EFFECT OF GRAZING TALL FESCUE ENDOPHYTE TYPES ON SUBSEQUENT FEEDLOT PERFORMANCE AND CARCASS QUALITY

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1 EFFECT OF GRAZING TALL FESCUE ENDOPHYTE TYPES ON SUBSEQUENT FEEDLOT PERFORMANCE AND CARCASS QUALITY S. K. Duckett, M. A. McCann, J. G. Andrae, T. D. Pringle, J. N. Carter 1, and D. R. Gill 1 SUMMARY Research was conducted to determine the effect of grazing tall fescue pastures with different endophyte types on subsequent feedlot performance and carcass quality of beef steers. Twenty-four steers were transported to Stillwater, OK after grazing tall fescue endophyte infected (EI), free (EF), or non-toxic (NT) pastures for 63 d at the Central Georgia Experiment Station. At the end of the finishing period (112 d), steers were harvested and carcass data collected. At the completion of the grazing study, NT and EF steers were heavier (P < 0.05) than EI. Overall average daily gains in the feedlot were similar (P > 0.05) between treatment groups. Live weights were 114 and 132 lb lower (P < 0.05) for EI at d 0 and 112 on feed, respectively, than EF and NT. Thus, EI cattle did not compensate in the feedlot for the lower gains in the grazing period and remained lighter in weight than EF or NT at harvest. Steers finished after grazing NT pastures returned $161 more per head compared to EI due to numerical advantages in carcass weight and quality grade. INTRODUCTION Tall fescue is the predominant cool season perennial grass in the eastern United States. Poor animal performance has been a problem associated with tall fescue pastures due to the ingestion of the fungal endophyte (a fungus within the plant) which causes toxicity problems known as "fescue toxicosis". However, the presence of fungal endophyte (Neotyphodium coenophialum) in tall fescue has been shown to positively impact plant persistence and agronomic performance. A new, non-toxic endophyte tall fescue (Max-Q ; Pennington Seed) has been developed. Previous research at The University of Georgia (McCann et al., 2000) has shown that grazing pastures containing this non-toxic endophyte fescue improves growth rates compared to endophyte-infected fescue pastures with similar stand persistence. However, no information is available on subsequent feedlot performance of cattle that grazed non-toxic endophyte fescue pastures. Lusby et al. (1988) found that cattle previously grazed on endophyte-infected fescue pastures can make significant compensatory gain during the first 50 d in the feedlot. The objective of this study was to determine the subsequent feedlot performance and carcass quality of cattle grazed on tall fescue endophyte infected, free, or non-toxic pastures. MATERIALS AND METHODS Replicated (n = 2) two ac paddocks of tall fescue monocultures were established at the Central Georgia Branch Experiment Station near Eatonton. Each paddock contained one of three treatments: non-toxic endophyte-infected tall fescue (NT), endophyte-free tall fescue (EF) or wild-type endophyte infected tall fescue (EI). Hereford-Angus crossbred steers initially weighing an average of 650 lb were randomly assigned to the treatment paddocks. The animals were provided with water, minerals, and shade in each paddock. Put-and-take grazing management was used to maintain similar forage 1 Oklahoma State University, Stillwater. The Univ. of Georgia, CAES, Dept. of Animal & Dairy Sci., 2000 Annual Report. 163

2 availability among the paddocks (2000 lb DM/ac) for a 63 d grazing period. Animal weights and rectal temperatures were collected at 28-d intervals during the grazing study. At the completion of the grazing study, real-time ultrasound measurements of fat thickness, ribeye area, and intramuscular fat content were collected on all animals. Twenty-four steers were then transported to the Willard Sparks Feedlot at Oklahoma State University, Stillwater. The cattle were allotted to pens (4 hd per pen) based on fescue endophyte type and fed for 112 d. All animals were implanted (Revalor-S) at the start of the finishing period. Rectal temperatures were collected upon arrival of the cattle at the feedlot and at processing (3 d after arrival). Live weights were recorded for each animal at 28 d intervals across the feeding period. At the end of the finishing period, the cattle were transported to a commercial packing plant, harvested, and carcass data collected. Feedlot performance and carcass quality data were analyzed according to the general linear model of SAS (SAS Inst. Inc., Cary, NC) with endophyte type in the model. Means were separated using the least squares means procedure of SAS. RESULTS The effect of tall fescue endophyte type on live weight gain, gain per acre, and rectal temperature during the grazing period are shown in Table 1. There was no treatment effect (P > 0.05) on rectal temperature; however, this may indicate that rectal temperature measurements taken at a single point in time are not an accurate measure of toxicosis. The animals on the EI paddocks exhibited heat stress during periods of elevated environmental temperatures. Average daily gain was higher (P < 0.05) on NT and EF pastures than on EI pastures. Gain per acre, a measure that accounts for both animal and plant performance, was lower (P < 0.05) for the EI treatment compared to the NT and EF treatments. There was no difference (P > 0.05) in gain per acre between the NT and EF paddocks; however, this result is only for the first yr of grazing and may change as additional data is collected on plant persistence by endophyte type. Differences in live weight and real-time ultrasound measures at the completion of the grazing period for the NT, EI, and EF pastures are shown in Table 2. Cattle grazing the NT and EF pastures had heavier (P < 0.05) live weights than EI at the completion of the grazing study. Ribeye area was larger (P < 0.05) for NT and EF cattle than EI; however, values were similar (P > 0.05) when corrected for differences in live weight (ribeye area/cwt LW). Fat thickness and percent intramuscular lipid were similar (P > 0.05) between the grazing treatments. Rectal temperatures of steers and average daily gains in the feedlot are shown in Table 3. Rectal temperatures were higher (P < 0.05) for EI steers than EF or NT on arrival at the feedlot in Stillwater, OK. However at processing (3 d after arrival), rectal temperatures were similar (P > 0.05) between treatments. Average daily gains were similar (P > 0.05) between treatments during the first 28 d (0 to 28 d) and last 28 d (84 to 112 d) on feed. From 28 to 56 d, average daily gains were higher (P < 0.05) for NT than EI or EF. From 56 to 84 d, average daily gains were higher (P < 0.05) for EF than EI or NT. Overall (0 to 112 d), average daily gains in the feedlot were similar (P > 0.05) between treatment groups. Figure 1 shows the change in live weight across time-on-feed. Live weights were 114 and 132 lb lower (P < 0.05) for EI at d 0 and 112 on feed, respectively, than EF and NT. Thus, EI cattle did not compensate in the feedlot for the lower gains in the grazing period and remained lighter in weight than EF or NT at harvest. Carcass data and values for all cattle after 112 d on feed are presented in Table 4. Carcass traits were similar (P > 0.05) between the treatment groups. However, numerical advantages were observed for NT (+ 82 lb) and EF (+ 61 lb) in carcass weight over EI. Fat thickness and yield grade were also numerically lower for NT than EI or EF. Overall, carcass values ($/cwt and $/hd) were higher (P < 0.05) for NT than EI. Carcass values for EF were intermediate to NT and EI. Steers finished after grazing NT returned $161 The Univ. of Georgia, CAES, Dept. of Animal & Dairy Sci., 2000 Annual Report. 164

