Clean Wool Weight Research Articles

Maintenance of Merino sheep fed varying protein roughages with or without supplements of chopped lucerne hay and wheat.

Merino wethers of 30 months of age were hand-fed in pens on low-(chaffed wheaten straw), medium-(84 per cent chaffed wheaten straw; 16 per cent chopped lucerne hay), and high-protein roughage (chopped wheaten hay, or 67.5 per cent chaffed wheaten straw : 32.5 per cent chopped lucerne hay) alone, or supplemented with wheat grain at daily or twice-weekly intervals. The experimental period was 26 weeks and emphasis was placed on the number of survivors, changes in body weight, and mean daily roughage intake. Data were also collected on wool production. No sheep survived on the low-protein roughage (LPR-2.7 per cent crude protein (CP) ). Seven out of 16 sheep in the medium-protein roughage group (MPR-5.2 per cent CP) survived for 26 weeks ; six of these, however, died in the following four weeks. All sheep survived on the two high-protein roughage diets (HPR(1) and HPR(2)-7.6 per cent CP). The wheat supplement increased the number of survivors in the LPR and MPR groups. There was no difference between results from the daily and twice-weekly supplemented groups. Mean daily roughage intake of the unsupplemented sheep increased at each level of protein in the roughage. Mean intake of chaffed wheat straw when fed alone was 220 g per sheep per day. The intake of the same straw when fed with chopped lucerne hay increased by 120 g per sheep per day in the group fed MPR, and by 344 g in the group fed HPR(1). The wheat supplement did not increase intake within any roughage group. Roughage intake was significantly decreased on the HPR(2) diet when a wheat supplement was given. Sheep fed HPR(2) grew more clean wool than sheep in the other unsupplemented groups. Differences between mean clean wool weights of daily and twice-weekly supplemented groups within each roughage group were not significant, but differences between the mean pooled wool weights of each supplemented roughage group were significant.

LAMB AND WOOL PRODUCTION FROM FIVE BREEDS ON RANGE

Rambouillet, Romnelet, Columbia, Targhee, and Suffolk sheep were evaluated under range conditions for the production of lamb and wool in the period 1960–1963. The production traits analyzed were: birth and weaning weight; face cover and neck wrinkling; fertility, prolificacy, weaned lamb production, and body weight of ewe; lamb survival to weaning; grease and clean fleece weight, staple length, wool grade, and percentage yield of clean wool by yearling and mature ewes.Lambs of Romnelet were lighter at birth than those of the other breeds. Targhee and Suffolk were the heaviest at birth. Romnelet and Columbia lambs were lighter at weaning than those of Rambouillet, Targhee, and Suffolk.Fertility, prolificacy, and weaned lamb production were essentially the same in the four range breeds. Suffolk produced more weaned lamb than the other four breeds. There were no breed differences in the survival of lambs.Columbia exceeded all other breeds in production of grease and clean fleece weight. Suffolk produced the smallest amount of wool. Staple length of Columbia ewes was 4.3, 7.5, 18.6, 23.7 mm longer than that of Romnelet, Targhee, Suffolk, and Rambouillet ewes.

Vital statistics for an experimental flock of Merino sheep. III. Factors affecting wool and body characteristics, including the effect of age of ewe and its possible interaction with method of selection

