ABSTRACT The interaction between pasture and supplementation in dairy production systems constitutes a very important part of the efficiency of dairy. This study evaluated the effect of the herbage mass (HM) on the milk production and solid concentration. Twenty Holstein cows were distributed into two groups, 10 assigned 2200 kg DM ha-1 (low herbage mass, LHM) and 10 with 2800 kg DM ha-1 (medium herbage mass, MHM). Herbage mass was measured above 5 cm. The experiment lasted 8 wk. The variables evaluated were DM intake (DMI), milk production and composition (fat and protein concentration). Effects of treatments on variables were evaluated using a repeated measure analysis over time. The results showed nonsignificant differences in the pasture DMI between LHM and MHM for weeks 1, 2, 3 and 5 (P > 0.05). During week 4, pasture DMI was 3 kg greater for LHM than MHM (P < 0.05). The milk production did not differ between treatments per week, but the average was 2.4 kg greater for LHM compared to MHM (P < 0.05). In conclusion, changes in the pasture availability increased milk production at LHM, but not enough to cause changes in solids concentration. This clearly shows that, LHM can increase milk and solids production.

ABSTRACT: This study evaluated the probability of pregnancy and associated factors for two times artificial inseminations (AI), 8 or 10 hours after automated activity monitoring (AAM) alarm on the first postpartum AI of 1,054 Holstein dairy cows. The estrus was synchronized by prostaglandin or estradiol-progesterone program. Stepwise logistic regression was performed to analyze the probability of pregnancy, and associated factors (activity, estrus intensity, parity, peripartum health, retained placenta, postpartum vaginal discharge, and season). The highest pregnancy rates were obtained with multiparous animals, inseminated ten hours after the AAM alarm, in the fall or winter season, with a high activity peak and estrus intensity (P < 0.05). Peripartum diseases, retained placenta, and postpartum vaginal discharge negatively influenced the pregnancy rate, regardless of parity. Thus, the optimization of AAM models by including on-farm measures like parity, peripartum health history, and environmental conditions may favor the correct identification of estrus and improve the AAM alarm regarding the ideal moment for AI, increasing the reproductive performance in dairy cows.

RESUMO: O objetivo deste estudo foi avaliar a probabilidade de prenhez e fatores associados para dois horários de inseminação artificial (IA), oito ou 10 horas após o alarme de monitoramento automatizado de atividades (AAM), na primeira IA pós-parto em 1.054 vacas leiteiras da raça Holandês. O estro foi sincronizado por protocolos a base de prostaglandina ou estradiol-progesterona. Regressão logística stepwise foi realizada para analisar a probabilidade de prenhez e fatores associados (atividade, intensidade do estro, paridade, saúde no periparto, placenta retida, descarga vaginal pós-parto e estação do ano). As maiores taxas de prenhez foram obtidas em multíparas, inseminadas 10 horas após o alarme do AAM, no outono ou inverno, com pico de atividade elevado e intensidade de estro (P < 0,05). Doenças no periparto, placenta retida e descarga vaginal pós-parto influenciaram negativamente a taxa de prenhez, independentemente da paridade. Assim, a otimização dos modelos de AAM, incluindo medidas rotineiras da fazenda como paridade, histórico de saúde no periparto e condições ambientais, podem favorecer a identificação correta do estro e melhorar o alarme do AAM em relação ao momento ideal para a IA, aumentando o desempenho reprodutivo nas vacas leiteiras.

ABSTRACT: This study evaluated the vaccine-induced serological response after administering four commercial formulations containing Bovine Viral Diarrhea Virus (BVDV) type-1, BVDV-2, and Bovine Herpesvirus type 1 (BoHV-1) to young heifers with circulating maternal antibody titers. The study also determined the anamnestic response to vaccinations after the complete metabolization of maternal antibodies when the calves reached six months. Eighty-seven Holstein heifers were selected and randomly distributed into four experimental groups based on the vaccine administered. The four vaccine-based experimental groups were as follows: vaccine A (n = 22), vaccine B (n = 22), vaccine C (n = 24), and vaccine D (n = 19), given on the 60th, 90th, and 180th day of life, respectively. Virus-neutralization (VN) tests were performed at baseline (day 60) and 30 days after administering the second (day 120) and third doses (day 210). We analyzed the effect of vaccine group (P ≤ 0.001), day of vaccination (P ≤ 0.001), and group versus vaccine day interaction (P ≤ 0.001) for antibody titers produced against BVDV-1, BVDV-2, and BoHV-1 using the PROC MIXED method (Statistical Analysis System -SAS 9.4). Antibody titers against BVDV-1, BVDV-2, and BoHV-1 were similar at baseline and on day 60 of life. The mean antibody titers were constant and persisted against BVDV-1 in heifers immunized with vaccines A and C. Heifers immunized with vaccine A alone had a similar effect against BVDV-2. Regarding BoHV-1, the antibody titers decreased between days 60 and 210 in groups B, C, and D. The antibody titer for heifers in group A also decreased between days 60 and day 120, and an intense increase in titers was observed on day 210. After being immunized with formulations B, C, and D, the frequency of animals with titers above protective levels for BVDV-1, BVDV-2, and BoHV-1 was very low or null. Indicators of anamnestic response were observed in heifers vaccinated with formulation A only. Therefore, it can be concluded that passive immunity negatively interferes with antibody production after vaccination.

