Intake and total apparent digestibility in lambs fed six maize varieties in the Brazilian Semiarid

The objective of this study was to evaluate the daily intake and total apparent digestibility of dry matter, organic matter, crude protein, gross energy, ether extract, neutral detergent fiber, acid detergent fiber, total and non-fibrous carbohydrates, total digestible nutrients, energy intake and nitrogen balance of silages of six maize varieties with early or super early cycles recommended to Northeast Brazil. Twenty-four male castrated lambs were lodged in metabolic cages. A completely randomized design with six treatments and four replications was used, with means compared by Tukey test at 5%. There were no differences among varieties for any of the evaluated variables regarding intake and apparent digestibility. Concerning the intake of digestible energy, metabolizable energy and the ratio content of digestible and metabolizable energy, significant differences were observed between varieties and BRS Assum Preto showed highest values of metabolizable energy (2.650,8 kcal/day). All of the treatments presented positive nitrogen balance and did not differ among themselves. The varieties asessed can be an additional option to the semiarid regions in Brazil.


Introduction
Corn crops have shown an important role in agricultural income, human and animal feeding the in Brazilian Northeast.However, the productivity of maize has decreased and this situation has been caused by unstable rainfall, low technology level adopted by producers and daily temperatures surpassing 40 ºC (Carvalho & Souza, 2007).
This local reality has created native vegetation dependence and low performance of their herds.To solve these problems it is necessary good management and use of native forages conserved and adapted to environment like hay or silage.These steps could even improve animal production rates.
Traditionally, maize plant has been used for silage because it presents high dry matter production and appropriate chemical composition, such as dry matter content in the harvest moment, minimum of 3% soluble carbohydrate in the original matter, low buffering, and provides a good microbial fermentation (Ferrari Júnior et al., 2005;Pereira et al., 2004).
Regional information lack about nutritional value of the genetic materials has been a great obstacle to the agribusiness of corn, since there are some difficulties to choose maize hybrids for silage production in semiarid zones.Thenceforth, chemical composition, intake, digestion, absorption and animal metabolism have been considered at the nutritional value evaluation of forages (Rodriguez et al., 2006).
The objectives of this study were to evaluate voluntary intake and total apparent digestibility of six maize varieties with early or super early cycles in lambs.

Material and Methods
The experiment was conducted at Embrapa Semiarido, in Petrolina, Pernambuco, Brazil (09º09"S and 40º22"W).The average regional precipitation was 570 mm per year, altitude of 365.5 m and annual average temperatures of 33.46 ºC (maximum) and 20.7 ºC (minimum), respectively.Climate conditions during roughage production period were considered normal for the annual period in this region (Table 1).
At the beginning, the area was prepared for planting through plowing, breaking up and harrowing the soil and leveling, as well.Furrows were opened spaced each other about 1 m before establishment of the corn tillage.
When grains presented hard farinaceous stage, plants were harvested at 81 days after planting, then stacking and chopping were performed through silage cutter stationary machine adjusted to produce particles of about 2 cm.Materials were ensiled into 18 concrete silos (capacity of 250 liters), internally coated with tarpaulin plastic.Each concrete silo was compacted by trampling and sealing was done with plastic tarpaulin and tapes, whereas opening was done 90 days later.
Twenty-four castrated and unknown breed lambs with body weight (BW) of 19 kg ±1.6 kg were used.The diet including corn silages as single exclusive roughage was offered twice daily (7h30min and 16h30min) and intake was adjusted to ensure orts about 15% of as fed matter.Water and mineral mixture were available to lambs all the time.
The experimental period took 5 days for sample collection and 17 days for adaptation of animals to feeding, cages and collection bags.Weightings were done at the beginning and end of each one.
Silage supply, orts from feed box and total production of feces were quantified during the experimental period; daily samples of around 300 g/treatment/day were collected from each material offered.Orts were collected in the morning, weighed and packed in plastics bags, identified and frozen to be analyzed afterwards.About 20% of feces were weighed and collected once daily from the total measurements.100 ml of hydrochloric acid with 2N concentration were put into samples to prevent fermentation, degradation and losses of nitrogen.Sampling around 10% from the total measurements of urine were obtained only in the morning and frozen for posterior analyses.A composite sample per animal was originated from daily samples.
Apparent digestibility of nutrients was carried out following technique described by Silva & Leão (1979).Total carbohydrates (TC) and non-fibrous carbohydrates (NFC) values were calculated as proposed by Sniffen et al. (1992) (mainly gas methane).Methane losses were calculated, when maintenance situation was considered, by using the model proposed by Blaxter & Clapperton (1965), where Cm = 3.67 + 0.062D, where, Cm = methane production (Kcal/100 Kcal of ingested energy) and D = apparent digestibility from gross energy into dry matter.
Variables were tested for checking of normal distribution occurrence before analysis of variance.Means were compared by Tukey test at 5% probability (P<0.05).Statistical analyses were done in the SAS program (SAS, 2002).

