Effect of storage system and tarpaulin color on nutritional quality and digestibility of stored lucerne hay in the irrigated Sonoran Desert

A field trial and a steer digestion trial were conducted to evaluate the effect of tarpaulin color on the quality and digestive attributes of lucerne (Medicago sativa) hay during a 20 week summer storage period in the irrigated Sonoran Desert of northwestern Mexico and the southwestern US. Lucerne hay was subjected to six treatments (four repetitions per treatment): stored roadside uncovered (UC), stored roadside and covered with a white plastic tarpaulin (WT), stored roadside and covered with a black plastic tarpaulin (BT), stored roadside and covered with a silver-colored plastic tarpaulin (ST), stored outside under a plastic hay barn (BC), and stored in an air-conditioned room (AC). During the 20 week storage period, daily maximum temperatures exceeded 38 °C for more than 16 weeks. Internal bale temperatures were 44.9, 44.1, 43, 42.9, and 40.7 °C for BT, UC, ST, WT, and BC, respectively, during the storage period. UC, WT, BT, and ST, at the end of the field trial, were heat damaged as indicated by an acid detergent insoluble nitrogen/nitrogen ratio greater than 0.14. BT bales had the greatest (P<0.05) heat damage of all treated hay. Total tract dry matter (DM) digestible contents were 668.0, 644.8, 651.5, 597.7, and 562.0 g/kg DM for BC, WT, ST, UC, and BT, respectively. Total tract crude protein (CP) digestible contents were 796.6, 786.2, 773.7, 720.8, and 71.90 g/kg CP for BC, WT, ST, UC, and BT, respectively. The authors concluded that valuable hay products, such as lucerne, should be protected from harsh environmental extremes during storage in hot desert climates. Protecting lucerne with a roof structure (BC) provided the best protection against the heat. Covering the hay with tarpaulins is another viable option, but not all tarpaulin colors are equally efficient. BT did no better than the negative control (UC). The white tarpaulin (WT) did a satisfactory job in protecting lucerne against the heat in comparison to BT and ST. Valuable hay products, such as lucerne, if stored during the summer in hot desert climates, should include an acid detergent insoluble nitrogen analysis to detect the presence of heat damage.