RESUMO: O objetivo desse estudo foi avaliar a resposta sorológica induzida após vacinação com quatro formulações comerciais contendo o BVDV-1, BVDV-2 e BoHV-1 em novilhas jovens com títulos de anticorpos maternos circulantes, assim como analisar uma possível resposta anamnéstica em vacinações, após a completa metabolização dos anticorpos maternais aos seis meses de idade. Foram selecionadas 87 novilhas Holandesas, distribuídas aleatoriamente em quatro grupos experimentais de acordo com as vacinas: vacina A (n = 22), vacina B (n = 22), vacina C (n = 24) e vacina D (n = 19), aplicadas aos dias 60, 90 e 180 de vida. Testes de vírus-neutralização (VN) foram realizados no momento basal (D60) e 30 dias após a aplicação da 2ª dose (D120) e 3ª dose (D210). Observou-se efeito do grupo (P ≤ 0,001), dia da vacinação (P ≤ 0,001), e interação grupo versus dia (P ≤ 0,001) para os títulos de anticorpos produzidos contra o BVDV-1, BVDV-2 e BoHV-1, por meio do comando PROC MIXED (Statistical Analysis System, versão 9,4). Os títulos de anticorpos contra o BVDV-1, BVDV-2 e BoHV-1 eram semelhantes no momento basal aos 60 dias de vida. Os títulos médios de anticorpos foram constantes e persistentes contra o BVDV-1 nas novilhas imunizadas com as vacinas A e C, porém apenas a vacina A teve este mesmo perfil contra o BVDV-2. Em relação ao BoHV-1, os grupos B, C e D apresentaram queda nos títulos de anticorpos do D60 ao D210, enquanto as novilhas do grupo A apresentaram queda do D60 ao D120, com aumento intenso dos títulos no D210. A frequência de animais com títulos acima dos protetores contra o BVDV-1, BVDV-2 e BoHV-1 foram muito baixos ou nulos após as vacinações nos animais imunizados com as formulações B, C e D. Sugere-se que a imunidade passiva interferiu negativamente na indução de anticorpos pelas vacinas, observando-se indicadores de resposta anamnéstica apenas para as novilhas vacinadas com a formulação A.

ABSTRACT: Protocols to artificially induce cows and heifers into lactation are effective and commercially available in Brazil. However, these protocols demand long hormonal treatments, which is debatable since little research has been done in the subject. To further understand artificial induction to lactation (AIL) protocols, we conducted two experiments. In experiment 1, our objective was to better characterize steroidal profile during an AIL protocol and assess the estradiol (E2) and progesterone (P4) serum profiles of Jersey cows (n=6) subjected to a conventional protocol. In experiment 2, we aimed to compare milk production and serum E2 concentrations of Holstein heifers induced into lactation by the standard AIL protocol (15 injections of E2 and 8 P4 injections) and by a short protocol in which the number of E2 injections and, consequently, the overall dosage of E2, were reduced (8 injections of E2 and 8 P4 injections). We hypothesized that a short AIL protocol (8 days) would be as efficient as the long standard protocol of 15 days. Our hypothesis was confirmed, since we demonstrated that a shorter protocol was able to induce lactation in Holstein heifers without hindering milk production.

RESUMO: Protocolos que induzem à lactação artificial em vacas e novilhas são eficazes e estão comercialmente disponíveis no Brasil. No entanto, esses protocolos demandam longos tratamentos hormonais, o que é discutível visto que poucas pesquisas foram feitas sobre o assunto. Para entender melhor os protocolos de indução artificial à lactação (IAL), realizamos dois experimentos. Foi testada a hipótese de que um protocolo curto (oito dias) de IAL é tão eficiente quanto o protocolo padrão de 15 dias. No experimento 1 objetivou-se caracterizar o perfil esteroidal durante um protocolo de IAL e avaliou-se os perfis séricos de estradiol (E2) e progesterona (P4) de vacas Jersey (n=6) submetidas a um protocolo convencional. No experimento 2 foram comparadas a produção de leite e as concentrações séricas de E2 de novilhas holandesas induzidas à lactação pelo protocolo padrão de IAL (15 injeções de E2 e 8 injeções de P4) e por um protocolo curto, no qual o número de injeções de E2 e, consequentemente, a dosagem geral de E2 foram reduzidas (oito injeções de E2 e oito injeções de P4). A hipótese foi confirmada, demonstrado que um protocolo mais curto induziu a lactação em novilhas holandesas sem prejudicar a produção de leite.

