Lamb Crop Research Articles

Cambendazole-Resistant Haemonchus contortus Strain in Sheep: Further Experimental Development

A strain of Haemonchus contortus, which had become partially resistant to cambendazole after 4 successive exposures to the drug in experimentally infected lambs (Kates, Colglazier, and Enzie, 1973), was subjected to additional drug exposures at increasing dose levels up to 60 mg/kg. After the 10th drug exposure, data from definitive controlled anthelmintic tests showed that the magnitude of resistance had increased substantially. In these terminal therapeutic trials, 2-fold (40 mg/kg) and 3-fold (60 mg/kg) increments in the ordinarily effective therapeutic dose level (20 mg/kg) of cambendazole resulted in efficacies of only 45 and 72%, respectively; whereas, in concomitant trials, both dose levels were almost 100% effective against the original cambendazole-sensitive strain of Haemonchus. The resistant strain showed no reversion in sensitivity after 2 passages in nonmedicated lambs between the 5th and 6th drug exposure trials. We reported the experimental development of cambendazole resistance in an ovine strain of H. contortus that had been highly sensitive to the drug (Kates et al., 1973). The known literature at that time on resistance to anthelmintics by various nematode species was also summarized. There have been no additional relevant publications in the interim. The purpose of this report is to present data on the increased level of cambendazole resistance that developed in this strain of H. contortus after additional exposures to the drug in lambs. MATERIALS AND METHODS The general procedures were similar to those described previously (loc. cit.). In those trials, the experimental H. contortus strain was exposed in 5 successive groups of lambs to drug levels of 5, 5, 10, 20, and 20 mg/kg. After the 5th drug exposure, feces were collected and cultured from the lambs to obtain infective larvae for the drug exposure trials reported here. However, it was necessary to passage this H. contortus strain twice through nonmedicated lambs until enough parasitefree animals became available from the next lamb crop for continuing the drug exposure trials. The resistant strain was then subjected to additional exposures during successive passages through 5 groups of lambs (Table I). Groups of 3 medicated and 3 nonmedicated control lambs were used for each of the 6th through 10th drug exposure trials. After each drug exposure test, fecal cultures were prepared from the lambs to provide infective larvae for inoculating the next test group. Thus, the experimental H. contortus strain was subjected, in sequence, to the following levels of cambendaReceived for publication 20 November 1973. * Animal Parasitology Institute, ARS, Beltsville, Maryland 20705. zole during successive passages through lambs: 5, 5, 10, 20, 20, 0, 0, 20, 40, 40, 60, and 60 mg/kg (Kates et al., 1973, and Table III). After the 10th drug exposure trial, definitive co trolled anthelmintic tests were conducted concomitantly with the cambendazole-exposed and cambendazole-sensitive parasite strains. In these trials, 3 groups of 8 lambs each were used for each strain; 2 groups were given 40 or 60 mg/kg cambendazole, respectively, and a comparable group was used as nonmedicated controls (Table II). Each lamb was given a standard dose of 5,000 infective larvae (+?<5% = 95% confidence interval) of the cambendazole-exposed or cambendazole-sensitive H. contortus strains. In all trials, the lambs of the principal groups were dosed at the appropriate drug level 27 to 28 days postinfection, and all lambs were necropsied for residual worm counts 10 or 11 days posttreatment in the 6th to 10th drug exposure trials (Table I). Treatments in the final definitive trials were given 24 days postinfection and the lambs were necropsied 5 days later (Table II). Efficacy det rminations were calculated in the usual manner. Differences between treatments and between paras te strains were subjected to analysis of variance. The authors are indebted to Dr. B. T. Weinland for this statistical analysis of the data. RESULTS AND DISCUSSION Relevant data from the 6th to 10th cambendazole exposure trials are given in Table I and from the final controlled anthelmintic tests in Table II. A recapitulation of the calculated efficacies obtained from all trials is given in Table III; this table also includes certain previously published data (Kates et al., 1973) for purpose of comparison. Data from the 6th to 10th drug exposure trials showed that there was a variable but suggestive increase in resistance to cambenda-

Growth and lifetime production of scottish blackface hill ewes in relation to the level of feeding during rearing

