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

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.

Effect of Slow-Release Urea Administration on Production Performance, Health Status, Diet Digestibility, and Environmental Sustainability in Lactating Dairy Cows

“…Reproductive performance remained unaffected by the treatment ( Table 2 ), which is in agreement with the findings of Hallajian et al (2021), who reported similar characteristics of the follicles, blood levels of progesterone, and milk urea nitrogen (MUN) between dairy cows fed exclusively with SBM or with the partial replacement of SBM, SRU [ 32 ]. These results show that feeding with SRU appears to overcome the possible negative effect of other NPN sources, such as feed grade urea, on both plasma urea nitrogen and overall reproductive performance [ 33 ].…”

“…Average weekly milk production in the two groups (a = p-value ≤ 0.05; x = p-value ≤ 0.1).Conversely,Galo et al (2003) [30], andGiallongo et al (2015) [31], did not show any gain in milk production when SBM was partially replaced by SRU.In the present study, DMI was significantly reduced in the treatment group (23.92 vs. 24.69 kg/head/d in control) (p = 0.04), positively affecting FCR. In fact, the FCR significantly improved (p < 0.0001) during treatment with an overall increase in feed efficiency at 6.9% due to the lower DMI and better milk production.These results agree with the findings ofSalami et al (2021), who reported a 3% enhancement in feed efficiency due to a significant reduction in feed intake without any effects on milk yield when the traditional protein sources were replaced with SRU in dairy cows' diets in Northern Europe[8].Reproductive performance remained unaffected by the treatment (Table2), which is in agreement with the findings ofHallajian et al (2021), who reported similar characteristics of the follicles, blood levels of progesterone, and milk urea nitrogen (MUN) between dairy cows fed exclusively with SBM or with the partial replacement of SBM, SRU[32]. These results show that feeding with SRU appears to overcome the possible negative effect of other NPN sources, such as feed grade urea, on both plasma urea nitrogen and overall reproductive performance[33].Body condition scores were not influenced by the treatment (Table2).…”

“…Body condition scores were not influenced by the treatment ( Table 2 ). Similarly, Neal et al (2014) [ 34 ] and Hallajian et al (2021) [ 32 ] did not report significant differences in terms of body weight and body condition in dairy Holstein cows fed with diets containing SRU compared with SBM control diets.…”

“…The partial replacement of SBM with SRU decreased the CFP of the treatment diet, expressed per 1 kilogram of diet (−10.98%; 449.91 vs. 505.41 g CO 2 -eq/kg diet) compared to the control diet due to the lower global warming potential (GWP) of SRU than SBM [ 24 ]. The highest GWP of soybean meal is mainly due to large transport distances and emissions related to land-use change (LUC), such as deforestation, which can lead to heavier emissions of greenhouse gases [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. These results agree with the findings of Salami et al (2021), who showed a 12% reduction in CFP (g CO 2 -eq/kg diet) when SBM and other plant-protein sources were replaced by SRU [ 8 ].…”

“…These results show that feeding with SRU appears to overcome the possible negative effect of other NPN sources, such as feed grade urea, on both plasma urea nitrogen and overall reproductive performance[33].Body condition scores were not influenced by the treatment (Table2). Similarly, Neal et al (2014)[34] andHallajian et al (2021) [32] did not report significant differences in terms of body weight and body condition in dairy Holstein cows fed with diets containing SRU compared with SBM control diets.Also, the treatment did not influence milk quality traits, as reported in Table3. These findings align with the main results found in the literature regarding dairy cows fed with an appropriate amount of slow-release urea[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].No treatment effects were found in the overall health condition monitored daily by the farm veterinary staff.The positive results observed after including SRU as a partial substitute for SBM underlined that ruminal kinetics and fermentation could be optimized in diets with a percentage of soluble protein higher than 30% of the total crude protein and 50% of degradable protein if combined with an adequate intake of nonstructural and rapidly fermentable carbohydrates.Despite the significant increase in the solubility of the protein fraction, no changes in milk quality or reproductive performance were observed.…”