Weight gain of weaned Hereford steers in the subtropics during winter : the effect of protein meal supplements.

Abstract

Proc, Aust. Soc, Anim, Prod. Vol. 18 WEIGHT GAIN OF WEANED HEREFORD STEERS IN THE SUBTROPICS DURING WINTER: THE EFFECT OF PROTEIN MEAL SUPPLEMENTS D.W. HENNESSY* and W.D. HOFFMAN** Three groups of Hereford weaners (mean live weight + 8-e-m. 15924 kg) were purchased in April, shortly after weaning, to study the effect of The weaners (7 per supplementation with protein meals in post-weaning growth. group) were rotated among 5 paddocks each 21 days from mid-May to November (174 days) and were supplemented with any of a mineral block, 1.75 kg cottonseed Cottonseed meal meal/steer or 2.63 kg cottonseed meal/steer twice weekly. liveweight change in those steers (P<O*Ol) increased significantly supplemented, compared with those offered a mineral lick with an apparent efficiency use of 2.3 g supplement/g liveweight change. Those steers offered a mineral lick lost 10 g/day of live weight, compared with gains in steers given the meal. INTRODUCTION Calving of cows in the subtropical north-east of New South Wales is, in general, between June and December from matings commencing in September of the previous year. This time has been chosen more for the convenience of marketing calves than appropriateness of season for conception, calving and lactation. Indeed, the digestibility of pastures, and the nitrogen (N) content of grasses, are lowest between May and October, being ca 50% and 8 g N/kg DM respectively. Cottonseed meal supplementation has been an important husbandry practice for improving production in steers (Hennessy et al. 1981) and fertility and calving rates in cows (Hennessy and Williamson 1988a). The period between May and October is critical for growth and survival of calves weaned in March and April but there are no production data on their Plunkett and Ternouth ($988) response to cottonseed meal supplementation. demonstrated that by-pass protein (Le. formaldehyde-treated casein) resulted in higher weight gains in early-weaned calves fed lucerne and sorghum grain. Therefore, in the experiment reported here supplementation with cottonseed meal was compared to a mineral lick for weaned Hereford steers to determine whether liveweight gains could be promoted in steers post-weaning and what implications this might have for weaner heifers selected for inclusion in the breeding herd. MATKRIALS AND METHODS Weaner Hereford steers, approximately 6-months old in April and weighing (mean + 8-e-m) 159 + 4 kg were stratified into three groups, according to live weight and allocated from these strata to three groups called Q, 1-75 and 2.63, These steers were placed into separate paddocks in mid-May after obtaining an initial liveweight, and shifted among a group of 5 paddocks every 21 days. The pastures consisted of Bahia grass (Paspalum notatum), carpet grass (Axonopus affinus), native grasses (e.g. Eragrostis, Bothrichloa, Cymbopogon, appilipedium), blady grass (Imperata cylindica) and the legumes, Bargoo jointvetch (Aeschpomene falcata) and Kenya clover (Trifolium semipilosum). Steers in each group were offered a mineral supplement, in a block, with the blocks replaced when necessary to ensure continual access of steers to minerals. Supplementary cottonseed meal was given twice-a-week to steers in meals of 1.75 or 2.63 kg/steer (equivalent to 500 and 750 g/day, respectively) N.S.W. Agriculture and Fisheries, Agricultural Research Station, Grafton, N.S.W. 2460. ** N.S.W. Agriculture and Fisheries, P-0. Box 376, Casino, N.S.W. 2470, 244 * . Proc. Aust. Soc. Anim.'Prod. Vol. 18 over 25 weeks from May to November. Samples of pasture were taken in May, July and October for estimation of digestibility and N content. Samples were taken by plucking leaves from patches in the pasture where the steers had been Cattle were weighed each 21 days directly off pasture at observed grazing. 