The development of the Australian Milking Zebu

R.H. Hayman

1. AMZ cattle on the F.D. McMaster Field Station at Badgery's Creek.

Tropical climates are generally inimical to dairy cattle originating from temperate zones, while cattle native to the tropics, although genetically well adapted to the stresses of climate and parasites which they encounter, are not high milk producers. Australia, which has approximately one third of its land mass lying north of the tropic of Capricorn, has no indigenous cattle and, as would be expected in a country settled by Europeans, the cattle introduced were Bos taurus.

As dairy animals, these did not perform as well as expected in the country's tropic and near-tropic areas and it was decided to make an attempt to improve their performance by introducing exotic (Bos indicus) genetic material, and by crossbreeding combined with selection among the filial generations to establish a new breed which would combine the hardiness and resistance to parasites of Bos indicus with the higher milking potential of Bos taurus. Two breeds, the Red Sindhi and the Sahiwal, small herds of which had been presented to the Commonwealth of Australia by the Government of Pakistan, were used as Bos indicus parent material. Both are accepted dairy breeds on the Indian subcontinent. Jerseys were chosen as the Bos taurus parent.

They were the most common dairy breed in Australia, particularly in areas of climatic stress, and were also generally accepted as being best able to withstand such stresses.

The crossbreeding programme was designed to take place in three stages.

R.H. Hayman, CSIRO, Division of Animal Genetics, F.D. McMaster Field Station, Badgery's Creek, N.S.W., Australia.

First stage

In the first stage, which was carried out on the F.D. McMaster Field Station of the Commonwealth Scientific and Industrial Research Organization (CSIRO) at Badgery's Creek, New South Wales, parental breeds were crossed and the filial generations mated inter se up to F₃, Sindhi and Sahiwal crossbreds being kept separate. All females in each generation were milked for at least their first lactation, and males for breeding were selected on the basis of their dams' performance. Milk production under Australian dairy conditions was the sole criterion of excellence. The general procedure is shown in Figure 2.

2. Stage 1 - Breeding programme at Badgery's Creek

This stage, which has been described elsewhere in detail (Hayman, 1972), revealed that Sahiwal crosses were on the whole superior milk producers. The breeding programme has in later years been concentrated on animals derived from Sahiwals. Although the better Sindhi crosses have been retained and their offspring used in the general breeding programme, crossbreeding with Sindhis has been otherwise discontinued. In both crosses there were considerable differences in production between the daughter groups of the various sires used, indicating that selection for milk production would be successful. A major obstacle to progress was encountered when it was discovered that a high proportion of the crossbred females from both breeds failed to continue in lactation after separation from their calves. This appears to have been due to their failure to let down milk without the stimulus provided by the presence of the calf, rather than any inherent lack of producing capacity (Hayman, 1973). This characteristic is not a handicap in regions where Bos indicus is native, but is a complete disqualification under Australian dairy conditions where cows are permanently separated from their calves six to ten days after the latter are born. It was exhibited by some 70 percent of filial generation females, all of which were culled from the herd.

Altogether 212 Jersey females were mated to 10 Sahiwal and 8 Red Sindhi sires, to produce 146 F₁, F₂ and F₃ Sahiwal cross female descendants, and 124 F₁, F₂ and F₃ Red Sindhi cross female descendants. Average first lactation production figures for these animals are shown in Table 1. Data from all lactations, including the 70 percent of filial generation animals which failed in their lactations, have been used to compile the table.

Selection differentials

Production figures from the animals retained in the herd were good, the best crossbred (an F₂ Sahiwal) having produced 4 649 kg of milk and 242 kg of butterfat in 305 days during her first lactation, which compares with a first lactation of 4 536 kg of milk and 242 kg of butterfat in 305 days from the best Jersey. Prospective sires were chosen from the male progeny of the best of these females. Selection differentials were not as great during the early years of this stage as they were later, when larger numbers of suitable females became available. However, maximum selection pressure was exerted at all times and numerous sires (8 F₁ and 6 F₂ Sahiwal, and 7 F₁ and 3 F₂ Red Sindhi crosses, respectively) were used to obtain as wide a sample as possible of the available genetic material. The selection differentials shown in Table 2 have been estimated from production figures which include the first lactation records of all dams.

