The Cellular and Molecular Basis of Sour Taste

Sour taste, the taste of acids, is one of the most enigmatic of the five basic taste qualities; its function is unclear and its receptor was until recently unknown. Sour tastes are transduced in taste buds on the tongue and palate epithelium by a subset of taste receptor cells, known as type III cells. Type III cells express a number of unique markers, including the PKD2L1 gene, which allow for their identification and manipulation. These cells respond to acid stimuli with action potentials and release neurotransmitters onto afferent nerve fibers, with cell bodies in geniculate and petrosal ganglia. Here, we review classical studies of sour taste leading up to the identification of the sour receptor as the proton channel, OTOP1. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Injury-induced cold sensitization in Drosophila larvae involves behavioral shifts that require the TRP channel Brv1

Nociceptive sensitization involves an increase in responsiveness of pain sensing neurons to sensory stimuli, typically through the lowering of their nociceptive threshold. Nociceptive sensitization is common following tissue damage, inflammation, and disease and serves to protect the affected area while it heals. Organisms can become sensitized to a range of noxious and innocuous stimuli, including thermal stimuli. The basic mechanisms underlying sensitization to warm or painfully hot stimuli have begun to be elucidated, however, sensitization to cold is not well understood. Here, we develop a Drosophila assay to study cold sensitization after UV-induced epidermal damage in larvae. Larvae respond to acute cold stimuli with a set of unique behaviors that include a contraction of the head and tail (CT) or a raising of the head and tail into a U-Shape (US). Under baseline, non-injured conditions larvae primarily produce a CT response to an acute cold (10°C) stimulus, however, we show that cold-evoked responses shift following tissue damage: CT responses decrease, US responses increase and some larvae exhibit a lateral body roll (BR) that is typically only observed in response to high temperature and noxious mechanical stimuli. At the cellular level, class III neurons are required for the decrease in CT, chordotonal neurons are required for the increase in US, and chordotonal and class IV neurons are required for the appearance of BR responses after UV. At the molecular level, we found that the transient receptor potential (TRP) channel brivido-1 (brv1) is required for these behavioral shifts. Our Drosophila model will allow us to precisely identify the genes and circuits involved in cold nociceptive sensitization.

An evolutionarily conserved gene family encodes proton-selective ion channels

Ion channels form the basis for cellular electrical signaling. Despite the scores of genetically identified ion channels selective for other monatomic ions, only one type of proton-selective ion channel has been found in eukaryotic cells. By comparative transcriptome analysis of mouse taste receptor cells, we identified Otopetrin1 (OTOP1), a protein required for development of gravity-sensing otoconia in the vestibular system, as forming a proton-selective ion channel. We found that murine OTOP1 is enriched in acid-detecting taste receptor cells and is required for their zinc-sensitive proton conductance. Two related murine genes, Otop2 and Otop3, and a Drosophila ortholog also encode proton channels. Evolutionary conservation of the gene family and its widespread tissue distribution suggest a broad role for proton channels in physiology and pathophysiology.

Novel Assay for Cold Nociception in Drosophila Larvae

How organisms sense and respond to noxious temperatures is still poorly understood. Further, the mechanisms underlying sensitization of the sensory machinery, such as in patients experiencing peripheral neuropathy or injury-induced sensitization, are not well characterized. The genetically tractable Drosophila model has been used to study the cells and genes required for noxious heat detection, which has yielded multiple conserved genes of interest. Little is known however about the cells and receptors important for noxious cold sensing. Although, Drosophila does not survive prolonged exposure to cold temperatures (≤10 ºC), and will avoid cool, preferring warmer temperatures in behavioral preference assays, how they sense and possibly avoid noxious cold stimuli has only recently been investigated. Here we describe and characterize the first noxious cold (≤10 ºC) behavioral assay in Drosophila. Using this tool and assay, we show an investigator how to qualitatively and quantitatively assess cold nociceptive behaviors. This can be done under normal/healthy culture conditions, or presumably in the context of disease, injury or sensitization. Further, this assay can be applied to larvae selected for desired genotypes, which might impact thermosensation, pain, or nociceptive sensitization. Given that pain is a highly conserved process, using this assay to further study thermal nociception will likely glean important understanding of pain processes in other species, including vertebrates.