SUMMARYA study was made of the effects of different levels of nutrition between 3 and 6 months and between 6 and 12 months of age on subsequent growth to mature size, longevity and lifetime production of Scottish Blackface female sheep on a hill farm. Treatment differences between 3 and 6 months were small and resulted in only a 3 kg live-weight advantage for the animals receiving a high level of feeding. Treatment differences between 6 and 12 months were considerable and resulted in a mean 14 kg advantage for animals receiving a high level of feeding. Those animals remained significantly heavier until 42 months of age and significantly larger, as depicted by skeletal measurements, until 54 months of age.A high level of feeding between 3 and 6 months of age had no significant long-term effect on wool growth ewe survival or lifetime lamb production, whereas a high level of feeding between 6 and 12 months of age had a significant positive effect on the mean number of lambs born per ewe over five lamb crops. This effect was not maintained to weaning, due to an apparently greater lamb mortality. Treatment effects on ewe survival and on flock lifetime production, although considerable, were not statistically different.It is concluded that any advantages of improved feeding during rearing were largely lost through the inadequacy of the adult nutritional environment and only when the latter was not limiting would higher standards of rearing be justified.

Post partum conception in lactating Awassi and East Friesian × Awassi dairy ewes

SummaryTwo attempts were made to increase the number of lamb crops in intensively managed dairy sheep flocks. Rams were introduced into the flocks for the first 100 days after lambing. The ewes were milked twice daily from parturition. In the first flock of 188 ewes, the lambs were weaned at birth. Half the ewes received a course of progesterone and PMS in the third week post partum. 49% of the treated ewes conceived at average of 49 days post partum, and 59% of the non-treated ewes at an average of 53 days post partum. The hormone treatment reduced milk yield by 17% in the ewes which conceived and by 26% in those which did not conceive. Milk yield was 7% lower in those ewes which conceived a second time. Yield in the subsequent lactation was very low. In the second flock, the lambs of 83 ewes were weaned 40 days after lambing. 89% of the sheep conceived at an average of 64 days after lambing. The pregnant ewes yielded 6% less milk than those ewes which did not conceive. Yield in the following lactation was satisfactory. The practical implications of the results in terms of the possibilities of future production in dairy flocks are discussed.

Production of an extra summer crop of lambs.

Production of an extra summer crop of lambs.

Pasture management and parasitism in the lamb crop

Nematode parasitism is a major problem in the development of intensive grazing systems for fat lamb production, a development which is essential to the progress of the sheep industry. An understanding of the epidemiology of the parasites concerned is the key to the formulation of effective control measures. In this context, the importance of the pasture as the link between parasite and host is receiving increasing recognition; so too is the significance of pasture management.

Reproductive performance of ewes in an early-weaning, controlled-breeding program.

A total of 48 crossbred ewes was used to study reproductive performance in a four consecutive lamb crop program which included early weaning (2 months) and subsequent breeding control treatments. Hormonal treatments included the use of fluorogestone acetate impregnated pessaries which were intravaginally placed and equine gonadotropin injections. Removal of the impregnated pessaries resulted in estrous activity within 2 to 3 days in the majority of both cyclic and anestrous ewes. In regard to total reproductive performance (breeding and lambing), a procedure involving utilization of the impregnated pessaries during two spaced periods was the most consistently effective procedure tested. An exception to this was in one study where treatment was initiated during anestrus in which an injection of equine gonadotropin given at the time of pessary withdrawal was the most effective treatment.

The Development and Survival of Free-living Stages of Trichostrongylus colubriformis and Ostertagia circumcincta on Pasture

Between June 1967 and September 1968 two series of grass plots were contaminated with faeces containing eggs of Trichostrongylus colubriformis and Ostertagia circumcincta. Grass samples were taken at regular intervals and examined for third stage larvae. The results indicate that while both species over-winter, O. circumcinta produced a larger and more persistent pasture infection the following spring. These observations suggest that the succession of species in the spring lamb crop can be explained by variations in the longevity of their larval stages.

