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

Because of its low cost per unit of nitrogen (N) compared with most sources of natural protein, urea (U) is typically the primary source of supplemental N in conventional steam-flaked corn-based finishing feedlot diets (Vasconcelos et al. 2009). Previous reports (Milton et al. 1997; Zinn et al. 2003) have shown that supplemental U has more positive effects on growth performance or dietary energy utilization when the diet contains a starch:acid detergent fibre (S:ADF) ratio of greater than 5.0. However, as a result of the cost of grains, the replacement of grains by co-products (i.e., dried distillers grain with solubles) in feedlot diets is a common practice (Klopfenstein et al. 2008). This change produces diets that contain a lower amount of starch and a greater amount of fibre (Carrasco et al. 2013). Thus, the S:ADF ratio in finishing diets can be reduced (i.e., from 5.0 to 3.0). Hypothetically, combining feed grade U with slowrelease urea (SRU) in this type of diet should elicit a better synchrony between starch (high rate of digestion) and fibre (low rate of digestion). Recent findings (López- Soto et al. 2014) indicate that the combination of U and SRU when there is a certain proportion (4.5 to 1) of S: ADF in the diet results in greater improvements in the microbial nitrogen flow and digestible energy of the diet. Because no information is available related to the growth performance and dietary energetics of finishing cattle to verify the findings of López-Soto et al. (2014), the aim of this experiment was to examine the effects of the supplementation of U and SRU in a diet with a S:ADF ratio of 4.5 vs. U supplementation in diets with different S:ADF ratios (3.5, 4.5 and 5.5) on growth performance, dietary energetics and carcass characteristics.

 

All animal management procedures were conducted within the guidelines of locally-approved techniques for animal use and care (NOM-051-ZOO-1995, NOM-062- ZOO-1995 and NOM-024-ZOO-1995).

 

Sixty crossbreed yearling steers (live weight average 372.4 ± 15 kg) approximately 20% Zebú breeding with the remainder represented by Hereford, Angus and Charolais breeds in various proportions, were used to evaluate the treatments effects on characteristics of growth-performance, dietary energetic and carcass characteristics. The trial was conducted at the Feedlot facilities located in Sinaloa, México (25°33′ N and 108°25′ W). The site is about 120 m above sea level, and has a tropical climate.The experiment lasted 70 days (November to January). Six weeks before initiation of the experiment steers were vaccinated for bovine rhinotracheitis and parainfluenza 3 (TSV-27, Pfizer Animal Health, México), clostridials (Fortress 7, Pfizer Animal Health, Mexico) and Pasteurella haemolytica (One Shot, Pfizer Animal Health, México), and treated for parasites (CYDECTIN® NF, Pfizer Animal Health, México; Trodax, Merial, México). Steers were injected with 1 × 106 IU vitamin A (Vita-Jec A& D “500”, Synt-ADE®, Fort Dodge, Animal Health, México) and were implanted with 200 mg of trenbolone acetate and 20 mg of estradiol 17β (Revalor H®, Intervet, México). Steers were blocked by weight into five blocks and assigned within blocks to 20 pens (3 steers/pen). Pens were 4.00 × 8.20 m with 19 m2 of shade, and were equipped with automatic waterers and fence-line feed bunks (2.37 m in length). Cattle were weighed at the start of experiment, at day 35 and before the steers were harvested (day 73). Based that the better responses on microbial duodenal flows and digestible energy of diet was observed only when U and SRU was combined at same proportion (0.80% of each) in diets which proportion of S:ADF is about 4.5 (López-Soto et al. 2014) and that previous reports (Milton et al. 1997; Zinn et al. 2003) have shown that supplemental U has more positive effects on growth performance or dietary energy utilization when the diet contains a ADF ratio of greater than 5.0, thus, to test our hypothesis, four treatments were formulated as follows.

 

 

Feed and refusal samples were collected daily for DM analysis, which involved oven drying the samples at 105°C until no further weight loss occurred (method 930.15, AOAC 2000). In addition, Kjeldahl N (method 984.13, AOAC 2000), ADF (Van Soest et al. 1991) and starch (Zinn 1990) were determined in feed samples.

