Different roughage: concentrate ratios in extruded feed, and feeding behavior of growing lambs

Animal performance is directly related to the food quality and intake. Analyzing feeding behavior is an important tool to evaluate diet efficiency. This study aims to evaluate the intake of dry matter, feeding behavior and ruminal movement amongst lambs fed with extruded feed in different roughage (R) : concentrate (C) ratios. An experiment was carried out in the Experimental Farm Capim Branco, Universidade Federal de Uberlandia, from December 7, 2016 to March 22, 2017. It involved 30 3-month-old crossbred lambs (Santa Ines x Dorper) with a mean weight of 20.67 ± 4.57 kg allocated in collective stalls equipped with feeder, water fountain, salt shaker, and wooden slatted floor. The experiment was conducted in a randomized complete design with 2 treatments and 15 replicates per treatment. The treatments consisted of roughage and concentrate extruded and mixed in the following ratio 30R:70C and 70R:30C. The dry matter intake (DMI), 24-hour feeding behavior and 5-minute ruminal movement were evaluated. The findings pointed to reduced DMI in relation to body weight for 30R:70C at the end of the experiment. Reduced rumination time, total chewing and ruminal movement were found for both ratios. However, shorter rumination time and total chewing had been recorded for 30R:70C at the beginning of the experiment. Extruded feed with 70R:30C increased rumination and total chewing and, consequently, ruminal movement.


Introduction
Animal performance is a direct function of the digestible dry matter intake. Food intake varies depending on a number of factors, including: the animal (live weight and its variation, production level, physiological state, and size), food (fiber, volume, filling capacity, energy density, and chewing needs), feeding conditions (availability of food, space in the trough, time of access to food, feeding frequency), and climatic conditions (MERTENS, 1994;GESUALDI JR et al., 2000).
The intake of diets with high levels of fiber is controlled by physical factors, such as the passage rate and rumen filling, whereas the intake of diets with high levels of concentrate (high energy density) is controlled by energy demand and metabolic factors (CONRAD et al., 1984;MERTENS, 1987; VAN SOEST, 1994). Therefore, the energy demand of ruminants defines the intake of diets with high caloric density, whereas the physical capacity of the gastrointestinal tract determines the intake of diets of low quality and energy density. As such, balancing an adequate roughage:concentrate ratio is influenced by age, quality of roughage, concentrate, and expected productivity.
One way to evaluate diet efficiency is based on the study of feeding behavior. Such a study provides the animal response to the diet and management methods with a view to improving productivity. Small ruminants have the ability to adapt to the most diverse feeding, management and environmental conditions, changing their parameters of feeding behavior to reach and maintain a certain level of intake compatible with nutritional requirements (CIRNE et al., 2014). Hence, the roughage:concentrate ratio can directly influence the ruminants' feeding behavior.
In addition to the animals' characteristics and the environment, the factors that most affect their feeding behavior are those related to the diet, namely: the amount of fiber, dry matter content, particle size, and Vet roughages with a high cell wall content tend to increase rumination time (FIGUEIREDO et al., 2013).
The evaluation of ruminal physiological parameters is another way to predict the quality of food.
For example, rumen motility guarantees food mixing inside to be more efficiently digested before leaving the rumen, when it needs to be in adequate particle size for food passage (THIAGO; GILL;SISSONS, 1992).
This study aims to evaluate the effect of 2 roughage:concentrate ratios (30R:70C and 70R:30C) on growing lambs' dry matter intake, feeding behaviour, and ruminal movement.

