Introduction

Dairy production in the tropical regions of Peru is one of the most important livestock activities, contributing significantly to the population's economy¹. The livestock system is largely based on extensive, traditional management, solely on natural pastures and/or cultivated forages used to satisfy the nutritional needs of the region's livestock^2,3. However, the quantity and quality of pasture varies throughout the year due to seasonal changes, affecting its availability during the dry season⁴. This problem generates insufficient nutritive value of the pasture, due to its high fiber and low protein content, limiting its consumption and digestibility^4,5.

Nevertheless, several supplementation strategies have been proposed for grazing^6,7. Multinutritional blocks (MNB) are an excellent alternative as a feed supplement to complement the nutrients needed by cattle when pasture availability is scarce⁸. Initially, MNB contain urea, binders, salt, vitamins and minerals to meet non-protein nitrogen requirements in poor quality pastures, thus improving rumen microbial activity⁹. However, by using locally available agro-industrial by-products in the production of these blocks, it would be possible to increase livestock productivity given their nutritional value, availability and low market price⁴.

The Peruvian Amazon has a great biodiversity of crops, including the production of 428000 t of oil palm and 9000 t of coconuts in the San Martin region¹. Palm kernel expeller (PKE) and coconut cake (Cocos nucifera) (CC) are by-products of the oil industry, obtained through mechanical or solvent extraction processes¹⁰. Nevertheless, PKE plays an important role in ruminant nutrition, is inexpensive and locally available, and also meets the nutritional needs of livestock, providing protein, energy, vitamins and minerals^11-13. Meanwhile, CC an ideal low-cost alternative by-product as a protein source for ruminant feeding^14,15. Because of its nutritional value, availability and low market price, using these by-products in animal feed is a good option^4,14,16. However, to our knowledge, there is little information on the effects of feeding dairy cattle with blocks made with by-products from local industry, such as PKE and CC. The objective of this study was to evaluate the effect of BMN made with agroindustrial by-products on the productive performance of dairy cattle under an extensive system.

Materials and methods

Study area. The study was conducted in the private cattle ranch "Rico Rico", located in the district of Yurimaguas, province of Alto Amazonas, Loreto region, Peru. Coordinates 03° 5' 5" South Latitude and 73° 1' 0" West Longitude, humid tropical climate, with a temperature between 27-29° C depending on the season, annual rainfall of 2115 mm per year¹⁷.

Animals and treatment. Before starting the study, the animals were treated against endoparasites and vaccinated against clostridia. Twelve milking cows of the Girolando breed of dairy attitude provided by the private cattle ranch "Rico Rico" were selected; the cows were 5 years old and had an average of 2.5 calvings, with live weight 450 ± 41 kg and 205 ± 20 days of lactation. The animals evaluated grazed about 20 h per day in paddocks with pastures dominated by Brachiaria (B. brizantha) and milking was performed daily (04:00 am). The stocking rate ha-1 was 1.5. The cows were distributed uniformly in groups of 3 in 4 pens in the same lactation period. The BMN were manually prepared in the field considering their nutritional value (Table 1). Nutrient characterization - analyses were performed at the Laboratory of Animal Nutrition and Food Bromatology (LNABA) of the Universidad Nacional Toribio Rodríguez de Mendoza de Amazonas (UNTRM).

Considering the preparation, solidification, molding and drying method proposed by Duressa & Bersissa.¹⁸, the preparation and extraction of multiple food blocks took approximately 4 weeks. The blocks were 15 cm high, 20 cm in diameter and weighed an average of 1.5 kg.

The experiment was conducted under a completely randomized design (CRD) with 4 treatments and 3 replicates. An experimental period of 30 days was established, 10 days of adaptation and an evaluation phase of 20 days with inter-daily sampling. With 4 treatments (T): T₀ (under grazing with Brachiaria (B. brizantha) and mineral salts without supplementation) and T₁, T₂ and T₃ were supplemented with blocks made in equal levels with 39.50 % molasses, 10 % urea, 5 % mineral salts, 5 % common salt, 5 % lime, 5 % cement, 9.5 % palm oil and for treatments T₂ and T₃ with 30 % CC and 30 % PKE, respectively. They were administered to the animals individually during milking with an average duration of 30 min. The test animals received no nutritional supplements or diet other than the treatments described.

