Definitions. Animal Science 144 Beef Cattle & Sheep Production R. D. Sainz Lecture 03

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1 Grazing management: range and pasture growth Animal Science 144 Beef Cattle & Sheep Production R. D. Sainz Lecture 03 Definitions Forage available (FA) herbage available for consumption by livestock and wildlife Forage demand (FD) amount of forage required to meet the nutritional needs of grazing animals Grazing pressure (GP) ratio of demand and availability at any given time: GP = FD / FA Animal unit (AU) number of animals that would have a total FD of 12 kg dry matter/day 1

2 Public lands leasing In many cases, lease rates are determined on an AUM (AU month) basis, and carrying capacities are expressed in this form as well. The primary decision the range manager must make is the stocking rate. Depending upon the grazing system used, stocking density is also a consideration. At low stocking rates, individual performance is high because grazing pressure is low; production/unit area is also low due to low animal numbers. At moderate stocking rates (and GP), individual performance declines due to restrictions on nutrient intake (qualitative and/or quantitative); production/unit area increases due to increased animal numbers. Critical stocking rate the SR at which individual performance starts to decline Spatial distribution of plants / plant communities varies with topology, soil type, aspect, past grazing history of livestock variable preferences for plant types, distance from water, shelter, etc. even livestock distribution is essential for proper utilization of the forage resource, and to avoid problems of over- or under-grazing parts of the range improvement cross fencing strategic placement of salt, minerals, water, supplements Spatial distribution Yearling heifers, = SR, GP (Hart et al., 1988) Pasture size (ha) , 34 Maximum distance to water (km) 5.4 km 1.4 Average herbage utilization 41 % 50 % near water 60% 50 % in back 25% 50 % Average daily gain 2

3 Temporal distribution mainly affects diet quality (as for rotational grazing) choice of breeding season Residue management In practice, it is often difficult to gauge pasture/range use during the season, and to estimate the optimal level of utilization. One approach that has proved very useful is to set target residue levels, so that there is enough residual plant material at the end of the grazing season to ensure adequate regrowth/germination during the following season. Adequate residual dry matter (RDM) are necessary to provide soil protection and a favorable micro-environment for grass and forb seedlings as they emerge. Recommendations for annual foothills range (CA): gentle slopes ( 15%) 600 lbs/acre (670 kg/ha) steeper slopes 800 lbs/acre (900 kg/ha) 3

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5 Riparian areas High gradient vs. low gradient Channel condition Access to floodplain Bank stability (looking downstream) Riparian zone Perennial creek Intermittent creek Macroinvertebrate habitat Macroinvertebrates observed Fish habitat Velocity depth regime Riffle embeddedness 5

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15 Feedstuffs Beef cattle can utilize a wide variety of feedstuffs. Feeds are classified into groups based on their nutrient content and physical form. Most common feeds can be placed in one of the following groups: Roughages high in fiber (cellulose and hemicellulose) and usually low to intermediate in energy protein content varies widely, depending on the plant species and stage of maturity examples are hay, grass, grain hulls, oilseed hulls Grains high in energy and relatively low in fibre most have a moderate protein content examples are corn, barley, oats Oilseeds high in protein, usually high in energy variable fiber content examples are soybeans, canola meal Byproducts variable nutrient content may contain a high level of moisture examples are distillers grains, sweet corn cannery waste, bakery waste, grain screenings, apple pomace 15