 

The estimations of expected DMI and dietary energetic were performed based on measures of initial and final shrunk body weight (SBW), assuming that SBWis 96% of full weight (NRC 1996). Average daily gains (ADG) were computed by subtracting the initial BW from the final BW and dividing the result by the number of days on feed. The efficiency of BW gain was computed by dividing ADG by the daily DMI. The estimation of expected DMI was performed based on the observed ADG and SBW according to the following equation: expected DMI, kg/day = (EM/NEm) + (EG/ENg), where EM (energy required for maintenance, Mcal/day) = 0.077W 0.75 (Garrett 1971), EG =ADG1.097 × 0.0557W0.75 (NRC 1984), NEm and NEg are 2.22 and 1.55 Mcal/kg, respectively (derived from tabular values based on the ingredient composition of the experimental diet; NRC 1996). The dietary NEg was derived from NEm by the equation: NEg = 0.877 NEm − 0.41 (Zinn et al. 2008). Dry matter intake (DMI) is related to energy requirements and dietary NEm according to the equation: DMI = EG/(0.877NEm − 0.41), and can be resolved for estimation of dietary NE by means of the quadratic formula: x  , where x = NEm, a = −0.41EM, b = 0.877 EM + 0.41 DMI + EG, and c = −0.877 DMI (Zinn & Shen 1998).

 

All steers were harvested on the same day. Hot carcass weights (HCW) were obtained from all steers at the time of slaughter. After carcasses were chilled in a cooler at _2°C to 1°C for 48 h, the following measurements were obtained: (1) LM area, taken by direct grid reading at the twelfth rib; (2) subcutaneous fat over the ribeye muscle at the twelfth rib taken at a location three-quarters of the lateral length from the chin bone end; (3) kidney, pelvic and heart fat (KPH) as a percentage of carcass weight; and (4) marbling score (USDA 1997).

 

Performance (gain, gain efficiency and dietary energetics) and carcass data were analysed as a randomized complete block design. The experimental unit was the pen. The MIXED procedure of SAS (SAS Institute Inc. 2004) was used to analyse the variables. The fixed effect consisted of treatment, and pen as the random component. Three contrasts were defined to answer: (1) the effect of U combination vs. U at same S:ADF ratio (4.5), (2) linear response of the S:ADF ratio in U treatments and (3) quadratic response of the S:ADF ratio in U treatments. F-test (numerator = 1 df, denominator = error df) was utilized to test contrasts. The analysis was carried out using SAS (SAS Inst., Inc., Cary, NC; Version 9.1). Contrasts were considered significant when the P-value was ≤0.05, and tendencies were identified when the P-value was > 0.05 and ≤0.10.

 

According to the determinations of starch and ADF obtained in the laboratory, the S:ADF ratio reached 101, 99, 102 and 101% of the planned for each treatment (Table 1). Treatment effects on growth performance of feedlot steers are shown in Table 2. U combination did not affect (P = 0.96) ADG, but tended to reduce DMI (5.1%, P = 0.06), and reduced DMI expressed as a percentage of live weight (5.8%, P = 0.02). In a few studies, the absence of effects on feed intake of the combination of U plus SRU products has been observed previously in steers fed a finishing diet (Tedeschi et al. 2002; Pinos-Rodríguez et al. 2010; Castañeda-Serrano et al. 2013). However, a tendency for reduction in DMI has been observed in steers fed diets containing 2.25% of a solution of SRU product based on calcium bond U (Duff et al. 2000). Taylor-Edwards et al. (2009) reported a 4.4% reduction in DMI when 0.8% of Optigen II replaced 0.8% of U, but these responses were noted only in the last 28 days of the 56 days of the experiment. As mentioned previously (materials and methods section) in the present experiment the DM intake was registered daily and DM intake pattern was consistent lower to urea combination treatment (SRU) throughout experiment. The basis for the inconsistencies in DMI responses to SRU supplementation is not certain, but may be related to the taste of SRU products and/or diet composition.

