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Effects of grazing strategy and stocking rates on wool quality and yield in the Andean Altiplano of Peru
Small Ruminant Research, 1 (1988) 127-134
127
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effects of Grazing Strategy and Stocking Rates on Wool Quality and Yield in the Andean Altiplano of Peru J.A. CAREY 1'5, B.F. CRADDOCK 2, A. FLOREZ 3 and F.C. BRYANT 4'6
1Teller County Extension Director, Cripple Creek, CO 80813 (U.S.A.) 2Animal Science Department, Texas Tech University, Lubbock, TX 79409 (U.S.A.) aRange and Forages Department, Universidad Nacional Agraria, Lima (Peru) 4Range and Wildlife Management, Texas Tech University, Lubbock, TX 79409 (U.S.A.) 5At the time of research, the senior author was graduate research assistant, Animal Science Department, Texas Tech University. 6To whom correspondence should be addressed. (Accepted 18 February 1988 )
ABSTRACT Carey, J.A., Craddock, B.F., Florez, A. and Bryant, F.C., 1988. Effects of grazing strategy and stocking rates on wool quality and yield in the Andean Altiplano of Peru. Small Rumin. Res., 1: 127-134. Annual wool production of 120 native Corriedale ewes (age, 2.5-3.0 years; mean weight, 30 kg) was monitored from 1981 to 1983 in two experiments: (1) a rotational grazing system at three stocking rates (two, four and six ewes per hectare), and (2) continuous, rotational and common use rotational (with cattle) management systems at a stocking rate of three ewes per hectare. Greasy fleece weights, staple lengths and fiber diameters were recorded after shearing in 1982 and 1983. Stocking rates had no significant effect on greasy fleece weights per ewe. Greasy fleece weights per hectare increased proportionally with stocking rate. Fiber diameter decreased significantly ( P < 0.05 ) as stocking rate increased. Grazing strategy did not significantly affect staple length or fiber diameter between continuous and rotational grazing with sheep only, but greasy fleece weight was 9% greater ( P < 0.01) under continuous grazing. The common use rotational grazing system produced the lowest wool production with a significantly smaller ( P < 0.05) fiber diameter than the continuous and rotational grazing strategies with sheep only. Care should be taken to prevent overstocking with cattle under common use grazing if wool production is to be maintained. A reduction (P < 0.05) in greasy fleece weight was noted in lactating ewes compared to non-lactating ewes. The results indicate that ewes producing lambs are more sensitive to different grazing strategies than are open and dry ewes. Wool production did not appear to be a sensitive indicator of grazing treatment differences.
INTRODUCTION Woo1 is a m a j o r p r o d u c t o f t h e l i v e s t o c k i n d u s t r y i n P e r u . G r a z i n g p r a c t i c e s typically have been limited to continuous grazing throughout the year or other
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© 1988 Elsevier Science Publishers B.V.
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grazing practices dictated by herders (Bryant et al., 1986). Grazing systems and strategies to improve range conditions and maximize livestock production have been largely untested in Peru. A management system utilizing rotational grazing may allow stocking rates higher than normally used under continuous grazing, to potentially increase wool production per hectare. On improved pasture in New South Wales, Brown (1977) found that grazing management had little effect on wool production. However, Bell (1950) had substantiating evidence to support either a continuous or rotational grazing system. By the use of rotational grazing (Booysen and Tainton, 1978) a n d / o r different species of livestock (Morley, 1981), carrying capacity may be increased by forcing the animals to consume less palatable plants. This could be important in the Andes of Peru where tall, unpalatable bunchgrasses go virtually unused by sheep (Florez et al., 1986). Booysen and Tainton (1978) further stated that rotational grazing systems may increase carrying capacity because of the increased forage production induced by grazing. George and Pearse (1978) conducted a ten year stocking rate study in New South Wales on improved pasture at three stocking rates (8, 12, and 16 Merino ewes per hectare). They determined that increased stocking rate tended to reduce wool production but that seasonal effects had a greater impact on production than did the range of stocking rates. They suggested that increased production per hectare more than offset the decreased production per ewe. Langlands (1977) found that live weight gain of ewes was not sensitive to increased stocking rates but that wool production per animal declined at higher stocking rates. Brown (1977) reported that as stocking rate increased, greasy wool production, fiber diameter and staple length decreased, regardless of management system. The objectives of this study were: (1) to determine the effects of short-duration grazing at three stocking rates on wool production, and (2) to evaluate the effects of rotational grazing of cattle and sheep together against continuous and rotational grazing with sheep alone, on wool production of native Corriedale ewes in the Andes of Peru. STUDY
AREA
The study area was located on an agricultural cooperative in the Department of Junin, near Corprachancha, 45 km southeast of La Oroyo, Peru (11 ° 25' S, 76 ° 15' W). The range site is a glaciated upland and the vegetation is typically herbaceous, dominated by Festuca dolichophylla and Calamagrostis vicunarum (Wilcox, 1982). Elevation is approximately 4200 m with annual precipitation from 670 to 1033 mm. Precipitation is concentrated in a single wet season, generally lasting from October to April. Mean daily temperatures are relatively constant at 5 °C throughout the year. Frost occurs more than 300 days each year and diurnal temperatures vary as much as 20 ° C.
