ABSTRACT Nutritional management of high-producing dairy cows under heat stress conditions presents a significant challenge due to the increasing issue of global warming. The study aimed to explore the effects of Cr supplementation in the form of chromium propionate (CrP) on feed intake, lactation performance, and selected biochemical serum parameters in mid-lactation Simmental dairy cows under heat stress conditions. The experiment was conducted during July and August and lasted for 8 wk. The average temperature-humidity index (THI) was 76.45 ± 2.80 during the experimental period, indicating that the cows were under heat stress. The added CrP provided 0.34 mg Cr kg-1 DM of used ration. The supplementation of diet with CrP increased DM intake (4.11%, P < 0.01) and the yield of milk (4.48%, P < 0.01), 4% fat-corrected milk (4.08%, P < 0.01), milk fat (4.46%, P < 0.01), protein (4.21%, P < 0.01), lactose (3.79%, P < 0.01), and total solids (3.51%, P < 0.01). Additionally, CrP supplementation increased blood glucose concentrations (8.39%, P < 0.01), while reducing blood urea N (BUN) levels (14.85%, P < 0.05) and beta-hydroxybutyrate (BHB) levels (17.14%, P < 0.05). The use of CrP as additional dietary source of Cr significantly improved productive performances of dairy cows under heat stress conditions. It was indicated that supplemented Cr could have positive effect on glucose and N metabolism, as well as on energy metabolism of lactating cows at moderately high THI values.

Abstract: The objective of this study was to evaluate the effect of some factors on carcass traits and the phenotypic correlations between them. Records from 514 Simmental and 178 Simbrah bovine individuals born in Mexico between 2011 and 2018 were used. The variables evaluated were rib eye area (AOL), rump fat thickness (GC), back fat thickness (GD), adjusted intramuscular fat (GI), marbling (M) and carcass yield grade (R). Adjusted means and phenotypic correlations between traits were estimated with PROC MIXED and PROC CORR of SAS®. The fixed effects included in the models were breed, sex of the animal, herd, year of measurement, season of measurement, and age in days at measurement as a covariate; sire nested in breed was included as a random effect. The effect of breed was significan for GC (p<0.001), R (p<0.07) and GD (p<0.07). The effects of sex and season were significant (p<0.001) for all the evaluated traits. The correlations of AOL with all other traits were significant (p<0.001); negative with GI and M; and positive with GC, GD, and R. The correlations of GC with GD and R were important and positive (p<0.001). Selecting phenotypes to increase lean meat can lead to a decreased fat content. The positive phenotypic correlations between R and carcass quality traits would imply that the aforementioned traits can be improved without any adverse effects on them and R in the population.

Resumen: El objetivo fue evaluar el efecto de algunos factores en características de la canal y las correlaciones fenotípicas entre ellas. Se utilizó la información de registro de 514 bovinos Simmental y 178 Simbrah nacidos entre 2011 y 2018 en México. Las características evaluadas fueron área del ojo del lomo (AOL), grasa de la cadera (GC), grasa dorsal (GD), grasa intramuscular ajustada (GI), marmoleo (M) y grado de rendimiento en canal (R). Las medias ajustadas y las correlaciones fenotípicas entre características se estimaron con PROC MIXED y PROC CORR de SAS®. Los efectos fijos incluidos en los modelos fueron: raza, sexo del animal, hato, año de medición, época de medición y edad en días a la medición como covariable lineal; se incluyó al semental anidado en raza como efecto aleatorio. El efecto de raza fue significativo para GC (p<0,001), R (p<0,07) y GD (p<0,07). Los efectos de sexo y época fueron significativos (p<0,001) para todas las características evaluadas. Las correlaciones de AOL con las otras características estudiadas fueron significativas (p<0,001); negativas con GI y M; y positivas con GC, GD y R. Las correlaciones de GC con GD y R fueron importantes y positivas (p<0,001). La selección de fenotipos para aumentar la carne magra puede conducir a una disminución del contenido de grasa. Las correlaciones fenotípicas positivas entre R y los rasgos de calidad de la canal implicarían que los rasgos mencionados pueden mejorarse sin ningún efecto adverso en éstos y R en la población.

