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Sheep & Goat Research Journal, Volume 20, 2005 25 Summary This study was conducted to evaluate post-weaning growth, carcass traits and parasite burdens St. Croix White (STX) and Dorper X St. Croix White (DRP) lambs grazing guinea grass pastures during the wet and dry seasons. Lambs (77 d of age) were placed in guinea grass pastures (0.5 ha) in a rota- tional grazing system. Fecal egg count (FEC), packed cell vol- ume (PCV) and BW were measured weekly. Lambs were slaughtered at a BW of 30 kg. Carcass weight, fat thickness, rib eye area (REA), KPH and leg circumference were measured. Data were analyzed by SAS procedures. Total rainfall was 647.7 mm and 1495.3 mm for the dry and wet seasons, respectively. Forage availability was 432.5 ± 64.6 kg DM/ha and 1051.0 ± 261.9 kg DM/ha during the dry and wet seasons, respectively. The DRP lambs reached target weight sooner (P < 0.0008) than STX lambs (178.2 ± 6.3 d vs. 210.9 ± 6.7 d, respectively). Average daily gain was higher (P < 0.0002) for DRP than for STX lambs (90.3 ± 1.9 g/d vs. 79.1 ± 2.0 g/d, respectively). Car- cass weight was not different (P > 0.10) between breed type (13.5 ± 0.1 kg). The REA of DRP lambs was greater (P < 0.01) than that of STX lambs (9.36 ± 0.19 cm2 vs. 8.63 ± 0.21 cm2, respectively). Fat thickness was greater (P < 0.02) in DRP than in STX lambs (1.92 ± 0.10 mm vs. 1.57 ± 0.10 mm, respec- tively). Leg circumference was larger (P < 0.03) for DRP than for STX lambs (38.2 ± 0.3 cm vs. 37.3 ± 0.3 cm, respectively). There was no difference (P > 0.10) between DRP and STX lambs in FEC or PCV. Dorper-sired lambs reared under an extensive management system will reach market weight sooner than St. Croix White lambs and can tolerate parasite burdens similar to those found in the indigenous hair sheep in the U.S. Virgin Islands. Key words: Hair Sheep, Parasites, Tropics, Carcass, Cross- Breeding Post-weaning Growth and Carcass Traits of St. Croix White and Dorper X St. Croix White Lambs Grazing Pasture During the Dry and Wet Seasons in the U.S. Virgin Islands R.E. Dodson, A.J. Weis and R.W. Godfrey1 Agricultural Experiment Station, University of the Virgin Islands, St. Croix. 1 Corresponding author RR 1, Box 10,000, Kingshill, VI 00850. Phone: 340-692-4042; Fax: 340-692-0435; e-mail: rgodfre@uvi.edu Acknowledgements This study was funded by USDA-TSTAR Caribbean Grant 2003-34135-14084-S. The authors would like to thank W. Gonzales and C. Diaz for assistance with animal care and management. Volume 20, 2005 This manuscript submitted as part of the Hair Sheep Workshop sponsored by the National Sheep Industry Improvement Center and the NCERA-190 research project, June 21-23, 2005 at Virginia State University. 26 Sheep & Goat Research Journal, Volume 20, 2005 Introduction Caribbean agriculture is marked by limited land availability, variable rainfall throughout the year and year round exposure of livestock to parasites. In locations where the amount of land available for agriculture is limited, sheep can be the only feasible option for large- scale livestock production. The predom- inant breeds of sheep found throughout the Caribbean region consist of hair breeds, such as the St. Croix White and Barbados Blackbelly, as well as crosses of these two breeds. These hair breeds pro- duce relatively small lambs with light carcass weights at slaughter. Attempts to increase carcass weight by crossing with wool breeds have met with limited suc- cess (Godfrey and Collins, 1999; God- frey et al., 2000). These studies also reported that crossbred lambs (Suffolk X St. Croix White) had higher lamb mor- tality, higher fecal egg counts and lower hematocrit values while grazing guinea grass (Panicum maximum) pasture during the rainy season, when compared to purebred St. Croix White lambs. Previous research has determined that hair sheep lambs on St. Croix raised