The TRP Channels Pkd2, NompC, and Trpm Act in Cold-Sensing Neurons to Mediate Unique Aversive Behaviors to Noxious Cold in Drosophila

The basic mechanisms underlying noxious cold perception are not well understood. We developed Drosophila assays for noxious cold responses. Larvae respond to near-freezing temperatures via a mutually exclusive set of singular behaviors-in particular, a full-body contraction (CT). Class III (CIII) multidendritic sensory neurons are specifically activated by cold and optogenetic activation of these neurons elicits CT. Blocking synaptic transmission in CIII neurons inhibits CT. Genetically, the transient receptor potential (TRP) channels Trpm, NompC, and Polycystic kidney disease 2 (Pkd2) are expressed in CIII neurons, where each is required for CT. Misexpression of Pkd2 is sufficient to confer cold responsiveness. The optogenetic activation level of multimodal CIII neurons determines behavioral output, and visualization of neuronal activity supports this conclusion. Coactivation of cold- and heat-responsive sensory neurons suggests that the cold-evoked response circuitry is dominant. Our Drosophila model will enable a sophisticated molecular genetic dissection of cold nociceptive genes and circuits.

Selection for reproduction rate in Australian Merino sheep: direct responses

Two groups of Australian Merinos have been under selection for low (O) and high (T) reproduction rate since 1954, and a third (B) for high rate since 1959. The O and T groups were founded on Peppin ewes from one flock which had borne singles (or twins) in two successive years, mated to single- (or twin-) born rams from the same flock. The B group was founded on two quintuplet rams and ewes born in multiple births (13 in one intake, 91 in a second), from a medium-wool non-Peppin flock belonging to the Seears Brothers, of 'Booroola', Cooma, which had been under selection for multiple births for 10–15 years. In 1959, the lambing percentage of the flock (lambs born to ewes joined) was stated to be 170-180. Selection for both sexes in the early years of the experiment was based on the presence (or absence) of multiple births in the record of the dam's first three lambings, or in that of the ewe herself, again during her first three lambings. In later years this was combined with a dam's ranking coefficient based on all available records, the coefficient being based on deviations from average performance at the ages of record, and the heritability of repeated records. The sex of her litter mates was found to have no effect on a ewe's lambing performance. The litter size in which she was born had no effect on her lambing performance when she belonged to the O or B group, but twin-born ewes in the T group were sometimes at a disadvantage compared with singles-for their lambings at 2–4 years if their dams were adult, and for those at 5–7 years if their dams were 2-year-olds. Selection response was analysed by examining T – O and B – O differences in performance for ewes born in successive calendar years, the two criteria of performance being the percentage of ewes with at least one multiple birth in their first three lambings, and ranking coefficients based on the same lambings (at 2–4 years). A regression of each difference on time is an estimate of the annual rate of genetic change due to selection; no attempt has been made to relate such changes to what might be predicted from parameters. Adjustments were made for the handicap suffered by twin-born T group ewes by adding 10.0 to the percentage showing at least one multiple birth for those whose dams were adult, 3.4 to the 2-4-year-old ranking coefficient of those ex adults, and 2.6 to the 5-7-year-old ranking coefficient of those ex 2-year-old dams. No unbiased correction for age of dam was possible; instead, T – O and B – O differences were calculated separately for progeny of adults and progeny of 2-year-olds, and a weighted mean difference computed. The groups ran at Deniliquin until 1964, and at Armidale from 1965. In spite of the change in environment, and a bad drought in 1965, regression lines could be fitted to all differences except the 2-4-year-old ranking coefficient in group T. Initial responses in percentage of ewes with at least one multiple birth in their fist three lambings were 35.2 and 40.1 for T – O and B – O respectively, and the linear regression coefficients, measuring continuing response, were 2.39 ± 0.58 and 5.52 ± 1.33. The initial responses account respectively for 68 and 62% of the average superiority of the high lines during the experiment. Initial responses for ranking coefficients at 2-4 years of age were 8.2 and 21.7 for T – O and B – O respectively, corresponding approximately to 0.26 and 0 + 72 lambs born/ewe/lambing. Continuing responses fluctuated more than for percentage of ewes with multiple births; regression coefficients of 0.67 ± 0.17 were fitted for T – O from 1954–56 to 1964, and 3.6 ± 1.2 for B – O from 1961 to 1968. The former is equivalent to 0.02, and the latter to 0.11 lambs born per ewe per year. Initial responses contributed 57–76% of the average superiority of the high line (T or B) over O, depending on the regression coefficient used. For the 1968 drop, the difference in ranking coefficient at 2–4 years was equivalent to 0.38 lambs born/ewe/lambing for T – O, and 1.04 lambs born/ewe/lambing for B – O. Ranking coefficients based on lambings at 5–7 years are the result of selection on the ewes themselves, in addition to genetic gains. The T – O and B – O differences in these coefficients showed approximately the same rate of annual change as those at 2–4 years. Corrections were made to some data from T ewes in estimating response, but in practice twin ewes might give a lower performance at their early lambings. However, the actual performance of the flocks shows that any such disadvantage was not serious. In 1972, ewes aged 2–7 years in the three groups bore respectively 1.11, 1.36 and 2.10 lambs per ewe joined. Clearly, the reproduction rate has responded to selection, the rate of response being far higher in the B group than the T. Clearly, also, initial selection of the base animals made a major contribution to the superiority of the high lines, though there has also been a continuing response.