Seasonal changes in the level and composition of nematode worm burdens in young sheep

Abstract Seasonal changes in the level and composition of nematode burdens in young sheep during their first year were studied in successive lamb crops over a 3‐year period. Post‐mortem worm count data were obtained from groups of 10 lambs slaughtered at 28‐day intervals throughout each of the 3 years. Eighteen nematode species were recorded—14 Strongylidae, 2 Trichinellidae, 1 Metastrongylidae, and 1 Rhabditidae. Seasonal patterns of infection by most species were relatively constant during the period of study. Peak infections of Nematodirus occurred in the spring. Of the principal trichostrongyle species, the patterns of infection by Haemonchus contortus, Ostertagia spp., Trichostrongylus spp. of the small intestine, and Chabertia ovina presented similarities; infections rose rapidly to a peak in late summer/early autumn, followed by an abrupt decline to low numbers in winter. Duration of infection by these species was similar. Infection by Cooperia curticei and T. axei extended over a longer period and formed the major part of the worm burdens in animals entering their second year. Species that attained numerical dominance were, in order of succession, Strongyloides papillosus, Nematodirus spp., Ostertagia spp., Trichostrongylus spp. of the small intestine, C. curticei, and/or T. axei. In late autumn /early winter, after peak flock infection, a “self-cure” type reaction occurred which resulted in rapid elimination of the major part of infections by most species. Throughout the course of infection each year the patterns of increase and decline of mean strongyle egg counts (Nematodirus excluded) and mean total strongyle worm burdens were of similar shape. Considerable within-flock variation was recorded in faecal egg counts and in both level and composition of infections; this emphasises the need for adequate diagnostic samples and for caution in their interpretation.

Experimental copper deficiency in sheep

Two groups of weanling half-bred lambs were given a diet low in Cu, with or without a Cu supplement; castrate males were killed after 18 months, but females were kept on the diets for 40 months and produced two lamb crops. Unsupplemented animals developed low plasma and tissue Cu concentrations and there was a temporary loss of wool crimp between 6 and 12 months; growth, appetite and feed conversion efficiency were not, however, impaired. Lambs from the first crop from unsupplemented ewes had extremely low tissue Cu concentrations and brain cytochrome oxidase activities: lesions associated with swayback were observed in 7 out of 10, but they could not be attributed to Cu deficiency, since some of the pathological criteria for swayback were found in three lambs of normal Cu status from supplemented ewes. The latter lesions were thought to be secondary consequences of an intracranial deformity present in all first crop lambs at birth and attributable to vitamin A deficiency during late pregnancy. In the second lamb crop the intracranial abnormality did not recur: three out of seven lambs of low Cu status from unsupplemented ewes developed delayed swayback, while there were no comparable lesions in control lambs. Anaemia was not observed in ewes or lambs and the reproductive capacity of the two groups was equally good. These findings are discussed in relation to the specificity of the pathological criteria for swayback and the contrasting Cu requirements for particular body functions under experimental and certain field conditions.

Levels of first winter feeding in relation to performance of Cheviot hill ewes: VI. Life-time production form the hill

SUMMARYThe effects of different levels of first-winter nutrition over 3 years were studied on the subsequent life-time production from the hill of groups of North and South Country Cheviot ewe hoggs (sheep between 6 months and 1½12 years).Lamb production was examined in terms of the percentage of lambs born and reared per ewe alive at each lambing and was expressed as a mean of five lamb crops. An overall measure of flock life-time production was calculated from the data on lamb production. This was the total number of lambs weaned at a mean 15 weeks in each treatment group over five lamb crops expressed as the mean per experimental animal alive at 6 months.All productive components were analysed for differences between breeds, treatments, and weight-classes, i.e. those animals above or below average weight at 6 months.There were no significant treatment differences in life-time production, although the treatment groups showed different trends with increasing age. Higher production in early life following higher levels of first-winter nutrition was associated with less efficient later production and poorer ewe survival in a hard hill environment.It is concluded that improvement in first-winter nutrition above that available on the hill is undesirable and uneconomic without equal improvement in adult nutrition.

Sulfur-selenium-vitamin E interrelations in ovine nutrition.