during the dry season of the year have lower weaning weights (Wildeus et al., 1988). Low forage quality and quantity was thought to be the main reason for the decrease in lamb weight during the dry season. Wildeus and Collins (1993) also reported that lamb survival was lower during the rainy sea- son on St. Croix. During the wet season the forage quantity increases, but qual- ity may not be at desirable levels. The grasses are growing rapidly and contain a high level of moisture that may limit the lamb’s grass consumption so that they cannot meet their nutritional requirements for growth due to limited rumen capacity. Each of the aforemen- tioned studies indicates that there are negative aspects of both the dry and rainy seasons with regards to raising lambs on tropical grasses. The introduction of Dorper sheep into the United States has led to a high level of interest in this breed in the U.S. Virgin Islands for use in crossbreeding programs. Several farms in the U.S. Vir- gin Islands have purchased Dorper sheep to incorporate into their hair sheep flocks, and interest about the perform- ance of the breed under the local condi- tions is increasing. The Dorper was selected for use in crossbreeding with Caribbean hair sheep in this project due to its heavy muscling and the fact that it was developed for use in arid, tropical areas and that Dorpers have a fiber type more typical of hair than wool. There is very little information available on the ability of purebred and crossbred Dorper sheep to be productive under the condi- tions found in the Caribbean. Their abil- ity to survive in an area of elevated para- site burdens is unknown. This project was designed to evaluate the post-wean- ing growth, carcass traits and parasite burdens of St. Croix White and Dorper X St. Croix White lambs raised on guinea grass pastures during two times of the year. The study was conducted during the dry (January through May) and the wet (September through December) seasons on St. Croix, U.S. Virgin Islands. Materials and Methods Animals St. Croix White (STX) and Dorper X STX (DRP) lambs sired by two rams within each breed type were born in either July or November 2003. Lambs were weaned at 63 ± 3 d of age, kept in drylot pens (3.1 X 6.1 meters) and fed a commercial pelleted diet (PMI Nutri- tion, Mulberry, FL) at 2 percent BW•hd-1•d-1 with ad libitum access to guinea grass hay and water for two weeks. Ram lambs were surgically cas- trated at 70 d of age. All lambs were treated with ivermectin (Ivomec®, 0.2mg/kg) and placed in pastures as they individually attained 77 d of age in October (wet season) or February (dry season). Lambs were dewormed with ivermectin once during the wet season grazing at day 84 of grazing, but not dur- ing the dry season. Distribution of lambs by breed and gender during the wet and dry grazing seasons is shown in Table 1. Grazing treatments A rotational-grazing system was uti- lized to move the lambs through a set of five pastures (0.5 ha each) that con- tained guinea grass with less than 10 per- cent leucaena (leucaena leucocephela). The timing of pasture rotation was deter- mined by visual evaluation of forage quantity in each pasture. Wet-season grazing began in October, 2003 and dry- season grazing began in February, 2004. Herbage mass was measured at the start and the end of the grazing period in each pasture. Six 0.25 m2 plots, randomly selected in each pasture, were harvested to a stubble height of 75 mm. Sub-sam- ples (0.2 kg) were dried at 60° C for 48 h to determine forage dry matter per hectare (kg DM/ha). Quality traits of forage, determined on sub-samples col- lected at the start of grazing in a pasture, included percentage of CP, TDN and DM. Samples were sent to a commercial laboratory (Dairy One, Ithaca, NY) for analysis. Daily precipitation and high and low temperatures were also meas- ured throughout the grazing period. Animal