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    AFS The World s best tropical dairy breed

    Home page/ AFS Story / Heat Stress/ Performance/ Breeding/ Management/ Feeding/

    Technical Papers/News of Tropical Dairying/ Contacts/

    AFS(THE AUSTRALIAN FRIESIAN SAHIWAL)

    Australia's Tropical Dairy Breed

    Dr G.I. Alexander

    Queensland Department of Primary Industries

    GPO Box 46,Brisbane Queensland 4001 Australia

    (Presented by Dr M.L. Tierney to

    Ag China 86 Conference, Guangzhou CHINA)

    Introduction

    In the early 1960's a need was seen for a breed of dairy cattle which was tick resistant and would formthe basis of the dairy industry in Queensland in future years.

    Queensland is situated in the tropical and sub-tropical northern area of Australia, and the cattle tick(Boophilus microplus) is endemic throughout most of the dairying areas of Queensland. In the 1960's it

    was generally considered that there was a real possibility of chemical control of the cattle tick breakingdown completely.

    In the early 1950's Bos indicus genes had been introduced into Bos taurus beef cattle in Queenslandthrough, mainly, the introduction of Brahman cattle into the European breeds which had, themselves,been introduced many years earlier. The majorBos taurusbeef breeds were the Hereford, Shorthorn andAngus. The infusion ofBos indicusgenes was-seen to be a way of controlling cattle tick.

    The principal dairy breeds in Queensland in the early 1960's were the Jersey, Illawarra, Holstein-

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    Friesian, Ayrshire and Guernsey allBos taurusbreeds with relatively little natural resistance to the cattltick.

    In 1952, a small number of Sahiwal cattle had been introduced into Australia from Pakistan . As thSahiwal was recognised as the best of the dairy-typeBos indicus cattle a decision was taken in 1960 tdevelop a dairy breed based on approximately 50%Bos taurus genes and 50% Sahiwal genes. In 1965 iwas decided that theBos taurus component of the new breed should be the Holstein-Friesian. Thus, th

    Australian Friesian Sahiwal (AFS) Breed Development Programme was put in place.

    By the mid 1970's it was seen that the complete breakdown of the chemical control of ticks was fairlremote. However, a number of tropical countries, particularly in the South-East Asian region, werstarting to develop dairy industries. The local breeds of cattle were generally found to have very lolevels of milk production, while Bos taurus cattle of European breeding found difficulty in coping witthe tropical conditions and their production suffered markedly.

    Thus, the emphasis of the AFS Breed Development Programme changed to that of developing a breed odairy cattle that could perform well under tropical conditions, and to the development of genetiimprovement programmes within this new breed.

    This paper will discuss the development of the AFS breed, the production levels that have been achievedthe genetic improvement programmes that are in place, and the methods that can be used to incorporatthe AFS in developing dairying industries.

    Development of the AFS breed

    The first matings in the AFS programme took place in 1961 when Sahiwal bulls were mated to HolsteinFriesian, Illawarra and Jersey heifers.

    Early in the development programme, as a result of the emphasis in the Queensland dairy industr

    switching from the Jersey to the Holstein-Friesian - due to the latter's higher levels of milk production - iwas decided to concentrate on the Holstein-Friesian to supply theBos tauruscomponent of the breed.

    Limited data from tropical areas suggested that under most tropical conditions, a 50-50 mix of BoindicusandBos taurus genes would give optimum levels of both milk production and reproduction.

    As a result, it was decided that the breed should be based on a combination of 50% Holstein-Friesian an50% Sahiwal.

    The decision to base the breed on a 50-50 mix has subsequently been justified by a number of studiethat have looked at various levels of Bos taurus and Bos indicus gene contents at various locationthroughout the tropics.

    Reason (1986) has summarised the studies that have been done to date.

    (a) Milk production per lactation

    While most of the crossbreeding programmes reported here were designed on the premise of being sitspecific, results from these experiments lead to the general conclusion that 50% Bos indicus and 50Bos taurusgives close to the optimum milk production performance. A summary of a range of studies ipresented in Table 1.

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    (1) Syrstad (1985)

    (2) Sharma et al. (1982)

    (3) Amble and Jain (1967)

    (4) Sivasupramaaian et al. (1983)

    Madalena (1981)

    The results in Table 4 show the superiority of the 50% Bos taurusand 50%Bos indicusgenotype in thecombination of milk production and reproductive performance characteristics. This index gives a directmeasure of the efficiency of milk production by combining milk yield and length of intercalvinginterval. It can also provide a measure of economic value by including return per litre of milk in thecalculation. In the data reported by Syrstad (1985), a 50% Bos taurus cow produced more than twice themilk per day of intercalving interval than a 100%Bos taurusanimal.

