Feeding urea-molasses blocks reduced milk urea nitrogen in Iranian rural dairy cows

A Kiani, N Yosefi and A Azarfar

Department of Animal Science, Faculty of Agriculture, Lorestan University, PO Box 465, Khorramabad, Iran
arkashkia@gmail.com   ;   kiani.a@lu.ac.ir

Abstract

The aim of the study was to investigate the effect of feeding urea-molasses blocks (UMB) on milk urea nitrogen (MUN) and milk production in rural dairy cows. In the first experiment, physical characteristics, palatability and intake of six different UMB formulas (Allen 2007, B1, B2, B3, B4 and B5) were studied using six Iranian rural dairy cows. Average daily intake of cows from Allen 2007, B1, B2, B3, B4 and B5 blocks were 450, 655, 283, 615, 170 and 272 g, respectively. The B1 formula was the best as it had the best physical quality and the highest intake by the animals among the other formulas. In the second experiment, effects of supplementing rural dairy cows with UMB (B1 formula) on milk yield, milk composition and milk urea nitrogen (MUN) were investigated. Six crossbred Iranian rural dairy cows in a cross over design had either freely access (+UMB) or no access to (–UMB) urea-molasses blocks from 30-50 (P1) or 70-90 (P2) days in milk. Daily milk productions were continuously recorded for three months. Milk samples were taken on 45, 50, 85 and 90 day of lactation period.

Result showed that +UMB had significantly higher daily milk production in comparison to –UMB with 9.4 and 9.0 kg respectively. +UMB had similar percentage of milk protein and lactose but significantly lower fat and non-fat solid content compared to -UMB.  Milk urea nitrogen in +UMB were significantly lower than in –UMB (7.2 vs. 9.1 mg.dl^-1). In conclusion, UMB improved milk production presumably via more efficient use of non-protein nitrogen (urea) which is reflected in lower MUN in Iranian rural dairy cows

Key words: indigenous cows, small holder farms, straw based diet, urea-molasses blocks

Introduction

Small-holder dairy cow farmers held more than 4 million crossbred and indigenous dairy cows and produce about 66% of the annual milk production (about 6 million tones out of 9 million tons annually) in Iran (FAO 2010).  In spite of their great economical importance, both crossbred and indigenous dairy cows are mainly fed with poor feedstuffs such as wheat straw-based diets in rural area. Straw-based diets are usually deficient in one or more nutrients, notably, energy and protein. Different feeding strategies have been implemented to improve the quality of such diets. Among the others, supplementing diets with a ruminally available source of nitrogen such as urea has been long used as an effective feeding strategy.  However, when urea is included in these diets rapid release of nitrogen usually results in an imbalance between the supply of nitrogen and energy in the rumen for microbial protein synthesis. Excess nitrogen is mainly absorbed as ammonia (NH₃) by the rumen and is mainly lost to animal as urea at the cost energy. To avoid such a nitrogen loss, one may supplement the diets with a ruminally available source of carbohydrates such as molasses. However, under small-holder farm condition mixing molasses with the other portions of ration is usually a time consuming and labor inefficient process. Producing urea-molasses blocks (UMB) may overcome such problems at small-holder dairy farms level (Makkar et al 2007). Whether supplementing straw based diets with UMB improves the efficiency of N utilizations in dairy cows needs to be monitored on farm.

Milk urea nitrogen (MUN) is often used as an on-farm tool to monitor nutritional status in dairy cows (Roy et al 2011). Milk urea nitrogen is a non-protein component which is positively correlated to dietary protein degradability, and high level of rumen degradable protein (RDP) leads to high MUN values in dairy cows (Roseler et al 1993). Although urea is found in body fluids including milk, urine and blood (Gustafsson and Palmquist 1993), milk is the favorite body fluid for urea determination due to feasible sample collection. Thus, MUN in bulk tank is often used as a tool to monitor efficiency of nitrogen utilization in dairy cows (Hof et al 1997; Jonker et al 2002; Kauffman and St-Pierre 2001). Values for MUN in conventional dairy cow herds range between 12-16 mg/dl (Baker et al 1995) whereas reported values for rural dairy cows are limited, and there is a lack of information about the effects of UMBs on MUN in crossbred dairy cows under smallholder farm conditions.

The current study was consisted of two experiments. In the first experiment, daily intake of six different UMB by crossbred Iranian rural dairy cows was determined and the best formula was chosen based on its physical quality and its daily intake by the cows. In the second experiment, effects of feeding UMB to rural dairy cows hold under small-holder dairy farms condition on milk yield and compositions and MUN were studied.

Materials and methods

Experiment 1: UMB physical quality and intakes

The ingredients and chemical compositions of six UMBs (Allen 2007, B1-B5) are shown in Table 1.