sampling Lambs were weighed, fecal samples were collected to determine fecal egg counts (FEC) and jugular blood samples were collected to determine packed cell volume (PCV) at weekly intervals dur- ing grazing. The FEC were determined using the modified McMaster’s tech- nique. Total gain was determined as the difference between BW at the start and end of grazing. Average daily gain (ADG) was calculated as total gain/day to reach market weight. Carcass data Lambs were slaughtered at a body weight of 30 kg, which is the preferred weight for the local market. Cold car- cass weight, rib eye area measured between the 12th and 13th rib (REA), Table 1. Distribution of lambs during wet and dry season grazing. Wet Dry DRP STX DRP STX Male 8 6 8 8 Female 6 6 7 6 Sub-total 14 12 15 14 Total 26 29 Sheep & Goat Research Journal, Volume 20, 2005 27 fat thickness over the 12th rib, KPH percent and leg circumference were measured. Dressing percent was calcu- lated as (cold carcass weight divided by live weight) x 100. Economic analysis Economic data was calculated for the three local markets available to pro- ducers. Lambs could be sold as live ani- mals for religious slaughter at a rate of $2.21/kg (live). Carcasses could be sold to retail outlets at a rate of $3.96/kg (commercial) or to individual customers for personal consumption at a rate of $4.41/kg (individual). A variable to pro- vide an indicator of efficiency (how many days it took to generate $1 of rev- enue) was created by dividing the num- ber of days to reach market weight by the sale price. Statistical analysis Data were analyzed using general linear models procedures (SAS, 1996). Body weight, FEC and PCV were ana- lyzed using repeated measures proce- dures. The model contained the effects of breed, sex, days grazing, season and the appropriate interactions. The values for FEC were transformed using log10(FEC + 1) prior to analysis but results are presented as the untrans- formed least squares means. Carcass traits, ADG and economic data were analyzed using breed, sex and season and the appropriate interactions in the model. Mean separations were done using the PDIFF option of SAS. There was no significant effect of sex or the sex X breed and breed x season interactions for any trait so only breed and season effects are reported. Results are reported as least square means ± SEM. Results and Discussion Total rainfall during the dry season was 583.4 mm and 1495.30 mm during the wet season. This seasonal variation in rainfall affects both availability and quality of forage and can be a limiting factor to livestock production in the Caribbean. The dry period usually lasts from January through April, and Sep- tember through December is considered the wettest time of the year (Godfrey and Hansen, 1996). Forage quantity was greater (P < 0.008) during the wet season than during the dry season (Table 2) but there was no difference (P > 0.10) in quality as indicated by CP or TDN between seasons. Lambs spent more time (P < 0.03) in each pasture during the wet season than during the dry season (Table 2). The DRP lambs were heavier (P < 0.01) than the STX lambs in both sea- sons (Figure 1). Lambs allotted during the dry season were on pasture for 245 days, and during the wet season they were on pasture for 287 days. The num- ber of days it took to reach target weight (30 kg) was less (P < 0.0008) for DRP than for STX lambs, but there was no difference (P > .10) between seasons (Table 3). Total gain was not different (P > 0.10) between DRP and STX lambs but was greater (P < 0.03) during the dry than the wet season (Table 3). The start- ing weight of lambs was lower (P < 0.02) during the dry season than the wet sea- son (13.1 ± 0.5 kg vs. 14.9 ± 0.5 kg, respectively), which explains why total gain was greater during the dry season. Average daily gain was higher for DRP than for STX lambs (P < 0.0002) and