    AFS Breeding Programme

    In the early stages of the AFS breeding programme Sahiwal bulls were mated to Holstein-Friesian cowsto produce Fl (First cross) animals which were subsequently tested for both milk production and tickresistance.

    Both Alexander et al. (1984), with the AFS, and Hayman (1973) with the Australian Milking Zebu havereported that large numbers of Fl animals had to be culled from the programme due to a failure to letdown milk under machine milking conditions in the absence of the calf. Hayman reported a culling rateof 59% with the AMZ Fl animals, which were based on Jerseys crossed with either Sahiwal or Sindhisires.

    Alexander et al. (1984) reported that the culling rate of AFS Fl animals between 1977 and 1983 was60% for heifers not milking at 120 days. There were large differences in the culling rates of daughters ofdifferent Sahiwal sires with the rate varying from 28% to 85% for the daughters of the different sires.

    Reason et al. (1979) reported that the culling rate due to the failure to achieve lactation persistency insecond generation heifers was markedly reduced (mean of 28%) even though female progeny of failedFl heifers were retained in the breeding programme. This indicates that sire Selection plays an importantrole in eliminating this trait and that response is rapid (Stohoe and Waldron 1982). In later generationsthe "failure to milk" syndrome has virtually been eliminated.

    F2 and later generations were produced by inter-se matings to ensure that a genotype of approximately50% Sahiwal and 50% Holstein-Friesian was maintained in subsequent generations.

    Evaluation of F2, and Subsequent Generation Bulls

    Alexander et al. (1985) have described the bull proving programme which was commenced is 1976 inthe AFS breed.

    Between 1976 and 1984 young bulls were selected for testing from the progeny of mating the sons ofhigh producing cows to cows of similar high production. All bulls tested have been of F2 or latergeneration.

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    The matings were carried out either in Research Station or cooperating farmers' herds. Bull calves wercollected at between 1 and 6 months of age and transported to the Department's Artificial BreedinCentre at Wacol, Queensland.

    Up to ten bulls had been assembled at Wacol for each progeny test group. They were fed a standarration to 15-18 months of age and growth rate was measured. At that age semen production and ticresistance was evaluated.

    Tick resistance is known to have a high heritability, ranging from 40% in animals with a lowBos indicucontent (Hewitson, 1968, Wharton et al. 1970), to almost 80% in animals with greater than 50% Botauruscontent (Seifert, 1971).

    Bulls in the 1976 and 1977 test groups were tick tested by ranking them on their tick burdens resultinfrom natural paddock infestation. These rankings were based on a minimum of three counts.

    Selection for the 1978 and subsequent groups was based on a method of evaluating tick resistance tartificial infestations with 20 000 tick larvae (Utech et al. 1978). After infestation, the resulting engorgefemales (4.5-8.0 mm diameter) were counted on each of the 18th to 22nd days following infestation.

    A minimum resistance standard of 98% larval mortality was set (Reason and Clark, 1979) and a mealevel of 99.1% was achieved (Alexander et al. 1984).

    The bulls were not screened for heat resistance as all progeny have been evaluated in Queensland or th

    Northern Territory under natural conditions of high temperatures (> 30oC during at least the summemonths).

    Semen from the progeny test bulls was used to inseminate either AFS or Bostaurus(mainly HolsteinFriesian) cows or heifers. The resulting heifers had their milk and fat production recorded on a monthlbasis at least during their first lactation. Corrections were made for the genotype of the heifers.

    The aim was to produce a minimum of at least 20 daughters from each bull. This was not achieved in alcases.

    In 1983, the bulls in the 1976 and 1977 teams were evaluated using the technique of contemporarcomparison.

    The 1984 team of bulls was the first team that were the progeny of proven bulls. Subsequent teams havcontinued to be the progeny of proven bulls.

    Since 1984, the AFS bulls, along with all other dairy bulls in Australia, have been evaluated by th

    Australian Dairy herd Improvement Scheme (ADHIS) using the technique of Best Linear UnbiasePrediction (BLUP). This allows comparisons of bulls in different years.

    Under this scheme all bulls within a breed have an Australian Breeding Value (ABV) calculated. This ia measure of the genetic merit of the bull, relative to a base of the mean genetic merit of ArtificiaBreeding (AB) bulls of the breed in Australia in 1980-81.