 

In the present experiment, the decreases in DMI on SRU + U treatment was enough to increase feed efficiency (G:F) by 14.2% (P = 0.02) and to increase the dietary net energy (NE) by 7.2%. Duff et al. (2000) reported that the gain-to-feed ratio was improved by 4.4% (P < 0.01) when 100% of U (1.21% in the diet) and 100% of soybean meal (2.80% in the diet) were replaced by 2.25% of Ruma Pro (a SRU product) plus 1.76% of corn grain. Changes in the productivity and/or energy efficiency of cattle that have been fed diets containing SRU can be explained by improvements in N retention by decreases in ruminal ammonia concentration and increases in microbial flow to the duodenum (Akay et al. 2004; Alvarez-Almora et al. 2012). López-Soto et al. (2014) showed that steers fed a combination of U and SRU (Optigen) in a diet with a S:ADF ratio of 4.5 had higher (P = 0.04) flows of microbial N and digestible energy of diet than those fed U and those fed U plus SRU in diets with a S:ADF ratio of 3 or 6. They explained that the combination of feed grade U with SRU in diets containing a certain ratio of starch:fibre should promote a better synchrony between starch (high rate of digestion) and fibre (low rate of digestion). In contrast, other studies (Tedeschi et al. 2002; Pinos-Rodríguez et al. 2010) showed that SRU supplementation to finishing steers did not have positive effects on neither gain nor feed efficiency. The estimated S:ADF ratio of the experimental diets of studies conducted by Tedeschi et al. (2002) and by Pinos-Rodríguez et al. (2010) was over 5.4; thus, the high S:ADF ratios of the diets used in those studies could be a factor in the absence of effects on the performance and feed efficiency of steers fed a combination of U and SRU.

 

Compared with the U diets, combining U and SRU at a 4.5 S:ADF ratio increased (P < 0.01) by an average of 7.2% the observed-to-expected dietary ratio and reduced by 8.4% (P < 0.01) the apparent retention per unit DMI. This corroborates the findings of López-Soto et al. (2014), which reported an energetic advantage (increases in digestible energy) in cannulated steers when the combination of SRU + U was given at a ratio of starch and ADF identical to that used in the present experiment. In practical terms, if we consider that the diet composition of combined U treatment (SRU + U-4.5) andU treatment at the same S:ADF ratio (U-4.5, Table 1) were practically identical, the energy improvement observed for SRU + U-4.5 treatment represents the equivalent of an increase of 6.4% [(2.14 − 2.00)/2.18] of steam-flaked sorghum in the diet.

 

Table 2. Influence of treatments on growth performance and dietary energy of feedlot steers.

^aSRU + U-4.5 = 0.80% U plus 0.80% at 4.5 S:F ratio, U-3.5 = 0.80 U at 3.5 S:F ratio, U-4.50 = .80% U at 4.5 S:F ratio, and U-5.5 = 0.80% U at 5.5 S: F ratio.
^bProportion of starch vs. fibre acid detergent in diet.
^cSource of SRU was Optigen II, Alltech Inc., México, Guadalajara México.
^dThe initial and BW was reduced by 4% to adjust for the gastrointestinal fill.
^eThe estimation of dietary NE was performed based on observed ADG, DMI and average shrunk weight (SBW) and was estimated by means of the quadratic formula: x=  , where x = NEm, a = −0.41EM, b = 0.877 EM + 0.41 DMI + EG, and c = −0.877 DMI, where EM = maintenance coefficient of 0.077 Mcal/BW0.75 (NRC 1984), EG is the daily energy deposited (Mcal/day) estimated by equation: EG = ADG1.097 × 0.0557W0.75 (NRC 1984), and DMI is the average daily dry matter intake (Zinn et al. 2008).
^fObserved to expected dietary NE ratio was computed by dividing NE observed between expected diet NE, which was estimated based on tabular values for individual dietary ingredients (NRC 1996). gExpected DMI, kg/day = (EM/NEm) + (EG/ENg); where, NEm and ENg is the diet energy concentration.

 

The average observed DMI of steers fed U diets was 102% of the expected based on tabular (NRC 1996) estimates of diet energy density and observed SBW and ADG (Table 2), supporting the practicality of the prediction equations proposed by the NRC (1996) for the estimation of DMI in relation to SBW and ADG in feedlot cattle. Similar responses in DMI between diets containing different levels of forage have been observed previously in trials involving steam-flaked corn-based diets (Zinn et al. 1994; Calderon-Cortes and Zinn 1996). As the S:ADF ratio increased, the DMI, ADG, G:F and NE of diet increased (P ≤ 0.03) linearly. The increases in gain, feed efficiency or both, as a result of increases in energy density in diets are well documented (Zinn et al. 2008).

