Sheep & Goat Research Journal. Volume 20, 2005

Contents

Seasonal Acceptance of Fourwing Saltbush by Sheep When Crested Wheatgrass is the Alternative
Author: Christine W. Royer, R. D. Horrocks, Val J. Anderson, and Stephen B. Monsen
Feedlot Performance and Carcass Characteristics of Lambs Sired by Texel, Romanov, St. Croix or Dorset Rams from Polypay and St. Croix Ewes
Author: W.A. Phillips, M.A. Brown, H.G. Dolezal and G.Q. Fitch
Cost of a Maedi Visna Flock Certification Program and the Changes in Productivity and Economic Return
Author: J.W. Fisher and P.I. Menzies
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. VI
Author: R.E. Dodson, A.J. Weis and R.W. Godfrey
Post-weaning Growth and Carcass Traits of St. Croix White and Dorper X St. Croix White Lambs Fed a Concentrate Diet in the U.S. Virgin Islands
Author: R.W. Godfrey and A.J. Weis
Growth Performance of Barbados Blackbelly, Katahdin and St. Croix Hair Sheep Lambs Fed Pasture- or Hay-based Diets
Author: S. Wildeus, K.E. Turner, and J.R. Collins
Gastrointestinal Parasitism in Hair Sheep and Meat Goat Breeds Grazing Naturally Infected Pasture
Author: S. Wildeus and A. M. Zajac
Carcass and Growth Characteristics of Wethers Sired by Percentage White Dorper or Hampshire Rams 1
Author: J. A. Daniel and J. Held
Lamb Production of Dorper, Katahdin, and St. Croix Bred in Summer, Winter, or Spring in the Southeastern United States
Author: J.M. Burke: USDA, ARS, Dale Bumpers Small Farms Research Center, Booneville, AR
Postweaning Performance of Hair and Wool Sheep and Reciprocal-crosses on Pasture and in Feedlot
Author: M. A. Brown and H. S. Mayeux: USDA-ARS, Grazinglands Research Laboratory El Reno, OK

Article Summaries

Seasonal Acceptance of Fourwing Saltbush by Sheep When Crested Wheatgrass is the Alternative

Author: Christine W. Royer, R. D. Horrocks, Val J. Anderson, and Stephen B. Monsen
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Summary

Many sagebrush-grass ranges have been seeded to crested wheatgrass [Agropyron desertorum (Fischer ex Link) Shultes]. These ranges are generally nutritionally inadequate for sheep (Ovis aries L.), except for short grazing periods in the spring and fall. To increase production and diversity, particularly crude protein for late-season grazing, fourwing saltbush [Atriplex canescens (Pursch.) Nutt.] was planted in an existing stand of crested wheatgrass. Quantification of sheep forage preferences on these improved ranges aids in determining the length of the grazing season and the extent to which shrubs provide the supplemental nutrition required. This seasonal grazing study was conducted on a characteristic wheatgrass-saltbush, mixed-range pasture to determine sheep acceptance of fourwing saltbush when crested wheatgrass was the alternative available forage. Sheep preferences for grass and shrub in spring and winter were similar, averaging 84 percent grass and 16 percent shrub. Summer dietary preferences ranged from 69 percent to 93 percent grass and 7 percent to 31 percent shrub. Preference for fourwing saltbush was consistently lower than crested wheatgrass in all seasons. Sufficient amounts of the mixed pasture were grazed to reduce the need for supplemental feed, when compared to crested wheatgrass monoculture. The results of these grazing trials suggest fourwing saltbush can be useful in improving pasture nutrition for sheep in different grazing seasons.

Feedlot Performance and Carcass Characteristics of Lambs Sired by Texel, Romanov, St. Croix or Dorset Rams from Polypay and St. Croix Ewes

Author: W.A. Phillips, M.A. Brown, H.G. Dolezal and G.Q. Fitch
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Summary