Abstract This article presents the results of the culling of cows of the Simmental and Holstein breeds in the Republic of Kazakhstan. The purpose of the research was to study the actual number of culled cows of dairy productivity in the farms of the Republic of Kazakhstan to determine its norm. The object of research were cows of Simmental (18,462 heads) and Holstein (17,862 heads) breeds in various regions of the republic. The research was carried out according to generally accepted zootechnical methods using statistical data processing using RStudio. The results of the studies showed that the percentage of culling increases in cows of the Simmental and Holstein breeds and amounts to 19.7 and 22.9%, respectively. The analysis of the retirement of full-aged cows of the Simmental breed showed that the main causes are hoof diseases (up to 26%), low reproductive function (up to 21%), low productivity (up to 18%). Holstein cows had an increase in disposals in all categories except for disposals for various reasons, for problems with reproduction, the disposal is up to 21%. The determination of the relationship between productivity and retirement in the Simmental breed cows showed that with age and increased lactation, the proportion of retired cows also increases, in the Holstein breed, with increased productivity, the percentage of culled animals also increases.

Resumo Este artigo apresenta os resultados do abate de vacas Simental e Holstein na República do Cazaquistão. O objetivo do estudo foi estudar o número real de vacas abatidas na direção da produtividade leiteira nas fazendas da República do Cazaquistão para determinar sua norma. O estudo incluiu vacas Simental (18.462 cabeças) e Holstein (17.862 cabeças) em diferentes regiões da República. A pesquisa foi conduzida de acordo com métodos zootécnicos geralmente aceitos, adotando o processamento estatístico de dados, usando o RStudio. Os resultados da pesquisa mostraram que as vacas Simental e Holstein aumentaram a taxa de abate para 19,7% e 22,9%, respectivamente. A análise da alienação de vacas Simental de meia-idade mostrou que as principais causas são doenças dos cascos (até 26%), baixa função reprodutiva (até 21%) e baixa produtividade (até 18%). As vacas Holstein tiveram um aumento na alienação em todas as categorias, exceto a alienação por várias razões; devido a problemas reprodutivos, a alienação é de até 21%. A determinação da relação entre a produtividade e a alienação em vacas Simental mostrou que a proporção de vacas eliminadas aumenta com a idade e o aumento da lactação, enquanto a porcentagem de animais eliminados aumenta com a produtividade na raça Holstein.

Abstract A study on the study of the qualitative assessment of the behavior of dairy cattle according to the VAS system (visual analog scale) was conducted in the LLP "Agrofirme "AKAS", located in the West Kazakhstan region of the Republic of Kazakhstan. According to research, it follows that different seasons of time affect the conditions of detention in different ways. So, for the maintenance of cows in the summer, the distance of avoidance at the feeding site according to test 1 and 2 is within 3 meters, whereas in spring and autumn it was 2 meters. The difference between the reference norm and the household ration has been determined, from which it follows that the feeding ration of the farm corresponds to the norm of 12 kg of milk yield per head per day. The vitamin and mineral premix developed by us includes vitamins, minerals, including macro-microelements. The premix also includes components in the following ratio: phosphorus (P) – 5% of monocalcium phosphate, vitamin A – 1.2% of rovimix A 1000, vitamin D3 – 0.64% of rovimix D3, vitamin E – 16% of rovimix E-50, manganese (Mn) – 22.2%, copper (Cu) – 9%, zinc (Zn) – 19%, iodine (I) – 0.28%, selenium (Se) – 7.65 and cobalt (Co) – 0.14%, and feed chalk – 5% and chickpea flour – 13.89% are used as fillers as a source of calcium (Ca).. The average daily milk yield at the beginning of the experiment in both study groups was in the range of 10.6-10.8 kg. At the end of the experiment, the average daily milk yield in animals receiving premix exceeded their peers from the control group by 1.4 kg or 1.6%. According to the chemical composition of milk, the indicators of fat, protein and lactose were higher in the cows of the experimental group compared with the peers of the control group (for fat – 3.92>3.37, for protein – 3.32>3.23, for lactose - 4.16>4.01).

