Different Ground Corn Particle Size in Supplements for Young Bulls Grazing During Intensive System Production

Lucien Bissi da Freiria (  lucien.freiria@ifro.edu.br ) Instituto Federal de Rondonia: Instituto Federal de Educacao Ciencia e Tecnologia de Rondonia https://orcid.org/0000-0003-3715-5228 Joanis Tilemahos Zervoudakis Universidade Federal de Mato Grosso Nelcino Francisco de Paula Universidade Federal de Mato Grosso Mozart Alves Fonseca University of Nevada Reno Luciana Keiko Hatamoto-Zervoudakis Universidade Federal de Mato Grosso Pedro Ivo José Lopes da Rosa e Silva Universidade Federal de Mato Grosso Yasmim Rodrigues Vilas Boas e Silva Universidade Federal de Mato Grosso Adriano Jorge Possamai Cargill Animal Nutrition


Introduction
Currently, reducing the production cycle is an important way of intensifying beef production and for improving meat quality. In this sense, the growth phase requires attention since greater feed e ciency in this period can promote the slaughter of younger animals and provide areas for use by other animals (Euclides et al., 2001;Paulino et al., 2006). In the growth phase, the inclusion of a higher supplementation level (10 g/kg BC) for animals on pasture, mainly in tropical regions, is a good strategy and has the potential to improve performance because the livestock require nutrition to maximize production Fernandes et al., 2012).
In most of the diets for beef cattle, corn is used in high inclusions as an important starch source for ruminants (Owens et al., 1986;1997;Zinn et al., 2011). Strategies for improving available starch in the gastrointestinal tract, with techniques such as grain processing, have been extensively evaluated in feedlots (Huntington, 1997;Owens et al., 1997;Zinn et al., 2002Zinn et al., , 2007. However, most of these studies evaluated dent corn in feedlot diets (Owens and Soderlund, 2007); dent corn is less vitreous than int corn, which is typically fed in Brazilian feedlots (Correa et al., 2002). The int corn has a protein matrix surrounding the starch granules, with less starch available for microbial fermentation in the rumen (McAllister et al., 2006). Thus, processing (grinding) of int corn grain would be expected to have a greater bene t than grinding dent corn (Gouvêa et al., 2016).
In the beef cattle production system at pasture, it is important to consider the possible effects of processing/grinding corn grain in supplements on forage intake. Initially, the particle reduction size of corn grain with grinding would increase the surface area for microbial attachment and colonization (McAllister et al., 2006), with a potential increase in energy available to improve animal performance.
However, reducing the sizes of the grain particles may decrease chewing and rumination or increase the passage rate, impairing the rate and extension of ber digestion (Kung et al., 1983). On the other hand, the use of a larger particle of corn grain (whole) can reduce starch digestibility in the gastrointestinal tract (Owens and Soderlund, 2007).
We evaluated int corn grain with different degrees of grinding for use as supplements in terms of nutrient intake and digestibility, starch fecal concentration, growth performance and economics of Nellore bulls in the growth phase at pasture.

Materials And Methods
This trial was conducted at the Faculdade de Agronomia e Zootecnia, Universidade Federal de Mato Grosso (UFMT; Cuiabá, Mato Grosso, Brazil), following humane animal care and handling procedures, according to the UFMT guidelines (Protocol 23108.060964/13 − 6).

Experimental design and treatments
The experiment was conducted in the rainy-dry transition season at the beef cattle facility of the Sector Nutrition of Beef Cattle at Pasture, Universidade Federal de Mato Grosso -UFMT, from March 2016 to June 2016. The climate is classi ed as tropical (Aw in the Köppen international system), the average maximum temperature is 32.8°C, and the average minimum temperature is 19.7°C.
Sixty-four young bulls (Nelore) with an average age of 15 months and 305 ± 17.81 kg of body weight (BW) were used in the experiment to evaluate the effects of varying the ground corn size in their supplements on intake and nutrient digestibility, performance and economics. The experiment was structured in a completely randomized design with 4 treatments. The experiment lasted 90 days, divided into 3 experimental periods of 30 days.
Initially, the animals were weighed, identi ed, treated against ecto-and endoparasites by administration of ivermectin (Ivomec; Merial, Paulínea, Brazil), and allocated into 16 paddocks of 0.81 ha each, with 4 young bulls randomly allocated to 1 of 4 treatments. The paddocks were seeded with Brachiaria brizantha cv. Marandu forage and were tted with smooth wire fencing, waters, and feed bunks. The digestibility trial was conducted with one animal in each paddock between days 41 and 50. To evaluate intake and nutrient digestibility, 7 d were allowed for adaptation to external indicators, and 3 d were allowed for fecal sampling.
The supplement was provided at 10 g/kg BW daily at 10:00 am. The supplements were formulated to be isonitrogenous, with CP contents of approximately 22%. The proportions of the ingredients and the chemical composition of the forage and supplements are showed in Table 1.
The average sward height was randomly measured by reading 100 sampling points in each paddock with a measuring stick graduating in centimeters (Barthram, 1985). The forage mass in each paddock was estimated for each period (30 d (2016), for multiplied by the paddock area by dry weights of these clippings.
The paddocks were managed through continuous stocking (Allen et al., 2011). Forage samples to address the herbage chemical composition were collected using a hand plucking methodology (Johnson, 1978) to mimic forage selected by grazing bulls. Samples were collected from each pasture during each period and dried to a constant weight at 55°C under forced air, after, subsequent analysis of their chemical composition in to the laboratory. where 0.98 is the true digestibility coe cient of the intracellular content; NDF is the forage content of neutral detergent ber corrected for the residual ash and nitrogen; and iNDF is the forage content of indigestible neutral detergent ber.