Material and methods
The experiment was carried out in the Experimental Farm Capim  Ruminal movement was determined by auscultation once a week in the last 5 weeks of the experiment. It always took place in the morning, 1 hour after supplying day first food treatment. Auscultation was performed with the aid of a stethoscope for 5 minutes following the method by Radostits et al. (2007).
A randomized design with 2 treatments and 15 repetitions was used with repeated measures over time to assess feeding behavior (4 evaluation periods) and ruminal movement (5 evaluation periods). To evaluate dry matter intake, the bays were used as a repetition, therefore, each treatment had 3 bays as a repetition unit. The treatment averages were evaluated using Tukey's test and regression study. Significant was set at a 5%. Results and discussion The dry matter intake in relation to body weight (DMI%BW) was higher (p <0.05) for treatment 70R:30C, and no difference between treatments was found for intake in kilograms per animal (p> 0.05; Table 2). The average dry matter intake (DMI) was 1.13 kg animal -1 day -1 , which is within the recommended for the animal category, i.e., between 1.0 and 1.3 kg day -1 (NRC, 2007). The DMI%BW recommended by the NRC (2007)   A quadratic effect was found in the DMI per animal in kilograms per day, with greater consumption (p <0.05) towards the end of the experiment.
Meanwhile, a negative linear effect was found for the DMI%BW, with reduced DMI%BW at the end of the trial period. An explanation for this response of the DMI%BW is the animals' weight gain (Table 2); therefore, the DMI%BW was reduced despite increases in the intake.
These animals have low nutritional requirements when they are young.
As they are lighter, higher DMI%BW values are found even if they eat less food a day, since this intake is relative to body weight. However, as these animals grow, their nutritional needs increase, requiring greater daily intake to meet them; together with the high intake, the animals begin their fattening process, becoming heavier. As a result, the ratio between this intake and their body weight reduces (ZANINE; MACEDO JUNIOR, 2006 (from 0 to 105 days). This ADG was similar to that found by Carvalho et al. (2007), which was 171 g day -1 , in lambs fed with Tifton 85 hay and bran concentrate in the 60R: 40C ratio.  According to Van Soest (1994), the rumination time is influenced by the nature of the diet and is proportional to the cell wall content of roughage.
Therefore, concentrated foods, either finely ground or processed (pelletized or extruded), reduces rumination time, while roughages with a high cell wall content increase rumination time. Thus, the animals fed with the 70% roughage showed longer rumination and total chewing times due to the higher fiber content in their diet, even though it was finely ground in the food (fiber size of 2mm, manufacturer data). A quadratic effect (p <0.05) was observed in the rumination time for the 70R:30C treatment. When associated with the DMI%BW, which also decreased at the end of the experimental period (Table 2), this effect indicates that even when animals ingest extruded feed with a higher content of structural carbohydrates, with the intake decrease there is less fiber in rumen to stimulate rumination. In the experiment, quadratic effect (p <0.05) was observed during the time spent with chewing and resting, and at the end of the experiment the animals reduced the total time of chewing and increased the resting time. That is, when intake is reduced, ingestion and rumination also decrease; consequently, the time that the animal spends on other activities (such as resting) increases.
Confined animals tend to concentrate their period of ingestion shortly after the food is provided in the trough -between 1 and 3 hours, with variable intervals of small meals (FISCHER et al., 1997). Van Soest, Robertson and Lewis (1991) reported that rumination in adult animals lasts about 8 hours a day with variations between 4 and 9 hours. They observed that this behavior was mainly influenced by the nature of the diet, i.e., the more concentrated the diet, the shorter the time spent on rumination.
At the beginning of the experiment with 30R:70C, the animals spent on average 3.7 hours on ingestion, 1.7 hours on rumination, and 18.6 hours on resting; at the end, they spent on average 2.7 hours on ingestion, 1.3 hours on rumination, and 20.0 hours on resting. In turn, at the beginning of the experiment with 70R:30C, they spent on average 3.9 hours on ingestion, 3.4 hours on rumination, and 16.7 hours on resting. at the end, 2.7 hours on ingestion, 1.8 hours on rumination, and 19.5 hours on resting. The rumination values were below those proposed in the literature, but this did not influence either their weight gain, which remained constant throughout the experimental period (Table 3), or their DMI. This can be attributed to the extrusion process, which changed the food matrix and made its nutrients more digestible, thus improving their use by the animal. The animals fed with the 30R:70C ration had less ruminal movement than those that received the 70R:30C ration (p <0.05; Table 5), which was due to the higher non-fibrous carbohydrate (NFC) and lower neutral detergent fiber (NDF) content of the treatment with greater amount of concentrate (Table 1).
These characteristics lead to reduced ruminal pH and therefore reduced ruminal motility (NOCEK et al., 1984). However, it can be inferred that the use of extruded feed does not cause digestive problems in animals, as the ruminal movement of sheep in thermal comfort is 1 to 2 movements per minute (mov min -1 ) (FARIA, 2010), and the values found were 1.10 mov min -1 for the 30R:70C treatment and 1.15 mov min -1 for the 70R: 30C treatment. Therefore, the values found in this study are within the recommended. The lower ruminal movement observed in the 30R: 70C treatment can be explained by the lower DMI obtained by the lambs (Table 2). When consuming a higher content of concentrate, the animals reduced the DMI%BW due to a greater amount of nutrients with greater rumen fermentation capacity, thus reducing rumen movement and, consequently, the time spent on rumination (Table 3). In contrast, the treatment with 70% roughage showed greater ruminal movement, which is explained by the higher DMI along with the higher fiber quantity in this treatment (Table 1) (Table 5). This response pattern can also be associated with a reduction in DMI%BW in the period (Table 2) and a reduction in the times spent on ingestion, rumination and total chewing ( Table 4).
The findings seem to show that the DMI, the feeding behavior and the ruminal movement are influenced by the roughage:concentrate ratio of the diet and the food composition (physical form associated with the quantity of nutrients