Yambezia (1979), VII (ii).NATURE AND NURTURE IN ANIMAL PRODUCTION:A HERETICAL VIEW*}. OLIVERDepartment of Animal Science, University of Rhodesia|THE PURPOSE OF an inaugural lecture is to give the newly appointed in-cumbent to a chair an opportunity to state in public what he actuallyprofesses to know of his subject. As the first Professor of Animal ScienceI do not pretend to know everything about the subject because of thepublication explosion which has taken place over the last two or threedecades. The Librarian of this University reported in 1976 that:the number of scientific journals doubled every 11 years;30,000 of these were published in Western Europe alone and,over 1,000,000 scientific papers were published in that year.Our library acquires over 4,000 periodicals a year which occupy a shelfspace of 300m and a similar area is required for books!If one takes into account time spent in the administration of a depart-ment, teaching undergraduates and guiding post-graduate students, thereis not a great deal of time left for reading scientific journals and doing one'sown research. I think you will understand now what I mean when I say,that of the total knowledge of Animal Science that is available, I professto know very little. In fact I regard Animal Science as one of the tools bywhich the productivity of domesticated livestock may be enhanced. In myview this is the raison d'etre for the Animal Scientist's existence and, also,the reason why I shall profess more from the point of view of productionthan of science.My outlook is conditioned by life in a developing country where 90per cent of animal products are derived from cattle. About 55 per cent ofthe national herd is in the hands of large numbers of people who individuallyown small groups of cattle which are not very productive. The remainingcattle are owned by what are now called 'commerc'ial fanners' who, ingeneral, use up-to-date scientific methods and derive a comparatively highdegree of production from their cattle. Yet, irrespective of the numbers ofcattle they own, farmers have been misled or have misled themselves intothe belief that the productivity of all domesticated animals is dependenton their choice of sire. We know that offspring of parents tend to be similarto each other in appearance and, consequently, it is obvious to assume they* An inaugural lecture delivered before the University of Rhodesia on 17 May 1979.125126 NATURE AND NURTURE IN ANlMAU PRODUCTIONwill be similar in productive characteristics. Unfortunately, many of thesecharacters have very little relationship to parental productivity and this Iintend to illustrate from the research I have carried out with my colleagueshere and in the United Kingdom.The productivity of animals has two foundations Š nature and nurture.Nature has several definitions and for this purpose I use 'person's oranimal's innate character'. This innate character, in scientific terms, is ananimal's genotype or heredity potential and is created by fusion of maleand female gametes at the moment of conception. This genotype, this blue-print for development cannot be changed in any way known to man at thepresent time. Its full expression can be limited, however, if the raw materialsor nurture it requires are insufficient in quality or quantity or both.Nurture means nourishment and this consists of the total environment inwhich an organism finds itself. Nurture in animal production is synonymouswith environment and depends on a great many factors such as temperature,rainfall, soil type and so on. The main effect of interaction of these factorsone with another represents the environment of the organism. Thus at lastI have told you that I am going to speak about genotype and environmentand make some heretical remarks about some aspects of currently held animalproduction dogma.For many years animal geneticists have been revered, especially byfarmers, because of a widely-held belief that if we can select and multiplythose animals which are superior to the rest of the population fora number of productive traits, then the productivity of our herds andflocks will be greatly increased. For example, most dairy farmers believethat it is possible to purchase bulls whose daughters will produce substantiallygreater yields of milk than animals he already owns. Unless his cows areproducing to their full genetical potential, then such an idea is patentlyabsurd. In fact few dairy cows are ever given the chance to do so for lackof nurture.There is not enough time to describe in full exactly how geneticistsachieved such eminence. It was due in part to the work of Mendel, publishedin 1866 and ignored until 1900 when others rediscovered the principles ofsegregation and independent assortment of hereditary characters for traitsof a simple kind. The modern