Estimates were made of the effects of the following factors on 10 fleece and body characteristics measured on breeding ewes aged 1½ to 10½ years in three mating groups over a period of 15 years: age of ewe, single or twin birth, age of dam, the ewe's own lambing performance, the year in which measurements were made, and the year in which each set of ewes was born. Two groups (S and MS) were under selection for high clean wool weight at 15–16 months, with a ceiling on wrinkle score and fibre diameter, while the third (C) was a random control. Changes with age were present in all characteristics and were similar in the three groups. The finding that selection on wool weight at an early age had no effect on subsequent age changes in any characteristic is of considerable importance. Greasy and clean wool weight reached a maximum at 34 years, then declined by 0.3–0.2 1b per year. Percentage clean yield, fibre diameter, body weight, and wrinkle score had maxima at 5½ to 6½ years. Staple length fell consistently by approximately 0.2 cm per year, while face cover rose consistently but slightly. Crimp number rose, fell, and rose again, while fibre number rose, fell, and remained constant from 4½ years. The chief source of increase in wool weight from l½ to 3½ years was an increase in the total number of fibres. The chief source of the subsequent fall was a decrease in fibre volume, with a minor contribution from a fall in total fibre number after 6½ years. Twin-born ewes cut 0.21 lb (4.2% of the mean) less clean wool per year over their lifetime than single-born ewes, while the progeny of 2-year-old ewes cut 0.32 lb (6.4%) less than the progeny of adults. The main source of lower weight in each case was a lower total fibre number. Pregnancy lowered clean wool weight more than lactation, the separate effects being 0.87 and 0.38 lb respectively (17.4 and 7.7% of the mean) and the combined effect 1.25 1b or 25.1%. Pregnancy lowered total fibre number but lactation had no further effect. Mean clean wool weights over all ages in the C group varied from year to year, the range being from 1.08 lb (21.6%)below the mean to 0.97 lb (19.4%) above. Differences in total fibre number contributed between one-third and two-thirds of the variation. Ewes born in consecutive years in the S and MS groups showed marked upward trends in clean wool weight, fibre number, and staple length, with a marked downward trend in crimp number and a slight upward trend in body weight. These trends demonstrate direct and correlated responses to the strong selection for high clean wool weight at 15–16 months of age, and the associated slight selection against fibre diameter and wrinkle score. The mean annual increases in clean wool weight were 0.15 and 0.11 Ib (3.0 and 2.2%) in the S and MS groups, approximately 40% of the increase arising from increased total fibre number and 40% from increased staple length. The effects of age and lambing performance can be used to predict productivity in flocks of differing age structures. As the casting age rises to 54 years changes in productivity are negligible. With a rise in casting age to 7½ years the average clean wool weight of the flock would fall by 0.14 lb, with a slight decrease in staple length and crimp number. These changes need to be balanced against any increased lambing percentage or decreased annual genetic gain due to increased generation interval. Comparison with other available figures indicates that age changes may vary from one area to another.

Interactions between heredity and environment in the Australian Merino. III. Sire X Environment interactions

Interactions between sire and year (age), sire and drop (year), and sire and station in clean wool weight were estimated in data from five Merino strains at three stations. In general, interaction terms were small and non-significant, this being particularly so in the first two categories. Sire x station interactions were, in a few cases, of appreciable size. On the average the sire x station interaction component was approximately half as large as the component between sires. It was concluded that interaction will seldom appreciably hinder genetic progress from individual selection.

Selection schemes for improving both reproduction rate and clean wool weight in the Australian Merino under field conditions

Theoretical consideration has been given to 28 selection schemes which might readily be applied for the improvement of both number of lambs born and clean wool weight per head in Australian Merino sheep under field conditions. Two sets of relative weights were used, one lamb being considered equivalent to 5 or 10 lb of clean wool, and when both characters were selected in one sex, equal selection pressure was applied to each. Quality of wool is assumed to be safeguarded by preliminary culling of off-types. The schemes were investigated at two levels of twinning (15 and 30%). At both levels, the optimal method of ram selection was to select on clean wool weight among twin-born rams. At the lower level, the optimal method of ewe selection was to save twin-born ewes and to make up numbers by selecting on clean wool weight among those born as singles. At the higher level, this scheme was slightly exceeded in total genetic gain by one involving selection of ewes on their own 3-year-old reproduction rate. After 10 years of selection under the optimal scheme, an increase of about 40 lambs born per 100 ewes joined would be expected in reproduction rate, and about 1.2 lb clean wool in the cut per head. The gain in wool weight will be less (about 1 lb) if more rigorous culling on crimp is practiced, but the relative efficiency of the schemes near the optimum will not be changed. The tables presented could be used in flocks of any breed in which clean wool weight and reproduction rate were uncorrelated and to which approximately the same estimates of heritability, variances, and relative weights of lamb and wool could be applied.