Three experiments were conducted to evaluate interrelationships between S, Se and vitamin E in the nutrition of the ovine. In the initial experiment, a daily intake of 7.62 gm. S as sodium sulfate was found to be readily absorbed and excreted in large quantities (51.4% of ingested S) in the urine. The amount of water excreted via the urine was found to be greatly increased due to sulfate supplementation of the ration. Hence sodium sulfate was considered an excellent source of S as a potential competitor with Se in nutrition of the pregnant ewe. Hematocrits of ewes at 27–38 days prepartum appeared to be greater when ewes were fed a final level of 12.1 gm. S per head daily than when fed 3.0 or 21.3 gm. per head daily. The hematocrits of ewes fed 3.0 or 21.3 gm. S per head daily appeared to be below normal. Serum tocopherol levels were significantly affected by treatment and dietary Se depressed levels in what may have been a sparing action of Se in mobilizing tissue tocopherols. Serum tocopherol levels appeared to be increased as a result of feeding the intermediate level of S (final level, 12.1 gm. per head daily). Administration of vitamin E at 89 days or less of pregnancy appeared to exert a favourable effect on lambing percentage; the intermediate level of S also appeared to exert a favourable effect, but this was primarily a result of the 190% lamb crop that resulted when the ewes also were administered tocopherol. Five ewes fed the intermediate level of S and four fed the high level aborted in late pregnancy. These abortions occurred regardless of vitamin E or Se administration. Pathological changes in tissues of five lambs from ewes fed medium and high levels of sulfur were similar to those associated with WMD. There was no evidence that 0.75% to 1.32% dietary S in rations fed to ewes during late pregnancy were contributory to WMD in lambs born alive and surviving beyond 24 hr. of age. Administration of 1.5 mg. Se to 2- to 4-week old lambs creep fed diets containing less than 0.07 ppm Se and nursing ewes fed rations providing an equally low level of Se did not significantly increase gains over a 6 5-day feeding period.

Physiological factors affecting frequency and rate of lambing.

Data have been presented which suggest that a combination of breeding, management and hormonal therapy makes two lamb crops per year entirely feasible. Twenty-four percent of an experimental group of sheep actually completed two consecutive breedings and pregnancies within approximately a 12-mo. period. Although two lambings per year are physiologically possible, much basic research is needed before a large proportion of ewes can be consistently induced to produce two lamb crops per year. However, this should be the goal, as two lambings per year have many management and economic advantages over other lambing frequencies, such as three lamb crops in two years. Considerable progress has also been made in increasing the number of lambs born. Continued effort should be made to devise means to increase not only the number but also the viability of lambs produced.

A comparison of the body size, fleece weight and maternal performance of five breeds of sheep kept in one environment

Female sheep of five breeds (Scottish Blackface (B), South Country Cheviot (C), Welsh Mountain (W), Lincoln Longwool (L), and Southdown (S)) were purchased as lambs of 5–6 months old and subsequently kept as a single flock on a grassland farm until they were 4½ years old (Southdowns to 3½ years). The sheep were used in a crossbreeding experiment with up to six breeds of ram.The sheep were weighed and 8 body parts measured at frequent and regular intervals. The Blackfaces and Southdowns grew, relative to their mature size, a little faster initially than the Cheviots. Mature weights (lb.) were approximately B: 146, C: 145, W: 101, L: 197 and S: 129. The breeds differed in conformation but the order of maturity of the body parts was the same for each breed. Variances for body measurements decreased slightly with increasing age for early-maturing parts and increased a little for later parts. The coefficients of variation decreased slightly with increasing age. Variance in weight increased markedly with age (but not the C.V.) and showed the only large breed differences in variance.Fleece weight, after the first shearing, was strongly affected by the amount of wool shed prior to shearing. Shedding differed significantly between the breeds, Cheviots shedding most. Shedding was also related to the number of lambs born per ewe. The total weights (lb.) of wool produced from four shearings were B: 23·2, C: 20·0, W: 15·6, L: 55·5 and S (estimated from 3 shearings): 20·8.The numbers of lambs born per ewe totalled over three lamb crops were B: 5·81, C: 5·21, W: 4·53, L: 4·85 and S (estimated from two crops): 4·55. In survival to weaning, single-born lambs were no better than twins and crossbred lambs no better than purebred. Lambs born to Welsh mothers had the best survival; the other breeds did not differ significantly from each other. The breeds of ewe differed in the proportions of their twin lambs which had to be assisted at, or soon after, birth.When each breed of ewe was mated to the same breeds of ram, the weights of lambs born to Blackface mothers did not differ significantly at birth from those of lambs born to Cheviots but were heavier at weaning. Lambs from Welsh mothers were the lightest at birth and weaning.In relation to (live-weight)0·73 the maternal performance of the Welsh females was at least as good as that of the Blackfaces but the wool production was slightly poorer.