science of genetics arose from these findingsand since that time geneticists have sought to explain the nature of heredityin Mendelian terms. By about 1920 a great deal of knowledge had beenaccumulated in support of the Mendelian theory. From the predictions ofgeneticists and the hopes of farmers, the application of Mendelian geneticswas expected by all to lead to vastly improved productivity in domesticlivestock. Small wonder that geneticists were, and are still, held in thereverential awe I have already described.Early experiments with cattle appeared to support genetical theory.Thus the inheritance was explained, in Bos taurus cattle, of coat colour inthe Aberdeen Angus and the Shorthorn breeds, together with that of theJ. OLIVER 127horned and hornless (polled) condition. These characters, dependant on asingle pair of genes, have little or no importance in animal production. Insimple terms, animals are bred to provide products which can be soldprofitably by the fanner and used by consumers either within or withoutthe national economy. Before this can be achieved female domestic mammalsmust be fertile and produce enough milk to enable their offspring to growrapidly in early life and so be strong enough to fend for themselves oncethe dam is dry or, in other words, has ceased to lactate. The attemptedapplication of early genetical theory to elucidate the pattern of inheritanceof fertility and milk yield failed. This is due to the fact that the importantproductive characters in animals have a low heritability and their expressionvaries according to the total environment to which an animal is exposed.At first sight it would appear to be logical to choose the offspring ofhigh-yielding dairy cows as the parents of the next generation. Unfortunately,milk yield, like other productive characters, is an expression of an animal'sphenotype or outward appearance and so is not necessarily hereditable. Infact only 7 to 15 per cent of a dairy herd's ability to produce milk can beaccounted for by heredity while the rest is due to environment. The heredit-able part of milk yield became generally recognized by geneticists to bethe result of very many minor genes working together and for this pheno-menon the term polygenetic inheritance was coined. This mode of inheritancecan only be studied in large populations of animals and involves the use ofthat branch of mathematics referred to as Biometry. The pursuit of thiskind of knowledge has had a variety of names but 'quantitative genetics' seemsto be the most fashionable at the moment. It produces a voluminous litera-ture, much of which follows a repetitive theme and uses a great deal ofcomplicated mathematics to explain what has already occurred.The development of quantitative genetics has not led to much discern-able improvement of fertility and lactation yield. These are the two charac-teristics which are of fundamental importance to the productivity of beefcattle. My remarks are not intended to denigrate the valuable work whichthe study of quantitative genetics in general has produced. I do intend toindicate, however, that their contribution to the improvement of fertilityand milk yield in cattle is meagre and that the methods they advocate areolder than time. For example, geneticists give great importance to progenytesting, that is the assessment of merit in a sire by the performance of hisoffspring. The principle of the technique is implicit in the Biblical quotation'By their fruits ye shall know them' (Matthew 7:20). It was described byVarro, the Roman writer on agriculture, about 2,000 years ago and waspractised in the eighteenth century by the father of English animal husbandry,Robert Bakewell (1725-75), before Mendel was born. Bakewell's workwas so successful that a host of imitators followed his example and livestockimprovement became fashionable with wealthy landowners. Their farms andestates became centres from which new ideas spread through WesternEurope. The advances in animal production in the eighteenth century are128 NATURE AND NURTURE IN ANIMAL PRODUCTIONTable ICHANGES IN SLAUGHTER WEIGHTS (lbs) AT SMITHFIELDBeevesSheepLambs1710370281817958008050Source: Pawson (1957).shown by records from the Smithfield Meat Market (Table I), which isstill one of the largest of its kind. It is interesting to note that all this wasachieved before the so-called fathers of modern biological thought wereborn. There have been refinements in these ancient techniques which madethese changes possible and they can be practised on a much wider scaletoday by the use of artifical insemination but there have been no new ideasfrom geneticists to improve fertility and lactation yield.The main contribution of modern genetics has been an endeavour toquantify the part of a characteristic attributable to heredity