Response to selection in Australian Merino sheep. VIII.* Further results on selection for high clean wool weight with attention to quality

Results of selection for high clean wool weight per head with control of quality are reported for two selection groups over the period 1966–74. Results for the same experiment for the periods 1950–1959 and 1961–64 were reported earlier. Both groups were selected for high clean wool weight, one (S) with a ceiling on fibre diameter and degree of skin wrinkle, and the other (MS) with a lower limit on staple crimp frequency and a ceiling on skin wrinkle. Genetic progress in clean wool weight was greater in S than in MS over the 1966–74 period (0.12–0.15 lb/annum, compared with 0.06–0.09). This was to be expected from genetic correlations of clean wool weight with fibre diameter (low positive) and staple crimp frequency (high negative). The result supports the previous recommendation that staple crimp frequency is an inefficient way of controlling wool quality while attempting to improve quantity by selection, because its use severely restricts the likely progress in quantity. The actual rate of progress in the S group was similar to that in the period 1950–59, which was followed by a fall in superiority of the selected over the control group animals born during 1961–64. The recovery of response in the 1966–74 period negates the suggestion that the loss of response during the 1961-64 period was due to a 'plateau'. The most likely explanation is that a genotype x environment interaction occurred, such that the genetic gain made in the 1950-59 period could not be expressed in the poorer environments of 1960–65, but reappeared gradually under the improving environment of the 1966–74 period. Attempts to remove this interaction by regression of response on the mean clean wool weight of the unselected control group (as an index of the level of the environment) for each year, were not successful. The interaction is, therefore, not simply a case of all selection groups being equal when the environment is poor. ________________ *Part VII, Aust. J. Agric. Res., 26: 937 (1975).

Response to selection in Australian Merino sheep. VII. Phenotypic and genetic parameters for some wool follicle characteristics and their correlation with wool and body traits

