Effect of a partial mixed ration on the growth and development of replacement heifers under pasture in tropical conditions

Abstract

Introduction. Proper nutrition of replacement heifers is essential to optimize their growth, development, and productive performance in pasture-based dairy systems. The method of feed offer can influence nutrient intake and productive efficiency. Objective. To evaluate the effects of a partial mixed ration (PMR) versus separate component feeding (CON) on growth performance, development, and associated costs in replacement heifers managed under grazing conditions. Materials and methods. A comparative study was conducted on heifers fed from 3 to 15 months of age under two treatments: PMR and CON. Parameters measured included average daily gain (ADG), feeding costs, and estimated age to reach 60% of mature body weight, the target weight for breeding readiness. Results. Feeding costs per heifer were higher for the PMR group (₡358 905; $564.28) than for CON (₡318 095; $500.12). However, heifers receiving PMR exhibited significantly greater ADG, reducing the age to reach breeding weight by 1,7 months. This reduction enables earlier onset of first lactation and potentially extends productive lifespan. Additional costs associated with PMR use were mainly due to logistics and feed mixing but might be offset by long-term production benefits. Conclusion. Providing a partial mixed ration enhances growth and development in pasture-based replacement heifers, enabling a reduction in the age at breeding weight attainment and improving reproductive and productive efficiency. These findings support the adoption of nutritional strategies aimed at maximizing heifer performance in grazing dairy systems.