The failure of hormone therapy to induce an early lamb crop.

The failure of hormone therapy to induce an early lamb crop.

The post-natal development of the follicle population in English Romney Lambs

The follicle ratio S/P and the fibre ratio Sf/Pf have been determined for various post-natal ages of English Romney lambs in six lamb crops.A maximum site-sampling error has been determined for use in assessing the degree of significance of differences in values of the ratio S/P determined from successive skin samples from individual lambs. Variations encountered in these Romney lambs in the level of their follicle and fibre ratios, in their rates of change and in the degree of their association with live-weight changes show that rigid conclusions based on data from one lamb crop only are not justified. An intensive study of birth and 8-day old samples has shown that follicles may regress in the early post-natal life of the lamb.Not all follicle anlagen are initiated before birth and the ‘ceiling value’ of the adult ratio Sf/Pf is not necessarily determined or set pre-natally except in the sense of there being a genetic maximum which may or may not be attained. Low restricted follicle and fibre ratios at birth may increase rapidly postnatally and high ratios at birth may increase little, if at all, post-natally. The follicle and fibre ratio may increase even between the ages of 6 and 12 months.

Crossbred sheep production II. The repeatability of performance and the scope for culling

There are many flocks in Britain where first-cross ewes are mated with a Down ram in order to produce offspring of both sexes to be fattened for slaughter between 3 and 12 months of age. The ewes are normally bred out of hill ewes by rams of the special crossing breeds, the Border Leicester being the most popular example. Commonly the crossbred flock is maintained by the annual buying in of young sheep at 6 or 18 months old. These replace animals lost through normal wastage and those sold after a set number of lamb crops. In such a situation the flock owner relies on others to produce his crossbred ewes and can himself do nothing to improve their performance through selective breeding. He can only attempt to cull ewes with a poor performance. Any gains from such culling are, of course, temporary and must be maintained by a regular system of culling within each separate intake of females. The success of a culling scheme depends partly upon the extent to which future production is predictable from past performances. This is normally assessed by the correlation between an individual's successive records: the intra-class correlation or repeatability (t). The work reported here estimates the repeatability of various productive traits within two crossbred ewe flocks and considers the scope for culling within such flocks.

Birthcoat shedding in Wiltshire horn lambs

SUMMARYObservations on 160 Wiltshire lambs showed that shedding of the birth-coat occurred as a seasonal (normally May–July) phenomenon between the ages of 2 and 5 months. Denudation was usually considerable but not always complete. The average extent of denudation in 3 successive lamb crops was 89 %, 74 % and 92 %. Shedding usually spread progressively across the body according to a consistent, bilaterally symmetrical pattern.Shedding did not appear to be influenced by the sex of the lamb, birthcoat type (hairy or smooth), or by follicle density, ratio of secondary: primary follicles, or fibre diameter. However, a number of different causes of variation in shedding behaviour were found.1. Lambs born at different times tended to synchronise in onset of shedding so that they were more alike in the dates when they shed than in the ages at which they did so. Very early and very late-born lambs showed least effective synchronisation. Early lambs were older but still earlier than normal in commencing to shed; late lambs shed when younger than normal and in an atypical fashion. It was concluded that the age of the lamb, and an unknown environmental stimulus both interacted to influence shedding.2. There was a positive association between rate of gain in live-weight and earliness of shedding. Differences in level of nutrition seemed associated with differences in rate of shedding between individual lambs and also with overall differences in the average rates of shedding between years.3. Genetic variation in shedding was suggested by twins being more alike than half-sibs in some aspects of shedding, particularly when differences in level of nutrition were discounted.4. In Wiltshire foetuses the order and pattern of development of embryonic follicles in different body areas resembled closely the sequence and pattern of subsequent birthcoat shedding. A causal connection was postulated.In discussion it was suggested that there was a seasonally fluctuating environmental factor (possibly daylength), which was capable of reacting upon the Wiltshire lamb between the months of March and July. A hypothesis was developed to explain how such a stimulus could react upon the pelage follicles to produce the observed patterns of birthcoat shedding.

