Abstract:
Thirty high-producing multiparous Holstein cows were used in a completely randomized block design to compare a lysine deficient total mixed ration, which was sufficient in methionine, to the same diet supplemented with a rumen protected lysine product. The CPM-Dairy prediction model was used to estimate the nutrient requirements and adequacy or deficiency of amino acids. During the 21-day prepartum transition period, cows were fed 4 kg (dry basis) of the lysine deficient diet plus Eragrostis curvula hay ad lib. After calving, cows were fed the lysine deficient diet for the first three weeks and were then blocked according to the average production from day 19-21. Fifteen cows were allocated to each treatment and blocked into 15 groups of two each. Data on production parameters were analyzed for all cows and also separately for cows in the 10 highest production blocks. The experimental period was from day 22 to 120 postpartum. Lysine supplementation resulted in an optimal dietary lysine : methionine ratio in metabolisable protein of 7.2 : 2.4. Lysine supplementation did not affect dry matter intake, milk production, milk fat percentage, milk protein percentage, milk urea nitrogen, body weight or body condition score; but decreased the non-casein nitrogen and whey content of milk. Furthermore, milk casein, which is the milk nitrogen fraction most sensitive towards increased duodenal supply of lysine and methionine, was not affected. The rumen protected lysine product evaluated did not improve cow productivity, probably because the product was either unprotected from rumen degradation, or overprotected to the extent that the lysine was not available for absorption in the small intestine; or absorbed but could not be metabolised. Copyright
