<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>1405-3195</journal-id>
<journal-title><![CDATA[Agrociencia]]></journal-title>
<abbrev-journal-title><![CDATA[Agrociencia]]></abbrev-journal-title>
<issn>1405-3195</issn>
<publisher>
<publisher-name><![CDATA[Colegio de Postgraduados]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S1405-31952006000100049</article-id>
<title-group>
<article-title xml:lang="es"><![CDATA[Nivel óptimo biológico y económico de calcio en gallinas leghorn blancas de segundo ciclo de postura]]></article-title>
<article-title xml:lang="en"><![CDATA[Biological and economic optimum level of calcium in white leghorn of second cycle laying hens]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Hernández-Sánchez]]></surname>
<given-names><![CDATA[Josafat]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Cuca-García]]></surname>
<given-names><![CDATA[Manuel]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Pró-Martínez]]></surname>
<given-names><![CDATA[Arturo]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[González-Alcorta]]></surname>
<given-names><![CDATA[Mariano]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Becerril-Pérez]]></surname>
<given-names><![CDATA[Carlos]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Colegio de Postgraduados  ]]></institution>
<addr-line><![CDATA[Montecillo Estado de México]]></addr-line>
<country>Mexico</country>
</aff>
<aff id="Af2">
<institution><![CDATA[,Universidad Autónoma Chapingo Departamento de Zootecnia ]]></institution>
<addr-line><![CDATA[ Estado de México]]></addr-line>
<country>Mexico</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>02</month>
<year>2006</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>02</month>
<year>2006</year>
</pub-date>
<volume>40</volume>
<numero>1</numero>
<fpage>49</fpage>
<lpage>57</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S1405-31952006000100049&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S1405-31952006000100049&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S1405-31952006000100049&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="es"><p><![CDATA[Resumen El calcio es importante para una óptima producción y formación del cascarón del huevo porque un nivel inadecuado en la dieta de gallinas ponedoras puede afectar la calidad del cascarón y la producción de huevo. Se realizó un experimento con 250 gallinas Leghorn Hy-Line® W-98 para evaluar cinco niveles de Ca (2.74, 3.48, 4.06, 4.56 y 5.19%) en tres periodos (79 a 87, 88 a 96 y 97 a 105 semanas de edad) sobre la producción de huevo y la calidad del cascarón. No hubo interacción entre el nivel de Ca y periodo, pero los efectos principales mostraron que el nivel de Ca afectó (p&#8804;0.05) el consumo de alimento y Ca, peso del huevo y grosor del cascarón, pero no la masa de huevo, conversión alimentaria y gravedad específica del huevo. Hubo diferencias (p&#8804;0.05) entre periodos en todas las variables productivas y de calidad del cascarón, al avanzar la edad de las gallinas, excepto para peso del huevo. Los niveles óptimos biológicos de Ca para máxima masa de huevo y grosor del cascarón fueron 3.17 y 4.02 g ave-1 d-1, y el nivel óptimo económico fue 3.17 g ave-1 d-1.]]></p></abstract>
<abstract abstract-type="short" xml:lang="en"><p><![CDATA[Abstract Calcium is important for optimum performance and eggshell formation, since inadequate levels in the diet of laying hens may affect shell quality and egg production. An experiment with 250 Leghorn Hy-Line® W-98 was conducted to evaluate the effect of five calcium levels (2.74, 3.48, 4.06 and 5.19% and three laying periods (79 to 87, 88 to 96 and 97 to 105 weeks of age) on egg production and shell quality. There was no interaction between calcium level and laying period, but the main effects showed that: the calcium level of the diet affected (p&#8804;0.05) daily feed and calcium intake, egg weight, eggshell thickness but not egg mass, feed conversion and egg specific gravity. There were differences among periods (p&#8804;0.05) in all productive performance and eggshell quality as the age of the hens advanced, except in egg weight. The biological optimum levels for maximum egg mass and shell thickness were 3.17 and 4.02 g hen&#8722;1 d&#8722;1, and the economic optimum level was 3.17 g hen&#8722;1 d&#8722;1.]]></p></abstract>
<kwd-group>
<kwd lng="es"><![CDATA[Edad de la gallina]]></kwd>
<kwd lng="es"><![CDATA[gravedad especifica]]></kwd>
<kwd lng="es"><![CDATA[grosor del cascarón]]></kwd>
<kwd lng="en"><![CDATA[Age of laying hens]]></kwd>
<kwd lng="en"><![CDATA[specific gravity]]></kwd>
<kwd lng="en"><![CDATA[shell thickness]]></kwd>
</kwd-group>
</article-meta>
</front><back>
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