Four numerical characteristics-follicle depth, follicle curvature, number of follicles per unit area of skin, and ratio of number of secondary to number of primary follicles-describing the size, shape, and arrangement of wool follicles have been measured in Peppin Merino sheep at 4-5 months (weaning), 15-16 months (two-tooth shearing) and at later ages ranging from 2 1/2 to 7 1/2 years. Estimates of their repeatability, heritability and phenotypic, genetic, and environmental correlations with 10 wool and body characteristics are reported. All four follicle characteristics were found to be highly inherited and sufficiently correlated with wool characteristics to be of interest to both the wool biologist and the sheep breeder. Fixed environmental effects influenced the expression of some follicle characteristics, while others, notably follicle curvature at any age, were unaffected, and therefore potentially more useful as practical selection aids. Groups of sheep selected for clean wool weight with control of (i) fibre diameter and wrinkle score, and (li) crimp frequency and wrinkle score, exhibited changes in the four follicle characteristics, which agreed with what the genetic correlation estimates would predict. The role of follicle characteristics in the biology of genetic control of wool growth is portrayed by fitting causal models invoking follicle characteristics as intermediates between the gene and the wool character. The analysis separates three independent genetic control systems, the identity of which corresponds closely to factors postulated in previous theoretical studies.

Estimation of heterosis in Merino × Corriedale crosses with sheep

Reproduction rate data (lambs born, lamb survival rate, and lamb body weight) are presented for purebred Merino and Corriedale ewes and their reciprocal crosses. The four breeds were born in each of two years (1961 and 1962) and mated in each of two years (1963 and 1964, 1964 and 1966) to Dorset Horn rams. Heterosis was estimated as the superiority of the mean of the crossbreds over the mean of the purebreds, expressed as a percentage of the latter. The heterotic effect for lambs born per ewe joined was 1.9 % in 2-year-old ewes and 5.3 % in adults, the corresponding figures for lamb survival being 3.5 and 1.4 % for single-born, 17.2 and 12.0% for twin-born lambs. For mean age-corrected lamb body weight, 2-year-old ewes showed a heterotic effect of 3.7 % and adult ewes 2.0 %, while for pounds of lamb weaned per ewe joined the figures were 11.3 and 10.2%. Although some heterosis was exhibited, the mean of the crossbreds seldom exceeded that of the superior parent (the Corriedale), and there were sometimes differences between the reciprocal crosses, the Corriedale x Merino cross being superior in performance to the other. The potential for exploiting this degree of heterosis in reproduction rate cannot be assessed until the corresponding wool data have been analysed. In reproduction rate, the Corriedale was superior to the Merino, but again a final conclusion about their merits must await results on wool data.

Ovarian response to gonadotrophin by Merino ewes selected for fecundity

Medium-wool Merino ewes, from groups that, as a result of selection since 1954 for this character, have a low (O group) and high (T group) incidence of multiple births, were injected with 0,375,750, or 1500 i.u. pregnant mare serum gonadotrophin (PMSG) on day 13 or 15 of the oestrous cycle (day 1 is the day of oestrus). The two groups were compared on the basis of the occurrence of oestrus, number of ovulations, ovarian follicle score, plasma progesterone level, and weight of luteal tissue. Conception rate in the two groups was compared by examining the reproductive tracts on day 20 of pregnancy, when the number and size of embryos were assessed. Injection of PMSG on days 13 and 15 gave similar results, so these data were pooled for all subsequent comparisons. Dose response lines for PMSG were constructed, the above ovarian characters being used as response types, and the curves were compared by relative potency analysis. On the basis of number of ovulations, plasma progesterone, and luteal tissue weight, PMSG was approximately three times as potent in T ewes as in O ewes. That is, for a given dose of PMSG, the T ewes produced an ovarian response three times as great as that of O ewes. At low doses of PMSG (4 1500 i.u.) the T ewes also produced more follicles in the ovary than 0 ewes. With 1500 i.u. PMSG this was reversed, since the O ewes produced many follicles that did not ovulate. The relative loss of potential embryos by day 20 was similar in the O and T ewes examined, and increased with increasing dose of PMSG. In ewes given 1500 i.u. PMSG only 20-35% of potential embryos were recovered. Embryo size on day 20 was not significantly influenced by either group or dose of PMSG. In untreated ewes the normal ovulation rate differed significantly between the O group (1.00) and T group (1.50). Ovarian data collected from untreated adult ewes of the O and T groups substantiate the differences observed in the PMSG study. It is not yet known whether the between-group differences in fecundity have arisen through changes in pituitary gonadotrophin secretion, changes in ovarian sensitivity, or both.