129 All pastures grazed in this study were selected for homogeneity of available forage. Water was available to all experimental animals from a stream which flowed through all paddocks. No salt or other supplements were provided. METHODS
Stocking rate study The study was initiated in March 1981 with 60 freshly shorn, mature Corriedale ewes weighing approximately 30 kg. Twenty ewes were allotted to each of three treatment groups. By adjusting the number of hectares available for grazing, stocking rates for the three treatments were two, four or six ewes per hectare. Each pasture was divided into eight paddocks. Each paddock was grazed 6 days and rested 42 days. Ewes that died during the study period were replaced with dry ewes in order to maintain the appropriate grazing pressure for each treatment. Only fleeces from ewes that grazed on the pastures for both years were used in analyzing the results. At shearing time in March of 1982 and 1983, the fleeces were weighed and recorded and a mid-side sample of fleece was taken from each ewe on test. These samples were sent to Texas Tech University for further evaluation of staple length and fiber diameter. The samples were cleaned with acetone to remove grease and debris and staple length was measured and recorded. Fiber diameter was measured by microprojection (A.S.T.M., 1980). Treatment effects were compared by analysis of variance in a three treatmentX 2 year factorial using animals as replications. Fleeces were analyzed separately for ewes that did and did not wean a lamb. Orthogonal polynomials were used to compare the three stocking rates (Steel and Torrie, 1980). Treatments could not be replicated due to the size and nature of the experiment. Therefore animal variance within treatments was used for analysis (Coniffe, 1976).
Grazing strategy study In this study, an additional 60 mature Corriedale ewes were utilized. Twenty were allotted to each of three treatment groups: continuous grazing (CG), rotational grazing (RG), and rotational grazing with cattle (RGC). Stocking rates were set at three ewes per hectare. The RGC treatment was stocked with six bulls (mean weight 221 kg) and three bulls (mean weight 208 kg) in 1981 and 1982, respectively. Therefore, the sheep in the RGC group were subject to a higher grazing pressure. Each rotation pasture was divided into eight paddocks. In the sheep-only rotation, each paddock was grazed 6 days and rested 42 days. In the common-use rotation, sheep and cattle were separated with sheep being rotated one pasture ahead of the cattle. Each species grazed each
130
paddock for 6 days and was moved to the next paddock in sequence; thus, each paddock was rested 36 days. Ewes that died during the study period were replaced with dry ewes to maintain the desired grazing pressure for each treatment. Only fleeces from the ewes that were on test for both years were used in analyzing the results. Wool was collected and analyzed as described for the stocking rate study. Treatment effects were analyzed in the three treatment × 2 year factorial as described for the stocking rate study. Fleeces were analyzed separately for ewes that did and did not wean a lamb. Initial live weight of the ewes was corrected to a common turn-in weight by covariance analysis. Orthogonal contrasts were used to compare CG with RG and to compare the mean of CG and RG treatments with RGC (Steel and Torrie, 1980 ). Animal variance within treatments was used for analysis (Coniffe, 1976). RESULTS AND DISCUSSION
Stocking rate study There were no differences between results from 1982 and 1983. Therefore means for the two years were pooled. There were no differences in greasy fleece weights between the two, four and six ewes per hectare stocking rates. However, there was a significant (P < 0.05) linear effect in fiber diameter (25.5, 24.5, and 24.1/~m, respectively) as stocking rate increased (Table 1 ). The differences in staple length between the two, four and six ewes per hectare stocking rates resulted in a quadratic effect (P < 0.02 ) being 9.55, 8.99, and 10.27 cm, respectively (Table 1 ). The increased TABLE 1 Effects of stocking rates on mean greasy fleece weight, staple length and fiber diameter I Stocking rate (ewes/ha)
2 4 6 SEM 4
n
27 29 18
Fleece parameters Greasy weight (kg)
Staple length2 (cm)
Fiber diameter 3 (/~m)
3.15 2.99 3.00 0.134
9.55 8.99 10.27 0.095
25.5 24.5 24.1 0.513
'Means for greasy fleece weight, staple length, and fiber diameter are for ewes that weaned lambs. Means have been pooled for 1982 and 1983. 2Quadratic effect (P
131 staple l e n g t h at t h e highest s t o c k i n g r a t e is c o n t r a r y to t h e findings of B r o w n (1977) a n d L a n g l a n d s (1977) a n d we are u n a b l e to explain this finding. Wool p r o d u c t i o n in this s t u d y was n o t sensitive to i n c r e a s e d s t o c k i n g rate a n d density. T h i s c o n f i r m s findings o f M c M a n u s et al. (1964 } a n d George a n d P e a r c e (1978) t h a t s t o c k i n g r a t e s have little i n f l u e n c e on wool p r o d u c t i o n .
