The feed intake and grazing behaviour of cattle grazing a crop of Lablab purpureus cv. Rongai

Abstract

Eating behaviour and the diet selected by cattle progressively defoliating a crop of Lablab purpureus cv. Rongai were measured in three periods each of 12 days. Crop composition during defoliation was recorded.At the beginning of grazing the crop contained 2230 kg green leaf/ha but after 12 days' grazing the crop contained only 300 kg/ha. In the first 6 days cattle selected a diet which contained 85% green leaf but after 12 days' grazing the selected diet contained only 17% green leaf. As available leaf declined, grazing time increased from 465 min on day 1 to 685 on day 6 before declining to 490 min on day 12. Maximum grazing time occurred with a green leaf yield of 1185 kg/ha. The number of eating bites increased from 26000 to 44500 between days 1 and 6 and then declined to 30000 after 12 days' grazing. Grazing time and the number of eating bites were significantly correlated (r = 0·99).Bite size declined from 410 mg organic matter (OM)/bite on day 1 to 90 mg OM/bite on day 12. This decrease in bite size caused a linear decline (927 g/day) in estimated organic-matter intake. The rapid decline in bite size and intake was caused by the reduction in the quantity of leaf per unit area and the lack of desire of cattle to eat stem.It was concluded that the desire of cattle to select leaf is so strong that stem yield should be largely disregarded when considering Rongai as a grazing crop.