and that dueto environment. Furthermore, our knowledge has been enriched by theconcept of what is called the correlation between characters or, to use thetechnical term, traits. These data are by no means precise and although wespeak of heritability estimates they only give some idea whether or not atrait has a high, medium or low heritability, and, conversely, whether or notenvironment is of major or minor importance. Correlation, or associationbetween traits, is important because it gives an estimate of the effect ofselection for one trait on the performance of another. Traits may be positively,negatively or independently correlated. One of the most important correla-tions in animal production is that between live mass gain and food conver-sion efficiency. Thus if we select animals for growth rate we automaticallyselect for efficient food use. A useful negative correlation is that betweenlength of body in pigs and backfat thickness. Thus selection for length isaccompanied by decrease in backfat thickness which is important in deter-mining the price a farmer receives for his pigs. This knowledge has aneveryday practical application. As the pigs in a litter grow, some areshorter than others and the fanner knows they will be too fat if taken tobacon pig weight. Consequently he markets them as porkers and keeps thelong pigs as baconers. The need for this practice does not indicate muchprogress in over fifty years of selection for length. In fact it went too farand hind legs became too long, leading to lameness in pigs with attendantloss of feeding efficiency while many boars were unable to mount. Thepoint to be made here is that intense selection in one direction will beaccompanied by change in another, often to the detriment of the total per-formance of the organism.J-. OLIVER129My doctoral research was concerned with the factors affecting udderhealth. The techniques to reduce udder infection developed during my stayat the National Institute for Research in Dairying were subsequently testedon a very large scale in commercial farms in the United Kingdom and inNew York State. It took some years to get back into mastitis research whenI came back to Rhodesia but much productive work has been done fromour laboratory under the able control of Dr Maureen Milwid. It is not myintention to describe this work but it has confirmed and extended that of theNational Institute for Research in Dairying.So far as I am aware our laboratory is the only one in the world whereresearch into the problems of mastitis reduction in hand-milked herdshas been carried out (Milwid, Moore and Oliver, 1970). This appears tobe very odd when one considers that most animals in the world whichare kept to produce milk for human consumption are milked by hand.In this field the main contribution has been the introduction of an anti-bacterial teat lubricant at milking time and the important part which oldcows play in keeping the mastitis pot on the boil. Figure 1 illustrates themain points of one trial carried out in collaboration with Mrs MarionTitterton.Many productive characters in domestic livestock can be shown to bestrongly influenced by environment. Arriving in Rhodesia in 1958, I notedthat 90 per cent of all animal products came from beef cattle. These animalsprovide the main source of income to many people as well as having greatsocial significance to them. Furthermore, the national calving rate was lessNo cullingV. infectedV. infscUdŁScullingage5.04.5Ł4,0o1-3.5 %aŁ3.02 3 4 5Herd test no.Figure 1: INFECTION IN RELATION TO AGE IN HERDS WHICH DID OR DID NOTCULL IN A TWO-YEAR MASTITIS CONTROL PROGRAMME (Source:Titterton and Oliver (1979a)).13ONATURE AND NURTURE IN ANIMAL PRODUCTIONthan 50 per cent of cows mated, or more plainly, cows calved in alternativeyears. At that time the then University College had a farm and I was askedto set up those livestock enterprises which the farm could support. One ofthese was a herd of forty Mashona cows. Their breeding performance wasstudied and the results are shown in Table II.Table IITHE BREEDING PERFORMANCE OF COWS ATUNIVERSITY COLLEGE FARM 1960-3Number ofCows matedCalves bornPer cent1960362877.71961362672.2196240f3382.5196340$3792.5Ł 4 heifers added: 8 cows culled, 8 heifers addedSource.