The impact of fescue toxicosis & T-Snip score on post-weaning beef cattle performance

Abstract

It is well known that fescue toxicosis has a negative impact on cattle productivity. These studies were conducted to evaluate the effects of fescue toxicosis on post-weaning beef steers, as well as the impact of T-Snip score on performance of steers and heifers. We hypothesized that cattle that consumed an E+ diet would perform lower than cattle that did not. We also hypothesized that the cattle coming off of an E+ diet would remain at a lower weight than those that did not throughout the feeding period. T-Snip scores were also believed to be indicative of animal performance while consuming an E+ diet. A two-phase feeding trial was conducted to evaluate the aforementioned effects. 306 crossbred steers (288.8 [plus or minus]3.81 kg) were blocked by weight, T-Snip score, and color, and assigned to one of two treatments. The grow phase consisted of the first 54 days of the experiment. Throughout this period, high roughage, growing diets were fed to the steers. The treatment group was fed a diet containing toxic tall fescue seed, whereas the control diet was fed a seed-free diet. The finishing phase was day 54-slaughter. In this period, all animals were fed a common, corn-based finishing diet. For the first phase of the experiment, there were no differences between treatments for initial bodyweight (IBW), DMI, dry matter intake as a % BW (DMPW), ADG, GF, or end bodyweight (EBW). There was however differences between T-Snip star scores among treatments. In the control group, animals with 2 and 3 stars had a higher ADG (P[less than or equal to]0.05) (1.74 kg vs. 1.68 kg) than animals with 0, 1, & 4 stars (1.59 kg, 1.53 kg vs. 1.53 kg). In the E+ group, animals with zero stars had the lowest ADG (1.42 kg), animals with 1 or 2 stars had an increased ADG (1.65 kg vs. 1.63 kg) and animals with 3 or 4 stars had the highest ADG (1.74 kg vs. 1.76 kg) (P[less than or equal to]0.05). In the finishing phase, control animals had increased DMI (P<0.05) (8.33 kg vs. 7.82 kg). DMIPW, ADG, and EBW tended (P<0.10) to be higher for the control groups. There were no differences between T-Snip star scores among treatments during the finishing phase. HCW was higher for control animals than E+ animals (P[less than or equal to]0.05) (343.01 kg vs. 331.13 kg) Marbling scores were lower in E+ animals than control (P[less than or equal to]0.05) (4.41 vs. 4.71) Carcass value was higher for control treatment than E+ (P[less than or equal to]0.05) ($1486.93 vs. $1420.68). The only difference among T-Snip star scores occurred in the control group, where 0 star animals had increased backfat (BF) (P[less than or equal to]0.05). In another study we evaluated if performance of beef heifers grazing E+ pasture differed among T-Snip score. It was hypothesized that as T-Snip score increased (increased tolerance to E+ tall fescue) average daily gain of heifers would increase. 180 angus-based commercial heifers (343.22 [plus or minus] 17.87 kg) grazed E+ tall fescue pasture for 75 days. Each animal had a hair sample taken and submitted for a T-Snip score and tolerance rating, where animals with 0-1 star were considered susceptible, animals with 2-3 stars were average, and animals with 4-5 stars were considered the most tolerant to fescue toxicosis. As hypothesized, there were differences in ADG between tolerance ratings. ADG for susceptible animals was 0.20 kg, average animals gained 0.25 kg, and the tolerant heifers gained 0.29 kg/d (P=0.07). Average daily gains were as expected for heifers grazing E+ tall fescue pastures. Heifers identified as tolerant had 45% greater average daily gain than heifers identified as intolerant. The objective of this study was to determine if genetic testing for fescue tolerance used in cows had relevance for calves as well. This research demonstrated that genetic selection to improve fescue tolerance could improve progeny performance.