The control blocks (Allen 2007) was made according to the formula suggested by Allen (2007). In brief, to make the blocks, urea and salt were dissolved in 50 ml of tap water. Molasses was then added to the mixture. The other ingredients (wheat bran, rice bran and minerals) were gradually added to the urea-molasses mixture and manually mixed for 5 min. About one kg of each formula were poured in metal mould and manually pressed. The blocks were then left to air dried at shade for 7 days at ambient temperature. Quality characteristics of UMBs including mixing easiness, stickiness, amount of moisture leaching, ability to shape, easiness of separation from the moulds were evaluated by four individual examiners. Hardness (kg/cm²) of the UMB was measured using a penetrometer device (Dial Pocket Penetrometer Kit- H-4205, Humboldt Mfg. Co).

In the first experiment, daily intake of UMB were determined using six multiparous lactating crossbred Iranian cows (third parity; 467 ± 30 kg of live weight; 65 ± 30 days in milk). The cows were individually housed in the tie stalls in a rural dairy farm of at Alishter district, Lorestan, Iran. The cows were fed a straw based diet (including 50% wheat straw, 25% waste bread and 25% wheat bran) ad libitum with a 10% of daily refusal. The experiment lasted for fifteen days. During the first 10 days (adaptation period), 4 blocks (each about 1.5 kg) of each formula (in total 24 blocks) offered to the cows ad libitum, and daily intake for each formula was determined as the number of blocks consumed by the cows. During the last 5 days  a known amount of UMB were offered to the cows twice daily in the morning (10:00 to 12:00) and in the afternoon (16:00 to 18:00) and their residuals were recorded. The intake form UMB was determined as the difference between blocks weight before and after offering to the cows.

Experiment 2: UMBs and Milk yield

In the second experiment, the effects of UMB (B1 formula) on milk production and compositions were studied. Six multiparious lactating crossbred cows (third parity; 460±50 kg; 30 days in milk) were separated from the rest of the herd and individually housed in the tie stalls in a rural dairy farm of at Khoramabad district, Lorestan, Iran. In a cross over design with two periods, the cows were randomly assigned to one the two treatments. In the control treatment (no UMB) the cows were only fed with their regular ration (including 15% alfalfa, 35% wheat straw, 25% waste bread  and 25% wheat bran) ad libitum with a 10% of daily refusal, while in the +UMB treatment cows had free access to urea-molasses blocks (B1 formula) and were fed with the regular ration ad libitum. Each experimental period lasted 20 days (30-50 and 70-90 days in milk) with 17 days of treatment adaptation and 3 days of data collection. All cows were individually fed twice daily at 0800 and 1600 h with approximately 60 and 40 percent of total daily feed allocation at each feeding, respectively. Cows had free access to drinking water and were milked twice daily at 0830 and 1800 h. Milk production was recorded daily during the 90-days data collection period. Double milk samples (100 ml) were collected on days -1, 15 and 20 of each experimental period. Milk samples were preserved with 2-bromo-2-nitropropane-1-2-diol and stored at 4º C pending further chemical analysis. Milk samples were analyzed for protein, fat, lactose, solid not fat (SNF) and total solid contents using Milk-O-Scan 133B (Foss Electric, Denmark). Daily milk fat, lactose and protein (g) were calculated by multiplying the daily milk production and percentages. Milk urea nitrogen values were measured using Bentley Chemspec Instrument, which is based on a modified Berthelot reaction (Chaney and Marbach, 1962) to detect ammonia after urea hydrolysis (Bentley Instruments, Chaska, MN. Milk protein and fat yields were calculated by multiplying milk yield from the respective day by protein and fat contents of the milk for each cow.

Statistical analysis

Statistical analyses were carried out using the MIXED procedure of SAS 9.2 (2009). The models used were:

(1) Y_ij = µ + F_i + e_ij

                (2) Y_ijk=µ + Seq_i + Cow_ij +P_k+T_m+λ_m+e_ijk

where
Y_ij and Y_ijk are the dependent variables under examination,

µ is the population mean for the variable,

F_i is the fixed effect of UMBs formulas (i = 6; Allen 2007, B1, B2, B3, B4 and B5),

Seq_i is the fixed effect of sequence (i = 2; 1 and 2),

Cow_ij  is the random effect of cow within the sequence (i = 6; 1 to 6),

T_m is the fixed effect of treatment (m = 2;  -UMB and +UMB),

λ_m is residual effect of m^th treatment,

e_ij and e_ijk are random error associated with the observation i and ij, respectively.

Model 1was used to analyze data pertained to the first experiment. We used the second model to analyze data from the second experiment. For all statistical analyses, significance was declared at P<0.05. The Fisher’s protected least significant difference (LSD) test was used for multiple treatment comparisons using the LSMEANS of SAS 9.2 (2009).  