- Oliver (1966b).The data indicate the ease with which it was possible to increasethe calving rate of the herd by improving their diet in winter and byculling barren cows. Some authors claim that it is possible to select forfertility. From the evidence available to me fertility can be improved in anunselected population by culling infertile females. This is selection againstinfertility and should never be confused with selection for fertility, in whichas I have said, genetic improvement has been meagre. Similar remarks applyto selection against low milk yield. Although the heritability of fertility islow it must not be neglected. Unfortunately, the pedigree breeder buys andsells bulls on body shape. That may be good business but it is not livestockimprovement. If I had to buy a bull I would be looking for an animal froma cow that had produced at least eight heavy weaners in consecutive yearsand not one so fat that he could hardly walk or mount.A report by Coop (1962) described a classical analysis of the relation-ship between liveweight at mating and lambs weaned per 100 ewes mated.Results over four years for 11,258 sheep at various sites in New Zealandshowed that, within the Corriedale breed, as the liveweight of the ewesincreased the percentage of lambs weaned increased substantially. Corriedalesheep are a mutton breed which have a valuable fleece and a high proportionof twin births from ewes is common. Coop's work showed the over-ridingimportance of size within a breed on lambing percentage.J. OLIVER131130-!atEin0)100<uQ.Łoa0)ambs \1201101009080706080 90 100 110 120 130 140Liveweight at mating (lbs)150Figure 2: THE RELATION BETWEEN LAMBS WEANED PER IOO EWES MATED ANDLIVEWEIGHT AT MATING (Source: Coop (1962)).Research workers in other parts of the world began to mention that cowsize (within a breed) seemed to have an effect on fertility. Lamond (1970)in Australia stated that there was a target weight for each breed of cattlebelow which conception would not take place. In 1968 Ward at Makoholishowed that few Mashona cows conceived at weights less than 550 lb. andnone when body weight fell below 500 lb. At this stage research workersplaced a great deal of importance on fertility expressed as calves born per100 cows mated. Much useful knowledge became available in this way.However, I have always looked at the problem differently and am interestedin the weight of weaned calf per 100 cows mated. This criterion not onlytakes into account female fertility but, in addition, ability to produce milkand, in consequence, weight of weaner produced. This production of bigweaners is synonymous with strong and healthy calves and that is what cowproductivity on veld is all about. Most experiments with cows had investi-gated one or more factors affecting productivity but usually they were shortterm trials.Dr F. D. Richardson and I planned a long-term experiment in whichmany of the interacting factors affecting weaner production could beexamined. Mlezu Rural Technical Institute was the ideal site becausethere was a large number of students who could provide the substantialtechnical assistance required. The trial would provide more rewarding in-struction to them through handling groups of cattle treated in different132NATURE AND NURTURE IN ANIMAL PRODUCTIONways than would be possible where a single herd was managed in a con-ventional way.The reason for the low calving rate in Rhodesia in many herds wasmainly due to loss of weight in winter. From May to the onset of the rainsveld grasses have a low energy content and no digestible protein. In conse-quence cattle mobilize body tissue in order to maintain essential metabolicfunctions of the body and so lose weight. Basically, weight loss can beprevented by offering cattle a small quantity of protein-rich concentrate daily.The effect of the protein dietary supplement not only removes the need forthe mobilisation of body tissue but leads to an increase in appetite and,consequently, of energy. This is a simplified account of what takes placeand must suffice for my purpose.At Mlezu we induced wide ranges of weight and of weight changein cows on veld by offering different amounts of concentrates in winter andby weaning their calves at either 150 (early) or 240 (late) days of age. Earlyweaned calves were given concentrates each day until other calves wereweaned at 240 days- The feeding programme is shown in Table III. Thehigh plane of nutrition was designed to ensure that cows in that group didnot lose weight in winter.Table IIIFEEDING AT MLEZU (g/day)PlaneHighMediumFeed15 May-30 JuneJuly Aug.Cottonseed 450Maize Meal ŠCottonseed 225Maize Meal Š4504502252254509002254501 Sept-8 wksPost Partum4501350225675Source: Richardson, Oliver and Clarke (1975).A great deal of valuable information was amassed from the experimentwhich confirmed and extended existing knowledge. There is not time todescribe all our findings but I shall give you some of the main results. Weestablished the association between size of cow and calving rate and in addi-tion were able to calculate the proportions of probable calvings for cows whichhave lost a given percentage of body weight (Fig. 3). Knowledge of theseweight and calving-rate changes enables the cattle farmer to adjust theamount of food given to cows in order to achieve a given calving rate.Obviously we found that