Influence of Nutrient Supplementation on Body Weight and Condition and Pregnancy of Market Beef Cows Grazing Stockpiled and Spring-Growth Tall Fescue1

Professional Animal Scientist, Jun 2005 by Looper, M L, Aiken, G E, Flores, R, Rosenkrans, C F Jr

Abstract

Seventy-five crossbred, non-pregnant beef cows [age = 4.5 ± 0.2 yr; BW = 395 ± 10 kg; body condition score (BCS) = 4.3 ± 0.2] were purchased from local auctions during 2 yr to determine the effects of supplementation on BW, BCS, ADG, pregnancy rate, and net income of market cows grazing stockpiled and spring-growth, endophyte-infected tall fescue (Festuca arundinacea Schreb.). Cows were assigned to one of six pastures (two pastures per treatment each year) of tall fescue for 160 d (yr 1) or 147 d (yr 2) and one of three supplementation treatments: 1) soybean hulls (SH), 2) corn-soybean meal (CSB), or 3) not supplemented (control). Supplements were fed at 0.91 kg/d per cow. Cows were sold at a local auction at the termination of the experiment. Forage availability was not affected (P>0.10) by supplementation and averaged 3637 ± 239 kg DM/ha throughout the grazing period. Supplementation did not influence (P> 0.10) ADG; overall, cows gained 0.47 ± 0.14 kg/d. Cows supplemented with SH (493 ± 25 kg) or CSB (485 ± 25 kg) had heavier (P

(Key Words: Market Cows, Stockpiled Fescue, Soybean Hulls, Pregnancy.)

Introduction

Market beef cows account for 10 to 25% of the annual income of cow-calf production (Apple, 1999; Sawyer et al., 2004). Several studies have indicated that the feeding of market beef cows will increase carcass quality (Wooten et al., 1979; Cranwell et al., 1996; Schnell et al, 1997) and potentially increase net income (Apple, 1999). A recent survey of livestock auctions indicated that pregnancy status of replacement and market cows influenced their selling price (Troxel et al., 2002). Market cows often have thin body condition (Apple, 1999; Brown et al., 2003; Sawyer et al., 2004), and it is well established that decreased body condition hinders reproduction in cattle (Richards et al, 1989; Bossis et al, 1999). Thin cows have the potential to utilize energy and nitrogen more efficiently than fatter cows, resulting in compensatory gain (Freetly and Nienaber, 1998) and increased body condition (Matulis et al, 1987; Schnell et al., 1997). The feasibility of feeding market cows is largely dependent on feed costs (Rogers et al., 2004; Sawyer et al., 2004). Tall fescue is a commonly stockpiled cool-season forage because it provides sufficient forage growth and quality during winter months (Sleper and West, 1996; Hitz and Russell, 1998) and reduces winter feed costs approximately 60 to 75% when compared with conventional winter supplementation practices (BishopHurley and Kallenbach, 2001; Jennings et al., 2004).

Forage digestion may be reduced by the supplemental energy source (Chase and Hibberd, 1987). Soybean hulls (SH), which are high in digestible fiber, have a more positive effect on forage intake and digestibility than corn-based supplements (Ovenell et al., 1991; Marston et al., 1993). Steers grazing stockpiled tall fescue and fed supplemental SH had increased ADG compared with steers grazing stockpiled fescue and fed supplemental corn (Burris et al., 2000; Larson et al., 2000). Increasing value of market cows with the intent of selling pregnant replacement cows has not been studied previously. Further, data are limited on BW and condition changes of cows supplemented with either starch- or fiber-based energy sources and grazing stockpiled tall fescue. The objective of this study was to determine the effect of supplementation on BW, BCS, ADG, pregnancy rate, selling price, and net income of market cows grazing stockpiled and spring-growth, endophyte-infected tall fescue.

Materials and Methods

Forages. The experiment was conducted near Booneville (35° 5'' N; 94° 0' W) in west central Arkansas. Monthly precipitation data for the experiment site were collected during the 2 mo of stockpiling and during the months of grazing for both years (NOAA-NWS, 2004). To initiate the stockpiling process for tall fescue, pastures were clipped to a height of 10.2 cm and fertilized (October 1 in yr 1; September 26 in yr 2) with 40 kg N/ ha. Pastures were fertilized again in the spring (March 5 in yr 1; February 27 in yr 2) with 75 kg N/ha. Fescue pastures were characterized three times (initiation, mid point, and termination of grazing) during the experiment to determine forage availability and nutritive value. Forage availability was evaluated using a disk meter (Bransby et al., 1977). Forage height was recorded at 150 to 225 random locations (9 measurements/ha) in each pasture at the initiation, mid point, and at the termination of the experiment. To calibrate disk meter measurements, forage was clipped to ground level beneath the disk meter at five locations per pasture at the three sample periods. Samples were dried (60°C) in a forced-air oven for 72 h and weighed for calculation of regression equations of kg DM/ha and disk meter height. Random grab samples (20 samples/16 ha pasture) were utilized for evaluating nutritive value of forage at the three sample periods. Nutritive subsamples were ground to pass through a 2-mm screen and analyzed for CP (Kj el tech 1030 Auto Analyzer; Tecator, Hgans, Sweden), IVDMD, and ADF using the Goering and Van Soest (1970) procedure modified for use with the Ankom Daisy II In Vitro Digester® (Ankom Technology Corp., Fairport, NY). Endophyte infection rates of tall fescue pastures were determined from tillers at 100 randomly selected sites in each pasture. Approximately 90% of the tillers in each pasture were producing ergot alkaloids (immunoblot detection method; Agrinostics Ltd. Co., Watkinsville, GA). Forage samples were clipped at ground level from 25 randomly selected sites in each pasture to determine concentrations of ergovaline at the three sample periods. Samples were pooled and dried (38°C) in a forced-air oven for 5 d; concentrations of ergovaline were determined using HPLC as previously described (Craig et al., 1994).