Grazing strategy study T h e r e were no d i f f e r e n c e s b e t w e e n results f r o m 1982 a n d 1983 a n d m e a n s for t h e two y e a r s were pooled. G r e a s y fleece weights were 9% h i g h e r ( P < 0.01 ) u n d e r C G t h a n u n d e r RG. H o w e v e r , t h e r e was no d i f f e r e n c e b e t w e e n t h e average fleece weight o f t h e s e two t r e a t m e n t s (3.19 kg) w h e n c o m p a r e d to R G C (2.94 kg) ( T a b l e 2). F i b e r d i a m e t e r did n o t differ b e t w e e n C G a n d RG, b u t fiber d i a m e t e r was smaller ( P < 0.01) in t h e R G C t r e a t m e n t (23.3 g m ) t h a n t h e average o f t h e C G a n d R G t r e a t m e n t s (24.6/~m) ( T a b l e 2). S t a p l e l e n g t h did n o t differ b e t w e e n C G a n d R G t r e a t m e n t s , b u t t h e r e was a d i f f e r e n c e ( P < 0.05 ) b e t w e e n t h e average o f t h e s e two t r e a t m e n t s ( 10.05 c m ) a n d t h e R G C t r e a t m e n t ( 10.40 c m ) ( T a b l e 2). P r e v i o u s studies b y B r o w n (1977) a n d L a n g l a n d s (1977) r e p o r t e d t h a t as grazing p r e s s u r e increased, as in t h e R G C t r e a t m e n t , staple l e n g t h d e c r e a s e d w h e n greasy fleece weights a n d fiber d i a m e t e r decreased. We f o u n d t h e same t r e n d for ewes n o t w e a n i n g lambs in t h e R G C t r e a t m e n t , b u t ewes w e a n i n g TABLE2 Effects of continuous (CG), rotational (RG), and common use rotational grazing with cattle (RGC) on means for greasy fleece weight, staple length and fiber diameter1 Grazing strategy
CG vs. RG CG + RG vs. RGC SEM 3
n
28 vs. 26 54 vs. 17
Fleece parameters Greasy weight 2 (kg)
Staple lengt h2 (cm }
Fiber diameter2 (/~m)
3.35 vs. 3.04** 3.19 vs. 2.94 0.15
10.12 vs. 9.98 10.05 vs. 10.40" 0.10
24.0 vs. 25.1 24.6 vs. 23.3** 0.49
1Means for greasy fleece weight, staple length and fiber diameter are for ewes that weaned lambs. Since there was no difference (P > 0.10 ) between years, the means for these variables have been pooled. 2Adjusted by covariance with initial weight. 3Pooled standard error of the mean. *P < 0.05. **P < 0.01.
132
lambs in the RGC treatment had longer staple lengths with smaller fiber diameters and lighter greasy fleece weights. The lack of difference in either staple length or fiber diameter contrasted with significantly lighter (P < 0.1 ) greasy fleece weights under rotational compared to continuous grazing. Dunlop (1962) hypothesized that wool production is dependent on the live weight of the sheep, number of fibers per unit area of skin, fiber diameter and staple length. Therefore, differences between CG and RG in greasy fleece weights may be due to the number of fibers per area of skin, considering that body weight, staple length and fiber diameter did not differ. Lyne (1964) found that undernourishment in the adult life of sheep can cause temporary reduction in the number of active follicles and thought that this might be associated with fiber shedding. The 9% increase in greasy fleece weight under CG agrees with the conclusions of Brown et al. (1966). They reported higher greasy fleece weights for continuous grazing compared to rotation grazing at low stocking rates. Apparently, the continuously grazed ewes were able to select a more nutritious diet and this was reflected in higher fleece weights. Conversely, ewes in the RG treatment were apparently forced to consume a higher percentage of unpalatable bunchgrasses. Differences between the RGC treatment and the two sheep-only treatments might have been greater if one-half of the cattle had not been removed from the RGC treatment the second year of the study. A reduction ( P < 0.05 ) of 10% in greasy fleece weight was noted in lactating ewes (3.14 kg) compared to non-lactating ewes (3.52 kg) (Table 3). This agrees with the 10-14% reduction in annual greasy fleece production due to full cycle reproduction found in other studies (Slen and Whiting, 1956; Doney, 1958; Seebeck and Tribe, 1963; Brown et al., 1966). Brown et al. (1966) concluded that about one-third of the reduction in wool growth by Merinos during pregTABLE 3 Effects of lactation on means for greasy fleece weight, staple length, and fiber diameter for all treatment groups from both experiments Reproductive status
Lactating ewes Non-lactating ewes SEM 1
n
72 45
Fleece parameters Greasy weight (kg)
Staple length (cm)
Fiber diameter (/~m)
3.14 a 3.52 b 0.099
10.15 10.25 0.066
24.23 24.94 0.427
1Pooled standard error of the mean. a'bMeans in the same column with different superscripts differ significantly ( P < 0.01 ).