cows receiving the most food were heaviest atJ. OLIVER 133calving, produced most calves and these were heavier than others. Similarlythe heavier the cow, the greater her milk yield and, consequently, the heavierthe weaner produced. The effect of plane of nutrition and time of weaningon production of weaned calf per cow can be seen in the Table IV.Table IVPRODUCTION OF 240 d WEANER (kg) per COW/YEAR AND USEOF CONCENTRATES BY COW AND CALF AS A UNITAge atWeaning(Days)WEANER PRODUCTION150240MeanCONCENTRATES USED150240MeanHigh146180163426304365PlaneMedium140145143284148213of NutritionLow116107112106Nil55Mean134144268150Source: Richardson, Oliver and Clarke (1979).All of these associations were highly significant in biometrical termsand indicate the overwhelming effect of environment on the productivity ofbeef cattle. At the same time there are differences in calf growth rate whichare partly due to heredity and efforts are made to try to estimate this com-ponent of productivity by what is called performance testing. Robert Bake-well made extensive use of this technique. Briefly, bull calves are put on astandard diet designed to allow them to grow at their full genetical potential.Those which exhibit the highest growth rate are selected as future siresbecause growth rate is said to be strongly inherited, i.e. about 50 per cent.In view of the findings at Mlezu, particularly the fact that calf birth weightaccounts for over 56 per cent of the dam's lactation yield and the latteraccounts for 72 per cent of the variation in calf growth to 98 days andthat these differences persist to weaning and later in life, we must seriouslyreconsider the value of performance testing. May this be merely a reflectionof a farmer's choice of calf to put on test? Must we now question therelatively high heritability of growth rate? Substantial further research mustbe carried out before a much more accurate test can be made than thosein vogue today. However, this is a task for the animal production man andnot the geneticist.134NATURE AND NURTURE IN ANIMAL PRODUCTION-20 -15 -10 -5 0 +5 +10Body mass change from autumn peak to meanmass at start and end of mating seasonFigure 3: RELATION BETWEEN MASS CHANGE FROM AUTUMN PEAK TO MID-MATING AND SUBSEQUENT CALVING RATE (Source: Richardson, Oliverand Clarke (1975)).Earlier I said that time does not permit a full account of all the com-plex facets of genotype and environment and their interaction. For that reasonI have confined myself to an outline of the factors which affect fertilityand milk yield in beef cattle. I have stressed the importance of cattle inthe lives of people in this country and we know that they make a substantialcontribution to the gross national product. What I have not said, and do sowith whatever scientific reputation I may have, is the need for the applica-tion of statutory veterinary regulations throughout Africa. Without compul-sory dipping against tick-borne disease, preventive innoculation and thepower to control cattle movement to limit the spread of disease, all my pre-vious remarks might well be cast into limbo. Animal production can onlybegin where a viable state veterinary service exists.We must not forget the tribulations of the great pandemics whichdecimated the cattle population in 1896 and 1901. They were caused bythe Rinderpest and East Coast Fever which killed off 90 per cent of allcattle in Rhodesia (Oliver, 1966a). In an age where rapid transport is thenorm and the journey of 10,000 km is an overnight trip, it is difficult tovisualize an era when the trek ox was the only source of motive power.A good day's trek was only 25 to 30 km, and although this was not far,disease spread through the country with great rapidity. Eventually com-pulsory innoculation and control of cattle movement brought the Rinderpestunder control while compulsory dipping checked East Coast Fever. Thesediseases enabled the Government veterinarians to develop a system by whichmajor cattle losses through disease could be prevented.J. OLIVER 135Over the past three years many people have been prevented from dippingand innoculating their cattle with the result that about one million head, orone third of African-owned cattle, have died of disease. Even were it possibleto re-impose tomorrow statutory regulations governing cattle health, it willtake many years to restore the national herd to what it was three years ago.This will be due to a general shortage of veterinarians on the one handand a growing tendency for them to specialize in the lucrative cat and dogtrade in the towns. Future veterinary control of cattle disease is in evengreater jeopardy because few, if any, young people from this country areundergoing veterinary training at the present time. This is not due to lack ofinterest Š in fact interest is very