Energy expenditure in Awassi sheep grazing wheat stubble in the northern Negev Desert of Israel

摘要

In semi-arid Mediterranean areas, small grain aftermath stubble represents an important summer source of food for grazing flocks of small ruminants. Wheat stubble is a mediocre source of forage and flocks are grazed in summer under harsh conditions oftemperature and air dustiness. However, stubble grazing procedures are changing, water and shading are more frequently available between grazing sessions ("improved management"), and the biological soundness of this ancestral practice needs to be re-visited. The present study was aimed at evaluating the cost in energy of "improved" wheat stubble grazing, compared with feeding a similar diet indoors. The intake of stubble was first quantitatively and qualitatively evaluated in Awassi sheep. Ewes consumed daily 980+- 100 g day~(-1)of wheat stubble. Ewes were then housed and fed diets consisting of wheat hay, straw and grain formulated to be iso-energetic and iso-nitrogenous to diets consumed from wheat stubble. The average intake of ME was similar during the confinement and the pasture periods (6.4+-0.5 and 7.6+-0.8 MJ day~(-1)of ME, respectively). During 2 days of each period, animals were fitted with external electrodes and data loggers of heart rate and skin temperature. Energy expenditure (EE) wascalculated from oxygen consumption estimated as the product of heart beats rate measured for the two days by the amount of oxygen delivered to body tissues at each heart beat (O_2 pulse). The O_2 pulse was determined by simultaneously measurement of oxygen consumption and HR twice daily on two occasions, while grazing stubble and indoors. Energy expenditure and energy balance were not different in sheep while grazing wheat stubble (11.1 and -3.5 MJ day~(-1)) or fed indoors (11.1 and -4.8 MJ day~(-1)). Our data show that stubble did not cover nitrogen and energy requirements for maintenance, and that the cost of summer stubble grazing carried out under conditions described here is less than thought before.