Results and Discussion
Results obtained from six varieties of corn silages were similar to the ones found in the literature (Table 3).
Dry matter values were similar to results found by Senger et al. (2005) (24.1%) and Pereira et al. (2007) (25.8%), but lower results were obtained by Jaremtchuk et al. (2005) and Rosa et al. (2004) when early cycle genotypes were evaluated for them.All treatments, except for the early cycle variety named BR 5028 -São Francisco, presented CP contents higher than 6%, since this is considered a minimum level so that rumen bacteria might be developing properly (Van Soest, 1994).In addition, these values are according to assays performed in the Brazilian semiarid region.These numbers are also similar to data reported by Paziani et al.(2009) and Pereira et al. (2007), who showed an average percentage of CP of 6.7 and 6.4%, respectively.Miron et al. (2007) have also observed DM values of 34.1% and 6.2% of CP, evaluating corn silage in dry zones of the Middle East.
Gross energy contents were close between varieties, and these values were also similar to results found by De Boever et al. (1997), who reported average numbers of 4.628 Kcal/kg.Kirkland & Patterson (2006) observed results of 4.376 Kcal/kg in United Kingdom, and Nishida et al. (2007) also found results similar to this experiment (4.619 kcal/kg) when genotypes of corn silages were studied in Japan.
There were no differences (P>0.05) for nutrients intake or fibrous fractions (Table 4).
The amount of leftovers in the trough was predictable: approximately 15%, and it confirmed the occurrence of normal selection of the material, with greater share of stem parts and greater retention of leaf parts and ear.
Dry matter, organic matter, crude protein, total carbohydrates and neutral detergent fiber intakes were lower than the results obtained by Moreira et al. (2001), who observed intake of 752.6 g/day of DM, 694.7 g/day of OM, 43.1 g/day of CP, 640.2 g/day of TC and 447.8 g/day of NDF.However, these reported data were lower to ether extract and total digestible intake, with values of 5.9 g/day of EE and 359.0 g/day of TDN, respectively.
Intake of total digestible nutrients in g/day obtained in this research ranged from 373.2 to 481.2 g/day.These levels are according to NRC's (2007) recommendations, where minimum requirements of 350 g/day for animals with this body weight range and gains of 100g/day can be found.
Results found for intake in g/kg 0.75 /day of DM were higher than ones obtained by Freitas et al. (2003), when they evaluated HT01, HT47C, HT129, AG5011 and BR3123 corn genotypes and reported average intake of 60.7 g/kg 0.75 /day.Ribas et al. (2007) described results similar to those found in this study when voluntary intake of dry matter and crude protein from four hybrid corn silage (SHS 4040, QPM 129, AG 1051 and BRS 3060) were evaluated in lambs.These authors presented average  values for DM and CP intakes of 64.9 g/kg 0.75 /day and 4.9 g/kg 0.75 /day, respectively.Results lower than those found in this experiment were obtained by Vranic et al. (2008), when they observed intake of 49.8 g/kg 0.75 /day of OM and 31.3 g/kg 0.75 /day of NDF, in lambs fed corn silage.
Intakes of neutral detergent fiber, acid detergent fiber and ether extract (in g/kg 0.75 /day) were studied by Mizubuti et al. (2002) when they observed higher values than the ones found in this assay (41.3, 36.5 and 3.6 g/kg 0.75 /day, respectively), when corn, sorghum and sunflower silages were evaluated on feeding of lambs.Similarity of results between recommended varieties to semiarid and ones currently used to silage production in other regions was observed.
Measuring the intake of fibrous fractions' intake measurement is very important, since fiber can carry out several metabolic and physiological effects into animal organism.High contents of this fraction could cause energy dilution of the diet and increase compensatory intake so that the energetic levels recommended for development and production may be reached (Van Soest et al., 1991).
Intake of fractions of nutrients and fiber were statistically similar (P>0.05), in body weight percentage.Average of 3.1% BW to DM intake was similar to that found by Bueno et al. (2004), where they observed values of 3.14% BW when corn silage was fed to lambs in the south region of the São Paulo State.
