P. Dimsoski, J. Clay, and K.M. Irvin
Department of Animal Sciences
Three sire breeds (Cheviot, Rambouillet, and Suffolk) and three dam breeds (Florida Native, Native-X, and Synthetic-X) produced 698 matings in three season-management systems (Winter, Spring, and Late Fall) over a period of three years (1989, 1990, and 1991). Data were collected and analyzed for litter size born and weaned, growth, and carcass characteristics of lambs. The three management systems were regarded as intensive (Winter), extensive (Spring), and intermediate (Late Summer) according to requirements for labor and facilities. The highest value for litter size born was for Spring lambing (1.62), and the highest litter size at weaning was for Winter lambing (1.32), with the lowest litter size at weaning occurring for Late Summer lambing (1.00), and Spring lambing was intermediate (1.22). The Winter-born lambs were lighter but fatter (P < 0.05), and Spring-born lambs were leaner with higher leg conformation and carcass quality scores. The Late Summer-born lambs were not different from Spring-born lambs.
Factors that influence the choice of production system as listed by Notter and McClaugherty (1991) are: availability and cost of feedstuffs, availability of shelter at lambing, annual fluctuation in lamb prices, competition for labor from other farm enterprises, and cash flow patterns for the entire farm operation, all which affect profitability of the production system. The most important factor affecting profitability of a sheep enterprise, as suggested by several authors (Cloete and Heydenrych, 1987; Schoenian and Burfening, 1990; and Wilson and Morrical, 1991), is reproductive level, best measured by the number of lambs born within a specific interval, i.e., prolificacy (Wilson and Morrical, 1991). Management system influences productivity through prolificacy and the number of lambs marketed, as well as the weight and quality of marketed lambs, upon which income is based. The objective of this study was to evaluate the influence of three production systems (intensive, extensive, and intermediate) on litter size, lamb growth, and carcass characteristics in sheep.
Animals. Data were collected from three flocks of sheep, each maintained under a different management system (Winter, Spring, or Late Summer) at the Eastern Ohio Resource and Development Center at Belle Valley, for a period of 3 years (1989, 1990, and 1991). Three sire breeds (Cheviot, Rambouillet, and Suffolk) were randomly mated to three dam breeds (Synthetic-X, Native-X, and Florida Native).
Management Systems. The three management systems were distinguished by season of lambing and management practices as shown in Table 1. The Winter system represented the common practice of lamb producers in Ohio. Lambing was from January 1 through February 15 inside a barn. Following lambing, ewes with their lambs were placed in pens and fed hay and concentrate. Lambs were kept in feedlot until the end of the test. The Spring system, an alternative production system, used a minimum input of labor and maximum grazing. Lambing was on pasture without assistance. The pasture contained bluegrass, white clover, and fescue. After weaning, lambs remained on pasture until mid-November and were finished in feedlot. The Late Summer system was intermediate to Winter and Spring systems, characterized by a late breeding season, with lambing and weaning on pasture but finishing in feedlot.
Data and Analyses. The model used for analyzing litter size included breed of ewe, age of ewe, breed of ram, season-management system, year, interactions of breed of ewe with breed of ram, breed of ewe with system, breed of ram with system, year with system, ewe age with system, and ewe breed with ewe age. The model for analyses of growth and carcass traits included breed of ewe, breed of ram, season-management system, sex, and type of birth. Influence of the independent factors on litter size, growth, and carcass traits was analyzed by general linear models methodology. Least squares means for factor levels were obtained and compared using t-tests. More detailed description of materials and methods was provided by Dimsoski (1992).