 

Irrespective of the S:ADF ratio, U diets did not modify neither the dietary energy ratio nor the observedto-expected DMI. It has been observed that in highgrain diets (a starch:ADF ratio of greater than 5.0:1), U can be supplemented at a level 50% higher than the recommended with positive effects on growth performance or in dietary energy utilization (Milton et al. 1997; Zinn et al. 2003). One possible advantage to higher U levels in finishing diets might be related to the buffering effects of U as a result of its hydrolysis to CO2 and NH3 and the potential buffering effects via ammonia (Galyean 1996), and/or because the synchrony of ruminal degradation rates between feed grade U and starch is maybe more favourable in these types of diets. The observed-toexpected dietary energy and intake are an important and practical application of current standards for energetics in nutrition research (Zinn et al. 2008). Based on diet composition and measures of growth performance, there is an expected energy intake and hence an expected of DMI (NRC 1996). The estimation of dietary energy and the ratio of observed-to-expected DMI reveals differences in efficiency independently of ADG, providing important insight into potential treatment effects on the efficiency of energy utilization of the diet itself. In the present experiment, the absence of effects on observedto-expected DMI and dietary NE of the U treatments at different S:ADF ratios showed that starch and fibre at these proportions did not provide any energetic advantage when they were supplemented with U.

 

Treatment effects on carcass characteristics are shown in Table 3. Similar to previous reports (Pinos-Rodríguez et al. 2010; Holland & Jennings 2011), there were no effects of U combination on carcass characteristics. As the S:ADF ratio increased, carcass weight and LM area were increased linearly. The linear increases in HCW and dressing percentage, as a result of increased S:ADF ratio, was likely due to the concomitant linear increase in ADG (Block et al. 2001). In the same manner, an increased LM area has been a consistent response to an increased rate of ADG (Zinn et al. 2007).

 

Under the conditions of the current experiment, it was concluded that combining U with Optigen II in diets containing an approximate S:ADF ratio of 4.5:1 increases by 8% the dietary energy efficiency. This energetic advantage represents the equivalent of a 6% increase of grain in the diet. An additional point is that the use of the combination of U and SRU as an alternative source of non-protein nitrogen for finishing diets in feedlots willdepend on its cost and the relative prices of forage and grain.

 

The authors thank for the support received by the commercial feedlot ‘Ganadera Rubios’ during the development of the experiment.

 

This experiment was financed by PROMEP-SEP of México (project code: PROMEP/103.5/12/3360).

 

1. Akay V, Tikofsky J, Holtz C, Dawson K. 2004. Optigen 1200: controlled release of non-protein nitrogen in the rumen. In: Lyons TP, Jacques KA, editors. Proceedings from Alltechs 20th Annual Symposium of Nutritional Biotechnology in the Feed and Food Industries; May 23–26. Press, Nottingham (UK): Nottingham: Press.

2. Alvarez-Almora EG, Huntington GB, Burns JC. 2012. Effects of supplemental urea sources and feeding frequency on ruminal fermentation, fiber digestion, and nitrogen balance in beef steers. Anim Feed Sci Technol. 171:136–145.

3. [AOAC] Association Official Analytical Chemists. 2000. Official methods of analysis. 17th ed. Gaithersburg (MD): Association of Analytical Communities.

4. Block HC, McKinnon JJ, Mustafa AF, Christensen DA. 2001. Manipulation of cattle growth to target carcass quality. J Anim Sci. 79:133–140.

5. Calderon-Cortes JF, Zinn RA. 1996. Influence of dietary forage level and forage coarseness of grind on growth performance and digestive function in feedlot steers. J Anim Sci. 74:2310–2316.

6. Carrasco R, Arrizon AA, Plascencia A, Torrentera NG, Zinn RA. 2013. Comparative feeding value of distillers dried grains plus solubles as a partial replacement for steamflaked corn in diets for calf-fed Holstein steers: characteristics of digestion, growth-performance, and dietary energetic. J Anim Sci. 91:1801–1810.

7. Castañeda-Serrano RD, Ferriani-Branco A, Teixeira S, Garcia- Diaz T, Diego-Sofiati A. 2013. Slow release urea in beef cattle diets: digestibility, microbial synthesis and rumen kinetic. Agrociencia. 47:13–24.

8. Duff GC, Walker DA, Malcom-Callis KJ, Wiseman MW, Rivera JD, Galyean ML, Montgomery TH. 2000. Effects of a slow-release urea product on feedlot performance and carcass characteristics of beef steers. Poster session presented at: Proceedings of Western Section, American Society of Animal Science. Annual Meeting of American Society of Animal Science; Baltimore, MD, USA.

