Cattle Update: Improving Cowherd Reproduction Via Genetics (Part 2 of 2)

4/9/2008 10:07:00 AM

Cattle Update: Improving Cowherd Reproduction Via Genetics

 

(Part 2 of 2) Last week in this publication we focused on the positive impact of cross-breeding and how direct selection affects cowherd reproduction. This week, let's begin with some thoughts on Direct Selection and it's impact on herd reproduction: A well-entrenched view of both commercial and seedstock producers is that the "cows left standing" after culling on the components of reproduction (e.g., pregnancy status and calf loss) are genetically superior. By extension, it is presumed that a great deal of progress in reproduction is made through rigorous culling and the retention of heifers out of dams making it to advanced ages. Though this may seem like a reasonable deduction, it is generally not the case.

 

Unfortunately, little genetic headway is made by simply culling cows that do not achieve reproductive thresholds. This may seem counterintuitive. Why wouldn't getting rid of the offenders improve your genetics for reproduction? The main reason lies in the fact that measures of reproduction tend to be lowly heritable (estimates typically run between 5-20%). And, with lowly heritable traits, an animal's own performance is not a good indicator of its genetic level for the trait. Therefore, many open culls may be genetically above average or even superior for reproduction. By the same token, several cows kept because they are bred will be genetically inferior for it - certainly not an outcome that will yield much improvement.

 

So, how do we directly select for reproduction? Because a cow's reproductive performance is expressed later in life, and even then it only provides a very cloudy picture of her genetic merit, are we relegated to making little to no selection progress for reproduction? Heck no! We can clear the clouds with reproductive EPDs.

 

Though EPDs always provide the best estimate of an animal's genetic merit, they are especially valuable when applied to low-heritability traits. This is because, when an animal's own record is a poor indicator of its genetic makeup, gathering information on its relatives is the only means we currently have of getting a clear picture of the animal.

 

You may ask yourself, "If an animal's own performance does not tell us much, what can be gained by records on its relatives?" It is not that a single relative record brings much to the mix (obviously it adds even less than the animal's own record); it is that there is strength in numbers - an animal can have many relatives with records, but only one record on itself. Through the use of EPDs we utilize information on all of an animal's relatives and, in doing so, chip away at the cloud with each record that flows in.

 

With a low-heritability trait expressed later in life like reproductive function, the cloud clears slowly - but it will clear. In fact, if an animal has enough progeny records, we can see its genetic merit for reproduction as clear as a bell.

 

Fortunately the seedstock industry now has EPDs that are, for the most part, direct measures of reproductive function: stayability (STAY) and heifer pregnancy (HP). Researchers at CSU (Snelling et al., 1995) developed the prototype for STAY, which was unveiled to the industry by the RAAA a few years later. The US breeds currently calculating STAY: Gelbvieh, Limousin, Red Angus, Salers and Simmental.

 

Colorado State University later developed HP based on work by Doyle et al. (2000) and implemented it for the RAAA National Cattle Evaluation in 2001. While the Angus Association of America has released a trial version, the RAAA is the only breed to publish an official HP at this point. Unfortunately, neither STAY nor HP is currently calculated on non purebred seedstock, though there are plans to do so in the future.

 

Though STAY and HP have potential shortcomings (e.g., seedstock breeders' culling practices are probably not in lock step with the commercial industry and breed association culling records tend to be sketchy), in my opinion they are the most effective selection tools available for improving reproductive function. What's more, based on computer simulation efforts by USDA researcher M. D. MacNeil, the economic impact of stayability when selecting a sire to keep replacement females is nearly twice that of the next closest trait, while the relative importance of heifer pregnancy is on par with the most important carcass or growth traits (personal communication) - so these reproductive EPDs certainly warrant a great deal of attention in the selection process.

