Introduction

Goat farming stands out as an activity of cultural, social and economic relevance in the northeast region of Brazil. However, goat- derived products still lack standardization. The unsatisfactory productivity rates in the region caused by the seasonality of forage production make feedlot a reasonable strategy to intensify production of high-quality meat (^{Urbano et al., 2015}). Nutritional plans and techniques available in feedlot systems to enhance nutrient intake and animal performance allow reducing the age at slaughter and obtaining carcasses with high commercial value.

Feedlot diets are typically expensive due to the cost of concentrate feeds. However, the beneficial effects of dietary fiber cannot be neglected. Fiber maintains adequate ruminal conditions and promotes greater absorption of nutrients (^{Alves et al., 2016}), especially when correctly associated with sources of non-fibrous carbohydrates such as spineless cactus (^{Ferreira et al., 2012}). Correct associations between feed sources tend to enhance animal performance and, when the combination involves alternative feed sources, the beneficial effects also extend to the economics of the system.

Carcass is the most crucial element in the production chain of livestock systems focused on meat production since it contains the edible part with the highest economic value. As a result, farmers have sought increasing carcass weight under commercial conditions. According to ^{Gois et al. (2018)}, carcass weight is highly dependent on growth speed, which is strongly influenced by age at slaughter and nutritional management. Therefore, diets play a key role in improving performance of young animals and production of carcasses with high yield and attractive sensory and organoleptic properties (^{Osório et al., 2013}).

We hypothesized that different sources of fiber and sexual condition could improve the results of confined goats. Therefore, this study aimed to evaluate the effects of castration and the association of spineless cactus with elephant grass hay or sugarcane bagasse on nutrient intake, digestibility, performance, feeding behavior, and qualitative (pH and temperature) and quantitative (wheights and yields) carcass traits of feedlot kids.

Materials and Methods

Results

Fiber sources and sexual conditions did not affect (p>0.05) nutrient intake (kg/day): dry matter intake (DMI), crude protein (CPI), neutral detergent fiber (NDFI) and non-fibrous carbohydrates (NFCI) (Table 2).

The fiber source influenced (p<0.05) feeding behavior. The TSR was higher for animals fed SB, whereas the TSRU and TCT were higher for animals fed elephant grass hay (Table 3).

Final weight (FW), average daily gain (ADG), total gain (TG) and empty body weight (EBW), as well as qualitative carcass traits (pH and temperature at 0 and 24 hours post mortem) were not affected by diet, sexual condition, or their interaction (p>0.05) (Table 4). Hot carcass weight (HCW) and cold carcass weight (CCW) were affected (p<0.05) by sexual condition and fiber source, and were higher for intact animals, animals fed elephant grass hay (Table 4), respectively. There was a significant effect of diet (p<0.05) on hot carcass yield (HCY) and biological yield (BY), with better results for animals fed elephant grass hay (Table 4).

Discussion

The DMI was lower than that recommended by the NRC (2007) for kids (820 g/day), which may be related to the feeding habit of goats. Despite being versatile, goats are classified as intermediate feeders (^{Hoffmann, 1989}) and require longer periods for adaptation to new conditions, especially when removed from the Caatinga environment and allocated in individual pens with totally different diets, not only in terms of feed offered but also in terms of composition and assimilation. ^{Garcez et al. (2020)} report that even in feedlot systems, goats express selectivity and spend most of the time searching and selecting food, which influences both quality and quantity of the feed consumed besides chemical composition of leftovers causing variation in nutrient intake. Therefore, the typical feeding habit of goats not adapted to feedlot systems seems to have a greater influence on DMI than fiber source and sexual condition. Moreover, moisture content of diets, which contained 25 and 30% of spineless cactus, also contributed to the low DMI. Goats prefer less moist and more nutrient-rich feedstuffs, such as grasses, shrub and tree plants, due to their intrinsic selective capacity (^{Costa et al., 2015}; ^{Pinho et al., 2019}).

The study of ^{Lima Júnior et al. (2015)} corroborates our argument when they calculated DMI of feedlot goats fed diets containing 30% spineless cactus associated with Tifton 85 hay (415 g DM/day) and cassava hay (544 g DM/ day), reporting values lower than those obtained in the present study (567 and 670 g DM/day for BS and EGH, respectively).

