Effects of shearing, ambient cooling and feeding with byproducts as partial roughage replacement on milk yield and composition in Assaf sheep under heat-load conditions

Information is lacking in the literature on the effects of ambient cooling in combination with shearing and replacement of roughage with highly digestible byproducts on milk production in Assaf ewes. Two experiments were conducted in two sequential summer seasons. Experiment 1 measured the effects of sheep shearing and of shearing + ambient cooling during late pregnancy and lactation on lamb weight and milking performance of mature Assaf ewes. Experiment 2 measured the effects of altered dietary regime and its combination with shearing + cooling on milking performance of Assaf mature and first-lambing ewes. Experiment 1 demonstrated that ambient cooling under heat-load conditions decreases the temperature humidity index (THI) in the sheep barn by 3.8 units, and reduces lactating ewes' respiratory rate and rectal temperature relative to non-cooled ewes. Cooling of shorn ewes during late pregnancy increased lamb weight at birth relative to the non-sheared non-cooled (control) group. Effect of cooling shorn ewes was reflected in an 8.4% increase in intake, followed by a 7.4 and 9.7% increase in yields of milk and energy-corrected milk (ECM), respectively, as compared with the non-cooled ewes. The positive effect of shearing + cooling continued after termination of cooling at 80 d in milk. In Experiment 2, feeding the experimental diet to mature ewes increased intake, and yields of milk and ECM, and the dietary effect was complementary to the cooling effect. In first-lambing ewes, the diet increased milk and ECM production under the non-cooling, but not the cooling regime.