Over a 2-year period, crossbred lambs resulting from the mating of Texel (T), Romanov (R), and St. Croix (S) rams with Polypay (P) and S ewes, were finished during the summer and late fall to determine feedlot performance and carcass characteristics. A total of 175 wether lambs of the five genotypes (R x P, R x S, S x S, T x P and T x S) were fed a high-energy diet for an average of 110 d (Experiment 1). Purebred St. Croix lambs weighed less (P < 0.05) at the beginning and end of the finishing period, had the lowest average daily gain (ADG) (P < 0.05), and the lowest Gain:Feed (P < 0.10) of the five genotypes evaluated. All five genotypes produced carcasses with a quality grade ?? Choice. In a subsequent 2-year experiment (Experiment 2), 251 lambs sired by either Dorset or St. Croix rams from the ewes created in Exp.1 were used. Dorset-sired lambs were heavier (P < 0.10) at the end of the feeding period and had greater ADG (P < 0.10) than lambs sired by St. Croix rams. Wether lambs were heavier (P < 0.10), grew faster (P < 0.10) and ate more (P<0.05) feed than female lambs. Lambs from crossbred ewes were heavier (P <0.05) at the beginning and end of the finishing period and grew faster (P < 0.10) than lambs from purebred St. Croix ewes. When Dorset rams were used as the terminal sire, lamb feedlot performance was similar among the five ewe genotypes used in this study. Key words: Lambs, Crossbreeding, Feedlot, Carcass Quality, Carcass Cutability.

Cost of a Maedi Visna Flock Certification Program and the Changes in Productivity and Economic Return

Author: J.W. Fisher and P.I. Menzies
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Summary

Maedi Visna (MV) has been identified as a common viral infection in Ontario sheep. The Maedi Visna Flock Status Pilot Project (MVFSP) sets a protocol for control and eradication of this disease. A static normative model was designed to measure the economic benefit of such a program. Of the 16 producers enrolled on the program in 2002, 15 cooperated and were surveyed.

Two benefits were identified from being MV free: 1) higher purebred sheep sale prices and 2) improved ewe productivity. The benefits to purebred sheep breeders warrant eradication within sheep flocks. With only a 10 percent improvement in purebred price, even on only 25 percent of lambs sold for breeding stock, a producer should expect to breakeven on the added costs associated with the MVFCP program just shortly after becoming ?A? Status. This outcome was robust for all combinations of flock size, ewe and purebred sheep sale values, and bleeding costs.

Commercial sheep producers did not find the same positive outcome. With low prevalence of the disease, few benefits accrued. Only with prevalence levels over 10 percent with low bleeding costs and large flocks would commercial producers show a reasonable payback period of about six years, and then only with the Monitored Program. Payback would never be reached on the Whole-Flock Program for commercial sheep producers.

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. VI

Author: R.E. Dodson, A.J. Weis and R.W. Godfrey
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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 rotational grazing system. Fecal egg count (FEC), packed cell volume (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). Carcass 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, respectively). 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.

Post-weaning Growth and Carcass Traits of St. Croix White and Dorper X St. Croix White Lambs Fed a Concentrate Diet in the U.S. Virgin Islands

Author: R.W. Godfrey and A.J. Weis
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Summary

Growth and carcass traits of St. Croix White (STX; n = 22) and Dorper X St. Croix White (DRP; n = 18) lambs fed a concentrate ration were evaluated. Starting two weeks after weaning (63 d of age) lambs were fed a commercial diet at 4 percent BW•hd-1•d-1. Lambs were slaughtered at a BW of 30 kg. Carcass weight, fat thickness over the 12th rib, rib eye area (REA), percent KPH and leg circumference were measured. Days on feed was greater (P < 0.01) for STX than for DRP lambs (153.2 ± 6.8 d vs. 118.9 ± 7.4 d, respectively). Total weight gained was greater (P < 0.04) for STX than for DRP lambs (16.1 ± 0.5 kg. vs. 14.6 ± 0.5 kg, respectively). The ADG of DRP lambs was higher (P < 0.01) than that of STX lambs (125.1 ± 4.7 g/d vs. 108.1 ± 4.3 g/d, respectively). Carcass weight was not different (P > 0.10) between breed type (12.6 ± 0.2 kg). The REA of DRP lambs was greater (P < 0.02) than that of STX lambs (10.4 ± 0.4 cm2 vs. 9.0 ± 0.4 cm2, respectively). Fat thickness was not different (P > 0.10) between DRP and STX lambs (1.5 mm ± 0.2 mm). Percent KPH was higher (P < 0.001) in STX than in DRP lambs (3.6 ± 0.3 percent vs. 2.2 ± 0.3 percent, respectively). Leg circumference was greater (P < 0.007) for DRP than for STX lambs (37.3 ± 0.4 cm vs. 35.7 ± 0.4 cm, respectively). Cost of gain was higher (P < 0.05) for STX than DRP lambs (4.08 ± 0.02 S/kg. vs. 3.73 ± 0.02 $/kg, respectively). Sales of DRP resulted in greater (P < 0.03) net revenue than sales of STX in each market. Dorper X St. Croix White crossbred lambs fed a concentrate ration are economically feasible due to lower cost of gain, higher ADG and revenue.