9. Galyean ML. 1996. Protein levels in beef finishing diets: industry application, university research, and systems results. J Anim Sci. 74:2860–2870.

10. Garrett WN. 1971. Energetic efficiency of beef and dairy steers. J Anim Sci. 32:451.

11. Holland BP, Jennings JS. 2011. Using Optigen® to replace soybean meal nitrogen in dry-rolled corn-based finishing diets for beef steers. Poster session presented at: Science and Technolgy in the Feed Industry. 27th International Symposium of Alltech Inc.; Lexington, KY.

12. Klopfenstein TJ, Erickson GE, Bremer VR. 2008. Boardinvited review: use of distillers by-products in the beef cattle feeding industry. J Anim Sci. 86:1223–1231.

13. López-Soto MA, Rivera-Méndez CR, Aguilar-Hernández JA, Barreras A, Calderón-Cortés JF, Plascencia A, Dávila- Ramos H, Estrada-Angulo A, Valdés-García YS. 2014. Effects of combining conventional urea and a slow-release urea product on characteristics of digestion, microbial protein synthesis and digestible energy in steers fed diets with different starch:ADF ratios. Asian-Australas J Anim Sci. 27:187–193.

14. Milton CT, Brandt Jr. RT, Titgemeyer EC. 1997. Urea in dry rolled corn diets: finishing steers performance, nutrient digestion and microbial protein production. J Anim Sci. 75:1415–1424.

15. [NRC] National Research Council. 1984. Nutrient requirement of beef cattle. Washington (DC): National Academy Press.

16. [NRC] National Research Council. 1996. Nutrient requirement of beef cattle. 7th ed. Washington (DC): National Academy Press.

17. Pinos-Rodríguez JM, Peña LY, González-Muñoz SS, Bárcena R, Salem A. 2010. Effects of a slow-release coated urea product on growth performance and ruminal fermentation in beef steers. Italian. J Anim Sci. 9:16–19.

18. SAS Institute Inc. 2004. SAS/STAT User’s Guide: Version 9.1. Cary (NC): SAS Institute Inc.

19. Taylor-Edwards CC, Hibbard G, Kitts SE, McLeod KR, Axe DE, Vanzant ES, Kristensen NB, Harmon DL. 2009. Effects of slow-release urea on ruminal digesta characteristics and growth performance in beef steers. J Anim Sci. 87:200–208.

20. Tedeschi LO, Baker MJ, Ketchen DJ, Fox DG. 2002. Performance of growing and finishing cattle supplemented with a slowrelease urea product and urea. Can J Anim Sci. 82:567–573.

21. USDA. 1997. Official United States standars for grades of carcass beef. Washington (DC): United States Department of Agriculture.

22. Van Soest PJ, Robertson JB, Lewis BA. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J Dairy Sci. 74: 3583–3597.

23. Vasconcelos JT, Cole NA, McBride KW, Gueye A, Galyean ML, Richardson CR, Greene LW. 2009. Effects of dietary crude protein and supplemental urea levels on nitrogen and phosphorus utilization by feedlot cattle. J Anim Sci. 87: 1174–1183.

24. Zinn RA. 1990. Influence of steaming time on site digestion of flaked corn in steers. J Anim Sci. 68:776–781.

25. Zinn RA, Barreras A, Owens FN, Plascencia A. 2008. Performance by feedlot steers and heifers: ADG, mature weight, DMI and dietary energetics. J Anim Sci. 86:1–10.

26. Zinn RA, Barrajas R, Montaño M, Ware RA. 2003. Influence of dietary urea level on digestive function and growth peformance of cattle fed steam-flaked barley-based finishing diets. J Anim Sci. 81:2383–2389.

27. Zinn RA, Calderon JF, Corona L, Plascencia A, Torrentera N. 2007. Phase feeding strategies to meet metabolizable amino acid requirements of calf-fed Holstein steers. Prof Anim Sci. 23:333–339.

28. Zinn RA, Plascencia A, Barajas R. 1994. Interaction of forage level and monensin in diets for feedlot cattle on growth performance and digestive function. J Anim Sci. 72:2209.

29. Zinn RA, Shen Y. 1998. An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves. J Anim Sci. 76:1280–1289.