Influence of the addition of fish meal to diets of roughage or roughage and concentrate on the consumption and live-weight gain of growing cattle

Abstract

Two feeding trials were carried out to evaluate the influence of the addition of fish meal (F) to diets based on two tropical roughages of different nutritive value supplemented or not with a rumen degradable concentrate (C), on the intake and live-weight (LW) gain of growing cattle. A factorial 2 × 2 arrangement was used with the following treatments: zero or 300 g day −1 F supplementing diets of roughage or roughage plus 1.0 kg day −1 C. Twenty 190 kg Brahman × Holstein animals were used in each experiment over 12 or 11 week periods with basal diets of fresh forage or sorghum silage. The consumption of forage and silage in control treatments without supplements were 25.8 and 15.1 g kg −1 LW, the crude protein (CP) contents were of 81 and 69 g kg −1 dry matter (DM) and DM disappearances in nylon bags at 48 h (DMD48h) were of 579 and 400 g kg −1 DM. The N degradability of concentrate and fish meal were 0.88 and 0.36. Another two trials were carried out with rumen-fistulated animals to evaluate the influence of these supplements on some parameters of rumen digestion. It was found that forage DMD48h was slightly decreased and its rate of digestion in nylon bags was reduced ( P < 0.05) with F, but not with C. In the feeding trials F slightly increased ( P > 0.05) silage intake and decreased forage consumption, and the LW gain responses to this supplement varied with the quality of the roughage. They were higher with the silage of lower quality than with the forage, with increments of 0.33 and 0.16 kg day −1, respectively. These responses were very similar for each roughage given alone or supplemented with concentrate. LW gain was appreciably increased by F and C in both trials ( P < 0.01), but the magnitude of the responses per unit supplement was different between sources and roughages. LW gain increments were 50 and 108 g per 100 g F with forage and low quality silage, and 33 per 100 g C with both roughages. These results indicate that LW gain response to fish meal is very large with low quality tropical forages, and as its quality improves this response is appreciably reduced and tends to be similar to those obtained with concentrates based in degradable sources of nitrogen.