Resumo O estudo sobre a avaliação qualitativa do comportamento do gado leiteiro pelo sistema EVA (escala visual analógica) foi realizado na empresa Agrofirme AKAS LLP, localizada na região Oeste do Cazaquistão, da República do Cazaquistão. De acordo com estudos, diferentes estações do tempo afetam as condições de detenção de maneira diferente. Assim, para a manutenção de vacas no verão, a distância de evitação no local de alimentação, de acordo com os testes 1 e 2, está dentro de 3 metros, enquanto na primavera e no outono era de 2 metros. A diferença entre a norma de referência e a dieta econômica foi determinada, o que significa que a dieta alimentar da fazenda corresponde a uma taxa de 12 kg de produção de leite por cabeça por dia. A pré-mistura de vitaminas e minerais desenvolvida inclui macroelementos. Além disso, a composição da pré-mistura contém componentes na seguinte proporção: fósforo (P), 5% de fosfato monocálcico; vitamina A, 1,2% de Rovimix A1000; vitamina D3, 0,64% de Rovimix D3; vitamina E, 16% de Rovimix E50; manganês (Mn), 22,2%; cobre (Cu), 9%; zinco (Zn), 19%; iodo (I), 0,28%; selênio (Se), 7,65; cobalto (Co), 0,14%, além de 5% de giz forrageiro e 13,89% de farinha de grão-de-bico, usados como fonte de cálcio para enchimentos. A produção diária média para o início da experiência em ambos os grupos estudados foi de 10,6 a 10,8 kg. No final do experimento, a produção diária média dos animais que receberam a pré-mistura excedeu seus pares do grupo controle em 1,4 kg, ou 1,6%. Em termos de composição química do leite, os indicadores de gordura, proteína e lactose foram maiores nas vacas do grupo experimental em comparação com os pares do grupo controle (para gordura, 3,92 > 3,37; para proteína, 3,32 > 3,23; para lactose, 4,16 > 4,01, respectivamente).

RESUMEN Nariño (Colombia) tiene un gran potencial lechero; sin embargo, sus hatos presentan dificultades en el componente nutricional (desbalance energético) de las vacas, afectando su productividad. La presente investigación evaluó el efecto de un suplemento con grasa sobrepasante sobre la concentración de lípidos en la leche y la eficiencia reproductiva de las vacas. Para ello se utilizaron 21 vacas (Holstein x Simmental) entre segundo y tercer parto y se suministró: forraje + concentrado (T1); forraje + concentrado + 250 g/día de grasa sobrepasante (T2) y forraje + concentrado + 250 g/día de grasa sobrepasante enriquecida con omega tres (T3). El tiempo experimental fue desde el día 15 preparto hasta el día 105 de lactancia, donde se determinó la cantidad, calidad, composición de leche y el comportamiento reproductivo de cada animal. Para el análisis de los datos, se empleó un diseño mixto de medidas repetidas en el tiempo, donde los efectos fijos fueron los tratamientos, periodos y la interacción entre estos, mientras que el animal representó el efecto aleatorio, y la covariable fue la producción de leche estimada para la lactancia. Los resultados, revelaron movilización normal de tejido adiposo; la calidad composicional de la leche no varió entre los tratamientos, aunque T2 presento una mayor producción por lactancia estimada y T3 presento un mayor porcentaje del ácido graso C18:2. En los indicadores reproductivos no se vieron influenciados entre los tratamientos; concluyendo que, la dieta base ofertada en el hato, presenta un balance nutricional apropiados a los requerimientos de las vacas en producción.

ABSTRACT Nariño (Colombia) has high dairy potential; however, their herds present difficulties in the nutritional component (energy imbalance) of the cows, affecting their productivity. This research evaluated the effect of a bypass fat supplement on lipid concentration in milk and the reproductive efficiency of dairy cows. The study was based on 21 Holstein x Simmental cows between first and third calving and the following was supplied: forage + concentrate (T1); forage + concentrate + 250 g/day of bypass fat (T2) and forage + concentrate + 250 g/day of bypass fat enriched with omega-three (T3). The experiment was conducted from day 15 pre-calving until day 105 of lactation. During this period, milk quantity, quality, composition, and reproductive behavior were recorded. For data analysis, a repeated measure mixed design with time-series data was used, where the fixed effects were the treatments, periods, and their interaction, the animals represented the random effect, and the covariable was the estimated milk yield during lactation. The results showed normal mobilization of adipose tissue; the compositional quality of the milk did not vary across treatments, although T2 presented a higher estimated production per lactation, and T3 presented a higher percentage of fatty acid C18:2. In the reproductive indicators, they were not influenced between the treatments; concluding that the base diet offered in the herd presents a nutritional balance appropriate to the requirements of the cows in production.

