lb hd^-1 d^-1), while the other three allocation levels did not differ (avg. daily loss of 1.9 lb ha^-1 d^-1). Calves in the 2.25% BW hd^-1 d^-1 treatment had an ADG of 1.2 lb hd^-1 d^-1 while those in the 4.5% BW hd^-1 d^-1 had an ADG of 1.6 lb hd^-1 d^-1 (Table 1). Since the acres required to winter a cow-calf pair would double between the lowest and highest allocations, economic analyses suggest stockpiled tall fescue should be allocated levels at 3.0 percent BW hd^-1 d^-1. In addition, cow and calf performance data taken later in the spring at weaning time showed no significant differences between stockpile allocation treatments imposed during the winter.

Rob Kallenbach
Ag Ext-Plant Sciences
573-882-2801