The objective of the study was to determine, through deep learning, the predictability of milk yield from a cow's side-view, rear-view image, or a combination of the two. The data size of 1 238 image pairs (the side-view and rear-view images) from 743 Holstein cows in their first or second parity, and their corresponding first-lactation, 305-day milk yield values were used to train and test Deep Learning models. The data were first split into the training and testing data at a ratio of 80:20, respectively. The training data were augmented four times, then again divided into training and validation data at the ratio of 4:1, respectively. Three principal analyses were done, the prediction of milk yield using rear-view images, using side-view images, and using a merge of the side-view and rear-view images. In all three analyses, poor predictions were observed, i.e., R² values ranging from 0.30 to 0.38, the mean absolute error ranging from 1112.9 kgs to 1148.3 kgs, the root mean square error values ranging from 1401.2 kg to 1480.5 kg, and the mean absolute error percentages ranging from 17.0 to 17.6%. Hypothesis tests were done to check whether there was any difference between these three prediction models. There was no significant difference in performance between the prediction models. It was concluded that predicting the 305-day milk yield of Holstein cows using either view had the same level of accuracy, and no additional benefits were derived from using both the rear and side views.

Reactive oxygen species at supra-physiological levels trigger oxidative stress during cryopreservation, which can be neutralised by incorporating suitable antioxidants into the semen extender medium. This study was intended to explore the effect of asiatic acid (AA) as an antioxidant in semen extender on frozen-thawed sperm quality and in vivo fertility of bull sperm. Semen was collected from Holstein Friesian bulls for 10 consecutive weeks (total ejaculates = 60). Semen was cryopreserved with a Tris citric acid egg yolk-based extender supplemented with 0 (control), 20, 40, 60, and 100 μM AA. The supplementation of the extender with 40 and 60 μM AA improved (p < 0.05) post-thaw motility kinematics, plasma membrane integrity, acrosome integrity, sperm viability, and DNA integrity of bull sperm. Mitochondrial membrane potential was high (p < 0.05) with 60 μM of AA concentration in extender media. The catalase activity in seminal plasma was maintained (p < 0.05) when semen was added with 20, 40, and 60 μM of AA. The in vivo fertility was found to be significantly high with the semen extended with 60 μM AA. Conclusively, this study showed that AA supplementation in semen extender significantly improved sperm motility kinematics and cell integrity, conserved antioxidant enzyme activity, and improved in vivo fertility.

Resumo Por muitos anos, o objetivo da seleção em fazendas leiteiras foi focado em altos rendimentos, ignorando características de saúde, como resistência a doenças. Atualmente o interesse está em identificar geneticamente animais resistentes ao desenvolvimento de doenças infecciosas, por meio de genes candidatos. O complexo principal de histocompatibilidade bovina (bola) é um grupo de genes, ligados à resposta imune. O objetivo deste estudo foi associar os alelos do exon 2 do gene bola-DRB3.2 com a produção de leite e a contagem de células somáticas, parâmetro associado à incidência de mastite subclínica. Amostras de sangue foram coletadas de 157 vacas da raça Holandesa e seu DNA foi analisado pela técnica de PCR-RFLP. Foram detectados 32 alelos, sendo seis deles os mais frequentes (13,50% a 6,43%). São eles: bola-DRB3.2 *23, *24, *16, *25, *28 e *22. As contagens de células somáticas foram analisadas como indicadores de doença quando os registros foram superiores a 250.000 células/ml de leite. Com um modelo linear generalizado, o alelo *25 foi associado a uma baixa contagem de células somáticas e o *23 associado a uma alta contagem de células somáticas (p= 0,03). Foi detectada associação entre os alelos com os litros de leite (p= 0,0132). Não foi encontrada associação significativa com o percentual de proteína e gordura. Os alelos bola-DRB3.2 evidenciam-se como marcadores relevantes para detectar animais geneticamente resistentes à mastite e maior produção de leite.