 

Obviously, if you are a commercial producer you do not have the luxury of using STAY or HP to select replacement females; however, if you select sires with superior EPDs in these areas the reproductive function of your cowherd is likely to improve over time. Given their relationship to stayability, you may also gain some reproductive ground by selecting sires with lower milk, smaller mature size and better maternal calving ease EPDs. (In the future, these relationships will be accounted for in the computation of reproductive EPDs in the manner birth weight is incorporated in the prediction of calving ease - eliminating the benefit in considering them separately; however, they are not currently factored into the calculation of STAY or HP.)

 

Summary: In closing, I must reiterate that crossbreeding needs to be at the center of any effort to improve the reproductive function of your cowherd. The dramatic impact of heterosis on reproductive performance is crystal clear - no herd should be without it! Though reproductive improvement through selection is possible, it is generally limited to utilizing reproductive EPDs when selecting your herd sires. By combining crossbreeding with the selection of superior sires you will position your enterprise to excel in the most vital area of beef cattle production - cowherd reproduction.

 

Literature Cited:

Beckman, D. W., S. E. Speidel, B. W. Brigham, D. J. Garrick, and R. M. Enns. 2006. Genetic parameters for stayability and body condition score in beef females. Proc. West. Sect. Am. Soc. An. Sci. 57:93-95.

Cundiff, L. V., Nuiiez-Dorniguez, R., Dickerson, G. E., Gregory, K. E., and R. M. Koch. 1992. Heterosis for lifetime production in Hereford, Angus, Shorthorn, and crossbred cows. Journal of Animal Science. 70:2397-2410.

Doyle, S. P., Golden, B. L., Green, R. D., and J. S. Brinks. 2000. Additive genetic parameter estimates for heifer pregnancy and subsequent reproduction in Angus females. Journal of Animal Science. 78:2091-2098.

Martinez-Velazquez G., K. E. Gregory, G. L. Bennett and L. D. Van Vleck. 2003. Genetic relationships between scrotal circumference and female reproductive traits. Journal of Animal Science. 81:395-401.

Rogers, P. L., Gaskins, C. T., Johnson, K. A., and M. D. MacNeil. 2004. Evaluating longevity of composite beef females using survival analysis techniques. Journal of Animal Science. 82:860-866.

Snelling, W. M, Golden, B. L., and R. M. Bourdon. 1995. Within-herd genetic analyses

of stayability of beef females. Journal of Animal Science. 73:993-1001.

 

EDITOR's NOTE: Improving cowherd reproduction via genetics will be but one concept Dr. Shafer will focus on during the Ohio Beef Cattle Breeder Conference being hosted on the campus of The Ohio State University by Dr. Tom Turner and staff of the American Simmental Association on April 30 beginning at 3 p.m. Details follow below.

 

 

Source: Wade Shafer, ASA Director of Performance Programs

 

