Effects of genetic and environmental factors on pre-weaning and post-weaning growth in West African crossbred sheep

Effects of genetic and environmental factors on pre-weaning and post-weaning growth were studied in West African crossbred sheep. Effects of lamb genotype (7/8 Sahelian–1/8 Djallonké, 3/4 Sahelian–1/4 Djallonké and 1/2 Sahelian–1/2 Djallonké; hereafter denoted 7/8Sa, 3/4Sa and 1/2Sa, respectively), parity, type of birth, sex of lamb and year-season of lambing on birth weight, weaning weight, 8-month weight and pre- and post-weaning growth rates were determined. At birth 7/8Sa and 3/4Sa lambs were heavier (p<0.01) than 1/2Sa lambs. Lambs born to first-parity ewes were lighter (p<0.01) at birth than lambs of older ewes. At weaning and 8 months of age, lambs born to fourth-parity ewes were heavier (p<0.05) than those born to ewes of the other parities. Parity did not have any significant effects on pre-weaning growth rate. Lambs born in the rainy season of 2001 were significantly heavier at birth and at 8 months of age than those born in the dry season of 2001/02, but there was no difference between the two groups at weaning. Pre-weaning growth rate was significantly faster in lambs born in the dry season of 2001/02 but the reverse was true for post-weaning growth rate.     

Breed and environmental influences on weaner lamb production in Zimbabwe

Performance of the Dorper and Mutton Merino breeds and their crosses was assessed from 1,305 ewe and 1,453 lamb records from six lambing seasons. Dorper and Mutton Merino were mated in all combinations under an accelerated lambing system and crossbred females were mated to Suffolk rams. The Dorper and Mutton Merino breeds were not significantly different for fertility, pre-weaning lamb growth and survival. Suffolk sired lambs from crossbred ewes grew rapidly and were heaviest at birth and at weaning. They also survived better than lambs from the other breeding groups and this contributed to the higher weaning rate (P less than 0.05) in crossbred ewes. Weight of weaned lambs per ewe exposed to the ram per season was 12% higher (P less than 0.05) in the Dorper than the Mutton Merino ewes. However lifetime production was 28% higher (P less than 0.01) in Mutton Merino ewes due to significantly superior longevity. Crossbred ewes were highly productive. Individual heterosis was not significant but estimates were positive for most traits. Growth rate and survival of lambs increased as age of dam increased to 48 and 40 months respectively. Lambs born to previously non-lactating ewes were heavier and survived better than lambs born to ewes lactating in the previous season. Lambs born and reared as singles were 25% heavier at birth (P less than 0.001) and 52% heavier at weaning (P less than 0.001) than those born and reared as twins. Male lambs grew faster and were 7% heavier at weaning than females (P less than 0.001).     

Parameter estimates for number of lambs born at different ages and for 18-month body weight of Rambouillet sheep

Genetic parameters were estimated using REML with animal models for number of lambs born and 18-mo body weight in Rambouillet sheep. Number of lambs born was modeled either as repeated measurements on the same trait or as different traits at different ages. The original data for number of lambs born were separated according to age of the ewe into two classes: 2 and 3 yr, and older than 3 yr. Numbers of ewes with lambing records for the age classes were 653 and 466 with 1,106 and 1,118 records, respectively. For the data set that included all ages, the number of ewes was 684 with 2,224 records, and for 18-mo body weight the number of ewes measured was 557. For number of lambs born, the animal model included random genetic, permanent environmental, and residual environmental effects and fixed effects for age of ewe, year of lambing, and month of year of lambing. Lambing day within season was used as a covariate. For 18-mo body weight, year of birth of ewe was used as a fixed effect. Actual age in days when the ewe was weighed was used as a covariate. Estimates of heritability for number of lambs born by age group were .04, for 2- and 3-yr old ewes, and .06, for ewes greater than 3 yr old, from the two-trait (two age of ewe classes) analyses and .06 when all ages were included. Estimates of heritability for number of lambs born from the single-trait analyses were somewhat less than estimates from two-trait analyses. Estimate of genetic correlation between number of lambs born for the 2 and 3 yr and the >3 yr classes was near unity (1.00), which suggests that a repeated measures model for number of lambs born is adequate for making selection decisions. Estimate of genetic correlation between number of lambs born and 18-mo body weight was .35 with a heritability estimate of .48 for 18-mo body weight. The estimate of genetic correlation suggests that selection for increased number of lambs born would result in increased 18-mo body weight.     