Resumen Durante muchos años el objetivo de selección en las explotaciones lecheras estuvo focalizado en las altas producciones, ignorándose los rasgos de salud tales como la resistencia a enfermedades. Actualmente el interés está en identificar genéticamente los animales resistentes a desarrollar enfermedades infecciosas, por medio de genes candidatos. El complejo principal de histocompatibilidad Bovino (BoLA) es un grupo de genes, vinculado a la respuesta inmune. El objetivo del presente estudio fue asociar alelos del exón 2 del gen BoLA-DRB3.2 con producción de leche y conteo de células somáticas, un parámetro asociado a la incidencia de mastitis subclínica. Se tomaron muestras de sangre a 157 vacas de raza Holstein y su ADN se analizó por la técnica PCR-RFLP. Se detectaron 32 alelos de los cuales seis fueron los más frecuentes (13,50 % a 6,43 %). Éstos son: BoLA-DRB3.2 *23, *24, *16, *25, *28 y *22. Se analizaron los conteos de células somáticas como indicadores de enfermedad cuando los registros eran superiores a 250.000 cel/ml de leche. Con un modelo lineal generalizado se encontró al alelo *25 asociado con bajo conteo de células somáticas y el *23 asociado a un alto conteo de células somáticas (p= 0,03). Se detectó una asociación entre los alelos con los litros de leche (p= 0,0132). No se encontró asociación significativa con el porcentaje de proteína y de grasa. Los alelos del BoLA-DRB3.2 se evidencian como marcadores relevantes para detectar animales genéticamente resistentes a mastitis y una mayor producción lechera.

Abstract For many years the selection objective on dairy farms was focused on high yields, ignoring health traits such as disease resistance. Currently the interest is focused in genetically identifying animals that are resistant to developing infectious diseases, through candidate genes. The main Bovine Histocompatibility Complex (BoLA) is a group of genes linked to the immune response. The aim of the present study was to associate alleles of exon 2 of the BoLA-DRB3.2 gene with milk production and somatic cell count as a parameter to evaluate subclinical mastitis. Blood samples were taken from 157 Holstein dairy cows; their DNA was analyzed using the PCR-RFLP technique. Thirty-two alleles were detected, six of which were the most frequent. These are: BoLA-DRB3.2 *23, *24, *16, *25, *28 and *22, with a frequency ranging from 13,50% to 6,43%. Somatic cell counts were analyzed as disease indicators when the records were above 250,000 cells/ml of milk. Using a generalized linear model, allele *25 was found to be associated with a low somatic cell count and *23 was associated with a high somatic cell count (p = 0,03). An association was detected between the alleles and liters of milk (p = 0,0132). No significant association was found with protein and fat percentages. The BoLA-DRB3.2 alleles are evidenced as relevant markers to detect animals genetically resistant to mastitis and higher milk production.

ABSTRACT Global advances in reproductive biotechnology have allowed for the transfer of embryos from donor females with high genetic merit to recipients using the cryopreservation technique, which preserves an embryo of excellent quality and viability, thereby achieving a feasible pregnancy rate. The objective of this study was to evaluate the quality and viability of Holstein embryos that have been cryopreserved for more than 40 years under glycerol freezing. The embryos were transferred to the recipient heifers using a non-surgical method. Two 17-month-old Holstein heifers (360 kg live weights) which were clinically healthy and reproductively active were used as the recipients. Two bovine embryos of Grade 1 quality were thawed and evaluated for their morphology. Of the two embryo transfers, one pregnancy was achieved, resulting in the birth of a calf. Therefore, embryos frozen in liquid nitrogen and glycerol as a cryopreservative for more than 40 years maintained their quality and viability to produce a live calf.

RESUMO Os avanços globais em biotecnologia reprodutiva permitiram a transferência de embriões de fêmeas doadoras com alto mérito genético para receptoras, usando-se a técnica de criopreservação, que preserva um embrião de excelente qualidade e viabilidade, alcançando, assim, uma taxa de gravidez viável. O objetivo deste estudo foi avaliar a qualidade e a viabilidade de embriões Holstein, criopreservados por mais de 40 anos, sob congelamento de glicerol. Os embriões foram transferidos para as novilhas receptoras, usando-se um método não cirúrgico. Duas novilhas Holstein de 17 meses de idade (360kg de peso vivo), que eram clinicamente saudáveis e reprodutivamente ativas, foram utilizadas como receptoras. Dois embriões bovinos de qualidade Grau 1 foram descongelados e avaliados quanto à sua morfologia. Das duas transferências embrionárias, uma gravidez foi obtida, resultando no nascimento de um bezerro. Portanto, os embriões congelados em nitrogênio líquido e glicerol como criopreservante por mais de 40 anos mantiveram sua qualidade e viabilidade para produzir um bezerro vivo.