http://www.cattlenetwork.com/Content.asp?contentid=211942

Brasil: Futuro do agronegócio depende da pesquisa

Futuro do agronegócio depende da pesquisa

22/04/2008

Fonte: Folha de Londrina

O agronegócio tem papel importante na economia brasileira. Cerca de 5 milhões de propriedades rurais respondem por 27% do Produto Interno Brasileiro (PIB), geram 35% dos empregos e rendem US$ 39,92 bilhões (em 2006) de saldo comercial. No entanto, este desempenho pode estar ameaçado se não for enfocada a geração de riqueza através do conhecimento. Isso significa que se o trabalho de organização e de investimentos não começar agora, o Brasil poderá perder no futuro a oportunidade de protagonizar a demanda por alimentos e biocombustíveis no contexto mundial. Esse assunto foi tema de trabalho feito, em parceria público-privada, sobre inovação para o agronegócio e o desenvolvimento rural sustentável. Foram traçadas projeções para os próximos 15 anos. ''É a oportunidade de trabalho para a construção e para a transformação do futuro'', salientou o pesquisador Paulo Cruvinel, da Embrapa Instrumentação Agropecuária, de Brasília. Ele ministrou palestra em seminário técnico realizado pelo Instituto Agronômico do Paraná (Iapar), dirigido a pesquisadores do órgão, da UEL e da Embrapa Soja. Segundo ele, foram traçados quatro cenários para o agronegócio brasileiro considerando aspectos econômicos, ambientais, sociais e de capital humano. ''Pode haver um retrocesso no papel do agronegócio na economia brasileira em 15 anos. Por isso é importante trabalhar para alcançar o futuro desejado'', salientou Cruvinel. As hipóteses apresentadas vão desde a mais otimista ao cenário mais pessimista. No entanto, em todas as projeções, a pesquisa e a inovação têm papel de destaque para o desenvolvimento do agronegócio. No primeiro caso, o Brasil teria condições de expandir para conseguir inserção global. As oportunidades para isso estão nas projeções para ampliação do acesso aos mercados internacionais e expansão do comércio, estabilização dos preços das commodities em patamar elevado, aumento da demanda mundial por alimentos e por pesquisa agropecuária. A posição do País neste cenário deve ser assegurada, principalmente, pela aplicação da tecnologia. As pesquisas devem garantir a competitividade e a sustentabilidade do agronegócio, consolidando o Brasil como protagonista em agroenergia e biocombustíveis. ''É preciso agregar valor às commodities, desenvolver matérias-primas, processos e produtos para exploração de novos mercados e novos nichos'', comentou Cruvinel. Para isso, deve haver a garantia do desenvolvimento e da eficácia das pesquisas, fortalecendo mecanismos de propriedade intelectual. Já no segundo cenário projetado, os preços das commodities agrícolas permaneceriam com preços medianos devido à volatilidade, a economia global cresceria em ritmo moderado com crises e turbulências, a demanda por produtos agropecuários também seria mediana e os recursos naturais da maioria dos países continuariam sendo usados de forma predatória. Neste caso as oportunidades estariam na integração inter e intra-regional e no aumento da demanda por pesquisa agropecuária. As pesquisas continuariam em papel de destaque. No terceiro cenário, a expansão setorizada com inserção em nichos, os preços das commodities continuariam elevados, a economia mundial cresceria em ritmo acelerado, haveria aumento da demanda por produtos agropecuários, os recursos naturais seriam utilizados de maneira mais sustentável e o Brasil seria inserido no contexto mundial baseado apenas em commodities. Haveria a ameaça da ''especialização'' brasileira em produtos de baixo valor agregado. Além de aumentar a eficiência das pesquisas, a estratégia deverá garantir competitividade ao agronegócio brasileiro no mercado mundial através de parcerias para a geração e transferência de tecnologias voltadas à agricultura tropical. Já no processo de desarticulação e retrocesso - o cenário mais pessimista -, a projeção é de maior protecionismo nos fluxos comerciais internacionais, com degradação dos recursos naturais, preços das commodities influenciados pela alta volatilidade e inserção do Brasil no contexto mundial baseada predominantemente em commodities. As estratégias, neste caso, seriam o desenvolvimento de tecnologias orientadas à recuperação de áreas degradas e ao uso racional dos recursos hídricos, aumento da eficiência e eficácia das instituições de pesquisa, garantindo maior flexibilização institucional e normativa. Fernanda Mazzini

 

 

http://www.plantionapalha.com.br/view_noticia.php?cod_noticia=34396

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Agricultor já compra insumo para 2009

