Assessment of Forage Inclusion Strategies as a Means of Reducing Liver Abscesses in Finishing Feedlot Cattle
The average incidence of liver abscesses within beef cattle feedlots ranges from 12 to 32%;1, 2 but
can be as high as 95%.3 Liver abscesses in feedlot cattle are a cause of decreased performance
and reduced carcass value which have been estimated to decrease returns by $20 to $80 per
animal.2 Feeding greater levels of roughages in finishing diets can decrease the incidence of liver
abscesses. However, daily gains and feed efficiency are also reduced.
Tylosin phosphate (Tylan, Elanco Animal Health) is an antibiotic that is commonly fed to feedlot
cattle to decrease the incidence of liver abscesses. However, general concern that in-feed
application of medically important antimicrobials increase antimicrobial resistant pathogen threats to
human health remain. Hence, alternative strategies to control liver abscess that maintain or improve
cattle performance, efficiency, health, and welfare are warranted. Studies looking at the timing of
tylosin inclusion within the finishing period suggest that the greatest risk of liver abscess
development is in the early stages of finishing.4, 5 The typical range for roughage inclusion in
finishing diets is 8% to 10% of dry matter (DM).6
Canadian researchers hypothesized that greater inclusion of forage in the diet early in the finishing
phase would decrease the incidences of liver abscesses and prevent performance losses without
tylosin inclusion. Thus, a study evaluated different strategies of forage inclusion in finishing beef
cattle diets and their effects on growth performance, carcass quality, and liver abscesses as
compared with a typical finishing diet with or without tylosin.7 In this study, 360 sixty yearling
crossbred beef steers (882 lb initial weight) were used in a 175-day finishing experiment which was
split into 4 different feeding periods. The first period consisted of 49 days, and the last 3 periods
consisted of 42 days each. The steers were stratified by weight and randomly allocated across 24
pens, which were randomly assigned to 1 of 4 dietary treatments (15 steers/pen, 6 pens/treatment).
The treatments included: (1) positive control (+CTRL) fed a diet (7.5% forage on a diet DM basis)
with tylosin (10 grams/ton) fed throughout the entire finishing phase; (2) negative control (−CTRL;
control diet without tylosin) fed throughout the entire finishing phase; (3) a strategy with decreasing
forage (DECR) where forage concentrations in the ration decreased from the first to second period
and again from the second to the third period, but did not change from the third to the fourth period
(15%, 9%, 3%, and 3% of diet DM, respectively) without tylosin; and (4) a strategy with increasing
forage (INCR) where forage concentrations in the ration remained static for the first 2 periods (91
days) then increased every 42-day period (3%, 3%, 9%, and 15% of diet DM, respectively) without
tylosin.
The effect of the forage inclusion strategies on feedlot growth performance are shown in Table 1.
The +CTRL steers had greater average daily gain (ADG, 3.79 vs. 3.59 lb/day), shrunk total body
weight (BW) gain (668 vs. 634 lb), and a tendency for greater final BW (1550 vs. 1515 lb), than
INCR steers. In high-grain finishing diets, increases in the forage content of the diet can result in
greater dry matter intake (DMI) in feedlot cattle steers to help meet their energy needs.8 Thus, as
expected, a diet × period interaction was observed for DMI (period intake not shown in table), but it
did not differ among treatments over the full study. DECR steers, who were fed the high forage diets
(15% and 9%, respectively) had greater DMI than INCR steers (fed the 3% forage diet) during
periods 1 and 2. As the 2 experimental treatments switched diets, it would be expected that INCR
steers would have greater DMI than DECR steers in periods 3 and 4, however, this was not the
case.
The effect of forage inclusion strategy on carcass characteristics and liver abscesses are shown in
Table 2. Carcass weights tended to be lower for INCR steers compared with the other treatments (P
= 0.07). The INCR steer carcasses had lower rib fat thickness and yield scores (P = 0.04) than
−CTRL steers. No significant differences were observed in the percentage of total (P = 0.17) or
severe liver abscesses (P = 0.88) between treatments. However, the percentage of steers with
minor liver abscesses tended to be less (P = 0.055) for +CTRL (51.8%) and DECR (51.8%)
compared with −CTRL (62.2%) and INCR (64.3%).
The results of this study showed that greater dietary concentrations of forage earlier in the finishing
phase, with a subsequent decline thereafter, has the potential to decrease the proportion of minor
liver abscesses similar to typical finishing diets including tylosin, without affecting growth
performance or carcass quality. These researchers concluded that these data suggest that the
timing of forage inclusion is more detrimental to performance and carcass characteristics than minor
liver abscesses.