    To date, 22 bulls have been evaluated by ADHIS with ABV's with reliability of 30% or more. This is thequivalent of 10 effective daughters in at least 3 herds. The least number of actual daughters is 13, inherds, while the highest number of daughters is 66, in 21 herds. The average number of daughters pe

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    bull is 27 daughters in 12 herds. The higher the reliability, the less likely the ABV is to change as moreinformation becomes available.

    The 22 bulls have an average ABV of -1 litres of milk, +1 kg of fat, +0.02 % fat deviation, 0 kg ofprotein and -0.05 % protein deviation.

    Bulls with negative proofs have been culled, and there are currently seven bulls with plentiful amounts

    of semen available. These have, average ABV's of +88 litres of milk, +4 kg of fat, +0.02 % fatdeviation, +1.5 kg of protein and -0.11 % protein deviation.

    Only the very best of these bulls will be used to breed young bulls for future progeny testing. The bullscurrently being used to breed young bulls have average ABV's of +188 litres of milk, +10 kg of fat,+0.12% fat deviation, +2 kg of protein and 0.15% protein deviation.

    Production and Reproduction in AFS Cows.

    In discussing levels of production achieved by AFS cows it must first be stressed that the absolute levelsof production achieved under any situation depend more on management and feeding than on genetics.

    Under Australian conditions, where milk prices are relatively low, very high levels of production, whichwould require high levels of supplementary feeding , are not economic and are therefore not attempted.

    The production levels reported in this paper are from cattle grazed under extensive pasture conditions -not stall fed cattle under intensive conditions. Thus, with the Holstein-Friesian breed, the averagerecorded production in Queensland in 1985-86 was 3875 litres of milk and 148 kg of butterfat, with anaverage lactation length of 282 days. This is despite the fact that there appears to be little geneticdifference between Australian Holstein-Friesians and those in Europe and North America, whereaverage productions in excess of 6000 litres are common. The difference in production is due tonutrition and management - not genetics.

    (a) Milk and butterfat production

    Under these grazing conditions and in the relatively sub-tropical conditions which exist throughout mostof Queensland, the AFS cows in 1985-86 produced an average of 2944 litres of milk and 121 kg ofbutterfat with a test of 4.1% in an average lactation of 269 days.

    This compared with average figures for the Holstein-Friesian of 3875 litres of milk and 148 kg ofbutterfat at a test of 3.8% in 282 days.

    Thus, the AFS produced 76% of the milk and 82% of the fat of that produced by Holstein-Friesiansduring the same period. These figures are on a statewide basis.

    When compared on a within-herd basis, it was found that 38% of all AFS cows produced higher levelsof milk than Bos taurus herd mates of the same age. Similarly, 45% of AFS cows produced morebutterfat than their Bos taurus herd mates of the same age. This reflects the fact that the AFS cattlethroughout most of Queensland have not been run in the higher producing herds, where one wouldexpect the performance of the Holstein-Friesian to be superior.

    The overall comparison of the AFS and the Holstein-Friesian on a Statwide basis would be biased tosome degree against the AFS.

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    (b) Changes in production levels

    While considering the Statewide production levels it is of interest to examine the change in the relativeproductions of the AFS and the Holstein-Friesians over the last six years.

    In the period 1980-81 to 1982-83, the average lactation production of the AFS was 2268 litres of milkand 92 kg of fat. This compared with the average production of the Holstein-Friesian during the same

    period of 3430 litres of milk and 129 kg of fat. Thus, over this 3 year period, the AFS produced 66 % ofthe milk and 71 % of the fat produced by the Holstein-Friesian on a statewide basis.

    By contrast, during the period 1983-84 to 1985-86 the average productions were:-

    AFS: 2807 litres of milk and 116 kg of fat

    Holstein-Friesian: 3790 litres of milk and 145 kg of fat

    Thus, during this latter three year period, the AFS produced 74 % of the milk and 80 % of the fatproduced by the Holstein-Friesian.

    The performance of the AFS relative to the Holstein-Friesian improved by 8 % in milk production and 9% in fat production in the period 1983-84 to 1985-86 compared with the period 1980-81 to 1982-83.The significance of these time periods is that it is in the most recent 3 years that the progeny of provenAFS bulls were first starting to enter the recording system.

    (c) Elite Animals

    While the average production of the AFS cows in Queensland averaged 2944 litres of milk and 121 kgof fat, there were a number of elite cows with-productions well in excess of this. These high productionswere once again achieved under extensive pasture grazing conditions.