Abstract 23. An outbreak of respiratory distress was observed in Holstein cows immediately after consuming a new batch of corn-silage, presumably due to the presence of pneumotoxic gases. Signs were observed in 10% of the cows, and characterized as tachypnea, orthopneic position, cough and notable anxiety a few minutes after offering the silage. No deaths were recorded. Mild leucocytosis was observed in the hemogram. Nutritional analysis and nitrate determination of the corn-silage revealed usual values. Nitrous oxide and methane concentration were evaluated by gas chromatography and nitrogen oxides concentration directly with a portable device, resulting in acceptable values. Although high concentrations of toxic gases could not be evidenced in the air sampled on farm, the clinical signs observed coincide with those reported in cases of exposure to gases formed during corn silage processes. A greater emphasis is required in the evaluation of the corn to be ensiled, given the possible existence of factors that can generate the accumulation of potentially toxic gases for cattle that affect negatively their health and productivity.

Resumen. 27. Se describe un brote de enfermedad respiratoria en vacas Holando Argentino, inmediatamente luego del consumo de un nuevo silaje de planta entera de maíz, presuntamente con presencia de gases neumotóxicos. Se observaron signos en el 10% de las vacas, caracterizados como taquipnea, posición ortopnéica, episodios de tos y ansiedad, unos minutos luego del ofrecimiento del silaje. No se registraron muertes. En el hemograma se observó leucocitosis leve. El análisis de calidad nutricional del alimento y la concentración de nitratos en el silaje de maíz resultó con los valores habituales. Se evaluó la concentración de óxido nitroso y metano en una muestra de silaje de maíz recolectada herméticamente por cromatografía gaseosa, así como la concentración de óxidos de nitrógeno in situ con un instrumento portátil, resultando en valores aceptables. Aunque no se pudieron evidenciar concentraciones de gases elevadas en el aire del silaje muestreado en el tambo, los signos clínicos observados coinciden con los casos reportados de exposición a gases que se forman durante la fermentación del ensilado. Se debería tener en cuenta la evaluación del maíz a ser ensilado, dadas las posibilidades de que se genere la acumulación de gases potencialmente tóxicos para el ganado, que puedan afectar negativamente su salud y productividad.

Abstract This study examined the relationship between age at first calving and milk production in Holstein heifers within an intensive system in the dairy basin of Córdoba, Argentina. Retrospective data from 452 cows calving between 2016 and 2017, aged between 23 and 32 months, were collected. The results revealed a significant decrease in adjusted 305-day milk yield as age at first calving increased. Cows calving at 24 months yielded higher total milk production by the end of lactation compared to those calving at 31 and 32 months. A significant difference in daily milk yield during lactation was observed based on age at first calving, while no significant effect of calving year was found. Total daily milk yield was also influenced by age at first calving, with cows calving at 24 months exhibiting higher production compared to those calving at 32 months. The dry period, representing the days from drying off to the start of the subsequent lactation, was also influenced by age at first calving, with significant differences observed between cows calving at 23 and 31 months, as well as at 24 and 31 months. In terms of reproductive variables, a significant difference in the calving interval was found based on age at first calving. No significant interaction between age at first calving and calving year was identified for any of the analyzed variables. In conclusion, this study demonstrated that age at first calving has a significant impact on milk production in Holstein cows within an intensive system. The findings suggest that placing greater emphasis on achieving first calving between 23 and 25 months of age may enhance productive and reproductive efficiency in dairy farms.

Resumen Este estudio analizó la relación entre la edad al primer parto y la producción de leche en vacas Holstein en un sistema intensivo en la cuenca lechera de Córdoba, Argentina. Se recopilaron datos retrospectivos de 452 vacas que parieron entre 2016 y 2017, con edades comprendidas entre 23 y 32 meses. Los resultados mostraron que a medida que la edad al primer parto aumenta, la producción de leche ajustada a los 305 días disminuye significativamente. Las vacas que parieron a los 24 meses produjeron más leche total al final de la lactancia en comparación con aquellas que parieron a los 31 y 32 meses. Se observó una diferencia significativa en la producción diaria de leche en lactancia según la edad al primer parto, pero no se encontró un efecto significativo del año de parto. La producción diaria total de leche también fue afectada por la edad al primer parto, con las vacas que parieron a los 24 meses mostrando una mayor producción en comparación con las que parieron a los 32 meses. El período seco, que representa los días desde el secado hasta el inicio de la próxima lactancia, también fue influenciado por la edad al primer parto, con diferencias significativas entre las vacas que parieron a los 23 y 31 meses, y a los 24 y 31 meses. En cuanto a las variables reproductivas, se encontró una diferencia significativa en el intervalo entre partos según la edad al primer parto. No se encontró una interacción significativa entre la edad al primer parto y el año de parto para ninguna de las variables analizadas. En conclusión, este estudio demostró que la edad al primer parto tiene un impacto significativo en la producción de leche de vacas Holstein en un sistema intensivo. Los resultados sugieren que un mayor énfasis en alcanzar un primer parto a una edad entre los 23 y 25 meses podría mejorar la eficiencia productiva y reproductiva en las explotaciones lecheras.