Reproductive performance of Suffolk and Suffolk-cross ewes and ewe lambs exposed to vasectomized rams before breeding

Multiparous Suffolk and Suffolk-cross ewes were randomly allotted to treatments within breed and year to measure effects of ram exposure, during transition from anestrus to breeding activity, on reproductive performance. Treatments were: 1) ewes joined with two mature vasectomized Rambouillet rams for 15 d before breeding (DC), 2) ewes maintained across a net wire fence from two vasectomized rams for 15 d before breeding (FC) and 3) ewes maintained approximately 400 m away from rams (NC). At the end of the 15 d, all ewes were placed in one pasture and mated to three fertile Suffolk rams during a 34-d breeding season. A total of 96 Suffolk and 177 Suffolk-cross ewes was utilized during the 3-yr experiment. A greater (P less than .05) prebreeding ovulation percentage was observed in DC and FC than in NC ewes. Mating and lambing occurred approximately 6 d earlier for DC or FC ewes than for NC ewes. A similarly designed experiment was conducted using Suffolk and Suffolk-cross ewe lambs allotted to treatments within breed and year to measure effects of ram exposure during the natural breeding season, but prior to breeding. Treatment differences were not detected (P greater than .05) for date of first observed estrus, date of lambing, percentage of ewes lambing in the first 17 d of the lambing season, number of lambs born per ewe lamb exposed or number of lambs born per ewe lamb giving birth.     

Performance of Djallonké Sheep under an Extensive System of Production in Faranah,Guinea

A total of 147 ewes, 4 rams and 188 lambs of their progeny of the Djallonké breed of sheep were used to study the factors affecting reproductive and growth traits and the causes of lamb mortality. Data on ewes were collected during a 12-month period, while those on the lambs born to 123 of the ewes were collected until they were 12 months of age. The average fertility and abortion rates were 0.84 and 0.09. The fertility rate increased and the abortion rate decreased with increasing age of the ewes (p<0.05). The number of lambs born per ewe joined, litter weight at birth per ewe joined and litter weight at weaning per ewe joined were 1.28, 3.5 kg and 17 kg, respectively. The average numbers of lambs born per ewe, lambs born alive per ewe, lambs born dead per ewe and lambs per ewe that died between birth and weaning were 1.53, 1.43, 0.03 and 0.3, respectively. The age of the ewes significantly (p<0.05) affected all these traits except the number of dead lambs and the index of fertility (94%). The age of the ewes significantly (p<0.05) affected the birth weight and the weight at 6 and 12 months of age, whereas the lambing season significantly (p<0.05) affected all the growth traits studied. The type of birth was the most important source of variation in body weights of lambs. Sex had no significant (p>0.05) effect on the growth traits studied. The complex `starvation–bad management–light body weight at birth' caused 48% of the lamb mortality between birth and weaning, while diarrhoea, pneumonia and internal and external parasites caused approximately 52% of the lamb mortality over the same period. The seasonal raw mortality rate of the lambs before weaning was highest in the humid season.     

Effects of ewe breed and management system on efficiency of lamb production: II. Lamb growth, survival and carcass characteristics

