Abstract:
The objective of this study was to evaluate the effect of supplemented light on average daily gain (ADG), back fat thickness, eye muscle area (EMA), P8 (fat layer on the rump), feed conversion ratio (FCR) and body dimensions (by means of body measurements) of animals exposed to different levels of light supplementation. Thirty young Bonsmara bulls from the same farm were randomly divided into three homogeneous groups that consisted of 10 animals per group and were subjected to three different levels of light treatment (16 h, 24 h and normal photoperiod). The additional lights provided an average light intensity of 124 lux measured at eye level. The animals were housed in open pens and fed intensively ad libitum on a diet containing 11 MJ ME/kg DM and 14% CP for 84 days. An accredited operator did the ultrasound scanning, using a PIE Medical Falco 100 scanner to measure subcutaneous fat depth between the 12th and 13th rib, longissimus dorsi (eye muscle area) and P8 on days 1, 22, 51, 62 and 84 (end of the trial). Other data collected included body weight (taken every seven days starting on day one of the trial), shoulder height, body length and heart girth. The ADG, FCR and feed intake were calculated at the end of the trial. Results of this study demonstrate that light supplementation was significantly effective in improving the ADG and FCR, mostly at 24 h photoperiod. No differences between the groups were evident for body measurements and ultrasound parameters. The correlations between the ultrasound measurements and FCR, ADG and FI obtained in this study were low, except for the correlation between ADG and EMA which was high (0.64) (P<0.0001). A correlation of 0.66 was found between FCR and heart girth (HG), while HG and ADG showed a correlation of 0.58. The final results of this study concluded that supplemented light (24 h) led to an improvement in ADG and FCR of young beef bulls fed under intensive conditions.