higher (P < 0.002) during the dry season than the wet season (Table 3). Even though the total weight gain was not dif- ferent between breed type, ADG was dif- ferent due to the shorter time it took DRP lambs to reach the target weight. The difference in ADG between seasons is due to the combination of a lack of dif- ference in time to reach market weight and the higher total weight gained dur- ing the dry season. In semi-arid areas with long periods of little or no precipitation, tropical grasses can be low in energy and protein content, and growing lambs would be susceptible to under nutrition during these periods of low forage quality or quantity (Johnson et al., 1990). Wildeus et al. (1988) reported that hair sheep lambs on St. Croix have lower weaning weights when they are raised on pasture during the dry season of the year. This decrease in weaning weights is thought to be related to the low forage quality and quantity. The predominant forage, guinea grass, has an average crude pro- tein content of 8 percent (on a DM basis), which is acceptable for mainte- nance of animals, but is not considered adequate for lactating ewes (Wildeus et al., 1988). The legume leucaena (Leu- caena leucocephela) was reported to have crude protein content of 28 percent (Wildeus et al., 1988), but it was esti- mated to account for less than 10 per- cent of available forage in pastures in the present study. In the present study, the quality of the forage was similar between seasons, with quantity being the only difference. The nutritional analysis showed that the forage had 11 percent CP during both seasons. Kawas and Hus- ton (1990) recommend that hair lambs gaining 100 g/d require 29 percent to 75 percent TDN and 9.5 to 14.9 percent CP, on a DM basis, depending on BW of the lamb. The forage quality during both the dry and wet season exceeded these levels, which indicates that nutritional quality was adequate for the lambs at both times. Table 2. Pasture rotation frequency and forage quality. Season Mean ± SEM Minimum Maximum Rotation frequencya,d Wet 18.2 ± 2.0c 6 33 Dry 11.2 ± 2.1d 2 36 Dry matter, % Wet 29.7 ± 1.8 21.6 50.3 Dry 32.2 ± 1.6 18.2 49.1 Crude proteinb, % Wet 11.3 ± 0.7 6.9 15.2 Dry 11.7 ± 0.9 6.2 20.8 TDNb, % Wet 60.8 ± 0.4 59.0 65.0 Dry 60.9 ± 0.3 59.0 64.0 Forage DM , kg/ha Wet 1051.0 ± 261.9e 121.3 3339.3 Dry 432.5 ± 64.6f 20.7 1123.3 a Lambs were rotated through five 0.5 ha pastures b DM basis Means within a trait different superscripts are different: c,d P < 0.03; e,f P < 0.008 28 Sheep & Goat Research Journal, Volume 20, 2005 We have previously reported that Suffolk X STX lambs had higher aver- age daily gain, but lower feed efficiency, when compared to purebred St. Croix White lambs being fed a concentrate ration after weaning (Godfrey and Collins, 1999). In a subsequent study conducted to evaluate one quarter Suf- folk x three quarter St. Croix White lambs grazing pasture, mortality was too high (57.1 percent) to accurately evalu- ate their rate of gain (Godfrey et al., 2000). In a review of South African Sheep Performance Testing Scheme records, Schoeman (2000) found the Dorper had the highest feed efficiency and ADG of all breeds tested, except for the Finnish Landrace composites. The crossbred lambs in the present study had greater ADG than the local hair sheep which is most likely due to breed differences between the Dorper and St. Croix White. The DRP lambs had larger REA (P < 0.01), more back fat (P < 0.02), lower KPH (P < 0.06) and greater leg circum- ference (P < 0.0001) than STX lambs (Table 4). Results from our laboratory (Godfrey and Collins, 1999; Godfrey et al., 1999) have shown that St. Croix White lambs fed a concentrate diet tended to store fat in the body cavity as KPH and had very little external fat, compared to wool or hair crossbred lambs. In agreement with the present study, Godfrey and Weis (2005) reported that DRP lambs