Agricultor já compra insumo para 2009

15/04/2008

Fonte: Globo Rural

A safra de verão deste ano ainda está terminando e já tem agricultor comprando adubo para 2009. Em Mato Grosso, os produtores reclamam do preço. O agricultor José Chiarello já tem todo o adubo para o plantio da próxima safra na fazenda, que fica em Sinop, norte de Mato Grosso. Ele conta que fez a compra antecipada e mesmo assim pagou 560 dólares a tonelada, quase o dobro do que custava no ano passado. "Mesmo quem se antecipou e correu atrás para comprar em janeiro, que poucos têm essa possibilidade, já pagaram mais caro que no ano passado", diz José Chiarello. Para comparar o preço viemos até esta revenda de insumos em Sinop, norte de Mato Grosso. Segundo o proprietário, José Moreli, a tonelada de uma das fórmulas de adubo mais usadas na região, a base de nitrogênio, fósforo e potássio, dobrou em um ano. Em abril de 2007, a tonelada custava 300 dólares. Em janeiro desse ano saia por 560 reais e hoje não sai por menos de 750 dólares. "Os agricultores desta região normalmente compram os fertilizantes, sementes e defensivos entre maio e setembro. Esse ano, as compras iniciaram em janeiro, já comprando os insumos com medo do aumento", diz José Moreli, comerciante. Na maior parte das fazendas os barracões usados para guardar o adubo estão vazios e os agricultores que ainda não compraram esses insumos já começam a ficar mais preocupados. O seu Amélio Zanini ainda não fechou negócio com nenhuma revenda. Ele pretende plantar 500 hectares de soja. A comercialização deve ser feita no sistema de troca. Ele vai pagar os insumos com parte da soja que pretende colher. "Pra tu comprar uma tonelada de adubo hoje você precisa de 40 sacos de soja. No ano passado, o preço era 20 sacas", diz o agricultor. Em São Paulo nos fomos ouvir a associação nacional que representa as empresas de adubo. "A causa principal dos sucessivos aumentos é a diferença entre a demanda e a oferta. No lado da demanda nós não podemos nos furtar a dizer que a renda agrícola no mundo ficou cada vez maior. Vamos destacar China e Índia em que um volume enorme de habitantes passou a comer, coisa que não faziam. Então a demanda, seja de proteína vegetal ou animal aumentou drasticamente e por conseqüência arrastou consigo os preços das matérias-primas e fertilizantes. Um outro fator do lado da demanda é a agroenergia. Nós já estávamos habituados no Brasil a ter etanol, vindo da cana de açúcar, mas o mundo inteiro entrou neste mercado a partir de 2006 e com isso mais uma vez puxa a demanda por matérias-prima. E por fim, do lado da oferta, nós temos algumas restrições como nitrogênio, que nós vimos o que aconteceu com o petróleo. É um produto derivado de petróleo e gás natural com acréscimo de preços. No caso do fósforo nós tivemos alguns problemas ambientais em algumas plantas americanas que foram fechadas e no caso do cloreto duas inundações em duas importantes minas, uma na Rússia e uma no Canadá que diminuiu a oferta deste produto. Oferta menor, demanda maior, preço alto", explica o diretor executivo da Anda (Associação Nacional para difusão de adubos) , Eduardo Daher. O Brasil importa 50% do fósforo que usa, 70% do nitrogênio e 90% do potássio.

Embriones para Venezuela - ARG Natural Beef

martes 18 de marzo de 2008
Embriones para Venezuela - ARG Natural Beef
La empresa ARG Natural Beef, del grupo Corporación América, concretará el primer embarque de embriones y dosis de semen vacuno a Venezuela. Proximamente, 635 embriones y 7500 dosis de semen viajarán en dos termos consolidados a bordo de un avión de LAN y, con esta exportación, se concretará el paso inicial del acuerdo que el grupo presidido por Eduardo Eurnekian y la Corporación Venezolana Agraria pactaron en agosto de 2007. El objetivo de la operación es perfeccionar la genética y mejorar la ganadería venezolana que busca abastecer de carne a su país.

ARG NATURAL BEEF, aprovechando las 87.000 hectáreas ubicadas en las provincias de Chaco y Formosa, desarrolla un proyecto de creación de genética de vanguardia y producción de alta calidad de carne para exportar a los más exigentes mercados del mundo.

De esta forma, se desarrolla una línea de productos cárnicos Premium y Súper Premium y, siguiendo los esquemas de seguridad alimentaria más altos, se elabora una carne de alta calidad, cuidando las etapas desde la genética y la agricultura hasta el packaging, con personal altamente capacitado y tecnología de última generación.

