Effects of pasture improvement on reproduction and pre-weaning growth of Hereford cattle in central sub coastal Queensland.

Abstract

EFFECTS OF PASTURE IMPROVEMENT ON REPRODUCTION AND PREWEANING GROWTH OF HEREFORD CATTLE IN CENTRAL SUB-COASTAL QUEENSLAND L. 't MANNETJE* and D.B. COATES * Summary Three years data on cow live weights, conception rates, calving rates, av. daily calf liveweight gain and weaning weights are presented for four grazing systems, viz. native pasture at 0.17 cow/ha, sown pasture of green panic and Siratro at 0.51 and 0.68 cow/ha, and native pasture during summer at 0.34 cow/ha plus access to sown pasture during winter and spring at 1.00 cow/ha. Breeding performance expressed as live weight of calves weaned per cow mated was 166, 210, 221 and 193 kg, respectively. The practical significance of using sown pastures for cattle breeding is discussed. I. INTRODUCTION All published information about the impact of pasture improvement on beef production in southern Queensland concerns post-weaning growth. The effects on breeding performance of cows and pre-weaning growth of calves are important for deciding on the best ways of using improved pastures, For this reason we commenced a long-term study and this paper gives results for the first three years. II. ENVIRONMENT AND METHODS The work is in progress at the Narayen Research Station near Mundubbera (25041' S, 150�52' E). The climate is sub-tropical with a mean annual rainfall of 722 mm, of which 63% is received in the warm period from November until April inclusive. However, rainfall is very erratic and radiation frosts are frequent. These features result in varying periods of shortage of green feed. The area is part of the spear grass region (Shaw and Bisset 1955). The soils of the experimental area are mainly podzols (Dy) derived from granite and are of low nutrient status. The original vegetation was grassy woodland with narrow leaved ironbark (Eucalyptus crebra) as the dominant tree. (Coaldrake et al. 1972). Surrounding properties use this class of -m country, ringbarked, supplied with stock water and fenced, but without pasture improvement for cattle breeding. Store cattle are commonly sold at two to three years of age, The trial was designed to compare pasture systems, with the main emphasis on native versus sown pastures. Native pastures have low carrying capacity and they are never fertilized in commercial practice. Sown pastures on the other hand have much higher carrying capacity than could be maintained on native pasture, and superphosphate is an essential management requirement. Hence, a factorial arrangement of fertilizer and stocking rate between these two pastures would not be sensible. Four systems were chosen: (1) NP - 0.17 cow/ha; native pasture on country with trees killed, with bunch spear grass (Heteropogon contortus) *C.S.I.R.O. Division of Tropical Agronomy, St. Lucia, Queensland 257 as the main grass species. (2) SPL - 0.51 consisting glume) and fertilized cow/ha; sown pasture on cleared country, of green panic (Panicum maximum var. trichoSiratro (Macroptilium atropurpureum) , with 125 kg/ha of superphosphate each year. sown pasture as above, but higher (3) SPH - 0.68 cow/ha; stocking rate. (4) NPSP - a combination treatment with cows and calves confined to native pasture during' summer (November until April) at 0.34 cow/ha and with access to sown pasture for the rest of the year at 1.00 cow/ha. The stocking rate used for NP is based on commercial practice with breeding cows in the district. That for SPL was derived from stocking rate experiments with steers on this station, with adjustment for breeding cows. However, because of the arbitrary adjustment it was decided to incorporate a heavier stocking rate also (SPH). The stocking rates for the two components of NPSP are double those of NP and SPL, but for only half the year. The areas available were sufficient to carry a herd of 24 cows in each treatment. This involved a total of 324 ha. Subdivision into replicates would have meant small breeding herds with the associated problems of artificial herd management, particularly at mating time. It was therefore considered preferable to forego replication. In May 1972 each treatment was set stocked with 24 Hereford cows made up of equal numbers of three age groups. Cows that do not conceive in two consecutive years, or that develop physical defects are replaced by cows of a similar age group of proven breeding ability. Cows will be retained for their whole breeding life up to seven calvings. Each year mating takes place for nine weeks from Nov. 1 with one bull per treatment and bulls are changed regularly between treatments. Calves are weaned in April at which