Six silages were prepared from a primary growth of red clover using additives of 21 formic acid/t fresh crop together with formaldehyde at 0, 16, 34, 52, 77 or 117 g/kg crude protein (CP) in the crop. These silages were offered to appetite, either alone or with a urea supplement at 19·4 g/kg total dietary dry matter (D.M.), to 60 British Friesian steer calves with an initial mean live weight of 106 kg.
Formaldehyde treatment restricted silage fermentation, the effect increasing with level of application. However, butyric acid and 2, 3-butanediol content increased at intermediate levels of application. Protein degradation in the silages was reduced by formaldehyde treatment, as evidenced by a decline in ammonia-N and an increase in insoluble-N content with increasing level of formaldehyde application. The recovery of applied formaldehyde in the silages was low (less than 13%) but increased with level of application.
Intake, live-weight gain and feed conversion ratio followed quadratic trends, with formaldehyde having a deleterious effect at high levels of application. The decline in these production measurements was associated with declines in the apparent digestibility of D.M., organic matter (OM), N and energy with increasing level of formaldehyde application, although there was no effect of formaldehyde on cellulose digestibility. Urea supplementation tended to increase intake and live-weight gain at formaldehyde levels greater than 34 g/kg CP, and apart from the expected increase in N digestibility, did not affect the digestibility of other dietary components. As urea supplementation did not overcome the adverse effects of high levels of formaldehyde application on intake, live-weight gain and digestibility, it appears that the supply of rumen-degradable N was not the major limiting factor on these diets.
N retention followed a quadratic trend with level of formaldehyde application, increasing at intermediate levels (30–50 g/kg CP) and then declining markedly at the highest level of application. A similar trend was evident when N retention was expressed as a proportion of live-weight gain, suggesting possible formaldehyde effects on carcass composition. However, carcass composition data did not confirm any formaldehyde effect. Urea supplementation did not affect N retention, and N balance data indicated poor utilization of the supplementary urea N.
When considering the use of formaldehyde, relative to a formic acid control, in additives applied to red olover at ensiling, these data demonstrate little advantage in favour of formaldehyde and serious disadvantages when large quantities of formaldehyde are applied.