Así se obtiene un producto Súper Premium, carne producida solo a pasto, por lo que -de acuerdo con las investigaciones en la materia- posee mayor contenido de ácidos omega 3, ácido oleico conjugado, vitamina E y betacarotenos; todas sustancias con propiedades nutritivas favorables para la salud humana. Asimismo, esta carne tiene un menor contenido de colesterol y grasas totales. Las carnes vacunas Premium y Súper Premium llegan al consumidor como cortes enfriados, en packs especialmente preparados y fáciles de transportar.

La selección se apoya en el desempeño productivo de los animales y en su capacidad reproductiva. Fertilidad, adaptación a la alta producción bajo las condiciones ecológicas locales, y superior calidad de la carcasa -medida en vivo por ecografía- son las pautas selectivas que orientan el trabajo de mejoramiento genético de los planteles. El uso de los mejores toros producidos en los planteles, en el servicio de los rodeos comerciales, propaga en estos la superioridad genética obtenida por selección. Se cuenta con un programa de Transferencia Embrionaria que potencia la superioridad genética de las hembras; con este propósito, se seleccionan las mejores madres.

Razas
El proyecto se estructura en una amplia base de rodeo comercial, aproximadamente 21.000 vientres, y unos 4.000 vientres registrados.
El rodeo se basa en las razas Brangus negro y colorado, Braford y Bonsmara, estas últimas utilizadas para cruzas industriales sobre madres comerciales Brangus, para engorde “a pasto”.
Faena
El proceso comienza con la recepción de los animales, que son alojados en corrales vacunos, de acuerdo con las regulaciones de la Unión Europea. Posteriormente, se trasladan a un frigorífico para su faena, respetando rigurosamente las Buenas Prácticas de Manufactura, y también son inspeccionados por la autoridad sanitaria nacional.
Trazabilidad

La trazabilidad de la carne es la asignación de un número de identificación de un animal o grupo de animales en el momento de su nacimiento; para ello se utilizan etiquetas con códigos de barras o tags de radiofrecuencia que se colocan en la oreja del animal, lo que permite agregar información en el momento que se requiera a lo largo de la cadena de suministro, hasta su llegada a la góndola minorista. El sistema de marcación permite la identificación automática de los animales, tanto para el momento de la faena como para su posterior clasificación.
A lo largo de todo el procesamiento se respeta la trazabilidad de los cortes, desde el origen del animal hasta el producto final entregado al cliente. Nuestros selectos cortes vacunos son producidos de acuerdo con especificaciones propias, así como también respondiendo a requerimientos especiales de los clientes, ya sea en cuanto a su variedad y tamaño como a su envasado y rotulación.

Productos › Packaging
La carne envasada al vacío se exhibe en las heladeras a fin de que el comprador elija el corte deseado, que será colocado en una caja térmica, acondicionada con geles congeladores que garantizan su conservación durante 24 horas. De esta manera, el pack (o envase) puede llevarse como un simple equipaje acompañado, ya que está especialmente diseñado para permitir que el pasajero lo transporte con facilidad en viajes largos. Debido a que se trata de carne enfriada y no congelada, el cliente puede elegir consumirla al llegar a su hogar, o colocarla en el freezer para poder disfrutarla un tiempo después.