Parameters evaluated. Daily milk production (kg/animal/day), milk composition (protein, lactose, fat and total solids) were recorded with Lactoscan SPFP (Milkotronic, Bulgaria) and MilkoScan™ 7 RM (Foss®, Spain) devices. Daily BMN intake was calculated each day as the difference between the initial and final weight of the given blocks using a High Weight® TP9000 scale. Grass samples were collected from the paddocks according to the methodology of Carrere et al.¹⁹. The nutritional value of the Brachiaria (B. brizantha) diet is shown in Table 2. The relevant analyses were carried out at the LNABA of the UNTRM. The total nitrogen (TN) content to obtain the crude protein (CP) content²⁰, and the neutral detergent fiber (NDF), acid detergent fiber (FDA), and acid detergent lignin (ADL)²¹ fractions, with the ANKOM^® 220 equipment (ANKOM Technology, Macedonia NY-USA).

Statistical analysis. Analysis of variance (ANVA) was performed on DCA data collected with SAS Mean T values for milk quality and milk production were compared by Duncan's test, 95 % significance level.

Results

Dry matter intake (DM). The average BMN consumption during the evaluation period did not differ significantly (P>0.05) between T₁, T₂, T₃Table 3. However, the average consumption presented a slight variation for T₁, T₂, T₃ between 821, 804 and 776 g/animal/day, respectively.

Milk production and composition. Table 4 the results of milk production and composition for the 4 experimental treatments in lactating cows. Significant difference (p<0.05) was observed between the group of cows that did not receive block supplementation (T₀) and those that received (T₁, T₂, T₃) averages (3.81) and (5.03, 4.55, 6.24) kg/animal/day, respectively, were obtained. Milk composition, animals supplemented with BMN presented higher protein content (%) compared to non-supplemented animals. The values of lactose % and total solids % did not differ between treatments.

Figure 1, a 30 % increase in daily milk production in animals supplemented with BMN compared to animals consuming the control feed (T₀). However, during the experimental procedure, animals supplemented with T₃ treatment (BMN with 30 % PKE) presented a high difference of 5.55 to 6.24 kg in milk production, while T₁ and T₂ were similar from 4.00 to 5.03 and 3.9 to 4.55 kg, respectively.

Figure 1 Average milk production (kg/animal/day) over the experimental period between treatments 

Discussion

In the present study, DM intake of BMN in animals was not affected for any treatment. Kawas et al.²², suggested that BMN consumption is important to achieve the expected results of supplementation. In addition, the authors caution that consumption of blocks below 300 g/animal/day is unlikely to maximize consumption of the lower quality forages and, therefore, animal performance responses. Rodriguez Reyes et al.², when evaluating feeding strategies in dairy cows, reported an average value for DM intake through BMN of 700 and 897 g/animal/day. These intake values ensure a nutrient supply for rumen function and a sufficient amount of mineral intake to cover the daily needs of Obispo & Chicco.²³ cattle. In the present work, the average intake of the evaluated blocks was 821, 804 and 776 g/animal/day, considered optimal values for supplementation. This may be due to the positive effects of the properties of the ingredients used, acceptability, hardness and quality of the feed offered.

Milk production in cows supplemented with BMN showed a significant increase of 30 % in milk production. The average milk production of the experimental cows after 2 weeks of adaptation to BMN consumption until the end of the experiment increased from 5.2 to 6.24 kg/animal/day for the BMN treatments, while in the control group (T₀) it was observed that production declined from 3.9 to 3.81 kg/animal/day. In other studies, related to the use of BMN, Tekeba et al.²⁴ reported significant increases of 0.7 kg/animal/day representing 34 % in milk production in crossbred cows. Likewise, Rodriguez Reyes et al.² also reported that when BMN were added, cows increased their milk production from 3.40 to 7.87 kg, while the control group had a lower production of 2.1 to 5.92 kg/animal/day. More recent work by Gudiño-Escandón et al.²⁵ reported a significant increase in milk production among grazing cows fed BMN indicated an average increase in milk production of 0.84 kg/animal/day, with better results in the dry season.

Milk protein levels increased in the present study for animals supplemented with BMN. These results can be attributed to the higher intake of rations with supplementation levels, and to the higher concentrations of non-fiber carbohydrates, which result in higher microbial rumen synthesis, contributing 40 to 80 % of the protein demand in the mammary gland²⁶. However, no significant changes in milk fat or total solids were observed in this study, suggesting that the protein content in the milk composition of cows receiving BMN may not be biologically significant.

In the present study, we highlight the use of BMN elaborated from agroindustrial by-products as a dietary supplementation strategy for lactating cows, which can be very beneficial, since it resulted in a significant increase in milk production, as well as an improvement in productive behavior, rumen fermentation and increased consumption of pastures of low nutritional value. Finally, this positive response could be a practice to improve milk production. BMN are also easy to manufacture and supply to grazing cattle.