Progress 10/01/02 to 09/30/07
Outputs
The early neonatal period is a time of high losses lamb losses. In initial research we demonstrated, percentage Dorper breeding increases lamb vigor to a similar degree as other crossbreeding programs and produces lambs with perform somewhat similarly to other crossbred lambs although with reduced average daily gain relative to percentage Hampshire sheep. We also observed mid-gestation transport results in lighter lambs at birth. Additionally, we observed undernourishment around the time of conception can increase morbidity. Lambs born before full term are at risk for reduced survival and growth. Some ewes, for a variety of reasons, may have reduced nutrition and lose body condition during this time period. Thus, ewes which lose body condition during the breeding season may be at risk of having a reduced gestation length. Body condition scoring of ewes before and after mating could be a potential producer intervention to identify ewes at risk of having shorten gestation
length and thus low lamb survival. Therefore, this study was designed to determine if change in body condition score during the breeding season impacted gestation length. One-hundred eighty ewes (Hampshire, Columbia, Finn-Dorset-Targhee, Finn-Dorset-Targhee-Dorper, or Finn-Dorset-Targhee-Polypay) were exposed to rams (Hampshire, Columbia, or Polypay) fitted with marking harnesses. Ewes were maintained in Brookings, SD (44.3 N 96.8 W) and exposed to rams beginning on September 9, 2005. Ewes were maintained with the rams for 35 day breeding season. Breeding marks were recorded twice daily. Ewes were body condition scored by a trained evaluator the day rams were introduced, and by the same evaluator following removal of the rams. Pre- and post-ram exposure body condition scores were compared and ewes were classified as losing, gaining, or maintaining body condition. Gestation length was calculated as the number of days from observation of the breeding mark until day of lambing. Only ewes
which lambed were included in the analysis (140 ewes). Data were tested by ANOVA using JMP software (SAS Inc., Cary, NC) for effect of change in body condition, sire breed, and the interaction on gestation length. Change in body condition did not effect gestation length (P = 0.23). Although Columbia sheep had a significantly longer gestation length than Hampshire or crossbred sheep (P = 0.0002), there was no interaction of breed with change in body condition detected (P = 0.75). These data suggest that change in body condition during the breeding season does not impact gestation length.
Impacts
Our initial research indicated producers may limit lamb losses by crossbreeding and avoiding transportation of ewes during mid-gestation. Additionally, undernourishment around the time of conception leads to increased morbidity. However, change in body condition is not a useful tool for identification of ewes at risk of having a reduced gestation length and weaker lambs associated with shortened gestation length.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
To test the impact of transportation stress during gestation, 51 ewes were divided into 5 groups: transportation during early gestation (day 40-50 of gestation), mid-gestation (day 75-85 of gestation), late gestation (day 115-125 of gestation), at all time points or no transportation. Breeding marks were recorded twice daily, and date of first breeding mark was considered day 1 of gestation. Ewes in one group were all transported on the same day; therefore, for each transportation group a range of 10 days of gestation were represented. For the transportation, ewes were loaded on a trailer and transported for approximately 2 hours on a predetermined route of approximately 160 km. All transported ewes were transported with the same trailer on the same route. Data were tested for effects of transportation on gestation length using ANOVA with number of lambs born and sex of lambs born used as covariates. Data were tested for effects of transportation on birth weight,
crown to rump length, thoracic girth, and age adjusted weaning weight using ANOVA with sex, type of birth, and type of rearing as covariates. Weaning weights were adjusted to a constant age of 93 days (the mean age at weaning). Transportation did not effect gestation length (P = 0.69). Transportation did affect birth weight (P = 0.02) such that lambs born to ewes transported in mid-gestation were lighter than lambs born to ewes transported in early gestation, at all time points or not transported (4.0 +/- 0.2 kg vs. 5.0 +/- 0.2 kg, 4.9 +/- 0.2 kg, or 4.7 +/- 0.2 kg respectively; P > 0.04) and tended to be lighter than lambs born to ewes transported in late gestation (4.0 +/- 0.2 kg vs. 4.6 +/- 0.2 kg, respectively; P = 0.07). Lambs born to ewes transported in mid-gestation also tended to have reduced thoracic girths relative to lambs born to ewes transported in early gestation, late gestation, at all time points, or not transported (38.6 +/- 0.8 cm vs. 41.4 +/- 0.8 cm, 40.4 +/- 0.8
cm, 40.9 +/- 0.8 cm, or 40.4 +/- 0.8 cm, respectively; P < 0.10). Transportation did not affect crown to rump length or age adjusted weaning weights (P > 0.33). These results indicate mid-gestation transport results in lighter lambs at birth.
Impacts
Lighter lambs at birth are at higher risk of having morbidity and mortality problems. These results indicate transportation stress during mid-gestation results in lighter lambs at birth. Producers should avoid transportation stress during mid-gestation.
Publications
- Daniel, J.A., and Held, J.E. 2006. Carcass and growth characteristics of wethers sired by percentage White Dorper or Hampshire rams. Sheep and Goat Research (in press).
- Brake, D.G. and Daniel, J.A. 2005. Impact of nutrition and body condition score at conception on gestation length. J. Anim. Sci. 83(Suppl. 1):65.