Selection for fertility in Australian Merino sheep

Phenotypic and genetic parameters for fertility in sheep, in terms of number of lambs born and number weaned, have been estimated in a flock of medium Peppin Merinos. Repeatability of fertility traits over all ages is low, but there is an age effect, the record at 3 years of age having a higher value than those at 2 or 4 years. The regression of subsequent performance on a difference of 1 lamb at the initial lambing was higher for the difference between 1 and 2 lambs than between 0 and 1 lamb, which indicated that selection for twins is likely to raise fertility in the current flock more rapidly than selection against barrenness. The estimate of heritability for 2 years of age was negligible for each fertility trait, but the estimates for the 3-year-old record were higher, the value for lambs born being over 0.3. Mass selection for number of lambs born at 3 years of age would thus be expected to lead to appreciable genetic progress, while there would be at least some progress in number of lambs weaned. Phenotypic and genetic correlations were also estimated between fertility at different ages and 10 sheep and wool traits measured at 15–16 months of age. Phenotypically, fertility is positively correlated with body weight and negatively with skin wrinkle score. Genetically, it is suggested from the estimates that fertility is positively correlated with body weight and staple length and negatively correlated with fibre diameter, clean scoured yield, and wrinkle score. No phenotypic or genetic correlation was found between greasy or clean wool weight and either measure of fertility. The application of the findings to breeding for higher fertility is discussed. In an appendix, a maximum likelihood method of estimating heritability for all-or-none traits in half-sib data is presented.

Relationships among clean wool weight and its components. 2. The effect of maternal handicap and its influence on selection.

The average difference in clean wool weight between handicapped (twins and the progeny of young ewes) and unhandicapped (singles, the progeny of adults) animals of both sexes, born in the same year, was -0.34 � 0.07 lb (365 days' growth shorn at 16 months of age). 87% of the difference in wool weight arose from a difference in total number of fibres (or follicles) per sheep, the difference in output per follicle being negligible. Body weight, wrinkle score, and follicle population density were all lower in the handicapped animals. The difference in total follicle population arose from a deficiency in secondary but not in primary follicles. If the handicapped animals are not identified at selection, they will suffer a heavier culling rate if selection is on fleece weight, and estimates of differential culling rates are given. The effect on genetic progress and current production is, however, negligible with a handicap of this size. In fact, when the handicapped animals are twins, there are more animals available for selection than there would have been if the births had been single, and the higher selection differential arising from the smaller proportion saved more than offsets any deficiency from the handicap. The main effect of not identifying handicapped animals at selection is that twins will be selected against, with a resultant lowering of the twinning rate. The suggestion is made that management might possibly overcome the handicap, at least in part.

Hornedness and polledness in sheep. 5. Some effects of the horn alleles on characters in the Merino

The influence on certain characters of the three alleles which affect horn growth has been investigated in three flocks of medium Peppin Merinos. These alleles have been named P, P', and p. The characters investigated were: greasy and clean wool weight per head, body weight, wrinkle score, fibre number per sq. millimetre of' skin, fibre diameter, staple length, clean scoured yield, crimps per inch, face cover, and, on some sheep, spinning count, character, colour, and handle. Comparisons between Pp and pp rams and ewes revealed that Pp rams had a significantly lower fibre number and a higher fibre diameter than their pp halfb-rothers, but there was no other evidence of any relationship between horn genotype and the phenotype of the above characters in either sex. In comparisons between Pp and P'p sheep, rams showed no significant differences, although they had the same hornedness phenotypes as Pp and pp rams. Pp ewes cut more clean wool and greasy wool than P'p ewes at 12 months of age, but not at 22 or 30 months. Pp ewes also had a higher fibre number at 12 months and a lower fibre diameter at 22 months than P'p ewes. In the third flock, comparison \\-as made between P'P' plus P'p ewes, which have female horns, and pp ewes, which have either scurs or knobs. In none of the above characters was there any significant difference between ewes with and without, horns. The presence of P had no demonstrable effect on spinning count, character, colonr, or handle in either the Pp v. pp or the Pp v. P'p comparison. Sire x hornedness genotype interactions were found in the Pp v. P'p comparisons of body weight at 22 months for rams and spinning count for ewes.

EFFECT OF ESTRADIOL AND TESTOSTERONE INJECTIONS AND THYROIDECTOMY ON WOOL GROWTH IN SHEARLING SHEEP

An experiment was conducted to determine the effect of relatively high doses of estradiol and testosterone, with and without thyroidectomy, on clean wool production and certain endocrine glands of shearling sheep. The administration of 5 milligrams of estradiol intramuscularly at biweekly intervals to sheep with thyroids caused a reduction in the average weight of clean wool (p <.05) and fibre length (p <.01). This treatment produced increases (p <.01) in thyroid, pituitary, and adrenal weights. The administration of estradiol to thyroidectomized ewes reduced the weight of clean wool (p < 05) when compared with the thyroidectomized controls but no such response was observed in wethers. Testosterone administered at levels of 175 milligrams bi-weekly produced no effect on weights of clean wool, in ewes or wethers, but when it was administered to thyroidectomized animals average fibre lengths were decreased (p <.05).

