Effect of maternal mineral supplementation from lamb marking to weaning on live weight gain in lambs

Cereal crops can provide a valuable forage source for animals during winter and may be grazed by different livestock species and classes depending on the production system. However, mineral content of these crops is not in balance. Studies have shown that around 14% of barley forages are deficient in sodium (Na) and 30% are deficient in magnesium (Mg) compared to animal requirements (Dove et al. 2016). Also, the K concentration in dual-purpose crops are high which consequently reduce Mg absorption (Dove et al. 2016). Previous studies have shown that supplementation with Calcium(Ca), Mg and Na improved live weight gain in weaned sheep and suckling new born twin lambs grazing dual-purpose wheat (McGrath et al. 2015). For production systems based on autumn lambing, ewes and lambs may graze cereal crops from lamb marking to weaning. The current study sought to assess the effect of mineral supplementation to ewes grazing barley on live weight gain in lambs from lamb marking to weaning.The experiment was conducted in 2016 at Charles Sturt University, Wagga Wagga, NSW. Dual-purpose barley (cv. Moby) was sown in a 10 hectare paddock at a rate of 60 kg/ha and the paddock sub-divided into 8 x 1.25 ha plots. Merino ewes (n = 104; 3–5 years old) raising single and twin lambs (n = 164, 4–5 weeks old) were randomly allocated to plots after blocking for single or twin lambs at foot (13 ewes/plot). Ewes in each plot were provided either ad libitum access to a loose-lick mineral supplement containing calcium carbonate (limestone), magnesium oxide (Causmag® AL7) and sodium chloride (coarse salt) at a ratio of 2:2:1 (30 g/head/day) (supplemented) or no mineral supplementation (control).Lambs were weighed at lamb marking, 2 weeks after lamb marking and at weaning. Data were analysed using IBM SPSS statistics for windows. A linear mixed model was used for analysis of the data and the fixed factors were treatment, time points, rearing status and their interaction. Ewe and plots were random factors. Calcium, Mg and Na levels in barley forage appeared adequate for animal requirements (data not shown). The liveweight of twin raised lambs in the treatment group was significantly greater than the control group at weaning time (Table 1). This result shows that mineral supplementation of ewes grazing barley forages from lamb marking to weaning may improve the live weight of twin raised lambs at weaning despite the concentration of key minerals in forage appearing adequate. Ewes with multiple lambs generally produce more milk than single bearing ewes and have increased requirements for minerals such as Ca and Mg, and this may explain why superior growth rate occurred in twin raised lambs when ewes had a free access to minerals. Lamb management at weaning has important impact on post weaning mortality, lifetime productivity and profitability. Therefore, higher weaning weights may improve weaner survival and performance, increasing farm production (Kenyon et al. 2004).