Effectiveness of Antelope Pass Structures in Restriction of Livestock

A study was conducted to test the restrictive efficiency of 5 antelope pass structures upon cattle and sheep. Cattle and sheep were placed under 3 stress situations, female water, female young, and male-female, to test fence restrictive ability of individual antelope pass structures. No single structure restricted all classes and types of livestock. Depending upon livestock class and type, proper selection and use of antelope pass structure will restrict livestock movement without severely restricting antelope movement. An 81.3-cm (32 in) net-wire fence most effectively restricted sheep, but cattle were most effectively restricted by a 2.4-m X 1.5-m (8 ft X 5 ft) horizontal grill. It appears that a horizontal grill within a fence line with certain modifications and placement constraints will effectively restrict sheep and cattle but permit antelope passage. Fencing has been a standard livestock management practice since cattle and sheep were first introduced on western ranges. The use of fences to divide rangelands into manageable areas can achieve important livestock management objectives. May (1968) summarized a number of key advantages of fencing western ranges. These include more uniform distribution of animals, protection of overgrazed or treated areas, segregation of livestock classes or types, increased forage production and reduction in handling of livestock. Certain fence designs, however, have the important disadvantage of restricting movement of some wild ungulate species. Wildlife managers recognize fencing as a major management problem associated with the pronghorn antelope. Certain fences can restrict pronghorn movements to obtain food and/ or water, or to escape harsh weather (Yoakum 1978, 1980). Russell (1951) included net-wire fences as an important factor contributing to reductions in pronghorn numbers throughout the West. Newman (1966) found that Wyoming antelope numbers decreased substantially when animals were restricted by livestock fences. Antelope that were not allowed free movement over a largearea were in poor condition and showed signs of starvation. Other studies noted similar results (Mapston 1972, Russell 1951). A variety of structures are presently employed on western ranges depending upon the operation, livestock type, and class. Sheep operators prefer net-wire fencing; operations involving cattle may require use of barbed wire for restrictive purposes. Mapston (1972) suggested that both net-wire and certain barbed wire fences can cause serious problems for antelope by restricting both movement and feed selection, Bear ( 1969) found that sheep fences, I. 1 m (44 in) in height will restrict nearly all antelope, while net-wire structures 8 I .3 cm (32 in) high will restrict only fawns. On cattle ranges where barbed-wire fences are common, antelope were less restricted but often injured during passage, which resulted in permanent crippling or death (Spillett 1965). In all cases it appears that standard livestock fences Authors are graduate research assistant, assistant professor. associate professor, and arofessor. Deoartment of Animaland Range Sciences. New Mexico State University, Las Cruces 8’8003. This report is Journal Article 836, Agricultural Experiment Station, New Mexico State University, Las Cruces. Funding for this research was provided by the Bureau of Land Management. Manuscript received April 27, 1981. 22 have some negative effect upon antelope. After reviewing several studies Yoakum (1978, 1980) suggested measures to be taken to reduce mortality from fencing. These included minimizing construction of net-wire fences, using barbed wire fences with a smooth bottom strand at least 41 cm (16 in) above the ground and no stays between posts, providing special pass structures such as lay-down panels or antelope jumps along heavily traveled pathways and/ or migration routes, and maintaining large areas. The development of a structure to solve the antelope/fence problem has become an important research objective but no definite answer has been found. Spillett et al. (1967) concluded from field observations and experiments that maximum height for any vertical structure intended for antelope passage should be no greater than 8 I .3 cm (32 in). Kerr ( 1968) documented frequent use of 8 I .3-cm passes in net-wire fences and areas where woven-wire was replaced by barbed wire. Spillett et al. (1967) recommended that where vertical structures are required for livestock restriction only smooth wire be used to reduce injuries to antelope. Several studies have shown antelope passage is more frequent on horizontal modified cattleguards (Bear 1969, Spillett 1965, Pate 1969, Mapston 1970). Observations of antelope utilizing cattleguards as a means of passage are numerous (Mapston et al. 1970, Spillett and Zobell 1967, Pate 1969, Spillett 1965, Zobell 1%8a, 1968b). These observations indicate that antelope commonly leap 1.8-m and 2.1-m (6 and 7 ft) cattleguards when the width of the structure is no less than 1.8 m (6 ft). Mapston (1968) and Pate (1969) found that these horizontal devices worked effectively even to the extent of allowing passage of l-month-old fawns. Studies by Bear (1969) Newman (1966), and Mapston (1968) have verified movement of antelope in and out of pastures with net-wire perimeter fences when experimental horizontal passes were present. These studies indicated that problems associated with antelope restriction by livestock fences can be solved by use of low vertical passes or, preferably, horizontal cattleguard devices. Since research and observation have shown that antelope can negotiate passage, the effectiveness of such pass structures in restricting livestock movement becomes a concern. A limited number of studies have dealt with this matter (Cole 1956, Spillett et al. 1967) but results were not conclusive. Bear (1969) found that, although several vertical structures adequately restricted livestock, these structures were different than recommended for antelope passage. Mapston et al. (1970) concluded that a I .8-m (6 ft) horizontal grill would serve to restrict most livestock movement without restricting antelope. Sheep were not always effectively restricted by any structure, however. The problem of developing structures which will restrict livestock, but not antelope, needs further investigation. The objective of this study was to test the restrictive efficiency of 5 antelope passes on sheep and cattle. Materials and Methods Four vertical panel structures (Fig. I) and one horizontal grill (Fig. 2) were selected for tests involving livestock. An 81.3~cm (32 in) vertical net-wire fence was used as a control. This structure is commonly used as a standard livestock fence for sheep. Two JOURNAL OF RANGE MANAGEMENT 36(l), January 1983