Intake Estimation
Intake and nutrient digestibility were estimated just once during the period between the 41st day and the 50th day on the bulls in each paddock (16 animals, 4 bulls for each treatment) using the marker method. Chromium oxide, titanium dioxide and indigestible NDF (iNDF) were used to estimate the excretion of fecal matter (as dry weight), supplement intake and forage intake, respectively.
Fecal samples were collected on d 48, 49, and 50, directly from the rectum, at 16:00, 12:00, and 08:00 h on the rst, second, and third days of collection, respectively. The fecal samples were dried at 55°C for 72 h and proportionately composited throughout the day for each animal based on the fecal dry weights.
To estimate DM fecal excretion, 15 g of chromium oxide was provided for 9 d by esophageal infusion; the For determination of iNDF, 0.5 g samples of feces, forage, and supplement were placed in 5 by 5 cm polypropylene bags (nonwoven fabric, weight 100 g/m 2 ). The samples were weighed to allow for 20 mg DM/cm 2 of surface area (Nocek, 1988) and incubated in the rumen of a cannulated Nellore bull for a period of 288 h (Valente et al. 2011).
The fecal samples collected for the determination of DMI, ICS and forage intake in the digestibility trial were used (50 mg) for the determination of starch excretion in the feces according to the methodology proposed by Hall (2009), and the supplemental sample was analyzed for the determination of starch intake.

Performance and Economic Analysis
After 14 h of solid fasting, young bulls were weighed at the beginning and end of the experiment for daily weight gain and total weight gain. The economic analysis was determined by the nutrition costs (supplementation and land occupation), operation, acquisition of the animals (US$ 1.34/kg of BW), gross revenue, net pro t, area production, and pro tability during the feeding period.
The prices of the ingredients grain corn, soybean meal, mineral supplement and urea were 0.14, 0.25, 0.37 and US$ 0.49/kg, respectively. For the price of grinding corn based on the cost of the grinding machine with a 7 horse power motor, a price value of US$ 673.85, and consumption of 5.59 kW/h, ow rates for coarse ground corn (2.882 µm), medium ground corn (1.011 µm), and ne ground corn (0.621 µm) of 1,300, 1,000 and 700 kg/h, respectively, were calculated. The price of power consumption, taking into account the mean year in Brazil, had a value of US$ 0.25/kW.

Statistical Analysis
Nutrient intake and digestibility, fecal starch concentration, and performance data (initial weight; nal weight, daily weight gain, total weight gain) were analyzed using SAS/STAT software (SAS Inst. Inc., Cary, NC) as a randomized complete design with 4 treatments (4 corn grinding particle size). Only performance data considering the average of each paddock were considered 1 experimental unit, and another variable considered only each animal paddock. The model included the xed effects of the ground corn particle size.
When no signi cant interactions (P > 0.05) were detected, the main effects of the ground corn particle size were examined. Differences between ground corn particle sizes were tested by an ANOVA F-test using orthogonal contrasts, where we compared: 1-WC vs GC (whole grain versus ground corn); 2-CG vs MG (coarse ground grain versus medium ground grain); and 3-CG vs FG (coarse ground grain versus ne ground corn).