Lamb growth, survival and carcass characteristics were compared for progeny of either 1/2-Suffolk, 1/2-Rambouillet (Western) ewes or 1/2-Suffolk, 1/4-Rambouillet, 1/4-Finnsheep (1/4-Finn) ewes produced over 3 yr in three different management systems. System 1 lambs were born in late fall and fed to slaughter on a concentrate diet. System 2 lambs were born in January and February and grazed pure stands of alfalfa or ladino clover after weaning. System 3 lambs were born in March and April and remained with their dams on native bluegrass-white clover pasture throughout the grazing season. Lambs were slaughtered as males reached 55 kg and as females reached 50 kg. One-half of the males in System 1 were left intact; all males in Systems 2 and 3 were castrated. Lamb survival did not differ among systems. Lambs from yearling 1/4-Finn ewes had higher survival rates than lambs from yearling Western ewes, but at older ewe ages, progeny of the ewe groups did not differ in survival. Lambs in System 1 grew fastest (mean lifetime gains of 310 +/- 4 g/d) and were youngest at slaughter (156 +/- 3 d), and lambs in System 3 were oldest at slaughter (234 +/- 2 d). System 2 lambs differed considerably among years in growth rate and slaughter age (mean slaughter ages of 191, 230 and 193 d across years), primarily in response to differences in rainfall. Lifetime gains and slaughter ages of lambs did not differ between ewe breeds. Ram lambs grew 15% faster than wethers and were leaner. Differences among systems in carcass traits were small. System 1 lambs tended to be fattest and System 2 lambs leanest. Progeny of 1/4-Finn ewes had higher subjective scores for carcass fatness (e.g., feathering, flank fatness) and conformation but did not differ from progeny of Western ewes in objective measures of fatness (e.g., backfat, yield grade).     

THE INCIDENCE OF DYSTOCIA IN DORSET HORN EWES

The incidence of dystocia was recorded in flocks of Dorset Horn ewes lambing in winter, spring or summer and grazed at 8, 12 or 16 ewes per hectare over a ten-year period. The mean incidence of dystocia was 34% of ewes lambing. Significantly more ewes experience a difficult birth at winter (35%) and spring (39%) than summer (26%) lambings. Neither stocking rates nor pre-lambing ewe bodyweight were related to the incidence of dystocia. The incidence of dystocia was significantly greater in 2-year-old ewes than in any other age group. Foetal size was of major importance in the occurrence of dystocia. Approximately 60% of single and twin born lambs that had birth weights greater than 4.5 kg had a difficult birth whereas in lambs weighing less than 3.2 kg only about 10% were affected. Thirty-six per cent of all perinatal mortality was attributable to dystocia. Approximately 27% of single and 73% of twin presentations in assisted births were abnormal, 31% of all lambs assisted had 1 or both legs retained, 4% had posterior (including breech) presentations and the remaining 8% were of varied forms of malpresentation. Significantly more single male than female lambs experienced a difficult birth and the mean birth weights of single, twin and triplet born lambs that had a difficult birth were greater than the birth weights of singles, twins and triplets born normally.     

Frequency and cost of human intervention at lambing: an interbreed comparison

The frequency of human intervention during lambing was assessed for 708 lambs and 162 ewes in up to four deliveries. In total, 21.8 per cent of the lambs born alive required some assistance at birth and 9.4 per cent were delivered manually. Assistance was required less frequently by twin lambs and ewe lambs, and Scottish blackface lambs required assistance less frequently than Suffolk lambs. Approximately one-third of the ewes were assisted in at least one delivery and 10 per cent were assisted in all their deliveries; however, less than 20 per cent of ewes were assisted more than once. A quarter of the lambs needed some human intervention to suck successfully, and Suffolk lambs needed help more frequently. The lambs born to almost half the first-parity ewes needed help to suck, but at later deliveries the lambs born to less than a third of the ewes needed assistance. In blackface flocks the survival of 100 lambs required 4.6 hours of human intervention whereas in Suffolk flocks 28 hours were required.     