Efficiency of conversion of food to wool. I. Correlated response to selection for high and low clean wool weight

The offspring of two families of medium Peppin Merino sheep, one family being selected for high and the other for low clean wool weight per head at 15-16 months of age under grazing conditions, have also been shown to differ significantly in the ratio of wool production to food eaten in pens, on a ration slightly above maintenance. These ratios were in the proportion 108 : 100, and the difference between the families can be taken as reflecting closely a difference in net efficiency of conversion of food to wool. It may be concluded that selection for high clean wool weight per head under grazing conditions had also resulted in the selection of more efficient animals. Clean wool production per head in the two families was in the ratio 110 : 100 in the pens, compared with 124 : 100 under grazing. The difference under grazing probably results from both the higher efficiency of the family selected for high clean wool weight and a higher grazing intake by this family.

Comparison of estimates of repeatability and heritability for some production traits in Merino rams and ewes. 2. Heritability

Heritability estimates were calculated for 10 traits in rams and ewes of a medium-woolled strain of Australian Merino sheep. The traits were greasy wool weight, clean scoured yield, clean wool weight, body weight, wrinkle score, face cover score, fibre population density, fibre diameter, staple length, and crimps per inch. Estimates were made by dam-offspring correlations, measurement on the dams being at 15-16 months, on daughters at 15-16 months, and on sons at both 10-12 and 15-16 months. All estimates for both sexes lay between 0.3 and 0.6, except for fibre population density (0.24) and fibre diameter (0.12) in rams at 15-16 months and for clean wool weight (0.29) and face cover score (0.29) in rams at 10-12 months. The only significant sex difference lay in the lower figure for fibre diameter in rams at 15-16 months, but this is of doubtful importance as the corresponding figure for rams at 10-12 months (0.37) did not differ significantly from the ewe figure. All traits may be considered highly heritable, and the high values for the yearling rams indicate that consideration might be given to the selection of rams for production traits at an earlier age than the traditional one of 18 months or older.

Comparison of estimates of repeatability and heritability for some production traits in Merino rams and ewes. I. Repeatability

Repeatabilities of 10 traits, namely, greasy wool weight, clean scoured yield, clean wool weight, body weight, wrinkle score, face cover score, fibre population density, fibre diameter, staple length, and crimps per inch, were estimated in ewes and rams. Estimates ranged from 0.4 to 0.7 for the 10 traits in both sexes. In general, body weight was the most repeatable trait and face cover the least. There is no evidence of sex differences in repeatability of the traits studied. Correlations between pairs of records obtained at different ages were high in both rams and ewes. This finding, together with the high repeatability values for all the traits, suggests that selection of sheep based on a single record is probably sufficiently accurate for lifetime performance of these 10 traits in Merinos. The correlations between yearling records and subsequent records in ram were found to be in agreement with correlations between records taken at older ages. Early selection of rams for lifetime performance therefore is probably almost as efficient as selection at a later age, and it is suggested that this finding might also be found to apply to ewes.

Variation in feed intake as a cause of variation in wool production of grazing sheep

Observations were made to determine whether differences between sheep in wool production under field grazing conditions reflected differences between individuals in feed intake. Sheep were selected for high, intermediate, and low levels of clean wool weight per unit body weight under field grazing conditions, and the feed intakes and wool production of these sheep were subsequently measured under pen conditions. On controlled feed intakes differences between sheep and between groups were less than those under field grazing conditions or under ad libitum pen feeding conditions. It was concluded that a, significant portion of the differences in wool production at grazing was referable to differences in feed intake. The group of sheep having high levels of wool production per unit body weight were found to have higher efficiency of conversion of feed to wool and also to have higher levels of feed intake under ad libitum feeding conditions. The rate of wool production of the high group was 22 per cent. greater than that of the low group under conditions of equal feed intake and 37 per cent. greater under conditions of ad libitum feed intake.