    The percentage of AFS cows with elite 300 day productions were:

    It is these elite animals which are currently being used in the AFS genetic improvement programme.

    (d) Performance under tropical conditions

    The figures quoted to date have been under the relatively sub-tropical conditions which exist throughoutmost of the dairying areas of Queensland.

    The performance of the AFS relative to the Holstein-Friesian under tropical conditions is moreindicative of the potential of the AFS for developing dairying industries in tropical countries. Milkproduction and reproductive data are available from the Northern Territory of Australia, while growthrate data are available from Ayr in Northern Queensland.

    Over 5000 litres of milk : 2.5%

    4000 to 5000 litres of milk : 13.0%

    Over 200kg of fat : 2.8%

    160 to 200kg of fat : 16.0%

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    The Northern Territory data come from a property 40 km south-east of Darwin (lat. 12 28'S, long. 130

    50'E). The average minimum temperature in Darwin ranges from 190C in July to 250C in December,

    with the average maximum temperature ranging from 300C in July to 330C in December. The relativehumidity ranges from 64 % in winter to 85 % in summer.

    Under those conditions, and again in an extensive grazing situation, the AFS averaged 2556 litres of

    milk and 105 kg of fat, compared with Holstein-Friesian production of 2291 litres of milk and 82 kg offat. Thus, the AFS milk production was 11.6 % above that of the Holstein-Friesian, while butterfatproduction was 27.1 % above that of the Holstein-Friesian.

    Further, the AFS was found to have a 12.6 % shorter length of dry period than the Holstein-Friesian anda 18.2 % shorter intercalving interval. The interleaving interval for the AFS was 389 days, comparedwith 448 days for the Holstein-Friesian.

    Some data regarding growth rates are available from the Department's Ayr Research Station. Ayr issituated in the dry tropics at lat. 19 32'S and long. 147 25'E. It has a mean minimum temperature ranging

    from 11 C in July to 24 C in January, with mean maxima ranging from 250C in June to 340C in January.The relative humidity ranges from 64 % in September to 78 % in February.

    Under these conditions, AFS animals were found to have pre-weaning growth rates of 0.72 kg/day whenfed 10-12 % milk to a weaning weight of 91 kg. This was a 26 % faster growth rate than obtained forHolstein-Friesians.

    When grazed on pangola pasture at 17.5 animals/hectare plus ad lib concentrate (4:1 grain:meatmeal)from 8 to 26 weeks, the AFS calves gained at 0.82 kg/day to reach 162 kg by 26 weeks of age. When theconcentrate ration was restricted to 0.5 kg per day (c.f. 3.2 kg/day consumption under ad lib feeding),the AFS growth rate was 0.39 kg/day to reach a weight of 112 kg by 26 weeks. The growth rates for theAFS calves were some 11 % higher than those for Sahiwal-Jersey cross calves under the sameconditions.

    Future Genetic Improvement in the AFS Breed

    The genetic progress recorded to date with the AFS breed has been obtained through a conventional bullproving programme.

    Nicholas and Smith (1983) report that the maximum rate of genetic progress possible from such aprogramme is of the order of I % per year. With the relatively low numbers of AFS cattle currently inQueensland it is unlikely that this rate of genetic progress can be achieved through conventional bullproving.

    The same authors report that by using a Multiple Ovulation and Embryo Transfer (MOET) programme,rates of genetic gain of up to 2.5 % per year are possible.

    Such a programme has now been established at, the Queensland Department of Primary Industries'Warrill View Research Station. There, the elite cows of the AFS breed have been gathered into one herd.

    The MOET programme involves hormone treatment of these elite cows to produce multiple ovulationsfrom each cow. The embryos are then placed into recipient cows to carry the unborn calf until birth.

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    The aim of this programme is to produce ten pregnancies per year from each of 20 elite heifers. Thfemale progeny (80-120 per year) are mated so as to calve at approximately 2 years of age.

    The progeny of the elite cows will be selected on their own early lactation performance, as well as that otheir full and half sisters, and their dams' first three lactations. Young bulls will be selected on the basiof their female relatives' lactation performance.

    Such a programme allows the generation interval to be almost halved from 6 years to between 3 andyears. It also allows selection to be concentrated in the elite cows of the breed, greatly increasing thselection differential possible. These two factors combine to produce the higher rates of annual genetigain reported by Nicholas and Smith.

    The first progeny.of the elite cows in the MOET programme will commence their first lactation in 198and from then on both bulls and cows of very high genetic merit will be produced each year.

