Evaluation of formaldehyde-treated lucerne hay for protecting protein from ruminal degradation, and for increasing nitrogen retention, wool growth, live-weight gain and voluntary intake when fed to young sheep
Authors: Barry T. N. 
Published: March 2009

In three separate experiments, lucerne hay was sprayed with solutions of formaldehyde as it was being baled. Moisture content at baling was respectively 20, 28 and 34% in Expts 1, 2 and 3, the latter being considered higher than normal. Dry matter lost during 4 months of storage averaged 6·7% and was unaffected by formaldehyde treatment.

Increasing rates of formaldehyde application decreased the amount of plant nitrogen digested in the microbial stage of an in vitro system and increased the amount of nitrogen digested in the subsequent acid-pepsin stage (Expt 1 only). When the hays were fed at constant intake to sheep in metabolism cages, formaldehyde treatment depressed the concentration of ammonia and volatile fatty acids (VFA's) in rumen fluid and lowered the molar proportions of iso- and n-valeric acids, but caused either very little or no depression in apparent energy digestibility. It was concluded that formaldehyde treatment of the hays reduced protein degradation by rumen microorganisms and probably increased the amount of protein digested in the post-ruminal region of the digestive system, and that this was achieved without any serious effect on energy digestion.

The hays were also fed for 50 days at restricted and ad libitum intakes to young Komney sheep kept in outdoor pens, followed by a 55-day post-treatment period on spring pasture. Voluntary intake was high in both experiments and was unaffected by formaldehyde treatment in hay baled at normal moisture content. There was a tendency for formaldehyde treatment to cause a small increase in voluntary intake in hay baled at the highest moisture content, but this was counteracted by its effect in depressing digestibility, giving no increase in digestible dry-matter intake. Live-weight gains were low in relation to intake, giving a weight loss in most treatment groups. Formaldehyde treatment significantly reduced weight loss and the effect was still present at the end of the post-treatment period. From regressions of weight change on digestible energy intake, it was considered that formaldehyde treatment had brought about a small improvement in the efficiency with which energy was used below maintenance.

Wool growth rates appeared normal for the levels of intake achieved and were increased 14·5% by formaldehyde treatment at ad libitumintake and 5·5% at restricted intake. Residual responses to formaldehyde treatment in the post-treatment period averaged 8%. The total amount of extra clean wool produced from formaldehyde treatment over both periods was 46and94g respectively at the restricted and ad libitum intakes, representing only 1·5 and 3·0% of the annual fleece production. Wool growth on diets treated with formaldehyde in sheep feed at the maintenance level of energy intake is discussed in relation to the concentration of protein-bound sulphur-containing amino acids (SAA's) in the diet dry matter. It was concluded that large responses in wool growth from protein protection of forage diets are unlikely unless the concentration of SAA's in the dry matter can be considerably increased from their present low levels. It is suggested that the possibility of achieving this through plant breeding techniques be investigated.