16 Minerals Various minerals are required for growth, bone formation, reproduction and many other body functions Macrominerals are required in fairly large amounts Sodium (salt) Calcium (Ca) Phosphorus (P) Magnesium Mg) Potassium (K) Micro or trace minerals are required in very small amounts Iodine (I) Copper (Cu) Zinc (Zn) Sulphur (S) Selenium (Se) Mineral content is affected by the type and quality of the feedstuff. Adding supplementary minerals to the ration is usually required to ensure that the proper amounts of these elements are available to the animal. The type of supplementary mineral mix required is determined by the feeds in the ration and the animal's requirements. Some Symptoms of Mineral Deficiencies Calcium poor growth bowed leg bones brittle bones Phosphorous poor growth craving for wood, hair, soil poor conception rates Magnesium muscle tremors staggering, convulsions (grass tetany) Sodium (salt) poor growth chewing or licking of wood Selenium weakness, inability to stand white muscle disease retained placenta? Cattle nutrition Composition of forages is highly variable, but typically they are high in cell wall constituents (fiber). Digestion of fiber depends upon microbial action in the rumen, so that ruminant nutrition entails feeding the microbes first, then the animal. Cellulolytic microbes can break down plant cell walls for energy, but they must have a source of nitrogen (and sulfur, etc.) to support microbial growth. In dry/dormant plants, high fiber levels and low N levels can limit feed digestion, and therefore intake. Supplementation of such feeds with a source of N can greatly improve digestion, intake and performance. 16

17 Cattle nutrition On average, grazing herbivores consume about 2% of their body weight/day. This will vary with diet quality, physiological state, environmental factors, etc.. 17

18 The ruminant stomachs, as seen from the right side From: 18

19 Cattle nutrition A by-product of fermentation is gas: mainly CO 2, CH 4, and H 2. Normally, the gas phase of the rumen floats above the solid + liquid phase, and the excess is voided though eructation (belching). Under certain conditions, gases may become trapped in stable foams, which cannot be removed by eructation. This leads to a condition called bloat, which in severe cases can be fatal. Rumen contraction, rumination and eructation Rumen contraction, rumination and eructation 19

20 Rumen contraction, rumination and eructation Cattle nutrition Bloat can occur on pasture or in the feedlot. Pasture bloat results from the presence in some plants (notably legumes like clover or alfalfa) of saponins, which can form a frothy layer trapping gas bubbles. Prevention of pasture bloat may be accomplished by: never turning hungry stock out into pure legume pastures always providing a mixture of pasture species, with grasses and legumes together administering anti-bloat compounds, such as poloxalene (these are surfactants that reduce the surface tension of the liquid, preventing foam formation Animals grazing legume pastures must be watched closely; if severe bloating occurs, rapid action is needed to relieve gas pressure and prevent death. affect 3-5% of cattle Poisonous plants cost to beef industry» $300 M/yr (through death, reduced performance, cost of treatment, abortions, birth defects) hundreds of toxic plants some palatable, others only eaten when nothing else is available in quantity 20

21 Toxic compounds alkaloids 5-10% of forage plants E.g., larkspur, lupine, locoweed, death camas; not much affected by environmental conditions; usually affect CNS: altered respiration, excitation, incoordination, possibly death glycosides sugars complexed with toxic compounds (e.g., cyanogenic glycosides); generally change with environment, in response to stress (frost, drought); e.g. sorghum drought or frost causes release of prussic (hydrocyanic acid), which blocks O 2 transport to cells; Cause nervousness, abnormal breathing, muscle tremors, spasms, convulsions, death minerals nitrates (NO 3 ), selenium (Se) Nitrates high in invader species E.g., pigweed, lamb's quarters, Russian thistle also in stressed annuals (e.g., hail-damaged corn silage, drought-stricken oat forage) can accumulate in any forage plant > 1.5 % NO 3 is lethal; % is sublethal NO 3 NO 2 methemoglobin (cannot transport O 2 ) acute poisoning shows bluish membranes, staggering, shortness of breath, death; no treatment chronic poisoning shows watery eyes, unthriftiness, reduced milk production, lower gains; change feed ASAP Selenium Passively taken up by most plants A few will deposit in excess e.g., milk vetch, woody aster, goldenweed, prince's plum Mainly reflects soil Se > 250 ppm acute poisoning, death in 1 hr to several days < 200 ppm chronic poisoning, "blind staggers", reduced condition & appetite, wandering, paralysis ppm x several weeks alkali disease; dullness, emaciation, lameness (partial sloughing of hooves), hair loss 21

22 Fescue toxicity caused by endophyte (fungus) infecting plant 95% of all fescue pastures in SE US affected reduces gains (2 lb/d 1 lb/d) fescue foot endophyte-free seed now available Grass staggers AKA grass tetany winter tetany wheat poisoning magnesium tetany hypomagnesemia 22