Growth Performance of Barbados Blackbelly, Katahdin and St. Croix Hair Sheep Lambs Fed Pasture- or Hay-based Diets

Author: S. Wildeus, K.E. Turner, and J.R. Collins
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Summary

Two experiments evaluated growth of mixed-sex Barbados Blackbelly, Katahdin, and St. Croix hair sheep lambs raised on pasture or hay-based diets with moderate levels of energy supplementation. In Experiment 1, 36 ewe and wether lambs were allocated to a pasture or pen feeding group in May. Pasture animals rotationally grazed tall fescue pasture, while pen animals were offered chopped alfalfa hay, and both groups were supplemented with corn/soybean meal at 0.75% of body weight. In Experiment 2, 72 lambs were allocated to pen and pasture in April, and provided either a low or high crude protein concentration corn/soybean meal supplement at 1.5% of body weight. Pasture animals were continuously grazed, while pen animals were offered chopped mixed grass hay. In both experiments, starting and final body weights were higher (P < 0.05) in Katahdin than St. Croix and Barbados Blackbelly. In Experiment 1, daily gain was similar between Katahdin (84 g/d) and St. Croix (75 g/d), and higher (P < 0.01) than in Barbados Blackbelly (56 g/d). Daily gain was higher (P < 0.05) for lambs in pens (77 g/d) than for lambs on pasture (67 g/d). In Experiment 2, growth rates were higher than in Experiment 1, and Katahdin (109 g/d) grew faster (P < 0.05) than St. Croix (86 g/d) and Barbados Blackbelly (73 g/d). Growth was not affected (P > 0.10) by forage or supplement type, but wether lambs grew faster (P < 0.05) than ewe lambs. The growth rates in both trials were moderate and produced lambs of medium size, suitable primarily for the Muslim and Hispanic ethnic markets.

Gastrointestinal Parasitism in Hair Sheep and Meat Goat Breeds Grazing Naturally Infected Pasture

Author: S. Wildeus and A. M. Zajac
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Summary

Differences in indicators of gastrointestinal parasitism between species, breeds within species, and two grazing systems (goats only) were evaluated in a total of 66 does and 22 ewes (11 animals/breed/management system), representing four goat and two sheep breeds. Animals were either grazed continuously (does and ewes, n=66), or rotationally on 0.4 ha of pre-dominantly fescue pastures (does only, n=22). Fecal and blood samples were collected in 14-day intervals from mid-May until October. Animals were dewormed (ivermectin, sc, 0.3 mg/kg) by breed group when breed composites (five animals/breed) exceeded 1000 eggs/g. Data were analyzed in subsets for species, breed, and grazing management comparisons. Hair sheep had lower mean FEC (376 vs. 669 eggs/g; P < 0.01) and higher mean PCV (31.9 percent vs. 26.5 percent; P < 0.001) than the goats. Within hair sheep, Katahdin had lower FEC (242 vs. 518 eggs/g; P < 0.01) and were dewormed less frequently (2 vs 7) than the Barbados Blackbelly. In goats, Nubian and Spanish (1035 and 865 eggs/g, respectively) had higher (P < 0.01) mean FEC than Myotonic and Pygmy (413 and 359 eggs/g, respectively), and were dewormed five, four, three, and three times, respectively, during the experimental period. Fecal egg counts were similar in goats under rotational, compared to continuous grazing. Hair sheep appeared to be more resistant to parasites than goats, however, differences may have been masked by considerable breed variation within species. The anthelmintic treatment protocol may have prevented breeds from expressing their ability to tolerate gastrointestinal parasites.