Results
We hypothesized that a decrease in int corn particle size in the supplements of young bulls during grazing promotes a better use of starch in the total gastrointestinal tract, with less starch loss in the feces, increasing growth performance.
Mean forage masses of 4,473, 3,017, 1,415, 1,438 and 1,619 kg/ha were observed for dry matter mass, potentially digestible dry matter, green leaves, green stems and senescent stems, respectively (Table 2). For the ground corn particle sizes in the supplements of young bulls during grazing, there was no difference (P > 0.05) across the treatments for the intake of dry matter (DM), forage, supplement, organic matter (OM), crude protein (CP), neutral detergent insoluble ber corrected for contaminant ash or protein (NDFap), or indigestible neutral detergent insoluble ber (iNDF) ( Table 3). Similarly, the corn particle size in the supplements of young bulls during grazing did not alter (P > 0.05) the intake of digestible organic matter (DOM), digestible NDFap (D NDFap), total digestible nutrients (TDN), or grams of CP/kilogram of digestible OM (CP:DOM) (Table 3).
However, grinding the corn in the supplements promoted higher starch digestibility (P < 0.05) when comparing whole grain with all ground corn (WG vs. GC), with less fecal starch content (P < 0.05) ( Table 4). That variable showed that independent of the ground corn particle size, there was more e cient utilization of starch in the supplements for ground corn versus whole grain.
However, the use of ground corn for young bulls during grazing is not justi ed in relation to nutrient digestibility; because there was no difference (P > 0.05) in the nutrient digestibility of DM, OM, CP, NDFap, or TDN between whole and ground corn (Table 5).
Supplements with different ground corn particle sizes showed higher e ciency of starch use after grinding, but the same tendency was not con rmed for performance characteristics because, in the actual trial, animals did not show differences in body weight (kg), average daily gain (kg/day) or total gain (kg) ( Table 6).
Thus, applying the grinding process increased the costs for the animals by US$ 0.00, 0.28, 0.37 and 0.53/period and the total costs by US$ 499.68, 507.08, 506.73 and 504.95/period for whole corn and coarse, medium and ne ground grain corn, respectively (Table 7).
However, supplements with coarse ground corn promoted higher kilograms produced per hectare (209.3 kg), resulting in a higher economic return during the study period (12.67%) and a higher return per ha (US$ 250.97/ha/period) compared to the other supplements ( Table 7). The supplement with whole grain showed results close to that of supplementation with coarse ground grain corn. Supplementation with ne ground grain corn showed inferior economic performance results compared with the other treatments.