Data have been used from animals which failed to let down milk after being separated from their calves. Thus, selection is against poor dairy temperament as well as low production, and the two have not been separated. This selection differential is not comparable with that found in standard European herds, but there is no satisfactory way of distinguishing the two classes of animal. On the other hand, the selection differentials are reduced on the male side when females whose production would qualify them as bull breeders produce only female offspring. Their records consequently appear in the general mean instead of appearing as dams of sires.

Table 1. Mean first lactation production figures, with their standard errors for Jersey (parent) and filial generation females

3 and 4. Lismore, northern New South Wales. Promising young bulls from Badgery's Creek were progeny tested in these herds, belonging to cooperating dairy farmers in the area.

At this stage, progeny testing of prospective sires was out of the question: young bulls were required for mating with heifers of their own age and generation, and it was physically impossible to obtain progeny test data for this purpose.

Second stage

The second stage of the breeding programme was based on the progeny testing of young bulls from meritorious dams. In the later years of Stage 1 more young bulls of prospective merit were being born than could be used on the Field Station and arragements were made, with assistance from the New South Wales Department of Agriculture, to progeny test them in the herds of a group of cooperating dairy farmers in the Lismore area of northern New South Wales. Ten farmers, whose herds now number approximately 700 head, are in the group.

The objective in Stage 2 was to progeny test six bulls per year. As selected proven sires became available from the test, the best in each year was mated with the top 10 percent of producers in each of the cooperating herds in order to produce young sires for future progeny testing. The Badgery's Creek herd was maintained as a high-producing nucleus and source of young bulls with a higher level of Sahiwal blood (50 percent) than that available from the Lismore herds. The general procedure is shown diagrammatically in Figure 5.

Two screening tests

At the height of this stage of the programme up to 40 young bulls a year were becoming available for consideration as progeny test sires, and it was possible to extend the criteria of selection by exposing them to two screening tests, one to artificial climatic stress and the other to infestation with cattle tick.

Bulls were exposed to climatic stress in groups of four. Each group was first placed in a room at controlled dry and wet bulb temperatures of 21 and 18°C, respectively, for a week, and the following parameters were measured for each individual: rectal temperature, sweating rate, respiration rate, and daily food and water intake. The group was then transferred for a second week to a similar room in which dry and wet bulb temperatures were 38 and 24°C, respectively. The same parameters were again measured, and the animals ranked in order of least departure from the first week's parameter. The two last animals on the list were discarded and the remainder retained for further testing under higher levels of stress. At the conclusion of the testing period 12 animals were retained and these were tested for tick resistance. The development and implementation of this testing procedure has been reported in detail by Allen and Donegan (1974).

5. Stage 2 — Progeny testing and selection of sires.

This second screening for tick resistance, which has been shown by Hewetson and Nolan (1968) and Hewetson (1972) to be heritable, is carried out at the New South Wales Department of Agriculture's Cattle Tick Research Station at Wollongbar, in the area where the bulls are to be progeny tested. A critical requirement for the test is that the animals be maintained at pasture, being yarded for infestation and for counting of engorged females. The use of individual moated stalls, although desirable in certain specific experiments, may produce a degree of emotional stress which appears to influence the number of engorged females dropped by particular animals. For this reason screening tests are carried out wholly in the field. The bulls surviving the first screening are artificially infested with tick larvae, and then subsequently challenged with further infestations. The animals are ranked for resistance in inverse order of the number of engorged female ticks dropped at the challenge infestations. The seven highest ranking bulls are retained for entry into the progeny test. Of these the least fertile bull is dropped after the first nonreturn to service period. Progeny test matings commenced in 1962 and the resulting heifers had their first lactations in 1965, lactations in this stage of the programme being completed in 1972. The number of bulls in progeny test matings departed from the planned number of six per year, due to a variety of causes but mainly because in the early test years there were not always six bulls available. The actual number of sires tested each year and their highest and lowest contemporary comparisons are shown in Table 3, which also includes data from daughters of the first sons of selected sires (1972/73).