    Introduction of AFS Breed into Tropical Dairying Industries

    There are a number of options available for incorporating the ongoing genetic improvement which i

    being achieved in the AFS breed development programme into developing dairying industries in tropicacountries.

    A number of countries have attempted to improve their dairy industries either by importing pure Botauruscattle or by importing unselected Fl Sahiwal x Holstein-Friesian cattle.

    In the first situation it has been found that the Bos taurus cattle seldom produce at the levels that werattained in their country of origin. This applied particularly when the cattle were placed into eitherpasture grazing situation or a cut and carry feeding situation.

    The lack of adaptation to a tropical environment and the poorer capacity to produce under less favourabl

    feed conditions usually result, as indicated earlier, in pure Bos taurus cows not performing as well acows which are approximately 50 % Bos taurus and 50 % Bos indicus. This applies to both milproduction and reproduction.

    Two problems have usually been associated with the importation of unselected Fl Sahiwal x HolsteinFriesian cattle. Firstly, a proportion of animals will exhibit the "failure to milk" syndrome especially ithey are to be milked under a machine milking situation.

    Secondly, there is a problem in selecting sires to use over these Fl cattle. If they are mated to either purBos taurus(imported) or pureBos indicus (local) cattle the progeny will once again move away from thoptimum 50-50 mix ofBos indicusandBos taurusgenes.

    If they are mated to other Fl cattle, there is usually no scope for carrying out any type of genetiimprovement programme, and so although the optimum 50-50 gene mix would be maintained, no genetiprogress would be made.

    By making use of the AFS breed it is possible to develop an industry which is based on the optimum 5050 mix of Bos indicusand Bos taurusas well as taking advantage of the ongoing genetic programmecurrently in place with the AFS.

    There are several ways in which AFS genetic material could be used as the basis for a developing

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    As there are low numbers of purebred AFS cattle in Australia, the direct importation of either live cattleor embryos will be very limited, although 20 AFS heifers and cows have recently been exported fromQueensland to Malaysia. .

    As discussed earlier, there are plentiful supplies of semen from proven AFS bulls. This could be used ina grading up programme, based on purebred cattle - eitherBos indicusorBos taurus, or crossbred cattle,which are currently in the country.

    As proven AFS semen has become available, the number of doses of this semen exported from theWacol AB Centre in Queensland has risen dramatically. In 1984, just under 8,000 doses of AFS semenwere exported. This figure rose to 18,500 doses in 1985 and should be between 25,000 and 30,000 dosesin 1986. Most of this has been exported to South-East Asia and Central and South America.

    Thirdly, it would be possible to import Appendix 3 AFS (AFS x Holstein-Friesian) heifers which werethemselves in calf to AFS sires, so that their progeny would be Appendix 2 AFS animals. TheseAppendix 2 progeny could be graded-up through two more crossings with proven AFS semen to pureAFS. Such a grading-up programme would allow evaluation, in particular areas, of gene combinationsof Bos taurus and Bos indicus other than 50-50. This may be appropriate in areas where the

    environment, management and feeding were better than in most tropical areas.

    Conclusion

    The Australian Friesian Sahiwal (AFS) has been developed as a tropically adapted dairy breed of cattle,based on a 50-50 mix of Sahiwal and Holstein-Friesian genes.

    Genetic improvement within the breed has, to date, been based on a conventional bull provingprogramme. A number of proven bulls and elite cows have been identified. Future genetic improvementwill be based on a Multiple Ovulation and Embryo Transfer (MOET) programme.

    While the Bos taurus breeds are generally the highest producing dairy breeds under temperateconditions, animals with a 50-50 mix ofBos indicusandBos taurus genes generally perform best undertropical conditions.

    The AFS not only offers the opportunity of using animals with such a gene mix in tropical countries, butthrough grading up programmes, advantage can be taken of the ongoing genetic improvement beingmade in the AFS breed.

