Effect of added sugar on preference and intake by sheep of hay cut in the morning versus the afternoon

Ruminants prefer hay cut in the afternoon to hay cut in the morning, presumably because hay cut in the afternoon contains higher concentrations of non-structural carbohydrates than hay cut in the morning. We determined if adding sugars (glucose and sucrose) to ground hay would account for differences in preference and affect intake of hay. Alfalfa hay cut either in the afternoon (PM) or the following morning (AM) was used in the trials. Glucose and sucrose were added to AM hay (AMS) to make its sugar content similar to PM hay. During the first trial, lambs received a choice of either: (1) AM and PM hay; (2) AMS and PM hay; or (3) AMS and AM hay. Lambs preferred PM to AMS or AM hay. We also studied how increasing the concentration of added sugars affected preference for hay. Lambs received a choice of AM hay and AM hay with either 1, 2, 3, or 4% added sugar. On the first day of the trial, lambs ate similar amounts of each hay type, regardless of the amount of sugar added. By the end of the trial, lambs preferred hay with 2, 3, or 4% added sugar compared with AM hay without added sugar. During the intake trial, lambs ate similar amounts of AM, AM hay with added starch and sugar (AMSS), and PM hay. After the intake trial, a final preference trial determined that prolonged exposure to AMSS hay increased preference for AMSS hay compared with AM hay. Our results indicate that preference for PM hay is likely related to increased levels of sugars, such as glucose and sucrose, and that lambs learn about the post-ingestive benefits of exogenous sugars added to hay.