Ratios as criteria for selection in animal or plant breeding, with particular reference to efficiency of food conversion in sheep

Ratios are frequently advocated as criteria for selection, in either animal or plant breeding; for example, production per unit of food eaten is currently receiving attention, particularly with Merino sheep. Clean wool weight per head (W) is already widely used as a selection criterion, but suggestions have been made that wool weight per pound of body weight (B) or per unit skin area (estimated as B0.6, or measured) should be used instead, as estimates of the efficiency of conversion of food into wool. This paper develops formulae for writing the heritability of any ratio, as well as its genetic correlations with its numerator and its denominator, in terms of the relationships between the numerator and the denominator. From these formulae the likely result of selecting for the ratio can be predicted, for a given range of values of the genetic and phenotypic parameters of the numerator and denominator. The formulae can be used for any ratio, provided gene x environment interactions and epistasis can be neglected. In particular, it is shown that the genetic correlation between W and W/B or W/B0.6 is consistently positive for a wide range of values of the parameters of W and B, so that selection for high wool weight will also increase efficiency, as measured by either ratio. The genetic correlation between B and W/B or W/B0.6, on the other hand, is nearly always negative, sometimes very strongly so, and selection for high values of W/B or W/B0.6 will decrease body weight. The theoretical predictions are confirmed by results from experimental selection groups, in which the observed correlated responses are all in the predicted direction, and in most cases agree well in magnitude. It is suggested that more information is required on the importance of body size itself, in relation to factors such as fertility and survival, before the value of selection on W/B or W/B0.6 can be accurately assessed.

Vital statistics for an experimental flock of Merino sheep. I. Death rates in adult sheep, in relation to method of selection, age and sex

Estimates of death rates are given for four mating groups in a flock of approximately 1000 Merino ewes, for each year of age from 1½ to 10½. Three of the groups are under selection for clean wool weight and other characters, and the fourth is an unselected control. The flock is run under extensive grazing conditions, and death rates are based on ewes dead or missing between one pen-mating and the next. Between 1951 and 1957, the average death rate for ewes 1½ to 7½ years old was 2.2 per cent. per annum, while at the older ages the average was no higher than 7.3 per cent. During the drought year 1957-58 losses averaged 3.8 per cent. for ewes up to 6½ years old, then rose steeply with age to 45.6 per cent. for ewes 9½ years old. In neither period did the selected groups differ from the unselected control. Starting with the 1953 drop, all rams in the unselected control group have been retained for the study of age effects on them. Average losses to date in each age group have been less than 5 per cent.

THE INFLUENCE OF PROTEIN AND ENERGY CONTENT OF THE RATION ON LAMB AND WOOL PRODUCTION OF RANGE EWES

Two feeding experiments were carried out with range ewes to determine the influence of the protein and energy content of the ration on lamb and wool production. When the energy content of the ration was increased approximately 10 per cent during early pregnancy [digestible crude protein (D.C.P.) intake was approximately 0.14 pound and digestible energy intake was approximately 3.2 therms daily on the basal ration], body weight gains and wool production of the ewes were increased (P < 0.05 and P < 0.01, respectively), but birth weights of the lambs in one experiment and 6-week weights of the lambs in both experiments were not affected significantly. However, when the energy content of the ration was increased during late pregnancy and early lactation (D.C.P. intake between 0.12 and 0.24 pound and digestible energy intake approximately 3.7 therms in Experiment 1, and 2.7 therms in Experiment 2, daily on the basal ration), body weight gains of the ewes were not affected, wool production was depressed (not significant in all cases), birth and 6-week weights of single lambs and birth weights of twin lambs in Experiment 1 were not affected. In Experiment 2, increasing the energy content of the ration reduced (P < 0.05) the birth weights of twin lambs.When the protein content of the rations was increased (from 0.16 to 0.20 to 0.24, and from 0.12 to 0.14 to 0.16 pound D.C.P. intake daily in Experiments 1 and 2, respectively), there was no increase in body weights of the ewes or birth weights of single lambs, but there was an increase (P < 0.05) in the birth weights of twin lambs and an increase (P < 0.01) in wool production of the ewes. Increasing the protein content of the rations increased the 6-week weights of single and twin lambs in Experiments 1 and 2 (P < 0.05). The results of these experiments suggest that the minimum average protein requirement for pregnant and lactating ewes was approximately 0.10 and 0.11 pound D.C.P. per pound of T.D.N. intake for maximum lamb and wool production, respectively.A nitrogen-balance and wool-growth study using non-pregnant, mature ewes showed that increasing the energy intake at low levels of protein intake caused a reduction in the apparent but not the "true" digestibility of the protein, no change in the biological value of the protein, and a reduction in weight of clean wool produced. At a higher level of protein intake, an increase in energy content of the ration resulted in no change in the apparent or true digestibility of protein but in an increase in wool production.