Abstract. The objective of this work was to evaluate the duration of productive life, survival to subsequent calving, discards and deaths in different crosses of dairy breeds in a grazing commercial dairy farm. Retrospective data from a commercial farm in the province of Santa Fe, Argentina, were analyzed. The period evaluated ranged from August 1, 2017, to January 12, 2021. The database consisted of 1,342 lactations of pure Holstein breed (HO; n: 799 cows), 344 lactations of HO x Jersey cross (JY; n: 164 cows), 190 lactations of the JY x Montbeliarde cross (MO; n: 96 cows) and 316 lactations of the MO x HO cross (XB; n: 134 cows). No significant differences were found between the survival curves of the productive life variable between the pure HO breed and the evaluated crosses (p=0.1281). When the survival to subsequent calving was analyzed, it was found that all the crosses were superior both in the second and in the third calving, with respect to the pure HO cows. No significant differences were found in culling and mortality variables between HO cows and the different crosses. It is concluded that the length of the productive life was similar between the pure breed HO and the studied crosses JY, MO and XB. Finally, culling and deaths were similar between the purebred (HO) and the JY, MO and XB crosses, although MO cows showed the lowest mortality rates.

Resumen El objetivo de este trabajo fue evaluar la duración de la vida productiva, la supervivencia a los partos posteriores, los descartes y muertes en diferentes cruzamientos de razas lecheras en un tambo comercial a pastoreo. Se analizaron datos retrospectivos de un tambo comercial de la provincia de Santa Fe, Argentina. El período de tiempo evaluado fue desde el 1 de agosto del 2017 al 12 de enero del 2021. La base de datos constaba de 1342 lactancias de raza Holstein puras (HO; n: 799 vacas), 344 lactancias de cruza HO x Jersey (JY; n: 164 vacas), 190 lactancias de la cruza JY x Montbeliarde (MO; n: 96 vacas) y 316 lactancias de la cruza MO x HO (XB; n: 134 vacas). No se hallaron diferencias significativas entre las curvas de supervivencia de la variable vida productiva entre la raza HO pura y los cruzamientos evaluados (p=0,1281). Cuando se analizó la supervivencia a los partos posteriores, se encontró que todos los cruzamientos fueron superiores tanto en el segundo como en el tercer parto, con respecto a las vacas HO puras. No se encontraron diferencias significativas en las variables descarte y muerte entre las vacas HO y las diferentes cruzas. Se concluye que la longitud de la vida productiva fue similar entre la raza pura HO y los cruzamientos estudiados JY, MO y XB. Finalmente, los descartes y las muertes fueron similares entre la raza pura (HO) y los cruzamientos JY, MO y XB, aunque las muertes en las vacas MO mostraron los menores valores.

Abstract 27. The objective of this study was to evaluate the effect of two doses of equine chorionic gonadotropin (eCG) in a J-Synch protocol, using 107 cows with calves at foot, Holstein, Brown Swiss, and their crosses, with a body condition (CC) of 2.5 (scale 1-5), and a silvopastoral system. The trial consisted of two treatments (T): T1 = 1 dose of eCG (n=52) and T2 = 2 doses of eCG (n=55). On day 0, an intravaginal device (BID) containing 0.5 g progesterone (P4) and 2 mg estradiol benzoate (BE) was administered. On day 6, the DIB was removed and 500 μg Cloprostenol (PGF2α) + 400 IU of eCG was administered. The base of the tail was painted, to determine estrus manifestation. Unpainted animals were inseminated at 60 h and painted animals at 72 h, + 100 µg of (GnRH). At T1 treatment, the size of the corpus luteum (CL) was measured on days 14 and 30 after insemination, and blood samples were taken. At T2 treatment, a second dose of 400 IU of eCG was administered on day 14, and CL size was measured, as well as on day 30, and blood samples were taken. The pregnancy diagnosis was made 40 days after the IATF, by ultrasonography. The highest pregnancy rate was observed in T2 (58.2%), and in cows in estrus (56.6%). No statistical differences were observed between treatments (p=0.7). Serum P4 concentrations were not different. Similarly, the diameter of the CL at days 14 and 30 post IATF did not differ (p>0.05). However, the size of the CL at days 14 and 30, is clearly related (p<0.001). In conclusion, a second dose of eCG on day 14 in the J - Synch protocol had no effect on pregnancy but a tendency to improve performance in Ecuadorian Amazonian cows.