Effect on the ewe and lamb of low zinc intake throughout pregnancy

Throughout pregnancy, 30 primiparous Finn cross ewes were given a low Zn (less than or equal to 1 ppm) semi-purified diet. A 100-g hay supplement was fed three to seven times/week. Supplemental Zn (20 ppm) was provided in the drinking water of 14 ewes. At parturition, lambs were removed from ewes before suckling. Viable lambs not taken for tissue analysis were given 200 ml cow colostrum and raised on an artificial feeder. Throughout gestation, unsupplemented (-Zn) ewes gained less weight and had lower plasma Zn levels than Zn-supplemented (+Zn) ewes. One -Zn ewe was not pregnant, three aborted, one resorbed, one delivered mummified twins at term and two delivered malformed lambs. Average weight of lambs born to -Zn ewes d 136 or later (excluding mummified twins and one weighing less than 20% as much as its twin) was 1.8 +/- .6 (SE) kg. Only three lambs born to -Zn ewes were vigorous enough to put on the artificial feeder; none survived. One +Zn ewe was not pregnant. Of 23 lambs born to the remaining +Zn ewes, five were used for tissue analysis, two lambs of triplets were born dead, twins born d 138 died at birth. One twin died 6 d after birth. The 14 remaining lambs were weaned in good health. Average birth weight of +Zn lambs was 3.3 +/- 1.0 kg. Increased salivation was seen in -Zn ewes after 6 wk of low Zn intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: II. Reproduction of F1 ewes in fall mating seasons

Objectives were to estimate effects of sire breed (Dorset, Finnsheep, Romanov, Texel, and Montadale), dam breed (Composite III and northwestern whiteface), mating season (August, October, and December), ewe age (1, 2, and 3 yr), and their interactions on reproductive traits of F1 ewes. A total of 1,799 F1 ewes produced 3,849 litters from 4,804 exposures to Suffolk rams during 35-d mating seasons over 3 yr. Ewes were weighed at breeding. Conception rate and ewe longevity (present or absent at 42 mo of age) were determined. Number born and litter birth weight were recorded, and number and weight at weaning and 20 wk of age were analyzed separately for dam- and nursery-reared litter mates. Total productivity through 3 yr of age for each ewe entering the breeding flock was calculated as the sum of 20-wk weights for dam- or nursery-reared lambs. Interactions of sire breed x mating season, sire breed x ewe age, and mating season x ewe age were generally significant, whereas interactions of sire breed, mating season, and ewe age x dam breed were seldom detected. Interactions of sire breed x mating season were often due to changes in rank as well as magnitude, indicating the importance of matching sire breed to a specific mating season. The number born to Dorset-, Texel-, and Montadale-sired ewes was not affected by dam breed; however, Finnsheep-sired ewes out of northwestern whiteface dams were more prolific than Finnsheep-sired ewes out of Composite III dams, and the opposite situation existed for Romanov-sired ewes. Least squares means of sire breeds (P < 0.001) for total productivity of dam-reared lambs were 98.5, 103.5, 106.9, 124.6, and 154.9 kg/ewe entering the breeding flock for Texel, Dorset, Montadale, Finnsheep, and Romanov, respectively. Superior reproduction of Romanov-sired ewes was due to greater conception rate and prolificacy for each mating season and ewe age, as well as greater ewe longevity. Total productivity of F1 ewes by Composite III dams (125.6 kg) was greater (P < 0.001) than for ewes born to northwestern whiteface dams (109.7 kg), and the effect of mating season increased (P < 0.001) from August to October to December. Litter weight at 20 wk of age of 2- and 3-yr-old ewes was similar but greater (P < 0.001) than for 1-yr-old ewes. Experimental results provide comprehensive information about the appropriate use of these breeds in crossbreeding systems to meet specific production-marketing objectives.     

乌鞘岭半农半牧区冷季暖棚全舍饲对绵羊生产效益的影响

于2008年12月－2009年4月在乌鞘岭半农半牧区随机选择10个牧户,各牧户草地类型一致,绵羊体况相近,其中5户采用全舍饲的饲养模式（试验组）,另外5户采用放牧+补饲的饲养模式（对照组）,开展冷季不同饲养模式对绵羊生产效益影响的试验。结果表明,试验组和对照组母羊体质量在产羔后1个月内分别下降了1.17和2.71 kg。产羔1个月后试验组母羊体质量开始恢复,而对照组母羊体质量持续降低;产羔后3个月对照组母羊平均掉膘5.96 kg,占体质量的13.91%,试验组体质量增加0.68 kg。两组羔羊的初生体质量差异不显著(P>0.05),但试验组羔羊生长速度高于对照组,羔羊2月龄体质量及出栏体质量显著高于对照组(P<0.05)。经济效益分析表明,试验组收入较对照组高出20.27元·只-1。     

