Bird species responses to rangeland management in relation to their traits: Rio de la Plata Grasslands as a case study.

Areas used for livestock production and dominated by native grasses represent a unique opportunity to reconcile biodiversity conservation and livestock production. However, limited knowledge of individual species' responses to rangeland management restricts our capacity to design grazing practices that favor endangered species and other priority birds. In this work, we applied Hierarchical Modelling of Species Communities (HMSC) to study individual species responses, as well as the influence of traits on such responses, to variables related to rangeland management using birds of the Rio de la Plata Grasslands as a case study. Based on presence-absence data collected in 454 paddocks across 46 ranches we inferred the response of 69 species considering imperfect detection. This degree of detail fills a major gap in rangeland management, as species-level responses can be used to achieve targeted conservation goals other than maximizing richness or abundance. We found that artificial pastures had an overall negative impact on many bird species, whereas the presence of tussocks had a positive effect, including all threatened species. Grassland specialists were in general sensitive to grass height and tended to respond positively to tussocks but negatively to tree cover. Controlling grass height via adjustments in stocking rate can be a useful tool to favor grassland specialists. To favor a wide range of bird species in ranches, a mosaic of short and tall native grasslands with patches of tussocks and trees is desirable. We also found that species-specific responses were modulated by their traits: small-sized birds responded positively to tussocks and tree cover while large species responded negatively to increasing grass height. Ground foragers preferred short grass while birds that scarcely use this stratum were not affected by grass height. Results on the influence of traits on bird responses are an important novelty in relation to previous work in rangelands and potentially increase our predicting capacity and model transferability across grassland regions.

Herbage mass and allowance and animal genotype affect daily herbage intake, productivity, and efficiency of beef cows grazing native subtropical grassland.

The beef sector in Campos grasslands must increase animal productivity without external inputs, while reducing environmental impact. The objective of this study was to estimate herbage intake (g/metabolic body weight [MBW]/d) of straightbred (Hereford/Angus) and crossbred (F1 of Hereford × Angus) beef cows grazing subtropical native grassland with High and Low herbage allowance (HA, 5 vs. 3 kg DM/kg bodyweight [BW]) during gestation and lactation and its relationship with biological efficiency of cow-calf productivity. Herbage intake (estimated via n-alkanes C32:C33 ratio) was measured during early (Ge1, -163 d prior calving) and mid to late [Gm1 (-83) and Gm2 (-90 d prior calving)] gestation and lactation (L0, L1, and L2, 60, 47, and 31d following calving) periods in 24 to 36 cows, selected to create 8 groups (4 per block) of HA × cow genotype treatment. Cows grazed native grassland year-round, under High and Low HA (except in winter). We analyzed the effect of cow genotype (straightbred vs. crossbred cows) and HA (High vs. Low) on herbage mass and height, daily herbage intake rate (DMI), cow body condition score (BCS), calf average daily gain (ADG) and BW at weaning (BWW) and g of calf weaned/kg DMI. High allowance improved DMI during lactation periods (High 115.6 vs. Low 94.1 ± 5.3; P < 0.05 g/MBW/d). Crossbred cows decreased DMI during gestation (Crossbred 81 vs. Straightbred 94 ± 4.3; P = 0.05 g/MBW/d) compared with straightbred cows. Crossbred and High HA improved biological efficiency, 40.0 vs. 26.2 and 36.0 vs. 29.7 g of calf/kg DMI, respectively. High allowance increased herbage mass and sites with greater canopy height that allow greater DMI, positively associated with cow BCS at weaning, calf ADG, BWW, and g of calf/kg DMI. Crossbred cows reduced DMI during gestation showing no greater annual DMI. Animal productivity and biological efficiency can be improved using High HA and crossbred cows, which should decrease the environmental impact of cow-calf systems.

Seasonal Effect on Feed Intake and Methane Emissions of Cow-Calf Systems on Native Grassland with Variable Herbage Allowance.

The aim of this study was to measure methane emissions (CH4) and herbage intake, and, on the basis of these results, obtain the methane yield (MY, methane yield as g CH4/kg dry matter intake (DMI) and Ym, methane yield as a percentage of Gross Energy intake), from beef cows grazing on native grasslands. We used forty pregnant heifers, with two treatments of herbage allowance (HA) adjusted seasonally (8 and 5 kg dry matter (DM)/kg cattle live weight (LW), on average), during autumn, winter and spring. Methane emissions (207 g CH4/d), organic matter intake (OMI, 7.7 kg organic matter (OM)/d), MY (23.6 g CH4/kg DMI) and Ym (7.4%), were similar between treatments. On the other hand, all variables had a marked increase in spring (10.8 kg OM/d and 312 g CH4/d), except for Ym. The methane emission factor from Intergovernmental Panel on Climate Change (IPCC) Tier 2 estimated with these results was 78 kg CH4/head/year. The results show that methane emissions and intake were influenced by the season, but not by the HA analyzed in this study. This information for cow-calf systems in native grasslands in Uruguay can be used in National greenhouse gases (GHG) inventories, representing a relevant contribution to global GHG inventories.

Influences of nutrition and metabolism on reproduction of the female ruminant.

Beef cows and ewes grazing native pastures are exposed to cycles of undernutrition that reflect the seasonal variations of biomass production. In grazing dairy cows, the physiological undernutrition during early lactation due to increased demands for lactation and low dry matter intake is exacerbated by the need to get sufficient intake from pasture and the extra grazing energy costs. Undernutrition has profound impacts on reproduction by affecting multiple reproductive processes at different levels of the reproductive axis. The objective of this paper is to review the influence of undernutrition on reproductive events of the adult female ruminant, with emphasis on both grassland and mixed rain-fed grazing farming systems. The comparative endocrinology and reproductive biology among ewes, beef and dairy cows may provide a comprehensive knowledge of the metabolic and reproductive adaptation to feed restriction. Understanding the critical underlying physiological mechanisms by which nutrition affects reproduction is the base of focus feeding strategy to improve the reproductive performance of the female ruminant.