The objective of this work was to evaluate the longevity and its relationship with productive variables of Nelore cows in grazing systems of the Bolivian tropics. Retrospective data were used corresponding to 259 Nelore breed cows, primiparous and multiparous discarded with a total of 800 births, in the period between 2005 and 2019, belonging to the Cooperativa Agropecuaria Integral San Juan de Yapacaní (CAISY) located in the San Juan Japanese Communities, Santa Cruz, Bolivia. The variables analyzed were: Live weight of cow (WC) in kg, Weight of the calf at birth (WCB) in kg, Weight of calf at weaning (WCW) in kg, Total weight of weaned calf (WWC) in kg, Age at first calving (AFC) in months, Number of calvings (NC), Longevity (L) in days, Calf Index (CI) in kg, Accumulated Productivity (PAC) in kg, Total calf production (CP) in kg, Efficiency of Stock (ES) in kg. In order to respond to the main objective of this work, the relationship between the life longevity of the cow and the other productive variables was studied. For this, first principal component analysis (PCA) was carried out, by means of which the space dimension of the productive variables was reduced creating new linearly independent variables and in this way avoid problems of multicollinearity in the model, because the productive variables in some cases turned out to be correlated. Then, the first three main components that explain 77% of the total variability of the data were retained and interpreted as follows: The PC1 was high and directly correlated with the variables NC, Kg produced total, % of stock efficiency, PAC and Kg produced meat / day, therefore can be thought of as an indicator of "productive efficiency". PC2 was an indicator of "efficiency in rebreeding" since it presented altar and direct correlations with WC and AFC. PC3 was high and directly correlated with birth weight and weaning weight, which is interpreted as an indicator of "breeding efficiency". Finally, a multiple linear regression model was adjusted considering Longevity as a function of productive efficiency, breeding efficiency and rebreeding efficiency (p-value <0.0001 in the three cases). 87% of the total variability of L (days) is explained by the model. It is concluded that Longevity is related to productive indicators for this group of Nelore cows in grazing systems of the Bolivian tropics.

The objective of the present work was to analyze the evolution of the productive indicators over time in Nelore cows of the Bolivian tropics. The period between 1991 and 2016, corresponding to 3899 calvings of Nelore cows were used for the research work which belong to the Technology Center on Agriculture and Livestock in Bolivia belonging (FUNDATION CETABOL) and the Cooperativa Agropecuaria Integral San Juan de Yapacan&iacute; were used. Cows were ordered by birth period into three groups (1991-2000; 2001-2010; 2011-2016). The following variables were analyzed: Age at first calving in days, Live weight of cow in kg, Calf weight at birth in kg, Calf weight at weaning in kg, Calving interval in days, Longevity in days, Accumulative Productivity in kg Total calf production (CP) in kg. The age at first calving has decreased compared to the decade of 1991-2000, however the last period (2011-2016) has increased one more month compared to the period (2001-2010) showing significant differences (p&le;0.05). The weights of the cows and the calving interval followed the same behavior in the sense of decreasing, showing that in the period 2011-2015, the cows had the lowest live weight and the lowest calving-calving interval. The calf weight at birth showed an increase in the last two periods with significant difference (p&le;0.05) with the period 1991-2000. That the longest-lived cows were those from the 1991-2000 period, showing significant differences (p&le;0.05). The cows of the period 2001-2010 presented the best value of the Accumulated Production (p&le;0.05), although the highest production of kg of weaned calf was for the cows of the period 1991-2000. It was concluded of the evolution of the productive indicators over time in Nelore cows from the Bolivian tropics individually showed an improvement in their indicators, although the analysis of the more complex indicators did not show an improvement in the results.

