Strategies of energy supplementation for cattle fed tropical forage and infrequently supplemented with protein

Our objective was to evaluate the effects of different energy supplementation strategies in Nellore heifers fed tropical grass forage and infrequently supplemented with nitrogen (N) compounds on voluntary intake, digestion, ruminal fermentation and fibre dynamics, urinary excretion char-acteristics, N balance, and hormonal and blood metabolic profile. Five rumen and abomasum fistulated Nellore heifers, averaging 332 kg of body weight, were used in a 5 x 5 Latin square design. The five treatments were: control, without supplementation; supplementation of 660 g of crude protein (CP) every 3 days; supplementation of 660 g of CP every 3 days and daily sup-plementation with 440 g of starch; supplementation of 660 g of CP and 1320 g of starch every 3 days; and supplementation of 660 g of CP and 1320 g of starch every 3 days, but starch sup-plementation was performed one day after CP supplementation. On average, treatments did not affect (P > 0.44) voluntary forage intake. However, the forage intake varied over the three-day supplementation cycle. Forage intake was depressed (P < 0.05) by protein supplementation alone on the first two days of the supplementation cycle, but increased on the third day. Only the concomitant supplementation with protein and starch caused a constant intake over the days. Ruminal fibre digestibility and the ruminal N balance were improved by supplementation (P < 0.05). A concomitant evaluation of serum urea N, rumen ammonia N, blood transaminases, and urinary excretion indicated that protein supplementation alone caused a hepatic N overload, which was improved when starch was concomitantly provided with protein. We concluded that infrequent protein supplementation causes negative impacts on hepatic metabolism and depresses voluntary forage intake, remarkably on the day the supplementation occurs. However, these negative effects on intake can be eliminated with adequate energy provision concomitantly with protein supplementation.