Results and discussion

Physical characteristics of UMBs

Beside urea and molasses, other ingredients were also used in UMB formulas. Thus, physical quality of UMB was different based on the proportion of their ingredients (Table 2). Higher molasses content led to a higher stickiness, a better ability of shaping and easiness of separation from the moulds. As the fiber content of the formula increased moisture leaching and ability of shaping in the UMBs were decreased (Table 2). The B1 had better grades for mixing easiness, stickiness, moisture leaching, ability to shape, easiness of separation from moulds compared to Allen 2007 formula. The UMB hardness ranged from 1 to 5 kg/cm² (Table 2). The hardness is a factor that greatly affects animal intake (Hadjipanayiotou et al 1993). In the present study, the B2 formula showed the highest hardness value, but the lowest daily intake among the UMBs. Our finding showed that B1 with the 2.4 kg/cm² had the highest intake among the UMB formulas.

Intakes from UMBs

Daily intakes from different UMB formulas are displayed in Table 2. The highest intake was observed for B1 and B3 (650 and 615 g/head/d, respectively). The B1 blocks had the best physical characteristics, but the B3 blocks felt apart when offered to the cows which may partly explain the higher intake values of the B3 formula compared to the others formulas. The highest daily intake from urea-molasses was reported to be 700 g for growing cows with 250 kg body weight (Sansoucy 1995; Schiere et al 1989) which was slightly higher than those which observed for the B1 and B3 formulas in the current study. Nikkhah (1988) studied the intake from UMBs by indigenous Sarabi cows, and reported that Sarabi cows consumed 845 to 1500 g per head per day from UMBs (Nikkah 1988). In our study the cows had only limited access to the blocks (4 hours daily), while in Nikkhah’s study blocks were offered to the Sarabi cows as ad libitium. This may explain why the daily intake from UMBs was lower in our study compared to those reported by Nikkhah (1988). This is further confirmed by the fact that in the adaptation period when the cows had freely access to the blocks all the time, the daily intake of the blocks was increased.

UMB supplementation and milk production and composition

Our results show that the effect of UMBs on milk production is period-dependent (Figure 1). In the P1, supplementing dairy cows’ ration with UMB decreased milk production, while in the P2 milk yield was increased by UMB supplementation. These findings suggest that the UMB supplementation improved lactation persistency in the Iranian rural dairy cows. Similarly, Perera et al (2007) reported an improved lactation persistency with UMB supplementation in rural dairy cows (Perera et al 2007). Misra et al (2006) reported that supplementation of UMB licks increased milk yield in crossbred cows during dry season feeding in rain-fed agro-ecosystem in India.  More recently, Tekeba et al (2012) evaluate the effect of UMB supplementation on milk production in local dairy cow (Fogera) and crossbred dairy cows in the north-western part of Ethiopia. They reported that offering UMB during dry season improved milk yield in both local and cross bred dairy cows.

Figure 1. Daily milk production in Iranian rural dairy cows fed ration supplemented with (+UMB) or without (-UMB) and held under smallholder farm conditions

In the present study, supplementing dairy cows with urea-molasses blocks significantly decreased milk fat percentage and percentage of solid- non-fat in milk, while it had no effect on milk concentrations of lactose and protein.  In agreement with the present study, supplementing dairy cows with 3 kg per week of UMB increased milk production under small-holder dairy farm conditions at six villages in India (Kunju 1998). Milk fat percentage was also increased when the cows allowed having free access to UMBs due to increased straw intake (Kunju 1998).  In another on-farm trial, homemade concentrate mixture and grass hay were supplemented with 300 g.d^-1 per head of UMB in ten cross bred cows. When the cows received UMB, daily dry matter intake through concentrate (kg/d) was significantly decreased but roughage intake was increased. Both milk yield and milk fat were increased by UMB supplementation however the other milk compositions did not changed (Sahoo et al 2009).

UMB supplementation and milk urea nitrogen

The average MUN in the Iranian rural crossbred dairy cows was 8.5 mg/ml (ranged between 4.2-13.1 mg/dl, n=35) which was lower than those which recommended for conventional dairy cow herds (12-16 mg/dl) (Baker et al 1995).  The lower values of MUN in crossbred rural dairy cows may indicate a shortage of protein or ruminally degradable protein intake. It has been shown that MUN level increases with high intake of ruminally degraded protein (Baker et al 1995). When the Iranian rural dairy cows were supplemented by UMB, the MUN values were significantly decreased. A low MUN in the UMB supplemented cows indicates that there is either a shortage of protein intake or that protein is being used more efficiently. The latter is supported as daily milk production was higher in the UMB supplemented cows compared to the not supplemented animals (Table 3).

In conclusion this study showed that supplementing Iranian crossbred rural dairy cows’ rations with urea-molasses blocks decrease the milk urea nitrogen which might be due to increased efficiency of protein utilization. This effect is reflected in improved milk yield notably in the second period of lactation.

Acknowledgments

The authors thank Research deputy of Lorestan University for financing this project.

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Received 14 October 2012; Accepted 7 December 2012; Published 4 January 2013

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