Introduction

The use of alternative feeds as byproducts that help supply ruminant animal demand for nutrients in times of low pasture supply, mainly during winter or drought periods, arouses the interest of researcher’s different areas, including feeds conserved. The primary sector annually generates tons of organic byproducts with excellent nutrient composition¹⁾ that could be transformed into meat, milk, skin and wool by ruminants² and consequently can reduce threats of environmental pollution, since part of this byproduct is improperly stored or discarded in environment. Recent research has suggested partially replacing cereals grains by agricultural byproducts in feed animal^2,3,4, in order to promote more sustainable production. In addition, the use of byproducts of different fonts of raw material may contribute to meet consumer demand, regarding the sustainability of animal production systems and maintaining the integrity of the environment.

The use of agricultural and industrial byproducts is present from the production of chemical products to animal feed^1,5. The grape destined for wine industry and juices, for example, generation quantities of byproducts, as pomace and seeds, which offer risks economic and environmental⁶. However, this byproduct is an alternative source of fiber, have low commercial cost, chemical composition of quality⁷ and has traditionally been incorporated in ewe diets and lambs^8,9,10. Recent study showed the viability for storage in the form of silage, with satisfactory amounts of residual sugars and fibers, which meet the desirable characteristics of feed conserved¹¹. It is also an alternative for ensure silage throughout the year and proper destination of this byproduct. The use of byproducts evens can contribute with small farms which haven’t areas of lands available for crops intended for the production of traditional silage, as whole corn and forages.

The use of grape pomace in diets for lambs had showed results considerable on nutritional composition, performance, nutrient consumption and acceptability by animals^10,12,13. Although there are results in the performance of lambs with the inclusion of only grape pomace, the supply of this byproduct in the form of silage and the limitations of the respective levels of inclusion, related to the fiber content and ether extract of the seeds deserve to be investigated, since there is variety in the grape cultivars that can offer different effects qualitative on the silages and performance of animals. Based on this hypothesis, this work was carried out with the objective of evaluating the inclusion 0, 10, 20, 30 % of grape pomace silage (Vitis labrusca L. cv. Isabel) in diets of lamb and its effects on nutrient intake and digestibility, nitrogen balance and behavior ingestive.

Material and methods

Results and discussion

In order to evaluate the DM and nutrient intake of the diets, it was observed that the inclusion of grape pomace silage influenced (P<0.05) in linearly increasing only the consumption of EE (Table 2). The EE in GPS was due to the higher density of the seeds (610 g kg^-1 DM) in comparison to the bark and pulp (390 g kg^-1 DM) constituting the grape pomace¹¹ and seeds, in turn, have a high oil concentration²⁷. Therefore, this behavior can be explained by the higher concentration of EE in the GPS and providing an increase in the concentration this nutrient in the diet, according to the increase of GPS levels inclusion.

The increase in EE in diets and intake is often observed according to the increased level of inclusion of grape residues of up to 15 %, respectively^10,12,13. The maximum level of EE of 32.9 g kg^-1 DM offered in the diet with 30 % of inclusion in this work, does not exceed the maximum limit 50 g kg^-1 DM proposed by Palmquist and Mattos²⁸.

The mean intake of DM (3.80 of live weight percentage), met the requirements of the animals and presented value higher than recommended in the NRC²⁹ is 3.51 % for the animal category analyzed with 30 kg and daily weight gain of 300 g/d. The FDNI recommended by Mertens^{(30 )} for ruminant animals should maintain an intake of NDF of around 1.2 % of their live weight, thus in this study the NDFI was 1.43 %, that could be related to the amount of fibrous fractions of diets of each treatment.

These values of nutrient intake (Table 2) agrees with a study¹⁰ that found values for DMI of 1,192, 1,144 and 1,127 g kg^-1 for levels of 0, 10 and 20 % respectively, of inclusion of grape marc silage in diets for lambs, as well as other nutrients that are in the range for the interval observed by these authors on nutrient consumption. Some authors¹²⁾ found DMI of 1,445.8, 1,379 and 1,482.4 g d^-1 of lambs feed with levels of 0, 5 and 10 % of wine grape pomace. Lambs fed with 10 % of wine grape pomace did not increase their DMI and had greater average daily gain that lambs in the both supplementation 0 and 5 %. Despite value DMI was higher than this study, the nutrient intake not was influenced for inclusion of grape pomace.