3 more per head compared to EI. Additional research is needed with larger animal numbers to further determine the effect of prior grazing treatments on carcass quality and value. Table 1. Effect of tall fescue endophyte type on grazing performance of steers. EI a NT a EF a Daily gain, lb/d 1.65 c 2.60 b 2.49 b Gain per hectare, lb/ac 169 c 273 b 278 b Rectal temp, F wild-type endophyte-infected (EI). Table 2. Effect of grazing tall fescue endophyte types on real-time ultrasound measures of fat thickness, ribeye area, and intramuscular lipid at the end of the 63 d grazing period. Live weight (LW), lb 847 c 955 b 966 b 21 Fat thickness, in Ribeye area, in c 8.24 b 8.14 b 0.27 Ribeye area, in 2 /cwt LW Intramuscular lipid c, % wild-type endophyte-infected (EI) for 63 d. d Estimated quality grade from ultrasound intramuscular lipid: % = Select; % = Choice-. The Univ. of Georgia, CAES, Dept. of Animal & Dairy Sci., 2000 Annual Report. 165

4 Table 3. Effect of grazing tall fescue endophyte types on subsequent feedlot performance. Rectal temp at arrival, F b c c 0.30 Rectal temp at processing, F Average daily gain, lb d d c 5.35 b 4.32 c 0.33 d c 3.33 c 5.10 b 0.26 d d wild-type endophyte-infected (EI) for 63 d prior to entry into feedlot. Figure 1. Effect of grazing tall fescue endophyte types on subsequent feedlot live weight gains. Live weight, lb Time, d Endophyte Infected Non-toxic endophyte Endophyte free The Univ. of Georgia, CAES, Dept. of Animal & Dairy Sci., 2000 Annual Report. 166

5 Table 4. Effect of tall fescue endophyte type on subsequent carcass quality and value. Hot carcass weight, lb Fat thickness, in Ribeye area, in Ribeye area, in 2 /cwt HCW KPH, % Yield grade Marbling score b Quality grade c % Choice Carcass value d, $/cwt HCW f e ef 2.59 Carcass value d, $/hd f e ef wild-type endophyte-infected (EI) for 63 d prior to entry into feedlot. b Marbling score code: = Slight, = Small. C Quality grade code: 2 = Standard+, 3 = Select-, 4 = Select+, 5 = Choice-, 6 = Choice!, 7 = Choice+. d Grid pricing, $/cwt HCW: base $ (Choice, yield grade 3); premiums of $5.59 for > Choice-, $2.5 for yield grade 2, and $4 for yield grade 1; discounts of $25.50 for yield grade 4, $9.75 for Select, and $23.10 for heavy weight carcass. ef Means in the same row with uncommon superscripts differ (P < 0.05). REFERENCES McCann, M. A., J. A. Bandurant, L. L. Hawkins, N. S. Hill, C. S. Hoveland, F. N. Thompson, G. C. M. Latch, and J. H. Bouton Alleviating tall fescue toxicosis with non-toxic endophytes. J. Anim. Sci. 78 (Suppl. 1):123. Lusby, K. S., W. E. McMurphy, S. Muntz, J. Cantrell, C. A. Strasia, and S. D. Kraich Carryover effect of fescue endophyte on feedlot performance of steers. Okla. St. Anim. Sci. Res. Rep. MP- 125:142. The Univ. of Georgia, CAES, Dept. of Animal & Dairy Sci., 2000 Annual Report. 167