EFFECTS OF PHOTOPERIOD AND FEEDING WHOLE MAIZE, WHOLE BARLEY, OR ROLLED BARLEY ON GROWTH-PERFORMANCE AND DIET DIGESTIBILITY IN VEAL CALVES

Fifty-seven black and white male dairy calves, reared from 48 to 222 k g liveweight, were used to study the effects of photoperiod and feedin g whole maize (75%; WM), whole barley (80%; WE) or rolled barley (80%; RE) based diet after weaning. Photoperiod treatments were 10 h of lig ht (L):14 h of dark (D), 16L:8D, 10L:14D for 6 weeks then followed by 16L:8D, or 16L:8D for 6 weeks then followed by 10L:14D. During weeks 1 7 and 20, 30 calves of uniform weight, ten per feeding treatment, unde rwent two digestibility trials. Exposure to 16L:8D photoperiod or a ch ange from 16L:8D to 10L:14D increased similarly weight gain by 5.6% an d feed intake by 9.5% without affecting feed efficiency. Calves fed WM consumed less feed (P < 0.05), had similar average daily gain (ADG) a nd were 25% more efficient than calves fed WE but calves fed RE had a lower average daily feed intake (P < 0.05), had similar ADG and were 1 0% more efficient than WE-fed calves. Calves fed RE had a tendency to have higher (P=0.07) carcass weight and dressing percentage (118.8 kg and 53.6%, respectively) than calves fed WE (115.4 kg and 52.0%, respe ctively). Body and meat composition, meat color, and haematocrit and h aemoglobin levels were not significantly affected by feeding or photop eriod treatments, Digestibility of dry matter (DM), energy (E), nitrog en, starch (S), phosphorus (P) and copper (Cu) were higher (P < 0.05) for calves fed WM compared to those fed WE. Furthermore, digestibility of DM, E, S, P and Cu were reduced (P < 0.05) in the diet containing WE compared to the diet containing RE. Diet did not affect energy inta ke even though, when expressed as a percentage of energy intake, calve s fed WM retained more E (P < 0.05) than those fed WE (77.2 vs 64.7%) and calves fed RE had a higher E retention (69.8%) than those fed WE. Nitrogen intake and excretion were higher (P < 0.05) for the calves fe d WE compared to those fed WM; there was no significant difference bet ween both barley diets. Nitrogen retention was not affected by the die ts. Blood urea level of calves fed WE was also 28.8% higher than blood urea level of calves fed WM. There was no significant effect of photo period treatments on diet digestibility, E and N retentions, and blood urea levels nor was there any significant interaction with diet treat ments except on body weight changes. In conclusion, our results indica ted positive effects of long-day photoperiod on growth performance but also showed evidence of photorefractoriness to subsequent photoperiod exposure. There was no effect of photoperiod on feed digestibility an d feed efficiency. Digestibility and energy retention were lower with whole barley as compared with whole maize diet but were improved by ro lling barley thus improving feed efficiency.