Abstract
Simple SummaryMethionine (Met) deficiency in the diet can limit milk protein production and lead to excessive nitrogen (N) excretions to the environment by dairy cows. We demonstrated that the supplementation of a new rumen-protected Met product to a Met deficient diet increased milk protein yield and decreased manure N excretions of high producing dairy cows. Increased blood flow to the mammary glands and increased apparent total tract digestibility of dietary crude protein seem to be the underlying mechanisms for those improvements in production and the environmental sustainability.The study objective was to determine the effects of rumen-protected methionine (Met) by microencapsulation (RPM) on amino acid (AA) supply to the udder, milk production, and manure nitrogen (N) losses of dairy cows. A corn and soybean-based diet deficient in metabolizable Met (~10 g/d) was supplemented with RPM providing 0, 11.0, 19.3, and 27.5 g/d of Met. Dry matter intake (DMI), milk production, plasma essential AA (EAA), mammary plasma flow (MPF), and fecal (FN) and urinary N (UN) outputs (g/d) were determined. The RPM increased linearly milk yield, milk protein yield, and energy corrected milk yield (p < 0.040) without affecting DMI. Milk protein yield increased by 50 g/d for the 19.3 vs. 0 g/d dose (p = 0.006) but the rate of increment decreased for 27.5 g/d dose. Plasma Met, and MPF increased linearly with RPM dose (p < 0.050). Apparent total tract digestibility of crude protein (p = 0.020) and FN (p = 0.081) decreased linearly with RPM. The UN did not change but total manure N decreased linearly with RPM (p = 0.054). The RPM (19.3 g/d) seemed to help cows overcome the metabolizable Met deficiency while mitigating manure N excretions to the environment.
Highlights
Methionine (Met) is one of the most limiting amino acids for lactating dairy cows in the US [1]
Dairy cows convert only 25–30% dietary crude protein into milk protein while the balance is excreted in urine and feces [7,8]
Each rumen-protected methionine (Met) by microencapsulation (RPM) dose mixed in 100 g of ground corn was top-dressed separately on the basal diet of individual cows immediately after the diet was delivered in the morning
Summary
Methionine (Met) is one of the most limiting amino acids for lactating dairy cows in the US [1]. The data of non-ruminant species highlight that dietary Met deficiencies can decrease the digestion of proteins in the small intestine and increase fecal N losses [2,3,4]. Once excreted into the environment, most of the urinary N is volatilized readily to ammonia that contributes to air and water pollution [5]. Fecal N is transformed gradually to ammonia, nitrate, and nitrous oxide that contribute to air and water pollution, and global warming [6]. Dairy cows convert only 25–30% dietary crude protein into milk protein while the balance is excreted in urine and feces [7,8]. Feeding to alleviate dietary EAA deficiencies and enhance EAA supply to the udder is critical in improving the economic and environmental sustainability of dairy production [10]
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