Temperature-humidity index and reproductive performance of dairy cattle farms in Lima, Peru.

Background: Heat stress results in a mild reduction in milk production, while long-term heat stress exposure can severely affect the productive and reproductive performance in dairy cattle. Aim: 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 from four dairy farms in four different Lima localities as reproductive performance indicators, along with an index of heat stress and maximum daily temperature-humidity index (max THI), during a 3-year period. In order to establish the relationship between the max THI and the reproductive performance indicators, a multiple regression analysis was carried out, which considered farm and year as explicative variables. Results: The regression model showed an adjusted R2 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 in the pregnancy rate and a 1.74% drop in the conception rate were 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 in max THI significantly affected the reproductive performance of intensive dairy cattle farms in Lima.

Efficacy of physical and chemical treatments on the inactivation of bovine leukosis virus present in milk.

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.