This study evaluated the leaf area index (LAI) recovery mechanisms and forage accumulation rates on the regrowth of different grass species subjected to different defoliation intensities. For that purpose, plots of Pennisetum clandestinum (kikuyugrass), Lolium multiflorum (annual ryegrass), and Avena strigosa (black oats) were defoliated from 20 to 80 % of their initial heights (25, 20, and 25 cm, respectively). At different increments in height, forage samples were collected to ground level and used to estimate tiller population density (TPD), leaf area per tiller (LA), and forage mass. From these data, we calculated the leaf area index (LAI), average leaf area index (aLAI), and average and instantaneous forage accumulation rate (FAR and IFAR, respectively). Data were plotted over time (days) to describe LAI recovery and forage accumulation rates. As the defoliation intensity increased, greater canopy heights were needed for pastures to achieve their maximum forage accumulation rates, which required longer regrowth intervals. The need for high tiller recruitment after defoliation, which delayed canopy LAI recovery, seemed to be one of the main cause. Thus, grazing management strategies that involve costly tiller recruitment could decrease both overall forage production and sward persistence over time. However, the plant ability to recover LAI after successive intense defoliations seems to be species-dependent and related to their phenotypic plasticity.

Tangolagrass (Brachiaria arrecta × Brachiaria mutica) is a stoloniferous warm-season grass considered as an alternative to forming permanent grasslands in waterlogged tropical regions. However, information about grazing management targets for such species is still scarce. This two-year study aimed to identify pre-grazing canopy heights that do not compromise both leaf lamina production and nutritive value of tangolagrass pastures, and to test whether lower canopy height could decrease stolon elongation process. To this end, three pre-grazing canopy heights (20, 30, or 40 cm, all lowered in 40% of their initial heights) were assigned to nine 390-m² plots grazed by cattle. Herbage, leaf, and stem accumulation rates were not different among treatments (57, 23, and 27 kg DM ha⁻¹ d⁻¹, respectively; p > 0.05). Also, neutral detergent fiber (NDF) and acid detergent fiber (ADF) were similar among treatments (56 and 24% DM, respectively; p > 0.05), but crude protein (CP) was greater (p = 0.0180) in pastures managed with 30 cm (24.7% DM × 22.5% DM). Thus, pre-grazing canopy heights between 20–40 cm combined with low levels of defoliation (up to 40% of the initial height) provide the same primary productivity in tangolagrass pastures. However, stolon elongation could not be reduced within such canopy height targets.

This study aimed to evaluate the milk fatty acid (FA) composition of unsupplemented dairy cows grazing on elephantgrass (Pennisetum purpureum Schum. cv. Pioneiro) pastures under three grazing management strategies: pre-grazing height of 120 cm with defoliation intensities of 50 and 70% of the initial height (treatments 120/50 and 120/70) and pre-grazing height of 90 cm with defoliation intensity of 70% (treatment 90/70). Treatments were repeated three times in a complete randomized block design. Tester animals were six multiparous Holsteins cows grouped into pairs according to days in milk and milk yield and allocated to blocks. Individual milk samples were collected after the first and second days of grazing (two-day occupation period) and analyzed for FA composition. Milk fat from 120/50 and 90/70 treatments resulted in higher concentrations of C4:0, C6:0, C17:0 anteiso, rumenic acid (RA), vacenic acid (VA), trans-12 C18:1, trans-13/14 C18:1, cis-11 C18:1, cis-12 C18:1, cis-9, trans-12 C18:2, trans-11, cis-15 C18:2, and total polyunsaturated fatty acids. Additionally, both SCD₁₄ (cis-9 14:1/14:0 + cis-9 14:1) and SCD_RA (RA/VA + RA) desaturase indices were reduced in milk fat from cows subjected to 120/50 and 90/70 treatments. On average, the milk fat levels of RA and VA observed in our study were greater than those reported in most studies with tropical grass-based diets and similar to levels usually found in cows grazing on temperate pastures. Overall, our results showed that milk with a desirable fatty acid composition is produced by cows grazing on a tropical grass (elephantgrass cv. Pioneiro), with the combination of a pre-grazing height of 120 cm and a defoliation intensity of 50% of the initial height, being a practical management strategy to achieve this goal.