Abstract In the industry of bull semen freezing centers, one-step and two-step semen dilution protocols are two standard and well-known methods in semen freezing process. As the freezing/thawing processes cause detrimental effects on sperm function, the addition of antioxidants can improve sperm characteristics. Hesperidin (Hesp) is an antioxidant used as the male reproductive protective agent. Therefore, the aim of this study was to investigate two different dilution methods, as well as to evaluate Hesp supplementation influence on sperm characteristics in fresh and frozen thawed semen. Semen samples were collected from 12 Simmental bulls. Two separate examinations were conducted in, with and without Hesp supplementation groups. Statistical analysis was performed by an independent t-test, Mann Whitny test, MANOVA and ANOVA tests. In comparison to the one and two-step dilution protocols without Hesp supplementation, the two-step dilution showed greater cryoprotective potential. In the Hesp supplemented group, each semen sample was divided into six equal parts for experimental groups (dilution step method/µM of Hesp). In the both one and two step dilution protocols, significant improvements were detected in semen motility parameters by Hesp administration. Also, oxidative stress status was reduced in seminal plasma of Hesp treatment groups. Interestingly, in comparison with Hesp dosage, 1µM was shown to have greater semen cryoprotective potential. In conclusion,

ABSTRACT The objective of this trial was to investigate the potential benefits of enzyme and probiotic supplementation on the growth performance, nutrient digestibility, carcass traits, and meat quality of Simmental cattle. Sixty Simmental steers (367.75±4.69 kg) were randomly divided into three groups: control (fed basal diet), BC1 group (fed basal diet and 10 g/d brewer’s yeast and cellulase supplementation per cattle), and BC2 group (fed basal diet and 20 g/d brewer’s yeast and cellulase supplementation per cattle). A 10-d preparation period was followed by a 120-d experimental period. The results showed that the final weight of the BC2 group was greater than that of the control group. Also, feed conversion ratio of the BC2 group was better than that of the control group. Net meat weight increased by 3.86% in the BC2 group compared with the control group. The apparent digestibility of neutral detergent fiber, acid detergent fiber, and crude protein of the BC2 group was greater than that of the control group. Dietary supplementation with brewer’s yeast and cellulase supplementation could improve the growth performance and nutrient digestibility of Simmental cattle.

The aim of this study was to determine the prevalence of cattle infected by Hypoderma, a parasite that causes great economic losses in the world, especially in the Ardahan region. A total of 31 095 cattle skins were randomly selected between 15 November 2020 and 15 March 2021 and examined. The prevalence of warbles was 47.3%. The proportions of cattle with warbles on the skin on their backs were 76.6% in one-year-old and younger animals, 60.9% in two- and three-year-old animals, and 16.5% in cattle that were four years old or more. It was determined that 53.6% of the cattle with warbles on the back skin were indigenous breeds, 47.6% were Simmental and Montofon crosses, and 36.2% were domestic breeds. The average number of larvae was 8.2. Interviews with the owners of the infected animals revealed that hide loss was on average 10% in liveweight, with a 5% to 8% in the milk production of dairy cows. In the animals under investigation the total economic loss from warbles caused by damage to the hide was calculated as US$114 188. Thus, it is important to carry out preventive practices regularly to limit the spread of the parasite and prevent economic loss in Ardahan.