The literature reports that DMI in ruminants can be physically limited by rumen filling, which is regulated by the proportion of total dietary NDF (^{Mertens, 1997}, ^{Alves et al., 2016}). Goats, in turn, have a high intake capacity of forages with high NDF content (^{Formiga et al., 2020}). When assessing fiber levels for goats, ^{Branco et al. (2011)} indicated a limitation in DMI from 35% of NDF in the diet, lower than the present study. However, diets had comparable NDF levels (40%), which led to similar NDF and DMI. The lack of effect of treatments on DM led to similar intakes of CP, NFC and TDN.

According to ^{Pessoa et al. (2013)}, the carbohydrates present in the spineless cactus have high degradation rates, which may favor diet digestibility. An increase in dietary NFC concentration changes the microbial environment in the gastrointestinal tract of goats by increasing the amount of energy available in the rumen for bacterial growth (^{Ma et al., 2014}; ^{Ma et al., 2015}; ^{Pinho et al., 2019}). This can increase nutrient digestibility. Thus, a greater inclusion of spineless cactus in sugarcane bagasse-based diets increased the digestibility of DM, CP and NFC in this treatment.

^{Muniz et al. (2012)} evaluated the ruminal kinetics of the fibrous fraction of roughages, finding that an increase of approximately 3% lignin content in the feed, as found in the present study, decreases nutrient digestibility, justifying the lower values for EGH. Lignin is considered a limiting factor for fiber degradation due to its barrier effect that prevents microbial adhesion and colonization (^{Cabral et al., 2020}).

The high digestibility of sugarcane bagasse- based diets reduced rumination and increased TSR since both DMI and NDFI, which could influence this characteristic, were similar between treatments. However, the low digestibility of elephant grass-based diets increased TSRU and, consequently, TCT, although feeding times were similar between diets.

In addition to the NDF level, fiber composition can influence behavioral activities, especially rumination due to physical barriers to the digestive action of microorganisms (^{Azevedo et al., 2013}; ^{Ramos et al., 2016}). Thus, diets with similar NDF levels but composed of different feeds can predispose animals to different expenditures in daily activities (^{Carvalho et al., 2011}).

Similarity of DMI and nutrient intake between treatments resulted in similar animal performance. Feed intake affects animal performance, since the ingested nutrients are converted into animal products (^{Pompeu et al., 2012}).

Daily and total weight gain of kids were lower than the average 120 g/day expected by the NRC (2007). It is relevant to highlight that DMI did not reach the expected target (820 g/ day), which would explain the low weight gain.

Regarding sex, it directly influences animal physiology. According to ^{Pellegrini et al. (2012)}, intact males have higher growth speed than castrated males due to the anabolic effects of testosterone (^{Paim et al., 2011}). It explains the higher results for HCW and CCW in intact animals (10.8 and 10.56 kg) in relation to castrated kids (9.86 and 9.64 kg). Both HCW and CCW are direct measures of body tissue composition (muscle, bone and fat).

Castration increases fat deposition in the carcass (^{Gois et al., 2018}). In goats, fat deposition occurs primarily in the form of visceral fat, which is lost during evisceration (^{Rodrigues et al., 2013}). Thus, it does not significantly influence the final carcass weight and yield.

The HCW and CCW results, although the highest for kids fed elephant grass hay, were similar to the findings of ^{Lima Junior et al. (2015)} for HCW (10.22 and 9.45 kg) and CCW (9.57 and 8.85 kg) for goats fed Tifton 85 hay and cassava hay associated with spineless cactus, respectively. This indicates that sugarcane bagasse and elephant grass hay are good alternatives to Tifton hay. The increase in hot carcass yield (HCY) and biological yield (BY) are in line with the increase in carcass weight. In a study with feedlot goats, ^{Salles et al, (2013)} reported lower BYs (50.95%) than those obtained in the present study for both forage sources (55,32 and 59,76% for SB and EGH, respectively). Biological yield was influenced by fiber source, most likely because when considering the empty body weight, this parameter is affected by variations in the gastrointestinal tract contents (^{Bezerra et al., 2017}), which depends on diet intake.

The pH at 24 hours postmortem averaged 5.6, which is within the recommended range of 5.5-5.8 for carcasses of small ruminants after cooling (^{Della Malva et al., 2016}). Therefore, it is possible that pre-slaughter handling procedures were carried out without animal stress. The temperature at 24 hours postmortem was high, possibly due to the cold chamber setup.

In conclusion, feeding intact or castrated kids with sugar cane bagasse or elephant grass hay does not affect nutrient intake and performance. However, feedlot goats fed elephant grass hay improve carcass traits if kept intact, which is our recommend combination of strategies.