Narasin, salinomycin, flavomycin supplementation in Nellore cattle

Narasin

Narasin is a ionophore that alters rumen fermentation dynamics (Miszura et al., 2018), plasma metabolites by increasing glucose levels (Sardinha et al., 2020) and reducing urea concentration (Polizel et  al., 2020). It is used in beef cattle industry to enhace animal performance (Silva et al., 2015; Polizel et al., 2020).

Salinomycin

Salinomycin is also a ionophore used to improve animal production by favorably altering the acetate:propionate (Ac:Pr) ratio (McClure et  al. 1980; Bagley et  al., 1988).

Flavomycin

Flavomycin (bambermycin) is a non-ionophore antibiotic that inhibits peptidoglycan synthesis of the bacterial cell wall (Volke et al., 1997). It also appears to have indirect benefits on gut tissue protein turnover by suppressing gram-negative pathogenic bacteria (Edwards et  al., 2005), as well as gram-positive bacteria which might allow increased dietary fermentation, resulting in a greater propionate molar proportion (Edrington et al., 2003).

Study

Although feed additives have similar ruminal action mechanisms, animal performance might vary depending on: the animal, dose and type of diet (Bretschneider et al., 2008). Based upon this, it was hypothesized that supplementation with narasin, salinomycin, or flavomycin would impact nutrient digestibility, modify rumen fermentation parameters, and improve productivity of B. indicus Nellore cattle fed a forage-based diet. In order to test this hypothesis, researchers designed a study where they could assess the impacts of narasin, salinomycin, or flavomycin supplementation by evaluating  rumen fermentation characteristics and apparent nutrient digestibility (experiment 1), as well as feed intake, and growth (experiment 2). The experiment was carried out with B. indicus cattle which was fed a high-forage diet for a period of 140 days. These studies were conducted at the University of São Paulo, in Piracicaba campus.

Materials and methods

Experiment 1

Thirty-two rumen-cannulated B. indicus Nellore steers [initial body weight (BW) = 220 ± 12.6 kg; age = 20 ± 1.0 mo] were assigned to individual pens. Within block (n = 8), animals were randomly assigned to 1 of 4 treatments:

1. Forage-based diet without feed additives (CON)
2. CON diet + 13 ppm of narasin (NAR),
3. CON diet + 20 ppm of salinomycin (SAL)
4. CON diet + 3 ppm of flavomycin ( FLA).

The administration rates for NAR, SAL, and FLA were used according to manufacturer’s recommendation. The experimental period lasted 140 d and was divided into 5 periods of 28 d each (0, 28, 56, 84, 112, and 140 d).

Sampling

Samples of the supplement were collected weekly, pooled across all weeks within each period, and analyzed to establish a nutrient profile. From days 23 to 27 (period 1), 51 to 55 (period 2), 79 to 83 (period 3), 107 to 111 (period 4), and 135 to 139 (period 5), total fecal production was individually collected to
determine apparent nutrient digestibility. Total fecal production was collected and quantified twice a day using an electronic scale.

Individual shrunk body weight (BW) was collected on day 0 after 14 hr of feed and water withdrawal to determine initial BW and for establishing randomized blocks and treatments. Forage, supplement, and total dry matter intake (DMI) were recorded daily from each pen by collecting and weighing non-consumed feed (forage only).

Experiment 2

One hundred and sixty-four B. indicus Nellore bulls (initial shrunk BW = 299 ± 2.5; age = 23 ± 3.0 mo) were assigned to pens in a randomized complete block design according to their shrunk
BW (after 14 hr of feed and water restriction).

The experimental period lasted 140 d, divided into 5 periods of 28 d each. Bulls were kept in a covered feedlot (10 pens per treatment; 4 to 5 bulls perpen). Within blocks (n = 10), animals were  randomly assigned
to the same treatments as in experiment 1.

Sampling 

At the beginning (day 0) of the experimental period, individual shrunk BW was recorded after 14 hr of feed and water withdrawal to determine animal initial BW and to perform the randomization of the animals into blocks and treatments.

To calculate average daily gain (ADG) and feed efficiency (G:F), bulls were individually weighed on days 0, 28, 56, 84, 112, and 140 (final days of each period) after 14 hr of feed and water restriction. DMI was evaluated daily from each pen within each period by collecting and weighing non-consumed feed weekly.

Hay and total DMI of each pen were divided by the number of bulls within each pen and expressed as kilogram per bull/day. Within each pen, total BW gain and total DMI of each period
were used for bull G:F calculation. Samples of feed and orts were collected weekly, and pooled across all weeks within each period for further nutrient profile analysis as mentioned for experiment 1.

Results and Discussion

Consistent with findings from Reffett-Stabel et al. (1989) it was observed that total tract digestibility of nutrients was not affected by salinomycin supplementation when cattle consume corn-silage based diets. However, other authors have reported that supplementing flavomycin or monensin resulted in similar or reduced dry matter digestibility in beef cattle consuming forage-based diets.

Feed additives influence ADG, G:F, and DMI of animals offered a high-concentrate diet (Duffield et al., 2012; Golder and Lean, 2016). Similar results were observed, except for DMI, in animals offered a high-forage diet (Bretschneider et al., 2008). In the current study (experiment 2 only), intake was 7.9%, 8.8%, and 10.7 % greater for animals offered NAR compared with CON, FLA, and SAL, respectively. Similar results were observed when intake was expressed as BW percentage. Corroborating the obtained results from the previous study, Miszura et al. (2019) reported an increase of 7.55% in DMI by adding narasin in high forage-based diets.

It should be noted that DMI in the present experiment was not depressed by the inclusion of salinomycin in the diet, despite previous research reporting such outcome in forage and feedlot fed cattle.

According to previous studies, inclusion of feed additives in beef cattle diets normally influenced G:F by improving or maintaining ADG and reducing DMI.  Within the current study, only narasin improved ADG by 14.8%, 11.8%, and 7.8% compared with CON, SAL, and FLA, respectively. This resulted in heavier animals at the end of the supplementation period.

Conclusions

The obtained results for this experiment suggest that supplementing narasin to B. indicus Nellore cattle for 140 d might be a feasible alternative for optimizing rumen fermentation characteristics. Resulting in productivity improvements in grazing beef cattle.

Source:“Effects of supplementation with narasin, salinomycin, or flavomycin on performance and ruminal fermentation characteristics of Bos indicus Nellore cattle fed with forage-based diets.” Journal of Animal Science. April 2021