Response to selection in Australian Merino sheep. III. Single character selection for high and low values of wool weight and its components

Direct and correlated responses are reported for 10 traits in eight pairs of lines under selection for high and low values of single characteristics : clean wool weight per head, clean wool weight per unit skin area (measured only in the groups under selection for it), body weight, wrinkle score, fibre number per unit skin area (adjusted for body weight), fibre diameter, staple length, and percentage clean yield. All groups showed overall divergence in the character under selection, though response was not always symmetrical, and in two cases (long staple and low fibre number) there was no continuing response after the initial response to extreme selection of the base parents. In all except one case, whenever previous estimates of genetic correlation were at the level of 0.2 or higher, correlated responses were in the predicted direction, though not always symmetrical in magnitude. The exception was a previously reported negative correlation between fibre number and staple length, which was not exhibited under selection for either character. Where two characters of a pair were under selection, reciprocal responses agreed in sign; magnitude will be examined in a later paper. Wool per unit area was shown to have a greater influence on clean wool weight than that of surface area, with staple length on this occasion being the most important component of wool per unit area. Reasons for an apparent decrease in the relative importance of fibre number are discussed. Three other points of importance in sheep breeding are again emphasized by these results : 1. Crimp in several pairs of groups was a poor indicator of fibre diameter. 2. Increases in clean wool weight were associated with falls in crimp number, even though fibre diameter actually became finer; diameter, not crimp, should therefore be used as a guide to wool quality. 3. The absence of genetic correlations DL and NL indicates that selection can be for high N (fibre number) with high L (staple length) and low D (fibre diameter) -in other words, a desirable fleece -with no impeding genetic correlations.

Vital statistics for an experimental flock of Merino sheep. V. The effects pf age of ram, maternal handicap, and year of measurement on 10 wool and body characteristics for unselected rams

Estimates were made of the effects of the following factors on 10 fleece and body characteristics measured on rams aged 1½ to 5½ years in a randomly bred control flock, for rams born 1953 to 1957 inclusive: age of ram, single or twin birth, age of dam, and the year in which measurements were made. Changes with age were present in all characteristics and the ranges of the age deviations from the overall mean were larger in magnitude than the corresponding figures for ewes. Greasy and clean wool weights showed a similar pattern of change with age as ewes. For greasy wool weight the age deviation increased from –2.4 lb at 1½ years to 1.1 lb at 3½ years and then declined to 0.5 lb at 5½ years of age. The corresponding figures for clean wool weight were –0.7 to 0.5 lb. falling to –0.2 lb at 5½ years of age. Other characteristics showed different patterns of change with age from the corresponding figures for ewes. Staple length, crimps per inch, yield, and fibre population density decreased with age over the range available, whilst face cover, body weight, fibre diameter, and wrinkle score increased. The fitted mean difference in clean wool weight between rams and ewes was 33%, largely attributed to differences in body area (25%) with a smaller contribution from staple length (7%). Twin-born rams cut 0.28 lb of clean wool weight per year less than single-born rams over the five shearings, whilst the progeny of 2-year-old dams did not differ significantly from the progeny of adults. Large between-year differences occurred for most characteristics. For clean wool weight the range was from –1.52 to 1.44 lb, fibre volunme being the most important component, while for body weight the range was –18.6 to 19.7 lb.

The influence of age structure on total productivity in breeding flocks of Merino sheep. I. Flocks with a fixed number of breeding ewes, producing their own replacements

In a flock of breeding ewes of fixed size, the number of age groups of rams and ewes influences the annual rate of genetic gain in any character under selection. The number of ewe age groups also influences the number of surplus stock aged 1½ years, and the number cast for age, as well as the amount and quality of wool obtained. The latter is also influenced by the proportion of ewes which rear no lambs, one, or two, as well as the proportion themselves born in multiple births or as the progeny of young ewes. In this paper, all these influences are considered in determining the age structure of the breeding flock which gives the greatest number of surplus stock and the greatest relative wool return. To combine the two, relative weights have to be given to wool and surplus stock. One such set of weights has been used, and the conclusion has been drawn that two age groups of rams, with either five or six age groups of ewes, give optimal return, the number of ewe groups depending on the level of reproduction rate. This conclusion depends on the relative weights used. In cases where numbers of animals are of supreme importance, such as after a drought or at a time of increasing pasture improvement, then retaining ewes to an older age would increase the number of surplus young stock.