RESUMEN Los aditivos de origen vegetal para alimento animal, también conocidos como fitobióticos, son muy prometedores para compensar una deficiencia de sustancias biológicamente activas importantes en la dieta. Este estudio tuvo como objetivo evaluar el efecto del Germivit como suplemento alimenticio del ganado de diferentes edades. En el primer experimento, cuatro grupos de terneros (10 animales en cada grupo) Simmental de 9 meses de edad fueron alimentados con Germivit a una dosis de 0,0; 0,5; 0,7 y 0,9 kg-1 de peso corporal vivo, respectivamente. En el segundo experimento, tres grupos de vacas preñadas (10 animales en cada grupo) recibieron Germivit a una dosis de 0,0; 0,25 y 0,50 g kg-1 de peso corporal vivo, respectivamente. La composición morfológica de la sangre recogida se estudió utilizando un analizador hematológico automático PCE-90vet. La composición bioquímica de la sangre se estudió utilizando un analizador bioquímico Stat Fax 1904, y el estado inmune de los animales se evaluó utilizando métodos generalmente aceptados en veterinaria: células inmunocompetentes por formación espontánea de rosetas; inmunoglobulinas por el método de inmunodifusión radial; fagocitosis usando cultivo de S. aureus; actividad de la lisozima sérica por el método fotoelectrocolorimétrico; y actividad bactericida del suero determinando el grado de inhibición del crecimiento de la mezcla de cultivo diario de E. coli en un medio nutritivo líquido. Germivit contribuyó a una mejora de los parámetros bioquímicos e inmunológicos en los terneros. En las vacas se observó un aumento de los parámetros morfológicos de la sangre, mejoró su estado inmunológico y sus terneros nacieron con altos índices de resistencia natural y salud. Germivit tuvo un efecto positivo sobre el estado funcional del ganado.

ABSTRACT Plant-based feed additives, also known as phytobiotics, show great promise to compensate deficiencies of important biologically active substances in the diet. Therefore, this study aimed to evaluate the effect of Germivit on the feed supplement of cattle of different ages. In the first experiment, four groups of 9-month-old Simmental calves (10 animals in each group) were fed with Germivit at 0.0, 0.5, 0.7, and 0.9 g kg-1 live body weight, respectively. In the second experiment, three groups of pregnant cows (10 animals in each group) received Germivit at 0.0, 0.25, and 0.50 g kg-1 live body weight, respectively. The morphological composition of the collected blood was studied using a PCE-90vet automatic hematology analyzer. The blood biochemical composition was studied using a Stat Fax 1904 biochemical analyzer, and the immunological status of the animals was evaluated using generally accepted methods in veterinary medicine: immunocompetent cells by spontaneous rosette formation; immunoglobulins by the radial immunodiffusion method; phagocytosis by using S. aureus culture; serum lysozyme activity by the photoelectrocolorimetric method; and bactericidal activity of serum by determining the degree of growth inhibition of the mixture of daily culture of E. coli in a nutritive culture broth. Germivit contributed to the improvement of the biochemical and immunological parameters in the calves. In the cows, an increase in the morphological parameters of blood was observed, their immune status improved, and their calves were born with high rates of natural resistance and health. Germivit had a positive effect on the functional state of cattle.

Resumen El objetivo fue presentar resultados de investigación sobre mejoramiento genético de bovinos productores de carne realizados por el Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, así como los retos y perspectivas de investigación a corto, mediano y largo plazo en dicha área del conocimiento. Se utilizaron tesis de maestría, trabajos de congresos y artículos científicos publicados de 1987 a 2020. En los últimos 34 años, se logró caracterizar productiva y reproductivamente animales Bos indicus y Bos taurus x Bos indicus en condiciones tropicales, implementar evaluaciones genéticas multirraciales para las poblaciones Simmental-Simbrah y Charolais-Charbray, determinar la importancia de los efectos maternos en características de crecimiento y estimar la heredabilidad y correlaciones genéticas para características de crecimiento y reproductivas de machos y hembras en animales Bos taurus y Bos indicus, comprobar que la interacción genotipo-ambiente es un factor importante en la expresión de peso al destete en Simmental, desarrollar factores de ajuste de edad de la madre para pesos al nacimiento y destete, desarrollar un prototipo de evaluación genética nacional para permanencia productiva y otro para fertilidad de vaquillas, estimar la diversidad genética de las poblaciones Simmental, Charolais y Simbrah, e identificar SNP asociados a características de crecimiento en Simmental y Simbrah. En el corto plazo, se espera desarrollar índices de selección y predecir el mérito genético de características de canal; en el mediano, realizar evaluaciones genómicas para tolerancia al estrés calórico, consumo de alimento residual y características de salud; y a largo plazo, realizar predicciones genómicas a través de razas.