great Š but the unpalatable fact is thereis nowhere to send them. South Africa will admit only four foreign studentsa year, while the United Kingdom does not want any, and entry requirementsthere are three 'A's at the A-level examinations in Chemistry, Physics andMathematics, and for every place available there are two candidates withsuch qualifications. The British Veterinary Schools prefer to take their ownpeople whose qualifications they understand rather than outsiders whosequalifications and motivation they often have reason to doubt. Once thiscountry is at peace we shall probably have to recruit veterinarians on con-tract. In the long term, however, we must produce our own veterinarians but,at the same time, we must make a careful re-appraisal of the kind of vete-rinary structure which can grow in a developing country.This veterinary base of which I have spoken is a prime example of theover-riding importance of nurture over nature. In discussing it I have notstrayed outside my self-imposed brief which is to talk about bovine fertilityand productivity. Implicit in the evidence I have given is the assumptionthat cows are free from reproductive diseases which cause abortion andwhich can be controlled by preventive innoculation. Now that I have estab-lished my case I have one last brick to throw. That is against the animalphysiologists who are not sure whether or not they should undergo a metamor-phasis to forsake their lawful business and join the latest bandwagon calledgenetic engineering.Over 30 years ago at Cambridge, multiple ovulation was induced insheep by means of hormones. The eggs were fertilized, implanted in a rabbit,flown to Pietermaritzburg, then transferred into ewes which carried themto full term. The technique has been extended to pigs using tissue cultureand to cattle using surgery for ova collection and subsequent implantation.More recently the technique has been applied in humans under the sensationaltitle of test-tube babies. What nonsense!In theory, of course, we can now create a breed of genetically superioranimals but superior in what way? Certainly not for fertility and milk yield.Transplant the ova from the super cow into a beef cow on veld, neglect thecow and the result is an unnecessary and expensive waste of time. Evenunder optimal conditions the technique is uncertain because of the difficultyof arranging for the embryo and the uterine wall to be at a compatible136NATURE AND NURTURE IN ANIMAL PRODUCTIONphysiological state so that implantation can take place. No doubt the in-genuity of man will overcome the difficulties of so-called genetic engineering.A more appropriate term would be genetic contrivance for the physiolo-gist and genetic connivance for the geneticist. Implicit in heat synchroniza-tion and mass insemination is the mistaken belief that high production issynonymous with high conception rate, that high conception rate is synony-mous with high calving rate and that this is synonymous with high productionof weaned calf. These concepts are only true if the dam is kept up to weightand size for her age and breed during her working life. The badly nurturedcow may abort, or she may have a difficult calving and die, or she may beso weak she abandons her calf and, at best, she lives to rear a miserablecalf whose chances of survival are remote.By this time many of you will be wondering what this heretic recom-mends. First, we must accept that, within a given environment, mass ofweaned calf per 100 cows mated is the criterion by which productivity ofbeef cattle must be judged under our extensive conditions. This can beachieved by strategic hand feeding in winter, adjusting stocking rates so thatveld productivity is maintained, by adopting rotational grazing and by plant-ing tropical legumes so that veld productivity is enhanced.Second, we must promote the traditional skills which have been provento be essential to successful animal husbandry. This must be carried outthroughout the country and applied to the majority of cattle owners whetherthey have large or small groups of cattle. This concept applies to our ownagricultural students who will provide the future hierarchy of scientistsand extension officers. Why is it that former Chibero and Gwebi Collegestudents are in great demand while our own have difficulty in finding jobs?There are two reasons. Firstly, many students today refuse to take jobs out-side the main cities. Second, and of much greater importance, the diplomaholders have mastered traditional husbandry skills. These give a man self-confidence, help him to make maximum use of agricultural teaching andmake him of immediate use to his employers. Most universities in the worldinsist on approved practical farm experience either before entry to the courseor during a practical year after