|Coffey, Kenneth - University Of Arkansas|
|Caldwell, James - Lincoln University Of Missouri|
Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2015
Publication Date: 11/30/2015
Citation: Coffey, K.P., Coblentz, W.K., Caldwell, J.D., Ogden, R.K. 2015. Pre- and post-weaning performance by cows and calves that grazed toxic or non-toxic endophyte-infected tall fescue pastures prior to weaning. Professional Animal Scientist. 31:577-587.
Interpretive Summary: Tall fescue is the predominant cool-season pasture grass in the Upper South, but most tall fescue pastures are infected with the (toxic) wild-type endophyte (E+). The negative impacts on performance by cattle grazing E+ tall fescue pastures are well documented, but suitable remedies to negate these impacts are limited. One potential remedy is a newly developed non-toxic endophyte-infected tall fescue (NE+). In order to study how grazing cattle perform on NE+ tall fescue, we compared pre- and post-weaning performance by spring-calving beef cows and calves grazing E+ tall fescue with that of cows and calves grazing the NE+ tall fescue. Steers reared on NE+ tall fescue pastures had greater weaning weights than those reared on E+ pastures, and these advantages generally were retained throughout subsequent backgrounding and feedlot phases of production. More importantly, cows grazing NE+ pastures had greater calving rates (85.1%) than those grazing E+ pastures (44.7%). The same was true for first-calf heifers, with a 90.6% calving rate for those on NE+ pastures and only a 64.1% rate for those on E+ pastures; these differences occurred even though all heifers were developed on non-toxic pastures following weaning. Based on the improved calf performance, combined with dramatic improvements in reproductive rates, novel endophyte technology could provide much-needed relief from tall fescue toxicosis throughout the entire tall-fescue region. However, further evaluations are needed to determine plant vigor and persistence under continual year-round grazing for more years so that adequate economic evaluations can be conducted.
Technical Abstract: The negative impacts on performance by cattle grazing tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] pastures infected with the wild-type endophyte Neotyphodium coenophialum (E+) are well documented and reviewed, but suitable remedies to mitigate these negative impacts are limited. Our objectives were to compare pre- and post-weaning performance by spring-calving cows and calves grazing E+ tall fescue with that by cows grazing a non-toxic endophyte-tall fescue association developed at the Univ. of Arkansas (NE+). Gelbvieh x Angus crossbred cows (n=136; 492±19.2 kg initial BW) were stratified by weight and age and allocated randomly to one of four 10-ha pastures in year 1 and one of eight 10-ha pastures in year 2. The pastures were allocated randomly prior to establishment such that half contained E+ and half contained NE+. Cows confirmed as pregnant by rectal palpation began grazing the experimental pastures on October 15 in year 1 and November 30 in year 2. Cows remained on their assigned pastures until weaning in year 2, but were removed from NE+ pastures in the summer of year 1 because of low forage mass from extremely dry summer conditions. After weaning, calves grazed bermudagrass pastures followed by cool-season annuals. Cow BW and pregnancy rate were greater (P < 0.05) and hair scores were lower (P < 0.05) at weaning from those grazing NE+ vs. E+ pastures. Actual and adjusted weaning weight, and calf gain from birth to weaning were greater (P < 0.05) from NE+ compared with E+ pastures. Steers weaned from NE+ were heavier (P < 0.01) at weaning, at feedlot transport, and at the end of the feedlot period, and produced heavier hot carcasses (P < 0.05) than steers weaned from E+, but post-weaning growth rates and carcass quality and yield grades did not differ (P = 0.33) between NE+ and E+. Heifers weaned from NE+ tended (P < 0.10) to be heavier at weaning and had greater (P < 0.10) subsequent calving rates, but post-weaning gains did not differ (P = 0.33) between forages . Therefore, replacing toxic tall fescue pastures with non-toxic, novel endophyte-infected tall fescue may improve cow reproductive performance, calf growth, and cow and subsequent heifer reproductive performance. Negative impacts of E+ on nursing calves were not compensated for during later production stages on non-toxic feedstuffs, but those impacts on growth rates did not persist and cause further negative impacts on post-weaning animal growth.