Abstract
Forages cut at sundown usually contain a greater concentration of nonstructural carbohydrates (NSC) than those cut at sunrise. Maceration can speed up the rate of moisture loss of cut forage during field drying and reduce NSC utilization by plant cells. We aimed to evaluate the effects of cutting time and forage maceration on feed preference, apparent total tract digestibility of nutrients, and N balance in growing steers. A mixed sward of birdsfoot trefoil and timothy grass was divided into two halves, with the first half cut at sundown (1800 h) after a sunny day and the second half at sunrise (0600 h) the next day. Approximately 50% of the sundown- and sunrise-cut herbage were macerated. Forages were harvested as hay resulting in four treatments: 1) sunrise-cut hay (AM); 2) AM plus maceration (AM-M); 3) sundown-cut hay (PM); and 4) PM plus maceration (PM-M). Hays were offered as the sole feed source to four crossbred steers (296.1 ± 7.25 kg) according to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Each period lasted 21 d with 14 d for diet adaptation and 7 d for collection. Hays cut at sundown had 15% greater NSC than those cut at sunrise. A cutting time by maceration interaction was found (P < 0.05) for intake and apparent digestibility of crude protein (CP), indicating that these two variables decreased more when maceration was applied to sundown- versus sunrise-cut hays. Similarly, interaction effects were observed (P < 0.05) for total digestible nutrients and digestible energy, showing that maceration decreased the energetic value of sundown-cut hays but did not change that of sunrise-cut hays. Steers fed hays cut at sundown had decreased urinary N excretion and improved retained N (P < 0.05), whereas N retention was reduced by maceration (P < 0.05). In addition, six crossbred steers were used to assess feed preference, 2 wk before (period 1) and 1 wk after (period 2) the digestibility trial. Animals were randomly assigned to receive a sequence of the four hays combined in pairs. The intake rate was greater for sundown- than sunrise-cut hays, and it was decreased by maceration. Steers showed the greatest preference for PM hay, while AM-M was the most rejected. In conclusion, shifting forage cutting from sunrise to sundown increased hay NSC concentration, which resulted in improved N utilization and preference. Forage maceration during field drying decreased CP concentration and N retention in beef steers under the conditions of our study.