Effects of supplement feed on cattle behaviour on pasture

Genetics, supplement feed, environment, and management affect cattle behaviours and diurnal patterns on pasture, thus reflecting individual and/or group difference in time budgets. The aim of this study was to investigate effects of supplement feed on grazing behaviour and distance travelled by Zebu heifers during mid-rainy season in Tanzania. 18 heifers aged 3-5 years were assigned to one of three treatments: pasture only (PO), pasture plus supplement (PS), and supplement only (SO). Supplements were distributed twice daily before and after pasture, and consisted of ad lib access to untreated straw plus concentrate (5 kg / heifer / day) for the PS group, and ad lib access to treated straw plus concentrate (5 kg / heifer / day) for the SO group. The restricted pasture management of 8 hours daily grazing time (0900-1700) included the PO and PS groups only. For 11 consecutive days on pasture, behavioural observations, distance travelled, weather type, and temperature was recorded during two daily observation bouts from 0900-1200, and 1400-1700. Behavioural observations included scan intervals every 10 min, registering location on pasture according to a grid map, and activity within one of six behaviours: (1) grazing, (2) walking without grazing, (3) ruminating while standing, (4) ruminating while lying, (5) resting, and (6) other. Additionally, six days of behavioural observations during supplement feeding times were conducted. Mean initial bodyweights (BW) prior to trial was 229 ± 39 kg for all animals, and after one month on trial mean BW gains were 13.2 ± 4.2 kg, 31.3 ± 6.8 kg, and 23.2 ± 7.4 kg, for the PO, PS, and SO groups, respectively. As predicted, providing heifers with supplement feed decreased time spent grazing (in % of total time) during morning (PO=88.4 ± 2.1, PS=78.5 ± 2.9, P ≤ 0.05) and afternoon (PO=72.1 ± 4.8, PS=60.3 ± 4.8, P=0.10) observation bouts. Thus, morning activity created significant differences in resting (PO=2.9 ± 1.3, PS=7.5 ± 1.7, P ≤ 0.05) and other behaviours (PO=2.2 ± 0.6, PS=5.4 ± 0.7, P ≤ 0.01). During the afternoon, a further decline in time spent grazing successively increased time spent resting (PO=7.7 ± 2.6, PS=11.5 ± 1.8, P=0.25) and other behaviours (PO=2.9 ± 0.5, PS=6.6 ± 1.2, P ≤ 0.05). Ruminating while standing had the largest increase in percent of time from morning (PO=1.0 ± 0.6, PS=1.8 ± 0.6, P=0.40) to afternoon (PO=7.2 ± 2.5, PS=10.9 ± 2.9, P=0.34). Distances travelled remained equal between PO and PS groups on pasture, with slightly longer distances travelled during morning (PO=692.9 ± 64.6 m, PS=643.3 ± 50.3 m, P=0.55) v than afternoon (PO=600.4 ± 68.5 m, PS=595.5 ± 63.7 m, P=0.96) bouts. When blocked by weather categories, the PO group (1575.0 m) walked significantly farther than the PS group (1362.5 m) during overcast weather (P ≤ 0.05). In addition, the PS group consistently spent less time grazing than the PO group, and differences were significant in three of four weather categories (mixed overcast: P=0.18, overcast: P ≤ 0.0001, mixed sunny: P ≤ 0.0001, and sunny: P ≤ 0.05). During supplement feeding, there were significant individual differences in time spent eating concentrate (P ≤ 0.01), walking/relocating (P ≤ 0.05), and eating straw (P ≤ 0.05) within the PS group, yet no individual differences were found in time spent grazing on pasture (P=0.54).