No variations (P>0.05) were observed in the apparent digestibility of nutrients as a function of the increase in the GPS contents (Table 3). Factors such as the similarity in the NDF contents of the diets (Table 1), the absence of differences in DM consumption and the association between grape pomace silage and other foods, may be associated with the similarity between the digestibility of nutrients in the diets.

Reduction in the digestibility of DM and nutrients was observed in sheep diets³¹ by associating 50 % dehydrated grape residue to different energy sources, that according to the authors, the digestibility of the diets was affected by the low digestibility of the dehydrated grape residue of 30 % determined in vitro. It was also observed a significant reduction in the digestibility for the diets of red grape marc³². These authors related the decrease of digestibility with the presence of tannins and the high lignin content in grape marc. However, the values found for nutrient digestibility of the present study (Table 3) are superior to the study by Zalikarenab et al³². For DDM the average value was of 678.6 ± 0.62 g kg^-1 DM also observed as higher as the value found by others³³ with DDM of 285 g kg^-1 DM of when evaluating the digestibility of silage bagasse for ruminants.

It is likely that the digestibility values of the diets observed in the present experiment are due to the better utilization of grape pomace silage by the animal, considering 461.2 g kg^-1 DIVDM of the byproduct used (Table 1). However, it is worth mentioning that the digestibility values of the nutrients found in this work, refer to the grape pomace of the Isabel Vitis Labrusca L. variety¹¹ and because there are not yet studies with this variety in the lamb feed, it is not possible to draw comparisons between the results obtained. In addition, differences in digestibility may be related to variations between the byproducts used in the diets, in addition to the type of processing and additive used for conservation. According to Rogério et al³⁴ processing in the fruit agro industries results in a great variation in the chemical composition of the generated residues, being observed variations even between lots that have undergone the same type of processing.

The parameters of ingestion, fecal excretion, urinary excretion and nitrogen retention were not influenced (P>0.05) by the diets (Table 4), and possibly that the use of isoproteic diets and crude protein consumption were not influenced by diets, are the reasons for the similarity observed for the nitrogen balance between diets and similar CP levels. The positive balance of the nitrogen contents with mean values of 8.53 g d^-1 of nitrogen retain and 239.78 g kg^-1 nitrogen ingested may indicate, that there was retention of protein in the animal body, providing conditions so that no weight loss occurred and probably the protein requirements were met by the diets³⁵. The results of the present study indicated that the experimental diets had a balanced supply of protein and energy, which in turn may have improved the use of dietary protein.

Evaluated diets with dehydrated grape residue and different levels of urea for lambs found average values of 22.62 g d^-1, for retention of N³⁶. According to the authors, the high value can be explained by the fact that the animals are growing and required high amounts of protein for tissue formation. When replacing sorghum silage with dehydrated fruit coproducts, no difference was observed for nitrogen balance between diets³⁷. According to these authors, this fact indicates that the animals retained protein from the diet and the objective of the study was reached, besides these products are good alternative for use during feed shortage and potentially reduce feed costs.

Despite the observed values for N retained in the present study, 8.53 g d^-1, are lower than those observed elsewhere³⁶⁾ showed no damage to the development of the animals. However, the values are close to retained N and higher for ingested, fecal and urine N, to those found by others¹³ when they included grape residue in diets with 11% CP to feed lambs. N retention is closely linked to the balance and timing of degradation between carbohydrates and dietary proteins. According to some authors¹⁵, higher nitrogen retentions are a reflection of the better balance between energy and protein characteristic of each food, allowing greater efficiency in protein utilization.

The excretion of N via feces was less than the excretion described by Van Soest³⁸ for ruminants, 6 to 8 % of the ingested protein, since for consumption of CP 221.4 g d^-1 obtained in this research, and losses fecal excretion of 13.3 g N d^-1. It can be inferred that the amount of tannin present in the grape pomace did not cause damage to protein degradation or that the maximum amount of GPS, 16.5 % present in the diet with a 30 % inclusion, was not sufficient to cause this effect undesirable. Min et al³⁹ reported that the tannins can affect the digestion process by means of complex formation with enzymes and mainly with proteins, which would cause lower degradation, absorption and consequently higher excretion of protein via feces.

