Different combinations of sodium monensin and virginiamycin during feedlot finishing of Nellore cattle

Abstract

Context The use of two feed additives, to maximise rumen fermentation, in finishing diets offered to feedlot cattle may positively impact performance. Aims This study, conducted at the São Paulo State University feedlot, Botucatu campus, Brazil, was designed to evaluate the effects of the combined use of monensin (MON; 30 mg/kg of dry matter; (DM)) and virginiamycin (VM; 25 mg/kg of DM) in high-concentrate diets during the adaptation and finishing periods on feedlot performance, carcass traits, feeding behaviour, blood gas profile, rumen morphometrics and apparent total tract digestibility of nutrients of Nellore cattle. Methods The experiment was designed as a completely randomised block, replicated six times (3 bulls/pen), in which 72 20 months of age yearling Nellore bulls (388.0 ± 31.1 kg) were fed in 24 pens for 90 days according to the treatments: (1) MON during the entire feeding period (T1), (2) MON + VM during adaptation and only VM during the finishing period (T2), (3) MON + VM during the entire feeding period (T3), and (4) VM during the adaptation and MON + VM during the finishing period (T4). The adaptation program consisted of ad libitum feeding of three diets over the adaptation period of 19 days with concentrate level increasing from 69% to 84% of diet DM. Key results Overall, bulls fed on T2 had a greater DM intake (P < 0.01), final bodyweight (P = 0.04), average daily gain (P = 0.03), hot carcass weight (P < 0.01), final Longissimus muscle area (P = 0.05), Longissimus muscle area daily gain (P = 0.01), improved carcass G:F (P < 0.01) and increased dressing percentage (P < 0.01). Similarly, bulls fed on T2 were faster to consume 1 kg of either DM (P < 0.01) or neutral detergent fibre (P < 0.01) after 60 days on feed. Furthermore, bulls fed on T2 presented a greater (P = 0.05) cell proliferation index in the rumen papillae. Conclusions According to the results, Nellore yearling bulls should be fed high-concentrate diets containing MON and VM during adaptation, and only VM during the finishing period to improve overall feedlot performance. Implications The use of both MON and VM proved to be helpful only during the adaptation period.

The Potential of Shortening the Adaptation of Nellore Cattle to High-Concentrate Diets Using Only Virginiamycin as Sole Feed Additive

“…Moreover, since the feeding of VM as the sole feed additive increased the DMI without positive impacts on ADG, the cattle fed VM14 had a feed efficiency negatively impacted by 9.4 and 7.5% when compared to the bulls fed MON14 and MONVM14, respectively. It has been previously reported that VM does not negatively impact DMI ( 8 , 11 ) as MON does ( 7 ). As a result, the cattle fed VM14 increased the cost to gain a kilogram of BW by 11.8 and 8.0% in relation to animals receiving MON14 and MONVM14, respectively.…”

“…The cattle fed VM14 showed a greater DMI per meal during feeding behavior evaluations on both adaptation and finishing periods, which explains the greater DMI throughout the study, expressed either in kilograms or as percent of BW, when compared to the cattle fed MON14 or MONVM14 since no differences in meals per day or meal length were detected. It is documented in the literature ( 7 , 8 ) that the negative effect of MON on DMI is related to a lower DMI per meal. As a result, the cattle consuming VM14 increased the DMI fluctuations by 22% (0.90 vs. 0.74 kg; Table 2 ) throughout the study in relation to the cattle fed MON14; however, the average daily fluctuation, expressed in percent, was 6.78 and 5.35% for the cattle fed VM14 and MON14, respectively.…”

“…Among potential feed additives that might be recommended for feedlot cattle, virginiamycin (VM) is a growth promoter that does not decrease the DMI and improves feedlot performance (11), and it was the second feed additive mostly used by Brazilian nutritionists in 2019 (12). When VM was evaluated as an alternative to MON (8), authors reported that Nellore bulls fed VM as the sole feed additive during adaptation reached a DMI of 2% of the initial body weight (BW) in 4.3 days on average, whereas those fed MON needed 20.7 days to reach a similar intake. The DMI is an important indicator to evaluate how well cattle are either accepting or adapted to the diets (6), and the faster cattle reach a DMI of 2% of BW, the more adapted they are to the diets.…”

“…Monensin is known for its negative effect on dry matter intake (DMI), which typically results in a positive effect on the feed efficiency of feedlot cattle ( 7 ). Furthermore, the DMI is usually lower during adaptation when compared to the finishing period ( 8 ), and the use of a feed additive, such as the MON, may decrease even further the DMI in this period. Since finishing diets in Brazil contain less energy than a typical feedlot diet in North America ( 9 , 10 ), the use of a feed additive that does not impact the DMI, especially during adaptation, may be recommended.…”

The 2019 Brazilian survey on nutritional practices provided by feedlot cattle consulting nutritionists

“…Sodium monensin, the most popular feed additive among feedlot consulting nutritionists (Table 10), is an ionophore, which has been cited in all past Brazilian (Millen et al, 2009;Oliveira and Millen, 2014;Pinto and Millen, 2019) and American surveys (Samuelson et al, 2016) as the primary type of feed additive used in finishing diets. Virginiamycin has been cited as the secondary feed additive used by their clients in finishing diets, since the combination of monensin and virginiamycin in finishing diets has become popular in the past four years based on promising results related to increasing carcass weight (Rigueiro et al, 2020). However, we cannot guarantee, based on the results of this survey, that all nutritionists' clients that use virginiamycin as secondary feed additive also use sodium monensin as their primary feed additive.…”