En el local de ARG NATURAL BEEF (Aeropuerto Internacional de Ezeiza) , usted puede elegir entre los diferentes cortes que se encuentran en las heladeras, donde la mercadería se mantiene entre –2° y +2.5° C, respetando así los protocolos de la carne fresca envasada al vacío.
Vendedores bilingües/ trilingües, altamente capacitados, podrán informarle acerca de nuestros productos:
• Características de los diferentes cortes en cuanto a sabor y terneza; también las mejores formas de cocinarlos.
• Es una carne de exportación de primera calidad que se comercializa en forma directa, con lo que se evitan intermediarios, fletes, etcétera.
• Por eso, llega a usted a precios inferiores a los que normalmente se encuentran en los distintos puntos de venta del mundo.
Asimismo, lo asesorarán sobre:
• Países a los cuales usted puede ingresar carne fresca argentina.
• Cómo mantener la cadena de frío, según usted desee consumir el producto al llegar a su destino o bien refrigerarlo o conservarlo en el freezer. Para ello, se acondiciona el producto en un envase conservador térmico con geles refrigerantes.
• Origen y trazabilidad de los vacunos, explicando número de lote, campo de procedencia, etcétera.
• Seguridad Sanitaria: con los cortes, se entrega al pasajero un certificado sanitario que provee el Senasa (Servicio Nacional de Sanidad y Calidad Agroalimentaria) ya que, por convenios preexistentes con los diferentes países, es el único instrumento legal (en este único punto de venta) para que el pasajero pueda llevarse carne fresca en los aviones, desde la Argentina.


