Reproductive behavior of crossbred dairy cows grazing an intensive silvopastoral system under tropical dry forest conditions

ABSTRACT It is widely accepted that selection for high milk yield in dairy cows has negatively affected their reproductive performance. After calving, dairy cows experience a nutritional imbalance due to an asynchrony in the occurrence of the lactation and dry matter intake peaks. In the tropics, this situation is exacerbated due to poor quality and/ or availability of the diet. A study was carried out to describe the nutritional and reproductive behavior of two-to-four parturition crossbred cows (Gyr (Bos indicus) x Holstein (Bos taurus)) divided in two groups according to their calving to first service interval (CFSI): Group 1: ≤50 days CFSI, n=7; Group 2: ≥50 days CFSI, n=8. Animals were grazing in an intensive silvopastoral system (ISS) based on Leucaena leucocephala and Cynodon plectostachyus and also received protein, energy and mineral supplementation. Dry matter (DMI) and nutrient intake were individually estimated and correlations between reproductive and nutritional parameters were performed. Additionally, serum progesterone concentration was monitored. Group 2 had greater forage and total DMI and milk production than Group 1 (P<0.05). Hence, Group 2 had greater nutrient intake from forages than Group 1 (P<0.05). Group 1 had a positive nutritional balance and an optimum reproductive performance compared to Group 2, which had a negative energy balance and lengthier days with open intervals (P<0.05). It was corroborated that protein and energy are required in adequate levels, to ensure that uterus undergoes involution correctly and ovarian activity starts soon in the postpartum period.

摘要 学界普遍认为，针对奶牛高产奶量的选育工作已对其繁殖性能产生了负面影响。奶牛产后会因泌乳高峰与干物质采食量高峰出现不同步，进而引发营养失衡。在热带地区，由于日粮品质欠佳或供应不足，该状况会进一步恶化。本研究旨在阐述2~4胎次杂交奶牛（吉尔牛（Bos indicus）×荷斯坦牛（Bos taurus））的营养与繁殖表现，试验根据奶牛产后首次配种间隔（calving to first service interval, CFSI）将其分为两组：组1：CFSI≤50天，n=7；组2：CFSI≥50天，n=8。试验牛群在以银合欢（Leucaena leucocephala）和密穗狗牙根（Cynodon plectostachyus）为基础的集约化农林复合饲草系统（intensive silvopastoral system, ISS）中放牧，并补充蛋白质、能量与矿物质饲料。本研究对个体干物质采食量（dry matter intake, DMI）及营养物质采食量进行了估算，并分析了繁殖参数与营养参数间的相关性；此外还监测了血清孕酮浓度。组2的饲草干物质采食量、总干物质采食量及产奶量均显著高于组1（P<0.05），因此组2的饲源营养物质摄入量也显著高于组1（P<0.05）。与组2相比，组1的营养平衡为正，且繁殖性能更佳；而组2存在能量负平衡，且空怀天数更长（P<0.05）。本研究证实，需保证充足的蛋白质与能量摄入，才能确保奶牛产后子宫顺利复旧，并尽快启动卵巢活动。