Carcass and Growth Characteristics of Wethers Sired by Percentage White Dorper or Hampshire Rams 1

Author: J. A. Daniel and J. Held
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Summary

To evaluate the use of percentage Dorper rams as terminal sires in the Upper Midwest, 72 Finn-Dorset-Targhee (FDT) ewes were mated to one of two 3/4 White Dorper-1/8 East Fresian- 1/8 Corriedale (WD) rams and 77 FDT ewes were mated to one of two Hampshire rams in single-sire mating groups. Thirty-seven WD-sired and 55 Hampshire-sired wethers were utilized for the study. All male lambs were castrated by elastration at 1 day of age. Wethers were maintained as a group until slaughtered at a commercial packing plant. Carcass data were collected at slaughter. Hampshire-sired wethers tended to have greater birth weights (4.8 ? 0.14 kg vs. 4.4 ? 0.15 kg; P = 0.06) and had greater adjusted weaning weights (33.4 ? 0.85 kg vs. 30.4 ? 1.01 kg; P = 0.03) than WD-sired wethers. Hampshiresired wethers had greater post-weaning average daily gain (0.36 ? 0.02 kg/day vs. 0.28 ? 0.01 kg/day, respectively; P = 0.0002), greater finished weights (57.8 ? 0.7 kg vs. 51.7 ? 0.8 kg, respectively; P = 0.0001), greater hot-carcass weights (29.1 ? 0.4 kg vs. 26.6 ? 0.5 kg, respectively; P = 0.0001), less fat over the ribeye (0.46 ? 0.02 cm vs. 0.55 ? 0.03 cm, respectively; P = 0.03) and thinner body walls (2.2 ? 0.06 cm vs. 2.5 ? 0.1 cm, respectively; P = 0.001) than WD-sired wethers. Hampshire-sired wethers grew faster and produced leaner carcasses than wethers sired by percentage WD rams.

Lamb Production of Dorper, Katahdin, and St. Croix Bred in Summer, Winter, or Spring in the Southeastern United States

Author: J.M. Burke: USDA, ARS, Dale Bumpers Small Farms Research Center, Booneville, AR
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Summary

Ewe production traits and ability to breed out of season were compared for the Dorper (DO), Katahdin (KA), and St. Croix (SC) breeds between 2000 and 2005. Sheep were managed on grass pasture and were supplemented with corn/soybean meal and free-choice, trace-mineral mix. Ewes were exposed to rams of their respective breeds in late summer (August/September), winter (December), or spring (April/ May) for 30-day breeding periods. Lambs were weighed at birth and 60 days of age. Pregnancy and lambing rates and litter birth weight were greater for all breeds bred in winter and lowest in spring. Pregnancy losses were greater and birth weights reduced for DO and KA ewes less than two years of age bred in the spring compared with other seasons. Birth weights of lambs were not affected by season, but weaning weights were greatest for all breeds when ewes were bred in summer. Relative efficiency at weaning (kg of lamb produced/kg ewe weight) was greatest for summer-bred ewes and greatest for KA compared with DO and SC ewes. In summary, DO, KA, and SC ewes are capable of out-of-season breeding in Arkansas. However, relative efficiency and weaning weights were lowest for spring-bred ewes and fertility of yearling ewes of all breeds was reduced during spring breeding.

Postweaning Performance of Hair and Wool Sheep and Reciprocal-crosses on Pasture and in Feedlot

Author: M. A. Brown and H. S. Mayeux: USDA-ARS, Grazinglands Research Laboratory El Reno, OK
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Summary

Lambs from three diallel-mating plans (Dorset-St. Croix, n=140; Rambouillet-Gulf Coast, n=80; Katahdin-Suffolk, n=78) and a terminal-cross mating plan (Suffolk rams mated to Dorset, St. Croix and reciprocal-cross ewes, n=100) were used to evaluate postweaning grazing performance of traditional meat breeds and tropically adapted breeds of sheep.

Tropically adapted breeds generally had lower postweaning performance than wool breeds in both grazing and feedlot management with the exception that purebred Katahdin and Suffolk were comparable in gain on bermudagrass. Tropically adapted x wool breed lambs were generally intermediate between the parental purebreds except in the Katahdin x Suffolk diallel where there was an indication of heterosis for feedlot ADG and possibly pasture ADG. In general, all lambs performed poorly on forages compared to performance on mixed diets in feedlot. These results indicated a consistent advantage in direct breed effects for wool breeds over tropically adapted breeds in feedlot management systems. The results also suggest that there is little expression of genetic effects in sheep managed on forages, although direct effects for heat adaptation in tropically adapted breeds may compensate for the superior direct breed effects for growth in the wool breeds under summer grazing.