Fuente: ARG Natural Beef y Diario La Nación

Publicado por Jorge Elias en 7:45:00 AM
Etiquetas: Nutrición

Cattle Update: Improving Cowherd Reproduction Via Genetics

Cattle Update: Improving Cowherd Reproduction Via Genetics   A beef cow's job is not an easy one. She is expected to conceive at slightly over one year of age to calve by the time she is two and rebreed shortly after that while weaning a healthy, viable calf. Furthermore, we demand that she consistently repeats this cycle for the rest of her life - one stumble and, in the words of California's terminating governor, hasta la vista, baby!   To be sure, producers are best served when the cow successfully performs her task for many years, as the longer her productive life the more profitable she is to the enterprise. Is there anything that can be done to help her out? Certainly, there are environmental factors we can manage that will give her a leg up. For example, by providing adequate nutrition, a proper vaccination regimen and mating her to easy-calving sires (particularly when she is young) we increase the odds of her success. While a cow's environment has a substantial impact on her reproductive performance, her genetic makeup can too. This paper explores the genetics of female reproduction and offers suggestions on how to improve the reproductive performance of your cowherd via genetics.   Crossbreeding: The obvious place to start a discussion about the genetics of female reproduction is with the factor that far and away has the greatest affect on it - crossbreeding. It has long been recognized that crossbreeding enhances virtually all aspects of reproductive performance. Studies too numerous to list here have established the reproductive superiority of crossbred over straightbred cows.   In one of an abundance of studies with similar findings, scientists at the Meat Animal Research Center (MARC) concluded that two-breed rotational cross cows produced 20% more calves over their lifetime than straightbreds due to the favorable impact of heterosis on dam fertility/longevity and calf survivability brought about by the improved calving and mothering ability of the dam (Cundiff et al., 1992). Furthermore, they estimated that when mated to a bull of another breed the two-breed cross cows would wean 36% more weight over their lifespan than straightbred cows raising straightbred calves. The dramatic increase is attributable to the positive influence of heterosis on reproduction and production in the dam and well as increased growth and survivability in their calves.   Given the overwhelming evidence of the crossbred cow's reproductive supremacy and the fact that reproduction is a major piece of the profitability puzzle (by most accounts exceeding all other functions by a wide margin in relative importance), it is difficult to conceive of a situation where a commercial enterprise would not benefit financially from a crossbred cowherd.   Am I implying that selecting animals within a breed for reproductive performance is not a worthwhile endeavor? No! Reproductive progress can be made via selection (which I will address later); however, it would take years of intense selection within a breed to yield the kind of improvement that can be achieved in one fell swoop by simply crossbreeding.   Therefore, crossbreeding makes a logical cornerstone in any effort to enhance cowherd reproductive performance. With crossbreeding as the foundation, the selection of superior animals of multiple breeds as inputs to the crossbreeding system can be considered a supplemental means of further boosting reproductive function; however, identifying reproductively superior animals has its challenges, as I will explain.   Indirect Selection: Because the assessment of a cow's reproductive performance is generally determined later in her life, it seems logical to look for early indicators to hasten the process. For example, it is a commonly-held belief that females with a propensity toward fatness will excel reproductively.   Though research has shown that increased fatness, to a point, is strongly and favorably associated with reproductive performance on a phenotypic scale, the few attempts to assess the relationship on a genetic level show an unfavorable, though weak, relationship. Using data from the Red Angus Association of America (RAAA), researchers at Colorado State University (CSU; Beckman et al., 2006) derived genetic correlations ranging from -.12 to -.22 between body condition at various ages and stayability (by industry convention, the probability of a cow remaining in the herd through 6 years of age). At the American Simmental Association (ASA), we have found a correlation of -.19 between an animal's genetic propensity for backfat in the feedlot and their inherent stayability. We (ASA) have also calculated a -.11 genetic correlation between backfat and heifer pregnancy (the likelihood of a heifer being pregnant at the end of the breeding season) using RAAA data.   Admittedly, these unfavorable correlations between fatness and reproduction may seem illogical. We have all seen a higher proportion of thin cows open at pregnancy test time. Keep in mind, however, that the aforementioned correlations are genetic. The relationships we actually observe, i.e., phenotypic correlations, are influenced by a combination of underlying environmental and genetic relationships. There is little question that females within a herd lucky enough to experience an environment for increased body condition (e.g., extra energy intake) are likely to have better reproductive performance than their herd mates. Furthermore, this strong and positive environmental relationship between fat and reproduction apparently overwhelms what appears to be a slightly negative genetic relationship - yielding the strong, favorable phenotypic relationship we typically observe.   Frankly, there is not enough evidence about the genetic relationship between fatness and reproductive function to make recommendations based on it at this time; however, though it may fly in the face of conventional wisdom, it appears that selecting "easy-fleshing" genotypes will not gain us ground reproductively.   Scrotal circumference has been considered as a predictor of female reproductive performance. Though the preponderance of evidence indicates a strong to moderately favorable relationship between scrotal circumference and age at puberty in related females, research is less clear on the relationship between scrotal circumference and subsequent measures of reproduction. In a study based on a large population involving several breeds at the MARC, Martinez-Velazquez et al. (2003) found a slightly unfavorable (.15) relationship between scrotal circumference and age at first calving and no relationship between scrotal circumference and 1st pregnancy, 1st calving and 1st weaning rates. Their conclusion was that selection on scrotal circumference would not be effective in improving female reproduction. These findings are in agreement with some studies and contradicted by others. For those interested, Martinez Velazquez et al. (2003) provides and excellent literature review on the subject. Given the conflicting evidence, it may not be advisable to base selection decisions on scrotal circumference with the intent of enhancing maternal reproduction.   As for other traits that may be related to reproductive function, Rogers et al. (2004) found that increased levels of milk EPD increased the risk of females being culled. This finding is consistent with ASA data showing an unfavorable (-.15) genetic correlation between milk and stayability. Other ASA genetic correlations of note: -.26, .40, and -.19 between stayability and mature weight, maternal calving ease and marbling, respectively. Based on these findings, we would expect females that are inherently lower milking, smaller mature sized, easier calving and less marbled to stay in the herd longer; however, none of these relationships are strong enough to make a sizable impact on stayability by selecting for them. Furthermore, other than mature weight because of its strong relationship to early growth, determining the genetic level of a young heifer for these traits by simply observing them (which is what most commercial producers are limited to) is not possible. Therefore, a different tack will be required if we wish to improve reproductive performance via selection. Namely, select for it directly - which, as I will point out, is not a trivial task.   Next week, Part 2 of this article begins with a focus on Direct Selection.     Source: Wade Shafer, ASA Director of Performance Programs   http://www.cattlenetwork.com/agrilabs_content.asp?contentid=210241