0730 h but the initial and final live weights of the study were made on cattle removed from feed and water for 15 hours. Statistical analysis , Live weight and liveweight changes over 174 days were analysed by least square analysis in the programme GENSTAT (Alvey et al. 1980), with initial live weight included as a covariate. Both linear and quadratic contrasts were included as a function of level of supplementation in the analysis. BESULTS Digestibility (estimated from an in vitro; Alexander and McGowan 1961) changed from 62, 49, 55% and N content from 19, 8, 10 g/kg DM which reflected the change from late summer through winter to a poor spring, following heavy frosts in late-June (min. temp. -4'C at the site, and which is a typical seasonal pattern for this subtropical environment. Cottonseed meal significantly (P<O.Ol) increased liveweight change and the live weight of Hereford weaners over 174 days at grazing (Table 1). Table 1 Live weight, liveweight change and efficiency of supplement use of weaner steers supplemented with two rates of cottonseed meal . There was no significant effect of supplementation on weaner live weight during the first 30 days when pasture quality remained high, suggesting that some substitution effect on pasture intake may have occurred or alternatively, body composition changes were occurring which were not detected by weighing. However, following heavy frosting in late June, supplements reduced the rate of loss during July and significantly (P~0.01) improved gain during August through to October (Fig. 1) suggesting that the meal enhanced, rather than reduced pasture intake. 245 Proc. Aust. Soc. Anim. Prod. Vol. I8 Fig. 1. Liveweight change of three groups of steers given no cottonseed meal or meal at 1.75 m or 2.63 m kg/steer/meal during monthly periods when grazing The large weight losses whic'h occurred in non protein-supplemented steers during July, reflects, primarily, the rapid drop in pasture N content from 19 to 8 g N/kg DM which is a feature of areas of the subtropics subjected to frosting. During August and September, rising soil temperatures presumably initiate pasture growth in the C4-grass species with a higher digestibility and All steers were observed eating the N content than during frost periods. cottonseed meal although amounts consumed varied between steers within a group. After three weeks, the consumption pattern remained constant between feeding times with the meal consumed within 30 min of offering. DISCUSSION Cottonseed meal was used, apparently, with a high level of efficiency for liveweight gain over the 174 days of the study. Assuming pasture intake was not increased, and by attributing the difference between the loss in unsupplemented steers and the gain in supplemented steers all to cottonseed At the current price of meal, then the efficiency of use was 2.3 g/g gain. cottonseed meal ($300/tonne) and liveweight prices of S130/kg live weight, the net benefit of 1 kg of cottonseed meal in this study was $0.58. However, cottonseed meal invariably increases the intake of low N tropical forages (Hennessy and Williamson 1988b) which would reduce the efficiency of the supplements use. However, subtropical pastures are used, in general, for extensive grazing by cattle and as such are low-quality feeds with low inputs of fertilisers maintaining only low stocking rates (1 cow/3 ha). Hence, a 10% --increase in forage intake due to supplementation would not perceptibly reduce stocking rates nor reduce the net economic benefits below those suggested. A second goal of the study was to use the response of the young weaner steers as a model for heifers selected for the breeding herd. Assuming heifers would 246 Proc. Aust. Soc. Anim. Prod. Vol. 18 respond similarly to steers then 50% should be showing oestrus activity when at a mean live weight of 223 kg (Cohen et al. 1980) if mating was delayed to early November. Oestrus activity may even be higher in supplemented cattle than in those described by Cohen et al. (1980) because of the supply of branched-chain amino acids from non-rumen-degradable cottonseed meal. Waghorn (1986) reported an association (r = 0.45) between ovulation rate and plasma concentrations of these acids in ewes supplemented with maize gluten. Nettle et al. (1987) suggested that the control of ovulation rate in ewes was sensitive to amino acid supply when he found higher rates in ewes supplemented with protected casein (high in essential amino acids) than in ewes supplemented with protected gelatine (low in essential acids), Higher calving rates occurred in heifers supplemented with cottonseed meal and early-mated (at 15 mo) compared with nonsupplemented heifers (27 mo) in an earlier study nearby (Hennessy and Williamson 1988a)`indicating the potential of protein meal supplementation to enhance growth of young stock and their fertility during winter and the ensuing dry early-summer in the subtropics. ALEXANDER, R.H. and MCGOWAN, M. (1961). J. Br. Grassl. Soc. 16:275, ALVEY, N.G. and 17 others (1980). 'GENSTAT; A General Statistical Program'. (Numerical Algorithms Group Ltd.: Oxford, U-K). COHEN, R.D.H., GARDEN, D.L. and LANGLANDS, J-P. (1980). Anim. Prod. 31:221. HENNESSY, D-W., WILLIAMSON, P.J., LOWE, R-F. and BAOGENT, D-R. (1981). J. 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