133 n a n c y a n d l a c t a t i o n s t e m s f r o m a d e c r e a s e in f i b e r n u m b e r s a n d t w o - t h i r d s f r o m a d e c r e a s e in fiber v o l u m e . O b s e r v a t i o n s o n t h e n u m b e r o f fibers p e r u n i t a r e a of s k i n b y B r o w n et al. (1966) i n d i c a t e d t h e r e m a y be a g r e a t e r d e c r e a s e d u r i n g p r e g n a n c y t h a n d u r i n g l a c t a t i o n , a l t h o u g h t h i s c h a n g e w a s e v i d e n t in b o t h p h a s e s o f p r o d u c t i o n in t h e s t u d y of S l e n a n d W h i t i n g (1956). T h e s e r e s u l t s i n d i c a t e t h a t ewes p r o d u c i n g l a m b s are m o r e s e n s i t i v e to d i f f e r e n t grazing s t r a t e g i e s t h a n are n o n - p r o d u c i n g ewes. Overall, h o w e v e r , wool p r o d u c t i o n did n o t a p p e a r to b e a s e n s i t i v e i n d i c a t o r o f t r e a t m e n t differences. ACKNOWLEDGEMENT R e s e a r c h w a s f u n d e d u n d e r U S A I D G r a n t No. A I D / D S A N / X 1 1 - G - 0 0 4 9 as p a r t of t h e S m a l l R u m i n a n t C o l l a b o r a t i v e R e s e a r c h S u p p o r t P r o g r a m in coo p e r a t i o n w i t h U n i v e r s i d a d N a c i o n a l A g r a r i a , L a M o l i n a , L i m a , Peru. T h i s is t e c h n i c a l article T - 5 - 1 9 5 f r o m t h e College o f A g r i c u l t u r a l Sciences, T e x a s T e c h U n i v e r s i t y , L u b b o c k , T X , U.S.A.
REFERENCES A.S.T.M., 1980. Standard test methods for diameter of wool and other animal fibers by microprojection. Annual Book of A.S.T.M. Standards. Part 33: Textiles, Fibers, Zippers. pp. 466-508. Bell, J.M., 1950. Rotation versus continuous grazing. J. Range Manage., 3: 226-227. Booysen, P.D. and Tainton, N.M., 1978. Grassland management: Principles and practices in South Africa. In: D.N. Hyder (Editor), Proc. 1st Int. Rangeland Congr., Soc. Range Manage., Denver, CO, U.S.A., pp. 551-554. Brown, T.H., 1977. A comparison of continuous grazing and deferred autumn grazing of Merino ewes and lambs at 13 stocking rates. Aust. J. Agric. Res., 28: 947-961. Brown, G.H., Turner, H.N., Young, S.S.Y. and Dolling, C.H.S., 1966. Vital statistics for an experimental flock of Merino sheep. Aust. J. Agric. Res., 17: 557-581. Bryant, F.C., Florez, A. and Schlundt, A.F., 1986. Sheep production, stocking rates, and rotational grazing in the Andes of Peru. In: D.J. Joss, P.W. Lynch and O.B. Williams (Editors), Proc. 2nd Int. Rangeland Congr., Soc. Range Manage., Adelaide, Australia, pp. 225-226. Coniffe, D., 1976. Comparison of between and within herd variance and grazing experiments. Irish J. Agric. Res., 15: 39-46. Doney, J.M., 1958. The fleece of Scottish blackface sheep. IV. The effects of pregnancy, lactation, and nutrition on seasonal wool production. J. Agric. Sci., 62: 63. Dunlop, A.A., 1962. Interactions between heredity and environment in the Australian Merino. Aust. J. Agric. Res., 13: 503. Florez, A., Bryant, F.C. and Schlundt, A.F., 1986. Grazing strategies and sheep production in the Andes of Peru. In: D.J. Joss, P.W. Lynch and O.B. Williams (Editors), Proc. 2nd Int. Rangeland Congr., Soc. Range Manage., Adelaide, Australia, pp. 236-237. George, J.M. and Pearse, R.A., 1978. An economic analysis of a 10 year rate of stocking trial with fine-wool Merino sheep that lambed in winter, spring or summer. Aust. J. Exp. Agric. Anim. Husb., 18: 370-380. Langlands, J.P., 1977. The intake and production of lactating Merino ewes and their lambs grazed at different stocking rates. Aust. J. Agric. Res., 28: 133-142.