The presence of tannins causes nitrogen partition, causing a lower proportion to be excreted in the urine, directing their excretion into the feces⁴⁰. This behavior was not observed in the present experiment, the urinary excretion of N 16.14 g d^-1, was superior to the fecal excretion of N 10.76 g d^-1. When the rate of protein degradation exceeds that

of carbohydrate fermentation, a large amount of nitrogen compounds can be eliminated via urine³⁸.

There were no differences for intake of DM and NDF (Table 5), what can indicate that palatability was not negatively affected by the inclusion of silage GPS of cultivar Isabel Vitis Labrusca L. cultivar Isabel (P>0.05). Gao et al¹³ when evaluating the inclusion of up to 15 % of grape residue in diets of lambs, found that the values lower for DM intake and NDF intake were increased with higher inclusion levels.

The time spent with consumption, rumination, idle time lying down and total chewing were not influenced (P>0.05) by the inclusion of GPS (Table 5). The absence of effects of diets on these parameters may be due to the similarity between the roughage and concentrated levels of the diets, as well as the levels of fiber, consumption and digestibility of DM and NDF. In addition to the moisture content, caused by the use of silage, it has facilitated the consumption of diets by animals, making the time spent on feeding easier.

The time spent on rumination is proportional to the cell wall content, particle size and effectiveness of the food fiber, with a greater need to process the fiber, as well as more time for feed consumption³⁸. Also regarding the influence of the NDF content on the ingestive behavior, Cardoso et al⁴¹ evaluated diets with different NDF levels (25, 31, 37 and 43 %), observed no change in ingestive behavior and reported that variations in intake were observed in diets with NDF contents higher than those observed in the present experiment, or when there is greater amplitude between the fiber contents in the evaluated diets.

The time spent with ingestive behavior the diets influenced only the length of time that the animals remained idle in standing (Table 5). This parameter showed a quadratic behavior with a maximum point estimated at 17.73 % of GPS (P=0.041). Although there were no great variations in the NDF content and the NDF consumption was not influenced by the levels of grape pomace silage inclusion. Considering fiber content as a parameter, it is expected that the idle time will decrease as the NDF content in the diet increases, that is, the greater the need to process dietary fiber, the shorter the permanence of idle animals^42,43. As observed in the present study for the level 0 % of inclusion with the highest content NDF of 454.4 g kg^-1 DM with the lower idle time of 315 min^-1. This is due to the fiber characteristics of the sorghum silage⁴⁴, and in the present study it presented a lower ADF content and a higher NDF content than GPS and also in the diet (Table 1).

When considering the total fiber content through the sum of NDF and ADF (725 g kg^-1 of fiber total) for level of inclusion of 30 % GPS, the value of 320 min d^-1 of idle time may have been influenced by total content fiber. This is due to the fiber characteristics of the GPS¹¹, composed 610 g kg^-1 of DM of seeds, 390 g kg^-1 of DM pulp residue and husks. The seeds represented the highest proportion in silage and contributed to increase the levels of NDF and ADF in the diet at the level of 30% of inclusion (Table 1), which may have been demanded a greater need for rumination and less idle time between the levels of inclusion (Table 5). For confined lambs, the inclusion of GPS can keep them active and contribute to stress reduction and encourage rumination natural behavior.

The efficiency of ingestion and rumination of DM and NDF were not influenced (P>0.05) by the treatments with the different levels of inclusion. This behavior can be justified by the consumption of DM and NDF (1,235.5 and 461.6 g d^-1), respectively, which did not show significant variation (P>0.05) between treatments. According to several works^45,46 the ingestion and rumination efficiencies of DM and NDF are directly related to the consumption of DM and NDF, which may be influenced by particle size, quality and diet content.

Conclusions and implications

Grape pomace silage can be used to feed lambs up to 30 % inclusion in diets containing 55 % roughage, without causing changes in nutrient intake and digestibility, as well as nitrogen balance and ingestive behavior. The grape pomace silage has favorable characteristics for use in diets for lambs, with silage being a good alternative for its storage, in addition to offering the correct destination for this byproduct.