Background: Heat stress result in a mild reduction on milk production, while long term heat stress exposure can severely affect the productive and reproductive performance in dairy cattle. Aim: The objective of this study was to quantify the relationship between reproductive performance and temperature-humidity index in dairy cattle farms in Lima, Peru. Methods: Monthly service, conception and pregnancy rates were measured on four dairy farms from four different Lima localities as reproductive performance indicators, along with an index of heat stress, maximum daily temperature humidity index (Max THI), during a three-year period. In order to establish the relationship between the max THI and the reproductive performance indicators, a multiple regression analysis was made which considered the variable farm and year as explicative variables. Results: The regression model showed an adjusted R-squared of 33.5% with an estimated standard error of 5.75% and was highly significant (p<0.001). The regression coefficients for Max THI for the variables pregnancy rate and conception rate were significant (p<0.0001). With every increasing unit of Max THI, a 0.84% drop of the pregnancy rate, and a drop of 1.74% of the conception rate was estimated by the model. The regression coefficient of Max THI for the service rate variable was not significant. Conclusion: It was concluded that the increase of the Max THI significantly affected the reproductive performance of intensive dairy cattle farms in Lima.

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Purpose The objective of the present study was to evaluate the efficacy of pasteurization, freezing, the addition of formaldehyde and peroxymonosulfate on the inactivation of the bovine leukemia virus (BLV) present in milk. Materials and Methods A sheep bioassay was carried out in 40 sheep, which were intraperitoneally inoculated with leukocytes from milk infected by the BLV previously treated with one of the virus inactivation methods. Five study groups were evaluated: (1) control group: milk without previous treatment, (2) pasteurization group: milk treated by pasteurization, (3) freezing group: milk treated by freezing for 36 hours, (4) formaldehyde group: 0.1% formaldehyde, and (5) peroxymonosulfate group: 0.05% peroxymonosulfate. The inoculated animals were followed for 10 weeks. Results At week 10 post-inoculation, all the animals (8/8) of the control group and the peroxymonosulfate group were seropositive to BLV, while no animals were seropositive (0/8) to BLV in the remaining three groups. Statistically significant differences were found between the pasteurization, freezing and formaldehyde groups with respect to the control (p<0.001) and peroxymonosulfate groups (p<0.001). Conclusion The results indicate that pasteurization, freezing and formaldehyde processes are efficient in inactivating the BLV and can be used in milk to prevent the transmission of the virus.

El estudio tuvo como objetivo determinar el efecto del score de condición corporal (SCC) al momento de la inseminación artificial sobre la tasa de concepción (TC) de vacas Holstein criadas bajo un sistema intensivo. Se evaluaron 1851 inseminaciones de un establo de Lima, Perú. El SCC fue evaluado a través de observación visual en una escala de 1 al 5, formando dos grupos: SCC <3 y SCC ≥3. El diagnóstico de preñez se hizo entre los días 35 y 42 pos-servicio. La TC general (TCG) y a la primera inseminación fue significativamente superior en vacas con SCC ≥3 que en vacas con SCC <3 (p<0.01), sin diferencias significativas a la segunda y tercera inseminación. El SCC tuvo un efecto significativo sobre la TC a la primera inseminación en vacas multíparas (p<0.05), mas no en vacas primíparas. El SCC no tuvo un efecto significativo sobre la TCG ni a la primera inseminación en vacas servidas en épocas de estrés calórico (octubre-junio), en tanto que las vacas inseminadas con SCC ≥3 durante la época de confort térmico presentaron una mejor TCG y a la primera inseminación que aquellas con SCC <3 (p<0.05). En conclusión, el SCC al momento de la inseminación artificial tiene un efecto significativo sobre la TC en vacas criadas en un sistema de producción intensivo en Lima.

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