134 Lyne, A.G., 1964. Effect of adverse nutrition on the skin and wool follicles in Merino sheep. Aust. J. Agric. Res., 15: 788-793. McManus, W.R., Arnold, G.W. and Paynter, J.R., 1964. Variation in wool characteristics with season and stocking rate. Aust. J. Exp. Agric. Anita. Husb., 4: 405-411. Morley, F.H.W., 1981. Management of grazing systems. In: F.H.W. Morley (Editor), Grazing Animals. Elsevier Sci. Publ. Amsterdam, The Netherlands, pp. 379-400. Seebeck, R.M. and Tribe, D.E., 1963. The relation between the lamb production and the wool production of the ewe. Aust. J. Exp. Agric. Anita. Husb., 3: 149-156. Slen, B.F. and Whiting, F., 1956. Wool growth in mature range ewes as affected by stage and type of pregnancy and type of rearing. Can. J. Agric. Sci., 36: 8-13. Steel, R.G.D. and Torrie, J.H., 1980. Principles and Procedures of Statistics (2nd Edition). McGraw-Hill Book Co., Inc., New York, U.S.A. Wilcox, B.P., 1982. Plant communities and soils of the central Andes of Peru. M.S. Thesis. Texas Tech Univ., Lubbock, Texas, U.S.A.
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Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effects of Grazing Strategy and Stocking Rates on Wool Quality and Yield in the Andean Altiplano of Peru J.A. CAREY 1'5, B.F. CRADDOCK 2, A. FLOREZ 3 and F.C. BRYANT 4'6
1Teller County Extension Director, Cripple Creek, CO 80813 (U.S.A.) 2Animal Science Department, Texas Tech University, Lubbock, TX 79409 (U.S.A.) aRange and Forages Department, Universidad Nacional Agraria, Lima (Peru) 4Range and Wildlife Management, Texas Tech University, Lubbock, TX 79409 (U.S.A.) 5At the time of research, the senior author was graduate research assistant, Animal Science Department, Texas Tech University. 6To whom correspondence should be addressed. (Accepted 18 February 1988 )
ABSTRACT Carey, J.A., Craddock, B.F., Florez, A. and Bryant, F.C., 1988. Effects of grazing strategy and stocking rates on wool quality and yield in the Andean Altiplano of Peru. Small Rumin. Res., 1: 127-134. Annual wool production of 120 native Corriedale ewes (age, 2.5-3.0 years; mean weight, 30 kg) was monitored from 1981 to 1983 in two experiments: (1) a rotational grazing system at three stocking rates (two, four and six ewes per hectare), and (2) continuous, rotational and common use rotational (with cattle) management systems at a stocking rate of three ewes per hectare. Greasy fleece weights, staple lengths and fiber diameters were recorded after shearing in 1982 and 1983. Stocking rates had no significant effect on greasy fleece weights per ewe. Greasy fleece weights per hectare increased proportionally with stocking rate. Fiber diameter decreased significantly ( P < 0.05 ) as stocking rate increased. Grazing strategy did not significantly affect staple length or fiber diameter between continuous and rotational grazing with sheep only, but greasy fleece weight was 9% greater ( P < 0.01) under continuous grazing. The common use rotational grazing system produced the lowest wool production with a significantly smaller ( P < 0.05) fiber diameter than the continuous and rotational grazing strategies with sheep only. Care should be taken to prevent overstocking with cattle under common use grazing if wool production is to be maintained. A reduction (P < 0.05) in greasy fleece weight was noted in lactating ewes compared to non-lactating ewes. The results indicate that ewes producing lambs are more sensitive to different grazing strategies than are open and dry ewes. Wool production did not appear to be a sensitive indicator of grazing treatment differences.
INTRODUCTION Woo1 is a m a j o r p r o d u c t o f t h e l i v e s t o c k i n d u s t r y i n P e r u . G r a z i n g p r a c t i c e s typically have been limited to continuous grazing throughout the year or other
0921-4488/88/$03.50
© 1988 Elsevier Science Publishers B.V.