Relationships among clean wool weight and its components. I. Changes in clean wool weight related to changes in the components

This paper is the first of a series presenting results from selection experiments with medium-wool Merino sheep, initiated by the Commonwealth Scientific and Industrial Research Organization (C.S.I.R.O.) in 1947. Clean wool weight (W) is discussed in relation to its five components: smooth body surface area (S), degree of skin wrinkling (R), fibre number per unit skin area (X), fibre cross-sectional area (A), and staple length (L). Statistical difficulties are encountered in relating a whole to one of its parts. Various methods have been used in the past, a common one being the gross correlation between clean wool weight and a component. It is shown that, given the variances and covariances of the components, and assuming that all relationships are mainly linear, this gross correlation can be predicted. The influence on the gross correlation of the relationships among the components is discussed, and it is shown that N and L will give the highest correlations with W for a range of values of phenotypic variances and covariances of the components which have been reported in the literature. Some selected combinations of extreme values, which might be encountered in specific strains, will increase the importance of other components. A study of the phenotypic and genetic variances and covariances of the components, and of the factors influencing them, is therefore likely to be more rewarding than a study of the gross correlations between clean wool weight and a component. One difficulty with the gross correlation technique is that if the variances of some components were more inflated by sampling errors than others, the correlation coefficients would be biased. A simple method, the "percentage deviation technique", is presented, which analyses means, and so avoids this possible bias. It has the added advantage of apportioning variation in clean. wool weight among the five components. Use of this technique on data from the C.S.I.R.O. selection experiments shows that in this flock N and L are more closely associated with W than are the other components. In each case the association is positive and accounts, on the average, for 0.3-0.4 of the phenotypic variation in W. There is little difference between the two components in their phenotypic association with W, but there is an indication that N may have a higher genetic association. Selection for W has increased N and L, as well as W itself, but has not changed body size.

Wool Fiber Density of Shropshire Lambs

Wool fiber densities are discussed, results being obtained from 10 Shropshire lambs, sampled at 20 and 52 weeks of age. Seven body regions were considered: neck, back, dock, shoulder, side, hip, and belly. Fiber measurements were made near the base end of each lock by the method proposed by Hardy and Wolf (1942). The average fiber density at 20 weeks of age was 2517 fibers per square centimeter compared with 1970 fibers per square centimeter at 52 weeks of age. The high and low density regions when the lambs were 20 weeks of age were also high and low regions at the age of 52 weeks. The density at 20 weeks was highly correlated with density at 52 weeks. However, certain individual regions were not significantly correlated at the two periods. The dock, back, and shoulder fiber densities at 20 weeks are significantly correlated with the fiber density at 52 weeks for the same locations. From all considerations, analysis was to be limited to only one region. From weight of clean wool and body measurements, it was possible to estimate the fiber density of the sheep at 52 weeks of age. The estimated value ranked the sheep in practically the same order as did the measured fiber density. The wool producing area upon which the fiber density was estimated was based on a formula developed from sheep volume measurements. Differences between sheep, body regions, locks and ages are all highly significant. The differences within the regions may be due to order of sampling or more likely to gradients within the 16 square inch area sampled. The fiber density moreover changed during the growth period from 20 to 52 weeks. Indications were that the number of wool producing follicles remained constant but that they were spread out by the skin growth. A method for early selection of sheep for wool production has been developed, use being made of fiber density, fiber diameter, fiber length, body weight and body size. The correlations between the estimates and scoured value of clean wool at 52 weeks were highly significant. A significant regression relationship existed between these estimates and clean wool at 52 weeks. This provides a method of estimating from weanling measurements the clean wool content of a fleece at 52 weeks.