Effect Of Methionine Supplementation On Productive Performance Of Dairy Cattle PDF Download

Efficient utilization of feed protein by cattle, because of its impact on economics and the environment, is a major concern for animal nutritionists and producers. Ruminants play an important role in food production (milk and meat) and are major sources of protein for human livelihoods. Two experiments were conducted to assess the value of guanidinoacetic acid (GAA) with or without methionine (Met) on nitrogen retention, methionine flux, and methylation reactions in cattle. As well, a study was conducted to investigate the effectiveness of 2 ruminally protected methionine sources for lactating dairy cows. Another study evaluated effects of abomasal infusions of casein on dairy cattle production. The first experiment examined the effect of abomasal infusions of GAA (0, 10, 20, 30, or 40 g/d GAA) combined with either 0 or 12 g/d of methionine on creatine synthesis and plasma homocysteine concentrations in 6 ruminally cannulated Holstein heifers (520 kg initial body weight). This study demonstrated that plasma creatine was increased by GAA supplementation. Plasma homocysteine was not affected by GAA supplementation when heifers received 12 g/d methionine, but it was increased when 30 or 40 g/d of GAA was supplemented without methionine (GAA-linear x Met, P = 0.003). This experiment demonstrated that post-ruminal GAA supplementation increased creatine supply to cattle and spares arginine utilization. In the second study, effects of GAA supplementation on nitrogen retention and methionine flux were evaluated in 7 ruminally cannulated Holstein steers (161 kg initial body weight) limit-fed a soybean hull-based diet. Treatments were provided abomasally and included 0 or 6 g/d of L- methionine and 0, 7.5, and 15 g/d of GAA. Steers received continuous abomasal infusions of an essential amino acid mixture devoid of methionine to ensure that no amino acid besides methionine limited animal performance, and energy was supplied by ruminal infusion of volatile fatty acids and abomasal infusion of glucose. Whole body methionine flux was measured using continuous jugular infusions of 1-13C-L- methionine and methyl-2H3-L- methionine. Nitrogen retention was elevated by methionine supplementation (P