Mating Behavior of the Ram in the Multi-Sire Pen

Seven breeding pens, containing varying numbers and combinations of yearling and mature rams each 48 hours, were observed continuously for 8 days. When a particular combination of rams was placed in a pen, the dominance of one ram was quickly established. Mature rams were always dominant over yearling rams and were more dominant over yearling rams than were yearling rams dominant over other yearlings. Mature rams tended to be less dominant over other mature rams than were yearlings over yearlings. Dominance rating had highly significant effects on number of teases, mountings, matings and matings per mount. The dominant rams largely controlled activity in the pens under most circumstances. However, when more than one ewe was in heat, the dominant ram often found it impossible to completely curtail the mating activity of the subordinate ram or rams. Dominant rams were also more successful in completing copulation than subordinate rams. The presence of more than one ram in a pen increased only slightly the total number of matings for the pen, thus reducing the average number of matings per ram below that of the pens containing only one ram. The average number of matings per ram for the dominant rams in combination pens was only slightly less than the average number of matings in the single ram pens. The greater the dominance of one ram, for pens containing equal numbers of rams, the less the total mating activity. This was due primarily to the reduced mating activity of the subordinate ram. All single rams averaged more matings than rams in any of the combination pens. Pens containing single mature rams provided the most efficient use of individual rams. These single mature rams accomplished significantly more matings per ram than all other combinations except those pens containing single yearling rams and combinations of two mature rams. The ram combination composed of two mature rams and one yearling ram provided the most matings per pen followed closely by the combination composed of two mature rams. The two combinations produced significantly more matings per pen than all other combinations except the single mature rams. The total and average ram effects for the various ram combinations had highly significant effects on number of matings per day, teases per day and matings per mount. Number of mountings was not significantly affected. The total number of teases was in almost direct proportion to the number of rams in the combinations and the proportion of mature rams. Dominant rams which are sterile or of low fertility or genetically inferior could greatly reduce the lamb crop, extend the lambing season, or affect the average merit of the lamb crop and thus reduce production and genetic gain.

Characters of economic importance in Welsh Mountain sheep

1. The influence of seasonal, maternal and genetic variation on body weight and fleece characters of Welsh Mountain sheep is reported.2. Fertility and rearing ability of ewes improved from first to third lamb crop.3. Male lambs were on average 0·4 lb. heavier at birth than females. Birth weight increased with number of pregnancies of the dam.4. Early growth of the lamb between birth and marking (24 days old) used partly as a measure of milk production of the ewe, was greater in males than in females. Lambs born to older ewes made the greatest gains over this period, although the trend was not significant.5. Weaning weight of the lamb was affected by the dam's weight at tupping, the number of preceeding pregnancies, her milk yield and also by the season in which the lamb was born. Despite these effects weaning weight proved a good guide to the weight (at subsequent matings) at 1½ and 2½ years old.Heritability by intra-sire parent-offspring regression was 0·51±0·07 (P&lt;0·001) and repeatability was 0·43 (P&lt;0·001).6. Fleece weight was not affected by season or age of ewe. However, the heaviest lambs at weaning tended to have heaviest fleeces the following year.Heritability by intra-sire daughter-dam comparison was 0·58±0·11 (P&lt;0·001) and repeatability was 0·46 (P&lt;0·001).7. Staple length measured on the mid-side of the animal had a repeatability between years of 0·56 (P&lt;0·001) while heritability by daughter-dam regression was 0·38±0·ll (P&lt;0·001).8. Fourteen Welsh Mountain rams were progeny tested. Nine of the rams were purchased at local sales and 5 were home bred. They were not selected for the traits examined.No statistically significant differences were obtained between sire progeny groups for weaning weight and fleece weight.

Crossbred lamb production from cast-for-age Blackface ewes

Many thousands of cast-for-age Blackface ewes in Scotland and England are transferred each year to lower ground after producing four or five lamb crops on their native hill farms. It is then customary to use on them rams of another breed, often the Border Leicester, with a view to the production of more profitable lambs than can be obtained from pure-breeding (Bywater, 1945). Such is the scale on which this procedure is practised that it becomes an important consideration in any breeding plan for hill sheep that the cast ewes should be adapted to this phase of their careers as well as to that which precedes it on the hills. The outcome of selection work with Blackface sheep consequently cannot be fully assessed until the cast ewes have reared crossbred lambs, and have been finally disposed of.