Temperature and Temperature Humidity Index Changes during Summer to Autumn in a Temperate Zone May Affect Liveweight Gain and Feed Efficiency in Sheep

Lamb finishing during summer in southern Australia faces the challenges of dry paddock feed of low nutrient value and energy concentration, combined with periods of high temperature that reduce appetite. One potential forage to overcome these challenges is camelina, a brassica with a high lipid concentration. Liveweight gain (LWG) and feed efficiency (FE) of a pelleted diet containing 15% camelina hay (CAM) were compared with an equivalent diet based on oaten hay (STD), a feed commonly used during dry seasons. The experiment was conducted under summer to autumn conditions using 56 maternal Composite (Composite) wether lambs (4 months, 28–38 kg liveweight) and 56 Merino wether yearlings (15 months, 37–43 kg liveweight). Animals were maintained in group pens (8/pen) and weekly average feed intakes per pen and liveweights per pen were determined in a shaded well-ventilated animal house. The LWG and FE for both animal types were significantly lower during weeks 5–8 compared with weeks 1–4. These changes coincided with a higher proportion of daytime maxima exceeding 28 °C (50% vs. 21%) and night-time hours exceeding 22 °C (15% vs. 9%). The experiment indicated that the LWG and FE of sheep fed the CAM diet were less affected by the elevated temperatures than sheep fed the STD diet during weeks 5–8. However, further research under controlled environmental conditions is required to further validate these results.