The effect of a perennial wheat and lucerne biculture diet on feed intake, growth rate and carcass characteristics of Australian lambs

Abstract

A pen feeding study was conducted using 10 month old Poll Dorset × Merino ewe lambs to test the effect of perennial wheat forage on growth rates and carcass characteristics in comparison to annual wheat forage. Individual lambs (n = 48) were fed one of four diets, namely perennial wheat (PW), annual wheat (W), perennial wheat + lucerne (alfalfa) (PW + L) or annual wheat + lucerne (W + L). Lambs were monitored for 28 days during which daily forage quality, forage mineral content, feed intake and weekly liveweight change were recorded. At the completion of the feeding period all lambs were slaughtered in a commercial abattoir. At 24 h post-slaughter the left hand side longissimus lumborum muscle (LL) was removed and assessed for quality attributes. Feed intake increased over the 28 days with W fed lambs eating a greater amount compared to PW fed lambs. The addition of lucerne to the cereal forage (PW + L and W + L) increased feed intake (P < 0.001) of the lambs. However, there were no independent dietary effects on liveweight, carcass weight, carcass traits, including yield parameters, pH declines or fresh colorimetrics. Both the W and PW diets had potassium (K) concentrations greater than 3%. Sodium (Na) deficiency was greater in the PW diet. This indicated that lambs fed these diets would be exposed to impaired calcium (Ca) metabolism and reduced magnesium (Mg) absorption. The addition of lucerne to both cereal forages increased the intake of Ca and Mg and lowered the tetany index. Preferential selection of lucerne was observed in lambs fed the PW + L diet compared to those fed W + L. However, the Na deficiency was not resolved by the addition of lucerne and the dietary cation-anion difference (DCAD) remained high for all diets. Low Na content and consequential effects of a high K:Na + Mg ratio may have limited the expression of higher growth rates (range 55–110 g per day) from the different diets offered. The high DCAD implies calcium homeostasis would be challenged by all diets. This study establishes the value of perennial wheat as a novel forage source as there were no unfavorable effects on lamb carcass parameters, however the mineral imbalances in the forage would need to be managed in the same way as they are presently managed in grazing systems using dual-purpose annual wheat.