Glaucia Azevedo do Amaral

Faecal index to estimate intake and digestibility in grazing sheep

SUMMARY The current research was carried out to evaluate the use of crude protein and fibre components in faeces for estimating intake and digestibility in sheep fed with pearl millet (Pennisetum americanum (L.) Leeke). The equations were developed from four trials in metabolism cages with 16 sheep in each trial. Eachanimal received a different quantityof millet leaves in the diet: 0·015, 0·020 and 0·025 dry matter (DM) as a proportion of liveweight (LW) and ad libitum with at least 0·2 of daily feed refusals. Organic matter intake (OMI, g/day) was measured, through the difference between offer and refusals; total faeces were collected for 5 days, which was used to determine faecal crude protein (CPf, g/day and g/kg of organic matter (OM)), faecal neutral detergent fibre (NDFf, g/day and g/kg OM), faecal acid detergent fibre (ADFf, g/day and g/kg OM) and OM digestibility (OMD). Linear regression equations were calculated to determine the relationship between OMI and CPf (P<0·001, R 2 =0·90, relative prediction error (RPE=14·02%). A multiple linear equation was generated for OMI including CPf and NDFf (P<0·001, R 2 =0·94; RPE=9·25%). Hyperbolic (single and multiple) and exponential models were tested to estimate OMD, where the hyperbolic multiple model including CPf and NDFf showed lower RPE (3·90%). These equationsforestimatingOMIandOMDwereevaluatedonsheepgrazingP.americanumfertilized withincreasing levels of nitrogen (N) (50, 100, 200 and 400 kg N/ha), comparing measured and estimated OMI. The intake estimated by multiple regression (CP and NDFf) showed a higher R 2 (0·98) and lower RPE (5·25%) than the simple (CPf only) linear equation (R 2 =0·94; RPE=20·45%). The results demonstrated the feasibility of using the faecal index generated in metabolism cages for estimating intake and digestibility in sheep grazing P. americanum.

Perfilhamento em pastagens de azevém em sucessão a soja ou milho, sob diferentes métodos e intensidades de pastejo

The objective of this work was to evaluate tiller density, herbage mass, pattern of tiller population, and sward stability index in Italian ryegrass (Lolium multiflorum) pastures established after soybean or corn, subjected to different stocking methods and grazing intensities by sheep. Rotational or continuous stockings were evaluated under moderate (forage allowance equivalent to 2.5 times the potential consumption of lambs) and low grazing intensities (equivalent to 5.0 times). It was used a completely randomized block design, with a 2x2x2 factorial arrangement with four replicates. Evaluations were done monthly, between August and October 2010, during the pasture period. The tiller population density differed significantly with stocking methods and grazing intensities and was higher in the area previously cultivated with soybean, in the evaluation performed in August. The highest herbage masses were observed in pastures established after soybean at low‑grazing intensity, whereas the lowest were observed in pastures established after corn with moderate grazing intensity. During the reproductive period, tillering density reduced, and the individual tiller mass increased. Moderate grazing intensity reduces the percentage of fertile tillers. Reduction in tiller density during flowering does not affect the sward stability index.

Diet Switching by Mammalian Herbivores in Response to Exotic Grass Invasion

Invasion by exotic grasses is a severe threat to the integrity of grassland ecosystems all over the world. Because grasslands are typically grazed by livestock and wildlife, the invasion is a community process modulated by herbivory. We hypothesized that the invasion of native South American grasslands by Eragrostis plana Nees, an exotic tussock-forming grass from Africa, could be deterred by grazing if grazers switched dietary preferences and included the invasive grass as a large proportion of their diets. Bos taurus (heifers) and Ovis aries (ewes) grazed plots with varying degrees of invasion by E. plana in a replicated manipulative experiment. Animal positions and species grazed were observed every minute in 45-min grazing session. Proportion of bites and steps in and out of E. plana tussocks were measured and used to calculate several indices of selectivity. Both heifers and ewes exhibited increasing probability of grazing E. plana as the proportion of area covered by tussocks increased, but they behaved differently. In agreement with expectations based on the allometry of dietary preferences and morphology, ewes consumed a low proportion of E. plana, except in areas that had more than 90% E. plana cover. Heifers consumed proportionally more E. plana than ewes. Contrary to our hypothesis, herbivores did not exhibit dietary switching towards the invasive grass. Moreover, they exhibited avoidance of the invasive grass and preference for short-statured native species, both of which should tend to enhance invasion. Unless invasive plants are highly palatable to livestock, the effect of grazing to deter the invasion is limited, due to the inherent avoidance of the invasive grass by the main grazers in the ecosystem, particularly sheep.