had higher KPH than the STX lambs did, but there was no differ- ence in back fat when lambs were fed a concentrate diet. The trimness of hair sheep carcasses may be useful when mar- keting the meat to consumers who are interested in purchasing leaner cuts of meat for dietary or perceived health rea- sons. Notter et al. (2004) also reported an increase in muscling in Dorper-sired lambs. The larger REA and leg circumfer- ence of the DRP lambs compared to the STX lambs in the present study is indica- tive of more muscling on the carcass. There was no difference in FEC or PCV (P > 0.10) between DRP and STX lambs. In both groups of lambs there was an elevation of FEC and a decrease in PCV between days 21 and 84 during the dry season. This corresponded to a period where the weight gain was decreased (Figure 1). The lambs were not treated with anthelmintic during this time and FEC and PCV returned to levels that were similar to those at the start of the grazing, and BW began increasing. The DRP lambs had elevated FEC around day 161, but this may have been due to the fact that by then 40 per- cent of the DRP lambs had reached mar- ket weight and were removed from the pasture, and an increase in FEC of one or two lambs could account for the elevated mean. During the wet season there was only a slight elevation in FEC between day 21 and 42 (Figure 2), and there was a decrease in weight gain at that time as well (Figure 1). Burke and Miller (2002) reported that Dorper crossbred lambs were less tolerant than hair-breed lambs when faced with an elevated-parasite challenge. This is in contrast to the cur- Figure 1. Weight of St. Croix White (open circles) and Dorper X St. Croix White (closed circles) lambs grazing guinea grass pastures during the dry (upper panel) and wet (lower panel) seasons on St. Croix. The dry season grazing lasted for 245 d and the wet season grazing lasted for 287 d. During both seasons the Dorper lambs were heavier than the St. Croix White lambs (P < 0.01). Sheep & Goat Research Journal, Volume 20, 2005 29 rent study where both the STX and DRP lambs exhibited an elevation in FEC during grazing in the dry season that was temporary, even though the lambs were not treated with anthelmintic at that time. During the dry season FEC was higher (P < 0.001) than during the wet season (Figure 2), but there was no dif- ference (P > 0.10) in PCV (Figure 3). The higher FEC during the dry season was unexpected, but it may have played a role in the lower ADG (Table 3), as well as the plateau in BW between day 21 and 84 (Figure 1). Neither FEC nor PCV reached levels that were deemed abnormal during either season. However, three lambs (1 DRP and 2 STX) died of parasitism between day 81 and day 88 of the wet season, even though FEC was low and PCV was within the normal range for our sheep at this time (Figure 2). Parasitism was confirmed based on the large numbers of adult worms found in the gastrointestinal tract of these lambs during necropsy. During the 45- day period prior to the deaths, 626 mm of rain fell, accounting for 64 percent of the total rainfall during the 245-day, wet-season grazing period. One possible explanation for the lack of an increase in FEC during this time is that the Haemonchus contortus entered a diapause or arrested development phase during the wet season (Johnson et al., 1990; Wildeus and Collins, 1993) and were not shedding eggs that could be detected in the feces. If the parasites were in a dormant state, that would also explain why there was no detected decrease in PCV at that time as well. Gerisch and Antebi (2004) have studied the nema- tode Caenorhabditis elagans as a model of molecular mechanisms of environmental signaling due to its ability to arrest at the third larval stage (L3) in response to sen- sory inputs. Perhaps Haemonchus contor- tus possesses some ability to detect envi- ronmental cues outside of the host and