Litter Size Born and Weaned. Number of lambs born was influenced (P < 0.01) by dam age and lambing season (Table 2), and these results were reported previously by Dimsoski et al. (1992, 1994). Litter size born in Late Summer was lower (P > 0.05) than that in Spring. Results indicated the expected reduction in prolificacy of fall-bred relative to spring-bred ewes. Similar results were reported by Vesely and Peters (1965), Dickerson and Glimp (1975), Notter and Copenhaver (1980), and Fogarty et al. (1984). Litter size born for Late Summer lambing was lower than reported in other studies. This could be due to the fact that the breeding season for Late Summer lambing was from March 23 to May 5, which was earlier than in the other studies. Litter size born was highest for Synthetic-X (1.52), and lowest for Florida Native (1.26), with Native-X being intermediate (1.45). Contrary to litter size born where the highest value was for Spring lambing (1.62), the highest litter size at weaning was for Winter lambing (1.32), with the lowest litter size occurring for Late Summer lambing (1.00), and Spring lambing was intermediate (1.22). This was expected because Synthetic-X was developed for high reproductive performance under the same environment as this trial. Sire breed did not influence (P > 0.05) litter size. Age of dam affected litter size (P < 0.05). Three-, 4-, and 5-year-old ewes had the highest litter size (1.65), while 1-year-olds had the lowest (1.00). Six-year-old and older ewes had lower litter sizes than 3-, 4-, and 5-yr-olds but larger litters than 1- and 2-year-olds. Similar curvilinear effects of age of dam on prolificacy were reported by Sidwell and Miller (1971), Dickerson and Glimp (1975), Martin et al. (1981), Clarke and Hohenboken (1983), Ercanbrack and Knight (1985), and Gunn et al. (1986). Ewe breed by system interaction influenced (P < 0.01) both litter size born and litter size weaned. Highest (P < 0.05) litter sizes born for ewe breed by system combination were for Synthetic-X lambing in Winter and Spring systems, 1.67 and 1.66, respectively; however, for litter size weaned, only Synthetic-X in the Winter system had a higher (P < 0.05) value. Lamb losses from birth to weaning were higher in the Spring system (25%) than in Winter and Late Summer systems (11%). However, pregnancy rates (number of mated to number of ewes that lambed) were 80,95, and 29% for Winter, Spring, and Late Summer, respectively; therefore, the Spring system produced the most lambs. In addition, on a separate trial where lambing date for Spring system was 2 weeks later (late April to first half of May), lamb losses for Spring system were not higher than 10% (J. Clay, unpublished). The Spring system appeared to maximize lamb production.
| Table 1. Season management calendar. | |||
| System | |||
| Item | Winter | Spring | Late Summer |
| Vasectomized teaser
ram exposure |
July 24 to August 8 | November 7 to November 22 | March 8 to March 23 |
| Breeding season | August 8 to September 22 | November 22 to January 5 | March 23 to May 5 |
| Lambing season | January 1 to February 15 | April 15 to May 30 | August 15 to September 22 |
| Lambing site | Barn | Pasture | Pasture |
| Castration | 10 4 days of age | June 5 | October 5 |
| Weaning date | 50 8 days of age | July 15 | November 15 |
| Postweaning management | Feedlot | Pasture, feedlot | Feedlot |
| Table 2. Least squares means and standard errors for litter size born and weaned by dam breed, sire breed, year, system, and damage at lambing. | |||||
| Class1 | |||||
| Effect | Litter size | 1 | 2 | 3 | 4 |
| Dam breed2 | Born | 1.45 ± 0.07ab | 1.26 ± 0.10a | 1.52 ± 0.10b | . . . |
| Weaned | 1.19 ± 0.08 | 1.12 ± 0.12 | 1.22 ± 0.11 | . . . | |
| Sire breed | Born | 1.35 ± 0.08 | 1.41 ± 0.08 | 1.45 ± 0.08 | . . . |
| Weaned | 1.23 ± 0.09 | 1.22 ± 0.09 | 1.08 ± 0.12 | . . . | |
| Year | Born | 1.44 ± 0.85 | 1.45 ± 0.09 | 1.33 ± 0.10 | . . . |
| Weaned | 1.21 ± 0.09 | 1.16 ± 0.09 | 1.17 ± 0.12 | . . . | |
| System3 | Born | 1.49 ± 0.08ab | 1.62 ± 0.05a | 1.12 ± 0.18b | . . . |
| Weaned | 1.32 ± 0.09 | 1.22 ± 0.06 | 1.00 ± 0.21 | . . . | |
| Dam age3 | Born | 1.00 ± 0.23a | 1.40 ± 0.08a | 1.65 ± 0.05b | 1.63 ± 0.09b |
| Weaned | 0.98 ± 0.27 | 1.21 ± 0.09 | 1.25 ± 0.06 | 1.26 ± 0.10 | |
| 1 Dam breed: 1 = Native-X, 2 = Florida native, and 3 = Synthetic-X; sire breed: 1 = Cheviot, 2 = Rambouillet, and 3 =
Suffolk; year: 1 = 1989, 2 = 1990, and 3 = 1991; system: 1 = Winter, 2 = Spring, and 3 = Late Summer; age of dam at
lambing: 1, 2, 3 through 5, and > 6 years old.