128
grazing practices dictated by herders (Bryant et al., 1986). Grazing systems and strategies to improve range conditions and maximize livestock production have been largely untested in Peru. A management system utilizing rotational grazing may allow stocking rates higher than normally used under continuous grazing, to potentially increase wool production per hectare. On improved pasture in New South Wales, Brown (1977) found that grazing management had little effect on wool production. However, Bell (1950) had substantiating evidence to support either a continuous or rotational grazing system. By the use of rotational grazing (Booysen and Tainton, 1978) a n d / o r different species of livestock (Morley, 1981), carrying capacity may be increased by forcing the animals to consume less palatable plants. This could be important in the Andes of Peru where tall, unpalatable bunchgrasses go virtually unused by sheep (Florez et al., 1986). Booysen and Tainton (1978) further stated that rotational grazing systems may increase carrying capacity because of the increased forage production induced by grazing. George and Pearse (1978) conducted a ten year stocking rate study in New South Wales on improved pasture at three stocking rates (8, 12, and 16 Merino ewes per hectare). They determined that increased stocking rate tended to reduce wool production but that seasonal effects had a greater impact on production than did the range of stocking rates. They suggested that increased production per hectare more than offset the decreased production per ewe. Langlands (1977) found that live weight gain of ewes was not sensitive to increased stocking rates but that wool production per animal declined at higher stocking rates. Brown (1977) reported that as stocking rate increased, greasy wool production, fiber diameter and staple length decreased, regardless of management system. The objectives of this study were: (1) to determine the effects of short-duration grazing at three stocking rates on wool production, and (2) to evaluate the effects of rotational grazing of cattle and sheep together against continuous and rotational grazing with sheep alone, on wool production of native Corriedale ewes in the Andes of Peru. STUDY
AREA
The study area was located on an agricultural cooperative in the Department of Junin, near Corprachancha, 45 km southeast of La Oroyo, Peru (11 ° 25' S, 76 ° 15' W). The range site is a glaciated upland and the vegetation is typically herbaceous, dominated by Festuca dolichophylla and Calamagrostis vicunarum (Wilcox, 1982). Elevation is approximately 4200 m with annual precipitation from 670 to 1033 mm. Precipitation is concentrated in a single wet season, generally lasting from October to April. Mean daily temperatures are relatively constant at 5 °C throughout the year. Frost occurs more than 300 days each year and diurnal temperatures vary as much as 20 ° C.
129 All pastures grazed in this study were selected for homogeneity of available forage. Water was available to all experimental animals from a stream which flowed through all paddocks. No salt or other supplements were provided. METHODS
Stocking rate study The study was initiated in March 1981 with 60 freshly shorn, mature Corriedale ewes weighing approximately 30 kg. Twenty ewes were allotted to each of three treatment groups. By adjusting the number of hectares available for grazing, stocking rates for the three treatments were two, four or six ewes per hectare. Each pasture was divided into eight paddocks. Each paddock was grazed 6 days and rested 42 days. Ewes that died during the study period were replaced with dry ewes in order to maintain the appropriate grazing pressure for each treatment. Only fleeces from ewes that grazed on the pastures for both years were used in analyzing the results. At shearing time in March of 1982 and 1983, the fleeces were weighed and recorded and a mid-side sample of fleece was taken from each ewe on test. These samples were sent to Texas Tech University for further evaluation of staple length and fiber diameter. The samples were cleaned with acetone to remove grease and debris and staple length was measured and recorded. Fiber diameter was measured by microprojection (A.S.T.M., 1980). Treatment effects were compared by analysis of variance in a three treatmentX 2 year factorial using animals as replications. Fleeces were analyzed separately for ewes that did and did not wean a lamb. Orthogonal polynomials were used to compare the three stocking rates (Steel and Torrie, 1980). Treatments could not be replicated due to the size and nature of the experiment. Therefore animal variance within treatments was used for analysis (Coniffe, 1976).