There was no variety effect (P>0.05) on dry matter apparent digestibility, organic matter, crude protein, neutral detergent fiber, acid detergent fiber, total carbohydrates, non fibrous carbohydrates, ether extract or gross energy (Table 5).Aksu et al. (2004) described average values for dry matter apparent digestibility, organic matter, crude protein, neutral detergent fiber and acid detergent fiber of 59.3, 64.1, 48.3, 55.3 and 63.3%, respectively, when studying corn silage on Morkaraman lambs feeding, with around 31 kg BW, in the semiarid regions of Turkey.It is important to remark that values observed by these authors were lower than those obtained in the current research.Digestibility coefficient of the fibrous fractions (NDF an ADF) are according to results by Mizubuti et al. (2002).They reported similar values for digestibility of fibrous fractions (50.8% for NDF and 64.4% for ADF), when lambs with average body weight of 35 kg were used.
Apparent gross energy results from the present study were similar to those obtained by Ribas et al. (2007) (66.6%), who evaluated apparent digestibility from four corn hybrids in lambs.Yet results from this experiment were higher than the ones described by Freitas et al. (2003), who evaluated five corn hybrids in lambs and obtained average values of 61.1%.Valadares Filho et al. (2006) also reported lower results than those obtained im this assay (57.4%) in the Tabela Brasileira de Composição de Alimentos.
Regarding energy balance from the searched silages, differences were observed (P<0.05) over all variables, except for gross energy voluntary intake (P>0.05)(Table 6).
Metabolizable energy intakes ranged from 1.510.5 to 2.650.8kcal/day and were higher than the ones recommended by the NRC (2007), whose requirements are around 590 kcal/day for lambs with 20 kg of BW and daily gains of 100 g.Super early BRS Assum Preto variety presented values for digestible energy intake and metabolizable per kg 0.75 /day higher than Gurutuba and BRS Caatingueiro.This probably happened because that material presented high gross energy contents in association with high apparent digestibility from the gross energy.There was no negative balance, because in all evaluated silages appropriate levels of metabolizable energy were provided to the animals.This fact can be corroborated by Freitas et al. (2003) and Ribas et al. (2007).
By considering the ratio between digestible and metabolizable energy intakes and dry matter intake (DEI/DMI and MEI/DMI), lower values for BRS Caatingueiro were evidenced, compared with other varieties studied (P<0.05).Results obtained for dry matter intake from these varieties   in association with digestible and metabolizable energy intakes could explain the highest values for DEI/DMI and MEI/DMI.These ratios are important in the foods nutritive evaluation, since they are parameters of energy efficiency use.However, high efficiency ratios are only interesting when high dry matter intake can be reached, which was observed in this experiment through minimum requirements indicated by the NRC (2007) for lambs with this body weight range and daily gains of 100 g.Such results might appoint the use of these silages as quality alternative roughage to the semiarid.
There were no differences for ingested nitrogen and fecal and urinary nitrogen excretions in grams per day or nitrogen balance (P>0.05)(Table 7).
Super early BRS Assum Preto and BRS Caatingueiro presented higher values of nitrogen absorbed per kg 0.75 than BR5033 -Asa Branca.In the current experiment, all silages showed positive nitrogen balance.Freitas et al. (2003) and Ribas et al. (2007) found results higher than those obtained by this study (4.8 and 4.7 g/day of nitrogen absorbed, respectively).
Negative nitrogen balance of 0.28 g/day was observed by Vranic et al. (2008), who reported nitrogen intake of 9.4 g/day and fecal and urinary nitrogen excretions of 5.8 and 3.9 g/day, respectively, which were lower than ones presented by this survey.As for N absorbed/N intake ratio, Ribas et al. (2007) had similar results (32.2% N absorbed/N intake).These authors even observed values close to those found by this experiment when they studied five corn genotypes, including one early cycle material.
Positive nitrogen balance observed in all treatments showed appropriate protein use, since probably there was no body reserve mobilization during the experimental period.Also, there were no protein losses during silage intake from the evaluated varieties, and these facts are very important to the semiarid, because soil and climate conditions and the regional production systems require optimization of forage use.

Table 1 -
Meteorological data during experimental period 1 Rainfall in days; 2 Rainfall in millimeters; 3 Relative humidity in the air (%).

Table 2 -
Features of the corn varieties used

Table 3 -
Chemical-bromathological composition of silages of the corn varieties evaluated

Table 4 -
Nutrients and fibrous fractions intake from the six varieties of corn silage

Table 7 -
Nitrogen balance from the six varieties of corn silages