Discussion
The dry matter of forage mass remained greater than the threshold indicated as limiting to animal selectivity, 4,262 kg/ha (Euclides et al., 1992) and 2,000 kg/ha (Minson, 1990). However, during the trial, in the rainy-dry transition season, a decrease in green leaves and an increase in the senescent part of the forage were observed due to the lower abundance of rain. This condition is marked by a reduction in the leaf:stem ratio, promoting increased thickness and ligni cation of the cell wall (Minson, 1990). The performance of animal grazing is associated with the quality and quantity of the forage mass. According to Paulino et al. (2008), the integrative measure of the quantity and quality aspects of forage is determined by the potentially digestible dry matter (pdDM) of the forage mass. It reveals the real ability to support animal performance in the area used. Therefore, Paulino et al. In this experiment, the supplementation level (10 g/kg BW) resulted in a reduction in forage intake, but it was less than 10 g/kg BW in all treatments. Supplementation likely replaces forage intake because, in the literature, when the supplementation level is less than 3 g/kg BW, it could provide increased forage and total dry matter intake, and when the supplementation level is higher than 5 g/kg BW, it could promote a reduction in forage intake and a maintained or reduced total dry matter intake (Paulino et  Nevertheless, the higher supplementation level provides protein and energy for animals in conditions of lower mass volume, which could favor the animal replacing forage intake (which has less energy and a higher mass volume) with supplementation, being more metabolically comfortable for the animals, but does not always reduce their total dry matter intake . Sales et al. (2008) showed that an increase in supplementation levels (0, 3.44, 5.36, and 6.28 g/kg of BW) decreased forage intake but maintained the same dry matter intake for cattle during grazing (dry season). All animals were supplied the same supplementation level in the actual trial, with an average dry matter intake of 19.50 g/kg BW and a slightly greater value of 18.01 g/kg BW than that found by Sales et al. (2008) at a higher supplementation level (6.28 g/kg BW). This result is in agreement with Detmann et al. (2010); for animals that prefer a reduced mass intake, a lower volume and higher energy are provided by supplements. Supplementation with ground corn of different particle sizes did not change the nutrient or forage intake of the animals in the pastures. A reduction in int corn grain particle sizes and higher starch release in the rumen are expected to occur with increased fermentation (Cole et al., 1976; Aschenbach et al., 2011; Gouvêa et al., 2016), reducing the ruminal pH, which is negatively implicated in microbial fermentation of ber because cellulolytic bacteria are pH sensitive, and their growth is inhibited when their ruminal pH is below 6.0 (Russell and Wilson,1996). However, this experiment did not observe a change in forage intake with reduced corn particle size.
It is possible that grinding grain int corn was not su cient to release the starch while reducing ruminal pH. In accordance with Owens et al. (1986Owens et al. ( , 1997, the reported process of grinding corn did not e ciently rupture the protein matrix. Nevertheless, grinding int corn promoted much better starch digestibility and a lower starch content in feces than whole grain. These results are in agreement with Schwandt et al. (2016), who found int corn for cattle feedlot to have a decreased (dry-rolled) grain corn particle size, an increase of in situ starch disappearance after a 24 h incubation, and a decreased fecal starch content.
These results regarding total tract starch digestion, mainly during grazing, might be explained by the reduction of the particle size with grinding compared with whole corn, increasing the surface area available for microbial attachment and colonization (Philippeau et al., 1999 Owens and Soderlund (2008) reported improved starch digestion in ruminal and postruminal environments, which could be attributed to more extensively processed grain (steam-aked and high moisture). Turgeon et al. (1983) reported that starch digested postruminally was not in uenced by corn particle size, suggesting that the improved total tract starch digestion was due to the extent of ruminal digestion.
On average, the treatments with ground corn resulted in 77% total tract starch digestion, 22 percentage points higher than whole grain starch digestion. That difference might occur because there was an increase in ruminal digestibility. In a review, Owens and Soderlund (2008) discussed that in feedlot cattle, starch digestion in the rumen and total tract is higher for dry-rolled corn than whole corn, but in the same comparison of processing, there was no observed difference in starch digestion in the small or large intestine, which showed differences for corn particle size and higher ruminal digestibility only.
However, in terms of the entire digestive tract for starch digestion with ground or whole grain, the difference indicates there was a higher pass rate of starch by another compartment in the digestive tract.
Zinn et al. (2002) a rmed that more starch in the large intestine may reduce its pH, impairing the growth of microorganisms that digest ber. However, hypostases were not con rmed here because the use of ground corn of different particle sizes or whole corn in the supplements did not promote differences in nutrient digestibility, including ber digestion.
Nevertheless, the literature indicates there is higher starch digestion in the small intestine, which is more energy e cient. There are minor losses due to methane and calories for digestion in the rumen, but glucose absorbed in the small intestine is directed for accumulation in the visceral fat, not in the tissue as intramuscular or subcutaneous fat, so it has less economic value (McLoad et al., 2007).
Thus, in any study with supplementation levels above 5 g/kg BW for cattle during grazing in the dry season, NDF digestibility was maintained at 50-60% Sales et al., 2008), which was slightly greater than the actual value. This might suggest two a rmations: rst, that particle size reduction of corn does not in uence NDF digestibility, and second, higher-level inclusion of supplements for animals during grazing reduces their dependency on the forage mass for nutrient digestibility.
The performance of animals in pastures was not in uenced by the different levels of grinding of corn in the supplements. In feedlots, Schwandt et al. (2016) also did not nd a difference in the performance of animals fed dry-rolled corn grain coarse, medium or ne. Perhaps higher starch availability demonstrated an increase in starch digestibility and a decrease in starch fecal concentration, which may not be enough to improve performance because there is no difference in total digestible nutrient (TDN) intake.
According to Valadares Filho et al. (2016), for a performance of 1 kg/day for animals during grazing, the growth phase requires an intake of 4.89 kg TDN/day. There was no difference among the treatments in terms of TDN intake, with a medium value of 5.01 kg/day, which may explain the slightly higher gain than expected.
In general, the economic analysis showed that grinding the corn created an increased period cost compared to that of supplying whole corn by 6.12, 6.51 and 7.11%. According to Gorocica-Buen l and Loerch (2005), con icting reports have been published on the bene ts of grinding corn, and the lack of response in diet digestibility and beef cattle feedlot performance to corn grinding suggests that the additional cost of grinding corn may not be justi ed. In this experiment, as it did not affect nutrient intake or digestibility, the same nding as in feedlots, grinding may not be justi ed.
However, even with the cost of grinding, when coarse ground grain was supplied, a slightly greater net revenue (+ 11.51%) and return per ha (+ 12.8%) were observed compared with whole grain, which occurred due to numerical differences in performance, which implicate reduce in total cost for kg produced. However, medium ground grain and ne ground grain had worse economic results than coarse ground grain. Therefore, grinding corn improves the e cient utilization of starch in the total tract compared with whole corn but was not enough to increase growth performance. Thus, using economic analysis is determinant in de ning coarse ground grain corn as a better strategy in supplementing beef cattle during grazing.

Conclusion
The coarse grinding of corn in the supplement improved the e cient utilization of starch with less starch in the feces. Thus, coarse ground corn has a higher economic performance and is a better strategy for supplementing young bulls during grazing.

Declarations
Author's contributions     Table 4 The effects of ground corn particle size in supplements for young bulls during grazing: starch intake, starch digestibility and fecal starch   The effects of ground corn particle size in supplements of young bulls during grazing: animal performance  Table 7 The effects of ground corn particle size in supplements of young bulls during grazing: economic