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.

Vital statistics for an experimental flock of Merino sheep. II. The influence of age on reproductive performance

Estimates are given for various characteristics associated with reproduction rate, at each age of ewe from 2 to 10 years. In general, reproduction rate rose with increasing age to a peak, with a subsequent fall, the 10-year-old figure, however, being in most cases above the 2-year-old one. The peak occurred at 5–6 years for number of ewes lambing per ewe joined, at 6 years for survival rate of both single and twin lambs and for number of lambs weaned per ewe joined, at 7 years for number of lambs born per ewe joined, and at 7–8 years for number of multiple births per ewe joined. The estimates are used to predict the reproduction rate of flocks with different age structures, the conclusion being that the average number of lambs weaned per ewe joined would increase with the age of the oldest group of ewes even up to 8–9 years. Data from other sources are summarized for comparison. If survival rate can be improved, particularly for lambs from multiple births, then the older ewes will show an even greater advantage. Formulae are given which enable various criteria for reproduction rate, such as lambs weaned per ewe joined, to be broken into components whose relative importance can be assessed.

The relationship between live measurements and edible meat in Merino wethers

Seventy-five Merino wethers of a medium Peppin strain were slaughtered at 7 months of age after a series of live measurements had been made, weights then being taken of carcass and of edible meat after boning out. Fat content was insufficient for trimming, and bone weight was obtained by difference. Weight of edible meat was highly correlated (0.95) with liveweight before slaughter, and the inclusion of any other measurement in a multiple correlation analysis failed to raise this value. Variation in bone weight contributed only 25% of the variation in carcass weight, and the ratio of meat to bone was positively correlated (0.54) with liveweight before slaughter. If total amount of edible meat is accepted as the criterion for meat production, liveweight before slaughter was a satisfactory predictor for these sheep. It is suggested that simplification of criteria along these lines is desirable to aid in the selection of sheep for meat production, though more work is required on sheep of other ages and other breeds.

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.

Grazing management of native pastures in the New England region of New South Wales. II. The effect of size of flock on pasture and sheep production with special reference to internal parasites and grazing behaviour

The effect of flock size on pasture and animal productivity, on parasitic infection, and on grazing behaviour was investigated in a grazing experiment over a period of 3 years. Merino sheep, undrenched, and stocked at the rate of one sheep per acre on native pasture dominated by Bothriochloa ambigua S.T. Blake, were used in five flock sizes, vie. 2, 4, 8, 16, and 30 animals. Flock size did not significantly affect the forage available or the botanical composition of the pastures, but liveweight gains and wool production were significantly lower in the flock of two sheep than in the other flocks. Observations indicated that the reduced productivity of the smallest flock was associated with reduced grazing time consequent on changes in grazing behaviour. No consistent significant differences in worm egg counts were observed in faecal samples from the different flocks. The results indicate that although under fairly extensive grazing conditions a unit of two sheep may be unsatisfactory in some respects, flocks of four sheep could give information on pasture or animal production or on parasitism comparable with that from larger flocks of up to 30 animals.

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.

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.

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.

