Genetic parameters for nitrogen fractions content in Mexican Brown Swiss cattle milk
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Genetic parameters for nitrogen fractions content in Mexican Brown Swiss cattle milk Luis Antonio Saavedra-Jiménez 1 & Rodolfo Ramírez-Valverde 1 José Guadalupe García-Muñiz 1
&
Rafael Núñez-Domínguez 1 & Agustín Ruíz-Flores 1 &
Received: 8 August 2018 / Revised: 28 March 2019 / Accepted: 15 May 2019 # Springer Nature B.V. 2019
Abstract Nitrogen plays an important role in the metabolism of living organisms due to the variety of physiological functions that involve molecules that contain it. This study aimed to estimate genetic parameters for milk nitrogen fractions and the casein:protein ratio in Mexican Brown Swiss population. Milk samples from 317 cows were used to determine total (TN), non-protein (NPN), and non-casein (NCN) nitrogen. Then, crude (CP), true (TP), and whey (WP) proteins, and casein (Cas) percentages were obtained. In addition, the ratios (%) Cas:CP (CCP) and Cas:TP (CTP) were calculated. (Co)variance components and genetic parameters were estimated using an animal model. The pedigree included 2616 animals. Heritabilities were obtained from single-trait and genetic correlations from bivariate analyses. The variation among cows was large for the studied traits. Heritability estimates could be regarded as high (> 0.7) for NCN, WP, CCP, and CTP, while for the rest of the traits, the estimates were from moderate to low magnitude. Genetic correlations estimates differed in magnitude, ranging from − 0.9 to 0.9. There is enough additive genetic variability to achieve genetic improvement for the traits studied; therefore, they could be considered in a breeding program for the studied population. Keywords Casein . Casein:protein ratio . Total nitrogen . Whey protein
Introduction Human population is increasing and this would increase the need for animal products of high nutritional quality, such as bovine milk. Among milk components, proteins are important for the human population, and although it is not considered as an energy source, its energy contribution promotes the reduction of fat in dairy products, which is one of the reasons why market niches have emerged. There are opportunities to feed older adults with products fortified with protein. Likewise, athletes need proteins for regeneration and muscle recovery. Hence, milk composition must be an important part of any genetic improvement program in dairy cattle. According to Rodrigues et al. (2010), Ruska and Jonkus (2014), and Rafiq et al. (2016), protein (%) in milk could be * Rodolfo Ramírez-Valverde [email protected] 1
Departamento de Zootecnia. Posgrado en Producción Animal, Universidad Autónoma Chapingo, Km. 38.5 Carretera México-Texcoco, C.P. 56230 Chapingo, Estado de México, Mexico
estimated from the total amount of nitrogen times 6.38. Milk crude protein (CP) is composed of casein (77.2%; Cas), whey protein (17.5%; WP), and non-protein nitrogen (5.2%; NPN) (Guo et al. 2007). Caseins play an important role in cheese production (Emmons et al. 2003). Whey protein is dispersed in the serum, but do not contribute
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