Formaldehyde content of milk: 2.Cows fed on grass silage preserved with formaldehyde-containing additive and on formaldehyde-treated urea

In two different experiments silages prepared with formaldehyde-containing additives were fed to cows with and without formaldehyde-treated urea, and formaldehyde was determined on both the silage and the milk. The silage additive contained 20 % HCHO and 30 % 80-% acetic acid and it was used at the rate of 5 l/ton raw material. The treatment levels of urea were 1.4-1.5 g HCHO/100 g urea. Twenty-two Friesian cows were used in Experiment 1 and 20 Ayrshire cows in Experiment 2. In Both experiments they were divided into two groups, one of which had silage as the only source of formaldehyde and the other both silage and HCHO-treated urea. Exp. 1 lasted 18 weeks and Exp. 2 13 weeks. The average daily milk yield in Exp. 1 was 14.2kg and in Exp. 2 it was 22.8kg FCM. When the experiments started at least 4monthshadelapsed from the preparation of the silages. In Exp. 1 the silage contained on average 13.0 mg HCHO/kg (10-16 mg/kg, n = 5) and in Exp. 2 it contained 64 mg HCHO/kg (45-90 mg/kg, n = 8). Judged by the fermentation criteria both silages were of good quality, but according to organoleptic tests the quality of the silage was better in Exp. 1 than in Exp. 2. In Exp. 1 the cows received HCHO from the silage at the average rate of 0.13 g/day and one group also received 2.01 g HCHO/day from the treated urea (altogether 2.14 g/day). Formaldehyde was found in the milk of four cows on the latter diet but in only one milk sample from three of them and in two samples from one. The HCHO content of these samples was 0.2-0.3 mg/l. In Exp.2 the cows in the two groups received HCHO from the silage at the average rates of 1.47g and 1.58g/day. In addition those in the latter group received 1.29g HCHO from the HCHO-urea (altogether 2.87g/day).The average formaldehyde content of the milk in the former group was 0.3mg/1(0-0.7mg/l) and in the HCHO-urea group 0.6mg/l(0.3-1.0mg/l). When the only source of formaldehyde was silage, there was a highly significant positive correlation between the HCHO content of the diet and that of milk, but when the cows received formaldehyde from both silage and HCHO-urea, the correlation was not significant. It thus appears that formaldehyde is transferred more easily to milk from silage than from HCHO treated urea.