Effects of dietary protein concentration and balance of absorbable amino acids on productive responses of dairy cows fed corn silage-based diets

Abstract

A cyclical changeover design experiment (3-wk periods; 12-wk total) was conducted to evaluate whether improving the balance of absorbable AA would allow the feeding of less crude protein (CP) without compromising production, thereby reducing the potential environmental pollution from dairy farms. Sixteen multiparous Holstein cows were assigned to 1 of 8 dietary treatments as total mixed rations (TMR) containing [dry matter (DM) basis] 45% corn silage, 5% coarsely chopped wheat straw, and 50% concentrate mixture. The 8 treatments were formulated to differ in dietary CP (14 and 16%; DM basis) and in the balance of absorbable AA achieved by changing the main protein source (MPS) of the concentrate mixtures [replacing soybean meal (SBM) with corn byproducts (CBP), dried corn distillers grains (DDG), and some corn gluten meal], and by adding a mixture of rumen-protected Lys and Met (RPLM). Feeding lactating dairy cows corn silage-based diets with 16% CP promoted significantly higher DM intakes and milk yields, and lower feed N-use efficiency than feeding diets with 14% CP. Replacing SBM with CBP significantly increased milk yields and decreased milk fat and protein concentrations, but had no effect on the efficiency of conversion of feed N into milk N. With 16% CP diets, the addition of RPLM decreased feed N use efficiency. A significant effect was observed for the MPS × RPLM interaction on milk protein concentrations. Plasma Lys concentration was lower with diets based on CBP, and plasma Met increased with RPLM. We did not find clear benefits of RPLM in facilitating a reduction of dietary protein without loss of production.

Short communication: Relationship between the efficiency of utilization of feed nitrogen and 15N enrichment in casein from lactating dairy cows

“…The dietary CP level in experiment 1 increased with the increase in ERDP:FME ratio and, in experiment 2, the 1.0% UC diet had the highest CP level. The NUE was significantly higher for the large-deficiency diet (experiment 1), and lowest for the 1.0% UC diet (experiment 2), agreeing with the well-known direct relationship between N excretion in milk and intake of protein (Cabrita et al, 2007(Cabrita et al, , 2011Nadeau et al, 2007). Additionally, when the dietary N Concentrates were named according to their urea content: U0 = 0%, U5 = 0.5%, and U10 = 1.0%.…”

Technical note: Stearidonic acid metabolism by mixed ruminal microorganisms in vitro1

“…Chemical analysis of TMR was done as described by Cabrita et al (2011), and fatty acid methyl esters (FAME) were prepared by direct transesterification ' (Sukhija and Palmquist, 1988), with heptadecanoic acid (1 mg, Sigma-Aldrich Inc.) as the internal standard.…”

Effects of protein sources on concentrations of hydrogen sulphide in the rumen headspace gas of dairy cows

“…Recording of hydrogen sulphide concentrations in rumen headspace gas commenced at 0930 h. Immediately after the last collection, the cows were offered the morning meal (1315 h), with the afternoon meal being offered at the normal time (1730 h). Samples of feeds and protein sources were taken each day and analysed for DM (oven drying), ash (furnace), CP (microKjeldahl with Se catalyst), ether extract (extraction with petroleum ether using Gerhardt Soxtherm 2000 Automatic equipment, Foss, Hillerød, Denmark), NDF, ADF and ADL (van Soest detergent methodology with amylase and without sodium sulphite; using Fibretec equipment, Foss) and starch (enzymatic) according to Cabrita et al (2011a). AAs were analyzed on dried samples after initial oxidation with performic acid according to Dewhurst et al (2007).…”