    References

    Alexander G.I., Reason G.K. and Clark C.H. (1984) The development of theAustralian Friesian Sahiwal - a tick resistant dairy breed World Animal Rev.51:27-34

    Alexander G.I., Tierney M.L. and Reason, G.K. (1985) Selection of AustralianFriesian Sahiwal dairy cattle for milk and fat production. Proceedings 3rdAAAP Animal Science Congress, Seoul, Korea P.227-229

    Amble V.N. and Jain J.P. (1967) Comparative performance of different gradesof crossbred cows on military farms in India. J. Dairy Sci. 50: 1695-1702

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    Cheah P.F. and Kumar R.A. (1984) Preliminary observations of theperformance of Bos taurus x Sahiwal Dairy Cattle. Report of the VeterinaryInstitute. Kulaniz, Jahore,

    Hayman H.H. (1973) Bos indicus and Bos taurus crossbred dairy cattle inAustralia: II - Effect of calf removal and prolactin treatment on lactation incrossbredBos indicusxBos taurusfemales. Aust. J. Agric. Res. 24: 449-456

    Hewitson R.W. (1968) Resistance of cattle to cattle tick Boophilus microolus II- The inheritance of resistance to experimental infestations. Aust. J. Agric Res.19:497-505

    Louca A. and Legates J.E. (1968) Production losses in dairy cattle due to daysopen. J. Dairy Sci. 51:573-583.

    Madalena F.E. (1981) Cross breeding strategies for dairy cattle in Brazil. WorldAnim, Rev. 38:23-30

    Nicholas F.W. and Smith C. (1983) Increased rates of genetic change in dairycattle by embryo transfer and splitting. Animal Prod, 36: 341-353

    Olds D., Cooper T. and Thrift F.A. (1979) Effect of days open on economicaspects of current lactation. J. Dairy Sci. 62:1167-1170

    Raheja K.L. and Bhat P.N. (1982) Note on the comparative performance ofthree zebu breeds and their Fl crosses with Holstein-Friesian for certaineconomic traits. India J. Anim, Sci. 52(5) :333-336

    Reason G.K. (1986) The comparative performance of dairy cattle breeds in a

    stressful environment at Darwin, Northern Territory. M.Sc. Thesis School ofAustralian Environmental Studies, Griffith University, Brisbane, Australia.

    Reason G.K. and Clark C.H. (1979) Tick resistance evaluations in a dairy breeddevelopment programme. Proc. Inaugural Conf. Aust. Assoc. Animal breedingand Genetics, Armidale p. 234-235

    Reason G.K., Clark C.H. and Goodchild I.K. (1979) Comparative milkproduction of first, second and third generation females in a dairy breeddevelopment programme. Proc, Inaugural Conf. Aust. Assoc. Animal Breedingand Genetics. Armidale p. 65

    Seifert G.W. (1971) Variation between and within breeds of cattle in resistanceto field infestations of the cattle tick (Boophilus microplus)., Aust, J. Agric,Res. 22:159

    Sharma J.M., Dhingra M.M. and Gurung B.S. (1982) Note on the genetic andnon-genetic factors affecting some production traits in crossbred (Friesian xSahiwal) cattle. Indian J. Anim, Sci 52(1) :42-45

    Sivasupramaniam G., Clark H.H. and Nordin Keling M. (1983) An Interim

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    report of milk yield and calving intervals of imported Freisain, Jersey and AMZcattle on Majuternak farms. Proc. Malaysia Soc. Anim. Prod. 5:105-117

    Stokoe J. and Waldron M. (1982) An evaluation of the milking ability ofAustralian Friesian Sahiwal heifers. Proc. Aust. Assoc. Animal Breeding andGenetics 3:153-154

    Syrstad 0. (1985) Heterosis in Bos taurus x Bos indicus crosses. LivestockProd. Science 12:299-307

    Teodoro R.L., Lemos A.M., Barbosa R.T. and Madalena F.E. (1984)Comparative performance of six Holstein-Friesian x Guzera grades in Brazil: 2.Traits related to the onset of the sexual function. Anim. Prod. 38:165-170

    Touchberry R.W., Rottensten K. and Andersen H. (1959) Associations betweenservice interval, interval from first service to conception, number of servicesper conception and level of butterfat production. J. Dairy Sci. 42:1157-1170

    Utech K.B.S., Wharton R.H. and Kerr J.D. (1978) Resistance to Boophilusmicroplus (Canestrini) in different breeds of cattle Aust, J. Agric, Res 29:885-895

    Vaccaro L.P. de (1973) Some aspects of the performance of purebred andcrossbred dairy cattle in the tropics: 1. Reproductive efficiency in females.Animal Breeding Abstracts 41(12):571-591

    Wharton R.H., Utech K.B.W. and Turner H.G. (1970) Resistance to the cattletick Boophilus microplus in a herd of Australian Illawarra Shorthorn cattle: itsassessment and heritability. Aust, J. Agric. Res. 21:163-181

    Home page/ AFS Story / Heat Stress/ Performance/ Breeding/ Management/ Feeding/

    Technical Papers /News of Tropical Dairying / Contacts/

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