Grazing strategy study In this study, an additional 60 mature Corriedale ewes were utilized. Twenty were allotted to each of three treatment groups: continuous grazing (CG), rotational grazing (RG), and rotational grazing with cattle (RGC). Stocking rates were set at three ewes per hectare. The RGC treatment was stocked with six bulls (mean weight 221 kg) and three bulls (mean weight 208 kg) in 1981 and 1982, respectively. Therefore, the sheep in the RGC group were subject to a higher grazing pressure. Each rotation pasture was divided into eight paddocks. In the sheep-only rotation, each paddock was grazed 6 days and rested 42 days. In the common-use rotation, sheep and cattle were separated with sheep being rotated one pasture ahead of the cattle. Each species grazed each
130
paddock for 6 days and was moved to the next paddock in sequence; thus, each paddock was rested 36 days. Ewes that died during the study period were replaced with dry ewes to maintain the desired grazing pressure for each treatment. Only fleeces from the ewes that were on test for both years were used in analyzing the results. Wool was collected and analyzed as described for the stocking rate study. Treatment effects were analyzed in the three treatment × 2 year factorial as described for the stocking rate study. Fleeces were analyzed separately for ewes that did and did not wean a lamb. Initial live weight of the ewes was corrected to a common turn-in weight by covariance analysis. Orthogonal contrasts were used to compare CG with RG and to compare the mean of CG and RG treatments with RGC (Steel and Torrie, 1980 ). Animal variance within treatments was used for analysis (Coniffe, 1976). RESULTS AND DISCUSSION
Stocking rate study There were no differences between results from 1982 and 1983. Therefore means for the two years were pooled. There were no differences in greasy fleece weights between the two, four and six ewes per hectare stocking rates. However, there was a significant (P < 0.05) linear effect in fiber diameter (25.5, 24.5, and 24.1/~m, respectively) as stocking rate increased (Table 1 ). The differences in staple length between the two, four and six ewes per hectare stocking rates resulted in a quadratic effect (P < 0.02 ) being 9.55, 8.99, and 10.27 cm, respectively (Table 1 ). The increased TABLE 1 Effects of stocking rates on mean greasy fleece weight, staple length and fiber diameter I Stocking rate (ewes/ha)
2 4 6 SEM 4
n
27 29 18
Fleece parameters Greasy weight (kg)
Staple length2 (cm)
Fiber diameter 3 (/~m)
3.15 2.99 3.00 0.134
9.55 8.99 10.27 0.095
25.5 24.5 24.1 0.513
'Means for greasy fleece weight, staple length, and fiber diameter are for ewes that weaned lambs. Means have been pooled for 1982 and 1983. 2Quadratic effect (P
131 staple l e n g t h at t h e highest s t o c k i n g r a t e is c o n t r a r y to t h e findings of B r o w n (1977) a n d L a n g l a n d s (1977) a n d we are u n a b l e to explain this finding. Wool p r o d u c t i o n in this s t u d y was n o t sensitive to i n c r e a s e d s t o c k i n g rate a n d density. T h i s c o n f i r m s findings o f M c M a n u s et al. (1964 } a n d George a n d P e a r c e (1978) t h a t s t o c k i n g r a t e s have little i n f l u e n c e on wool p r o d u c t i o n .
Grazing strategy study T h e r e were no d i f f e r e n c e s b e t w e e n results f r o m 1982 a n d 1983 a n d m e a n s for t h e two y e a r s were pooled. G r e a s y fleece weights were 9% h i g h e r ( P < 0.01 ) u n d e r C G t h a n u n d e r RG. H o w e v e r , t h e r e was no d i f f e r e n c e b e t w e e n t h e average fleece weight o f t h e s e two t r e a t m e n t s (3.19 kg) w h e n c o m p a r e d to R G C (2.94 kg) ( T a b l e 2). F i b e r d i a m e t e r did n o t differ b e t w e e n C G a n d RG, b u t fiber d i a m e t e r was smaller ( P < 0.01) in t h e R G C t r e a t m e n t (23.3 g m ) t h a n t h e average o f t h e C G a n d R G t r e a t m e n t s (24.6/~m) ( T a b l e 2). S t a p l e l e n g t h did n o t differ b e t w e e n C G a n d R G t r e a t m e n t s , b u t t h e r e was a d i f f e r e n c e ( P < 0.05 ) b e t w e e n t h e average o f t h e s e two t r e a t m e n t s ( 10.05 c m ) a n d t h e R G C t r e a t m e n t ( 10.40 c m ) ( T a b l e 2). P r e v i o u s studies b y B r o w n (1977) a n d L a n g l a n d s (1977) r e p o r t e d t h a t as grazing p r e s s u r e increased, as in t h e R G C t r e a t m e n t , staple l e n g t h d e c r e a s e d w h e n greasy fleece weights a n d fiber d i a m e t e r decreased. We f o u n d t h e same t r e n d for ewes n o t w e a n i n g lambs in t h e R G C t r e a t m e n t , b u t ewes w e a n i n g TABLE2 Effects of continuous (CG), rotational (RG), and common use rotational grazing with cattle (RGC) on means for greasy fleece weight, staple length and fiber diameter1 Grazing strategy
CG vs. RG CG + RG vs. RGC SEM 3
n
28 vs. 26 54 vs. 17
Fleece parameters Greasy weight 2 (kg)
Staple lengt h2 (cm }
Fiber diameter2 (/~m)
3.35 vs. 3.04** 3.19 vs. 2.94 0.15
10.12 vs. 9.98 10.05 vs. 10.40" 0.10
24.0 vs. 25.1 24.6 vs. 23.3** 0.49
1Means for greasy fleece weight, staple length and fiber diameter are for ewes that weaned lambs. Since there was no difference (P > 0.10 ) between years, the means for these variables have been pooled. 2Adjusted by covariance with initial weight. 3Pooled standard error of the mean. *P < 0.05. **P < 0.01.
