EVALUATION OF THE PRODUCTIVE RESPONSE OF GRAZING COWS WITH TWO VARIETIES OF SORGHUM SILAGE SUPPLEMENTED DURING THE DRY SEASON IN THE SOUTHWEST OF THE STATE OF MEXICO

Background. The southwestern region of the state of Mexico is an area with a livestock vocation. Cattle graze grasslands dominated by African Star (EA) grass (Cynodon plectostachyus) with scattered trees. In the dry season and due to the lack of forage of adequate quality and quantity, farmers use grain-based supplements. Forage conservation practices are little practiced. Objective. To evaluate two varieties of sorghum silage in the productive response of dual-purpose cows in the dry season. Methodology. 12 multiparous cows of different racial composition (GR) were used Holstein (H), Brown Swiss (PS), Girolando (GI), Beefmaster (BM) and Brahman x PS (BPS), at different stages of lactation (early, medium and late), divided into two groups with the same number of cows, randomly assigning sorghum silages of the Top Green (TG) or Sweet Cane (CD) variety (treatment (TX)), 1.7 and 1.8 kg of matter dry (DM) cow/day, respectively. In addition, the cows received 5 kg DM cow/day of a balanced concentrate of 18% crude protein (CP). The cows grazed during the day in pastures dominated by EA grass with scattered trees. The experiment lasted 8 weeks, two weeks of habituation period and six weeks (experimental periods (EP)) for sampling and recording of productive variables. Results. There were no significant differences (P > 0.05) in the productive response due to the variety of sorghum silage, racial group, or lactation stage. Significant differences were detected in dry matter intake (kg/cow/day), milk yield (kg/cow/day), weight and weight change (kg), due to PE. The lactation stage had no significant effect on the response variables (P > 0.05), except on DM intake. The TX*PE interaction had no effect on the productive response variables, while the GR*PE interaction had significant effects on CMS, weight and weight change. Implications. Knowledge of other forage species conserved as silages, alternatives to corn in the supplementation of dairy cattle, contributes to the development of supplementation strategies less susceptible to current climatic variations. Conclusion. The silage of two varieties of sorghum, Top Green or Caña Dulce, did not have significant differences in the productive response of lactating cows in the dry season. The Top Green variety produced 22% more dry matter than the Caña Dulce variety, so under the conditions in which the experiment was carried out it would be the most recommended variety to grow as a forage supplement.