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Productive and reproductive behavior of Nelore cows of different ages in a grazing system of the Bolivian tropics Resumen El objetivo del trabajo fue evaluar el comportamiento productivo y reproductivo de vacas adultas y en crecimiento de la raza Nelore en condiciones de pastoreo del trópico boliviano. El trabajo de investigación se realizó de octubre de 2016 a octubre de 2017 en la Hacienda Ganadería E7, Santa Cruz, Bolivia. Se utilizaron 100 vacas para el estudio. Se dividieron en dos grupos: Grupo adulto: GA, 28 vacas ≥ 5 años de edad y Grupo en crecimiento: GC, 72 vacas ≤ 5 años de edad. Los pesos entre ambos grupos analizados para GA y GC mostraron diferencia entre ellas (p≤0,05) durante todo el ensayo. Las vacas adultas tuvieron los menores intervalo parto-parto (GA: 380±28; GC: 506 ±18 días, p≤0,003), El estado corporal entre ambos grupos analizados también mostró diferencias entre los grupos (p≤0,05) el mejor estado corporal (GA: 2,4±0,06; GC: 2,2±0,02, p≤0,002), el mayor peso vivo adulto (GA: 461 ±7; GC: 418±5 kg, p≤0,0001) y mayor peso del ternero sin mostrar diferencias p≥0,05 (GA: 34,1±0,8; GC: 32,3±0,5 kg). Se concluye que las vacas adultas poseen un mejor comportamiento productivo y reproductivo, y además sería importante mantener en el rodeo un porcentaje mayor de ellas para los sistemas estudiados. Palabras clave: peso adulto; estado corporal; intervalo parto-parto: peso el ternero al nacimiento Abstract The objective of the work was to evaluate the productive and reproductive behavior of adult and growing cows of the Nelore race under grazing conditions of the Bolivian tropics. The research work was carried out from October 2016 to October 2017 at rancher farm E7 in Colonia San Juan, Santa Cruz, Bolivia. 100 total cows were used for the study. They were divided into two groups: Adult group: GA, 28 cows ≥ 5 years of life and Growing group: GC, 72 cows ≤ to 5 years of life. The weights between both groups analyzed for GA and GC showed differences between them (p≤0.05) throughout the trial. The body condition between both groups analyzed also showed differences between the groups (p≤0.05). Adult cows had the lowest calving interval (GA: 380 ± 28, GC: 506 ± 18 days, p≤0.003), the best body condition (GA: 2.4 ± 0.06, GC: 2.2 ± 0.02, p≤0.002), the highest live weight (GA: 461 ± 7, GC: 418 ± 5 kg, p≤0,0001) and greater weight of the calf without showing differences p≥0.05 (GA: 34.1 ± 0.8, GC: 32.3 ± 0.5 kg). It is concluded that adult cows have a better productive and reproductive behavior, and it would also be important to maintain a greater percentage of them in the herd for the systems studied. Keywords: adult weight; body condition; calving interval; weight the calf at birth.

The objective of the work was to evaluate if the multiparous adult cows presented any difference in the values of blood biochemistry compared to young primiparous Nellore cows of the Bolivian tropics. During the month of February 2021, a study was carried out with 14 multiparous adult cows and 13 young primiparous cows, belonging to the Technology Center on Agriculture and Livestock in Bolivia (FUNDACION CETABOL) in Santa Cruz, Bolivia. The following variables were analyzed: Albumin, Total Protein, Globulin, Urea, Alkaline phosphatase, Aspartate transaminase, Glucose. The mean values and standard errors of the days of life of the cows used, according to the group they belonged to at the time of blood sampling and measurement were: Adult cows of 4561 ± 95 days and young cows of 1535 ± 99 days showing differences significant (p≤0.001). The all values of Albumin (g / dL), Total Protein (g / dL) and Urea (mg / dL) have values between normal ranges and without showing significant differences between adult cows and young cows. With the exception of Globulin (mg / dL) which has values above the normal ranges, although without showing significant differences between adult cows and young cows. The alkaline phosphatase enzymes were above the upper range, although without showing significant differences between both groups. For the enzyme aspartate transaminase, the values are between the normal ranges and without showing significant differences between both groups. The glucose values were found between the normal ranges for adult cows and for young cows and without showing significant differences between both groups. It is concluded that multiparous adult cows did not present any difference in blood biochemistry values compared to young primiparous Nellore cows of the Bolivian tropics.