Lambs grazed on saltbush are more hydrated at slaughter

Abstract

Dehydration in livestock before slaughter not only compromises animal welfare, but reduces carcass yields and reduces profits to farmers and abattoir processors. Dehydration is attributed to a failure to drink in lairage. Strategic feeding with saltbush may prevent the dehydration of lambs before slaughter. Saltbush, which is widely used to revegetate saline land, has high concentrations of sodium chloride. Ingesting a high sodium diet is known to increase the ionic concentration of the extracellular fluid and stimulate the lamb’s thirst. In this work, we tested the hypothesis that if the lambs maintain the high water requirement when they arrive in lairage, and consequently drink more water, they will be more hydrated and have less carcass shrinkage. Urine specific gravity, muscle dry matter percentage and urine weight are considered to be useful indicators of the hydration status of lambs (Pethick et al. 2003). High urine specific gravity (USG) occurs when the urine is concentrated. Concentrating the urine is a physiological mechanism used by an animal to conserve water when dehydrated. This study was conducted 20 km from Goomalling, Western Australia. Fifty (2 x 25) 6 month old merino lambs (average liveweight of 38 kg) grazed either a saltbush-dominant saline pasture or a ‘control’ barley stubble/pasture plot. Both groups were supplemented with approximately 200 g/d of barley grain. Following 14 weeks of grazing, the lambs were commercially slaughtered after undergoing a 24 hour period in farm curfew, followed by transport to the abattoir and 24 hours in lairage. After slaughter, 2 g samples of the m. semimembranosus (SM) and the m. semitendinosus (ST) were taken and used to calculate muscle dry matter percentage. The bladder of each sheep was also collected after slaughter and the urine extracted, weighed and a sample taken to determine USG.