Effects of replacing soybean meal with slow-release urea on milk production of Holstein dairy cows

S Hallajian,H.M Yarahamdi,J Fakhraei,K.J Khorshidi

doi:10.4314/sajas.v51i1.6

S Hallajian, H.M Yarahamdi + Show 2 more

Open Access

https://doi.org/10.4314/sajas.v51i1.6

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Abstract

The study investigated the effects of replacing soybean meal (SBM) with slow-release urea (SRU) on milk production, milk composition, and rumen fermentation of Holstein dairy cows. Sixteen Holstein cows weighing between 550 and 680 kg in mid lactation were randomly assigned to four dietary treatments in a 12-week study. The treatments consisted of T1: a diet containing 16.7% crude protein (CP), T2: T1 with 0.5% SRU replacing plant protein, T3: T1 with 0.75% SRU replacing plant protein, and T4: T1 with 1.00% SRU replacing plant protein. Animals were fed three times a day with feed being offered ad libitum. Dry matter intake (DMI) and average daily gain (ADG) were not affected by the level of SRU. Feeding SRU did not affect milk production and milk composition significantly, but milk fat and milk urea nitrogen (MUN) levels were increased. Significant differences were observed in ruminal volatile fatty acid (VFA) concentration. Feeding SRU increased butyrate concentration with no significant effects on concentrations of acetate or propionate. Significant differences were observed in cholesterol, triglyceride, high-density lipoprotein (HDL), low-density lipoprotein (LDL), and nonesterified fatty acid (NEFA) concentrations, but glucose, very-low-density lipoprotein (VLDL) and β-hydroxybutyrate (BHB) levels were not affected significantly by the treatments. Thus, feeding SRU altered the release rate of ammonia and provided more ammonia nitrogen (NH3-N) for microbial protein synthesis in the rumen.

Highlights

Soybean meal (SBM) is the most widely used protein supplement for the nutrition of the dairy cows, because of its high quality and high protein content (Gidlund et al, 2015)
Treatments consisted of T1: control diet in which 57% SBM was included, T2: control diet supplemented with 0.5% slow-release urea (SRU), T3: control diet supplemented with 0.75% SRU, and T4: control diet supplemented with 1% SRU (Table 1)
The results showed that replacing SBM partially with SRU did not affect BW (P >0.05)

Summary

Introduction

Soybean meal (SBM) is the most widely used protein supplement for the nutrition of the dairy cows, because of its high quality and high protein content (Gidlund et al, 2015). Soybean meal is produced from the residue after oil extraction It has a desirable amino acid balance and high essential amino acid concentrations, and can be used as a protein source (Lopes et al, 2017). The use of non protein nitrogen (NPN) as a protein replacement in ruminant diets appeals to the industry (Golombeski et al, 2006). Ruminants can use these products as a source of nitrogen (N) for microbial synthesis. Nitrogen compounds are decomposed by rumen microbial enzymes, and microorganisms can use these products to make their own proteins (microbial proteins) to produce milk (Broderick et al, 2009; Highstreet et al, 2010; Gardinal et al, 2017). Urea hydrolyzation increases rumen pH, allows ammonia to be absorbed into the blood, and causes advanced ammonia toxicity and disorders

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