Abstract The National Institute of Forestry, Agricultural and Livestock Research in Mexico has been active for decades in researching genetic improvement in beef cattle. This review uses master theses, congress papers and scientific articles published from 1987 to 2020 to summarize much of the relevant research, and addresses research challenges and outlook over the short-, medium- and long-term in this area. Research done over the last 34 yr has evaluated the productive and reproductive performance of Bos indicus and Bos taurus x Bos indicus beef cattle raised under tropical conditions. Multibreed genetic evaluations have been done for Simmental-Simbrah and Charolais-Charbray populations in Mexico. Analyses have quantified the importance of maternal effects on growth traits, and estimated heritability and genetic correlations for growth and reproductive traits in male and female Bos taurus and Bos indicus animals. The genotype-environment interaction has been confirmed to influence expression of weaning weight in Simmental cattle. Age adjustment factors have been developed for maternal age for weights at birth and weaning, and prototypes of national genetic evaluation were developed for stayability and heifer fertility. Genetic diversity has been quantified for Simmental, Charolais and Simbrah populations, and SNPs identified that are associated with growth traits in Simmental and Simbrah populations. Short-term goals include development of selection indices and prediction of the genetic merit of carcass traits. Over the medium-term, emphasis is needed on genomic evaluations for tolerance to heat stress, residual feed intake and health traits, while in the long-term the goal is to make inter-breed genomic predictions.

RESUMEN El objetivo del estudio fue determinar la relación existente entre la rickettsemia de A. marginale y las interacciones agroambientales y genéticas en bovinos de doble propósito en Arauca, Colombia. Se tomaron muestra de sangre a 269 hembras de 14 fincas, tanto en la época seca como de lluvias y fueron analizadas con las técnicas de Wright y Hemacolor(r). Se evaluó la interacción entre la presencia de A. marginale con las variables grupo racial, época del año, edad y número de partos, mediante el análisis de varianza. Se encontró 66.6% de animales positivos en la época seca y 100% en la época lluviosa para A. marginale (p<0.001), presentando valores de rickettsemia entre 0 y 0.14% (promedio: 0.04%). La rickettsia A. marginale presentó interacción con el grupo racial (p<0.05), siendo más resistentes los animales criollos y cruces de Pardo Suizo x cebú y de Simmental x cebú y susceptibles los animales con predominio Bos taurus. La edad, numero de parto, condición corporal y época no fueron dependientes para la rickettsemia.

ABSTRACT The aim of this study was to determine the relationship between the rickettsemia of A. marginale and environmental and genetic interactions in dual-purpose cattle in Arauca, Colombia. Blood samples were taken from 269 females from 14 farms, both in the dry and rainy seasons, and were analysed with the Wright and Hemacolor(r) techniques. The interaction between the presence of A. marginale with the variables breed type, season, age and parity was evaluated by analysis of variance. Resulted showed that 66.6% of positive animals to A. marginale were found in the dry season and 100% in the rainy season (p<0.001), presenting rickettsemia values between 0 and 0.14% (average: 0.04%). The rickettsia A. marginale showed interaction with the breed type (p<0.05), the creole animals and crosses of Brown Swiss x zebu and Simmental x zebu being more resistant, whereas Bos taurus animals were more susceptible. Age, parity number, body condition and season were not dependent on rickettsemia.