time cows are pregnancy-tested. Weighings are carried out at four weekly intervals. after an overnight period of 16 h without feed or water. The weather for the period under consideration was characterised by a cold dry winter in 1972 (20 days below OoC in July and a total of only 16 mm of rain for July, August and September), followed by above average spring rains ; 1973 had above average winter rainfall and only a few frosts; 1974 had a very cold winter and cool spring, while the first half of 1975 had dry spells in January-February and April-May. According to visual observations of pasture conditions there was always adequate feed in NP and SPL, but SPH was grazed low each year in late winter and spring. There was enough feed in the native pasture of NPSP, but the sown pasture was grazed short at the end of each grazing period. III, RESULTS AND DISCUSSION 1. Cow weights The mean weight of cows in May 1972 was 445 kg. Mean cumulative 258 weight changes together with breeding events are shown in Figure 1. To avoid inequalities between treatments only the weights of pregnant or lactating cows were used. Cows on all treatments had fluctuating weights with the main loss at the time of calving. This coincides partly with the period of lowest feed supply, which usually begins to decline after June. However, reduced gains or small losses before calving were recorded only for NP in 1974 and 1975 and for SPL in 1974. The cows on sown pastures had better weight gains and consistently higher body weights than those on NP. The advantage of cows going on to sown pasture during winter on the NPSP treatment is clearly shown. 2. Reproduction and pre-weaning growth All data in Table 1 are means of three years, except calving percentage which is for two years only. TABLE 1 There are not enough data on conception and calving rates to attempt to distinguish between treatment means. The results of all treatments except SPH are in general agreement with the mean calving percentage of 78 reported by Bewg, Plasto and Daly (1969) for Hereford cows on native pasture on basaltic country at the Brian Pastures Research Station, Calf performance differences between the treatments were consistent over the three years. ADG for calves on SP was always appreciably higher than for those on NP, resulting in up to 40 kg higher mean weaning weights. There were no consistent stocking rate effects in the sown pasture treatments., The Reproductive Index is a useful overall measure of breeding efficiency and it shows clearly the advantage of pasture improvement. We had expected a greater advantage of NPSP over NP because the cows graze sown pasture during the crucial winter months. The beneficial effects on cow weights during that period of the year were evident, but calf data, although better than those of NP were still much below those of SP. We believe that the summer grazing period at double the stocking rate as on NP may be responsible. Although there was no apparent shortage of feed there would have been less opportunity for selective intake. This is reflected in lower rates of liveweight gain by the cows on NPSP compared to cows on NP during the summers of 1973/74 and 1974/75. Although our results are only preliminary, definite advantages in terms of 'calf performance from using sown pasture have already been shown. Although such advantages may be appreciated by some graziers from their own observations, it is still common practice in Queensland to use the least developed or the worst pastures for breeders. Higher weaning weights of steers have obvious advantages in terms of subsequent marketing possibilities. Other work on this station has shown that steers weaned onto sown pasture will gain about 150 kg in a year. It is therefore feasible to achieve an as fat marketable steer of 470 kg live weight at two years of age, in contrast to marketing store cattle from this class of country. Similarly, high weaning weights of heifers should make it possible to mate at 15 months of age at a weight in excess of 300 kg, thereby gaining a year in their reproductive life. This aspect is now being studied. Additional benefits may be expected from the maintenance of higher live weight of cows. There is also the ability to run the same herd on a smaller area (one third to a quarter), or conversely a larger herd can be kept on the same area. IV. REFERENCES BEWG, W.P., PLASTO, A.W. and DALY, J.J. (1969). Queensland Journal of agricultural and animal sciences 26: 629. = COALDRAKE, J.E., TOTHILL, J.C., McHARG, G.W. and HARGREAVES, J.N.G. (1972). CSIRO Division of Tropical Pastures, Technical Paper No. 12. SHAW, N.H. and BISSET, W.J. (1955). Australian Journal of agricultural Research i 539. 6: 260