Grazing management of native pastures in the New England region of New South Wales. I. Pasture and sheep production with special reference to systems of grazing and internal parasites

In a 4-year grazing experiment with Merino sheep, on a native pasture dominated by Bothriochloa ambigua S.T. Blake, three rates of stocking and continuous v. rotational grazing were compared. The effects of these treatments on the forage available and the botanical composition of the pasture and on sheep liveweights, size of sheep, wool production, wool fibre diameter, and parasitic infestation, both with and without drenching with phenothiazine, mere studied. The effects of seasonal conditions on the above and on the chemical composition of the pasture were also recorded. No consistently significant differences between grazing treatments in their effects on the pasture or on sheep liveweights or parasitic infestation were recorded, although during the final 3 years the total forage available was less under heavy stocking. Seasonal variations in total forage mere not marked, but, production of green forage increased greatly in the spring and declined to a very low level during winter. Similarly, sheep liveweights increased during spring and summer and declined in the winter. These liveweight changes were significantly correlated with the amount of green forage available. Wool fibre diameter showed similar seasonal fluctuations but the maximum diameter was attained earlier than maximum liveweight. Coincident with a spring rise in the amount of green forage there was also an increase in the percentages of crude protein and phosphorus in the green components of the pasture. Liveweight gains of the drenched sheep were significantly greater from the beginning of each experimental year in the late spring (November) to late winter (August) in all stocking treatments. In the spring, when the quality of the pasture improved and worm egg counts were low, drenching had no effect on liveweight gains in three out of four years. Drenching also significantly improved wool production and resulted in an increase in skeletal size of sheep in three out of four years. Drenching reduced egg counts of the parasites Oesophagostomum spp. and Haemonchus contortus (Rudolphi) Cobb but was less effective against Trichostrongylus-Ostertagia spp. For all grazing treatments there was no significant difference in the amount of wool produced per head, but over the 4-year period 56 per cent. more wool per acre was produced from the heavy than from the light rate of stocking.

The influence of various factors on some methods of estimating fibre and follicle population density in the skin of Merino sheep. I. Methods of delineating area of natural skin

Many factors may influence measurement of skin area for estimation of fibre or follicle population density. This paper analyses the influence of method of delineation (hairpin calliper, Hardy clipper, or Carter biopsy punch), type of sheep (wrinkled or plain), body region, and sheep individuality on the mean density estimated and on the error of estimation. With either a biopsy punch or a 1 in.2 hairpin calliper in the midside region, sampling errors of the order of 8–11 per cent. were found for density estimates in a series of field observations on Merino and Corriedale ewes, with between-sheep coefficients of variation ranging from 13 to 18 per cent.

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.

Adjustments for faecal worm egg counts from cattle based on faecal consistency and on age and body weight of host

Results are reported of studies to determine whether interpretations of worm egg counts per gram of faeces as an indication of the population fluctuations among gastro-intestinal helminths of cattle would benefit from adjustments to the egg counts for faecal consistency, and for changes in faecal output associated with the age and body weight of the host. Adjustments for faecal consistency proved of little value. Adjustments for age or body weight, however, were found to be important, and factors for adjustment to a standard age or weight are tabulated. Under field conditions age is more readily ascertained than weight, and estimates showed that prediction of faecal output from age varied only slightly from prediction from body weight.

Observations on survival and growth to weaning of lambs from ewes with defective udders

Although work has been published showing relationships between milk production of the ewe and growth of the lamb, little has been done to investigate the effects of physical impairment or deficiency in mammary function in the ewe on the survival and growth of the lamb. This point has been studied by examining data for survival, birth weight, daily gain in weight to weaning age, and weaning weight from 621 Merino lambs born in the F. D. McMaster Field Station, C.S.I.R.O., flock from 1946 to 1949. When the performance of lambs from ewes having impaired or imperfect udder function was compared with that of lambs whose dams had normal function it was found that the lambs from ewes having defective function had a lower survival rate, a lower daily gain in weight to weaning age, and lower weight at weaning. The differences were statistically significant. Examination of the dry ewe flock in 1946 revealed that approximately 6 per cent. of all ewes aged from 1 to 7 years had damaged or imperfect udders. There was an association between age and incidence of defective udders, the incidence being highest among the oldest ewes. Culling of affected ewes from the flock was found to have very little effect in increasing the overall percentage of lambs raised to weaning age, or increasing their weaning weight. It is doubtful if culling for this fault would be beneficial in the average commercial Merino flock.