Production data

A detailed study has been made of the production data obtained during the course of Stage 2 of the breeding programme. This has been published (Franklin et al., 1974) and shows that heritabilities for milk and total fat production are of the order of 0.23–0.27. These values must be considered satisfactory from the point of view of developing a new breed. A brief picture of the results obtained during this period is presented below. Between 1965 and 1972 first lactations were recorded from the daughters of progeny test sires. These were all obtained under the normal dairying conditions of the north coast of New South Wales, where yields are low by generally accepted standards. The low mean yields (1 375–1 820 kg milk) are a reflection of the practice of open grazing under hard conditions, where production and rainfall vary greatly from season to season. No pressure was brought to bear on cooperators to replace their Bos taurus cattle with the Australian Milking Zebu (AMZ), but virtually all have done so now. This argues, perhaps even more than comparative production figures, that this animal is meeting requirements.

Table 2. Comparisons between first lactation production of dams whose sons were used as sires, and first lactation production for their respective generations (means and standard errors)

¹ A = mean production for dams of sires; B = mean production for generation; C = selection differential (B-A).

Table 3. Ranges in contemporary comparisons of sires tested in Stage 2

The nature of the progeny testing programme did not allow worthwhile comparisons between AMZ heifers and Jersey, although it is recognized that such comparisons would have brought out clearly the relative merits of the two groups. But some comparative data are available from Badgery's Creek. These are given in Table 4, which shows mean first lactation production figures for all Jerseys milked on the F.D. McMaster Field Station, together with records from AMZ bred and reared there, and comparable groups of Jersey and AMZ heifers bred in the Lismore area, but reared and milked on the Field Station.

The figures in the table show that there is little difference between Jersey and AMZ heifers under conditions of optimum management. In other words, the Bos taurus potential for production is equalled by that of the new breed. Means for all records, including short lactations, are shown in the table and demonstrate the effectiveness of selection against milk let-down problems. In F₁ F₂ and F₃ females some 70 percent of the population were discarded because of short lactations. This figure fell to less than 10 percent in AMZ heifers, and sires currently selected from the progeny test include some whose daughters have all failed to exhibit the trait.

Third stage

The third stage of the breeding programme is now in progress. In this stage only the sons of sires selected in the progeny test, out of females selected for their own high production, are being submitted to screening and progeny testing.

The final object of the exercise is the development of a dairy animal containing between three eighths and one half Bos indicus blood, and selected for milk production, tolerance to hot climate stress, and resistance to ticks. The cooperating herds now form a nucleus from which females are being disseminated to other herds in northern New South Wales and Queensland. Some animals have also been sent to Malaysia. At the same time the selected sires are being placed in government AI centres. Semen from these sources is now being used both in Australia and overseas. Young bulls with satisfactory hot room and tick resistance performance, but surplus to progeny test requirements, are being placed in Australian dairy herds which have difficulty in gaining access to AI. Surplus females from cooperators’ herds are also being made available to other breeders in northern New South Wales and Queensland, and the breed is gradually spreading.

Table 4. Means and standard errors for first lactation records of Jersey and AMZ heifers

¹ Precise birth dates unknown.
² Age at first calving increased over normal age because of other experimental procedures.

References

Allen, T.E. & Donegan, S.M. 1974. Aust. J. Agric. Res. (In press)

Franklin, I., Hayman, R.H., Hewetson, R.W., Packham, A.H. & Rendel, J.M. 1974. Aust. J. Agric. Res. (In press)

Hayman, R.H. 1972. Aust. J. Agric. Res., 23: 519 – 532.

Hayman, R.H. 1973. Aust. J. Agric. Res., 24: 449–456.

Hewetson, R.W. & Nolan, J. 1968. Aust. J. Agric. Res., 19: 323–333.

Hewetson, R.W. 1972. Aust. Vet. J., 48: 299–303.