the first year at University. How can anyoneexpect to take a responsible position in agriculture if he has not masteredthe traditional skills on which the industry is based?You can imagine my astonishment over twenty years ago when I dis-covered that practical experience was not a qualification for entry to ourdegree in Agriculture. Our degrees are second to none in the opinion ofexternal examiners from the United Kingdom and South Africa. Many ofour graduates have made highly successful careers in research, teaching andin many branches of the commercial sector. In the main these were peoplewith practical farming experience. Now that the majority of our studentslack these skills we must provide facilities for them to be acquired. Third,we must find ways to persuade the small farmer in particular to adopt therelatively simple techniques which lead to increased cattle production. ThisJ. OLIVER 137will involve a substantial injection of capital into the developing farmingsector but, of greater importance, is the need to expand our agricultural ex-tension of knowledge services at different levels.Many people outside this country agree that we have the finest animalresearch, extension and veterinary services in Africa. They have enabled usto create a highly productive cattle industry which is capable of substantialexpansion once our political problems are sufficiently resolved to permit therehabilitation of cattle production. However, I, whose life has been devotedto research in animal production, offer my final heresy. Have we not reacheda stage in this country when the basic problems of cattle productivity havebeen solved and should we now give more attention to extension and lessto research?ReferencesCOOP, A. E. 1962 'LiveweightŠproductivity relationships in sheep', New ZealandJournal of Agricultural Research, V, 249-64.LAMOND, D. R. 1970 'The influence of undernutrition on reproduction in the cow',Animal Breeding Abstracts, XXXVIII, 359-72.MILWID, Maureen S., MOORE, Judy J. and OLIVER, J. 1970 'The incidence ofintramammary infection in some dairy herds in the Salisbury area', XVIII Inter-national Dairy Congress, IE, 632 (En).OLIVER, J. 1966a 'The origin, environment and description of the Mashona cattle ofRhodesia', Experimental Agriculture, II, 81-8.OLIVER, J. 1966b 'The productivity of Mashona cattle', Experimental Agriculture, II,119-28.OLIVER, J. 1975 'Some problems of mastitis control in hand milked dairy herds',Proceedings of the I.D.F. Seminar on Mastitis Control, 1975 (I.D.F. Bulletin,Document 85), 188-92.OLIVER, J. and RICHARDSON, F. D. 1976 'The relationship between conceptionrate in beef cattle and body-mass change', Beef Cattle Production in DevelopingCountries, Proceedings of the Conference . . . 1974 . . . (Edinburgh, Univ. ofEdinburgh, Centre for Tropical Veterinary Medicine), 154.PAWSON, H. C. 1957 Robert Bakewell (London, Crosby Lockwood).RICHARDSON, F. D., OLIVER, J. and CLARKE, G. P. Y. 1975 'Analysis of somefactors which affect the productivity of beef cows and of their calves in a marginalrainfall area of Rhodesia: 1: Factors affecting calving rate' Animal Production,XXI, 41-9.RICHARDSON, F. D., OLIVER, J. and CLARKE, G. P. Y. 1977 'Analysis of somefactors which affect the productivity of beef cows and of their calves in a marginalrainfall area of Rhodesia: 2: The yield and composition of milk of suckling cows',Animal Production, XXV, 359-72.RICHARDSON, F. D., OLIVER, J. and CLARKE, G. P. Y. 1979 'Analysis of somefactors which affect the productivity of beef cows and of their calves in a marginalrainfall area of Rhodesia: 3: Factors affecting calf birth weight, growth to 240days and use of concentrates by cows and their calves', Animal Production,XXVIII, 199-211.138NATURE AND NURTURE IN ANIMAL PRODUCTIONRICHARDSON, F. D. 1979 'Analysis of some factors which affect the productivityof beef cows and of their calves in a marginal rainfall area of Rhodesia: 4: Thegrowth and efficiency of live-weight gain of weaned and sucking calves at differ-ent ages', Animal Production, XXVIII, 213-22.RICHARDSON, F. D. and OLIVER, J. 1979 'The growth and nitrogen metabolismof young sucking calves', The Rhodesian Journal of Agricultural Research, XVII,3-18.TITTERTON, Marion and OLIVER, J. 1979a 'The effect of mastitis control measureson the prevalence of udder infection and cell counts of herd bulked milks in handand machine milked dairy herds', The Rhodesian Journal of Agricultural ResearchXVII, 19-29.TITTERTON, Marion and OLIVER, J. 1979b 'Factors affecting cell counts ofherd bulked milks and of individual quarter milks of Rhodesian dairy cows', TheRhodesian Journal of Agricultural Research, XVII, 89-98.WARD, H. K. 1958 'Supplementation of beef cows grazing on veld', The RhodesianJournal of Agricultural Research, VI, 93-101.