RESUMEN Objetivo. Comparar la fertilidad de vacas cruzadas Suizo Pardo x Cebú y Simmental x Cebú criadas en un ambiente tropical. Materiales y métodos. Se evaluaron características reproductivas de 185 vacas cruzadas Suizo Pardo x Cebú y Simmental x Cebú con diversos porcentajes de raza europea. El pastoreo de las vacas fue rotacional. El ordeño fue dos veces al día con la ayuda (amamantamiento) del becerro, el cual se mantuvo atado cerca de la vaca mientras ella se ordeñaba. Las características se evaluaron ajustando un modelo de mediciones repetidas (excepto para edad a primer parto). Periodo interparto, edad a primer parto, días abiertos, periodo parto-primer servicio y peso al parto fueron analizados con PROC MIXED de SAS. Tasa de gestación a primer servicio y servicios por concepción, se analizaron con PROC GENMOD del mismo programa. Resultados. Las vacas Simmental x Cebú se sirvieron después del parto 39 días antes (p<0.05) y tuvieron 47 días abiertos menos (p<0.05) que las Suizo Pardo x Cebú. El periodo interparto de las vacas Simmental x Cebú fue 45 días más corto (p<0.05) que el de las Suizo Pardo x Cebú. Las vacas Simmental x Cebú pesaron 34 kg más al parto (p<0.05) que las Suizo Pardo x Cebú. Conclusiones. Las vacas Simmental x Cebú tuvieron mejor fertilidad que las Suizo Pardo x Cebú.

ABSTRACT Objective. Compare the fertility of Brown Swiss x Zebu and Simmental x Zebu crossbred cows reared in a tropical environment. Materials and methods. Reproductive traits of 185 Brown Swiss x Zebu and Simmental x Zebu crossbred cows with diverse percentages of European breed were evaluated. Grazing of cows was rotational. The milking was twice daily with the help (suckling) of the calf, which was kept tied next to the dam while she was milked. Traits were evaluated fitting a repeated measures model (except for age at first calving). Calving interval, age at first calving, days open, interval from calving to first service, and weight at calving were analyzed with PROC MIXED of SAS. Pregnancy rate at first service and services per conception were analyzed with PROC GENMOD of the same software. Results. Simmental x Zebu cows started to re-bred 39 days earlier after calving (p<0.05) and had 47 fewer days open (p<0.05) than Brown Swiss x Zebu cows. The calving interval of the Simmental x Zebu cows was 45 days shorter (p<0.05) than that of the Brown Swiss x Zebu cows. Simmental x Zebu cows were 34 kg heavier at calving (p<0.05) than Brown Swiss x Zebu cows. Conclusions. Simmental x Zebu cows had better fertility than Brown Swiss x Zebu cows.

RESUMEN Objetivo. Estimar parámetros genéticos para peso a los ocho meses de edad (W8M), edad al primer parto (AFC) y primer intervalo entre partos (FCI) usando parentesco genómico y por pedigrí. Materiales y métodos. Se utilizaron 481, 3063 y 1098 registros fenotípicos para W8M, AFC y FCI, respectivamente. La información genómica estuvo compuesta por una población de 718 animales genotipados con un chip que incluyó 30106 marcadores genéticos tipo polimorfismo de nucleótido simple (SNP). Modelos univariado y bivariado fueron construidos bajo la metodología del mejor predictor lineal insesgado convencional (BLUP) y genómico en una etapa (ssGBLUP). Resultados. Las heredabilidades para W8M, AFC y FCI variaron desde 0.25 a 0.26, 0.20 a 0.22 y 0.04 a 0.08, respectivamente. Los modelos de AFC y FCI con la metodología ssGBLUP disminuyeron ligeramente el error y aumentaron la varianza genética aditiva, respectivamente. Conclusiones. La inclusión de información genómica mejora levemente la precisión de las estimaciones genéticas en esta población. Sin embargo, una población de animales genotipados más grande y con mayor conectividad genética por parentesco permitiría aumentar para los criadores el potencial de la metodología ssGBLUP en ganado Simmental de Colombia.

ABSTRACT Objective. To estimate genetic parameters for weight at eight months of age (W8M), age at first calving (AFC) and first calving interval (FCI) using pedigree and genomic relationship. Materials and methods. Phenotypic data on 481, 3063 and 1098 animals for W8M, AFC and FCI were used, respectively. The genomic information came from a population of 718 genotyped animals with a density chip of 30,106 single nucleotide polymorphism markers (SNP). Univariate and bivariate models were used under the conventional (BLUP) and single step genomic best linear unbiased predictor (ssGBLUP) methodologies. Results. The heritabilities for W8M, AFC and FCI ranged from 0.25 to 0.26, from 0.20 to 0.22 and from 0.04 to 0.08, respectively. The AFC and FCI models under ssGBLUP slightly decreased the error and increased the additive genetic variance, respectively. Conclusions. The inclusion of genomic information slightly increases the accuracy of the genetic estimates in this population. However, a larger amount of genotyped animals and with a higher genetic relationship connectivity would allow breeders to increase the potential of the ssGBLUP methodology in Colombian Simmental cattle.