Straightbred comparison of a composite population and the Suffolk breed for performance traits of sheep

A terminal sire Composite population was formed by mating Columbia rams to Hampshire-Suffolk crossbred ewes. Subsequent generations were produced by inter se mating. The objective was to compare Composite sheep to purebred Suffolks for numerous performance traits. Young ewes lambing at 1 yr of age were evaluated separately from mature ewes (2, 3, 4, and 5 yr old) of each population. Composite and Suffolk populations did not differ significantly in components of litter weaning weight per young ewe joined. Mature Composite ewes produced more wool than Suffolk ewes. Fertility of mature ewes did not differ significantly between populations. The greater prolificacy (P less than .01) of mature Suffolk ewes was offset by a lower survival to weaning (P less than .01), particularly for twin-born lambs. Consequently, mature Composite and Suffolk ewes did not differ for number weaned and litter weaning weight per ewe joined. The average birth weight of lambs born to young and mature Composite ewes was greater (P less than .02) than the average birth weight of Suffolk lambs. The average weaning weight of lambs born to young Composite ewes was greater (P less than .05) than that of lambs born to young Suffolk ewes. Breed differences were not detected for preweaning daily gains, weaning weights, and postweaning daily gains of ewe lambs born to mature ewes. Likewise, weights of ewes at 125 d of age and weights of mature ewes at breeding did not differ significantly between breeds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of ewe breed and management system on efficiency of lamb production: III. Meat characteristics

Effects of management system, ewe breed, sex, and legume grazing on cooking and sensory characteristics and shear force of lamb meat were estimated from data collected on animals produced in three management systems. System 1 lambs were born in late fall and fed to slaughter on a concentrate diet. System 2 lambs were born in January and February and grazed pure stands of alfalfa or ladino clover after weaning. System 3 lambs were born in March and April and remained with their dams on native bluegrass-white clover pasture throughout the grazing season. Lambs were progeny of either 1/2-Suffolk, 1/2-Rambouillet ewes or 1/2-Suffolk, 1/4-Finnsheep, 1/4-Rambouillet or Dorset ewes and were sired by Suffolk rams. Lambs were slaughtered at 50 (females) to 55 kg (males). One-half of the males in System 1 were left intact; all males in Systems 2 and 3 were castrated. Mean age at slaughter was 156, 204, and 234 d for lambs in Systems 1, 2, and 3, respectively. Cooked weight of loin chops averaged 68.5% of uncooked weight and did not differ among systems. Shear force was greatest for System 1 lambs and least for System 3 lambs in yr 1, but systems did not differ in shear performance in yr 2. System differences in tenderness favored System 3 lambs. Although mean flavor intensity was least for System 2 lambs, the frequency of high-intensity, potentially objectionable flavors was highest for these lambs and especially for those grazing alfalfa. In general, however, sensory characteristics did not differ greatly among production systems, and correlation analysis revealed little potential to use carcass traits to predict meat characteristics.     

Studies on transmission of maedi virus to lambs

Lambs born to 5 ewes in 3 successive years were studied for presence of maedi virus and its antibodies. In the middle of the first-year pregnancies the ewes and the only ram of the colony were inoculated with maedi virus. No antibodies or viraemia could be detected in the lambs at birth. After sucking colostrum, antibodies appeared in the lambs of the ewes which themselves were seropositive, and reached their peak in a few days. Maternal antibodies disappeared within 12 weeks in all the lambs. Neutralizing antibodies were demonstrated in the colostrum and their content declined rapidly after lambing. Virus was isolated from the milk of 2 ewes in the third year of the studyIn the first year the spread of maedi virus was demonstrated to only 1 of the lambs, but in the other 2 years maedi virus was detected in tissues of half of the lambs sacrificed at 3–12 weeks of age. It was concluded that lambs born to chronically infected ewes are readily infected, indicating excretion of virus by ewes. The study yielded no information on the specific routes of transmission, except for the finding of the virus in milk of 2 ewes in the third year of the study. No evidence was obtained of transplacental transmission of maedi.     

