Effects of a combining feed grade urea and a slow-release product on performance, dietary energetics and carcass characteristics of steers fed finishing diets

Abstract

Recent findings have shown that microbial nitrogen flow and digestible energy of diet are increased when urea (U) is combined with a slow-release urea product (SRU) in diets with a starch:acid detergent fibre (S:ADF) ratio of 4.5, while feed grade U has shown greater effects on growth performance or dietary energy utilization when the diet contains a S: ADF ratio of greater than 5.0. These results can be partially explained by the better synchronization of ruminal degradation rates between those U sources with the carbohydrates of the diets. Therefore, 60 crossbreed steers (372.4 ± 15 kg) were used to evaluate the effects of combining U and SRU in a diet with a S:ADF ratio of 4.5 vs. U that was supplemented in diets with different S:ADF ratios (3.5, 4.5 and 5.5) on growth performance, dietary energetics and carcass characteristics. U combination did not affect average daily gain (ADG), but reduced dry matter intake [DMI, as % of body weight (BW)] enough to increase feed efficiency (G:F) and dietary net energy (NE). As the S:ADF ratio increased, the DMI, ADG, G:F and NE of diet increased linearly. Irrespective of the S:ADF ratio, U diets did not modify neither the observed-to-expected NE ratio nor the apparent retention per unit DMI, while U combination increased by 7.2% and 8.4%, respectively, the observed-to-expected dietary ratio and the apparent retention per unit DMI. U combination had no effect on carcass characteristics. As the S:ADF ratio increased, carcass weight and LM area were increased linearly. Combining feed grade U and SRU in diets with a 4.5 starch:fibre ratio resulted in positive effects on the efficiency of utilization of dietary energetics.

Effects of Combining Feed Grade Urea and a Slow-release Urea Product on Performance, Dietary Energetics and Carcass Characteristics of Feedlot Lambs Fed Finishing Diets with Different Starch to Acid Detergent Fiber Ratios

“…Those researchers argued that those results can be partially explained by the possible synchrony of ruminal degradation rates between urea and starch. At lower S:F ratios it is expected a lower positive effects, therefore, absence of improves of observed NE ratio over expected in urea treatment at 4:1 S:F ratio is not aberrant (observed-to-expected DMI = 0.98), as mentioned above, absence of improvements of observed NE ratio over expected (averaging 0.98) with conventional urea supplementation in diets with S:F ratios of 3, 4.5, and 5.5 was previously reported (López-Soto et al, 2015). The observed-to-expected dietary energy and intake are an important and practical application of current standards for energetics in nutrition research (Zinn et al, 2008).…”

“…It is important to consider that different responses of animals can be caused not only by different sources of urea supplementation but also by dietary variations (UIP level among others). However, in a growth-performance study conducted with feedlot steers, Lopez-Soto et al (2015) with a similar urea combination as in the present experiment in a diet with a S:F ratio of 4.5 observed a 6% of increases on NE of diet and decreases of 6% on the apparent retention per unit DM, while diets with conventional urea did not modify neither the observed-to-expected NE ratio nor the apparent retention per unit DMI, when was included in diets with a S:F ratios of 3, 4.5, and 5.5. It has been observed that in high-grain diets (ratio of starch vs ADF greater than 5 to 1) urea can be supplemented at 50% higher than that recommended with positive effects on growth performance and in dietary energy utilisation (Milton et al, 1997; Zinn et al, 2003).…”

“…Recent findings in a digestion trial showed that when conventional urea was combined with a SRU in diets with a ratio of starch-to-acid detergent fibre (S:F) of 4:1, the digestible energy (DE) was improved by 2% over the expected (p = 0.04) level; while, according to the expected DE values, the predicted DE was 1.00 time to the expected values with urea plus SRU in diets with lower (3:1) or greater (6:1) S:F ratios, and for those that were fed with only urea in diets with a similar ratio of 4:1 (López-Soto et al, 2014). Similarly, increases of 6% on net energy (NE) of diet was observed in feedlot cattle when were fed with a diet with a S:F ratio of 4.5 supplemented with a urea combination, while diets with conventional urea did not modify the observed-to-expected NE ratio when was included in diets with an identical S:F ratio (López-Soto et al, 2015). This is surprising, if is considers that different responses of animals can be caused not only by different sources of urea supplementation but also by dietary variations (i.e.…”

“…This is surprising, if is considers that different responses of animals can be caused not only by different sources of urea supplementation but also by dietary variations (i.e. rumen undegradable intake protein level); however, the differences on observed-to-expected DE and dietary NE obtained by Lopez-Soto et al (2014; 2015) between SRU and for those that were fed with only urea in diets with a similar ratio of S:F justifies the need to confirm these results in a lamb performance trial. To test the findings of Lopez-Soto et al (2014; 2015) on the impact on the dietary energetics, the objectives of this experiment was to examine, in feedlot lambs, the magnitude of the responses on dietary energetics with combining urea and a SRU in diets containing different (3:1, 4:1, or 5:1) S:F ratios.…”

A Meta-Analysis of the Effects of Slow-Release Urea Supplementation on the Performance of Beef Cattle

“…Several studies have evaluated graded levels of SRU supplementation with inconsistent results on the performance of beef cattle [26,27,36]. The variation in the utilisation of urea levels may be due to several factors, such as the continuous availability of fermentable carbohydrate, level of RDP and nitrogenous compounds in the basal diet, feeding regiment-ad libitum or restricted feeding-and adaptation to urea feeding [37].…”