Resumen El objetivo del estudio fue analizar las frecuencias alélicas de 28 Polimorfismos de un solo nucleótido (SNP) localizados en genes candidatos para crecimiento en bovinos, así como determinar su efecto sobre rasgos de peso vivo en hatos de las razas Charolais y Simmental. Se tomaron muestras de pelo de 313 animales provenientes de cinco hatos ubicados en cuatro municipios de Tamaulipas y se genotipificaron con la tecnología de Sequenom Mass Array. Todos los marcadores resultaron ser polimórficos en las poblaciones evaluadas y sus frecuencias alélicas fueron significativamente diferentes entre razas (P<0.05). El análisis de asociación determinó que en los animales de la raza Charolais, el marcador PRL+2723 tiene un efecto significativo (P=0.0350) sobre el peso al nacimiento y el marcador localizado en el gen GHR (GHR-6.1), sobre peso al destete (P=0.0226). El GHR-6.1 también se asoció con el peso al año en los animales de la raza Simmental. El marcador LEP-3100 (P=0.0249) también tuvo un efecto significativo sobre el peso al destete en los animales Simmental. El panel probado es polimórfico en las dos razas evaluadas y tres de los marcadores tuvieron efecto significativo en los parámetros de peso vivo evaluados, por lo que tienen el potencial de validarse y usarse como una herramienta adicional en la selección y mejoramiento genético del ganado de carne en Tamaulipas.

Abstract A full understanding of how specific genes affect live weight variables is required for their incorporation into genetic improvement programs. An analysis was done of the allelic frequencies of 28 single nucleotide polymorphisms (SNP) located in candidate genes for growth in cattle to identify their effect on live weight traits in Charolais and Simmental herds in the state of Tamaulipas, Mexico. Hair samples were collected from 313 animals and genotyped using the Sequenom MassARRAY system. Genotype analysis showed that all the markers were polymorphic in the evaluated populations and their allelic frequencies were significantly different between the two breeds (P<0.05). An association analysis found that in the Charolais population the marker PRL + 2723 had a significant effect (P= 0.0350) on birth weight and the marker GHR-6.1 affected weaning weight (P= 0.0226). In the Simmental population GHR-6.1 was associated with yearling weight and the marker LEP-3100 (P=0.0249) had a significant effect on weaning weight. The tested 28 SNP panel is polymorphic in both breeds and three of the markers had a significant effect on the evaluated live weight parameters. They can therefore be potentially validated for use as tools in the selection and breeding of beef cattle in Tamaulipas.

Individual and maternal breed additive effects and heterosis exist for most economically important traits in cattle. Crossbreeding may therefore be valuable for emerging and commercial beef farmers in improving the productivity of their herds. Calves were produced by mating Afrikaner, Bonsmara and Nguni cows to Afrikaner, Bonsmara, Nguni, Angus and Simmental bulls. The cows used were from Vaalharts Research Station or were purchased from other herds. Data were collected over three years. Individual and maternal additive effects and individual heterosis were estimated simultaneously as continuous linear variates. The estimated genetic effects were then used to predict production levels that may be achieved through implementation of top-cross, two-breed rotation, and terminal sire crossbreeding systems. The individual estimates of the genetic effects were relatively small and in most cases were not different from zero, with the exception of the maternal additive effects of Nguni on preweaning traits and their individual additive effect on cow weight, which were less than those of Bonsmara. However, the alternative crossbreeding systems differed across traits. The straight-bred breeding system was least efficient, followed by the crisscross system (+2%) and the terminal sire system that utilized Simmental (+4%), with the terminal sire system utilizing Angus being on average most efficient (+8%). The inter-generational genetic differences in cow weight that resulted from the use of different breeds of sire increased its standard deviation by 5 to 6% in rotational crossing. Despite the relatively small magnitude of the genetic effects, advantages of crossbreeding systems became evident.