Effects of evening feeding and extended photoperiod on growth, feed efficiency, live animal carcass traits and plasma prolactin of beef heifers housed outdoors during two Manitoba winters

Abstract

The effects of evening feeding and extended photoperiod on feedlot performance, live animal carcass traits and plasma prolactin were investigated in crossbred beef heifers in two consecutive Manitoba winters (1998–1999; exp. 1 and 1999–2000; exp. 2) using a 2 × 2 factorial design. Heifers were fed in the morning (1000 exp. 1 and 0900 exp. 2) or evening (2000) and exposed to natural winter photoperiod (NP) of <15 h or extended winter photoperiod (EP) of 16–19 h (65 lux exp. 1, 51 lux exp. 2) in outdoor partially covered pens. Heifers (n = 48; 276.9 ± 19.4 kg, mean ± SD) in exp. 1 were given a 60% forage: 40% concentrate backgrounding ration for 56 d followed by a 25% forage: 75% concentrate finishing ration for 70 d. In exp. 2, heifers (n = 48; 228.8 ± 18.8kg) were given the backgrounding ration for 170 d. Mean ambient temperature during the backgrounding and finishing periods in exp. 1 was -13.7 and 0.5°C, respectively. During the backgrounding period of exp. 1, evening feeding increased (P = 0.05) growth rate 10.1%, and tended (P = 0.08) to improve feed efficiency by 9.0%; EP tended (P = 0.08) to improve feed efficiency by 9.0%. During the finishing period there was a time of feeding × photoperiod interaction (P = 0.02) for feed efficiency with a tendency for most efficient gains in the morning-fed NP heifers. There were no main or interaction effects of time of feeding and photoperiod on ultrasonically measured subcutaneous fat depth or longissimus dorsi muscle area in exp. 1. Plasma prolactin was elevated by EP on day 42 (photoperiod × day; P < 0.01) of exp. 1. Mean ambient temperature during exp. 2 was -5.1°C, and there were no main or interaction effects of time of feeding or photoperiod on weight gain, dry matter intake or feed efficiency. However, subcutaneous fat depth was reduced by EP on day 156 (photoperiod × day; P < 0.01). Plasma prolactin did not change during the first 107 d of exp. 2, but subsequently rose in all but the morning-fed EP treatment group. The results indicate that both evening feeding and extended photoperiod can impact growth and feed efficiency of beef cattle during winter-feeding. Key words: Feedlot heifers, beef cattle, evening feeding, extended photoperiod, light, prolactin