Effect of Fungal Biomass in Moldy Alfalfa Hay on Preference by Dairy Calves with No Previous Exposure to Moldy Feeds

A study of 141-kg dairy calves evaluated their preference for alfalfa hay that contained different amounts of fungal biomass, which was estimated by the glucosamine assay. Alfalfa that was harvested at different maturities and stored at varying DM contents was chopped and blended to produce four forage treatments. The four forage treatments included hay that had 1) low NDF content and a low amount of fungal biomass, 2) high NDF and low fungal biomass, 3) high NDF and moderate fungal biomass, and 4) high NDF and high fungal biomass. Forage treatments were offered in pair combinations with two feeders per calf; treatments were switched from one feeder to the other on alternate days. The four forage treatments were offered in such a way that all six pair combinations were tested in each period. Each of the two trials was designed as a 6 x 6 Latin square. Preference data were collected for the 6-d periods and were analyzed as a split plot. Difference in intake of paired forage treatments was the response variable. Hay preference declined as either fiber content of hay or amount of fungal biomass in hay increased. Forage intake of each treatment relative to mean intake was 3.3, 0.8, –0.5 and –3.7 kg/6 d for forage treatments 1, 2, 3, and 4, respectively. Low preference for molded hay would probably result in greater feed sorting and lower intakes when calves have a choice of feedstuffs.