can regulate its reproductive pattern to suit the environmental conditions. The only differences detected between the wet and dry seasons were forage quantity and rainfall amount. Whether or not Haemonchus contortus has the ability to respond to these environmental signals is unknown at the present time. In our lab, we have reported that even with just 25 percent wool genetics, crossbred hair lambs were unable to tol- erate the high parasite loads experienced by native hair sheep in the tropics during the wet season (Godfrey et al., 2000). In a study comparing the Dorper to the Red Maasai (Schoeman, 2000), the Dorper had higher mortality rates due to sus- pected parasitism by Haemonchus contor- tus. The Dorper had higher FEC and Table 3. Growth traits of STX and DRP lambs during the dry and wet seasons. Breed Season Trait DRP STX Dry Wet Days to target weight 178.2 ± 6.3a 210.9 ± 6.7b 188.8 ± 6.3 200.4 ± 6.6 Total gain, kg 15.8 ± 0.5 16.5 ± 0.5 16.9 ± 0.5c 15.4 ± 0.5d ADG, g/d 90.3 ± 1.9e 79.1 ± 2.0f 90.6 ± 1.9e 78.8 ± 2.0f Means in a row within breed or season are different: a,b P < 0.0008; c,d P < 0.03; e,f P < 0.0002 Table 4. Carcass traits of STX and DRP lambs during the dry and wet seasons. Breed Season Trait DRP STX Dry Wet Hot carcass weight, kg 13.7 ± 0.1 13.3 ± 0.1 13.6 ± 0.1 13.4 ± 0.1 Dressing percent 43.3 ± 0.4 42.2 ± 0.4 42.9 ± 0.4 42.7 ± 0.4 Rib eye area, cm2 9.36 ± 0.19a 8.63 ± 0.21b 8.8 ± 0.2 9.2 ± 0.2 Back fat, mm 1.92 ± 0.10c 1.57 ± 0.1d 1.92 ± 0.10c 1.57 ± 0.10d KPH, % 2.5 ± 0.2e 3.0 ± 0.2f 3.1 ± 0.2c 2.4 ± 0.2d Leg circumference, cm 38.2 ± 0.3g 37.3 ± 0.3h 38.6 ± 0.2i 36.9 ± 0.3j Means in a row within breed or season are different: a,b P < 0.01; c,d P < 0.02; e,f P < 0.06; g,h P < 0.03; i,j P < 0.0001 Figure 2. Fecal egg counts (FEC) of St. Croix White (open symbols) and Dorper X St. Croix White (closed symbols) lambs grazing guinea grass pastures during the dry (triangles) and wet (circles) seasons on St. Croix. FEC was higher during the dry season than during the wet season (P < 0.001). 30 Sheep & Goat Research Journal, Volume 20, 2005 lower PCV and subsequently higher mortality rates (Baker et al., 1999; Schoeman, 2000). Burke and Miller (2004) have reported that Dorper cross- bred lambs were less resistant and required anthelmintic treatment sooner than St. Croix White lambs, when exposed to a high parasite load. In con- trast, St. Croix White sheep have demonstrated tolerance to high parasite loads during the tropical rainy season (Godfrey et al., 2000). Because all the lambs in the present study were slaughtered at a target weight (30 kg) there were no differences (P > 0.10) in the revenue generated among the three markets that are available to local sheep producers (Table 5). In the previous study by Godfrey and Collins (1999) where wool x hair and hair lambs were fed a concentrated ration, the crossbred lambs had higher ADG. How- ever, the lower feed efficiency of the crossbreds and the high cost of the imported feed eliminated any economic advantage of the growth and size of the wool-sired lambs. There were differences detected in the efficiency of the lambs for the three markets. In each market the efficiency was greater (P < 0.002) for the DRP than for the STX lambs (Table 5). Since this variable is a measure of how many days the lambs take to produce $1 of revenue, the shorter time to reach tar- get weight and the higher ADG of the DRP lambs contributed to the difference in efficiency. Conclusion Forage differed between seasons by amount but not quality. The DRP lambs had higher ADG, shorter time to reach target weight and heavier muscled car- casses, based on REA and leg circumfer- ence but more back fat than STX lambs. Regardless of season, DRP lambs reached the target weight approximately 30 days sooner that STX lambs. This did not impact their sale value, but was reflected in an increased efficiency. The DRP