Resumen 23. El objetivo de este estudio fue evaluar el efecto de dos dosis de gonadotropina coriónica equina (eCG) en el protocolo J-Synch, utilizando 107 vacas con cría al pie, de razas Holstein, Pardo Suizo y sus cruzas, con una condición corporal (CC) de 2,5 (escala 1-5), y un sistema silvo-pastoril. El estudio consistió de dos tratamientos (T): T1 = 1 dosis de eCG (n=52), y T2 = 2 dosis de eCG (n=55). El Día 0 se aplicó un dispositivo intravaginal (DIB) con 0,5 g de progesterona (P4) y 2 mg de benzoato de estradiol (BE). Al día 6, se retiró el DIB y se administraron 500 μg de Cloprostenol (PGF2α) + 400 UI de eCG. Se pintó la base de la cola, para determinar manifestación de estro, inseminando animales despintados a las 60 horas y pintados a las 72 horas, + 100 µg de (GnRH). En el T1 se midió el tamaño de cuerpo lúteo (CL) en los días 14 y 30 después de la inseminación y se tomaron muestras de sangre. En el T2, se administró una segunda dosis de 400 UI de (eCG) al día 14, y se midió el tamaño de CL, al igual en día 30, y se tomaron muestras de sangre. El diagnóstico de gestación se realizó a los 40 días después de la IATF, mediante ultrasonografía. La mayor tasa de preñez fue en el T2 (58,2%), y en vacas en estro (56,6%), sin evidenciar diferencias relevantes (p=0,7). Las concentraciones séricas de P4, no difieren. Asimismo, el diámetro del CL de los días 14 y 30 post IATF (p>0,05). Sin embargo, la magnitud del CL en los días 14 y 30, están claramente relacionados (p<0,001). En conclusión, una segunda dosis de eCG al día 14 en el protocolo J-Synch, no tuvo influencia sobre la preñez, pero si una tendencia a desempeñarse mejor en vacas de la Amazonía Ecuatoriana.

Resumen El cruzamiento permite aprovechar las diferencias genéticas aditivas entre razas, también permiten hacer uso de la heterosis y de la complementariedad. Por lo tanto, se necesita generar información de la eficacia de las cruzas en comparación con las razas puras, bajo las condiciones de interés. El objetivo fue cuantificar el impacto de los efectos genéticos aditivos y no aditivo para días a primer estro (DPE), días a primer servicio (DPS), días abiertos (DA), servicios por concepción (SPC), intervalo entre partos (IP) y duración de la gestación (DG). Se utilizó la información productiva y genealógica de hembras provenientes de un dialelo entre Holstein (HO) y Suizo Pardo (SP), un total de 148 vacas de las razas HO (n=43), SP (n=64) y sus cruzas reciprocas HO-SP (n=20) y SP-HO (n=21). Se utilizaron contrastes para estimar la heterosis individual y las diferencias entre los efectos genéticos directos y entre los efectos genéticos maternos con base en los modelos de Dickerson. Los resultados mostraron que la heterosis y las diferencias entre los efectos maternos no fueron significativos (P>0.05) para ninguna de las características estudiadas. Las diferencias entre efectos genéticos directos solo fueron importantes (P<0.05) para SPC y DG. En conclusión, la heterosis generada por el cruzamiento entre HO y SP no influyó sobre la eficiencia reproductiva de las hembras. Los efectos maternos no fueron diferentes entre HO y SP. Los efectos genéticos directos para SPC y DG favorecieron a la raza SP.

Abstract Crossbreeding allows taking advantage of additive genetic differences between breeds, they also allow making use of heterosis and complementarity. Therefore, it is necessary to generate information on the efficacy of crosses compared to pure breeds under the conditions of interest. The objective was to quantify the impact of additive and non-additive genetic effects for days to first estrus (DFE), days to first service (DFS), days open (DO), services per conception (SPC), calving interval (CI) and gestation length (GL). The productive and genealogical information of females from a diallel between Holstein (HO) and Brown Swiss (BS), a total of 148 cows of the breeds HO (n=43), BS (n=64) and their reciprocal crosses HO-BS (n=20) and BS-HO (n=21), was used. Contrasts were used to estimate individual heterosis and differences between direct genetic effects and between maternal genetic effects based on Dickerson models. The results showed that heterosis and differences between maternal effects were not significant (P>0.05) for any of the traits studied. Differences between direct genetic effects were only important (P<0.05) for SPC and GL. In conclusion, the heterosis generated by the crossbreeding between HO and BS did not influence the reproductive efficiency of females. Maternal effects were not different between HO and BS. Direct genetic effects for SPC and GL favored the BS breed.