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Progress 01/01/04 to 12/31/04
Outputs
Stress on pregnant females can have profound impacts on survival and development of the offspring. Nutritional restriction of pregnant females is a stress that has been extensively studied during mid and late gestation. However, very little work has been done on nutritional restriction of pregnant females immediately prior to and following conception and its impact on development of the offspring. During this period nutrient needs of the offspring are minimal and have been thought to be largely outside of the impact of maternal nutrient status. To test impact of nutritional restriction around conception on lamb survival, crossbred ewe lambs were assigned to be undernourished (U; n=34) or well-fed (W; n=34). At 30 days before breeding, U ewes were fasted for 2 days, and then group fed 50% of the requirements of replacement ewe lambs (NRC, 1985). W ewes were fed concentrates at 3-4% of body weight/day. Ewes were exposed to a teaser ram by fence-line contact for two
weeks prior to exposure to semen-tested rams fitted with marking harnesses. Twenty-four hours after marking, one-half of the U ewes were switched to the W group, and one-half of the W ewes were switched to the U group and fed the restricted diet for 30 more days. This made a total of four treatment groups: UU (undernourished pre-breeding and undernourished post-breeding), WU (well-fed pre-breeding and undernourished post-breeding), UW (undernourished pre-breeding and well-fed post-breeding), and WW (well-fed pre-breeding and well-fed post-breeding). By 30 days after the last breeding date, all ewes were on 100% maintenance diet for pregnant ewe lambs. Ewe's body condition score (scale 1-5) was recorded at the initiation of the study, at conception, and 30 days after conception. Lamb's birth date, birth weight, morbidity and mortality were recorded. Gestation length was calculated as the number of days from the ewe's breeding mark until the lamb's birth date. Gestation length and lamb
birth weight were analyzed as a 2 X 2 factorial using GLM procedures for SAS. CATMOD was used to analyze effect of treatment on morbidity and mortality. Undernourishment of the ewe before or after conception did not alter gestation length (p = 0.6005). However, four ewes lambed at 141 days of gestation or less; these ewes were all in undernourished before conception. Since ewes were fed by group, there was some variation in body condition score at conception within treatment groups. Thin ewes (BCS <3) had a shorter gestation length than good or fat condition ewes (BCS 3 and > or = 4, respectively; p = 0.0212). There was a tendency for an interaction of body condition score with post conception nutrition (p=0.0624). Undernourishment of the ewe before or after conception did not effect lamb birth weight (p = 0.3854). However, there was an interaction (p = 0.0505) between pre (ewe undernourished before conception) and post (ewe undernourished after conception) for lamb morbidity. These
results indicate that poor body condition at conception can result in shortened gestation length. Furthermore, undernourishment around the time of conception can increase morbidity.
Impacts
Ewes in thin body condition at conception have shorter gestation lengths. Short gestation length is often associated with increased mortality. These data indicate ewes need to be in adequate body condition at conception.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
The early neonatal period is a time of high losses lamb losses. One approach to reducing neonatal losses would be to introduce breeds with genetics reported to have increased lamb vigor. One breed that has been reported to have increased lamb vigor is the Dorper. In order to evaluate the ability of utilizing percentage Dorper breeding to enhance lamb vigor, as well as modify other production traits of interest, commercial Finn-Dorest-Targhee (FDT) composite ewes were exposed to 3/4 Dorper 1/8 East Fresian 1/8 Corriedale rams (n=4). At birth lambs were assigned a vigor score (scale of 0 to 5 with 0 being near dead and 5 being actively nursing before dry) to assess lamb vigor. Vigor scores were collected on 730 sheep consisting of purebred Columbia and Hampshire breeding, FDT composite, or FDT composites crosses to contain 3/8 Dorper, 3/16 Dorper, 1/2 Hampshire or 1/2 Polypay breeding. Mean vigor score was significantly effected by breed (P = 0.004). Sheep of 3/8 Dorper
breeding had a greater vigor score than purebred Columbia and Hampshire sheep (3.82 versus 3.51 and 3.54 respectively, P < 0.033) and tended to have a greater vigor score than 3/16 Dorper and 1/2 Hampshire sheep (3.82 versus 3.58 and 3.63 respectively, P < 0.0095). Sheep of 1/2 Polypay breeding also had a greater vigor score than purebred Columbia and Hampshire sheep (3.73 versus 3.51 and 3.54 respectively, P < 0.058). In terms of other production traits of interest, 3/8 Dorper sheep did not differ from 1/2 Hampshire sheep for birthweight (P = 0.5475), actual weaning weight (P = 0.2716), adjusted weaning weight (P = 0.5067), or ribeye area (P = 0.2224). However, 3/8 Dorper sheep had a reduced post-weaning average daily gain relative to 1/2 Hampshire sheep (P = 0.0367). In some preliminary breeding work, 61% of 3/8 Dorper ewe lambs exposed in a 35 day breeding season for February lambing lambed with a 120% lambing rate (lambs born/ewe lambing times 100). Seventy-seven percent of 3/8
Dorper yearling ewe lambs exposed in a 35 day breeding season for September lambing lambed with a 155% lambing rate. In summary, thus far percentage Dorper breeding increases lamb vigor to a similar degree as other crossbreeding programs and produces lambs with perform somewhat similarly to other crossbred lambs although with reduced average daily gain relative to percentage Hampshire sheep.
Impacts
We anticipate this work will aid producers in making decisions which should help to reduce neonatal lamb losses. Crossbreeding will enhance lamb vigor relative to the use of purebred sheep. Use of the Dorper breed appears to be an acceptable cross to use in this manner.
Publications
- No publications reported this period
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