2 Influence (P < 0.10) on litter size born. 3 Influence (P < 0.01) on litter size born. ab Means within a row with a common superscript do not differ (P > 0.05). | |||||
Lamb Growth. The results for influence of dam breed, sire breed, sex, and management system were reported by Dimsoski et al. (1993). Preweaning daily gain of lambs was different (P < 0.05) for different ewe breeds in all three systems (Table 3). Preweaning daily gain was 0.514, 0.415, and 0.394 pounds for lambs of Native-X, Florida Native, and Synthetic-X ewes, respectively (Table 4). Differences among breeds of dam for postweaning daily gain were significant only for the Winter system. However, Native-X had a highest (P < 0.05) lifetime daily gain across systems (0.415 vs 0.367 and 0.353 pounds for Florida Native and Synthetic-X, respectively), and within the Spring system (0.332, 0.301, and 0.305 pounds for Native-X, Florida Native, and Synthetic-X, respectively). These results implied that Native-X dams had better milking ability, not only under optimal conditions (Winter system) but also under a more restricted environment (Spring system). More rapid growth resulted in a younger (P < 0.05) slaughter age for lambs of the Native-X ewes.
Carcass Characteristics. The results for influence of breed, season of lambing (management system), and sex on carcass characteristics of lambs were reported by Dimsoski et al. (1994). System influenced (P < 0.01) all carcass traits except the ribeye area (Table 4). Spring lambs were heaviest and oldest (P < 0.05) at the end of test and at slaughter. Winter lambs were younger (P < 0.05) at slaughter (130 days) compared with Spring and Late Summer lambs (270 and 200 days, respectively). Consequently, Winter lambs had the lowest (P < 0.05) hot carcass weight, chilled carcass weight, quality grade, and leg conformation score (Meat Evaluation Handbook, 1983). Winter lambs also had the thickest backfat and percentage of kidney and pelvic fat. Also, the Winter system produced lambs that weighed less. Thus, an intensive management system where animals were fed concentrate diet and were confined, which restricted exercise, tended to shift metabolism toward fat production at a younger age. The Spring system produced leaner and better quality carcasses (i.e., higher quality grade and leg conformation score) compared with Winter (P < 0.05). Carcass traits of Late Summer lambs were similar to those of Spring lambs, except for dressing percentage, which was closer to that of Winter lambs. Notter et al. (1991) reported higher carcass quality for lambs born in November to January that were creep fed until weaning and finished on a high energy diet compared with lambs born in March and April that were creep fed until the onset of spring grazing and finished on pasture. Jones et al. (1984) reported no differences in carcass characteristics and composition between concentrate- and pasture-fed lambs when adjusted for subcutaneous fat. They concluded that, within breed, live weight or carcass weight was more important in determining body composition than growth performance or plane of nutrition, except for animals with a very high growth performance. This is not supported by the current study, because the pasture-fed lambs (Spring system), although heavier (P < 0.05) (93.3 pounds) at the end of the test than concentrate-fed lambs (84.5 pounds), had less actual and adjusted backfat and a lower percentage of kidney and pelvic fat. Ely et al. (1979) reported that a pasture plus concentrate system (comparable to Spring and Late Summer system) produced the highest quality carcasses.