Resumen El objetivo fue calcular los parámetros, correlaciones y describir las tendencias genéticas de caracteres reproductivos en ganado Holstein de México en tres periodos diferentes de tiempo, en hembras nacidas entre 2006 y 2019, usando registros de la asociación Holstein de México. Los parámetros reproductivos calculados fueron: intervalo parto a primer servicio (IPPS), el número de servicios por concepción (NSC), los días abiertos (DAB), el intervalo entre partos (IEP) y la edad al primer parto (EPP). Los componentes de la varianza fueron estimados utilizando máxima verosimilitud restringida en un modelo animal, para calcular parámetros genéticos (heredabilidad en sentido estricto (h2), repetibilidad (r) y correlaciones genéticas) y correlaciones fenotípicas. También se estimaron varianzas genéticas aditivas y valores genéticos en tres periodos de tiempo (P1: 2006-2009, P2: 2010-2013 y P3: 2014-2017). Las heredabilidades calculadas fueron de 4 a 9 % y las repetibilidades del 8 al 9 %, valores cercanos a reportes previos para características de fertilidad. Las correlaciones fenotípicas fueron positivas para casi todos los parámetros reproductivos y las genéticas fueron positivas en un rango amplio (0.13-0.99). Los análisis por periodos mostraron cambios, posiblemente derivados de la influencia de la importación y uso de germoplasma de toros extranjeros (principalmente de los Estados Unido de América y Canadá) que implementan selección genómica e incluyen características fertilidad. La presente investigación ha permitido actualizar la información de parámetros reproductivos y genéticos en caracteres de fertilidad que podrán ser incorporados a las evaluaciones genéticas nacionales.

Abstract The objective was to calculate the parameters, correlations and describe the genetic trends of reproductive traits in Holstein cattle from Mexico in three different periods of time, in females born between 2006 and 2019, using records of the Mexican Holstein association. The reproductive parameters calculated were: calving to first insemination interval (CFI), number of services per conception (NSC), days open (DO), interval between calving (IBC), and age at first calving (AFC). The components of variance were estimated using restricted maximum likelihood in an animal model, to calculate genetic parameters (narrow-sense heritability (h2), repeatability (r) and genetic correlations) and phenotypic correlations. Additive genetic variances and genetic values were also estimated in three periods of time (P1: 2006-2009, P2: 2010-2013 and P3: 2014-2017). The calculated heritabilities were from 4 to 9 % and the repeatabilities from 8 to 9 %, values close to previous reports for fertility traits. Phenotypic correlations were positive for almost all reproductive parameters and genetic correlations were positive over a wide range (0.13-0.99). Analyses by period showed changes, possibly derived from the influence of the import and use of germplasm from foreign bulls (mainly from the United States of America and Canada) which implement genomic selection and include fertility traits. The present research has made it possible to update the information on reproductive and genetic parameters in fertility traits that can be incorporated into national genetic evaluations.

ABSTRACT Various studies have evaluated the use of electronic devices to automatically record the grazing behavior of dairy cows. Linking individual grazing behavior of dairy cows with the modifications in grazing behavior across the grazing session through the use of automatically registered indicators, would allow the development of decision-making tools in grazing management. The objective of the present study was to evaluate the use of the activity level (AL) recorded with an accelerometer during the grazing-down process of a pasture grazed by dairy cows as a possible criterion for decision-making related to grazing management. A completely randomized design was used to evaluate the AL of dairy cows in two contrasting pasture-based dairy production systems: A pasture-based system with high concentrate supplementation level and high herbage mass (HM), using high-yielding dairy cows (GRAZSUP), and a pasture-based system with minimal concentrate supplementation level and medium HM, using Holstein New Zealand strain (GRAZ). Pre-grazing HM was higher in GRAZSUP than in GRAZ (+750 kg DM ha-1), while forage removed was higher in GRAZ than in GRAZSUP (+1.9 kg DM cow-1 d-1). Although the production system influenced the characteristics of the pasture and the ingestive behavior of the dairy cows, when AL was evaluated as the proportion of the initial AL recorded at a time-point of the grazing-down process, there were no differences in each of the times evaluated. In conclusion, AL of grazing dairy cows was significantly affected during the grazing-down process, reflecting the modifications in grazing behavior across grazing session.