132
lambs in the RGC treatment had longer staple lengths with smaller fiber diameters and lighter greasy fleece weights. The lack of difference in either staple length or fiber diameter contrasted with significantly lighter (P < 0.1 ) greasy fleece weights under rotational compared to continuous grazing. Dunlop (1962) hypothesized that wool production is dependent on the live weight of the sheep, number of fibers per unit area of skin, fiber diameter and staple length. Therefore, differences between CG and RG in greasy fleece weights may be due to the number of fibers per area of skin, considering that body weight, staple length and fiber diameter did not differ. Lyne (1964) found that undernourishment in the adult life of sheep can cause temporary reduction in the number of active follicles and thought that this might be associated with fiber shedding. The 9% increase in greasy fleece weight under CG agrees with the conclusions of Brown et al. (1966). They reported higher greasy fleece weights for continuous grazing compared to rotation grazing at low stocking rates. Apparently, the continuously grazed ewes were able to select a more nutritious diet and this was reflected in higher fleece weights. Conversely, ewes in the RG treatment were apparently forced to consume a higher percentage of unpalatable bunchgrasses. Differences between the RGC treatment and the two sheep-only treatments might have been greater if one-half of the cattle had not been removed from the RGC treatment the second year of the study. A reduction ( P < 0.05 ) of 10% in greasy fleece weight was noted in lactating ewes (3.14 kg) compared to non-lactating ewes (3.52 kg) (Table 3). This agrees with the 10-14% reduction in annual greasy fleece production due to full cycle reproduction found in other studies (Slen and Whiting, 1956; Doney, 1958; Seebeck and Tribe, 1963; Brown et al., 1966). Brown et al. (1966) concluded that about one-third of the reduction in wool growth by Merinos during pregTABLE 3 Effects of lactation on means for greasy fleece weight, staple length, and fiber diameter for all treatment groups from both experiments Reproductive status
Lactating ewes Non-lactating ewes SEM 1
n
72 45
Fleece parameters Greasy weight (kg)
Staple length (cm)
Fiber diameter (/~m)
3.14 a 3.52 b 0.099
10.15 10.25 0.066
24.23 24.94 0.427
1Pooled standard error of the mean. a'bMeans in the same column with different superscripts differ significantly ( P < 0.01 ).
133 n a n c y a n d l a c t a t i o n s t e m s f r o m a d e c r e a s e in f i b e r n u m b e r s a n d t w o - t h i r d s f r o m a d e c r e a s e in fiber v o l u m e . O b s e r v a t i o n s o n t h e n u m b e r o f fibers p e r u n i t a r e a of s k i n b y B r o w n et al. (1966) i n d i c a t e d t h e r e m a y be a g r e a t e r d e c r e a s e d u r i n g p r e g n a n c y t h a n d u r i n g l a c t a t i o n , a l t h o u g h t h i s c h a n g e w a s e v i d e n t in b o t h p h a s e s o f p r o d u c t i o n in t h e s t u d y of S l e n a n d W h i t i n g (1956). T h e s e r e s u l t s i n d i c a t e t h a t ewes p r o d u c i n g l a m b s are m o r e s e n s i t i v e to d i f f e r e n t grazing s t r a t e g i e s t h a n are n o n - p r o d u c i n g ewes. Overall, h o w e v e r , wool p r o d u c t i o n did n o t a p p e a r to b e a s e n s i t i v e i n d i c a t o r o f t r e a t m e n t differences. ACKNOWLEDGEMENT R e s e a r c h w a s f u n d e d u n d e r U S A I D G r a n t No. A I D / D S A N / X 1 1 - G - 0 0 4 9 as p a r t of t h e S m a l l R u m i n a n t C o l l a b o r a t i v e R e s e a r c h S u p p o r t P r o g r a m in coo p e r a t i o n w i t h U n i v e r s i d a d N a c i o n a l A g r a r i a , L a M o l i n a , L i m a , Peru. T h i s is t e c h n i c a l article T - 5 - 1 9 5 f r o m t h e College o f A g r i c u l t u r a l Sciences, T e x a s T e c h U n i v e r s i t y , L u b b o c k , T X , U.S.A.
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134 Lyne, A.G., 1964. Effect of adverse nutrition on the skin and wool follicles in Merino sheep. Aust. J. Agric. Res., 15: 788-793. McManus, W.R., Arnold, G.W. and Paynter, J.R., 1964. Variation in wool characteristics with season and stocking rate. Aust. J. Exp. Agric. Anita. Husb., 4: 405-411. Morley, F.H.W., 1981. Management of grazing systems. In: F.H.W. Morley (Editor), Grazing Animals. Elsevier Sci. Publ. Amsterdam, The Netherlands, pp. 379-400. Seebeck, R.M. and Tribe, D.E., 1963. The relation between the lamb production and the wool production of the ewe. Aust. J. Exp. Agric. Anita. Husb., 3: 149-156. Slen, B.F. and Whiting, F., 1956. Wool growth in mature range ewes as affected by stage and type of pregnancy and type of rearing. Can. J. Agric. Sci., 36: 8-13. Steel, R.G.D. and Torrie, J.H., 1980. Principles and Procedures of Statistics (2nd Edition). McGraw-Hill Book Co., Inc., New York, U.S.A. Wilcox, B.P., 1982. Plant communities and soils of the central Andes of Peru. M.S. Thesis. Texas Tech Univ., Lubbock, Texas, U.S.A.