In addition to leaner and better quality carcasses, the Spring management system had highest pregnancy rate and highest litter size born. The higher mortality rate of spring-born lambs can be reduced by having late-April instead of mid-April lambing. In addition, older (260 days), spring-born lambs had bigger and better quality carcasses than younger (125 days), winter-born lambs. This can be important in obtaining larger quantities and better quality of lamb's wool, an additional income to sheep enterprises.
| Table 3. Least squares means for lamb growth traits by system1 and dam breed. | |||||||
| System | Dam
breed2 |
n | Preweaning
ADG |
Postweaning
ADG |
Lifetime
ADG |
Final
weight |
Slaughter age |
| (Pounds) | - (Days) - | ||||||
| * | * | * | |||||
| Winter | 1 | 29 | 0.646a | 0.640a | 0.640a | 86 | 121 ± 2a |
| 2 | 10 | 0.543b | 0.545b | 0.547b | 80 | 135 ± 4b | |
| 3 | 4 | 0.520b | 0.735a | 0.632 | 85 | 124 ± 7 | |
| * | * | * | |||||
| Spring | 1 | 86 | 0.487a | 0.252 | 0.332a | 93 | 255 ± 3a |
| 2 | 32 | 0.392b | 0.256 | 0.301b | 91 | 275 ± 5b | |
| 3 | 27 | 0.384b | 0.264 | 0.305b | 95 | 287 ± 5b | |
| * | |||||||
| Late
Summer |
1 | 20 | 0.442a | 0.431 | 0.438 | 91 | 192 ± 4a |
| 2 | 6 | 0.301b | 0.417 | 0.365 | 84 | 209 ± 7b | |
| 3 | 4 | 0.334b | 0.407 | 0.384 | 82 | 198 ± 9 | |
| * | * | * | * | ||||
| Average | 1 | 135 | 0.514a | 0.365 | 0.415a | 91a | 215 ± 5a |
| 2 | 48 | 0.415b | 0.340 | 0.367b | 86b | 235 ± 9b | |
| 3 | 35 | 0.394b | 0.334 | 0.353b | 91a | 258 ± 10b | |
| 1 See Table 1.
2 1 - Native-X; 2 = Florida Native; 3 = Synthetic-X. 3 n = Number of lambs. * Effect (P < 0.05) of dam breed. ab Means within a column and system with a common superscript do not differ (P > 0.05). | |||||||
| Table 4. Least squares means for lamb carcass traits by system. | |||
| Season-management system1 | |||
| Trait | Winter | Spring | Late Summer |
| Weight off-test, pounds2 | 84.5a | 93.3b | 88.8a |
| Slaughter weight, pounds2 | 80.3a | 86.9b | 82.6a |
| Hot carcass weight, pounds2 | 46.2a | 50.4b | 48.7b |
| Chilled carcass weight, pounds2 | 45.0a | 49.1b | 47.7b |
| Quality grade2 | 11.1a | 11.3b | 11.4b |
| Backfat thickness, inches2 | 0.20a | 0.14b | 0.14b |
| Adj. backfat thickness, inches2 | 0.22a | 0.15b | 0.16b |
| Leg conformation score2 | 10.8a | 11.3b | 11.5b |
| Percentage kidney and pelvic fat2 | 3.3a | 3.1b | 3.1ab |
| Yield grade2 | 3.3a | 2.9b | 2.9b |
| Ribeye area, inches | 2.23 | 2.27 | 2.27 |
| Ribeye area per 99.88 pounds2 final weight | 4.6a | 4.3b | 4.5ab |
| Dressing, % | 54.6a | 53.1b | 55.1a |
| 1 Season-management systems are described in Table
1.
2 Season-management system effect (P < 0.01). ab Least squares means in a row with same superscripts do not differ (P > 0.05). | |||
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