Evaluation of factors affecting milk production and composition in dual-purpose systems

Resumen

Objective: This study aimed to evaluate the genetic and environmental effects on milk production and composition in dual-purpose cows in the Veracruz tropics.

Methodology: A population of 79 cows grouped by crossbreeds in different proportions of Zebu*Holstein (17), Zebu*Swiss (50), and Zebu*Holstein*Swiss (12) was used. Milk samples were collected at 28-day intervals and analyzed using infrared (IR) spectrophotometry (MilkoScan FT-120, A/S FOSS Electric®). Adjusted means were estimated using PROC GLM from SAS®. The fixed effects included in the model were: genotype, herd, season, lactation number, year, and cow identification. The response variables were: lactation duration (days), production (kg), fat, protein, and lactose (%).

Results: The duration of lactation averaged 307 ± 71.95 days, with total production of 1,240 ± 468.19 kg. The values for protein, fat, and lactose were 3.18 ± 0.41, 3.49 ± 0.82, and 4.42 ± 0.47, respectively. Significant differences (p < 0.05) were found for the effects of year, calving season, and number of calvings on lactation duration (319 ± 6.6 days) during the dry season and total milk production per lactation during the same season (1,239 ± 40.6 kg) by number of calvings. The longest lactation duration was reported in primiparous cows (345 ± 7.5 days). The effect of sampling season on milk composition was significant (p < 0.05) in the rainy season for protein (3.4 ± 0.03 %) and fat (3.8 ± 0.08%).

Study limitations: This study is limited to a dual-purpose production system with crossbred cattle of different racial composition, under the management and environmental conditions of the participating herds.

Conclusions: The results indicate that milk production and composition are influenced by environmental factors and by differences between the groups evaluated.