Seasonal Fluctuation an Inhited Development of Populations of Dictyocaulus filaria in Ewes and Lambs

The fluctuation of populations of Dictyocaulus filaria in sheep was studied under field conditions in which animals are housed during the winter and grazed from late spring to autumn. A comparison was made between residual pasture contamination with overwintered larvae, the fecal larval deposition by ewes from June and both of these factors combined as sources of infection for spring born lambs. Ewes and lambs were killed serially over a year and worms were recovered from the lungs and counted. It was found that during the stabling period most of the ewes were carrying moderate numbers of D. filaria. However, while the vast majority of lungworm populations in the winter was inhibited in development at the early fifth larval stage, virtually all worms in the spring were adults. Any one source of infection studied contributed to the acquisition of important burdens of D. filaria by lambs as well as ewes. Worm counts reached peak in all lambs by November and this pointed to only one important Dictyocaulus generation per grazing season. It would also appear that larvae picked up by ewes and lambs as the grazing season advanced had become inhibited in development with the inhibition rate being most marked in autumn.     

Evaluation of the ovine callipyge locus: IV. Genotypic effects on reproductive traits

A resource population of ewes derived from Dorset and Romanov grandparents was generated over 5 yr to provide genotypic and phenotypic data to estimate effects of each callipyge genotype on component traits of reproduction. Effects on ovulation rate were estimated from data recorded by examination of ovaries from serially slaughtered ewe lambs (n = 174) born in 1994 and 1995. Productivity and longevity through 5 yr of age were recorded on a total of 265 F2 ewes produced in 1996 through 1998. Number of lambs born, birth weights, and weaning weights of lambs were calculated for each ewe. Weaning weight was recorded for each lamb and adjusted for age to 56 and 32 d for dam- and nursery-reared lambs, respectively. Longevity was determined as a binary trait based on the presence or absence of the ewe in the breeding flock at 5 yr of age. Ewes generated 937 records for breeding weight and 925 records for conception rate, which was determined on ewes exposed and still present at the start of each lambing season. Seven hundred seventeen records were analyzed for traits based on the number of ewes lambing. Genotypes for the causative callipyge mutation were determined using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay. Each ewe was classified into 1 of 4 genotypes; NMatNPat, NMatCPat, CMatNPat, or CMatCPat, where N represents wild type and C represents the mutant allele. The mean ovulation rate of the ewe lambs genotyped NMatNPat was greater (P < 0.02) than that exhibited by NMatCPat; however, the estimated difference of 0.25 ovum in the ewe lambs did not affect the number born. The live weight of NMatCPat ewes at breeding was 2.5 kg less than that of other genotypes (P < 0.01). The callipyge genotype class did not significantly affect conception rates, fecundity, maternal ability, or ewe longevity. Maintaining a ewe flock to produce homozygous mutant rams for use in terminal sire mating systems presents no unusual problems from a reproduction standpoint.     

Does sward height grazed by ewes in mid- to late-pregnancy affect indices of colostrum intake by twin and triplet lambs?

AIMS: To determine if sward height grazed by ewes in mid- to late-pregnancy affects subsequent indices of colostrum intake by twin and triplet lambs, and the extent of the variation in colostrums intake between twin and triplet litter-mates. METHODS: Blood samples were collected from 75 twin and 46 triplet litters, respectively, 24-36 h after birth. Samples were not collected from lambs that died before this age. Lambs were born to ewes which had grazed one of four sward heights (2, 4, 6 and 8 cm) during mid- to late-pregnancy. Serum samples were analysed for gamma-glutamyl transferase (GGT) activities and glucose concentrations. The number of lambs present at weaning was used to determine lamb survival rate. RESULTS: GGT activities of lambs born to ewes that grazed swards 2 cm high were lower than those born to ewes that grazed swards 4 and 6 cm high (p=0.053 and p=0.037, respectively). Glucose concentrations were higher in twin than triplet lambs (p=0.003) and in lambs born to ewes grazed on swards 6 cm high than those born to ewes grazed on swards 2 cm high (p=0.033). These differences were not evident after correction for differences in birthweight. There was significant (p<0.001) variation within litter-mates for GGT activities and glucose concentrations in both twins and triplets. The blood constituent status of lambs that died before the 24-36 h collection period is not known. However, lambs which died after this period had significantly lower GGT activities (p=0.009) and glucose (p=0.010) concentrations at the time of sampling than those which survived. CONCLUSIONS: Farmers should ensure twin- and triplet-bearing ewes in mid- to late-pregnancy are grazing at least 4 cm of herbage to ensure colostrum intake of lambs in the postpartum period is not adversely affected.     