lambs grew rapidly and could tolerate parasite burdens similar to those found in the indigenous hair sheep. The heav- ier crossbred lambs can lead to an increase in the amount of marketable product for sheep producers without increasing costs for parasite control in an extensive management system in the U.S. Virgin Islands. Further studies need to be done using a larger sampling of sires within each breed type so that inferences are not being made from a small sample size. Table 5. Revenue generated from sales and efficiency of St. Croix White and Dorper X St. Croix White lamb production. Breed Revenue DRP STX Livea $66.72 ± 0.15 $66.64 ± 0.16 Commercialb $50.85 ± 0.52 $51.92 ± 0.55 Individualc $56.63 ± 0.58 $57.82 ± 0.61 Efficiencyd (number of days to produce $1 of revenue) Live 2.7 ± 0.1e 3.2 ± 0.1f Commercial 3.5 ± 0.1g 4.1 ± 0.1h Individual 3.2 ± 0.1g 3.6 ± 0.1h a Sold as live animal to ethnic consumers for $2.21/kg b Sold as carcass to local grocery stores at $3.96/kg c Sold as carcass to individual consumers ate $4.41/kg d Efficiency = number of days to slaughter / sale price Means in a row are different: e,f P < 0.0007; g,h P < 0.002 Figure 3. Packed cell volume (PCV) of St. Croix White (open symbols) and Dor- per X St. Croix White (closed symbols) lambs grazing guinea grass pastures during the dry (triangles) and wet (circles) seasons on St. Croix. There was no differ- ence (P > 0.10) between breeds or seasons. Literature Cited Baker, R.L., D.M., Mwamachim J.O., Audho, E.O. Aduda, and W. Thorpe. 1999. Genetic resistance to gastro-intestinal nematode parasites in Red Maasai, Dorper and Red Maasai X Dorper ewes in the sub- humid tropics. Anim. Sci. 69: 335- 344. Burke, J.M, and J.E. Miller. 2004. Rela- tive resistance to gastrointestinal nematode parasites in Dorper, Katahdin, and St. Croix lambs under conditions encountered in the southeastern region of the United States. Sm. Rum. Res. 54:43-51. Gerisch, B., and A. Antebi. 2004. Hor- monal signals produced by DAF- 9/cytochrome P450 regulate C. ele- gans dauer diapause in response to environmental cues. Development 131: 1765-1776. Godfrey, R.W., H.A. Buroker, and B.M. Pannagl. 1999. Growth and carcass traits of St. Croix White (SCW) and Barbados Blackbelly x SCW (BBSC) lambs in the tropics. J. Anim. Sci. 77(Suppl. 1): 239. Godfrey, R.W., and P.J. Hansen. 1996. Reproduction and milk yield of Hol- stein cows in the US Vir- gin Islands as influenced by time of year and coat color. 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Small Ruminant Collaborative Research Support Program, Davis, CA. Kawas, J. R., and J. E. Huston. 1990. Nutrient requirements of hair sheep in tropical and subtropical regions. Page 37 in Hair Sheep Production in Tropical and Sub Tropical Regions with Reference to North- east Brazil and the Countries of the Caribbean, Central America, and South America. M. Shelton and E.A.P. Figueiredo ed. Small Rumi- nant Collaborative Research Sup- port Program, Davis, CA. Milne, C. 2000. The history of the Dor- per sheep. Sm. Rum. Res. 36: 99- 102. Notter, D.R., S.P. Greiner, and M.L. Wahlberg. 2004. Growth and car- cass characteristics of lambs sired by Dorper and Dorset rams. J. Anim. Sci. 82:1323-1328. The SAS System for Windows (v 8) 1999. Cary, NC: SAS Institute Inc. Schoeman, S.J. 2000. A comparative assessment of Dorper sheep in differ- ent production environments and systems. Sm. Rum. Res. 36: 137- 146. Wildeus, S., K.T. Traugott, C. Wildeus, and L.R. McDowell. 1988. Growth and lambing performance of hair sheep grazing native pastures during the dry season on St. Croix, Vir- gin Islands. Proc. of the Caribbean Food Crop Society. pp.109 113. Wildeus, S., and J.R. Collins. 1993. Hair sheep performance in an extensive, native pasture system: A five year summary. UVI Research 5:1 3, Uni- versity of the Virgin Islands, St. Croix. Sheep & Goat Research Journal, Volume 20, 2005 31