Does sward height grazed by ewes in mid- to late-pregnancy affect indices of colostrum intake by twin and triplet lambs?

AIMS: To determine if sward height grazed by ewes in mid- to late-pregnancy affects subsequent indices of colostrum intake by twin and triplet lambs, and the extent of the variation in colostrum intake between twin and triplet litter-mates.

METHODS: Blood samples were collected from 75 twin and 46 triplet litters, respectively, 24–36 h after birth. Samples were not collected from lambs that died before this age. Lambs were born to ewes which had grazed one of four sward heights (2, 4, 6 and 8 cm) during mid- to late-pregnancy. Serum samples were analysed for gamma-glutamyl transferase (GGT) activities and glucose concentrations. The number of lambs present at weaning was used to determine lamb survival rate.

RESULTS: GGT activities of lambs born to ewes that grazed swards 2 cm high were lower than those born to ewes that grazed swards 4 and 6 cm high (p=0.053 and p=0.037, respectively). Glucose concentrations were higher in twin than triplet lambs (p=0.003) and in lambs born to ewes grazed on swards 6 cm high than those born to ewes grazed on swards 2 cm high (p=0.033). These differences were not evident after correction for differences in birthweight. There was significant (p<0.001) variation within litter-mates for GGT activities and glucose concentrations in both twins and triplets. The blood constituent status of lambs that died before the 24–36 h collection period is not known. However, lambs which died after this period had significantly lower GGT activities (p=0.009) and glucose (p=0.010) concentrations at the time of sampling than those which survived.

CONCLUSIONS: Farmers should ensure twin- and tripletbearing ewes in mid- to late-pregnancy are grazing at least 4 cm of herbage to ensure colostrum intake of lambs in the postpartum period is not adversely affected.     

Toxoplasma gondii-induced abortion in sheep

Twenty-nine of 200 (14.5%) ewes on a farm in Cobleskill, NY aborted or had dead lambs during the lambing seasons of 1985 and 1986. Thirteen of 15 ewes that aborted had high Toxoplasma gondii antibody titers (1,024), via the modified agglutination test, and T gondii was isolated from the tissues of 1 fetus. In the 1987 lambing season, 5 ewes aborted, but not because of T gondii infection. Toxoplasma gondii antibodies were detected in 73.8% of sera obtained from 592 ewes in January 1987, indicating enzootic toxoplasmosis on this farm. Seropositivity increased with age; 40.2% of 1-year-old ewes had detectable antibody vs 89.2% of 2-year-old ewes.     

Serum alkaline phosphatase values in lambs in relation to preparturient maternal nutrition and litter size

Serum alkaline phosphatase (SAP) levels were investigated in lambs at birth and 24 hours, 48 hours and 4–6 weeks of age. The lambs were born to ewes which had been on two different planes of nutrition during the last 8 weeks of gestation. At this stage, maternal nutrition directly affects the rate of foetal growth and subsequent birth weight. At birth, lambs born to ewes on the higher nutritional plane had higher SAP values than lambs born to the other ewes. The values at birth reflected the greater intra-uterine growth and birth weight of lambs born to the better nourished ewes. Within the same nutritional group, lambs born in larger litters had lower SAP values than lambs in smaller litters, reflecting the slower foetal growth rate and smaller birth weight of the individuals in the larger litters. The trends in SAP levels present in the early stages were still evident at 4–6 weeks of age.